Sensor-based compliant control method for robotic arms

Abstract

The present invention discloses a sensor-based compliant control method for a robotic arm, including: determining redundant joints according to the number of degrees of freedom of the robotic arm and the sensor measurement dimension; obtaining the external force on the robotic arm through the sensor; calculating the desired posture of the robotic arm under the control of the external force, and obtaining the control amount of the non-redundant joints through the inverse kinematic solution, and controlling the corresponding joint movement accordingly. The present invention realizes the compliant dragging of the robotic arm by splitting the redundant joints and hybrid control, thereby reducing the system cost and design complexity; and does not restrict the redundant degrees of freedom, thereby ensuring the degrees of freedom of compliant dragging.

Description

Technical Field

[0001] The present invention relates to the technical field of surgical robots, and in particular to a sensor-based compliant control method for a robotic arm. Background Art

[0002] The robot-assisted surgery system is a system that uses medical devices such as laparoscopes and thoracoscopes and related equipment to perform surgery inside the human body cavity. Doctors usually control the master hand in a master-slave manner to remotely control the movements of each arm to perform surgery and achieve the purpose of minimally invasive surgery. During the preparation for surgery, various surgical instruments need to be installed, which requires the surgical robot arm to be moved to the specified position. Compared with buttons or inching to control the surgical robot arm, the dragging method is more efficient and does not require additional manpower.

[0003] The existing implementation methods include zero-force dragging based on current loop and compliant control based on sensor. Zero-force dragging based on current loop is usually limited by structural morphology and dynamic parameter characteristics, which can easily lead to some joints being unable to be dragged under force in strange forms, thus affecting the overall dragging effect. Compliance control is based on the signal feedback from the sensor to control the robotic arm, and changes in response to changes in environmental forces, which can more effectively affect the subjective feeling of the doctor dragging the surgical robotic arm, allowing the surgical robotic arm to respond to the doctor's dragging intention. In the existing dragging technology for implementing compliant control, admittance control is generally adopted, that is, a sensor is installed at the end of the surgical robotic arm. After the sensor detects the external force, the admittance controller outputs a new desired position according to the external force, drives the surgical arm to the desired position, and achieves a compliant effect. However, in order to ensure control safety, the surgical robotic arm is generally designed with redundant structures, which makes it impossible to directly apply compliant control. At present, there is also a way to add constraint equations to solve the positions of each joint, but this also limits the degree of freedom of the draggable surgical robotic arm. In addition, the number of measurement dimensions of the sensor can be increased, but as the sensor dimension increases, the price will generally be higher, and the complexity of the system will increase. Summary of the invention

[0004] Purpose of the invention: In view of the above-mentioned deficiencies, the present invention proposes a sensor-based compliant control method for a robotic arm, which does not restrict redundant degrees of freedom, ensures the degrees of freedom of compliant dragging, and can reduce system costs and design complexity.

[0005] Technical solution:

[0006] A sensor-based compliant control method for a robotic arm, comprising:

[0007] Determine redundant joints based on the number of degrees of freedom of the robot arm and the sensor measurement dimensions;

[0008] Obtain the external force on the robotic arm through sensors;

[0009] The expected position and posture of the robot arm under the control of the external force is calculated, and the control quantity of the non-redundant joint is obtained by inverse kinematics solution, and the corresponding joint movement is controlled accordingly.

[0010] The expected position of the robot arm under the control of the external force is calculated as follows:

[0011] Obtain the desired position and posture of the robot arm under the control of external forces in the sensor coordinate system;

[0012] The desired posture is transformed to the robot base coordinate system according to the transformation relationship between the redundant joint coordinate system and the sensor coordinate system and the transformation relationship between the redundant joint coordinate system and the robot base coordinate system.

[0013] Select the redundant joint closest to the hand-held drag point to establish the redundant joint coordinate system.

[0014] Controlling the corresponding joint movement according to the control amount of the non-redundant joint is specifically: controlling the joint by means of a position loop so that it reaches a desired angle.

[0015] According to the control amount of the non-redundant joint, the corresponding joint movement is controlled as follows:

[0016] The joints are controlled by means of current loops to obtain the current position of each joint of the robot arm, and the expected position of each joint of the robot arm is obtained according to its expected posture, so as to obtain the expected current of the motor of each joint of the robot arm and control it accordingly.

[0017] The redundant joints are determined according to the number of degrees of freedom of the robot arm and the sensor measurement dimensions:

[0018] The number of redundant joints is determined by the difference between the number of degrees of freedom of the surgical robot and the sensor measurement dimension, and the redundant joints are selected based on the principle that the redundant joints are indirect measurement dimensions of the sensor and are closer to the hand-grip dragging point.

[0019] The hand-grip dragging point is the location where the sensor is installed, and the sensor is installed at the end of the mechanical arm.

[0020] After the external force applied to the robot arm is acquired through the sensor, it is filtered by using mean filtering and / or low-pass filtering.

[0021] Compared with the prior art, the present invention has the following significant advantages:

[0022] 1. Reduce system cost and complexity: When the system has redundancy relative to the sensor signal, compared with the method of increasing the sensor dimension, this method splits the redundant joints and uses hybrid control to achieve smooth dragging of the robot arm, reducing system cost and design complexity;

[0023] 2. Guaranteeing the freedom of smooth dragging: Compared with the method of adding constraints to achieve dragging, the present invention does not restrict redundant degrees of freedom, thereby ensuring the freedom of smooth dragging. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the sensor-based compliant control method of a robotic arm of the present invention;

[0025] Figure 2 This is a flow chart of the compliant control of the robot arm;

[0026] Figure 3 A schematic diagram of a surgical robot arm according to an example of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the mechanical arm compliance control method based on the force sensor of the present invention comprises the following steps:

[0029] (1) Select redundant joints for manual dragging and determine the compliant control action points accordingly;

[0030] The redundant joints are determined according to the number of degrees of freedom of the surgical robot arm and the sensor measurement dimension, the hand-grip drag point is determined according to the sensor installation position, and the redundant joint coordinate system is established based on the hand-grip drag point, with its origin as the action point Q for compliant control; specifically, it includes:

[0031] (11) Determine the number of degrees of freedom and sensor measurement dimensions of the surgical robot arm;

[0032] In the present invention, a RPPR configuration (joint combination is rotation-translation-translation-rotation) mechanical arm is taken as an example. Figure 3 As shown, J1 is a rotation joint, J2 is a lateral movement joint, J3 is a longitudinal movement joint, and J4 is a rotation joint, that is, the number of degrees of freedom of the surgical robot arm is 4; the present invention takes a three-dimensional force sensor as an example, that is, it detects the forces in the three directions of x, y, and z, and the measurement dimension is 3. The hand-held drag point is the position where the sensor is installed. The present invention takes the end installation as an example, that is, Figure 3 Middle O point;

[0033] (12) Determine the number of redundant joints by the difference between the number of degrees of freedom of the surgical robot arm and the dimension measured by the sensor, select the redundant joints to establish a redundant joint coordinate system, and determine the action point of the compliant control;

[0034] In the present invention, since the number of degrees of freedom of the surgical robot arm is 4 and the measurement dimension of the force sensor is 3, one redundant joint is selected. The redundant joint is selected based on the two principles that the redundant joint is the indirect measurement dimension of the sensor and is closer to the hand-grip drag point to feel the magnitude of the force, so J4 can be selected; this joint controls the deflection of the surgical robot arm, is the indirect measurement dimension of the three-dimensional force sensor, and is closer to the hand-grip drag point O; thus, a redundant joint coordinate system can be established, and its origin is the point of action of the compliant control; when there are multiple redundant joints, a redundant joint closer to the hand-grip drag point is selected to establish a redundant joint coordinate system;

[0035] (2) Obtaining the external force applied to the robotic arm;

[0036] The raw data of the external force on the manipulator collected by the force sensor is obtained, and then the raw data is filtered to obtain the filtered external force on the manipulator; usually, mean filtering and / or low-pass filtering are used;

[0037] (3) Compliant control of the robotic arm;

[0038] Calculate the expected posture P0 of the robot under the control of the external force, and transform it to the robot base coordinate system to obtain the corresponding expected posture P B , the control quantity of non-redundant joints can be solved by inverse kinematics, and the dragging of non-redundant joints can be achieved through position loop control or current loop control; Figure 2 As shown, specifically including:

[0039] (31) According to the filtered external force on the manipulator obtained in step (2), the desired position P of the manipulator is obtained through the admittance controller O In the present invention, since the desired posture of the robotic arm is calculated by the external force on the robotic arm collected by the force sensor, the posture is also the desired posture of the sensor, and O is the sensor position;

[0040] (32) The transformation relationship between the redundant joint coordinate system and the sensor coordinate system is calculated based on the structural parameters and joint positions of the robot arm, and the desired position P of the robot arm is converted to O Transform to the redundant joint coordinate system and obtain the corresponding pose P Q ; Among them, the origin of the redundant joint coordinate system is the action point Q of the compliant control, and the origin of the sensor coordinate system is the installation position O of the sensor;

[0041] (33) According to the structural parameters and joint positions of the manipulator, the transformation relationship between the redundant joint coordinate system and the robot base coordinate system is calculated, and the pose P in the redundant joint coordinate system is converted to Q Transform to the robot base coordinate system and obtain the corresponding desired pose P B ;

[0042] (34) According to the expected position P of the manipulator in the robot base coordinate system B and its current posture to calculate the control quantity θ of the non-redundant joints of the surgical robot arm, and control the corresponding joint motion accordingly;

[0043] For the control quantity θ, the joint can be made to work in the position loop to reach the desired angle; or the joint can be made to work in the current loop to obtain the current position θ0 of each joint of the robot arm, and then the desired posture P can be obtained. B The expected position of each joint of the robot arm is obtained, so that the expected current I of the motor of each joint of the robot arm can be obtained and controlled accordingly;

[0044] (4) Redundant joint control: Redundant joints can work in current loop mode and can be dragged directly by hand.

[0045] The present invention separates the redundant joints of the surgical robot arm and performs mixed compliant dragging on the redundant joints and non-redundant joints. For non-redundant joints, compliant control is performed through the data of the force sensor, and the admittance controller is usually used to convert the desired posture to achieve the dragging of the non-redundant joints; for redundant joints, the dragging is directly achieved manually; the present invention does not limit the redundant degrees of freedom, ensures the degrees of freedom of compliant dragging, and can reduce system cost and design complexity.

[0046] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations (such as quantity, shape, position, etc.) can be made to the technical scheme of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A sensor-based compliant control method for a robotic arm, characterized in that: include: The number of redundant joints is determined by the difference between the number of degrees of freedom of the surgical robot and the sensor measurement dimension, and the redundant joints are selected according to the principle that the redundant joints are the indirect measurement dimensions of the sensor and are closer to the hand-grip drag point, and the hand-grip drag point is the location where the sensor is installed. The sensor is installed at the end of the robotic arm; Obtain the external force on the robotic arm through sensors; The expected posture of the robot arm under the control of the external force is calculated, and the control quantity of the non-redundant joint is obtained by inverse kinematics, and the corresponding joint movement is controlled accordingly.

2. The method for controlling the compliance of a robot arm according to claim 1, characterized in that: The expected position of the robot arm under the control of the external force is calculated as follows: Obtain the desired posture of the robot arm under the control of external force in the sensor coordinate system; The desired posture is transformed into the robot base coordinate system according to the transformation relationship between the redundant joint coordinate system and the sensor coordinate system and the transformation relationship between the redundant joint coordinate system and the robot base coordinate system.

3. The method for controlling the compliance of a robot arm according to claim 2, characterized in that: Select the redundant joint closest to the hand-held drag point to establish the redundant joint coordinate system.

4. The method for controlling the compliance of a robot arm according to claim 1, characterized in that: Controlling the corresponding joint movement according to the control amount of the non-redundant joint is specifically: controlling the joint by means of a position loop so that it reaches a desired angle.

5. The method for controlling the compliance of a robot arm according to claim 1, characterized in that: According to the control amount of the non-redundant joint, the corresponding joint movement is controlled as follows: The joints are controlled by means of current loops to obtain the current position of each joint of the robot arm, and the expected position of each joint of the robot arm is obtained according to its expected posture, so as to obtain the expected current of the motor of each joint of the robot arm and control it accordingly.

6. The method for controlling the compliance of a robot arm according to claim 1, characterized in that: After the external force applied to the robot arm is acquired through the sensor, it is filtered by using mean filtering and / or low-pass filtering.

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