WO2025128509A1

WO2025128509A1 - System for tension member break detection

Info

Publication number: WO2025128509A1
Application number: PCT/US2024/059294
Authority: WO
Inventors: Poya KHALAF; Gabriel F. BRISSON
Original assignee: Intuitive Surgical Operations Inc
Current assignee: Intuitive Surgical Operations Inc
Priority date: 2023-12-14
Filing date: 2024-12-10
Publication date: 2025-06-19
Anticipated expiration: 2026-06-14

Abstract

A computer-assisted system including a manipulator assembly configured to support an instrument with a tension member to actuate a degree of freedom of the instrument. The manipulator assembly is configured to modulate a tension metric of the tension member. The computer-assisted system further includes a control system. The control system configured to make a first determination of whether the tension metric corresponds to a high-tension state, make a second determination of whether a tension drop of the tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold, and make a third determination of whether, after the tension drop, the tension metric is below a low-tension threshold. The control system is further configured to determine, based on the first, second, and third determinations, whether there is a break in the tension member, and perform an action in response to a determined break in the tension member.

Description

SYSTEM FOR TENSION MEMBER BREAK

DETECTION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing date of U.S. Provisional Patent Application 63/610,013 filed on December 14, 2023, which is hereby incorporated by reference herein in its entirety.

BACKGROUND

Field of Invention

[0002] The present invention generally provides improved computer-assisted devices, systems, and methods.

Overview

[0003] Computer-assisted systems can be used to perform a task at a worksite. For example, a computer-assisted system may include a handheld, motorized tool assembly. As another example, a computer-assisted system may include a manipulator system that may include one or more manipulator arms to manipulate instruments for performing the task. [0004] Example computer-assisted systems include industrial and recreational manipulator systems. Example computer-assisted systems also include medical manipulator systems used in procedures for diagnosis, non-surgical treatment, surgical treatment, etc.

[0005] Some computer-assisted systems include one or more instruments that are articulated in order to perform various procedures. In some computer-assisted systems, articulation of an instrument and/or movement and control of the one or more manipulator arms, if present, is provided, at least in part, with one or more tension members (e.g., cables). In such systems, it is desirable to quickly and accurately detect whether a tension member is broken.

SUMMARY

[0006] It should be appreciated that the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination, as the present disclosure is not limited in this respect. Further, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various nonlimiting embodiments when considered in conjunction with the accompanying figures. [0007] In general, in one aspect, one or more embodiments relate to a computer- assisted system that includes a manipulator assembly configured to support an instrument, the instrument including a tension member to actuate a degree of freedom of the instrument, where the manipulator assembly is configured to modulate a tension metric of the tension member. The computer-assisted system further includes a control system with one or more processors, the control system communicatively coupled to the manipulator assembly. The control system is configured to make a first determination of whether the tension metric corresponds to a high-tension state. The control system is further configured to make a second determination of whether a tension drop of the tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold. The control system is further configured to make a third determination of whether, after the tension drop, the tension metric is below a low-tension threshold. The control system is further configured to determine, based on the first determination, the second determination, and the third determination, whether there is a break in the tension member, and perform an action in response to a determination that there is the break in the tension member. The action includes an act selected from the group consisting of: providing a signal and an ameliorative activity.

[0008] In general, in one aspect, one or more embodiments relate to a method for detecting a break in a tension member of a computer-assisted system. The computer-assisted system includes a manipulator assembly configured to support an instrument, where the instrument includes a tension member to actuate a degree of freedom of the instrument. The manipulator assembly is configured to modulate a tension metric of the tension member. The computer-assisted system further includes a control system with one or more processors that is communicatively coupled to the manipulator assembly. Operations of the method are performed by, or done with, the control system. The method includes making a first determination of whether the tension metric corresponds to a high-tension state. The method further includes making a second determination of whether a tension drop of the tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold. The method further includes making a third determination of whether, after the tension drop, the tension metric is below a low-tension threshold. The method further includes determining, based on the first determination, the second determination, and the third determination, whether there is a break in the tension member and performing an action in response to a determination that there is the break in the tension member. The action includes an act selected from the group consisting of: providing a signal and an ameliorative activity.

[0009] In general, in one aspect, one or more embodiments relate to a non-transitory machine-readable medium comprising a plurality of machine-readable instructions executed by one or more processors associated with a computer-assisted system. The computer- assisted system includes a manipulator assembly configured to support an instrument, where the instrument includes a tension member to actuate a degree of freedom of the instrument. The manipulator assembly is configured to modulate a tension metric of the tension member. The plurality of machine-readable instructions causing the one or more processors to perform a method. The method includes making a first determination of whether the tension metric corresponds to a high-tension state. The method further includes making a second determination of whether a tension drop of the tension metric corresponding to the high- tension state occurs at a rate exceeding a rate threshold. The method further includes making a third determination of whether, after the tension drop, the tension metric is below a low- tension threshold. The method further includes determining, based on the first determination, the second determination, and the third determination, whether there is a break in the tension member and performing an action in response to a determination that there is the break in the tension member. The action includes an act selected from the group consisting of: providing a signal and an ameliorative activity.

[0010] In general, in one aspect, one or more embodiments relate to a non-transitory machine-readable medium comprising a plurality of machine-readable instructions executed by one or more processors associated with a computer-assisted system. The computer- assisted system includes a manipulator assembly configured to support an instrument, where the instrument includes a tension member to actuate a degree of freedom of the instrument. The manipulator assembly is configured to modulate a tension metric of the tension member. The plurality of machine-readable instructions causing the one or more processors to perform a method. The method includes determining whether there is a break in the tension based on a determination that the tension metric, through a time interval, is less than a broken threshold. The method further includes performing an action in response to a determination that there is the break in the tension member. The action includes an act selected from the group consisting of: providing a signal and an ameliorative activity.

[0011] In general, in one aspect, one or more embodiments relate to a non-transitory machine-readable medium comprising a plurality of machine-readable instructions executed by one or more processors associated with a computer-assisted system. The computer- assisted system includes a manipulator assembly configured to support an instrument, where the instrument includes a first tension member and a second tension member to actuate a degree of freedom of the instrument. The manipulator assembly is configured to modulate a first tension metric of the first tension member and a second tension metric of the second tension member. The first tension member and the second tension member form an antagonistic pair, such that tensioning the first tension member biases the degree of freedom toward moving in a first direction and tensioning the second tension member biases the degree of freedom toward moving in a second direction, the second direction opposing the first direction. The plurality of machine-readable instructions causing the one or more processors to perform a method. The method includes determining whether the antagonistic pair is broken based on a determination of whether an average relative displacement of the first tension member and the second tension member is greater than a common displacement threshold.

[0012] Other aspects of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

[0014] FIG. 1 shows an example computer-assisted system, in accordance with one or more embodiments.

[0015] FIG. 2 shows an example of a manipulator assembly, in accordance with one or more embodiments.

[0016] FIG. 3 shows an example instrument, in accordance with one or more embodiments.

[0017] FIG. 4 depicts the use of tension members manipulate a distal end of an example instrument, in accordance with one or more embodiments.

[0018] FIG. 5 depicts an actuator system, in accordance with one or more embodiments.

[0019] FIGs. 6A, 6B, and 6C depict antagonistic actuator systems, in accordance with one or more embodiments. [0020] FIG. 7 depicts another antagonistic actuator system, in accordance with one or more embodiments.

[0021] FIG. 8 depicts a system, in accordance with one or more embodiments.

[0022] FIG. 9A depicts a first set of fictional tension metric data with respect to time.

[0023] FIG. 9B depicts a second set of fictional tension metric data with respect to time.

[0024] FIG. 10 shows a flowchart, in accordance with one or more embodiments.

[0025] FIG. 11 shows a flowchart, in accordance with one or more embodiments.

[0026] FIG. 12 shows a flowchart, in accordance with one or more embodiments.

[0027] FIG. 13 shows a flowchart, in accordance with one or more embodiments.

[0028] FIG. 14 shows a flowchart, in accordance with one or more embodiments.

[0029] FIG. 15 shows a flowchart, in accordance with one or more embodiments.

DETAILED DESCRIPTION

[0030] Specific embodiments of the disclosure will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

[0031] In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0032] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements, and is not to limit any element to being only a single element unless expressly disclosed, such as by the use of the terms “before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.

[0033] This disclosure describes various devices, elements, and portions of computer- assisted systems and elements in terms of their state in three-dimensional space. As used herein, the term “position” refers to the location of an element or a portion of an element (e.g., three degrees of translational freedom in a three-dimensional space, such as along Cartesian x-, y-, and z-coordinates). As used herein, the term “orientation” refers to the rotational placement of an element or a portion of an element (e.g., three degrees of rotational freedom in three-dimensional space, such as about roll, pitch, and yaw axes, represented in angle-axis, rotation matrix, quaternion representation, and/or the like). As used herein, and for a device with a kinematic series, such as with a repositionable structure with a plurality of links coupled by one or more joints, the term “proximal” refers to a direction toward a base of the kinematic series, and “distal” refers to a direction away from the base along the kinematic series.

[0034] As used herein, the term “pose” refers to the multi-degree of freedom (DOF) spatial position and orientation of a coordinate system of interest attached to a rigid body. In general, a pose includes a pose variable for each of the DOFs in the pose. For example, a full 6-DOF pose for a rigid body in three-dimensional space would include 6 pose variables corresponding to the 3 positional DOFs (e.g., x, y, and z) and the 3 orientational DOFs (e.g., roll, pitch, and yaw). A 3-DOF position only pose would include only pose variables for the 3 positional DOFs. Similarly, a 3-DOF orientation only pose would include only pose variables for the 3 rotational DOFs. Further, a velocity of the pose captures the change in pose over time (e.g., a first derivative of the pose). For a full 6-DOF pose of a rigid body in three-dimensional space, the velocity would include 3 translational velocities and 3 rotational velocities. Poses with other numbers of DOFs would have a corresponding number of velocities translational and/or rotational velocities.

[0035] Aspects of this disclosure are described in reference to computer-assisted systems, which can include devices that are teleoperated, externally manipulated, autonomous, semiautonomous, and/or the like. Further, aspects of this disclosure are described in terms of an implementation using a teleoperated surgical system, such as the da Vinci® Surgical System commercialized by Intuitive Surgical, Inc. of Sunnyvale, California. Knowledgeable persons will understand, however, that inventive aspects disclosed herein may be embodied and implemented in various ways, including teleoperated and nonteleoperated, and medical and non-medical embodiments and implementations. Implementations on da Vinci® Surgical Systems are merely exemplary and are not to be considered as limiting the scope of the inventive aspects disclosed herein.

[0036] In fact, and as will be described herein, aspects of the instant disclosure are applicable to any system (e.g., computer-assisted system) employing a tension member actuated by an actuator assembly including at least one actuator, where a tension applied to the tension member by the actuator assembly can be determined (e.g., through a tension sensor) or otherwise estimated (e.g., using an issued tension command in view of the actuator assembly). As such, it is emphasized that techniques described with reference to surgical instruments and surgical methods may be used in other contexts. Thus, the instruments, systems, and methods described herein may be used for humans, animals, portions of human or animal anatomy, industrial systems, general robotic, or teleoperated systems. As further examples, the instruments, systems, and methods described herein may be used for nonmedical purposes including industrial uses, general robotic uses, sensing or manipulating non-tissue work pieces, cosmetic improvements, imaging of human or animal anatomy, gathering data from human or animal anatomy, setting up or taking down systems, training medical or non-medical personnel, and/or the like. Additional example applications include use for procedures on tissue removed from human or animal anatomies (with or without return to a human or animal anatomy) and for procedures on human or animal cadavers. Further, these techniques can also be used for medical treatment or diagnosis procedures that include, or do not include, surgical aspects.

[0037] Referring now to the drawings, in which like reference numerals represent like parts throughout the several views, FIG. 1 shows an example computer-assisted system (100), in accordance with one or more embodiments.

[0038] While FIG. 1 shows the computer-assisted system (100) as a medical system, the following description is applicable to other scenarios and systems, e.g., medical scenarios or systems that are non-surgical, non-medical scenarios or computer-assisted systems, etc. [0039] In the example, a diagnostic or therapeutic medical procedure is performed on a patient (190) on an operating table (110). The computer-assisted system (100) may include a manipulator system (130) (e.g., a patient-side robotic device in a medical example). The manipulator system (130) may include at least one manipulator arm (150A, 150B, 150C, 150D), each of which may support a removably coupled instrument (160) (also called tool (160)). In the illustrated procedure, the instrument (160) may enter the workspace through an entry location (e.g., enter the body of the patient (190) through a natural orifice such as the throat or anus, or through an incision), while an operator (not shown) views the worksite (e.g., a surgical site in the surgical scenario) through a user interface system (120).

[0040] An image of the worksite may be obtained by an imaging instrument (160) including an imaging device (e.g., an endoscope, an optical camera, an ultrasonic probe, etc. in a medical example). The imaging instrument (160) can be used for imaging the worksite, and may be manipulated by one of the manipulator arms (150A, 150B, 150C, 150D) of the manipulator system (130) so as to position and orient the imaging instrument. The auxiliary system (140) may process the captured images in a variety of ways prior to any subsequent display. For example, the auxiliary system (140) may overlay the captured images with a virtual control interface prior to displaying the combined images to the operator via the user interface system (120) or other display systems located locally or remotely from the procedure. One or more separate displays (144) may also be coupled with a control system (142) and/or the auxiliary system (140) for local and/or remote display of images, such as images of the procedure site, or other related images.

[0041] The number of instruments (160) used at one time generally depends on the task and space constraints, among other factors. If it is appropriate to change, clean, inspect, or reload one or more of the instruments (160) being used during a procedure, an assistant (not shown) may remove the instrument (160) from the manipulator arm (150A, 150B, 150C, 150D), and replace it with the same instrument (160) or another instrument (160).

[0042] Various classes and types of instruments (160) can be used, or exchanged during a process or procedure, according to the needs of a procedure or process undertaken by one or more manipulator arms (e.g., 150A, 150B, 150C, 150D) of a computer-assisted system (100). Instruments (160) may include, but are not limited to: monopolar and bipolar instruments for dissection, coagulation, sealing, transection, and/or cutting of tissue; suction and irrigation instruments; clip appliers; and instruments for visualization of the procedure site (e.g., visual camera, infrared camera. Some instruments (160), such a monopolar and bipolar instruments, can be “energized” or apply electrical cortical stimulation in a tunable manner (e.g., “on” or “off’).

[0043] The computer-assisted system (100) may include a control system (142). The control system (142) may be used to process input provided by the user interface system (120) from an operator, such as to control the computer-assisted system (100). The control system (142) may also be used to process signals from other devices, from sensors, from any networks to which the control system (142) connects, etc. Example sensors include those associated with actuators or joints of the computer-assisted system, such as motor encoders, rotary or linear joint encoders, torque sensors, tension sensors, current sensors, accelerometers, force sensors, inertial measurement units, optical or ultrasonic sensors or imagers, RF sensors, etc. The control system may further be used to provide an output, e.g., a video image for display by the display (144). The control system (142) may further be used to control the manipulator system (130). [0044] The control system (142) may include one or more computer processors, non- persistent storage (e.g., volatile memory, such as random access memory (RAM), cache memory), persistent storage (e.g., a hard disk, an optical drive such as a compact disk (CD) drive or digital versatile disk (DVD) drive, a flash memory, etc.), a communication interface (e.g., Bluetooth interface, infrared interface, network interface, optical interface, etc.), and numerous other elements and functionalities.

[0045] A computer processor of the control system (142) may be part or all of an integrated circuit for processing instructions. For example, the computer processor may be one or more cores or micro-cores of a processor. The control system (142) may also communicate with one or more input devices, such as a touchscreen, keyboard, mouse, microphone, touchpad, electronic pen, or any other type of input device.

[0046] A communication interface of the control system (142) may include an integrated circuit for connecting the control system (142) to a network (not shown) (e.g., a local area network (LAN), a wide area network (WAN) such as the Internet, mobile network, or any other type of network) and/or to another device, such as another control system (142). [0047] Further, the control system (142) may communicate with one or more output devices, such as a display device (e.g., a liquid crystal display (LCD), a plasma display, touchscreen, organic LED display (OLED), projector, or other display device), a printer, a speaker, external storage, or any other output device. One or more of the output devices may be the same or different from the input device(s). Many different types of control systems exist, and the aforementioned input and output device(s) may take other forms.

[0048] Software instructions in the form of computer readable program code to perform embodiments of the disclosure may be stored, in whole or in part, temporarily or permanently, on a non-transitory computer readable medium such as a CD, DVD, storage device, a diskette, a tape, flash memory, physical memory, or any other computer readable storage medium. Specifically, the software instructions may correspond to computer readable program code that, when executed by a processor(s), is configured to perform one or more embodiments of the invention.

[0049] A control system (142) may be connected to or be a part of a network. The network may include multiple nodes. Each node may correspond to a computing system, or a group of nodes. By way of an example, embodiments of the disclosure may be implemented on a node of a distributed system that is connected to other nodes. By way of another example, embodiments of the invention may be implemented on a distributed computing system having multiple nodes, where each portion of the disclosure may be located on a different node within the distributed computing system. Further, one or more elements of the aforementioned computing system may be located at a remote location and connected to the other elements over a network.

[0050] An example of a manipulator assembly (200) in accordance with embodiments of the present disclosure is shown in FIG. 2. A manipulator assembly (200) may include a manipulator arm (250) and an instrument (260). The manipulator arm (250) may correspond to a manipulator arm (e.g., 150A, 150B, 150C, 150D) in FIG. 1. As described above, during operation, the manipulator arm (250) generally supports an instrument (260) extending distally from the manipulator arm (250), and effects movements of the instrument (260).

[0051] In minimally invasive scenarios, an instrument (260) may be positioned and manipulated through an entry location, so that a kinematic remote center is maintained at the entry location. Images of the worksite, taken by an imaging device of an imaging instrument such as an optical camera, may include images of the distal ends of the instruments (260) when the instruments (260) are positioned within the field-of-view of an imaging device.

[0052] In the example shown, a distal instrument holder (214) facilitates removal and replacement of the mounted instrument.

[0053] As may be understood with reference to FIG. 1, manipulator arms (250) are proximally mounted to a base of the manipulator assembly. Alternatively, manipulator arms (250) may be mounted to separate bases that may be independently movable, e.g., by the manipulator arms (250) being mounted to single-manipulator-arm carts, being provided with mounting clamps that allow mounting of the manipulator arms (250) directly or indirectly to the operating table at various locations, etc. An example manipulator arm (250) includes a plurality of links and joints extending between the proximal base and the distal instrument holder.

[0054] In embodiments such as shown for example in FIG. 2, a manipulator arm includes multiple joints (such as revolute joints JI, J2, J3, J4, and J5, and prismatic joint J6) and links (204, 206, 208, and 210). The joints of the robotic arm, in combination, may or may not have redundant degrees of freedom.

[0055] In the example shown, the instrument (260) may be releasably mounted on an instrument holder (214). The instrument holder (214) may translate along a linear guide formed by the prismatic joint (J6) at the link (210). Thus, the instrument holder (214) may provide in/out movement of the instrument (260) along an insertion axis. The link (210) may further support a cannula (216) through which the instrument shaft of the instrument (260) extends. Alternatively, the cannula (216) may be mechanically supported by another component of the manipulator arm (250) or may not be supported at all.

[0056] Actuation of the instrument (260) in one or more degrees may be provided by actuators of the manipulator assembly (200). These actuators may be integrated in the instrument holder (214), or drive drivetrains in the instrument holder, and may actuate the instrument (260) via a transmission assembly (270).

[0057] While FIG. 2 shows an external housing of the transmission assembly (270), additional components of the transmission assembly (270) are discussed below. Similarly, additional components of the instrument holder (214) are discussed below, including a detailed description of an example interfacing of the instrument (260) with the manipulator arm (250) at the instrument holder (214) and the transmission assembly (270). Also, a more detailed description of the example instrument (260) is provided below in reference to FIG. 3. [0058] FIG. 3 depicts an example instrument (260) that includes a transmission assembly (370), an instrument shaft (380), a wrist assembly (390), and an end effector (350) at a distal portion (384) of the instrument shaft (380). In general, an instrument (260) can include a transmission assembly (270) or backend mechanism, an instrument shaft extending distally from the transmission assembly (270) to an end effector or to a wrist assembly. The instrument (260) with a wrist assembly can also include an end effector. Example end effectors include forceps, graspers, a cutting tool, or a cauterizing tool coupled to the wrist assembly. In some instances, end effectors can be categorized as an energy-emitting end effector (e.g., used on a bipolar instrument) or a non-energy-emitting end effector. The wrist assembly can then be used to move and operate the end effector when enacting a desired procedure. Tension members (e.g., cables) that are connected to the wrist assembly and/or elements of the end effector extend through the instrument shaft and connect to the transmission assembly. The transmission assembly may provide a mechanical coupling of the tension members to motorized axes provided by actuators. Thus, movement and tension in the tension members as needed to position, orient, and operate wrist assembly and/or the end effector can be controlled through operation of the actuators.

[0059] The instrument shaft (380), in one or more embodiments, has a proximal portion (382) terminating at a chassis (372) of the transmission assembly (370) and a distal portion (384) terminating at the wrist assembly (390) of the instrument (260). The instrument shaft (380) may be any suitable shaft that couples the wrist assembly (390) and the end effector (392) to the transmission assembly (370). In one or more embodiments, the shaft (380) defines at least one passageway through which one or more tensions members (e.g., cables, not shown) or other transmission members suitable for the transmission of mechanical energy such as movement, force, or torque may be routed from the transmission assembly (370) towards the wrist assembly (390). In some embodiments, other components (e.g., electrical wires, push-rods, optical fibers, etc.) may also be routed through the shaft.

[0060] The wrist assembly (390) is configured to provide a rotational degree of freedom (e.g., a pitch rotation) of the end effector (392). The end effector (392) is configured with a yaw rotation degree of freedom that may further be used for opening and closing jaw elements of the end effector (392). Depending on the design, one, two, or more tension members may be used to control a degree of freedom for the instrument. In an example, two unique tension members are used to control each of a pitching, a yawing, and a jaw opening for a jawed instrument. In another example, some of the tension members are coupled to multiple degrees of freedom, and four tension members are used in combination to control a pitching, a yawing, and a jaw opening for a jawed instrument.

[0061] In one or more embodiments, the tensions members are routed through the shaft to other elements of the transmission assembly (370) and may be operated by transmission elements (374). In the example of FIG. 3, the transmission elements (374) include capstans. In one example, a separate capstan (or more generally, transmission element (374)) may be provided for each of the tension members. Four capstans may, thus, be provided to actuate the wrist assembly (390) and the end effector (392), in the example. Operation of the four capstans causes movement of the four tension members to produce the desired movement (pitch, yaw, and/or grip) of the end effector (392). Specifically, a first capstan may move a first tension member in a proximal direction (pulling the tension member) by winding up the first tension member. Simultaneously, a second capstan may move a second tension member in a distal direction (releasing the tension member) by unwinding the second tension member when the first and the second tension members operate in an antagonistic manner. The second tension member may also be operated independently from the first tension member.

[0062] In the example of FIG. 3, the transmission elements (374) further include gears (e.g., spur gears) for rolling or rotation of the instrument shaft (380), the wrist assembly (390), and the end effector (392) about a roll axis of the instrument shaft (380). Accordingly, in the example of FIG. 3, the transmission assembly (370) includes example five transmission elements (374) that are capstan and tension member-based, or gear-based. Other types of transmission elements such as, for example, metal bands, rubber belts, metal wires, pulleys, screw drives, chains and sprockets, etc., may be used without departing from the disclosure. [0063] In one or more embodiments, the transmission assembly (370) further includes receive couplings (378). In the example of FIG. 3, one receive coupling (378) may be coupled with one of the transmission elements (374). Accordingly, the transmission assembly (370), in the example of FIG. 3, includes five receive couplings (378). Each receive coupling (378) may be designed to engage with a corresponding drive coupling of the manipulator arm (250) or other repositionable structure. When a receive coupling (378) is engaged with a drive coupling, mechanical energy may be transmitted over the combination of the drive coupling and a receive coupling. For example, a torque or velocity may be transmitted from an electric motor or any other type of actuator to a capstan and subsequently used to drive or apply tension to one or more tension members.

[0064] The chassis (372) may provide structural support for mounting and aligning the components (e.g., the transmission elements and the receive couplings) of the transmission assembly (370). The chassis (372) may further function as part of a housing of the transmission assembly (370).

[0065] In one or more embodiments, the chassis (372) may also include external features (not shown) that interface with elements of a drive interface, which may be part of the instrument holder (214) to releasably lock the instrument (260) to the instrument holder (214) or other repositionable structure. Recesses, clips, or other elements may be included in the external features.

[0066] FIG. 4 depicts, in greater detail, a partial cutaway view of an example wrist assembly (390) and end effector (392) each actuated using a set of tension members. As illustrated in the example, the wrist assembly (390) includes a proximal clevis (420), a distal clevis (430), and an end effector (392). Tension members (451, 452, 453, and 454) are attached to the end effector (392), extend along solid surfaces of guide channels in the end effector (392), the distal clevis (430), and the proximal clevis (420), and from there extend back through the instrument shaft (380) to the transmission assembly (370). The depicted end effector (392) includes jaws (442, 444), each having a grip portion attached to a circular hub. A first pin (425) in the proximal clevis (420) attaches the distal clevis (430) to the proximal clevis (420) and allows the distal clevis (430) to rotate about a pivot axis defined by the first pin (425). The proximal clevis (420) includes guide channels (432) for tension members (451, 452, 453, and 454), and openings (e.g., opening (424)). The openings of the guide channels (422) direct the tension members (451, 452, 453, and 454) into the guide channels (432) of the proximal clevis (420). [0067] Similarly, in the example shown in FIG. 4, guide channels in distal clevis (430) define a radius about a second pin (435) at which the tension members (451, 452, 453, and 454) act on the distal clevis (430) when rotating the distal clevis (430) about the second pin (435). The second pin (435) in the distal clevis (430) is perpendicular to the first pin (425) and defines a pivot axis for the end effector (392) as a whole or the jaws (442, 444) individually. In the illustrated example of FIG. 4, the working tips of jaws (442, 444) have a surface for gripping and may be used, for example, in forceps or cautery applications. Alternatively, “gripping,” which closes the jaws (442, 444) can be a cutting action when the tips of the jaws (442, 444) are blades that cooperatively cut as scissors. Thus, gripping can perform different functions depending on the end effector (392) attached to or otherwise employed on - or as part of - the instrument (260).

[0068] It is noted that the example wrist assembly (390) and end effector (392) depicted in FIG. 4 uses a small number of parts. In particular, the low number of tension members (451, 452, 453, 454) used to actuate the wrist assembly (390) and the end effector (392) facilitate implementation of a small diameter for the wrist assembly (390) and the instrument shaft (380).

[0069] FIG. 5 depicts a actuator system (500) employing two tension members, namely, a first tension member (502) and a second tension member (504), attached to a pulley (506) that enact rotation about a central axis (508) of the pulley (506). This, the actuator system (500) provides a single degree of freedom. The first tension member (504) and the second tension member (504) are wrapped or wound, at least partially, around a capstan (510). Generally, the first tension member (502) and the second tension member (504) are wrapped or wound around the capstan (510) such that a nominal amount of tension is applied to the first tension member (502) and the second tension member (504). The capstan (510) can be driven by an electric motor (not shown) or other type of actuator, and driven accordingly. The capstan (510) can apply tension to the first and second tension members (502, 504) causing a proportionate change in the degree of freedom at the pulley (506). In the actuator system (500) of FIG. 5, rotation of the capstan (510) results in the movement, or operation, of both the first tension member (502) and the second tension member (504). In other instances, an actuator system can be configured such that the first tension member (502) and the second tension member (504) are operated independently.

Still, in other instances, the first tension member (502) and the second tension member (504) (or any group of two or more tension members) can be operated in an antagonistic manner. In antagonistic operation, for example, the unwinding or lengthening of one tension member corresponds with the simultaneous, and at least partially independent, winding, or shortening of an antagonistically paired tension member. Examples of actuator systems employing tension members that operate in an antagonistic manner are described in FIGS. 6A-6C. While FIG. 5 depicts an actuator system (500) where tension is applied to the first tension member (502) and the second tension member (504) by rotation of the capstan (510), in general, operation of tension members can be realized through many types of actuation such as linear actuation. An example of linear actuation is translation of drive elements directly or indirectly coupled to tension members.

[0070] Tension members, such as those seen in FIGS. 5-7 (where figures 6A-6C and 7 are described below) can be used to actuate one or more degrees of freedom of an instrument such as the wrist assembly (390) of FIG. 4. For example, depending on the design, one, two, or more tension members are be used to control a degree of freedom (DOF) for the instrument. In some designs, tension members are dedicated to the DOFs they move, and are not shared among DOFs. In a specific example, six tension members are used to control a pitching, a yawing, and a jaw opening for a jawed instrument. In this example, each of these three DOF (i.e., pitch, yaw, and jaw opening) is moved by using a separate pair of tension members coupled with an actuator system such as that depicted in FIG. 5. In some designs, at least one tension member is coupled to move multiple degrees of freedom, and is shared among these multiple DOFs. In a specific example, four tension members are used in combination to control three DOFs for a jawed instrument: a pitching DOF, a yawing DOF, and a jaw opening DOF for a jawed instrument.

[0071] Further, while FIG. 5 depicts the use of a pulley (506), it is noted that in many instances, such as the example wrist assembly (390) and end effector (392) depicted in FIG. 4, pulleys are not employed for various reasons outside the scope of this disclosure. Considering again FIG. 4, instead of pulleys, the wrist assembly (390) guides the tension members (451, 452, 453, and 454) as described above using solid surfaces (i.e., the surfaces of guide channels). Thus, it is noted that that the use of a pulley (506) in FIG. 5, and below in FIGS. 6A-6C, is to promote understanding through depiction of a simplified system and does not imply or impose a limitation on the instant disclosure.

[0072] FIG. 6A depicts an antagonistic actuator system (600) including a first disk (602) and a second disk (604). The first disk is circular has a first radius, r_x (603). The second disk (604) is also circular and has a second radius, r₂ (607). The first radius (603) and the second radius (607) need not be the same. The first disk (602) and the second disk (604) can be independently rotated about a first rotational axis and a second rotational axis, respectively. Rotation can be provided, for example, using a dedicated actuator for each of the first and second disks (602, 604). In the depiction of FIG. 6A, the first rotational axis is disposed at the geometric center of the first disk (602) and the second rotational axis is disposed at the geometric center of the second disk (604). However, in general, the rotational axis of a disk need not reside at its geometric center and/or a disk can have eccentricity such that rotation of a disk results in eccentric motion. In the example shown, a first tension member (502) is connected, at a first attachment point (612), to the first disk (602) and a pulley (506) at a pulley attachment point (610). Similarly, a second tension member (504) is connected to the second disk (604), at a second attachment point (614), and the pulley (506) at the pulley attachment point (610). In the depiction of FIG. 6A, the pulley (506) can rotate about its central axis subject to the constraints imposed by the first tension member (502) and the second tension member (504). However, in general, a rotational axis of the pulley (506) need not reside at its geometric center nor does the pulley (506) need to be substantially circular. In the example of FIG. 6A, the pulley (506) is circular and is characterized by a pulley radius, r_p (605) and the pulley radius (605) need not equal either the first radius (603) or the second radius (607).

[0073] Like the actuator system (500) of FIG. 5, the antagonistic actuator system (600) of FIG. 6A provides a single degree of freedom at the pulley (506) (i.e., rotation about its central axis). However, as seen in the FIG. 6 A example, the antagonistic actuator system (600) involves coordination (i.e., synchronized and complimentary rotation), at least partially, between actuation of the first disk (602) and the second disk (604) to manipulate the degree of freedom at the pulley (506).

[0074] To illustrate this point, FIG. 6B depicts the rotation of the pulley (506) in a counter-clockwise direction over a degree of freedom (DOF) angle, 6_dof (620) given in radians from its initial orientation depicted in FIG. 6A. Further, FIG. 6B depicts the clockwise rotation of the first disk (602) and the second disk (604) over a first angle,

(in radians), and a second angle, 0₂ (624) (in radians), respectively, relative to their initial orientations as depicted in FIG. 6A.

[0075] Herein, “displacement” of a tension member is defined as the change in length of the tension member resulting from the actuation of one or more associated degrees of freedom. In the example of FIG. 6B, an expected displacement of the first tension member (502), A_1? is given by r₁0₁, and an expected displacement of the second tension member (504) is given by r₂0₂. Generally, a sign convention is established to properly prescribe mathematical relationships between elements of an actuator system such as the antagonistic actuator system of FIG. 6B. For the case of FIG. 6B, clockwise rotation of the pulley (506) will be considered positive. Further, clockwise rotation of the first disk (602) will be considered to cause a negative-valued displacement in the first tension member (502) and clockwise rotation of the second disk (604) will be considered to cause a positive-valued displacement in the second tension member (504). This sign convention is depicted in FIG. 6B. This sign convention establishes that the “spooling in” or “winding” of a tension member about a disk results in a negative displacement and the “spooling out” or “unwinding” about a disk results in a positive displacement of the tension member.

[0076] In a fictional scenario where the first tension member (502) and the second tension member (504) are infinitely stiff, and further given the case where the first disk (602), second disk (604), and pulley (506), are each circular and each rotating about its respective geometric center, the rotation of the pulley (506) by the DOF angle (620) relates to the first angle (622) and second angle (624) according to the relationship (using the above-described sign convention):

[0077] Notably, whether rotation of a disk in a given direction, clockwise or counterclockwise, results in the winding or unwinding of a tension member is dependent on the configuration of the disk and tension member. For example, in the example antagonistic actuator system (600) depicted in FIGS. 6A and 6B, counter-clockwise rotation of the pulley (506) corresponds to clockwise rotation of the both the first disk (602) and the second disk (604). However, FIG. 6C depicts an alternative configuration. Notably, in the configuration depicted in FIG. 6C, counter-clockwise rotation of the pulley (506) corresponds to clockwise rotation of the first disk (602), as in FIGS. 6 A and 6B, but to counter-clockwise rotation in the second disk (604). One with ordinary skill in the art will recognize that many different sign conventions may be used to establish mathematical relationships for the kinematics of an actuator system (e.g., antagonistic actuator system (600) of FIG. 6B) and that embodiments of the instant disclosure are not limited to any particular sign convention. Further, for actuator systems composed of more than two tension members, and/or actuator systems where displacement of a tension member can affect multiple degrees of freedom, the establishment of an absolute sign convention may not be possible. In these instances, the sign convention may change dependent on, for example, the pairwise comparison of different tension members.

[0078] For a pair of tension members (e.g., first tension member (502) and second tension member (504)) that form an antagonistic pair with respect to a given degree of freedom (e.g., as depicted in FIG. 6C) the sign convention can be established using opposing directions relative to the given degree of freedom. For example, FIG. 6C depicts a first direction (630) associated with the first tension member (502) and a second direction associated with the second tension member (504). The first direction (630) and the second direction (640) are defined such that tensioning the first member (502) biases the degree of freedom toward moving in the first direction (630) and tensioning the second tension member biases the degree of freedom toward the second direction (640), the second direction (640) opposing the first direction (630).

[0079] EQ. 1 is less applicable for situations where any of the first disk (602), second disk (604), or pulley (506) have eccentric motion (e.g., have eccentricity). Establishment of a generalized equation for any combination of eccentric motion is beyond the scope of this disclosure, however, it is emphasized that embodiments disclosed herein are not limited to configurations without eccentric motion.

[0080] Further, where the first tension member (502) and the second tension member (504) are not adequately modeled as infinitely stiff, A_x may not equal A₂. For example, for the antagonistic actuator system (600) depicted in FIG. 6B, (— /r₂)0i va&'j not equal 0₂. Herein, an average relative displacement, A, of a group of M tension members, where M > 2, that form an antagonistic actuator system is defined as the cumulative and absolute deviation in displacement of the antagonistic actuator system relative to an identically configured system formed of infinitely stiff tension members normalized, at least in part, by the number of tension members in the system. In practice, it may not be possible to determine the deviation in displacement of an antagonistic actuator system from an idealized antagonistic actuator system. However, the deviation in displacement of a tension member from an idealized (i.e., infinitely stiff) version of that tension member can be approximated by comparing the observed displacement of the tension member (e.g., the encoded movement of a disk driving the tension member) to an expected displacement of the tension member given the observed displacement of another tension member of the antagonistic actuator system. The expected displacement of a tension member, say the m^t/l tension member of an antagonistic actuator system of M tension members (M > 2), is represented herein as A_m. Further, as stated, the expected displacement of the m^th tension member can be determined relative to the observed displacement of another tension member in an antagonistic actuator system, say the n^th tension member where n A m. This determination can be represented as a function f, where A_m;n = f(m; A_n). In other words, f(m; A_n) returns the expected displacement of the m^th tension member, A_m, given the observed displacement of the n^th tension member, A_n. The function f, as defined, implicitly adopts a relative sign convention between the m^th and n^th tension members. Thus, the absolute deviation in displacement of the m^th tension member from an idealized version of the m^th tension member given the observed displacement of the n^th tension member is

where n A m. Using EQ. 2, an average relative displacement, A, of a group of M tension members, where M > 2, that form an antagonistic actuator system can be formulated as

[0081] EQ. 3 can be explained through examples. As a first example, consider again the antagonistic actuator system (600) of FIG. 6B. Recall that FIG. 6B depicts the rotation of the pulley (506) in a counter-clockwise direction over a degree of freedom (DOF) angle, 6_dof (620) given in radians from its initial orientation depicted in FIG. 6A. Further, FIG. 6B depicts the clockwise rotation of the first disk (602) and the second disk (604) over a first angle, (622) (in radians), and a second angle, 0₂ (624) (in radians), respectively, relative to their initial orientations as depicted in FIG. 6A. In this system, the expected displacement of the first tension member (502) given an observed displacement of the second tension member (504), A_1;2, is given by — A₂. That is, (I; A₂) = — A₂ = — r₂0₂. Similarly, the expected displacement of the second tension member (504) given an observed displacement of the first tension member (502), A_2;1, is given by —A_x. That is, (2; A_x) = — A_x = —r₁0₁. Thus, using EQ. 2, the absolute deviation in displacement of the first tension member from an idealized version of the first tension member given the observed displacement of the second tension member is |A_X — A_1;2 | = |A_X — (— A₂) |. The absolute deviation in displacement of the second tension member from an idealized version of the second tension member given the observed displacement of the first tension member is |A₂ — A_2;1| = |A₂ — (— A_x) |. Substituting these expressions into EQ. 3 yields - (2|A₁ + A₂ |) = |A₁ + A₂ |. Using

2(2-1) concrete numbers, consider the case for the antagonistic actuator system of FIG. 6B, where the first tension member is “spooled in” by 1.1mm (i.e., A_x = —1.1mm) and the second tension member is “spooled out” by 1.05mm (i.e., A₂ = 1.05mm). Under the configuration depicted in FIG. 6B, if the first and second tension members were ideal (e.g., perfectly stiff), then A_x would necessarily equal — A₂. However, the observed displacements of the first and second tension members result in an average relative displacement, A, of | — 1.1mm + 1.05mm| = 0.05mm. Thus, the average relative displacement quantifies a deviation of the tension members of an antagonistic actuator system from an ideal antagonistic actuator system, where the ideal antagonistic actuator system, by definition, has an average relative displacement of zero. The use of the average relative displacement to detect a break in a tension member of an antagonistic actuator system is described later in the instant disclosure. It is noted that, for example in the antagonistic actuator system of FIG. 6B, that when r_x equals r₂ the change in orientation of the first disk (602), 0_1? and the change in orientation of the second disk (604), 0₁₍ can be used as direct substitutes to quantify the displacements of the first and second tension members, respectively. Thus, in some instances, the average relative displacement can be given in units such as radians.

[0082] As a second example of the application of EQS. 2 and 3, FIG. 7 depicts an example complex antagonistic actuator system (700). As depicted in FIG. 7, the example complex antagonistic actuator system (700) as a composite pulley (702) with two radii, namely, a first pulley radius, r_{p l}, and a second pulley radius, r_{p 2}. A third tension member (710) is connected between a third disk (704), defined by a radius r₃, and the composite pulley (702). A fourth tension member (712) is connected between a fourth disk (706), defined by a radius r₄, and the composite pulley (702). A fifth tension member (714) is connected between a fifth disk (708), defined by a radius r₅, and the composite pulley (702). The sign convention that “spooling in” or “winding” of a tension member about a disk results in a negative displacement of the tension member is applied to the example complex antagonistic actuator system (700) of FIG. 7. The displacement of the third tension member (710) is represented as A₃. Eikewise, the displacement of the fourth tension member (712) is represented as A₄ and the displacement of the fifth tension member (714) is represented as A₅. [0083] In view of the configuration depicted in FIG. 7, the pairwise deviations of the third (indexed as 3), fourth (indexed as 4), and fifth (indexed as 5) tension members (710, 712, 714) are given as:

[0084] EQS. 4 can be substituted in EQ. 3 resulting in

Thus, EQ. 5 represents the average relative displacement of the three tension members grouped in an antagonistic manner as depicted in FIG. 7.

[0085] EQS. 2 and 3 are applicable to antagonistic actuator systems with greater complexity than that depicted in FIG. 7. In general, tension members of an antagonistic actuator system can actuate, independently or dependently, one or more degrees of freedom. Further, the antagonistic actuator system can be composed of disks, pulleys, or other driver and follower mechanisms (z.e., linear actuators) such that the expected displacement of a tension member relative to another tension member can be non-linear. Additionally, it is noted that in instances where the actuation of a degree of freedom is not linear with the displacement of a tension member, for example, an eccentric pulley or a pulley where a distance between a contact point between the tension member and the pulley and the axis of rotation of the pulley is variable (e.g., the pulley is a cam), the expected displacement of a tension member with respect to another tension member (z.e., EQ. 2) may only be estimated without a knowledge of the actual change in the degree of freedom.

[0086] As previously discussed, the average relative displacement is usable to quantify the cumulative and absolute deviation in displacement of the tension members of an antagonistic actuator system relative to an identically configured system formed of infinitely stiff tension members. The cumulative and absolute deviation in displacement can further be normalized, for example, by the number of tension members in the antagonistic actuator system, to support a comparison of average relative displacements between antagonistic actuator systems of differing numbers of tension members. An additional benefit to an average relative displacement that is normalized is that a single common displacement threshold (described later in the instant disclosure) can be defined for comparison against the average relative displacement across antagonistic actuator systems with differing numbers of tension members. While EQS. 2 and 3 can be used to determine the average relative displacement of an antagonistic actuator system, other equations can be formulated for this purpose. Thus, the determination of the average relative displacement is not limited to EQS. 2 and 3 as described herein. In general, any equation or method that calculates a cumulative and absolute deviation in displacement of the tension members of an antagonistic actuator system can be used with embodiments of the instant disclosure without limitation.

[0087] Tension members such as the first tension member (502) and the second tension member (504) illustrated in FIG. 5 or FIGS. 6A-6C may be made of a variety of materials such as metals/metal alloys, polymers, composite materials, etc. Under certain conditions (e.g., wear over time, exposure to chemicals, overload, abuse, etc.), tension members may tear or break.

[0088] Embodiments disclosed herein relate to methods and systems for detecting a break in a tension member such as a tension member used to actuate a wrist assembly (390) and/or end effector (392) of an instrument (260). However, it is emphasized that while tension members have been introduced and described herein under the context of an instrument (260) and/or a manipulator arm (250) of a computer-assisted system (100), the methods and systems disclosed herein are not limited to these systems, subsystems, tools, and processes. In general, and as will be demonstrated, the methods and system for detecting a break in a tension member are applicable to many systems employing a tension member as long as a tension metric of the tension member can be determined either through direct measurement or estimation (e.g., modeling) based on one or more indirect measurements (e.g., current supplied to an actuator).

[0089] As stated, embodiments of the instant disclosure detect a break in a tension member based, at least in part, on a “tension metric” of the tension member. In the example described below, the tension metric is proportional to the tension applied to the tension member. However, in other implementations, the tension metric may have a nonlinear or piece- wise linear relationship with the tension applied to the tension member, where the nonlinear or piecewise linear relationship is monotonic. The tension metric is indicative of the tension applied to a tension member but does not need to be a measurement of force applied to the tension member. Embodiments of the instant disclosure can be readily applied to systems where the tension of its tension members is directly measured, estimated through measurements of corresponding parameters (e.g., strain, current drawn by an actuator that indicates an actuator torque corresponding to tension). Thus, the tension metric may be given in units of force (e.g., Newtons (N)), torque (e.g., Newton-meter (N-m)), stress (e.g., Pascal or N/m²), strain (% elongation (e)), or some other unit (e.g., result of a function), given that the selected unit system is self-consistent. As such, the term “tension metric” is adopted herein as a unit-agnostic representation of the “tensile state” of a tension member, where the “tensile state” of a tension member indicates, or can be transformed to indicate, a tension applied to the tension member. For example, a torque can be converted (e.g., through a cross-product) to a tension or vice versa such that the tension metric, in some implementations, is a torque. Or, in instances where more than one tension member is used and the tension members have different diameters (i.e., at least two unique diameters), the tensile state of the tension members may be given as stress (i.e., tensile force normalized by the cross-sectional area of the tension member) such that the tensile state of the tenson members can be directly compared. As an additional example, in instances where more than one tension member is used and the tension members are composed of different materials (e.g., a metallic tension member and a polymer tension member) the tensile state of the tension members may be given as their stress, determined either from a determination of tension or torque informed by the cross-sectional area, divided by the their respective moduli of elasticity resulting in a measurement of strain. The use of strain as a tension metric allows for the direct comparison of tensile states of tension members of different materials (and cross-sectional areas).

[0090] In this example, the tension metric of one or more tension members is determined at a series of sequential timesteps. In one or more embodiments, the tension metric is determined from a tension metric sensor configured to measure the tension metric (e.g., tension, torque, etc.) or some measurement convertible to the tension metric. For example, in instances where tension is applied to a tension member using a rotary actuator (e.g., an assembly including an electric motor and a capstan or disk), the tension metric sensor can be a torque sensor (e.g., measuring the torque applied to a driving shaft of the motor). In other embodiments, the tension metric is determined using a “disturbance observer” that estimates the tension metric in the tension member based on a “commanded tension metric” issued to an actuator that is driving the tension member and causing the tension while accounting for a state of the actuator (and other associated driving hardware, for example, driving disks (“disks”), capstans, etc.). The “state” may include, for example, the current velocity of the actuator such that inertial effects can be added/subtracted from the commanded tension to estimate the tension in/on the tension member.

[0091] FIG. 8 depicts a disturbance observer (800) in accordance with one or more embodiments. The disturbance observer (800) depicted determines the tension metric for a given tension member using the position, velocity, and/or acceleration of an actuator that drives the tension member. It is noted that, in general, position, velocity, and acceleration can be determined from each other through integration and differentiation. The position, velocity, and/or acceleration of the actuator is determined using an encoder, where based on the configuration of the encoder the encoder may measure one or more of position, velocity, and acceleration; referenced hereafter as encoder data (804). As illustrated, for a given tension member, a commanded tension metric (802), such as a torque or electrical current convertible to a tension metric, commanded to the actuator associated with the tension member (e.g., from a controller or control system) is obtained. Further, the encoder data (804) of the actuator is obtained. A model of the actuator and other associated hardware used to drive the tension member (e.g., capstans, driving disks, etc.) is used to compute the tension metric for effectuating a desired actuation of the actuator and associated driving hardware according to the encoder data (804) without consideration of the tension member, where the desired actuation corresponds with the actuation intended by the commanded tension metric (802). Thus, the model determines the modeled tension metric without the tension member (806). Dependent on an established sign convention, the modeled tension metric without the tension member (806) is added or subtracted to/from the commanded tension metric (802) resulting in an estimated tension metric (810) of the tension member as depicted by operator (808) in FIG. 8. That is, the estimated tension metric (810) is determined from the commanded tension metric (802) while accounting for the physical effects (e.g., inertia, friction, etc.) of the actuator and associated hardware used to apply the tension metric to the tension member.

[0092] Regardless of how the tension metric is determined, a break in the tension member is detected through evaluation of the tension metric. FIGS. 9 A and 9B each depict fictional tension metric values for a tension member over indexed timesteps, where the index i is used to reference select tension metric values. As stated, the tension metric can be given in a variety of units, however, herein, regardless of the unit of the tension metric, the tension metric is defined to be positive when the tension member is “in tension” and a higher-valued tension metric indicates a greater level of tension, stress, and/or strain applied to the tension member. As such, a negative-valued tension metric would indicate that the tension member is in compression.

[0093] FIG. 9A further depicts a low-tension threshold (902) that has the same units as the tension metric. Additionally, FIG. 9A depicts a rate threshold (904), with units of a change in tension metric with respect to a change in time, and an average threshold (906), with the same units of the tension metric. The low-tension threshold (902), rate threshold (904), and average threshold (906) will be referenced later in the instant disclosure.

Similarly, FIG. 9B depicts a broken threshold (952) with units identical to the tension metric employed.

[0094] FIGS. 10-15 depict flowcharts that outline the steps, processes, and/or elements to detect a break in a tension member, in accordance with one or more embodiments. Specifically, FIG. 10 outlines a method for detecting a break in a tension member that, immediately prior to break, was in a relatively high-tension state. It is expected that a tension member that breaks while under a high-tension state is characterized by a rapidly evolving tension metric and is distinguished herein as a “fast” break. FIG. 11 outlines a method for detecting a break in a tension member that, immediately prior to the break, was in a state of relatively low tension. It is expected that a tension member that breaks while in a state of relatively low tension is characterized by a slowly evolving tension metric (or, at least a slower evolution relative to a “fast” break) and is distinguished herein as a “slow” break. The fast and slow tension member break methods depicted in the flowcharts of FIG. 10 and 11 are described on the level of individual, discrete, and countable timesteps. This level of description is provided to aid the understanding of the reader. Additionally, upon describing embodiments of the fast and slow tension member detection methods, these methods are described with respect to the time series tension metric data depicted in FIGS. 9 A and 9B, respectively. The flowcharts of FIGS. 12-14 describe aspects of the fast and slow break detection methods in greater generality than their counterparts of FIGS. 10 and 11. Finally, the flowchart of FIG. 15 depicts an example of the combined usage of the fast and slow tension member break detection methods. That is, while embodiments for detecting a break in a tension member disclosed herein may be partitioned into a “fast” detection method and a “slow” detection method, this partitioning may be considered as a matter of convenience in describing the methods and systems of the instant disclosure. In general, the “fast” and “slow” tension member detection methods need not be considered separate. Thus, embodiments of the instant disclosure include the general case of detecting a break in a tension member regardless of whether that break is considered “fast” or “slow.” This point is emphasized because, as will be demonstrated below and in accordance with one or more embodiments, the classification of a break in a tension member as “fast” or “slow” is determined as a result of detecting the break.

[0095] While the various steps and/or blocks in these flowcharts are presented and described sequentially, one of ordinary skill will appreciate that some or all of the steps and/or blocks may be executed in different orders, may be combined or omitted, and some or all of the steps and/or blocks may be executed in parallel. Additional steps may further be performed. Furthermore, the steps and/or blocks may be performed actively or passively.

For example, some steps may be performed using polling or be interrupt driven in accordance with one or more embodiments of the invention.

[0096] As stated, embodiments disclosed herein relate to methods and systems for detecting a break in a tension member. In one or more embodiments, in addition to detecting a break, the break is classified as either “fast” or “slow.” Or rather, embodiments disclosed herein are capable of detecting breaks in tension members under high tension metrics, where in the event of a break changes in the tension metric evolve rapidly (i.e., a “fast” break) and detecting breaks in tension members experiencing relatively low tension metrics where changes in the tension metric evolve less rapidly (or not at all under certain circumstances) (i.e., a “slow” break).

[0097] The flowchart of FIG. 10 depicts, in an example, the elements to detect a break in a tension member where the break, once detected, is characterized as a “fast” break, in accordance with one or more embodiments. One or more of the Blocks in FIG. 10 may be performed by various components of systems, previously described with reference to FIGS. 1-4. Further, blocks of the flowchart of FIG. 10 may be executed on one or more processors, e.g., of the control system of the computer-assisted system (100).

[0098] In Block 1002, two thresholds are obtained, namely, a low-tension threshold, Thi, and a rate threshold, Th2. Examples of the low-tension threshold (902) and the rate threshold (904) are depicted with the example plot of FIG. 9A. The low-tension threshold (902) has the same units as the tension metric. So, for example, if the tension metric is given as a torque and has units of N-m (“Newton meters”), then the low-tension threshold (902) likewise is a torque with units of N-m. The rate threshold (904) has units of a change in tension metric with respect to a change in time (e.g., N-m/s). [0099] In Block 1004, for a first tension member in a set of at least one tension member, the tension metric of the first tension member at an i^th timestep, T^\ is determined. In the notation

represents the tension metric, the superscript identifies the m^th tension member (e.g., the first tension member), and the subscript indicates the timestep. As such, in one or more embodiments, using this notation, the tension metric of other tension members can be considered at a timestep i, as appropriate.

[00100] Block 1016 represents a decision. In Block 1016, the tension metric of the first tension member at the i^th timestep, T^\ is compared to the low-tension threshold (902), Thi. If the tension metric of the first tension member at the i^th timestep, T^\ is greater than or equal to the low-tension threshold (902), Thi, then the flowchart of FIG. 10 proceeds to Block 1018. In Block 1018, the timestep is advanced a step and the flowchart returns to Block 1004. In one or more embodiments, evaluation of Blocks 1002, 1004, and 1016 (and the remaining Blocks as yet described) occurs in real-time such that advancement of the timestep in Block 1018 can proceed at the sampling rate of the tension metric. That is, detection of a break in a tension member according to the method depicted in FIG. 10 is achieved nearly instantaneously with the break (or, at least before acquiring the tension metric at the timestep immediately posterior to the break).

[00101] Continuing with FIG. 10, if in Block 1016 it is determined that the tension metric of the first tension member at the i^th timestep, T^\ is less than the low-tension threshold (902), Thi, then the flowchart of FIG. 10 proceeds to Block 1020.

[00102] In Block 1020, a tension metric rate of change for the first tension member, rate (T^¹^), is determined. In one or more embodiments, the tension metric rate of change is taken as the difference between the tension metric of the first tension member at the i^th timestep, T^\ and tension metric of the first tension member at the (i — k')^th timestep, divided by the time elapsed between the i^th timestep and the (i — k)^th timestep, where k is an integer and k > 1. Mathematically, the rate of change for the first tension member, rate (T^¹^), can be written as

1 where t_t and t(_£_fc) represent the time, t, at the i^th and (i

timesteps, respectively. The tension metric rate of change of the first tension member can also be expressed as

where EQ. 7 may be considered an average of the rates of change determined between adjacent timesteps in the range [(i — k), i].

[00103] In Block 1022, the tension metric rate of change for the first tension member, rate , is compared to the rate threshold (904), Th2. Using the convention that “high” tension metrics have a greater value than “low” tension metrics (e.g., See ordinate axis of FIG. 9A), a drop in tension (or a “tension drop”) in the first tension member between the i^th and the (i — k)^t/l timestep is characterized by a negative-valued tension metric rate of change. As such, a negative-valued rate threshold, indicates that the tension metric has experienced a net decrease going from the (i — k)^t/l timestep to the i^th timestep. Using this convention, the rate threshold would be negative-valued. However, one with ordinary skill in the art will recognize that the selected sign convention is arbitrary such that other sign conventions can be used without departing from the scope of this disclosure. For example, a sign convention where a tension member under relatively high tension has a lower tension metric than the tension member under relatively low tension can be used as long as the elected sign convention is implemented consistently, which, in this example would mean that the rate threshold is positive-valued.

[00104] Continuing with FIG. 10, if, in Block 1022, the tension metric rate of change is greater than or equal to rate threshold (904), TI12, this indicates that the first tension member did not experience a notable net (or average) tension drop between the (i — k)^t/l and i^th timesteps and the flowchart of FIG. 10 proceeds to Block 1018. If, however, the tension metric rate of change is less than the rate threshold (904), TI12, it may be said that the first tension member experienced a notable drop in tension and the flowchart of FIG. 10 proceeds to Block 1024.

[00105] In Block 1024, it is determined whether the first tension member corresponds to a “high-tension state.” In general, this determination is made by evaluating the tension metric of the first tension member over an interval immediately prior to the observed and significant (relative to the rate threshold) tension drop that occurred at the i^th timestep. Below, three embodiments for determining whether the first tension member corresponds to the high-tension state are enumerated. While these embodiments are discussed in detail, it is emphasized that other methods, based on the tension metric of the first tension member over an interval immediately prior to the i^th timestep, can be employed without departing from the scope of the instant disclosure.

[00106] In a first embodiment, an average tension metric of the first tension member, T^\ is computed over the interval [(i — p), (i — 1)] where p > 1, and compared to a predefined average threshold (906), T, to determine if the first tension member corresponds to the high-tension state. Thus, in this embodiment, an average threshold, T, may also be obtained as part of Block 1002. If the average tension metric of the first member, T^\ is greater than the average threshold,

> T), the first tension member is determined to correspond to the high-tension state.

[00107] In a second embodiment, the set of M tension members includes at least two tension members i.e., M>1). In this embodiment, to determine whether the tension metric of the first tension member corresponds to the high-tension state, an average tension metric is computed for all M tension members in the set of M tension members over the interval [(i — p), (i — 1)] where p > 1. That is, the average tension metrics T^\ ...,

are computed. The average tension metrics T^\ ...,

are also ranked from the highest-valued (the “top”) to the lowest-valued (the “bottom”). The tension metric of the first tension member corresponds to the high-tension state when the average tension metric of the first tension member, T^\ is in the top X average tension metrics where 1 < X < (M-l). In other words, in this embodiments, the first tension member corresponds to the high-tension state when its average tension metric over the interval [(i — p), (i — 1)] : p > 1, is greater than the average tension metrics of (M-X) tension members in the set of M tension members (subject to M > 1), the (M-X) average tension metrics computed over the same interval.

[00108] In a third embodiment, to determine whether the tension metric of the first tension member corresponds to the high-tension state a drop metric for the first tension member, drop^ is computed as

where p > 1. That is, EQ. 8 subtracts the tension metric of the first tension member at the i^th timestep from the average tension metric of the first tension member computed over the p timesteps immediately prior to the i^th timestep. The drop metric of the first tension member is compared to a drop threshold, Thdrop. The first tension member corresponds to the high- tension state when the drop metric of the first tension member is greater than a predefined drop threshold (i.e., drop^ > Th^). Thus, in this embodiment, the drop threshold, Thdrop, may also be obtained as part of Block 1002.

[00109] Regardless of which embodiment is used to determine if the tension metric of the first tension member corresponds to the high-tension state, if the first tension member is determined not to correspond to the high-tension state, the flowchart of FIG. 10 returns to Block 1018. However, when, in Block 1026, it is determined that the tension metric of the first tension member corresponds to the high-tension state, a break in the first tension member is detected. The detection of the break is made explicit in Block 1030. Block 1030 further specifies that the detected break of the first tension member is classified as a “fast” break, as previously described.

[00110] While the flowchart of FIG. 10 describes methods and systems for detecting a break in a “first” tension member of a set of at least one tension members, given a set of tension members the designation of a “first” tension member is arbitrary. Thus, the flowchart of FIG. 10 can be applied independently to each tension member in a set of at least one tension member (e.g., one, two, three, four, five, six, or more tension members) without limitation.

[00111] Returning to FIG. 9A, FIG. 9A illustrates an example sequence of tension metrics of a tension member at various timesteps. Further, FIG. 9A illustrates a case where the methods and systems for detecting a break in a tension member as described above with respect to FIG. 10, when applied to the sequence of tension metrics in FIG. 9A will result in a detected break in the tension member. For example, FIG. 9A clearly depicts that the tension metric at the i^th timestep is less than the low-tension threshold (902), Thi, thus satisfying Block 1016 of FIG. 10. Next, the tension metric rate of change is determined and depicted in FIG. 9A as a sloping line (905). Comparison of the example tension metric rate of change i.e., sloping line (905)) to the rate threshold (904), Th2, clearly demonstrates that the tension metric rate of change is less than the rate threshold (904) thus satisfying Block 1022 of FIG. 10. Finally, to determine whether the tension metric corresponds to the high-tension state i.e., Block 1026 of FIG. 10), it is stated that the first embodiment for making a high-tension correspondence is applied to the example of FIG. 9A. That is, the average tension metric over the interval of timesteps [(i — p), (i — 1)], where p > 1, is determined and compared to the given average threshold (906). As seen in FIG. 9A, the average tension metric is greater than the average threshold (906) satisfying Block 1026. Having satisfied Blocks 1016, 1022, and 1026, the flowchart of FIG. 10, for the example depicted in FIG. 9A, detects a break in the tension member (Block 1030).

[00112] The flowchart of FIG. 11 depicts, in an example, the elements to detect a break in a tension member where the break, once detected, is characterized as a “slow” break, in accordance with one or more embodiments. One or more of the Blocks in FIG. 11 may be performed by various components of systems, previously described with reference to FIGS. 1-4. Further, blocks of the flowchart of FIG. 11 may be executed on one or more processors, e.g., of the control system of the computer-assisted system (100).

[00113] Turning to FIG. 11, in Block 1102, two thresholds are obtained, namely a broken threshold, Ths, and a common displacement threshold, Tt . After Block 1102, the flowchart of FIG. 11 proceeds to Block 1004 that is identical to that already described with respect to FIG. 10. In Block 1004, for a first tension member in a set of at least one tension member, the tension metric of the first tension member at an i^th timestep, T^\ is determined. In Block 1106, it is determined whether the tension metric for the first tension member is below the broken threshold (952), Ths, throughout a time interval of the timesteps [(i — q), i], where q > 0. Block 1108 represents a decision based on the determination made in Block

1106. If it is determined that the tension metric for the first tension member, T> , is less than the broken threshold (952), Ths, for all values of j from (i — q) to i, then the flowchart of FIG. 11 proceeds to Block 1110 where a break in the first tension member is detected and the break is further classified as a “slow” break. If, however, the condition of Block 1108 is not met, then the flowchart of FIG. 11 proceeds to Block 1112.

[00114] Block 1112 determines the average relative displacement for the first tension member in view of all other tension members that interact with the first tension member in an antagonistic manner (i.e., tension members that are antagonistically coupled with the first tension member forming an antagonistic system). If the first tension member is not paired in an antagonistic manner with any other tension cable, then the average relative displacement is set to a value of zero. Otherwise, the average relative displacement is determined, for example, according to EQ. 3. In Block 1114, the average relative displacement determined in Block 1112 is compared to the common displacement threshold, Tt . If, in Block 1114, the determined average relative displacement is greater than the common displacement threshold, a break in tension member is detected in Block 1110. Otherwise, the flowchart of FIG. 11 proceeds to Block 1018 to increment the timestep and determine whether a break is detected in view of the new timestep.

[00115] Returning to FIG. 9B, FIG. 9B illustrates an example sequence of tension metrics of a tension member at various timesteps. Further, FIG. 9B illustrates a case where the methods and systems for detecting a break in a tension member as described above with respect to FIG. 11, when applied to the sequence of tension metrics in FIG. 9B will result in a detected break in the tension member (specifically, a “slow” break). For example, FIG. 9B clearly depicts that the tension metrics over the interval of timesteps [(i — q), i], where q > 0, all reside below the depicted broken threshold (952), Ths. Thus, Block 1108 is satisfied and the flowchart of FIG. 11, in view of the example tension metrics of FIG. 9B, proceeds to Block 1110 and detects a break in the tension member.

[00116] FIGS. 10 and 11 depict and discuss embodiments of the instant disclosure explicitly with direct references to timesteps of a sequence of tension metrics. However, embodiments of the instant disclosure can be described without explicit recitation of timesteps. To this end, FIG. 12 depicts, in an example, a flowchart that outlines the steps to detect a break in a tension member, where the break is characterized as a “fast” break, in accordance with one or more embodiments. Similarly, FIG. 13 depicts, in an example, a flowchart that outlines the steps to detect a break in a tension member, where the break is characterized as a “slow” break, in accordance with one or more embodiments.

[00117] Turning to FIG. 12, in Block 1202, a first determination is made of whether a tension metric of a tension member corresponds to a high-tension state. This determination is made, at least in part, based on the evaluation of the tension metric of the tension member prior to a tension drop, the tension drop determined in Block 1204. Three specific embodiments for determining whether the tension metric of a tension member corresponds to the high-tension state have been previously described and are not repeated here for brevity. [00118] In Block 1204, a second determination is made of whether a tension drop of the tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold. In one or more embodiments, the rate threshold is negative- valued such that a tension drop of the tension metric that “exceeds” the rate threshold is also negative-valued and strictly less than the rate threshold.

[00119] In Block 1206, a third determination is made of whether, after the tension drop determined in Block 1204, the tension metric resides below a low-tension threshold. That is, after experiencing a drop in tension (i.e., a tension drop), the tension metric of the tension member is evaluated to determine if the tension metric is below some low-tension threshold. [00120] In Block 1208, based on the first determination, the second determination, and the third determination, it is determined whether there is a break in the tension member. Finally, in Block 1210, in response to a determination that there is a break in the tension member, an action is performed. Example actions include providing a signal and/or an ameliorative activity. Various examples of ameliorative activities and the use of a provided signal are detailed below.

[00121] In accordance with one or more embodiments, in response to detecting a break in a tension member of an instrument supported by a computer-assisted system (100), the computer-assisted system (100) performs a responsive action that comprise part or all of an ameliorative activity. Responsive actions to a detected break in a tension member of a computer-assisted system (100) include, but are not limited to: generating an alert or alarm for a user, where the alert or alarm and be any combination of audio, visual, and haptic feedback (e.g. display of a text notification, emission of an audible tone, etc.); interrupting control, movement, or otherwise discontinuing operation of a manipulator system (130) by an operator using a user interface system (120) (e.g., exiting teleoperation); locking the actuators of one or more manipulator arms (250) (e.g., the manipulator arm (250) supporting the instrument); putting the actuators of one or more manipulator arms (250) (e.g., the manipulator arm (250) supporting the instrument) into a gravity-compensation mode wherein the manipulator arm (250) maintains a position or kinematic configuration but can otherwise be moved by an external force; inhibiting a function of other operation of one or instruments (e.g., of the instrument corresponding to the tension member break). Example function inhibition includes disabling energy application by an energy -emitting instrument; terminating a function of the instrument such as irrigation, suction, or imaging; or any combination thereof. Examples of inhibiting operation of an instrument includes inhibiting movement of DOF(s) of the instrument. Each of the response actions described above, or a combination of one or more of these actions with each other or an undescribed action, can be considered an ameliorative activity. Thus, in response to detecting a break in a tension member, the computer-assisted system (100), or component of the computer-assisted system (100) such as the control system (142), can perform an action where that action is an ameliorative activity.

[00122] For example, in response to a detected break in a tension member of a computer-assisted system (100), the computer-assisted system (100) may inhibit one or more functions of the one or more instruments controlled by the computer-assisted system (100). In an example, in response to a detected tension member break, the computer-assisted system (100) inhibits the movement of the DOF(s) controlled by the tension member detected as broken; or of all DOFs of the instrument with the detected tension member and/or some or all DOFs of the manipulator arm (250) supporting the instrument with the tension member detected as broken.

[00123] In an example, in response to detecting a break in a tension member of a first instrument, the computer-assisted system (100) may inhibit energy emission by that first instrument. In some instances, the computer-assisted system (100) still allows actuation of the non-energy-emission function(s) of the first instruments with inhibited energy emission, while in other instances, the computer-assisted system (100) also inhibits the non-energy- emission function(s) of the instruments with inhibited energy emission. In some instances, the computer-assisted system (100) may also inhibit one or more functions of one or more instruments that were performing a collaborative action with the instrument with the detected tension break, such as energy-emission functions, and/or movement of other non-energy- emission function(s). Example energy emissions include applying RF, microwave, ultrasonic, sonic, electrical (e.g., electrocautery), heat energy. Example other functions include physical movement, imaging or other sensing, irrigation, suction, etc.. Any appropriate technique can be used to inhibit energy emission. For example, the computer- assisted system (100) can determine if an instrument is an energy-emission instrument, and in response to a determination that the instrument is an energy-emission instrument, disable energy emission by the first instrument and/or stop commanding the instrument to emit energy. As another example, the computer-assisted system (100) inhibits energy emission to an instrument by ignoring all user input for that instrument to apply energy, or by stop commanding the instrument to emit energy, regardless of whether that instrument is an energy-emission instrument. In the second example, the computer-assisted system (100) need not distinguish if a given instrument is an energy-emission instrument.

[00124] In some implementations, in response to detecting a break in a tension member, the computer-assisted system (100), or a component of the computer-assisted system (100) such as the control system (142), can provide a signal. The signal may be provided to an external system or device, or to other components of the computer-assisted system (100) (e.g., a signal provided by the control system (142) and transmitted to the display (144)). In some implementations, the provided signal indicates (e.g., used as a “flag”) that a tension member is broken, where the indication is provided externally and/or internally to the computer-assisted system (100). The provided signal can include greater specificity or data related to the broken tension member, such as, but not limited to: an identifier of the tension member (z.e., tension member identification); the location of the broken tension member in the computer-assisted system (100) (e.g., a manipulator assembly (200)); components affected by the break (e.g., an instrument); a state or condition of the computer-assisted system (100) (e.g., a teleoperation mode); and functions of the computer- assisted system (100) rendered inoperable by the broken tension member (e.g., loss of control of one or more degrees of freedom). In some implementations, the provided signal triggers, or otherwise initiates, an ameliorative activity. For example, the provide signal can result in, or be realized as, an alert or alarm to a user where the alert or alarm and be any combination of audio, visual, and haptic feedback (e.g., display of a text notification, emission of an audible tone, etc.). Thus, in response to detecting a break in a tension member, the computer- assisted system (100), or component of the computer-assisted system (100) such as the control system (142), can perform an action where that action is providing a signal. In some implementations, the provided signal can communicate a command to a control system associated with the tension member. For example, the tension member can be part of an instrument (260), the instrument manipulated by a manipulator arm (250) of a computer- assisted system (100). Thus, the control system can control and alter aspects of the computer-assisted system (100), including the instrument (260) containing the tension member determined to be broken, other instruments (260), auxiliary functions, and the manipulator system (130).

[00125] In one or more embodiments, the response to a detected break of a tension member depends on the current configuration and use of the computer-assisted system (100) including the broken tension member. For example, dependent of the instruments in use under the computer-assisted system (100), the behavior and/or control of some instruments may be altered while others are unaffected (e.g., energy to electrical cortical stimulation instruments turned off while irrigation instruments remain active.) such as to control the computer-assisted system (100).

[00126] In one or more embodiments, in response to a detected break of a tension member in a group of two or more tension members grouped in an antagonistic manner (e.g., an antagonistic actuator system), the actuators of the tension members are “floated.” The term “floated” indicates that the actuator, and any associated hardware coupling the actuator to a tension member, is configured to facilitate back driving of the actuator by the application of external force (or torque, etc.). In a general example, floating an actuator releases or removes tension (in the sense of a force or pressure applied to the tension member) modulated, or otherwise enacted, by the actuator. As some examples, in various embodiments, “floating” an actuator comprises: (1) causing the actuator to physically disengage from driving the corresponding tension member, such as by disengaging the actuator from a transmission system coupling the actuator to the tension member, or by disengaging such transmission system from the tension member; (2) the control system iteratively commanding the actuator to the current position of the actuator as the actuator is displaced; (3) the control system commanding the actuator to apply no tension to the tension member; (4) the control system commanding the actuator to unwind or otherwise release the tension member; or (5) a combination of the foregoing. As a particular example, consider the antagonistic actuator system (600) of FIG. 6A. This antagonistic actuator system (600) has two tension members, namely a first tension member (502) and a second tension member (504). If a break of a tension member of the antagonistic actuator system (600) is detected, for example, according to Block 1114 of FIG. 11, then, in response, both the first disk (602) and second disk (604) and associated actuators are floated. By floating the actuators, or at least the directly paired actuators (and associated driving hardware), of antagonistically grouped tension members upon detection of a break in at least one of the grouped tension members, tension is released from the unbroken tension members mitigating movement at the distal end of the system (e.g., at the pulley (506) or at a wrist assembly (390) and/or end effector (392) of an instrument (260)). Floating of the one or more actuators of an actuation assembly can be implemented for one or more tension members that are not grouped in an antagonistic manner (e.g., the actuator system of FIG. 5). In such cases, it can still be beneficial to float one or more actuators associated with the degree(s) of freedom affected by the broken tension member. For example, as described in the actuator system (500) of FIG. 5, the tension members (502, 504) can have a nominal amount of tension. Consequently, the breaking of one tension member may result in the movement of the pulley (506) (even in the actuator system (500)) due to the nominal tension in the unbroken tension member. Thus, floating of the actuator and associated driving hardware (e.g., capstan (510) in FIG. 5) can mitigate modulation of the degree of freedom at the pulley (506) due to the nominal tension in the unbroken tension member(s). In accordance with one or more embodiments, actuators of an actuator system, whether an antagonistic system or not, are “actively” released. For example, “active” release indicates that the actuator is driven, to some extent, in a direction that would lengthen (or “spool out”) an associated tension member in response to a determination that a tension member in the associated actuator system is broken.

[00127] Turning to FIG. 13, in Block 1302, a first determination is made of whether, throughout a time interval, a tension metric of a tension member is less than a broken threshold. The broken threshold has the same units as the given tension metric for the tension member.

[00128] In Block 1304, it is determined whether the tension member is broken based on the first determination made in Block 1302. Simply, if the first determination is that the tension metric of the tension member is less than the broken threshold throughout the time interval, then the tension member is determined to be broken. If, at any time (e.g., timestep) in the time interval, the tension metric of the tension member is not determined to be less than the broken threshold, the tension member is not determined to be broken.

[00129] In Block 1306, based on a determination that the tension member is broken an action, such as providing a signal and/or an ameliorative activity, is performed. Example ameliorative activities include all of the examples discussed in conjunction with block 1208. [00130] A provided signal can be transmitted to an external system or device, or used within the computer-assisted system (100) itself (e.g., a signal provided by the control system (142) and transmitted to the display (144)). The provided signal can have some or all of the characteristics or functionality as the provided signal discussed in conjunction with block 1208, block 1306, and by the rest of this document.

[00131] In one or more embodiments, the signal communicates a command to a control system associated with the tension member. For example, the tension member can be part of an instrument (260), the instrument manipulated by a manipulator arm (250) of a computer-assisted system (100). Thus, the control system can control and alter aspects of the computer-assisted system (100), including the instrument (260) containing the tension member determined to be broken, other instruments (260), auxiliary functions, and the manipulator system (130).

[00132] Turning to FIG. 14, in an example, in Block 1402, a first determination is made of whether an average relative displacement of a first tension member and a second tension member is greater than a common displacement threshold, where the first tension member and the second tension member form an antagonistic pair.

[00133] In Block 1404, it is determined, based on the first determination of Block 1402, whether at least one of the first tension member and the second tension member is broken. Simply, if the average relative displacement is greater than the common displacement threshold then at least one of the first tension member and the second tension member is determined to be broken.

[00134] In Block 1406, based on a determination that there is a break in at least one of the first tension member and the second tension member an action, such as providing a signal and/or an ameliorative activity, is performed. Example ameliorative activities include those described in conjunction with block 1208, block 1306, and in the rest of this document.

[00135] In some implementations, a provided signal can be transmitted to an external system or device, or used within the computer-assisted system (100) itself (e.g., a signal provided by the control system (142) and transmitted to the display (144)). The provided signal can have some or all of the characteristics or functionality as the provided signal discussed in conjunction with block 1208, block 1306, and by the rest of this document.

[00136] As previously stated, the flowchart of FIG. 15 depicts an example of the combined usage of the fast and slow tension member break detection methods. The fast tension member detection method was outlined in FIG. 10, in accordance with one or more embodiments. Eikewise, the slow tension member break detection method was outlined in FIG. 11, in accordance with one or more embodiments. FIG. 15, thus, contains many of the same elements as those depicted in FIGS. 10 and 11 and retains the same block labels as found in FIGS. 10 and 11 for consistency, where applicable. Turning to FIG. 15, in Block 1502, four thresholds are obtained, namely, a low-tension threshold, Thi, a rate threshold, Th₂, a broken threshold, Ths, and a common displacement threshold, Tt . After Block 1502, the flowchart of FIG. 15 proceeds to Block 1004 that is identical to that already described with respect to FIG. 10. In Block 1004, for a first tension member in a set of at least one tension member, the tension metric of the first tension member at an i^th timestep, T^\ is determined. In Block 1106, it is determined whether the tension metric for the first tension member is below the broken threshold (952), Ths, throughout a time interval of the timesteps [(i — q), i], where q > 0. Block 1108 represents a decision based on the determination made in Block 1106. If it is determined that the tension metric for the first tension member, T> , is less than the broken threshold (952), Ths, for all values of j from (i — q) to i, then the flowchart of FIG. 15 proceeds to Block 1110 where a break in the first tension member is detected and the break is further classified as a “slow” break. If, however, the condition of Block 1108 is not met, then the flowchart of FIG. 15 proceeds to Block 1112.

[00137] Continuing with FIG. 15, Block 1112 determines the average relative displacement for the first tension member in view of all other tension members that interact with the first tension member in an antagonistic manner (i.e., tension members that are antagonistically coupled with the first tension member forming an antagonistic system). If the first tension member is not paired in an antagonistic manner with any other tension cable, then the average relative displacement is set to a value of zero. Otherwise, the average relative displacement is determined, for example, according to EQ. 3. In Block 1114, the average relative displacement determined in Block 1112 is compared to the common displacement threshold, Ttu. If, in Block 1114, the determined average relative displacement is greater than the common displacement threshold, a break in tension member is detected in Block 1110. Otherwise, the flowchart of FIG. 15 proceeds to Block 1016 and the remaining blocks of FIG. 15 are identical to those of FIG. 10. In FIG. 15, the sequence of blocks is organized to first detect for a “slow” break, if present, of the tension member and then check for the “fast” break at each new timestep. However, it is emphasized that the blocks of FIG. 15 need not be implemented exactly to the depicted sequence. In general, the blocks of FIG. 15 can be arranged to first detect, if present, a “fast” break followed by detection of a “slow” break at each new timestep.

[00138] Embodiments of the instant disclosure provide one or more of the following advantages. In general, a tension member may be used to actuate or control the motion or the function of (e.g., the supply of energy in the case of an energy-emitting end effector), at least, a portion of a device (e.g., wrist assembly and/or end effector of an instrument). Thus, detection of a break in a tension member reduces the likelihood of uncontrolled motion, control, and/or function of the affected device (i.e., wrist assembly) and/or unintended interactions between the affected device and its environment. For example, when a break in a tension member is detected according to the systems of methods disclosed herein, a response can be taken. In the case that the tension member is part of an instrument, like that of FIG. 3, where the tension member enacts some function or movement at the distal end of the instrument, the detection of a break in the tension member can signal (trigger, command, etc.) an adjustment to the instrument and/or associated systems (e.g., control system of a computer-assisted system, other instruments, auxiliary functions, other manipulator arms). For example, turning off electrical, ultrasonic, or radio frequency (RF) energy supplied to an associated instrument, stopping further motion commands to the instrument and allowing the tension members (including any tension members not determined to be broken) of the instrument to go slack (i.e., “floating” the associated actuator assembly), and selectively stopping one or more auxiliary functions (e.g., suction, irrigation, etc.) of the instrument depending on the instrument, procedure, and/or current state of the procedure.

[00139] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMS What is claimed is:

1. A computer-assisted system, comprising: a manipulator assembly configured to support a first instrument, the first instrument comprising a first tension member to actuate a first degree of freedom of the first instrument, wherein the manipulator assembly is configured to modulate a first tension metric of the first tension member; and a control system comprising one or more processors, the control system communicatively coupled to the manipulator assembly, the control system configured to: make a first determination of whether the first tension metric corresponds to a high-tension state, make a second determination of whether a tension drop of the first tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold, make a third determination of whether, after the tension drop, the first tension metric is below a low-tension threshold, determine, based on the first determination, the second determination, and the third determination, whether there is a break in the first tension member, and perform an action in response to a determination that there is the break in the first tension member, wherein the action comprises an act selected from the group consisting of: providing a signal and an ameliorative activity.

2. The computer-assisted system of claim 1 , wherein making the first determination comprises determining whether the tension drop is greater than a drop threshold.

3. The computer-assisted system of claim 1, wherein the control system is further configured to: determine a first metric average of the first tension metric prior to the tension drop, wherein making the first determination comprises: determining that the first metric average is greater than an average threshold.

4. The computer-assisted system of claim 1, wherein the first instrument further comprises a second tension member to actuate a second degree of freedom of the first instrument, wherein the manipulator assembly is further configured to modulate a second tension metric of the second tension member, and wherein the control system is further configured to: determine a first metric average of the first tension metric prior to the tension drop; and determine a second metric average of the second tension metric prior to the tension drop, wherein making the first determination comprises determining that the first metric average is greater than the second metric average.

5. The computer-assisted system of claim 1, wherein the control system is further configured to: make a fourth determination of whether, throughout a time interval, the first tension metric is less than a broken threshold, wherein determining whether there is the break in the first tension member is further based on the fourth determination.

6. The computer-assisted system of claim 1, wherein the first instrument further comprises a second tension member to actuate the first degree of freedom, wherein the manipulator assembly is further configured to modulate a second tension metric of the second tension member, wherein the first tension member and the second tension member form an antagonistic pair, such that tensioning the first tension member biases the first degree of freedom toward moving in a first direction, and tensioning the second tension member biases the first degree of freedom toward moving in a second direction, the second direction opposing the first direction, wherein the control system if further configured to: make a fourth determination of whether an average relative displacement of the first tension member and the second tension member is greater than a common displacement threshold, and determine, based on the fourth determination, whether the antagonistic pair is broken.

7. The computer-assisted system of claim 6, wherein the manipulator assembly comprises a first actuator that modulates the first tension metric of the first tension member, and a second actuator that modulates the second tension metric of the second tension member; and wherein the control system is further configured to, in response to the determination that the antagonistic pair of the first tension member and the second tension member is broken, causing the first and second actuators to float, wherein to cause the first and second actuators to float comprises removing or releasing modulation of the first and second tension members by the first and second actuators, respectively.

8. The computer-assisted system of claim 1, wherein the manipulator assembly comprises an actuator assembly to modulate the first tension metric, and wherein the control system is further configured to: determine an estimate of the first tension metric based on a model of the actuator assembly and a tension command issued to the actuator assembly, wherein the first determination, the second determination, and the third determination are made using the estimate of the first tension metric.

9. The computer-assisted system of claim 1, further comprising: a sensor configured to obtain a measurement of the first tension metric, wherein the first determination, the second determination, and the third determination are made using the measurement.

10. The computer-assisted system of claim 1, wherein the first tension metric is determined in a sequence of timesteps, and wherein: the third determination of whether the first tension metric is below the low-tension threshold is determined at a most recent timestep of the sequence of timesteps, or the rate of the tension drop for making the second determination is based on a difference in the first tension metric at a most recent timestep and the tension metric at a previous timestep in the sequence of timesteps.

11. The computer-assisted system of claim 1, wherein the first tension metric is determined in a sequence of timesteps, and wherein: the first determination of whether the first tension metric corresponds to the high- tension state comprises determining that a first metric average of the first tension metric, the first metric average taken over one or more timesteps prior to a most recent timestep, is greater than an average threshold.

12. The computer-assisted system of any of claims 1 to 11, wherein the first instrument further comprises another tension member to actuate another degree of freedom of the first instrument, wherein the manipulator assembly further comprises an actuator configured to modulate a tension metric of the another tension member, wherein the action comprises the ameliorative activity, and the ameliorative activity comprises causing the actuator to float, wherein causing the actuator to float comprises removing or releasing tension from the another tension member.

13. The computer-assisted system of any of claims 1 to 11, wherein the first instrument further comprises another tension member to actuate the first degree of freedom, wherein the manipulator assembly further comprises an actuator configured to modulate a tension metric of the another tension member, wherein the action comprises the ameliorative activity, and the ameliorative activity comprises causing the actuator to float, wherein causing the actuator to float comprises removing or releasing modulation of the another tension member by the actuator.

14. The computer-assisted system of any of claims 1 to 11, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises inhibiting energy emission by the first instrument.

15. The computer-assisted system of claim 14, wherein the ameliorative activity allows operation of a non-energy-emission function of the first instrument.

16. The computer-assisted system of any of claims 1 to 11, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises selectively adjusting one or more auxiliary functions of the first instrument.

17. The computer-assisted system of any of claims 1 to 11, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises: inhibiting teleoperation of the manipulator assembly; and commanding the manipulator assembly to maintain a kinematic configuration of the manipulator assembly.

18. The computer-assisted system of any of claims 1 to 11, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises: generating an alert detectable by a user.

19. A method for detecting a break in a tension member of a computer-assisted system comprising a manipulator assembly configured to support a first instrument, wherein the first instrument comprises a first tension member to actuate a first degree of freedom of the first instrument, wherein the manipulator assembly is configured to modulate a first tension metric of the first tension member, the method comprising: with a control system of the computer-assisted system comprising one or more processors and communicatively coupled to the manipulator assembly: making a first determination of whether the first tension metric corresponds to a high-tension state, making a second determination of whether a tension drop of the first tension metric corresponding to the high-tension state occurs at a rate exceeding a rate threshold, making a third determination of whether, after the tension drop, the first tension metric is below a low-tension threshold, determining, based on the first determination, the second determination, and the third determination, whether there is a break in the first tension member, and performing an action in response to a determination that there is the break in the first tension member, wherein the action comprises an act selected from the group consisting of: providing a signal and an ameliorative activity.

20. The method of claim 19, wherein making the first determination comprises determining whether the tension drop is greater than a drop threshold.

21. The method of claim 19, further comprising: determining, with the control system, a first metric average of the first tension metric prior to the tension drop, wherein making the first determination comprises determining that the first metric average is greater than an average threshold.

22. The method of claim 19, wherein the first instrument further comprises a second tension member to actuate a second degree of freedom of the first instrument, wherein the manipulator assembly is further configured to modulate a second tension metric of the second tension member, and further comprising: determining, with the control system, a first metric average of the first tension metric prior to the tension drop; and determining, with the control system, a second metric average of the second tension metric prior to the tension drop, wherein making the first determination comprises determining that the first metric average is greater than the second metric average.

23. The method of claim 19, further comprising: making, with the control system, a fourth determination of whether, throughout a time interval, the first tension metric is less than a broken threshold, wherein determining whether there is the break in the first tension member is further based on the fourth determination.

24. The method of claim 19, wherein the first instrument further comprises a second tension member to actuate the first degree of freedom, wherein the manipulator assembly is further configured to modulate a second tension metric of the second tension member, wherein the first tension member and the second tension member form an antagonistic pair, such that tensioning the first tension member biases the first degree of freedom toward moving in a first direction, and tensioning the second tension member biases the first degree of freedom toward moving in a second direction, the second direction opposing the first direction, and the method further comprising, with the control system: making a fourth determination of whether an average relative displacement of the first tension member and the second tension member is greater than a common displacement threshold, and determining, based on the fourth determination, whether the antagonistic pair is broken.

25. The method of claim 24, wherein the manipulator assembly comprises a first actuator that modulates the first tension metric of the first tension member, and a second actuator that modulates the second tension metric of the second tension member; wherein the method further comprises: causing, with the control system, the first and second actuators to float in response to a determination that the antagonistic pair is broken; and wherein causing the first and second actuators to float comprises: removing or releasing modulation of the first and second tension members by the first and second actuators, respectively.

26. The method of claim 19, wherein the manipulator assembly comprises an actuator assembly to modulate the first tension metric, the method further comprising: determining, with the control system, an estimate of the first tension metric based on a model of the actuator assembly and a tension command issued to the actuator assembly, wherein the first determination, the second determination, and the third determination are made using the estimate of the first tension metric.

27. The method of claim 19: wherein the computer-assisted system further comprises a sensor configured to obtain a measurement of the first tension metric, wherein the first determination, the second determination, and the third determination are made using the measurement.

28. The method of claim 19, wherein the first tension metric is determined in a sequence of timesteps, and wherein: the third determination of whether the first tension metric is below the low-tension threshold is determined at a most recent timestep of the sequence of timesteps, or the rate of the tension drop for making the second determination is based on a difference in the first tension metric at a most recent timestep and the first tension metric at a previous timestep in the sequence of timesteps.

29. The method of claim 19, wherein the first tension metric is determined in a sequence of timesteps, and wherein: the first determination of whether the first tension metric corresponds to the high- tension state comprises determining that a first metric average of the first tension metric, the first metric average taken over one or more timesteps prior to a most recent timestep, is greater than an average threshold.

30. The method of any of claims 19 to 29, wherein the first instrument further comprises another tension member to actuate another degree of freedom of the first instrument, wherein the manipulator assembly further comprises an actuator configured to modulate a tension metric of the another tension member, wherein the action comprises the ameliorative activity, and the ameliorative activity comprises causing the actuator to float, wherein causing the actuator to float comprises removing or releasing tension from the another tension member.

31. The method of any of claims 19 to 29, wherein the first instrument further comprises another tension member to actuate the first degree of freedom, wherein the manipulator assembly further comprises an actuator configured to modulate a tension metric of the another tension member, wherein the action comprises the ameliorative activity, and the ameliorative activity comprises causing the actuator to float, wherein causing the actuator to float comprises removing or releasing modulation of the another tension member by the actuator.

32. The method of any of claims 19 to 29, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises inhibiting energy emission by the first instrument.

33. The method of claim 32, wherein the ameliorative activity allows operation of a non-energy-emission function of the first instrument.

34. The method of any of claims 19 to 29, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises selectively adjusting one or more auxiliary functions of the first instrument.

35. The method of any of claims 19 to 29, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises: inhibiting teleoperation of the manipulator assembly; and commanding the manipulator assembly to maintain a kinematic configuration of the manipulator assembly.

36. The method of any of claims 19 to 29, wherein the action comprises the ameliorative activity, and wherein the ameliorative activity comprises: generating an alert detectable by a user.

37. A non-transitory machine-readable medium comprising a plurality of machine-readable instructions executed by one or more processors associated with a computer-assisted system, the plurality of machine-readable instructions causing the one or more processors to perform the method of any of claims 19 to 36.