A friction torque coupling compensation method for parallel robots

Abstract

The present invention discloses a friction torque coupling compensation method for a parallel robot. The method adopts a position and speed dual closed-loop feedback control strategy and applies a friction torque compensator that takes into account the load inertia of other joints and the servo proportional gain to suppress errors caused by friction torque disturbances. The friction torque compensation algorithm is stored in an independent operation register, and its operation cycle is synchronized with the servo update cycle. This method separates the friction torque compensator from the dual closed-loop control structure and is easy to modify and implement on existing robot control systems. It can compensate in real time for changes in friction disturbances caused by the coupling between joints and the mismatch between servo characteristics, thereby improving the tracking accuracy of each joint motor during starting and reversing, and further improving the control accuracy of the robot end.

Description

Technical Field

[0001] The invention relates to a friction torque coupling compensation method, in particular to a friction torque coupling compensation method for a parallel robot. Background Art

[0002] Industrial robot joint control systems generally employ a dual closed-loop position and velocity feedback control structure. This structure is simple, robust, and reliable, making it a dominant force in industrial control processes. However, frictional disturbances experienced by the robot's driven joint servo systems present an obstacle to improving system performance. These disturbances, such as creeping at low speeds and sudden changes in tracking error during speed reversal, affect the system's dynamic and static performance and reduce control accuracy. Furthermore, parallel robots are a class of nonlinear, strongly coupled, multi-input, multi-output systems. Variations in the inertia of the coupled joints and mismatches in servo gain characteristics exacerbate the effects of frictional disturbances on system tracking accuracy. Therefore, a friction torque coupling compensation method suitable for parallel robots is urgently needed. This method incorporates the inter-joint coupling and servo gain matching characteristics into the friction torque compensation algorithm to improve the motion control accuracy of parallel robots. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a friction torque coupling compensation method for a parallel robot that can improve the control accuracy of the robot end.

[0004] A friction torque coupling compensation method for a parallel robot of the present invention comprises the following steps:

[0005] Step 1: Calculate the equivalent load inertia. The process is as follows:

[0006] In the first step, the expected trajectory of the parallel robot is interpolated through the interpolation module. The interpolated code performs the inverse position solution of the parallel robot to obtain the expected rotation angle θ of each joint. di And it serves as the input of the position and speed double closed-loop control algorithm of each joint of the parallel robot;

[0007] The second step is to collect the expected rotation angle θ of each driving joint motor at the current moment. di , the equivalent load inertia m of the parallel robot's joint j acting on the parallel robot's joint i is calculated using the parallel robot's rigid body dynamics model ij , i, j = 1, 2, ..., n; n represents the total number of joints and is stored in the system data register for future use;

[0008] Step 2: Collect the expected angular velocity and angular acceleration of each driving joint motor of the parallel robot. The process is as follows:

[0009] The expected rotation angle θ of each driving joint motor at the current moment is collecteddi Perform first-order and second-order differentiation to obtain the expected angular velocity of each driven joint and angular acceleration Then the desired angular velocity of the driven joint is and angular acceleration Stored in the system data register for future use;

[0010] Step 3: Calculate the servo gain characteristic matching coefficient. The process is as follows:

[0011] Collect the current position and velocity of each driving joint in the dual closed-loop control system and the proportional gain K of the position controller pj , and the speed controller proportional gain K vj , j = 1, 2, ..., n; use the following formula to calculate the servo gain characteristic matching coefficient aij and store it in the system data register for future use:

[0012]

[0013] Step 4: Using the data in the system data register at the current moment, the following friction torque compensation algorithm is used to calculate the friction torque compensation value F of each joint of the parallel robot: fi , used to compensate the output of the speed controller:

[0014]

[0015] Among them, μ c =0.0014, indicating the Coulomb friction coefficient when the motor shaft moves, μ v =0.01, indicating the viscous friction coefficient when the motor shaft moves; m ij is the equivalent load inertia m of the parallel robot's joint j acting on the parallel robot's joint i ij , i, j = 1, 2, ..., n; represents the expected angular acceleration of joint j of the parallel robot j=1,2,…,n.

[0016] The technical effects of the present invention compared with the prior art are:

[0017] The method of the present invention can suppress errors caused by friction torque disturbances. The friction torque compensator is independent of the dual closed-loop control structure and can be easily retrofitted and implemented in existing robot control systems. It can compensate in real time for friction disturbances caused by the coupling between joints and the mismatch between servo characteristics, thereby improving the tracking accuracy of each joint's motor during starting and reversing, further enhancing the control accuracy of the robot's end-point. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a control block diagram of a friction torque coupling compensation method for a parallel robot according to the present invention;

[0019] Figure 2 This is a flow chart of the friction compensation execution adopted by the method of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0021] The core of the present invention is to propose a "compensation algorithm" that collects and calculates the expected speed, acceleration, equivalent load inertia, and controller proportional gain of the driving joint motor to achieve the output value of the compensation speed controller.

[0022] like Figure 1 As shown, a friction torque coupling compensation method of a parallel robot of the present invention comprises the following steps:

[0023] Step 1: Calculate the equivalent load inertia of the parallel robot's joint j acting on the parallel robot's joint i. The process is as follows:

[0024] In the first step, the expected trajectory of each joint of the parallel robot is interpolated through the interpolation module. The interpolated code performs the inverse position solution of each joint of the parallel robot to obtain the expected rotation angle θ of each driving joint motor. di And serve as the input of the position and speed double closed-loop control algorithm of each joint of the parallel robot (the double closed-loop control algorithm is the control system that comes with the existing parallel robot);

[0025] The second step is to collect the expected rotation angle θ of each driving joint motor at the current moment. di , using the rigid body dynamics model of the parallel robot (the rigid body dynamics models of each parallel robot can be found in "Parallel Robots" published by Machinery Industry Press, Xu Zhaotang and Liu Yuanwei in 2021. Page 108) to calculate the equivalent load inertia m of the joint j of the parallel robot acting on the joint i of the parallel robot ij , (i, j = 1, 2, ..., n), n represents the total number of joints and is stored in the system data register for future use;

[0026] Step 2: Calculate and store the expected angular velocity and angular acceleration of each driving joint motor of the parallel robot. The process is as follows:

[0027] The expected rotation angle θ of each driving joint motor at the current moment is collected di Perform first-order and second-order differentiation to obtain the expected angular velocity of each driving joint motor and angular acceleration Then the desired angular velocity of the motor driving the joint will be and angular acceleration Stored in the system data register for future use;

[0028] Step 3: Calculate the servo gain characteristic matching coefficient. The process is as follows:

[0029] Collect the current position and velocity of each driving joint in the dual closed-loop control system and the proportional gain K of the position controller pj (j=1,2,…,n) and the speed controller proportional gain K vj (j=1,2,…,n), use the following formula (i.e., servo gain matching algorithm) to calculate the servo gain characteristic matching coefficient α of the parallel robot joint j acting on the parallel robot joint i ij And store it in the system data register for future use:

[0030]

[0031] Step 4: Using the data in the system data register at the current moment, the following friction torque compensation algorithm is used to calculate the friction torque compensation value F of each joint of the parallel robot: fi , used to compensate the output of the speed controller:

[0032]

[0033] Among them, μ c =0.0014, indicating the Coulomb friction coefficient when the motor shaft moves, μ v =0.01, indicating the viscous friction coefficient when the motor shaft moves; m ij is the equivalent load inertia m of the parallel robot's joint j acting on the parallel robot's joint i ij , (i,j=1,2,…,n); represents the expected angular acceleration of joint j of the parallel robot (j = 1, 2, …, n).

[0034] Figure 2 The execution process of the friction torque coupling compensation method of the parallel robot is shown: the expected trajectory of the parallel robot is interpolated through the interpolation module, and the interpolated code executes the inverse solution of the position of the parallel robot to obtain the expected rotation angle of each joint motor and use it as the input of the position and speed dual closed-loop control algorithm; at the same time, the expected rotation angle, angular velocity, angular acceleration, and proportional gain of the joint motor are collected and stored in the data register, the equivalent load inertia is calculated using the rigid body dynamics model and stored in the data register, the servo gain characteristic matching coefficient is calculated using the servo gain matching algorithm and stored in the data register, and then the compensation value is calculated using the friction torque compensation algorithm in step four, and finally compensated into the dual closed-loop servo control algorithm.

[0035] It is worth noting that although the preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned implementation methods are merely illustrative and not restrictive. Relevant technical personnel in this field can be inspired by the present invention and make many forms without departing from the purpose of the present invention and the scope of protection of the claims. These all fall within the scope of protection of the present invention.

Claims

1. A friction torque coupling compensation method for a parallel robot, characterized in that The following steps are involved: Step 1: Calculate the equivalent load inertia. The process is as follows: In the first step, the expected trajectory of the parallel robot is interpolated through the interpolation module. The interpolated code performs the inverse position solution of the parallel robot to obtain the expected rotation angle θ of each joint. di And it serves as the input of the position and speed double closed-loop control algorithm of each joint of the parallel robot; The second step is to collect the expected rotation angle θ of each driving joint motor at the current moment. di , the equivalent load inertia m of the parallel robot's joint j acting on the parallel robot's joint i is calculated using the parallel robot's rigid body dynamics model ij , i, j = 1, 2, ..., n; n represents the total number of joints and is stored in the system data register for future use; Step 2: Collect the expected angular velocity and angular acceleration of each driving joint motor of the parallel robot. The process is as follows: The expected rotation angle θ of each driving joint motor at the current moment is collected di Perform first-order and second-order differentiation to obtain the expected angular velocity of each driven joint and angular acceleration Then the desired angular velocity of the driven joint is and angular acceleration Stored in the system data register for future use; Step 3: Calculate the servo gain characteristic matching coefficient. The process is as follows: Collect the current position and velocity of each driving joint in the dual closed-loop control system and the proportional gain K of the position controller pj , and the speed controller proportional gain K vj , j = 1, 2, ..., n; use the following formula to calculate the servo gain characteristic matching coefficient aij and store it in the system data register for future use: Step 4: Using the data in the system data register at the current moment, the following friction torque compensation algorithm is used to calculate the friction torque compensation value F of each joint of the parallel robot: fi , used to compensate the output of the speed controller: Among them, μ c =0.0014, indicating the Coulomb friction coefficient when the motor shaft moves, μ v =0.01, indicating the viscous friction coefficient when the motor shaft moves; m ij is the equivalent load inertia m of the parallel robot's joint j acting on the parallel robot's joint i ij , i, j = 1, 2, ..., n; represents the expected angular acceleration of joint j of the parallel robot j=1,2,…,n.

Images