WO2021133229A1 - Estimating the force on a robotic surgical instrument - Google Patents

Abstract

The invention relates to medical systems for minimally invasive interventions which are provided with a device for estimating the force occurring on the tip of a surgical instrument when it enters into contact with patient tissue, as well as forces at the level of the access port for the surgical instrument into the patient's body, and other forces which, during an operation, incidentally or foreseeably act on the part of a surgical instrument situated inside the patient's body. Use of the present system for estimating the forces acting on an instrument of a robotic surgical system allows operations to be performed to a high standard as a result of precise actions by the surgeon. This is achieved by means of the following features: the provision of seven degrees of freedom during the measurement of forces acting on an instrument: three linear degrees, three rotational degrees, and one degree of freedom during grasping; the use of multi-axis strain gauge sensors for determining the direction and modulus of the forces at work; the positioning of electrical circuits that are sensitive to electromagnetic interference at a distance from the area of influence of electrocoagulation; the use of an additional circuit for estimating the force of motion of the gripper; the use of external structures for mounting measuring elements, electrical circuits and mechanisms; the use of digital signal processing in order to eliminate interference.

Description

ASSESSMENT OF EFFORT ON A ROBOTIC SURGICAL INSTRUMENT

The technical field to which the invention relates

The invention relates to assisting surgical systems for minimally invasive surgical operations. More specifically, the invention relates to medical systems for minimally invasive intervention with a device for assessing the force arising at the tip of a surgical instrument when it touches the patient's tissue, as well as the forces at the level of the access opening of the surgical instrument into the patient's body and other forces that accidentally or expectedly act in the process. work on the part of the surgical instrument located in the patient's body.

Background of the invention

The development and implementation of feedback systems is an urgent direction in the development of robotic surgery. Feedback is a method that allows the surgeon to determine the amount and quality of influences applied to the tissues. In a classic abdominal operation, the surgeon's feedback is the visual perception of what is happening, as well as tactile sensations caused by touching the tissue with the hands or the surgical instrument used.

The direction of development of robotic surgery seeks to provide the surgeon with the sensations familiar to him from the experience of open surgery: a high-quality view of the working field and intuitive and logical control of instruments, but in the conditions of using modern minimally invasive technologies. To transfer tactile influences to the surgeon from contact with the patient's tissues, a complex solution of several problems is necessary:

• Creation of a system for assessing the forces acting on the actuator - tool;

• Processing of data on applied forces using the control system;

• Transfer of processed data about the acting forces to the surgeon for perception, assessment and decision-making.

Accurate force feedback (tactile force feedback) is an essential feature that ensures safety and improves the quality of procedures performed during robotic surgery. The task of creating force feedback is one of the key tasks for developers of robotic surgical systems and it is solved using various approaches.

Possible approaches to the creation of feedback systems, their analysis and disadvantages are detailed in the application US2018194013 A1, published on 12.07.2018. US2018194013 A1 describes a method for assessing the forces acting on an instrument of a robotic surgical system, which consists in indirect control, in which the actions of forces on the tip of the instrument are estimated / calculated by analyzing the forces arising in this case on the other, opposite end of the tool. For this, the forces acting from the tool on the console of the tool holder, on which this end of the tool is fixed, are measured by six degrees of freedom. Additionally, the distance from the instrument attachment unit to the trocar is calculated, according to the results of which correction factors are introduced when assessing forces. The force feedback system has the ability to indirectly estimate the position of the tool tip using a strain gauge external to the tool; the measuring elements of the system are located in a zone remote from the zone of electrocoagulation interference; and the system has the ability to calculate and compensate for the forces arising from contact with the trocar.

However, the force feedback described in the application does not have the ability to control the compression force of the jaws of a surgical instrument (one tactile sensation) and does not have the ability to assess the additional forces arising from the contact of the instrument and the trocar. The use of a strain gauge sensor with six degrees of freedom does not allow to unambiguously determine the nature of the measured forces, which reduces the efficiency of the system. In this arrangement, the same set of forces can be caused both by contact with the patient's tissues and by touching the trocar.

The existing force feedback loops for assisting surgical complexes do not allow solving the following set of problems, which reduces the efficiency of the robotic surgical complex as a whole:

1. It is sufficiently reliable and accurate to estimate the forces acting on the tool during the interaction of the executive surfaces of the tool and tissues along seven or more axes;

2. It is sufficient to reliably and accurately identify and evaluate forces, both controlled and involuntarily arising as a result of the interaction of other, non-executive surfaces of the instrument, with the patient's organs and tissues;

3. It is sufficient to reliably and accurately identify and evaluate the forces acting on the instrument in contact with the trocar;

4. Provide the ability to work in conditions of increased electromagnetic noise caused by electrocoagulation devices.

Thus, there is a need to improve the force estimation system for use in a force feedback loop for a robotic surgical device. It is the solution of the listed problems that the present invention is devoted to.

The essence of the invention

The technical problem to be solved by the present invention is to reliably determine the sources of forces acting on a surgical instrument during operation along seven or more axes, as well as to accurately measure these forces in conditions of increased electromagnetic noise. The technical result of the present invention consists in the development of a medical system for minimal invasive intervention with a new design and algorithm of the system for assessing the forces acting on the instrument of the robotic surgical system to solve the problem of obtaining data necessary for the implementation of a tactile feedback system in real time, while the system for assessing forces simultaneously meets the following requirements:

1. The ability to assess the forces acting on a surgical instrument of a robotic surgical system, applied to any part of its structure;

2. Unambiguous determination of the direction and numerical value of the force applied to the surgical instrument;

3. Possibility of uninterrupted operation of the force assessment system under conditions of using electrocoagulation with a surgical instrument;

4. The ability to measure the gripping force that occurs when the jaws of a surgical instrument are closed;

5. The force assessment system should have a minimal effect on the design of the tool used;

6. Ensuring the possibility of transmitting data on measured forces to external control systems of the robotic-surgical complex;

7. Resistance to electromagnetic interference from a household network;

8. Possibility of using measuring sensors of various types and operating principles for different degrees of freedom.

The developed design and algorithm of the force assessment system should accurately and differentially measure the impact forces on the surgical instrument during operation and transfer the measured data to the higher-level control system.

The solution to the problem and the achievement of the technical result is ensured, first of all, by a new scheme and structure of the force assessment system, which makes it possible to increase the efficiency and functionality of the robotic surgical complex.

The proposed system according to the present invention is designed to measure the forces acting on an instrument during a robotic surgery and transmit information containing the measurement results. The system is an integral part of the actuator of the robot-assisted surgical complex and implements the measurement functionality for the implementation of tactile feedback by the complex. The force evaluation system used in the force feedback loop should have the following functions:

• Measurement of data of forces applied to the tool using several multi-axis strain gauges; • Primary processing of data on applied forces with the provision of conditions for limiting the frequency characteristics of signals in order to reduce measurement noise and suppress the influence of electromagnetic interference;

• Transmission of processed data in real time to a higher-level control system using a wired or wireless communication interface. More specifically, the technical problem and the technical result are achieved due to the fact that the medical system of minimally invasive intervention includes a manipulator having a support configured to secure the trocar and to secure the drive of the surgical instrument of minimally invasive intervention, as well as a system for assessing the forces acting on the instrument during surgical operation, and the system for assessing forces includes a three-axis lower strain gauge sensor located on the support of the manipulator at the place of fixation of the trocar and being in direct contact with it, for measuring the forces applied to the instrument and directed along the x and y axes, a three-axis upper strain gauge sensor located on the support of the manipulator under the drive of the surgical instrument, for measuring the force applied to the instrument and directed along the z-axis, the sensor of the gripping force of the actuating surfaces of the tool, made in the form of a current sensor for the electric motor a tool drive that provides compression of the tool's actuating surfaces, a torque sensor of a surgical instrument, made in the form of a current sensor for an electric motor of a tool drive, which ensures rotation of a surgical instrument around its longitudinal axis, and the strain gauges are connected to the corresponding digital data processing modules, and the gripping force sensor and the torque sensor are connected to the corresponding motor control systems, the digital processing modules and the electric motor control systems are connected to the processing module, which is programmed to perform calculations by means of batch processing and synchronization of signals from strain gauges, a torque sensor and a gripping force sensor: forces directed along linear axes, instrument torques along the x and y axes relative to the trocar insertion point into the patient's body, instrument torque along the z axis, relate the point of entry of the trocar into the patient's body, the compressive forces of the instrument's executive surfaces, with each digital processing module programmed to use a digital low-pass filter and band-stop filter algorithm for the force data measured by the strain gauge, and the processing module is programmed to compensate for the force of gravity acting on the support of the manipulator and the instrument, compensating the forces caused by the trocar resistance to the movement of the instrument, and compensating for the dynamic characteristics of the elements located on the axis of rotation of the electric motors, the processing module is configured to transmit data to the control system of the robotic surgical complex.

In some embodiments of the invention, the medical system is characterized in that digital processing modules and motor control systems are connected to a data bus processing module, which is a wired or wireless connection.

In some embodiments of the invention, the medical system is characterized in that the digital processing modules are located near the strain gauges.

The force assessment system, which is part of the force feedback loop of the robotic surgical complex, solves the problem and achieves a technical result due to the presence of the following features:

1. Introduction of at least two points of control of the forces acting on the tool, with force transducers used at each point.

2. The location of the force sensors relative to each other in such a way as to obtain the most complete and reliable information, which ultimately increases the accuracy and simplifies and, as a consequence, reduces the calculation time.

3. Location of one of the force transducers directly at the trocar attachment site.

4. Reducing the requirements for force sensors and replacing 6-DOF sensors with 3-DOF sensors as a result of changing the measurement scheme, which significantly reduces the cost of the design, but at the same time increases the reliability and reliability of the measurement.

5. The use of a current sensor that measures the force of closing the jaws.

6. Using a current sensor that measures the rotational moment of the tool rotation around the longitudinal axis.

Brief Description of Drawings

The accompanying drawings, which are incorporated and form part of the present specification, illustrate embodiments of the invention, and together with the foregoing general description of the invention and the following detailed description of embodiments thereof, serve to explain the principles of the present invention.

FIG. 1 shows a block diagram of an implementation of a force feedback system integrated into a robot-assisted surgical complex.

FIG. 2 illustrates a schematic representation of a surgical instrument positioned on a support attached to a manipulator.

Fig. 3 depicts the architecture of the force assessment system.

FIG. 4 illustrates a surgical instrument and strain gauges in relation to a Cartesian coordinate system.

FIG. 5 illustrates a block diagram of a digital processing module.

FIG. 6 shows the frequency response of the low pass filter of the digital processing unit.

FIG. 7 shows the frequency response of a bandstop (notch) filter.

FIG. 8 illustrates a block diagram for measuring current drawn by a motor. FIG. 9 schematically depicts a visualization of the operation of the synchronization algorithm.

Terms and Definitions

For a better understanding of the present invention, below are some of the terms used in the present description of the invention. Unless otherwise specified, technical and scientific terms in this application have the standard meanings generally accepted in the scientific and technical literature.

In the present description and in the claims, the terms "includes", "including" and "includes", "having", "equipped", "containing" and their other grammatical forms are not intended to be construed in an exclusive sense, but, on the contrary, are used in a non-exclusive sense (ie, in the sense of "including"). Only expressions of the type “consisting of” should be considered as an exhaustive list.

In these application materials, the terms “robotic technological complex”, “robotic system”, “robotic complex”, “robotic surgical complex”, “robotic surgical system” mean complex systems or complexes in surgery using a robot assistant during an operation. "Robot assistive systems" or "robotic assisted surgical systems" are robotic systems designed to perform medical operations. These are not autonomous devices, robotic assistive systems are controlled by surgeons during the operation.

In these application materials, the term "mechatronic complex" or "mechatronic system" means a complex or system with computer control of motion, which is based on knowledge in the field of mechanics, electronics and microprocessor technology, computer science and computer control of the movement of machines and assemblies.

In this application, the term "operator" refers to the performing the operation of the surgeon. The terms "operator" and "surgeon" in the present description of the invention are synonymous.

In these application materials, the term "manipulator" is understood as a mechatronic mechanism designed to fix and move (change the position) of a surgical instrument during a surgical operation in accordance with given commands from the control system of the robotic surgical complex.

In this application, the term "surgical instrument", "instrument" means a special instrument of small size, which is fixed in a surgical robot for performing operations. During surgery, instruments can move, rotate, and rotate over a much wider range and much more accurate than the human hand. Depending on the type of operation, the appropriate tool is used that allows it to be carried out most efficiently. A miniature robotic surgical instrument performs tissue dissection, tissue movement, clamping, suturing, etc., which allows you to work with hard-to-reach parts of organs without the risk of damaging healthy tissues. In the present application, under the sign "tool execution surfaces", "tool execution part" means the tool surfaces or part of the tool with which the tool performs its service purpose. Typically, the actuation surfaces, such as jaws, are located at the end of the instrument inserted into the patient's body and perform complex movements initiated and controlled by the surgeon.

The term "connected" means functionally connected, and any number or combination of intermediate elements between the connected components (including the absence of intermediate elements) can be used.

In addition, the terms "first", "second", "third", etc. are used simply as conditional markers, without imposing any numerical or other restrictions on the enumerated objects.

Detailed description of the invention

The description of exemplary embodiments of the present invention below is provided by way of example only and is intended for illustrative purposes and is not intended to limit the scope of the disclosed invention.

The present solution refers in general to an integrated system for evaluating the forces in the force feedback loop, which is an integral part of the control system of the assisting surgical complex. In particular, the present solution is aimed at creating a system for assessing the forces affecting the patient's tissues and organs with a tool during a robotic-surgical operation. The use of such a system allows the surgeon to realize tactile sensations from the contact of the instrument surfaces with the patient's tissues, without creating sensations from the contact of the instrument with the trocar, which are forced to arise in the form of friction and various lateral forces when the instrument moves in the trocar during operation.

The system has direct or indirect mechanical connections with patient tissues and a hardware wired or wireless interface for data exchange with the control system of the robotic surgical system. The necessary connections for the implementation of the system are shown in the block diagram shown in Fig. one.

The structural diagram shows that the contour "Control system of the robotic surgical system - Manipulator - Instrument - Patient tissue" is a direct way of transferring the planned impacts from the control system to the patient. The “Patient tissue - Force assessment system - Robotic surgical system control system” contour is reversed and serves to control the actual exposure applied to the patient.

The instrument of a robotic surgical system is a complex device that has high requirements for the materials used, temperature ranges and tightness, which is caused by the need to sterilize it. Force assessment systems, elements of which are integrated directly into the instrument, as a rule, have a complex design, may require periodic calibration, and are susceptible to interference from electrocoagulation systems, which are widely used in minimally invasive robotic surgical interventions.

It should be noted that the feedback forces act not only directly on the surgical instrument, but also, through it, on the structural elements of the instrument attachment and the trocar, which provides access to the operated area.

The solution proposed according to the present invention is an instrument fastening structure located on the manipulator of a robotic-assisting surgical complex, which makes it possible to measure the forces acting on the working surfaces at the tool tip in a feedback loop.

FIG. 2 shows a schematic representation of a surgical instrument attachment structure. The attachment design is a support configured to position and secure the trocar thereon and to secure the instrument by securing the instrument drive. For precise positioning of the instrument, a trocar holder is used in the mount design. FIG. 2, numbers indicate the following structural elements: 1 - three-axis strain gauge (upper strain gauge); 2 - three-axis strain gauge sensor (bottom strain gauge gauge); 3 - trocar holder. The designations adopted in FIG. 2: 01 - the point of insertion of the trocar into the patient's body, around which two rotations of the instrument inserted into the trocar are made during the operation (zero point), the point is inside the trocar; A - the position of the end of the surgical instrument, which is inserted into the patient's body; B - the position of the opposite end of the surgical instrument installed in the drive of the surgical instrument. The angles of orientation (angles of rotation) of the surgical instrument in the horizontal plane and tilt are considered relative to the pivot point (zero point). Zero point 01 is defined as the origin.

The mechanical interaction of the elements of the instrument, the structure of the fastening of the surgical instrument and the elements of the manipulator is realized through two multi-axis strain gauges, one of which is located at one end of the instrument under the instrument drive, and the other at the place where the trocar is fixed. The location of the strain gauges is shown in FIG. 2.

This arrangement of strain gauges has the following advantages:

• Physical distance of the sensitive elements of the sensors from the electrocoagulation interference zone;

• Provides the ability to use various tools without changing their design;

• Allows you to evaluate forces in several degrees of freedom.

As multi-axis strain gauges, bending gauges based on strain gages, capacitive strain gauges or gauges of any other principle can be used. actions that allow you to measure the effort applied to them.

In a preferred embodiment of the invention, strain gauges with a sensitive element in the form of a strain gauge can be used as strain gauges. Sensors of this type have a high output impedance, and the signal has a low power, which limits its propagation in space.

The design allows you to implement the following features:

• Assess the forces acting on the tool in at least five degrees of freedom using two three-axis strain gauges (three linear degrees of freedom along the x, y, z axes and rotational moments around the x and y axes);

• Evaluate the gripping force (compression force), controlling one degree of freedom (the degree of freedom when gripping, compressing the executive surfaces of the surgical instrument);

• Assess the rotational / twisting force acting on the tool (three rotational degrees of freedom around the x, y, z axes);

• When evaluating forces, take into account the forces arising at the point of contact of the trocar with the patient's body;

• Ensure sufficient reliability of effort data in the presence of electromagnetic interference from electrocoagulation.

During operation, the executive surfaces located at the end of the instrument inserted into the patient's body (the executive part of the instrument) perform complex movements initiated and controlled by the surgeon. When resistance arises to the movement of the executive part of the instrument or when parts of the instrument come into contact with the patient's tissue, a bending of the sensitive element of the strain gauge along the corresponding axis occurs. Since the instrument, located in the fastening structure of the surgical instrument, contacts the manipulator at two points, one of which is the trocar location zone, and the other is the location of the surgical instrument drive, the effort is measured at both points and further joint processing of these signals.

The outputs of the strain gauges are connected directly to the digital processing modules, which amplify the signals and convert them into digital form. The digital processing modules can be located directly next to the strain gauges. The specified location is optional and can be changed if necessary, for example, when using strain gauges with a signal amplification board. However, the location of the digital signal processing module of strain gauges in close proximity to each used strain gauge is preferable, since it provides a high signal-to-noise ratio and resistance to external electromagnetic disturbances.

To measure the gripping / compressive force on the executive surfaces of the surgical tools such as jaws, current sensors for gripping / squeezing motors can be used. The principle of measuring the compression force is to increase the current consumption of the motors when resistance to the movement of the gripping elements of the tool structure occurs. Compression motors are part of the drive of the surgical instrument.

To measure the torque around the z axis, an electric motor current sensor can be used, which provides rotation around this axis. The principle of torque measurement is to increase the current consumed by the electric motor when resistance to movement occurs. The motors that rotate around the z-axis are part of the drive for the surgical instrument.

In a preferred embodiment of the invention, electric motors (electric motors) are used as motors. Each of the current sensors of the surgical instrument drive motors can be connected to a motor control system.

The digital processing modules and motor control systems are connected to the processing module via a data bus. The data bus can be RS485, CAN, Bluetooth, or some other wired or wireless data interface. The processing module is designed for group processing and synchronization of signals from strain gauges, torque transducer and gripping force transducer. The use of a separate device as a processing unit is optional. It can be combined with any digital processing module or with a control system. The control system uses the data received from the processing module to further organize feedback and transmit signals to the surgeon. The architecture of the force assessment system is shown in FIG. 3.

Below is one of the possible options for assessing the forces applied to the tool. The tool and strain gauges with respect to the considered coordinate system are shown in Fig. 4.

где F_{x -} сила, направленная вдоль оси х, F, - сила, направленная вдоль оси у, F - сила, направленная вдоль оси z, F_zi - показания верхнего тензометрического датчика вдоль оси z, F_X2 - показания нижнего тензометрического датчика вдоль оси х, F_y2 - показания нижнего тензометрического датчика вдоль оси у. Forces applied to the tool and directed along the x, y, z axes will cause strain gauges to deform along the corresponding axes. In this case, the forces directed along the x and y axes will be equal to the readings of the corresponding axes of the strain gauge sensor located near the trocar (lower strain gauge sensor). The force directed along the z-axis will be equal to the reading of the strain gauge located near the drive of the surgical instrument (upper strain gauge) on the z-axis. Linear forces along the corresponding axes:

where F _{x is the} force directed along the x axis, F is the force directed along the y axis, F is the force directed along the z axis, F _zi - readings of the upper strain gauge along the z axis, F _X2 - readings of the lower strain gauge along the x axis, F _y2 - readings of the lower strain gauge along the y axis.

где M_c - момент вращения вокруг оси х, М_у - момент вращения вокруг оси у, F_xj - показания верхнего тензометрического датчика вдоль оси х, F_yi - показания верхнего тензометрического датчика вдоль оси у, F_X2 - показания нижнего тензометрического датчика вдоль оси х, F_y2 - показания нижнего тензометрического датчика вдоль оси у, 5 - расстояние от нулевой точки до места контакта привода хирургического инструмента с тензометрическим датчиком. The evaluation of the torques is possible due to the location of the strain gauge transducer in direct contact with the trocar (lower transducer), and the second transducer on the drive of the surgical instrument (upper transducer). In this case, the rotational moments will be proportional to the difference in the readings of the strain gauges, taking into account the correction for the arm length. Due to this, the following expressions are valid:

where M _c is the moment of rotation about the x axis, M _y is the moment of rotation about the y axis, F _xj are the readings of the upper strain gauge along the x axis, F _yi are the readings of the upper strain gauge along the y axis, F _X2 are the readings of the lower strain gauge along the axis x, F _y2 - readings of the lower strain gauge along the y axis, 5 - distance from the zero point to the point of contact of the surgical instrument drive with the strain gauge.

где M_Rz - вращательный момент вокруг оси z, -потребляемый двигателем оси rz ток, kz - коэффициент перевода тока во вращательный момент для двигателя оси rz, M_G - вращательный момент сопротивления захвату, I_G - потребляемый двигателем оси захвата ток, kg - коэффициент перевода силы тока в усилие для двигателя оси захвата. To estimate the torque around the z-axis, as well as to estimate the gripping force, it is necessary to measure the amperage consumed by the motors that rotate around the z-axis and move the jaws of the tool during gripping / squeezing. In a preferred embodiment, electric motors (electric motors) are used as motors. As a rule, for electric motors, the dependence of the consumed current on the load applied to it is close to linear, with the exception of the dynamic characteristics located on the axis of rotation of the elements.

where M _Rz is the rotational moment around the z axis, is the current consumed by the motor of the rz axis, kz is the coefficient of conversion of current into the torque for the motor of the rz axis, M _G is the torque of resistance _{to the gripper, I G} is the current consumed by the motor of the gripping axis, kg is the coefficient converting the current into the force for the gripper axis motor.

The above expressions are not the only possible option for assessing the forces applied to the instrument, but they are sufficient to obtain reliable data necessary for the operation of the feedback system as part of a robotic surgical complex.

When developing the system architecture, the requirements for the system were taken into account, as well as the features of the transmission of analog and digital signals in real-time systems.

For more accurate processing of data from strain gauges and motor current sensors in the described design and method for assessing forces, the following requirements are imposed on the conversion and digital processing module:

• Providing the ability to convert signals from a three-axis strain gauge based on strain gages in digital form;

• Presence of a microprocessor for filtering and digital data processing;

• Availability of a digital interface for transferring processed data.

The block diagram of the digital processing module is shown in Fig. 5. Signals about the value of the force in three degrees of freedom, coming from the strain gauge, are converted into digital form by means of an analog-to-digital converter, and then fed to the microprocessor. The microprocessor carries out primary signal processing, which may include filtering, deadband algorithms, subtraction of the influence of gravity, and others. If necessary, the microprocessor can transmit the processed data using the transmit and receive module. The data bus can be a wired or wireless connection, for example, Bluetooth, Wi-fi, RS485, CAN or others.

In order to ensure the operation of the system in conditions of electromagnetic interference, it is advisable to use a digital low-pass filter, as well as a band-stop (notch) filter with a central frequency of 50 Hz for primary processing of signals from a strain gauge sensor. A digital low-pass filter is an algorithm used to suppress signals that exceed a specified frequency. An example of the frequency response of a low pass filter is shown in FIG. 6.

The use of a filtering algorithm in this system will allow suppression of obviously noise signals, the frequency of which exceeds the frequency of useful disturbances arising in the system.

In connection with the use in the operating room of a large number of electrical appliances operating from a 220 V 50 Hz electrical network, there is a need for additional filtering of analog signals with a suppression band in the 50 Hz zone. Since the digital processing device has a microprocessor, it is advisable to use a notch filter algorithm. An example of the frequency response of filters of this type is shown in FIG. 7.

The force exerted on strain gauges is caused by two main components: external forces arising as a result of resistance when the instrument touches the patient's tissues, and the force of gravity of the structural elements of the fastening of the instrument and the instrument itself. The signal generated by the force of gravity acting on the structural members is not useful for the system for evaluating the forces applied to the tool and needs to be eliminated (subtracted).

The tool in contact with the strain gauges always exerts a gravity-induced effect on them through the tool holder system. Signals caused by gravity acting on structural elements and tools are undesirable for onward transmission to the control system. One of the methods of gravity compensation is the subtraction of constant values from the signal of strain gauges, corresponding to the force of gravity and obtained before the operation by the calibration method. The principle of the technique is to determine the readings of strain gauges in the absence of external forces applied to the tool, except for the gravity of structural elements. For this, the values of the signals received from the strain gauges, when the tool is in a position ready for operation, are memorized by the processing module as a zero state. During further operation, the signals arising in the system will be the sum of the effects of gravity and the forces applied to the actuator of the tool, which will effectively subtract the gravitational component. The main advantages of the method are simplicity of implementation and low requirements for the computational power of the digital processing module. The disadvantage is the limitation of use for operations that require a significant in speed and amplitude of movement of the manipulator structure elements, which can create a different distribution of gravity loads on strain gauges.

The described method of compensating for the influence of gravity is not the only one possible for implementation within the framework of the described system for assessing the forces applied to the tool. It is possible to implement other algorithms that more effectively solve the problem of gravity compensation, for example, algorithms based on the motion model of the manipulator used, algorithms with frequency division of signals, for example, based on a high-pass filter, and others. The implementation of more efficient algorithms for compensation of gravity forces does not cause changes in the design and principle of operation of the described system for assessing the forces applied to the tool.

There is a possibility of using algorithms for the compensation of forces caused by the resistance of the trocar to the movement of the instrument and compensation for the dynamic characteristics of elements located on the axis of rotation of the motors in the force assessment system. The use of any algorithms for compensating the resistance of the trocar to the movement of the instrument and compensating for the dynamic characteristics of the elements does not cause changes in the design and the principle of operation of the described system for assessing the forces applied to the instrument.

Measuring the torque MR _Z AND the gripping force MG MAY be realized by measuring the current drawn by the motors. It is advisable to implement this measurement principle by integrating the measuring circuit into the motor control system, since the control system contains a microprocessor and a circuit for measuring the current flowing through the electric motor. To carry out the integration, a block diagram was developed as shown in FIG. eight.

The force applied to the structural elements causes resistance to movement, which is provided by the operation of the electric motor of the surgical instrument and causes an increase in the current consumed by it, flowing through the inverter and the current sensor. The current sensor readings are digitized using an analog-to-digital converter and transmitted to the motor control system. Electric motor control system has a connection with other elements of the system due to the module for receiving and transmitting data.

Thus, information about the applied forces was obtained due to various control loops, partly due to the use of strain gauges, and partly due to measuring the current strength of the motors. A data synchronization algorithm is used in the preferred embodiment of the invention to process the data supplied to the processing module (FIG. 3), which is the central unit for the force estimation system.

Algorithm for data synchronization in time - an algorithm that allows you to restore the sequence of events occurring in the system. One of the common methods is the organization of controlled delays, the duration of which depends on the type of event occurring and the structure of the information transmission path. A demonstration of this type of algorithm is shown in FIG. nine.

Simultaneous events 1, 2, and 3 have different latency times in the processing path, as can be seen on the left side of FIG. 9. Restoration of the sequence of events close to the real sequence is possible due to the organization of delays 1, 2, 3.

The disadvantage of algorithms of this type is an increase in the total system delay, but in modern conditions of performance of real-time systems based on microprocessors, this disadvantage is not significant due to the high sampling rate.

Data from the data processing module goes to the control system of the robotic surgical complex and is transmitted to the control system of the surgeon's controller.

The surgeon holds the controller in his hands and, moving it, generates a digital signal with the help of which the instrument is controlled through the control system of the robotic-surgical complex and the manipulator (Fig. 1). When the instrument comes into contact with the patient's tissue or trocar, forces are generated that act on the instrument. The force assessment system determines these forces, converts the information into a digital signal, which is transmitted to the surgeon's controller in the reverse order through the control system of the robotic surgical complex. The surgeon's controller is designed in such a way that it receives these signals and converts them into mechanical movements of the controller in the direction opposite to the movements of the surgeon's hand controlling the instrument.

The resulting resistance creates a sensation on the hand as if it were touching tissue. The intuitive movement of the instrument that coincides with the movements of the hand, as well as the sense of touching the tissue with the instrument, makes the surgeon feel that he is holding the instrument directly in the hand during the operation on the robotic surgical complex.

Further implementation of the above methods and the developed designs will allow achieving the following technical characteristics for the system for assessing the forces acting on the instrument of the robotic surgical system:

1. The number of degrees of freedom for assessing the effort - 7: three linear degrees of freedom along the x, y, z axes, three rotational degrees of freedom around the x, y, z axes, the degree of freedom at capture;

2. Sampling frequency: not less than 250 Hz;

3. Type of sensors for measuring forces: 3x-axis strain gauges, sensors of current consumed by motors;

4. Ability to work in conditions of interference created by the instrument with electrocoagulation.

The carried out modeling, design of structural elements, development of operating principles, principles and methods of data processing and transmission allow us to conclude about the consistency of the proposed hypotheses, the selected development approaches were theoretically substantiated, their advantages and disadvantages were indicated. The developed design will make it possible to implement a method for assessing the forces acting on the instrument of a robotic surgical system, which does not have the drawbacks of existing designs and allows you to completely solve the problem.

The use of a system for assessing the forces acting on the instrument of a robotic surgical system will allow high-quality operations due to the precise actions of the surgeon, reliable determination of the type and mechanical characteristics of the operated tissue. This is achieved due to the following characteristics:

1. Providing seven degrees of freedom when measuring the forces acting on the tool: three linear degrees, three rotational and one degree of freedom when gripping;

2. The use of at least two multi-axis strain gauges to determine the direction and modulus of acting forces;

3. Location of measuring and other electrical circuits, sensitive to electromagnetic interference, at a distance from the zone of exposure to electrocoagulation;

4. Using an additional contour for evaluating the force of the gripper movement;

5. The use of external, not located directly in the tool, structures for the installation of measuring elements, electrical circuits and mechanisms.

6. Reception and transmission of signals / commands in the control system of the force assessment system can be realized by wire or wireless;

7. Use of digital signal processing to eliminate interference;

8. Use of a digital processing module with support for various algorithms for processing measured data.

This system provides a contribution to robotic and / or computer-assisted surgery for minimally invasive intervention, offering a reliably accurate and source-differentiated assessment of the effect of forces on a robotic surgical instrument in conditions of electromagnetic noise, which would transfer the measured data to the superior control system of the robotic surgical complex.

Example. Laboratory tests of the prototype of the system were carried out from the condition of evaluating the error in measuring the forces under standard conditions for robotic surgery.

To test the possibility of evaluating the forces acting on a surgical instrument of a robotic surgical system, applied to any part of its structure, the following was performed.

A test bench was assembled using two 3-axis strain gauges, one of which is located at the attachment point of the surgical instrument drive, and the other at the attachment point of the trocar holder.

Current sensors were connected to the servo-drive for rotating the instrument around the longitudinal axis (rotation around the z-axis) and the servo drive, which provides compression of the executive surfaces of the surgical instrument, to measure the torque generated by the motors. A tool with previously known parameters of length and stiffness was installed in the tool drive unit. The distance between the strain gauges was recorded and measured.

A parallel mechanism of the hexapod type was used to provide a test effect on the test bench in six degrees of freedom. Hexapod is a mechanism consisting of two platforms - fixed and movable, driven by six independent precision servo motors. Each servo is equipped with position and developed force sensors, so that positioning can be carried out along 3 linear (X, U, Z) and three angular coordinates (rotation around the corresponding axes Ox, Oy, Oz), as well as assess the efforts along each of the coordinates ... The distal end of the surgical instrument was attached to the movable platform of the hexapod by means of fasteners. With the help of the hexapod control system, increments were made for each of the degrees of freedom with fixing the developed effort.

Signals in five degrees are obtained from readings of strain gauges. Sixth degree of freedom signal - rotation around the z-axis - from the drive current sensor, using a conversion factor.

As a result of the tests performed, the possibility of evaluating the forces by six degrees of freedom was found to be no worse than 10% of the readings taken as reference.

To measure the compressive force of the executive surfaces of the surgical instrument, a hollow flexible rubber tube of small diameter from 4 mm to 6 mm was used. One end of this tube is blocked, and a high-precision pressure sensor is connected to the other. With the help of the servo-drive of the tool, which provides compression of the executive surfaces of the tool, this tube was pinched and the created pressure inside the tube was recorded. By comparing the readings of the motor current sensor, which provides compression of the actuating surfaces, and the pressure inside the tube, the possibility of measuring the closing force (compression force) was evaluated. Thus, the proposed design of the force assessment system makes it possible to evaluate the forces acting on a surgical instrument of a robotic surgical system applied to any part of its structure, to assess the gripping forces that arise when the jaws of a surgical instrument are closed, to unambiguously determine the numerical values of the forces and their directions. In this case, the design of the surgical instrument itself does not undergo any changes.

Standard conditions for robotic surgery include electromagnetic interference (coagulation, manipulators, control systems, mobile phones, power cables, and others). The study of the influence of electromagnetic interference on the assessment of forces was carried out using a medical electrocoagulator, which is widely used in surgical interventions. Electrocoagulation is the main source of broadband interference caused by the generation of electrical discharges between the treated tissue and the surface of the surgical instrument.

Studies of the influence of electrocoagulator interference were carried out by recording readings from two 3-axis strain gauges, while these sensors of the force assessment system were sequentially located at several points in space with different distances from the working area of the electrocoagulator and a certain distance between themselves. Also, tests were carried out with a change in the output power of the electrocoagulator.

The second most common source of interference is the home network 240V 50Hz. Studies of the influence of the household network were carried out due to the sequential arrangement of the prototype of the force assessment system at several points in space with different distances from the 240V 50Hz power wire supplying the 500W load. The output signals were processed with the Fast Fourier Transform algorithm to construct a spectral representation of the signals to assess the impact at 50 Hz.

As a result of the tests, a low influence of external electromagnetic interference, a high signal-to-noise ratio, and high accuracy were revealed, which is due to the design of the force assessment system and the digital signal processing used. A low influence of electromagnetic interference and a high signal-to-noise ratio are achieved due to the location of strain gauge sensors by moving their sensitive elements away from the electrocoagulation interference zone and using digital filtering methods.

Thus, the possibility of uninterrupted operation of the force assessment system under the conditions of using electrocoagulation with a surgical instrument and resistance to electromagnetic interference from the household network was proved. Digital filtering techniques filter out most of the unwanted interference.

Tests were carried out with the following initial data: nominal load for strain gauges - 100 N, gain of the measuring path - 2000, number of analog-to-digital converter bits - 16 bits, sampling frequency - 14.7 kHz, the maximum current for the sensor for evaluating the torque of the drive of the z-axis, the compression axis of the tool working surfaces is 5 A.

As a result of the tests performed, the following results were obtained: the average error estimate is 5% of the measuring range, while the maximum error in the presence of external interference in the form of coagulation and electromagnetic interference using digital processing methods is up to 10%. The level of estimation error is satisfactory for most tasks in surgical laparoscopy. In addition, the total signal delay achieved with the help of the prototype, taking into account the amplification path and the module for receiving and transmitting data, is no more than 3 ms, which makes the system widely suitable for telecontrol. Although the present patent application relates to the invention defined in the claims appended below, it is important to note that this patent application contains the basis for the formulation of other inventions, which may, for example, be claimed as the subject of the amended claims of the present application or as the subject of the claims in separated and / or continuing application. Such an object can be characterized by any feature or combination of features described herein.

Claims

CLAIM 1. A medical system for minimally invasive intervention, including a manipulator having a support configured to secure a trocar and to secure a drive of a surgical instrument for minimally invasive intervention, a system for assessing forces acting on an instrument during a surgical operation, and the system for assessing forces includes - a three-axis lower strain gauge transducer, located on the manipulator support at the trocar attachment point and in direct contact with it, to measure the forces applied to the instrument and directed along the x and y axes, - a three-axis upper strain gauge sensor, located on the manipulator support under the drive of the surgical instrument, to measure the force applied to the instrument and directed along the z-axis, - a sensor of the gripping force of the actuating surfaces of the tool, made in the form of a current sensor for the electric motor of the drive of the tool, which provides compression of the actuating surfaces of the tool, - a torque sensor of a surgical instrument, made in the form of a current sensor for the electric motor of the instrument drive, which ensures the rotation of the surgical instrument around its longitudinal axis, and the strain gauges are connected to the corresponding digital data processing modules, and the gripping force sensor and the torque sensor are connected to the corresponding systems motor control, digital processing modules and electric motor control systems are connected to the processing module, which is programmed to perform calculations by means of group processing and synchronization of signals from strain gauges, a torque sensor and a gripping force sensor: - forces directed along linear axes, - tool torques along the x and y axes relative to the trocar insertion point into the patient's body, - tool torque along the z-axis relative to the trocar insertion point into the patient's body, - the forces of compression of the executive surfaces of the tool, wherein each digital processing module is programmed to use a digital low-pass filter and band-stop filter algorithm for the force data measured by the strain gauge, and the processing module is programmed to compensate for the gravity force acting on the support of the manipulator and instrument, compensating for forces caused by the resistance of the trocar the movement of the instrument, and compensation for the dynamic characteristics of the elements located on the axis of rotation of the electric motors, the processing module is configured to transmit data to the control system of the robotic surgical complex. 2. The medical system of claim 1, wherein the digital processing modules and motor control systems are connected to the processing module via a data bus, which is a wired or wireless connection. 3. A medical system according to claim 2, characterized in that the digital processing modules are located near the strain gauges.