JP7679467B2 - Limiting grip force and maintaining minimum jaw opening force in position control mode, and controlling grip force when transitioning between position control mode and force mode - Google Patents

Description

The subject technology relates generally to robots and surgical systems, and more specifically to controlling the gripping or releasing force of a surgical tool, such as a wrist jaw, in a robotic-assisted surgical system.

Minimally invasive surgery (MIS), such as laparoscopic surgery, uses techniques intended to reduce tissue damage during surgery. Laparoscopic procedures typically require making multiple small incisions in a patient, e.g., the abdomen, through which several surgical tools, such as an endoscope, scalpels, graspers, and needles, are then inserted into the patient. Gas is insufflated into the abdomen to insufflate it, thereby providing more space around the tips of the tools, making it easier for the surgeon to see (through the endoscope) and manipulate the tissue at the surgical site. MIS can also be performed using a robotic system in which the surgical tools are operatively attached to the distal end of a robotic arm, and a control system actuates the arm and its attached tool such that the latter mimics the movements of a user input device (UID) and tool-specific commands as the latter is being manipulated by the surgeon's hand.

The surgical tool may include a robotic wrist supporting a pair of opposing jaws. The wrist and jaws may move in multiple degrees of freedom to grasp, cut, suture, and perform other surgical tasks as controlled by commands from a remote operator. For example, actuators in a tool drive of the robotic arm may drive multi-axis motion (e.g., pitch and yaw) of the wrist jaws to pivot, open, close, or control the gripping or opening force between the jaws while moving the wrist to any angular position. The jaws may grasp tissue of a patient, hold a cutting instrument, and the like. Precise control of the gripping or opening force when opening and closing the jaws is important to prevent damage to tissue or to ensure accurate cutting by the instrument. In addition, the jaws may operate in a position mode in which the angle between the pair of jaws is commanded to a desired jaw angle, and a force mode in which the jaws are commanded to apply a desired gripping force. A smooth transition between the position mode and the force mode minimizes undesirable sudden changes in gripping force that may cause accidental dropping of any object being grasped.

Systems and methods are disclosed for limiting the grip force generated by closing the robot wrist jaws while operating in a position control mode where the jaws are commanded to a desired jaw angle before being commanded to generate a grip force. In the position control mode, or simply the position mode, the desired jaw angle is higher than a threshold corresponding to the angle at which both jaws contact an object between the jaws just simultaneously, or the angle at which the jaws begin to contact each other if there is no object to grasp. When the desired jaws are lower than the threshold, the wrist jaws are operating in a force control mode, or simply the force mode, and the desired jaw angle is translated into a desired grip force. The disclosed systems and methods limit the maximum amount of grip force when the jaws are in the middle of closing in the position mode to prevent damage to tissue that may be grasped by the jaws. The grip force may be estimated or measured. A feedback loop may analyze the desired jaw angle and the measured grip force to determine if the jaws are in the middle of closing in the position mode and if the measured grip force exceeds a pre-specified maximum grip force threshold. If so, the feedback loop may calculate a grip force error to limit the measured grip force to the pre-specified maximum grip force threshold.

In another aspect, a system and method are disclosed for achieving a minimum jaw opening force by the wrist jaws when operating in positional mode. Maintaining a minimum jaw opening force while the jaws are in the middle of opening in positional mode helps the jaws overcome resistance that may prevent the jaws from opening to a desired jaw angle. The opening force and jaw angle representing the jaw opening force may be measured or estimated. A feedback loop may analyze the desired jaw angle, the estimated jaw angle, and the measured jaw opening force to determine if the jaws are in the middle of opening in positional mode and if the measured jaw opening force is lower than a pre-specified minimum opening force threshold. If so, the feedback loop may calculate a jaw opening force error to maintain the jaw opening force above a pre-specified minimum opening force threshold.

In another aspect, systems and methods are disclosed for achieving a smooth transition in grip force when the wrist jaws transition between position mode and force mode. A smooth transition from position mode to force mode and vice versa minimizes undesirable abrupt changes in grip force that may cause the wrist jaws to accidentally drop a grasped object as the jaws traverse the discontinuity between the two modes. In one embodiment, to transition from position mode to force mode, a debouncing strategy may be used to ensure that the desired jaw angle is less than a threshold between position mode and force mode for a pre-specified minimum duration before the wrist jaws transition to force mode.

In one embodiment, the system and method may determine the desired grip force from the desired jaw angle and may measure or estimate the grip force. A feedback loop may analyze the desired jaw angle, the desired grip force, and the measured grip force to determine if the jaws are transitioning from position mode to force mode, if the error between the measured grip force and the desired grip force is greater than a pre-specified maximum force error, and if the desired grip force is increasing. If so, the feedback loop may set the desired grip force as the current measured grip force minus a pre-specified margin when the jaws transition from position mode to force mode.

In one embodiment, the feedback loop may analyze the desired jaw angle, the desired grip force determined from the desired jaw angle, and the measured grip force to determine whether the jaws are transitioning from a force mode to a position mode, whether the desired grip force is less than a minimum grip force value, whether the desired grip force is decreasing, and whether the absolute value of the error between the measured grip force and the minimum grip force is less than a pre-specified maximum force error. If so, the feedback loop may set the desired grip force to the minimum grip force value when the jaws transition from a force mode to a position mode.

A method for controlling a jaw gripping force generated by jaws of a gripper tool is disclosed. The method may include determining whether the jaws are in the middle of closing in a position mode based on a desired jaw angle between the jaws. The position mode is characterized by applying position commands to drive the jaws to a desired position at the desired jaw angle. The method also includes determining whether the measured grip force exceeds a maximum grip force threshold if the jaws are in the middle of closing in the position mode. If the measured grip force exceeds the maximum grip force threshold, the method further includes generating a grip force error that is combined with the position command to limit the measured grip force to the maximum grip force threshold.

Another method for controlling a jaw opening force generated by jaws of a gripper tool is disclosed. The method may include determining whether the jaws are in a position mode based on a desired jaw angle between the jaws. The position mode is characterized by applying a position command to drive the jaws to a desired position at a desired jaw angle. The method also includes determining whether a jaw angle error between the desired jaw angle and the measured jaw angle is greater than an error threshold if the jaws are in the position mode. The method further includes determining whether the measured opening force is less than a minimum opening force threshold if the jaw angle error is greater than the error threshold. The method further includes generating an opening force error that is combined with the position command to maintain the measured opening force above the minimum opening force threshold if the measured opening force is less than the minimum opening force threshold.

Yet another method for controlling a gripping force generated by the jaws of a gripper tool is disclosed. The method may include determining that the jaws are transitioning between a position mode and a force mode based on a change in a desired jaw angle between the jaws. During the position mode, the jaws are driven at a commanded jaw angle, which may be the desired jaw angle. During the force mode, the jaws are driven at a commanded gripping force determined based on the desired jaw angle having a negative value. The method also includes determining whether to adjust the commanded gripping force during the transition between the position mode and the force mode based on the commanded gripping force and the measured gripping force. If so, the method further includes adjusting the commanded gripping force to reduce a change in the measured gripping force otherwise determined based on the desired jaw angle during the transition.

The accompanying drawings are provided together with the following description of various aspects and embodiments of the subject technology for a better understanding of the present invention. The drawings and embodiments are illustrative of the present invention and are not intended to limit the scope of the present invention. It is understood that those skilled in the art may modify the drawings to generate drawings of other embodiments that still fall within the scope of the present invention.
FIG. 1 is a pictorial diagram of an exemplary surgical robotic system 1 in an operating room, in accordance with aspects of the subject technology. FIG. 1 is a schematic diagram illustrating one exemplary design of a robotic arm, tool drive, and cannula loaded with a robotic surgical tool, in accordance with aspects of the subject technology. 1A-1C are schematic diagrams illustrating an example tool drive with and without a tool loaded, respectively, in accordance with aspects of the subject technology; 1A-1C are schematic diagrams illustrating an example tool drive with and without a tool loaded, respectively, in accordance with aspects of the subject technology; FIG. 1 is a schematic diagram illustrating an end effector of an exemplary grasper having a robotic wrist, a pair of opposing jaws, and a pulley and cable system for coupling the robotic wrist and the pair of jaws to an actuator of a tool drive, in accordance with aspects of the subject technology. FIG. 1 is a schematic diagram illustrating an end effector of an exemplary grasper having a robotic wrist, a pair of opposing jaws, and a pulley and cable system for coupling the robotic wrist and the pair of jaws to an actuator of a tool drive, in accordance with aspects of the subject technology. FIG. 1 is a block diagram of an exemplary control system for controlling the position and gripping force of an end effector of a robotic surgical tool, in accordance with an aspect of the subject technology. 13 is a time plot showing commanded jaw angle, measured jaw angle, commanded grip force, and measured grip force of the wrist jaws when the measured grip force is not limited while the jaws are in the middle of closing in position mode. 11 is a time plot illustrating commanded jaw angle, measured jaw angle, commanded grip force, and measured grip force of the wrist jaws when a control system limits the measured grip force to a pre-specified maximum threshold while the jaws are in the process of closing in position mode, in accordance with an aspect of the subject technology. FIG. 11 is a flowchart illustrating a method for feedback control of a surgical robotic system for limiting the grip force of the wrist jaws to a pre-specified maximum threshold while the jaws are in the mid-closing motion in position mode by analyzing the desired jaw angle and the measured grip force, in accordance with an aspect of the subject technology. 13 is a time plot showing commanded jaw angle, measured jaw angle, commanded grip force, and measured opening force of the wrist jaws when the measured opening force is not maintained above a minimum level while the jaws are in the middle of opening in position mode. 11 is a time plot illustrating commanded jaw angle, measured jaw angle, commanded grip force, and measured opening force of the wrist jaws as the control system maintains the measured opening force above a pre-specified minimum opening force threshold while the jaws are in the middle of opening in position mode, in accordance with an aspect of the subject technology. FIG. 11 is a flow chart illustrating a method for feedback control of a surgical robotic system to maintain a wrist jaw opening force above a pre-specified minimum opening force threshold while the jaws are in the mid-opening motion in positional mode by analyzing a desired jaw angle, an estimated jaw angle, and a measured opening force, in accordance with an aspect of the subject technology. FIG. 1 is a block diagram of an exemplary control system for controlling the position and grip force of an end effector of a robotic surgical tool when the end effector is in position mode or force mode, or when the end effector transitions between position mode and force mode, in accordance with aspects of the subject technology. 13 is a time plot showing the commanded jaw angle, measured jaw angle, commanded grip force, measured grip force, and grip force controller activity for the wrist jaws when the jaw angle is set near a threshold between position mode and force mode without the debouncing algorithm; 11 is a time plot illustrating the commanded jaw angle, measured jaw angle, commanded grip force, measured grip force, and grip force controller activity for the wrist jaws as the control system sets the jaw angle near a threshold between position mode and force mode when using a debouncing algorithm, in accordance with an aspect of the subject technology. 13 is a time plot showing the commanded jaw angle, measured jaw angle, commanded grip force, and measured grip force of the wrist jaws when the change in measured grip force is unconstrained as the jaws transition from position mode to force mode and back to position mode. 11 is a time plot illustrating commanded jaw angle, measured jaw angle, commanded grip force, and measured grip force of the wrist jaws as a control system constrains the change in grip force as the jaws transition between position mode and force mode, in accordance with an aspect of the subject technology; FIG. 11 is a flow chart illustrating a method for feedback control of a surgical robotic system for using a debouncing algorithm when setting a desired jaw angle of the wrist jaws near a threshold between position and force modes, or for adjusting the commanded grip force to limit changes in the measured grip force when the jaws transition between position and force modes, in accordance with aspects of the subject technology. FIG. 1 is a block diagram illustrating exemplary hardware components of a surgical robotic system, in accordance with aspects of the subject technology.

Examples of various aspects and variations of the subject technology are described herein and illustrated in the accompanying drawings. The following description is not intended to limit the invention to these embodiments, but rather to enable one of ordinary skill in the art to make and use the invention.

A feedback control system and method are disclosed for controlling the gripping or opening force of an end effector of a surgical robotic arm, such as a wrist jaw. The wrist jaw may be coupled to an actuator of a tool drive via a cable to effect multi-axis movement of the wrist jaw. The feedback control system may command a pitch angle, a yaw angle, and a jaw angle between the jaws to the wrist jaw. When the commanded jaw angle is higher than a threshold, also referred to as a threshold for detents, the wrist jaw may operate in a position mode to move the wrist jaw to a commanded position and orientation. The commanded jaw angle may also be referred to as a desired jaw angle. When the commanded jaw angle is lower than a threshold for detents, the wrist jaw may operate in a force mode from a position and orientation in the position mode, and a desired grip force is generated by a grip force controller based on the commanded jaw angle. In one embodiment, the feedback control system may limit the maximum grip force when the jaws are in the process of closing in the position mode by analyzing the desired jaw angle, measuring or estimating the actual applied grip force, and determining if the measured grip force exceeds a pre-specified maximum grip force threshold. If so, the feedback control system may calculate the grip force error and adjust the grip force such that the measured grip force is limited to a pre-specified maximum grip force threshold.

In one embodiment, the feedback control system may maintain a minimum jaw opening force when the jaws are in the middle of opening in position mode. The feedback control system may measure or estimate the actual applied jaw angle. The feedback control system may also measure or estimate the actual applied jaw gripping or opening force. The feedback control system may determine if the jaws are in position mode by analyzing the desired jaw angle, the measured jaw angle, and the measured jaw opening force, if the difference between the desired jaw angle and the estimated jaw angle is greater than a threshold, and if the measured jaw opening force is less than a pre-specified minimum opening force threshold. If so, the feedback control system may calculate an opening force error and adjust the gripping or opening force to maintain the measured jaw opening force above the pre-specified minimum opening force threshold.

In one embodiment, the feedback control system may use a debouncing algorithm to prevent the wrist jaws from oscillating between position mode and force mode when the jaw angle is set near a detent. The feedback control system may determine if the desired jaw angle is less than a threshold for the detent for a pre-specified duration. If so, the feedback control system may switch the wrist jaws from position mode to force mode. In one embodiment, the debouncing algorithm may be one-sided such that the wrist jaws may transition back to position mode as soon as the desired jaw angle is equal to or greater than the threshold.

In one embodiment, the feedback control system may minimize undesired abrupt changes in grip force when transitioning between position mode and force mode. The grip force controller may calculate a current command for the desired grip force from the desired jaw angle. The feedback control system may measure or estimate the actual applied grip force. The feedback control system may analyze the desired jaw angle, the desired grip force, and the measured grip force to determine whether the jaws are transitioning from position mode to force mode, whether the error between the measured grip force and the desired grip force is greater than a pre-specified maximum force error, and whether the desired grip force is increasing. If so, the feedback control system may set the grip force as the measured grip force minus a pre-specified margin when transitioning from position mode to force mode.

In one embodiment, the feedback control system may analyze the desired jaw angle, the desired grip force, and the measured grip force to determine whether the jaws are transitioning from force mode to position mode, whether the desired grip force is less than a pre-specified minimum grip force value, whether the desired grip force is decreasing, and whether the absolute value of the error between the measured grip force and the minimum grip force is less than a pre-specified maximum force error. If so, the feedback control system may set the grip force to the pre-specified minimum grip force value when transitioning from force mode to position mode. In one embodiment, the pre-specified minimum grip force value may be set to 3 N.

1 is a depiction of an exemplary surgical robotic system 1 in an operating room, in accordance with aspects of the subject technology. The robotic system 1 includes a user console 2, a control tower 3, and one or more surgical robotic arms 4 on a surgical robotic platform 5, e.g., a table, bed, or the like. The arms 4 may be attached to a table or bed on which a patient rests, as shown in the example of FIG. 1, or may be attached to a cart separate from the table or bed. The system 1 may incorporate any number of devices, tools, or accessories used to perform surgery on a patient 6. For example, the system 1 may include one or more surgical tools 7 used to perform surgery. The surgical tools 7 may be end effectors attached to the distal ends of the surgical arms 4 to perform the surgical procedure.

Each surgical tool 7 may be manipulated manually, robotically, or both during surgery. For example, surgical tool 7 may be a tool used to enter, view, or manipulate the internal anatomy of patient 6. In one aspect, surgical tool 7 is a grasper such as a wrist jaw that can grasp patient tissue. Surgical tool 7 may be configured to be controlled manually by a bedside operator 8, robotically via actuated movement of a surgical robotic arm 4 to which it is attached, or both. Although robotic arm 4 is shown mounted on a table, in other configurations arm 4 may be mounted on a cart, ceiling, or sidewall, or another suitable structural support.

A remote operator 9, such as a surgeon or other human operator, may use the user console 2 to remotely operate the arms 4 and their attached surgical tools 7, referred to herein as teleoperation. The user console 2 may be located in the same operating room as the rest of the system 1, as shown in FIG. 1. In other environments, however, the user console 2 may be located in an adjacent or nearby room, or in a remote location, e.g., a different building, city, or country. The user console 2 may include a seat 10, a foot-operated control 13, one or more handheld user input devices (UIDs) 14, and at least one user display 15, e.g., configured to display a view of a surgical site within the patient 6. In the exemplary user console 2, the remote operator 9 sits in the seat 10 and views the user display 15 while operating the foot-operated control 13 and the handheld UID 14 to remotely control the arms 4 and the surgical tools 7 attached to the distal ends of the arms 4.

In some variations, a bedside operator 8 may operate system 1 in a "bed-facing" mode. In this mode, the bedside operator 8 (user) is present near the patient 6 and simultaneously operates a robotically driven tool (end effector attached to arm 4) via a handheld UID 14 held in one hand and a manual laparoscopic tool with the other hand. For example, the bedside operator's left hand may operate the handheld UID to control the robotically driven tool, while the bedside operator's right hand may operate the manual laparoscopic tool. Thus, in variations of system 1, the bedside operator 8 may perform both robotically assisted minimally invasive surgery and manual laparoscopic surgery on the patient 6.

During an exemplary procedure, the patient 6 is sterilely prepped and draped to achieve anesthesia. Initial access to the surgical site may be performed manually while the arms of the robotic system 1 are in a stowed or retracted configuration (thereby facilitating access to the surgical site). Once access is complete, initial positioning or preparation of the robotic system 1, including the arms 4, may be performed. The procedure then proceeds with a remote operator 9 at the user console 2 utilizing a foot control 13 and a handheld user input device 14 to operate various end effectors and possibly an imaging system to perform the procedure. Manual assistance may also be provided at the procedure bed or table by sterile gowned bedside personnel, e.g., a bedside operator 8, who may perform tasks such as evacuating tissue, performing manual repositioning, and changing tools for one or more of the robotic arms 4. Non-sterile personnel may also be present to assist the remote operator 9 at the user console 2. Once the procedure or surgery is complete, the system 1 and user console 2 can be configured or set to a state that facilitates various post-operative procedures, such as cleaning or sterilization, and entry or printing of medical records via the user console 2.

In one embodiment, the teleoperator 9 holds and moves the UID 14 to provide input commands to move the robotic arm actuator 17 of the robotic system 1. The UID 14 may be communicatively coupled to the rest of the robotic system 1, for example, via the console computer system 16. The UID 14 may generate spatial state signals corresponding to the movement of the UID 14, e.g., the position and orientation of the hand-held housing of the UID, which may be input signals for controlling the movement of the robotic arm actuator 17. The robotic system 1 may use control signals derived from the spatial state signals to control the proportional movement of the actuator 17. In one embodiment, the console processor of the console computer system 16 receives the spatial state signals and generates corresponding control signals. Based on these control signals, i.e., signals that control how the actuator 17 is energized to move the segments or links of the arm 4, the movement of the corresponding surgical tool attached to the arm may mimic the movement of the UID 14. Similarly, the interaction between the teleoperator 9 and the UID 14 may generate grip control signals, for example, that cause the jaws of the grasper of the surgical tool 7 to close and grip tissue of the patient 6.

The surgical robotic system 1 may include several UIDs 14, where each handheld user input device generates a respective control signal for controlling the actuator of the respective arm 4 and the surgical tool (end effector). For example, the teleoperator 9 may move a first UID 14 to control the movement of an actuator 17 in the left robotic arm, which responds by operating a linkage, gear, etc. in the arm 4. Similarly, the teleoperator 9 moves a second UID 14 to control the movement of another actuator 17, which operates another linkage, gear, etc. in the robotic system 1. The robotic system 1 may include a right arm 4 fixed to a bed or table on the right side of the patient, and a left arm 4 on the left side of the patient. The actuator 17 may include one or more motors controlled to drive the rotation of a joint of the arm 4, which may, for example, change the orientation of an endoscope or grasper of a surgical tool 7 attached to that arm, relative to the patient. The movement of several actuators 17 in the same arm 4 can be controlled by spatial state signals generated from a particular UID 14. The UIDs 14 can also control the movement of respective surgical tool graspers. For example, each UID 14 can generate a respective grasp signal to control the movement of an actuator, e.g., a linear actuator, that opens and closes the jaws of a grasper at the distal end of the surgical tool 7 to grasp tissue in the patient 6.

In some aspects, communication between the platform 5 and the user console 2 may be via a control tower 3, which may translate user commands received from the user console 2 (more specifically, from the console computer system 16) into robotic control commands sent to the arm 4 on the robotic platform 5. The control tower 3 may also transmit status signals and feedback from the platform 5 back to the user console 2. The communication connections between the robotic platform 5, the user console 2, and the control tower 3 may be via wired and/or wireless links using any suitable of a variety of data communication protocols. Any wired connections may optionally be built into the floor and/or walls or ceiling of the operating room. The robotic system 1 may provide a video output to one or more displays, including displays in the operating room and remote displays accessible via the Internet or other networks. The video output (video feed) may also be encrypted to ensure privacy, and all or part of the video output may be stored on a server or electronic health care record system.

FIG. 2 is a schematic diagram illustrating one exemplary design of a robotic arm, tool drive, and cannula loaded with a robotic surgical tool, in accordance with aspects of the subject technology. As shown in FIG. 2, the exemplary surgical robotic arm 112 may include a number of links (e.g., link 202) and a number of actuation joint modules (e.g., joint 204) for actuating the multiple links relative to one another. The joint modules may include various types, such as pitch joints or roll joints, which may substantially constrain the movement of adjacent links relative to others about a particular axis. Also shown in the exemplary design of FIG. 2 is a tool drive 210 attached to the distal end of the robotic arm 112. The tool drive 210 may include a cannula 214 coupled to its end for receiving and guiding a surgical instrument 220 (e.g., an endoscope, stapler, etc.). The surgical instrument (or "tool") 220 may include an end effector 222 at the distal end of the tool. The multiple joint modules of the robotic arm 112 can be actuated to position and orient a tool drive 210 that actuates an end effector 222 for robotic surgery.

3A and 3B are schematic diagrams illustrating an exemplary tool drive loaded with a tool and an exemplary tool drive unloaded with a tool, respectively, according to aspects of the subject technology. As shown in FIGS. 3A and 3B, in one variation, the tool drive 210 may include an elongated base (or "stage") 310 having a longitudinal track 312 and a tool carriage 320 slidably engaged with the longitudinal track 312. The stage 310 may be configured to couple to a distal end of a robotic arm, such that articulation of the robotic arm may position and/or orient the tool drive 210 in space. In addition, the tool carriage 320 may be configured to receive a tool base 352 of a tool 220, which may also include a tool shaft 354 extending from the tool base 352 through the cannula 214, with an end effector 222 (not shown) disposed at the distal end.

In addition, the tool carriage 320 may actuate a set of end effector articulations through a cable system or wires or the like (the terms "cable" and "wire" are used interchangeably throughout this application) operated and controlled by an actuation drive. The tool carriage 320 may include actuation drives of different configurations. For example, the rotary shaft drive may include a motor having a hollow rotor and a planetary gear transmission disposed at least partially within the hollow rotor. The multiple rotary shaft drives may be arranged in any suitable manner. For example, the tool carriage 320 may include six rotary drives 322A-322F arranged in two rows extending longitudinally along the base, which are slightly staggered to reduce the width of the carriage and increase the compactness of the tool drive. As shown clearly in FIG. 3B, rotary drives 322A, 322B, and 322C may be generally arranged in a first row, and rotary drives 322D, 322E, and 322F may be generally arranged in a second row slightly longitudinally offset from the first row.

4A and 4B are schematic diagrams illustrating an exemplary grasper end effector having a robotic wrist, a pair of opposing jaws, and a pulley and cable system for coupling the robotic wrist and pair of jaws to an actuator of a tool drive, in accordance with aspects of the subject technology. The following tool model and controller design are described with reference to an exemplary surgical robotic grasper, but it is noted that the proposed control system for position and grip force control can be adapted to any tool that includes an end effector coupled to a tool shaft via a robotic wrist that allows multi-axis motion (e.g., pitch and yaw) of the end effector. Similar tools include, but are not limited to, graspers, grippers, forceps, needle holders, retractors, and cautery instruments.

As shown in FIG. 4A, a pair of opposing jaws 401A and 401B are movably coupled to a first yoke 402 of the robot wrist via an extending axle 412 along a first axis 410. The first yoke 402 may be movably coupled to a second yoke 403 of the robot wrist via a second extending axle 422 along a second axis 420. The pair of jaws 401A and 401B may each be coupled to or integrally formed with pulleys 415A and 415B, respectively, via the extending axle 412, so that both jaws can rotate about the axis 410. Pulleys 425A, 425B, 425C, and 425D are coupled to the extending axle 422 and rotate about the axis 420. Pulleys 425A, 425B, 425C, and 425D are arranged in a first set of pulleys 425B and 425C on one side of the yoke 402 and a second set of pulleys 425A and 425D on the other side of the yoke 402. Pulleys 425A and 425C are outer pulleys and pulleys 425B and 425D are inner pulleys. Similarly, a third set of pulleys 435A, 435B, 435C, and 435D are coupled to a third elongated axle 432 and rotate about an axis 430 parallel to the axis 420.

The gripper 220 can be actuated to move one or both of the jaws 401A and 401B in various ways about the axis 410. For example, the jaws 401A and 401B may open and close relative to one another. The jaws 401A and 401B may also be actuated to rotate together as a pair to provide yaw motion of the gripper 220. In addition, the first yoke 402, pulleys 415A and 415B, and jaws 401A and 401B can rotate about the axis 420 to provide pitch motion of the gripper 220. Movement of the tool's robotic wrist and/or jaws can be actuated by controlling four independent cables 405A-405D. 4A, cable 405A can begin (or terminate) on one side of pulley 415A and run along pulleys 425A and 435A, while cable 405B is configured to terminate on the other side of pulley 415A and run through pulleys 425B and 435B. Similarly, another pair of cables 405C and 405D can be coupled to jaw 401B. For example, cable 405C extends from one side of pulley 415B to pulleys 425C and 435C, while cable 405D runs through pulleys 425D and 435D and terminates on the other side of pulley 415B. The third set of pulleys 435A, 435B, 435C and 435D are positioned to keep the cables 405A-405D fixed to the second set of pulleys 425A-425D and prevent the cables from slipping or sliding relative to the pulleys 425A-425D.

4A and 4B, the gripper 220 can be actuated to move the jaws 401A and 401B in various ways, such as gripping (e.g., jaws rotating independently about axis 410), yaw (e.g., jaws rotating together about axis 410), and pitch (e.g., jaws rotating about axis 420), by imparting motion to one or more of the pulleys 415A, 415B, 425A, 425B, 425C, and 425D, thereby imparting motion to the first yoke 402 and/or one or both of the jaws 401A and 401B. The cables 405A-405D can be grouped into two antagonistic pairs, i.e., the jaws rotate in one direction while one cable of the antagonistic pair is actuated or tensioned and the other cable is released. Meanwhile, when only the other cable is tensioned, the jaws rotate in the opposite direction.

For example, cables 405A and 405B are a first antagonistic pair for moving jaw 401A, and cables 405C and 405D are a second antagonistic pair for controlling jaw 401B. When cable 405A is tensioned (e.g., by at least one of rotary drives 322a-322f) while cable 405B is slack, jaw 401A closes (moves toward opposing jaw 401B). Meanwhile, when cable 405B is tensioned and cable 405A is slack, jaw 401A opens (moves away from opposing jaw 401B). Similarly, cable 405C closes jaw 401B (moves toward opposing jaw 401A) when tensioned, and cable 405D opens jaw 401B (moves away from opposing jaw 401A) while the other cable is slack. As another example, the gripping force between jaws 401A and 401B can be achieved by keeping both cables 405A and 405C under tension after the jaws are closed (contacting each other) (while cables 405B and 405D are relaxed).

If both cables of an antagonistic pair are tensioned simultaneously while both cables of the other pair are slack, pulley 415A or pulley 415B will not rotate. Instead, the first yoke 402, along with jaws 401A and 401B, is caused to pitch about axis 420 by pulleys 415A and 415B. For example, if both cables of a pair 405A and 405B are tensioned simultaneously while pair 405C and 405D are slack, the jaws (along with yoke 402) will pitch out of the page. On the other hand, when both cables 405C and 405D are tensioned simultaneously and pair 405A and 405B are left slack, the jaws will pitch into the page.

4B is a schematic diagram illustrating exemplary angle definitions for various movements of gripper 220, in accordance with aspects of the subject technology. The angles are defined with reference to axes 410 and 420, as well as axis 452 of first yoke 402 and axis 453 of second yoke 403. For example, as shown in FIG. 4B, angle (θ ₁ ) between axis 452 and axis 453 may represent the rotation angle of yoke 402 about axis 420, which may also be defined as the pitch angle (θ _pitch ) of gripper 220 (whereas in FIG. 4A , axis 452 of yoke 402 is superimposed on axis 453 of yoke 403, since the jaws remain in the reference position, i.e., there is no pitch movement). In addition, angles (θ ₂ ) and (θ ₃ ) may represent angles between each of jaws 401A and 401B and axis 452 of yoke 402 (as the origin), respectively. To distinguish between sides of axis 452, angles (θ ₂ ) and (θ ₃ ) may take on different signs. For example, as illustrated in FIG. 4B , angle (θ ₂ ) is negative and angle θ( ₃ ) is positive.

To perform control tasks, it is often useful to define a consistent coordinate frame for the joint angles. For example, one may further define the jaw angle (θ _jaw ) as the angle between the two jaws 401A and 401B, and the yaw angle (θ _yaw ) as the angle between the axis 452 and a line that bisects the jaw angle. As mentioned above, the pitch angle (θ _pitch ) may be defined as the angle (θ ₁ ) between the axis 452 and the axis 453. Thus,

Below, methods and systems are described for controlling the angular position and grip force of a distal end effector of a robotic surgical instrument. The end effector may include a robotic wrist and a pair of opposing members (e.g., jaws or claws), each movable between an open position and a closed position actuated by two antagonistic wires. As illustrated in Figures 3 and 4, a total of four wires may each be driven by an independent actuator or motor. The control system may include a feedback loop with position and velocity feedback from the actuators and force feedback measured on the four wires to provide the desired position and grip force. In some implementations, the actuator controller may implement a position plus feedforward current mode. For example, the position controller in a position mode may drive the distal end effector to a desired angular position in space based on the position feedback, and in a force mode, the grip force controller provides additional feedforward current based on the grip force measured by the load cells on the four wires to achieve the desired grip force between the opposing members.

FIGURE 5 is a block diagram illustrating a high level control system for controlling a surgical tool in accordance with aspects of the subject technology. The control system includes an input 560, a controller 562, a plant 564, an output 568, and a sensor and estimator 566 on a feedback path between the output 568 and the controller 562. The plant 564 may include tool actuators and end effectors (see, e.g., rotational drives 322A-322F of FIGURE 3B and cables 405A-405D of the wrist jaws of FIGURE 4A, also actuator unit 510 and cable and wrist link 512 of FIGURE 10). The controller 562 may include one or more processors configured with software instructions stored on memory to calculate the motion of the plant 564 in response to an input 560, which may indicate a desired movement of an end effector of the surgical tool, such as a desired theta _pitch , a desired theta _yaw , and a desired theta _jaw of the wrist jaws of FIGURE 4B. Thus, commands generated by controller 562 may drive the tool actuators to facilitate the desired movement of the end effector. In one embodiment, the desired theta _pitch , theta _yaw , and theta _jaw may be generated by UID 14 under control of teleoperator 9 of FIG. 1. Outputs 568, such as end effector position, velocity, cable tension, and grip or release force, may be measured directly or estimated by sensors and estimators 566 and fed back to controller 562 for closed-loop control.

In one embodiment, when the desired jaw angle θ _jaw of the wrist jaw is equal to or greater than the threshold, the desired θ _jaw , also referred to _as command θ jaw, may be treated as a position control command in position mode. The threshold is used to determine the detent and may correspond to the angle at which both jaws contact the object between them exactly at the same time. If there is no object to be grasped, the threshold is 0 degrees when the jaws begin to contact each other. In position mode, the controller 562 may convert the desired θ _jaw , as well as the desired θ _pitch and desired θ _yaw , into corresponding actuator position commands to drive the wrist jaws to the desired position and orientation. When the desired θ _jaw is below the threshold, the wrist jaws are operating in force control mode, or simply force mode, and the desired jaw angle is converted into a desired grip force command. The controller 562 may generate current commands in addition to the position commands to achieve the desired grip force.

In one embodiment, the controller 562 may limit the maximum amount of grip force when the jaws are in the middle of closing in position mode to prevent damage to tissue that may be grasped by the jaws. The grip force of the jaws may be estimated or measured by a sensor and estimator 566. The controller 562 may analyze the desired θ _jaws and the measured grip force to determine if the jaws are in the middle of closing in position mode and if the measured grip force exceeds a pre-specified maximum grip force threshold. If so, the controller 562 may calculate a grip force error to limit the measured grip force to the pre-specified maximum grip force threshold. For example, to determine if the jaws are in the middle of closing in position mode, the controller 562 may first verify that the desired θ _jaws are equal to or greater than the threshold for detents and thus have been in position mode for more than a pre-specified duration. The controller 562 may use a debouncing technique to verify that the desired θ _jaws are decreasing for a pre-specified length of time. In one embodiment, if the desired θ _jaws are sampled at a periodic frequency, the controller 562 may verify that the samples of the desired θ _jaws are decreasing for a pre-specified number of samples.

To determine whether the measured grip force exceeds a pre-specified maximum grip force threshold, the controller 562 may also use a debouncing technique. In one embodiment, the feedback control loop of the control system of FIG. 5 may operate with a loop cycle time. The grip force counter may increment by one count every control loop cycle while the measured grip force is less than the maximum grip force threshold minus a margin. In one embodiment, the grip force counter may stop incrementing after reaching the maximum count. When the measured grip force is greater than the maximum grip force threshold, the grip force counter may be reset. The debouncing technique may declare the measured grip force to exceed the maximum grip force threshold over a window spanning a number of loop cycles equal to the grip force counter when the measured grip force is greater than the maximum grip force minus a margin anywhere within the window.

As an example, assume that the measured grip force is initially below the maximum grip force threshold minus a margin and that the grip force counter is incrementing. When the measured grip force increases above the maximum grip force threshold, the grip force counter may be reset. The feedback control loop of the controller 562 may attempt to modify the actuator position command to drive the wrist jaws to limit the measured grip force to the maximum grip force threshold. However, even if the measured grip force falls below the maximum grip force threshold but remains above the maximum grip force threshold minus a margin, the feedback control loop may still consider the measured grip force to be greater than the maximum grip force threshold so as to limit the maximum measured grip force. Assume that the measured grip force falls below the maximum grip force threshold minus a margin for only a few loop cycles, but then increases above this level again. The grip force counter may increment until the number of loop cycles that the measured grip force is temporarily below the maximum grip force threshold minus a margin. As long as the measured grip force remains above the maximum grip force threshold minus the margin within a window spanning a number of loop cycles equal to the grip force counter (e.g., the number of loop cycles during which the measured grip force is temporarily reduced to be lower than the maximum grip force threshold minus the margin), the feedback control loop may still consider the measured grip force to be greater than the maximum grip force threshold for the entire duration of the window so as to limit the maximum measured grip force.

When the controller 562 determines that the jaws are in the process of closing in position mode and the measured grip force exceeds the maximum grip force threshold, the controller may limit the measured grip force to the maximum grip force threshold. In one embodiment, the controller 562 may calculate a grip force error that is the difference between the maximum grip force threshold and the measured grip force. A zero steady state type controller, such as a proportional-integral (PI) force controller, may be deployed to receive the grip force error and maintain or limit the measured grip force to the maximum grip force threshold. The output of the PI force controller may be combined with the output of an inverse kinematic matrix that acts on the error in the desired position and orientation of the wrist jaws to generate a compensated actuator position command. The compensated actuator position command is added to the existing actuator position command to drive the wrist jaws to limit the maximum amount of grip force when the jaws are in the process of closing in position mode at the desired position and orientation.

6A is a time plot showing the commanded θ _jaw 603, measured θ _jaw 605, commanded grip force 607, and measured grip force 609 of the wrist jaws when the measured grip force 609 is not limited while the jaws are in the process of closing in position mode. The threshold θ _jaw between position mode and force mode is set to 0 such that when the commanded θ _jaw 603 is equal to or greater than 0 degrees, the wrist jaws are operating in position mode. When the commanded θ _jaw 603 is less than 0 degrees, the wrist jaws are operating in force mode.

6A shows that from 20 to 35 seconds, and again from 44 to 47 seconds, the wrist jaws are operating in position mode. The measured θ _jaws 605 remain within a relatively narrow range as the commanded θ _jaws 603 change in position mode or in force mode, presumably because the jaws are gripping an object. During position mode, the commanded grip force 607, which is the desired grip force, may be set to a default value of 0 N since the wrist jaws are not operating in force mode. However, the measured grip force 609 may be much larger. For example, from 26 to 28 seconds, and from 31 to 35 seconds, when the jaws are in the process of closing or being held in a closed position in position mode, the measured grip force 609 exceeds 10 N and can be as high as 15 N because the measured grip force is not limited. In force mode (e.g., from 35 to 44 seconds and after 47 seconds), the grip force controller may set a commanded grip force 607 as a function of the commanded θ _jaw 603, and a feedback control loop may maintain the measured grip force 609 to be the same as the commanded grip force 607.

6B is a time plot showing the commanded θ jaw 613, the measured θ _{jaw 615} , the commanded grip force 617, and the measured grip force 619 of the wrist jaws when the control system limits the measured grip force to a pre-specified maximum threshold while the jaws are in the process of closing in position mode, in accordance with an aspect of the subject _technology . The maximum grip force threshold is set to 8.5 N.

In Fig. 6B, the time plot of the commanded θ _jaw 613 and the measured θ _jaw 615 are the same as the commanded θ _jaw 603 and the measured θ _jaw 605 of Fig. 6A when the measured grip force is not limited. During position mode, the commanded grip force 617 is again set to a default value of 0 N by the grip force controller. However, the measured grip force 619 is limited to a maximum grip force threshold of 8.5 N by the grip force controller during position mode when the jaws are in the process of closing or are held in a closed position (e.g., 27-30 seconds, 32-36 seconds, and 41-45 seconds). Note that the limit on the maximum grip force in position mode does not affect force mode. Thus, in force mode, the measured grip force 619 may be allowed to exceed the maximum grip force threshold of 8.5 N by following the commanded grip force 617.

7 is a flow chart illustrating a method 700 for feedback control of a surgical robotic system to limit the grip force of the wrist jaws to a pre-specified maximum threshold while the jaws are in the midst of closing in position mode by analyzing the desired jaw angle and the measured grip force, in accordance with aspects of the subject technology. Method 700 may be implemented by controller 562 of the control system of FIG. 5, which receives the desired θ _jaws from a user input and the measured grip force from sensor and estimator 566, and generates actuator position commands for driving the wrist jaws.

At block 701, the method 700 determines whether the wrist jaws are in position mode. In one embodiment, block 701 may determine whether the desired θ _jaws are equal to or greater than a threshold θ _jaw between position mode and force mode for more than a pre-specified period of time to ensure that the wrist jaws are in position mode. In one embodiment, the threshold θ _jaws may be set to 0. If the wrist jaws are not in position mode, the wrist jaws are in force mode and the grip force is not limited. At block 709, the method 700 generates actuator position commands without imposing constraints on the grip force. In one embodiment, in addition to generating actuator position commands, block 709 converts the desired θ _jaws to a desired grip force command to achieve the desired grip force.

If the jaws are in position mode, block 703 determines whether the jaws are in the process of closing. In one embodiment, block 703 may use a debouncing technique to determine whether the desired θ _jaws are decreasing for a pre-specified duration or for a pre-specified number of samples. In one embodiment, the jaws may be considered to be in the process of closing if the desired θ _jaws are held stationary without increasing. If the jaws are not in the process of closing, the grip force is not limited even when in position mode. Method 700 defaults to block 709 which generates an actuator position command without imposing any constraints on the grip force.

If the jaws are in the middle of closing in position mode, block 705 determines whether the measured grip force exceeds a pre-specified maximum grip force threshold. In one embodiment, block 705 may use a debouncing technique to determine whether the measured grip force is greater than the maximum grip force threshold minus a margin anywhere within a window spanning a number of samples equal to the grip force counter. In one embodiment, the measured grip force may be sampled at the loop cycle time of the feedback control system of FIG. 5. The grip force counter may be incremented by one for each control loop cycle in which the measured grip force is less than the maximum grip force threshold minus a margin. When the measured grip force is greater than the maximum grip force threshold, the grip force counter may be reset. As long as the measured grip force exceeds the maximum grip force threshold minus a margin anywhere within a window spanning a number of samples equal to the grip force counter, the measured grip force is considered to exceed the maximum grip force threshold for the entire window. Otherwise, the measured grip force does not exceed the maximum grip force threshold and method 700 defaults to block 709 which generates an actuator position command without imposing any constraints on the grip force.

If the measured grip force exceeds the maximum grip force threshold while the jaws are in the middle of closing in position mode, block 707 generates a compensated actuator position command to limit the measured grip force to the maximum grip force threshold. In one embodiment, block 707 may calculate a grip force error, which is the difference between the maximum grip force threshold and the measured grip force. A zero steady state type controller, such as a proportional-integral (PI) force controller, may receive the grip force error and generate the compensated grip force command. The output of the PI force controller may be combined with the output of an inverse kinematic matrix that acts on the errors in the desired position and orientation of the wrist jaw to generate the compensated actuator position command. The compensated actuator position command may be added to the existing actuator position command to drive the wrist jaw to limit the measured grip force to the maximum grip force threshold.

In another aspect, the controller 562 may maintain a minimum jaw opening force by the wrist jaws when operating in position mode. The minimum jaw opening force may also be referred to as a minimum grip force. Maintaining a minimum jaw opening force while the jaws are in the middle of opening in position mode helps the jaws overcome resistance that may prevent the jaws from opening to the desired jaw angle. The jaw angle and opening force of the jaws may be estimated or measured by the sensor and estimator 566. The controller 562 may analyze the desired θ _jaws , the estimated θ _jaws , and the measured opening force to determine whether the jaws are in the middle of opening in position mode, whether the jaw angle error between the desired θ _jaws and the estimated θ _jaws is greater than a threshold, and whether the measured opening force is lower than a pre-specified minimum jaw opening force threshold. If so, the controller 562 may calculate the opening force error between the pre-specified minimum jaw opening force threshold and the measured opening force to maintain the measured opening force above the pre-specified minimum jaw opening force threshold.

In one embodiment, to determine whether the jaws are partway open in position mode, the controller 562 may first verify that the desired θ _jaws are equal to or greater than the threshold for detent and therefore in position mode for a time greater than a pre-specified duration. The controller 562 may then determine whether the jaws partway open in position mode are experiencing resistance that prevents the jaws from opening to the desired θ _jaws . In one embodiment, the controller 562 may use a debouncing technique to verify that the desired θ _jaws are greater than the estimated θ _jaws and that the θ jaw error, which is the difference between the desired θ _jaws and the estimated θ _jaws , is greater than a θ _jaw error threshold for a pre-specified length of time. In one embodiment, if the desired θ _jaws and the estimated θ _jaws are sampled at a periodic frequency, the controller 562 may verify that the θ _jaw error is greater than a θ _jaw error threshold for _a pre-specified number of samples.

To determine whether the measured opening force is less than a pre-specified minimum jaw opening force threshold, the controller 562 may also use a debouncing technique. The jaw opening force counter may increment by one count for each control loop cycle in which the measured opening force is greater than the minimum jaw opening force threshold plus a margin. In one embodiment, the jaw opening force counter may stop incrementing after reaching a maximum count. The jaw opening force counter may be reset when the measured opening force is less than the minimum jaw opening force threshold. The debouncing technique may declare the measured opening force to be less than the minimum jaw opening force threshold throughout a window spanning a number of loop cycles equal to the jaw opening force counter when the measured opening force is below the minimum jaw opening force threshold plus a margin anywhere within the window.

As an example, assume that the measured opening force is initially higher than the minimum jaw opening force threshold plus a margin and the jaw opening force counter is incrementing. When the measured opening force is lower than the minimum jaw opening force threshold, the jaw opening force counter may be reset. The feedback control loop of the controller 562 may attempt to vary the actuator position command to drive the wrist jaws to maintain the measured opening force higher than the minimum jaw opening force threshold. However, even if the measured opening force increases higher than the minimum jaw opening force threshold but remains lower than the minimum jaw opening force threshold plus a margin, the feedback control loop may still consider the measured opening force to be less than the minimum jaw opening force threshold so as to maintain the minimum jaw opening force. Assume that the measured opening force rises higher than the minimum jaw opening force threshold plus a margin for only a few loop cycles, but then falls below this level again. The jaw opening force counter may increment up to the number of loop cycles that the measured opening force was temporarily higher than the minimum jaw opening force threshold plus a margin. As long as the measured opening force remains below the minimum jaw opening force threshold plus a margin within a window spanning a number of loop cycles equal to the jaw opening force counter (e.g., the number of loop cycles during which the measured opening force was temporarily higher than the minimum jaw opening force threshold plus a margin), the feedback control loop may still consider the measured opening force to be less than the minimum jaw opening force threshold for the entire duration of the window so as to maintain the minimum jaw opening force.

When the controller 562 determines that the jaws are in the middle of opening in position mode and the theta _jaw error is greater than the theta _jaw error threshold and the measured opening force is less than a pre-specified minimum jaw opening force threshold, the controller may maintain the measured opening force above the minimum jaw opening force threshold. In one embodiment, the controller 562 may calculate a jaw opening force error that is the difference between the minimum jaw opening force threshold and the measured opening force. A zero steady state type controller, such as a proportional-integral (PI) force controller, may be deployed to receive the jaw opening force error and maintain the measured opening force above the minimum jaw opening force threshold. The output of the PI force controller may be combined with the output of an inverse kinematic matrix that acts on the error in the desired position and orientation of the wrist jaws to generate a compensated actuator position command. The compensated actuator position command is added to the existing actuator position command to drive the wrist jaws to maintain a minimum amount of opening force when the jaws are in the middle of opening in position mode at the desired position and orientation.

8A is a time plot showing the commanded θ _jaw 803, measured θ _jaw 805, commanded grip force 807, and measured opening force 809 of the wrist jaws when the measured opening force 809 is not maintained above a minimum level while the jaws are in the process of opening in position mode. The threshold θ _jaw between position mode and force mode is set to 0 such that when the commanded θ _jaw 603 is equal to or greater than 0 degrees, the wrist jaws are operating in position mode. When the commanded θ _jaw 603 is less than 0 degrees, the wrist jaws are operating in force mode. The θ _jaw error threshold is set to 5 degrees and the minimum opening force threshold is set to 4.4 N.

8A shows that from 49-60 seconds and from 62-67 seconds, the wrist jaws are operating in position mode. The measured θ _jaws 805 remain within a relatively narrow range even as the commanded θ _jaws 803 set the jaws to close or open in position mode, likely because the jaws halfway open in position mode are resisted or constrained from opening fully to the commanded θ _jaws 803. From 49-52 seconds, 56-59 seconds, and 62-66 seconds, when the jaws are halfway open in position mode or maintained at the same θ _jaw , the θ _jaw error, i.e., the difference between the larger commanded θ _jaws 803 and the smaller measured θ _jaws 805, may be greater than the 5 degree θ _jaw error threshold.

During position mode, the commanded grip force 807 may be set to a default value of 0 N by the grip force controller. Even during force mode, the commanded grip force 807 is still set to 0 N. A positive value of the measured opening force 809 corresponds to the opening force of the jaws in position mode, and a negative value corresponds to the grip force in force mode when the jaws are closed. The measured opening force 809 in position mode generally follows the profile of the commanded θ _jaws 803 because the jaws are constrained to open up to the commanded θ _jaws 803. The result is a stronger measured opening force 809 when the commanded θ _jaws 803 are increased for a wider opening of _the jaws, and conversely, a weaker measured opening force 809 when the commanded θ jaws 803 are decreased for a narrower opening of the jaws. Because the feedback control loop cannot maintain the measured opening force 809 above the minimum opening force threshold of 4.4 N between 53 and 60 seconds, the measured opening force 809 may drop below the minimum opening force threshold.

8B is a time plot showing commanded theta _{jaw 813} , measured theta jaw 815, commanded grip force 817, and measured opening force 819 of the wrist jaws as the control system maintains the measured opening force 819 above a pre-specified minimum opening force threshold during _jaw opening in position mode, in accordance with an aspect of the subject technology. Theta _jaw error threshold is again set to 5 degrees and the minimum opening force threshold is set to 4.4 N.

In Figure 8B, the time plot of the commanded θ _jaw 813 and the measured θ _jaw 815 is nearly the same as the commanded θ _jaw 803 and the measured θ _jaw 805 of Figure 8A when the minimum jaw opening force is not maintained. During position mode, the commanded grip force 817 is again set to a default value of 0 N by the grip force controller. However, when the θ _jaw error, i.e., the difference between the larger commanded θ _jaw 813 and the smaller measured θ _jaw 815, is greater than the 5 degree θ _jaw error threshold, the measured opening force 819 is maintained above the minimum opening force threshold of 4.4 N during 30-43 seconds of position mode by the feedback control loop and the grip force controller. Specifically, the minimum measured opening force 819 is maintained when the jaws are in the middle of opening, maintaining the same θ _jaw , or even when they are in the middle of closing in position mode. Note that the minimum opening force threshold in position mode does not affect the force mode as the measured opening force 819 may be negative.

9 is a flow chart illustrating a method 900 for feedback control of a surgical robotic system to maintain the wrist jaw opening force above a pre-specified minimum jaw opening force threshold while the jaws are in the middle of opening in positional mode by analyzing the desired jaw _angle , estimated jaw angle, and measured opening force, in accordance with aspects of the subject technology. Method 900 may be implemented by controller 562 of the control system of FIG. 5, which receives the desired θ jaw, estimated or measured θ _jaw from user input, and the measured opening force from sensors and estimators 566, and generates actuator position commands for driving the wrist jaws.

At block 901, the method 900 determines whether the wrist jaws are in position mode. In one embodiment, the block 901 may determine whether the desired θ _jaws are equal to or greater than a threshold θ _jaw between position mode and force mode for more than a pre-specified period of time to ensure that the wrist jaws are in position mode. In one embodiment, the threshold θ _jaws may be set to 0. If the wrist jaws are not in position mode, the wrist jaws are in force mode and the minimum opening force is not enabled. At block 909, the method 900 generates actuator position commands without maintaining a minimum opening force. In one embodiment, the block 909, in addition to generating actuator position commands, converts the desired θ _jaws to a desired grip force command to achieve a desired grip or opening force.

If the jaws are in position mode, block 903 determines whether the jaws are prevented from opening to the desired θ _jaws by determining whether a θ _jaw error, which is the difference between the desired θ _jaws and the estimated or measured θ _jaws , is equal to or greater than a θ _jaw error threshold. In one embodiment, block 903 may use a debouncing technique to determine whether the desired θ _jaws are greater than the estimated θ _jaws and whether the θ _jaw error is equal to or greater than the θ _jaw error threshold for a pre-specified amount of time. In one embodiment, block 903 may detect whether the _jaws are in the middle of opening , remaining at a stationary θ _jaw , or in the middle of closing by determining whether the desired θ jaws are increasing, staying the same, or decreasing, respectively. If the θ _jaw error is less than the θ _jaw error threshold, method 900 defaults to block 909 which generates an actuator position command without maintaining a minimum opening force.

If the θ _jaw error is equal to or greater than the θ _jaw error threshold when the jaws are in position mode, block 905 determines that the measured opening force is less than a pre-specified minimum jaw opening force threshold. In one embodiment, block 905 may use a debouncing technique to determine that the measured opening force is less than the minimum jaw opening force threshold plus a margin anywhere within a window spanning a number of samples equal to the jaw opening force counter. In one embodiment, the measured opening force may be sampled at the loop cycle time of the feedback control system of FIG. 5. The jaw opening force counter may be incremented by one every control loop cycle in which the measured opening force is greater than the minimum jaw opening force threshold plus a margin. When the measured opening force is less than the minimum jaw opening force threshold, the jaw opening force counter may be reset. As long as the measured opening force is less than the minimum jaw opening force threshold plus a margin anywhere within a window spanning a number of samples equal to the jaw opening force counter, the measured opening force is considered to be less than the minimum jaw opening force threshold for the entire window. Otherwise, the measured opening force is greater than or equal to the minimum jaw opening force threshold and the method 900 defaults to block 909 which generates actuator position commands without maintaining a minimum opening force.

If the measured opening force is less than the minimum jaw opening force threshold and the theta _jaw error is equal to or greater than the theta _jaw error threshold when the jaws are in position mode, block 907 generates a compensated actuator position command to maintain the measured opening force above the minimum jaw opening force threshold. In one embodiment, block 907 may calculate a jaw opening force error that is the difference between the minimum jaw opening force threshold and the measured opening force. A zero steady state type controller, such as a proportional-integral (PI) force controller, may be deployed to receive the jaw opening force error and maintain the measured opening force above the minimum jaw opening force threshold. The output of the PI force controller may be combined with the output of an inverse kinematic matrix that acts on the desired position and orientation error of the wrist jaws to generate a compensated actuator position command. The compensated actuator position command is added to the existing actuator position command to drive the wrist jaws to maintain a minimum amount of opening force when the jaws are in the middle of moving open in position mode.

In another aspect, the controller 562 may adjust the commanded grip force to smooth the applied grip force when the wrist jaws transition between the position mode and the force mode. Smoothing the applied grip force during the mode transition minimizes undesirable sudden changes in grip force caused by changes in the jaw position and commanded grip force that may cause the jaws to accidentally drop the grasped object as the jaws pass the discontinuity between the two modes. During the position mode, the desired θ _jaws are equal to or greater than the threshold for detents. The position controller may convert the desired θ as well as the desired θ _pitch and desired θ _yaw into corresponding actuator position commands to drive the wrist jaws to the desired position and orientation. During the force mode, when the desired θ _jaws are below the threshold for detents, e.g., when the desired θ _jaws are negative with respect to a detent set at 0 degrees, the grip force controller may be enabled to interpret the desired θ _jaws as a grip force command and may convert the desired θ _jaws into a compensation current that may be added to the current for the existing position command to drive the wrist jaws to achieve the commanded grip force.

In one embodiment, to smooth the applied grip force during mode transitions, the feedback control system may use a debouncing technique when the detents are set at 0 degrees. The debouncing technique may prevent the grip force controller from being repeatedly enabled and disabled to generate oscillations in the commanded grip force as the desired theta _jaw oscillates around positive and negative values.

In one embodiment, the feedback control system may minimize sudden changes in grip force when the wrist jaws transition from position mode to force mode by analyzing the desired θ _jaws , the commanded grip force, and the measured grip force. The feedback control system may determine whether the commanded grip force is increasing due to the grip force controller being enabled, as indicated by the desired θ _jaws decreasing below a threshold for detent, and whether the error between the measured grip force and the commanded grip force is greater than a pre-specified maximum force error. If so, the feedback control system may set the commanded grip force as the measured grip force minus a pre-specified margin when the wrist jaws transition from position mode to force mode.

In one embodiment, the feedback control system may minimize sudden changes in grip force when the wrist jaws transition from force mode to position mode by analyzing the desired θ _jaws , the commanded grip force, and the measured grip force. The feedback control system may determine whether the commanded grip force is less than a pre-specified minimum grip force value, whether the commanded grip force is decreasing because the grip force controller has been disabled as indicated by the desired θ _jaws increasing above a threshold for detent, and whether the absolute value of the error between the measured grip force and the minimum grip force is less than a pre-specified maximum grip force error value. If so, the feedback control system may set the commanded grip force to the pre-specified minimum grip force value when the wrist jaws transition from force mode to position mode.

10 is a block diagram of an exemplary control system 1000 for controlling the position and grip force of an end effector of a robotic surgical tool when the end effector is in a position mode or a force mode, or when the end effector transitions between position and force modes, in accordance with aspects of the subject technology. In one embodiment, the end effector includes a wrist jaw. The robotic control system 1000 includes an input processing unit 502, an actuator command generator 504, a position controller 506, a grip force controller 508, a plant including one or more actuator units 510 and/or cables and wrist links 512, a slack controller 514, a position estimator 522, and a grip force estimator 524.

The input processing unit 502 and actuator command generator 504 receive the desired angular positions of the wrist jaws and convert the desired angular positions (via an inverse kinematic algorithm) into corresponding actuator position commands that are output to the position controller 506 and/or the grip force controller 508. For example, the input desired angular positions may include a desired θ _jaw , a desired θ _pitch , and a desired θ _yaw . The desired θ _jaw may be treated as a position command when the desired θ _jaw is equal to or greater than a threshold for a detent. When the desired θ _jaw is less than a threshold for a detent, the desired θ _jaw may be converted into a desired grip force command (e.g., a command grip force) by the grip force controller 508, which may generate a current command to achieve the desired grip force.

The position controller 506 may receive position feedback from position and/or velocity sensors on the actuator unit 510. Achieving the desired actuator position may then result in the desired position of the wrist jaw due to the kinematic relationship between the actuator and the wrist jaw. Because the actuator unit 510 is coupled to the robot wrist through an elastic cable (or wire) whose length may change with force, an estimation based only on the pure kinematic relationship between the actuator position and the wrist movement may not be accurate. The position estimator 522 may provide more accurate estimates of the wrist joint position and velocity to the actuator command generator 504 and the grip force estimator 524 by taking into account the cable elasticity in the estimation algorithm (e.g., using a Kalman filter). The estimated position and velocity information may then be used for accurate positioning of the wrist and for estimating friction.

In one embodiment, the grip force controller 508 takes feedback of the cable tension measured by a load cell or torque sensor on the cable wire. An algorithm can then be used by the grip force estimator 524 to estimate the grip force between the jaws based on the tension value measured on the cable. The grip force controller 508 may compare the estimate to the desired grip force and generate additional current commands to achieve the desired grip force. The wrist jaws may be coupled to the tool drive via four independent cables, each actuated by an independent motor. In one embodiment, the motors may be driven by current. The current command may include two parts, the first part of the drive current may be from the position controller 506 and the second part may be from the grip force controller 508. The two current commands may be summed and sent to the actuator unit 510.

The slack controller 514 may have the task of ensuring that the tension in the cables never drops below zero (or a predetermined positive value to compensate for slack). The cables are tension-only members of the end effector and cannot have negative forces applied to them. It is therefore desirable to prevent the tension in the cables from dropping to zero. To achieve this goal, the slack controller 514 may monitor the force values from the cable load cells and compare the minimum of the force values to a predetermined threshold. If the minimum force value across all cables drops below the threshold, the slack controller 514 may generate additional position commands to all actuators to ensure that the desired minimum tension is maintained.

To smooth the grip force applied during mode transitions, the input processing unit 502 may use a debouncing technique when the detents are set to 0 degrees. The debouncing technique may determine whether the desired θ _jaw is less than the threshold for the detents for a pre-specified minimum duration before allowing the grip force controller 508 to transition the wrist jaws from position mode to force mode. When transitioning from force mode to position mode, the input processing unit 502 may disable the grip controller 508 as soon as the desired θ _jaw is equal to or greater than the threshold for the detents. Thus, the debouncing technique may be one-sided. The debouncing technique prevents the grip force controller 508 from being repeatedly enabled and disabled, a condition that can cause oscillations in the commanded grip force as the desired θ _jaw oscillates around the detents.

11A is a time plot showing the commanded θ _jaw 1103, measured θ _jaw 1105, commanded grip force 1107, measured grip force 1109, and current command 1106 from a grip force controller (e.g., grip force controller 508 of FIG. 10) of the wrist jaws when the commanded θ _jaw 1103 is set near a threshold for detents without a debouncing algorithm. The threshold for detents is set to 0 so that when the commanded θ _jaw 1103 is equal to or greater than 0 degrees, the wrist jaws are operating in position mode. When the commanded θ _jaw 1103 is less than 0 degrees, the wrist jaws are operating in force mode. A positive grip force indicates a grip force in force mode and a negative grip force indicates a grip force in position mode.

11A shows the wrist jaws operating in position mode between times 11.6 and 12 seconds. After time 12 seconds, the commanded theta _jaw 1103 is set near the threshold for the detent due to the user input device (UID) being set to the detent. The measured theta _jaw 1105 remains above about 20 degrees, likely because the jaw is gripping an object. The grip force controller 508 is repeatedly enabled and disabled as the wrist jaws swing between position mode and force mode, causing oscillations in the commanded grip force 1107 and current command 1106 from the grip force controller 508 when the grip force controller 508 is enabled during force mode. The result is an undesirable large oscillation in the measured grip force 1109 observed between times 12 and 12.4 seconds. The measured theta _jaw 1105 also shows some undesirable oscillations due to oscillations in the measured grip force 1109.

11B is a time plot illustrating the commanded theta _jaw 1113, the measured theta jaw 1115, the commanded grip force 1117, the measured _grip force 1119, and the current command 1116 from the grip force controller 508 for the wrist jaws when a control system (e.g., the input processing unit 502 and the actuator command generator 504 of FIG. 10) uses a debouncing algorithm when the commanded theta _jaw 1113 is set near a detent, in accordance with aspects of the subject technology. The threshold for the detent is again set to 0. Between times 30.2 and 30.9 seconds, the wrist jaws are operating in position mode. After time 30.9 seconds, the commanded theta _jaw 1113 is set near the threshold for the detent.

The debouncing algorithm may allow the grip force controller 508 to transition the wrist jaws from position mode to force mode only if the desired θ _jaws are less than 0 degrees for a pre-specified minimum duration. Because the control system does not detect this condition, the wrist jaws remain in position mode and the grip force controller 508 is not enabled. As a result, the commanded grip force 1117 remains at its default value of 0 N and the current command 1116 from the grip force controller 508 also remains at 0. The measured grip force 1119 does not exhibit large swings and the measured θ _jaws 1115 do not exhibit the vibrations observed in FIG. 11A, ensuring a smooth application of the grip force (the measured grip force 1119 is shown as positive even though the wrist jaws remain in position mode).

Smooth application of grip force may also be important when the wrist jaws are gripping an object when transitioning between position mode and force mode. For example, during position mode, a non-zero measured grip force may be present when the wrist jaws are gripping an object even if the grip force controller 508 is not enabled. The grip force controller 508 may initially drive the commanded grip force from 0 N when the desired θ _jaws drop below a threshold for detents, indicating a transition from position mode to force mode. Similarly, when transitioning from force mode to position mode, the commanded grip force may be reset to a default value of 0 N output from the position controller 506 when the grip force controller 508 is disabled. As a result, there may be a sudden change in the measured grip force during the transition, which may cause the wrist jaws to drop the object.

12A is a time plot showing the commanded theta _jaw 1203, measured theta jaw 1205, commanded grip force 1207, and measured grip force 1209 of the wrist jaws when the control system makes no attempt to limit the change in measured grip _force 1209 as the wrist jaws transition from position mode to force mode and back to position mode. The threshold for the detent is again set to 0 so that when the commanded theta _jaw 1203 is equal to or greater than 0 degrees, the wrist jaws are operating in position mode. When the commanded theta _jaw 1203 is less than 0 degrees, the wrist jaws are operating in force mode.

The wrist jaws are initially operating in position mode. The commanded theta _jaw 1203 is initially at 0 degrees and the commanded grip force 1207 is initially at 0 N. The measured theta _jaw 1205 is at 25 degrees and the measured grip force 1209 is 8 N due to an object being held between the jaws. At time 27.5 seconds, the commanded theta _jaw 1203 goes negative, transitioning the wrist jaws from position mode to force mode. When the grip force controller 508 is enabled, the commanded grip force 1207 ramps up from 0 N until the commanded theta _jaw 1203 reaches its most negative value. However, the measured grip force 1209 experiences a sudden drop of 5 N during the transition before ramping up as commanded. At time 30 seconds, the commanded theta _jaw 1203 begins to become less negative. The commanded grip force 1207 begins to ramp down and the measured grip force 1209 complies as commanded. At time 31 seconds, the command theta _jaw 1203 goes positive, transitioning the wrist jaws from force mode back to one mode. When the grip force controller 508 is disabled, the measured grip force 1209 experiences an abrupt jump from 0 N to a static 8 N in position mode, with some overshoot. It is desirable to minimize the abrupt change in the measured grip force 1209 during the transition.

In one embodiment, the grip force controller 508 may adjust the commanded grip force to minimize sudden changes in the grip force of the wrist jaws when holding an object during the transition from position mode to force mode. For example, the grip force controller 508 may set the commanded grip force to the current measured grip force minus a pre-specified margin when the grip force controller 508 is enabled when the commanded θ _jaws fall below a threshold for detents and if certain conditions are met. Doing so can prevent the measured grip force from dropping to a value close to 0 N during the transition, thereby reducing the possibility of the jaws dropping an object held between the jaws. In one embodiment, the measured grip force may be generated by the grip force estimator 524 based on tension values measured in the cables and cables from the wrist link 512.

To evaluate the first condition for adjusting the commanded grip force, the grip force controller 508 may determine whether the commanded grip force is increasing or will increase due to the grip force controller 508 being enabled, as indicated by the commanded θ _jaw decreasing below a threshold for detent. For the second condition, the grip force controller 508 may determine whether the error between the measured grip force and the commanded grip force is greater than a pre-specified maximum force error. In one embodiment, the grip force controller 528 may use a debouncing technique for one or both of the conditions. If these two conditions are met, the grip force controller 508 may set the commanded grip force to the current measured grip force minus a pre-specified margin.

In one embodiment, the grip force controller 508 may adjust the commanded grip force to minimize sudden changes in the grip force of the wrist jaws when holding an object during the transition from force mode to position mode. For example, the grip force controller 508 may set the commanded grip force to a pre-specified minimum grip force value when the grip force controller 508 is disabled when the commanded θ _jaws become greater than a threshold for detents, and if certain conditions are met. Doing so instead of starting from the default 0N in position mode may reduce the change in the measured grip force as it rises up to the static grip force in position mode.

To evaluate the conditions for adjusting the grip force, the grip force controller 508 may determine whether the commanded grip force is less than a pre-specified minimum grip force value. The grip force controller 508 may also determine whether the commanded grip force is decreasing, as indicated by the commanded θ _jaw increasing toward or exceeding a threshold for a detent. In addition, the grip force controller 508 may determine whether the absolute value of the error between the measured grip force and the minimum grip force value is less than a pre-specified maximum grip force error value. In one embodiment, the grip force controller 528 may use a debouncing technique for one or more conditions. If all conditions are met, the grip force controller 508 may set the commanded grip force to a pre-specified minimum grip force value. In one embodiment, the pre-specified minimum grip force value may be set to 3 N.

12B is a time plot showing the commanded θ _jaw 1213, measured θ jaw 1215, commanded grip force 1217, and measured grip force 1219 of the wrist jaws as the control system limits the change in the measured grip force 1219 as the wrist jaws transition between position mode and force mode _, in accordance with an aspect of the subject technology. The threshold for the detent is again set to 0 such that when the commanded θ _jaw 1213 is equal to or greater than 0 degrees, the wrist jaws are operating in position mode. When the commanded θ _jaw 1213 is less than 0 degrees, the wrist jaws are operating in force mode. A pre-specified maximum grip force error value, which should not be exceeded by the absolute value of the error between the measured grip force and the commanded grip force, is set to be greater than 8N. A pre-specified minimum grip force value is set to 3N.

The wrist jaws are initially operating in position mode, with the initial states of commanded θ _jaw 1213, measured θ _jaw 1215, commanded grip force 1217, and measured grip force 1219 being the same as in FIG. 12A. At time 37.4 seconds, commanded θ _jaw 1203 becomes negative, transitioning the wrist jaws from position mode to force mode. However, instead of starting at 0 N in force mode, commanded grip force 1217 starts at about 6.2 N, which is obtained by subtracting a pre-specified margin from measured grip force 1219 at this point. Because the absolute value of the error between measured grip force 1219 and commanded grip force 1217 is less than a pre-specified maximum force error, the condition for adjustment to commanded grip force 1217 is met. As a result, measured grip force 1219 experiences a significantly smaller drop during the transition from position mode to force mode than would occur without the adjustment to commanded grip force 1217. The command gripping force 1217 remains at 6.2N until the command gripping force 1217 determined from the increasingly negative command θ _jaw 1213 is greater than 6.2N.

At time 39.8 seconds, the commanded theta _jaw 1213 begins to become less negative. The commanded grip force 1217 begins to ramp down and the measured grip force 1219 follows as commanded. At time 40.5 seconds, the commanded grip force 1217 remains at the pre-specified minimum grip force value of 3N instead of continuing to ramp down to 0N as would otherwise occur without the adjustment as the commanded theta _jaw 1213 goes positive to transition the wrist jaw from force mode to position mode. The condition for an adjustment to the commanded grip force 1217 is met because the measured grip force 1219 is less than the pre-specified minimum grip force value of 3N and the absolute value of the error between the measured grip force 1219 and the commanded grip force 1217 is less than the pre-specified maximum force error. As a result, the measured grip force 1219 experiences a significantly smaller change than it would without the adjustment to the commanded grip force 1217 as it jumps to a static 8N in the position mode during the transition. The commanded grip force 1217 remains at 3N until the commanded grip force 1217 determined from the commanded θ _jaw 1213 becomes 0N.

13 is a flow chart illustrating a method 1300 for feedback control of a surgical robotic system for using a debouncing algorithm when setting a desired θ _jaw of the wrist jaws near a threshold for return, or for adjusting a commanded grip force to limit changes in the measured grip force when the wrist jaws transition between position and force modes, in accordance with an aspect of the subject technology. Method 1300 may be implemented by controller 562 of the control system of FIG. 5 or grip force controller 508 of the control system of FIG. 10, which receives the desired θ _jaws from a user input and the measured grip forces from sensors and estimators 566 of FIG. 5 or grip force estimator 524 of FIG. 10, respectively, and generates a commanded grip force for driving the wrist jaws.

Starting in position mode at block 1301, method 1300 determines in block 1303 whether the desired θ _jaw is less than the threshold for detents for a minimum duration. In one embodiment, the minimum duration may be pre-specified or configurable. Block 1303 implements a debouncing algorithm to prevent the force mode from being repeatedly enabled and disabled, a condition that may cause oscillations in the commanded grip force when the desired θ _jaw is set near the threshold for detents. In one embodiment, block 1303 may determine whether the commanded grip force is increasing or will increase, as indicated by the desired θ _jaw decreasing below the threshold for detents. If the desired θ _jaw is not less than the threshold for detents for a pre-specified minimum duration, the wrist jaws remain in position mode at block 1301.

Otherwise, if the desired θ _jaws are less than the threshold for detents for a pre-specified minimum duration, the wrist jaws are transitioning from position mode to force mode. Block 1304 determines whether the commanded grip force is increasing. If this condition is false, block 1307 sets the commanded grip force as transformed from the desired θ _jaws , and the commanded grip force is not adjusted to limit the change in the measured grip force during the mode transition. Otherwise, if the condition of block 1304 is true, block 1305 determines whether the error between the measured grip force and the commanded grip force is greater than the maximum force error during the mode transition. The commanded grip force may be a default 0 N in the position mode before the mode transition. The measured grip force may differ from the commanded grip force before the mode transition because the wrist jaws may be gripping an object. In one embodiment, the maximum force error may be pre-specified or configurable.

If the condition of block 1305 is true, block 1309 sets the commanded grip force to the measured grip force minus a margin when the wrist jaws transition from position mode to force mode. In one embodiment, the margin may be pre-specified or configurable. Alternatively, if the condition of block 1305 is false, block 1307 sets the commanded grip force as transformed from the desired θ _jaws , and the commanded grip force is not adjusted to limit the change in the measured grip force during the mode transition.

When the wrist jaws are in force mode at block 1311, the method 1300 determines whether the desired θ _jaws are greater than or equal to the detent threshold at block 1313. In one embodiment, block 1311 may determine whether the commanded grip force is decreasing, as indicated by the desired θ _jaws increasing toward the detent threshold, and whether the desired θ _jaws are just below the detent threshold. If the desired θ _jaws are not greater than or equal to the detent threshold, the wrist jaws remain in force mode at block 1311.

Otherwise, if the desired θ _jaw is equal to or greater than the threshold for the detent, the wrist jaws are transitioning from force mode to position mode. Block 1315 determines whether the commanded grip force is decreasing and whether the commanded grip force is less than a minimum grip force during the mode transition. In one embodiment, the minimum grip force may be pre-specified or configurable. If the commanded grip force is not decreasing or is not less than the minimum grip force during the mode transition, block 1307 sets the commanded grip force as transformed from the desired θ _jaw , and the commanded grip force is not adjusted to limit the change in measured grip force during the mode transition.

Otherwise, if the commanded grip force is decreasing and if the commanded grip force is less than the minimum grip force during the mode transition, block 1317 determines whether the absolute value of the error between the measured grip force and the minimum grip force value is less than the maximum force error during the mode transition. In one embodiment, the maximum force error may be pre-specified or configurable. The maximum force error in block 1317 for the force to position mode transition may be the same or different than the maximum force error in block 1305 for the position to force mode transition.

If the condition of block 1317 is true, block 1319 sets the commanded grip force to the minimum grip force when the wrist jaws transition from force mode to position mode. Otherwise, if the condition of block 1317 is false, block 1307 sets the commanded grip force as transformed from the desired θ _jaws , and the commanded grip force is not adjusted to limit the change in measured grip force during the mode transition.

14 is a block diagram illustrating exemplary hardware components of a surgical robotic system in accordance with aspects of the subject technology. The surgical robotic system may include an interface device 50, a surgical robot 80, and a control tower 70. The surgical robotic system may include other or additional hardware components, and the diagram is provided as an example and not a limitation to this system architecture.

The interface device 50 includes a camera 51, a sensor 52, a display 53, a user command interface 54, a processor 55, a memory 56, and a network interface 57. The camera 51 and the sensor 52 may be configured to capture color and depth image information of the surgical robotic system. Images captured by the camera 51 and the sensor 52 may be projected onto the display 53. The processor 55 may be configured to operate an operating system to control the operation of the interface device 50. The memory 56 may store image processing algorithms, operating systems, program codes, and other data memories used by the processor 55. The interface device 50 may be used to generate a desired theta _pitch , theta _yaw , and theta _jaw of the wrist jaws under the control of a teleoperator.

The user command interface 54 may include interfaces for other functions such as a web portal. The hardware components may communicate via a bus. The interface device may communicate with the surgical robotic system through an external interface using the network interface 57. The external interface may be a wireless or wired interface.

The control tower 70 may be a treatment site mobile cart housing touch screen displays, computers to control the surgeon's operation of the robotic-assisted instruments, safety systems, graphical user interface (GUI), light sources, and video and graphics computers. The control tower 70 may include a central computer 71, which may include at least a visualization computer, a control computer, and an auxiliary computer, various displays 73, which may include team displays and nurse displays, and a network interface 78 that couples the control tower 70 to both the interface device 50 and the surgical robot 80. The control tower 70 may also house third party equipment, such as an advanced light engine 72, an electrosurgical generator unit (ESU) 74, and an insufflator and CO2 tank 75. The control tower 70 may provide additional features for user convenience, such as a nurse display touch screen, soft power and E-hold buttons, a user-facing USB for video and still images, and an electronic caster control interface. The auxiliary computer may also run real-time Linux and provide logging/monitoring and interaction with cloud-based web services. A central computer 71 in the control tower 70 may receive the desired theta _pitch , theta _yaw , and theta _jaw of the wrist jaws generated by the interface device 50 and implement the methods described herein for controlling the gripping or opening force of the jaws.

The surgical robot 80 includes an articulating operating table 84 with multiple integrated arms 82 that can be positioned over the target patient anatomy. A set of compatible tools 83 may be attached to or detached from the distal ends of the arms 82, allowing the surgeon to perform a variety of surgical procedures. The surgical robot 80 may also include a control interface 85 for manual control of the arms 82, operating table 84, and tools 83. The control interface 85 may include items such as, but not limited to, remote controls, buttons, panels, and touch screens. Other accessories such as trocars (sleeves, seal cartridges, and obturators) and drapes may also be manipulated to perform procedures with the system. In one embodiment, the multiple arms 82 may include four arms mounted on both sides of the operating table 84, with two arms on each side. For a particular surgical procedure, an arm mounted on one side of the operating table 84 can be positioned on the other side of the operating table 84 by extending under and crossing the operating table 84 and an arm mounted on the other side, resulting in a total of three arms positioned on the same side of the operating table 84. The surgical tool may also include a table computer 81 and a network interface 88, which may communicate with the control tower 70 to position the surgical robot 80.

The foregoing description, for purposes of explanation, used specific terminology to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that many of the specific details are not required to practice the present invention. Thus, the foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Clearly, many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to best utilize the present invention and various embodiments with various modifications suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the present invention.

The methods, devices, processes, and logic described above may be implemented in many different ways and with many different combinations of hardware and software. The controller and estimator may include electronic circuitry. For example, all or part of the implementation may be a circuit including an instruction processor, such as a central processing unit (CPU), microcontroller, or microprocessor; an application specific integrated circuit (ASIC), programmable logic device (PLD), or field programmable gate array (FPGA); or a circuit including discrete logic or other circuit components, including analog circuit components, digital circuit components, or both; or any combination thereof. The circuitry may include, by way of example, separate interconnected hardware components and/or may be combined on a single integrated circuit die, distributed among multiple integrated circuit dies, or implemented in a multi-chip module (MCM) of multiple integrated circuit dies in a common package.

The circuitry may further include or have access to instructions for execution by the circuitry. The instructions may be stored in a tangible storage medium other than a temporary signal, such as flash memory, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM), or on a magnetic or optical disk, such as a compact disk read only memory (CDROM), hard disk drive (HDD), or other magnetic or optical disk, or in or on another machine-readable medium. An article of manufacture, such as a computer program product, may include a storage medium and instructions stored in or on the medium, which, when executed by the circuitry in the device, may cause the device to perform any of the processes described above or shown in the figures.

The implementation may be distributed as a circuit among multiple system components, such as among multiple processors and memories, optionally including multiple distributed processing systems. Parameters, databases, and other data structures may be stored and managed separately, may be incorporated into a single memory or database, may be logically and physically organized in many different ways, and may be implemented in many different ways, including data structures such as linked lists, hash tables, arrays, records, objects, or implicit storage mechanisms. Programs may be parts of a single program (e.g., subroutines), separate programs distributed across several memories and processors, or may be implemented in many different ways, such as libraries, such as shared libraries (e.g., dynamic link libraries (DLLs)). A DLL may, for example, store instructions that, when executed by the circuit, perform any of the processes described above or shown in the figures.

Additionally, the various controllers described herein may take the form of processing circuits, microprocessors or processors, and computer-readable media storing computer-readable program code (e.g., firmware) executable by (micro)processors, logic gates, switches, application specific integrated circuits (ASICs), programmable logic controllers, and embedded microcontrollers. The controllers may be configured with hardware and/or firmware to perform the various functions described below and illustrated in the flow diagrams. Additionally, some of the components shown as being internal to the controller may be stored external to the controller and other components may be used.

[Embodiment]
(1) A method for controlling a gripping force generated by jaws of a gripper tool of a surgical robotic system, comprising:
determining, by a processor, that the jaws are in the process of closing in a position mode based on an input jaw angle between the jaws, the position mode being characterized by using position commands to position the jaws at the input jaw angle;
measuring a gripping force between the jaws in the position mode;
determining, by the processor, whether the measured grip force exceeds a threshold in the position mode;
and in response to determining, by the processor, that the measured grip force exceeds the threshold, generating a grip force error to limit the measured grip force to the threshold.
(2) determining that the jaws are in the process of closing in the position mode includes:
2. The method of claim 1, further comprising determining, by the processor, that the input jaw angle is greater than or equal to a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held.
(3) determining that the jaws are in the process of closing in the position mode includes:
2. The method of claim 1, comprising determining, by the processor, that the input jaw angle is decreasing for a minimum period of time in the position mode.
(4) determining whether the measured grip force exceeds the threshold value includes:
2. The method of claim 1, comprising determining, by the processor, that the measured grip force exceeds the threshold as long as the measured grip force exceeds the threshold minus a margin anywhere within a time window.
(5) The length of the time window is measured by a grip force counter, and the operation of the grip force counter is
incrementing the grip force counter by one each time the measured grip force is sampled when the measured grip force is less than the threshold minus the margin;
and resetting the grip force counter when the measured grip force is greater than the threshold.

(6) determining whether the measured grip force exceeds the threshold value includes:
6. The method of claim 5, further comprising determining, by the processor, that the measured grip force exceeds the threshold value for the entire length of the time window equal to the grip force counter when the measured grip force exceeds the threshold value minus the margin anywhere within the time window.
7. The method of claim 1, wherein the grip force error comprises a difference between the measured grip force and the threshold value.
(8) generating the grip force error so as to limit the measured grip force to the threshold value,
generating, by the processor, a compensated position command from the grip force error;
combining, by the processor, the compensated position command and the position command to generate an updated position command.
9. The method of claim 8, further comprising applying the updated position commands to drive the jaws to limit the measured gripping force to the threshold value.
(10) An apparatus for controlling jaws of a gripper tool of a surgical robot system, comprising:
a sensor configured to estimate a gripping force generated by the jaws to generate a measured gripping force;
1. A processor comprising:
determining that the jaws are in the process of closing in a position mode based on a desired jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the desired jaw angle;
determining whether the measured grip force exceeds a threshold in the position mode;
a processor configured to: in response to determining that the measured grip force exceeds the threshold, generate a grip force error to limit the measured grip force to the threshold and update the position command;
an actuator drive unit configured to apply the updated position commands to drive the jaws to limit the measured gripping force to the threshold value.

(11) The processor is configured to determine that the jaws are in the middle of closing in the position mode,
11. The apparatus of claim 10, further comprising determining that the desired jaw angle is greater than or equal to a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held.
(12) The processor is configured to determine that the jaws are in the process of being closed in the position mode,
11. The apparatus of claim 10, further comprising determining that the desired jaw angle is decreasing for a minimum period of time in the position mode.
(13) The processor is configured to determine whether the measured grip force exceeds the threshold,
11. The apparatus of claim 10, further comprising determining that the measured grip force exceeds the threshold as long as the measured grip force exceeds the threshold minus a margin anywhere within a time window.
(14) The length of the time window is measured by a grip force counter, and the grip force counter:
incrementing by one each time the measured grip force is estimated by the sensor when the measured grip force is less than the threshold minus the margin;
and resetting the grip force counter when the measured grip force is greater than the threshold.
(15) The processor is configured to determine whether the measured grip force exceeds the threshold,
15. The apparatus of claim 14, further comprising determining that the measured grip force exceeds the threshold value for the entire length of the time window equal to the grip force counter when the measured grip force exceeds the threshold value minus the margin anywhere within the time window.

16. The apparatus of claim 10, wherein the grip force error comprises a difference between the measured grip force and the threshold value.
(17) The processor is configured to generate the grip force error and update the position command,
generating a compensated position command from the grip force error;
and combining the compensated position command with the position command to generate the updated position command to limit the measured grip force to the threshold value.
(18) A surgical robot system, comprising:
an end effector including a pair of jaws;
a user interface device configured to generate an input jaw angle between the jaws;
a processor communicatively coupled to the end effector, the processor comprising:
determining that the jaws are in the process of closing in a position mode based on the input jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the input jaw angle;
measuring a gripping force between the jaws in the position mode;
determining whether the measured grip force exceeds a threshold in the position mode;
in response to determining that the measured grip force exceeds the threshold, generating a grip force error to limit the measured grip force to the threshold and updating the position command;
and applying the updated position commands to position the jaws to limit the measured gripping force to the threshold value.
(19) The processor is configured to determine that the jaws are in the middle of closing in the position mode,
determining that the input jaw angle is greater than or equal to a threshold jaw angle for more than a first minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
determining that the input jaw angle is decreasing for a second minimum period of time in the position mode.
(20) The processor is configured to determine whether the measured grip force exceeds the threshold,
20. The surgical robot system of claim 18, further comprising using a debouncing algorithm to determine that the measured grip force exceeds the threshold minus a margin.

(21) A method for controlling an opening force generated by jaws of a gripper tool of a surgical robotic system, comprising:
determining, by a processor, that the jaws are in a position mode based on an input jaw angle between the jaws, the position mode being characterized by using position commands to position the jaws at the input jaw angle;
measuring a jaw angle and an opening force between the jaws in the position mode;
determining, by the processor, in the position mode, whether a jaw angle error between the input jaw angle and the measured jaw angle is greater than a jaw angle error threshold;
determining, by the processor, in response to determining that the jaw angle error is greater than the jaw angle error threshold, whether the measured opening force is less than a minimum opening force threshold;
and in response to determining, by the processor, that the measured opening force is less than the minimum opening force threshold, generating an opening force error to maintain the measured opening force above the minimum opening force threshold.
(22) Determining that the jaws are in the position mode includes:
22. The method of claim 21, comprising determining, by the processor, that the input jaw angle is greater than or equal to a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held.
(23) determining whether the jaw angle error is greater than the jaw angle error threshold includes:
determining, by the processor, that the input jaw angle is greater than the measured jaw angle;
determining, by the processor, that the jaw angle error is greater than the jaw angle error threshold for at least a minimum period of time.
(24) Determining whether the measured opening force is less than the minimum opening force threshold comprises:
22. The method of claim 21, comprising determining, by the processor, that the measured opening force is less than the minimum opening force threshold as long as the measured opening force is less than the minimum opening force threshold plus a margin anywhere within a time window.
(25) The length of the time window is measured by an opening force counter, and the operation of the opening force counter comprises:
incrementing the opening force counter by one each time the measured opening force is sampled when the measured opening force is greater than the minimum opening force threshold plus the margin;
25. The method of claim 24, comprising resetting the opening force counter when the measured opening force is less than the minimum opening force threshold.

(26) Determining whether the measured opening force is less than the minimum opening force threshold comprises:
26. The method of claim 25, further comprising determining, by the processor, that the measured opening force is less than the minimum opening force threshold value over the entire length of the time window equal to the opening force counter when the measured opening force is less than the minimum opening force threshold value plus the margin anywhere within the time window.
27. The method of claim 21, wherein the opening force error comprises a difference between the measured opening force and the minimum opening force threshold.
(28) generating the opening force error to maintain the measured opening force higher than the minimum opening force threshold,
generating, by the processor, a compensated position command from the opening force error;
combining, by the processor, the compensated position command and the position command to generate an updated position command.
29. The method of claim 28, further comprising applying the updated position commands to position the jaws to maintain the measured opening force above the minimum opening force threshold.
(30) An apparatus for controlling jaws of a gripper tool of a surgical robot system, comprising:
A sensor comprising:
estimating an angle between the jaws to generate a measured jaw angle;
a sensor configured to estimate an opening force generated by the jaws to generate a measured opening force; and
1. A processor comprising:
determining that the jaws are in a position mode based on a desired jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the desired jaw angle;
determining, in the position mode, whether a jaw angle error between the desired jaw angle and the measured jaw angle is greater than a jaw angle error threshold;
determining whether the measured opening force is less than a minimum opening force threshold in response to determining that the jaw angle error is greater than the jaw angle error threshold;
in response to determining that the measured opening force is less than the minimum opening force threshold, generate an opening force error for updating the position command to maintain the measured opening force above the minimum opening force threshold; and
and an actuator drive unit configured to apply the updated position commands to position the jaws to maintain the measured opening force above the minimum opening force threshold.

(31) The processor is configured to determine that the jaws are in the position mode,
31. The apparatus of claim 30, further comprising determining that the desired jaw angle is greater than or equal to a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held.
(32) The processor is configured to determine whether the jaw angle error is greater than the jaw angle error threshold,
determining that the desired jaw angle is greater than the measured jaw angle;
determining that the jaw angle error is greater than the jaw angle error threshold for at least a minimum period of time.
(33) The processor is configured to determine whether the measured opening force is less than the minimum opening force threshold,
The apparatus of claim 30, further comprising determining that the measured opening force is less than the minimum opening force threshold as long as the measured opening force is less than the minimum opening force threshold plus a margin anywhere within a time window.
(34) The length of the time window is measured by an opening force counter, the opening force counter comprising:
incrementing by one each time the measured opening force is estimated by the sensor when the measured opening force is greater than the minimum opening force threshold plus the margin;
34. The apparatus of claim 33, configured to reset the opening force counter when the measured opening force is less than the minimum opening force threshold.
(35) The processor is configured to determine whether the measured opening force is less than the minimum opening force threshold,
35. The apparatus of claim 34, further comprising determining that the measured opening force is less than the minimum opening force threshold over the entire length of the time window equal to the opening force counter when the measured opening force is less than the minimum opening force threshold plus the margin anywhere within the time window.

36. The apparatus of claim 30, wherein the opening force error comprises a difference between the measured opening force and the minimum opening force threshold.
(37) The processor is configured to generate the opening force error and update the position command,
generating a compensated position command from the opening force error;
and combining the compensation position command with the position command to generate the updated position command to position the jaws to maintain the measured opening force above the minimum opening force threshold.
(38) A surgical robot system, comprising:
an end effector including a pair of jaws;
a user interface device configured to generate an input jaw angle between the jaws;
a processor communicatively coupled to the end effector, the processor comprising:
determining that the jaws are in a position mode based on the input jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the input jaw angle;
measuring a jaw angle and an opening force between the pair of jaws in the position mode;
in the position mode, determining whether a jaw angle error between the input jaw angle and the measured jaw angle is greater than a jaw angle error threshold;
determining whether the measured opening force is less than a minimum opening force threshold in response to determining that the jaw angle error is greater than the jaw angle error threshold;
in response to determining that the measured opening force is less than the minimum opening force threshold, generating an opening force error for updating the position command to maintain the measured opening force above the minimum opening force threshold;
and applying the updated position commands to position the jaws to maintain the measured opening force above the minimum opening force threshold.
(39) The processor is configured to determine whether the jaw angle error is greater than the jaw angle error threshold,
determining that the input jaw angle is greater than the measured jaw angle;
determining that the jaw angle error is greater than the jaw angle error threshold for at least a minimum period of time.
(40) The processor is configured to determine whether the measured opening force is less than the minimum opening force threshold,
39. The surgical robot system of claim 38, further comprising using a debouncing algorithm to determine that the measured opening force is less than the minimum opening force threshold plus a margin.

(41) A method for controlling a gripping force generated by jaws of a gripper tool of a surgical robotic system, comprising:
determining, by a processor, based on a change in an input jaw angle between the jaws, that the jaws are transitioning between a position mode and a force mode, the position mode being characterized by positioning the jaws at the input jaw angle and the force mode being characterized by actuating the jaws to a commanded grip force determined based on the input jaw angle having a negative value;
measuring the gripping force between the jaws; and
determining, by the processor, whether to adjust the commanded grip force during the transition between the position mode and the force mode based on the commanded grip force and the measured grip force;
and in response to determining, by the processor, to adjust the commanded grip force, adjusting the commanded grip force to smooth changes in the measured grip force during the transition between the position mode and the force mode.
(42) Determining that the jaws are transitioning between the position mode and the force mode comprises:
42. The method of claim 41, comprising determining that the jaws are transitioning from the position mode to the force mode when the input jaw angle is initially greater than or equal to 0 and becomes less than 0 for a minimum duration; or determining that the jaws are transitioning from the force mode to the position mode when the input jaw angle is initially less than 0 and becomes greater than or equal to 0.
(43) Determining that the jaws are transitioning between the position mode and the force mode comprises:
determining, by the processor, that the jaws are initially in the position mode when the input jaw angle is equal to or greater than a threshold jaw angle, the threshold jaw angle including a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
determining, by the processor, that the jaws transition from the position mode to the force mode when the input jaw angle is less than the threshold jaw angle for more than a minimum duration.
(44) During the transition, determining whether to adjust the commanded grip force includes:
44. The method of claim 43, further comprising determining, by the processor, to adjust the commanded grip force when the commanded grip force is increasing during the transition from the position mode to the force mode and a difference between the measured grip force and the commanded grip force is greater than a maximum grip force error.
(45) Adjusting the command grip force includes
45. The method of claim 44, further comprising: in response to determining, by the processor, to adjust the commanded grip force, setting the commanded grip force to the measured grip force minus a margin; or otherwise setting, by the processor, the commanded grip force based on the input jaw angle in the force mode.

(46) Determining that the jaws are transitioning between the position mode and the force mode comprises:
determining, by the processor, that the jaws are initially in the force mode when the input jaw angle is less than a threshold jaw angle, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
determining, by the processor, that the jaws transition from the force mode to the position mode when the input jaw angle is greater than or equal to the threshold jaw angle.
(47) During the transition, determining whether to adjust the commanded grip force includes:
47. The method of claim 46, further comprising determining, by the processor, to adjust the commanded grip force during the transition from the force mode to the position mode when the commanded grip force is decreasing, the commanded grip force is less than a minimum grip force, and an absolute value of the difference between the measured grip force and the minimum grip force is less than a maximum grip force error.
(48) Adjusting the command grip force includes
48. The method of claim 47, further comprising: in response to determining, by the processor, to adjust the commanded grip force, setting the commanded grip force to the minimum grip force; or otherwise setting, by the processor, the commanded grip force based on the input jaw angle.
49. The method of claim 41, further comprising: varying, by the processor, the commanded grip force in the force mode based on the input jaw angle following the transition from the position mode to the force mode when the commanded grip force is adjusted; or varying, by the processor, the commanded grip force in the position mode based on the input jaw angle following the transition from the force mode to the position mode when the commanded grip force is adjusted.
(50) An apparatus for controlling jaws of a gripper tool of a surgical robotic system, comprising: a sensor configured to estimate a gripping force between the jaws to generate a measured gripping force;
a processor, the processor comprising:
determining that the jaws transition between a position mode and a force mode based on a change in a desired jaw angle between the jaws, the position mode being characterized by positioning the jaws at the desired jaw angle and the force mode being characterized by actuating the jaws to a commanded grip force determined based on the desired jaw angle having a negative value;
determining whether to adjust the commanded grip force during the transition between the position mode and the force mode based on the commanded grip force and the measured grip force;
in response to a decision to adjust the commanded grip force, adjust the commanded grip force to smooth changes in the measured grip force during the transition between the position mode and the force mode.

(51) The processor is configured to determine that the jaws transition between the position mode and the force mode,
determining that the jaws transition from the position mode to the force mode when the desired jaw angle is initially greater than or equal to zero and becomes less than zero for a minimum duration;
determining that the jaws will transition from the force mode to the position mode when the desired jaw angle is initially less than 0 and becomes greater than or equal to 0.
(52) The processor is configured to determine that the jaws transition between the position mode and the force mode,
determining that the jaws are initially in the position mode when the desired jaw angle is equal to or greater than a threshold jaw angle, the threshold jaw angle including a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
determining that the jaws transition from the position mode to the force mode when the desired jaw angle is less than the threshold jaw angle for more than a minimum duration.
(53) The processor is configured to determine whether to adjust the commanded grip force during the transition,
53. The apparatus of claim 52, further comprising: determining to adjust the commanded grip force when the commanded grip force is increasing during the transition from the position mode to the force mode and a difference between the measured grip force and the commanded grip force is greater than a maximum grip force error.
(54) The processor is configured to adjust the command grip force,
54. The apparatus of claim 53, further comprising: in response to the decision to adjust the commanded grip force, setting the commanded grip force to the measured grip force minus a margin; or otherwise setting the commanded grip force based on the desired jaw angle in the force mode.
(55) The processor is configured to determine that the jaws transition between the position mode and the force mode,
determining that the jaws are initially in the force mode when the desired jaw angle is less than a threshold jaw angle, the threshold jaw angle including the jaws simultaneously contacting an object held between the jaws or the jaws beginning to contact each other without an object being held;
determining that the jaws will transition from the force mode to the position mode when the desired jaw angle is greater than or equal to the threshold jaw angle.

(56) The processor is configured to determine whether to adjust the commanded grip force during the transition,
56. The apparatus of claim 55, further comprising: determining to adjust the commanded grip force when, during the transition from the force mode to the position mode, the commanded grip force is decreasing, the commanded grip force is less than a minimum grip force, and an absolute value of the difference between the measured grip force and the minimum grip force is less than a maximum grip force error.
(57) The processor is configured to adjust the command grip force,
57. The apparatus of claim 56, further comprising: in response to the decision to adjust the commanded grip force, setting the commanded grip force to the minimum grip force; or otherwise setting the commanded grip force based on the desired jaw angle in the force mode.
(58) The processor,
51. The apparatus of claim 50, further configured to: vary the commanded grip force in the force mode based on the desired jaw angle following the transition from the position mode to the force mode when the processor is configured to adjust the commanded grip force; or vary the commanded grip force in the position mode based on the desired jaw angle following the transition from the force mode to the position mode when the processor is configured to adjust the commanded grip force.
(59) A surgical robot system, comprising:
an end effector including a pair of jaws;
a user interface device configured to generate an input jaw angle between the jaws;
a processor communicatively coupled to the end effector, the processor comprising:
determining, based on a change in the input jaw angle, that the jaws transition between a position mode and a force mode, the position mode being characterized by positioning the jaws at the input jaw angle and the force mode being characterized by actuating the jaws to a commanded grip force determined based on the input jaw angle having a negative value;
Measuring a gripping force between the pair of jaws; and
determining whether to adjust the commanded grip force during the transition between the position mode and the force mode based on the commanded grip force and the measured grip force;
in response to a decision to adjust the commanded grip force, adjust the commanded grip force to smooth changes in the measured grip force during the transition between the position mode and the force mode.
(60) The processor is configured to determine that the jaws transition between the position mode and the force mode,
determining that the jaws are initially in the position mode when the input jaw angle is equal to or greater than a threshold jaw angle, the threshold jaw angle including a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
determining that the jaws transition from the position mode to the force mode when the input jaw angle is less than the threshold jaw angle for more than a minimum duration;
The processor is configured to determine whether to adjust the commanded grip force during the transition,
determining to adjust the commanded grip force when, during the transition from the position mode to the force mode, the commanded grip force is increasing and a difference between the measured grip force and the commanded grip force is greater than a maximum grip force error;
The processor is configured to adjust the commanded grip force,
60. The surgical robot system of claim 59, further comprising: in response to the decision to adjust the commanded grip force, setting the commanded grip force to the measured grip force minus a margin; or otherwise setting the commanded grip force based on the input jaw angle in the force mode.

Claims (18)

1. An apparatus for controlling jaws of a gripper tool of a surgical robotic system, comprising:
a sensor configured to estimate a gripping force generated by the jaws to generate a measured gripping force;
1. A processor comprising:
determining that the jaws are in the process of closing in a position mode based on a desired jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the desired jaw angle;
determining whether the measured grip force exceeds a threshold in the position mode;
a processor configured to: in response to determining that the measured grip force exceeds the threshold, generate a grip force error to limit the measured grip force to the threshold and update the position command;
and an actuator drive unit configured to apply the updated position command to drive the jaws to limit the measured gripping force to the threshold value. The processor is configured to determine that the jaws are in the process of closing in the position mode,
2. The apparatus of claim 1, comprising determining that the desired jaw angle is equal to or greater than a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held. The processor is configured to determine that the jaws are in the process of being closed in the position mode,
The apparatus of claim 1 including determining that the desired jaw angle is decreasing for a minimum period of time in the position mode. The processor is configured to determine whether the measured grip force exceeds the threshold value,
2. The apparatus of claim 1, further comprising determining that the measured grip force exceeds the threshold as long as the measured grip force exceeds the threshold minus a margin anywhere within a time window. The length of the time window is measured by a grip force counter, the grip force counter
incrementing by one each time the measured grip force is estimated by the sensor when the measured grip force is less than the threshold minus the margin;
and resetting the grip force counter when the measured grip force is greater than the threshold value. The processor is configured to determine whether the measured grip force exceeds the threshold value,
6. The apparatus of claim 5, further comprising determining that the measured grip force exceeds the threshold value for the entire length of the time window equal to the grip force counter when the measured grip force exceeds the threshold value minus the margin anywhere within the time window. The device of claim 1, wherein the grip force error comprises a difference between the measured grip force and the threshold value. The processor is configured to generate the grip force error and update the position command,
generating a compensated position command from the grip force error;
and combining the compensated position command with the position command to generate an updated position command to limit the measured grip force to the threshold value. 1. A surgical robotic system, comprising:
an end effector including a pair of jaws;
a user interface device configured to generate an input jaw angle between the jaws;
a processor communicatively coupled to the end effector, the processor comprising:
determining that the jaws are in the process of closing in a position mode based on the input jaw angle between the jaws, the position mode being characterized by application of position commands to position the jaws at the input jaw angle;
measuring a gripping force between the jaws in the position mode;
determining whether the grip force measured in the position mode exceeds a threshold;
in response to determining that the measured grip force exceeds the threshold, generating a grip force error to limit the measured grip force to the threshold and updating the position command;
and applying the updated position commands to position the jaws to limit the measured gripping force to the threshold. The processor is configured to determine that the jaws are in the process of closing in the position mode,
determining that the input jaw angle is greater than or equal to a threshold jaw angle for more than a first minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held;
and determining that the input jaw angle is decreasing for a second minimum period of time in the position mode. The processor is configured to determine whether the measured grip force exceeds the threshold.
The surgical robot system of claim 9, further comprising using a debouncing algorithm to determine when the measured grip force exceeds the threshold minus a margin. 1. A method for controlling a gripping force generated by jaws of a gripper tool of a surgical robotic system, comprising:
determining, by a processor, that the jaws are in the process of closing in a position mode based on an input jaw angle between the jaws, the position mode being characterized by using position commands to position the jaws at the input jaw angle;
measuring a gripping force between the jaws while the jaws are in the process of closing in the position mode;
determining, by the processor, whether the grip force measured in the position mode exceeds a grip force threshold;
generating, by the processor, a grip force error in response to determining that the measured grip force exceeds the grip force threshold, the grip force error comprising a difference between the measured grip force and the grip force threshold; and
generating an updated position command based on the grip force error; and
applying the updated position commands to position the jaws, thereby limiting the grip force to the grip force threshold. Determining that the jaws are in the process of closing in the position mode includes:
13. The method of claim 12, comprising determining, by the processor, that the input jaw angle is greater than or equal to a threshold jaw angle for more than a minimum period of time, the threshold jaw angle comprising a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to contact each other without an object being held. Determining that the jaws are in the process of closing in the position mode includes:
The method of claim 12 including determining, by the processor, that the input jaw angle is decreasing for a minimum period of time in the position mode. Determining whether the measured grip force exceeds the grip force threshold includes:
13. The method of claim 12, comprising determining, by the processor, that the measured grip force exceeds the grip force threshold so long as the measured grip force exceeds the grip force threshold minus a margin anywhere within a time window. The length of the time window is measured by a grip force counter, the operation of which is determined by:
incrementing the grip force counter by one each time the measured grip force is sampled when the measured grip force is less than the grip force threshold minus the margin;
and resetting the grip force counter when the measured grip force is greater than the grip force threshold. Determining whether the measured grip force exceeds the grip force threshold includes:
17. The method of claim 16, further comprising determining, by the processor, that the measured grip force exceeds the grip force threshold for the entire length of the time window equal to the grip force counter when the measured grip force exceeds the grip force threshold minus the margin anywhere within the time window. Generating the updated position command
generating, by the processor, a compensated position command from the grip force error;
and combining, by the processor, the compensated position command and the position command to generate the updated position command.

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