US-20260124747-A1 - CONTROL METHOD OF ROBOTIC ARM AND CONTROL SYSTEM THEREOF

US20260124747A1US 20260124747 A1US20260124747 A1US 20260124747A1US-20260124747-A1

Abstract

A control method of a robotic arm is provided by an aspect of the present disclosure. The control method comprises using a driver for outputting a first driving force to control the robotic arm held in a first position, and using the driver for outputting a second driving force to control the robotic arm held in a second position. The second position is different to the first position. The control method also comprises the first driving force and the second driving force respectively having an anti-friction force and a kinetic force. The anti-friction force is greater than the kinetic force. The control method also comprises using a control loop, the first position and the second position for adjusting the second driving force to control the robotic arm. The first position and the second position are related to a friction force of the robotic arm.

Inventors

Ching-Wei Lee
Kuei-You Lin
Chun-Wen Lai

Assignees

TECHMAN ROBOT INC.

Dates

Publication Date: 20260507
Application Date: 20251016
Priority Date: 20241104

Claims (12)

1 . A control method of a robotic arm, comprising: outputting, by a driver, a first driving force to control the robotic arm located in a first position; outputting, by the driver, a second driving force to control the robotic arm located in a second position, wherein the first position is different to the second position, and the first driving force and the second driving force respectively include an anti-friction force and a kinetic force smaller than the anti-friction force; and adjusting, by using a control loop, the first position and the second position, the second driving force to control the robotic arm, wherein the first position and the second position are related to a friction force of the robotic arm.
2 . The control method of claim 1 , further comprising: receiving, by a controller, a command position information and an actual position information from a position encoder coupled to a joint motor as the driver; receiving, by a gain adjustment module, a current torque command information and a prior torque command information from a speed controller; calculating, by the gain adjustment module, a torque command absolute difference value between the current torque command information and the prior torque command information, and comparing the torque command absolute difference value with a counting threshold; obtaining a position absolute difference value between the command position information and the actual position information, when the torque command absolute difference value is smaller than the counting threshold; mapping, by the gain adjustment module, the position absolute difference value to a gain mapping curve to obtain a current gain value; and updating, by the gain adjustment module, the current gain value to the control loop.
3 . The control method of claim 2 , further comprising: activating, by the gain adjustment module, a counter to count, when the torque command absolute difference value is greater than or equal to the counting threshold; resetting the counter and obtaining the position absolute difference value, when a counting time of the counter is greater than two seconds; and keeping the counter counting, when the counting time of the counter is less than or equal to two seconds, wherein the counting threshold is 0.5 times a rated torque of the joint motor.
4 . The control method of claim 2 , further comprising: controlling, by a current controller, a rotation state of the joint motor according to the current gain value and a torque absolute difference value, wherein the torque absolute difference value is an absolute difference value between an updated torque command information generated by the speed controller according to a speed absolute difference value and the current gain value, and a current torque information of the joint motor sensed by a current sensor, wherein, the speed absolute difference value is an absolute difference value between a speed control information provided by the controller according to the current gain value, and an actual speed information generated by a speed calculator based on the actual position information.
5 . The control method of claim 4 , wherein the gain mapping curve is generated by the following steps: setting a resolution of the position encoder; setting a first gain interval, a second gain interval and a third gain interval; calculating, by the gain adjustment module, a gain dead zone position, a gain center position and a gain recovery position based on the resolution of the position encoder; and forming the gain mapping curve by using the first gain interval, the second gain interval, the third gain interval, the gain dead zone position, the gain center position and the gain recovery position.
6 . The control method of claim 5 , wherein a gain magnification of the first gain interval is 5, a gain magnification of the second gain interval is 80, and a gain magnification of the third gain interval is 1, wherein a number of position pulses at the gain dead zone position is 3, a number of position pulses at the gain center position is 0.00005 times the resolution, and the gain recovery position is 0.00025 times the resolution.
7 . A control system of a robotic arm, comprising: a driver, configured to output a first driving force to control the robotic arm located in a first position and output a second driving force to control the robotic arm located in a second position, wherein the first position is different to the second position, and the first driving force and the second driving force respectively include an anti-friction force and a kinetic force smaller than the anti-friction force; and a control loop, configured to adjust the second driving force to control the robotic arm according to the first position and the second position, wherein the first position and the second position are related to a friction force of the robotic arm.
8 . The control system of claim 7 , further comprising: a controller, coupled to a position encoder, coupled to a joint motor as the driver, of the robotic arm, and the controller configured to receive a position absolute difference value between a command position information and an actual position information provided by the position encoder; a speed controller, coupled to the controller and configured to generate a current torque command information and a prior torque command information; and a gain adjustment module, coupled to the controller, the speed controller and the position encoder and configured to receive the current torque command information, the prior torque command information and the position absolute difference value, to calculate a torque command absolute difference value between the current torque command information and the prior torque command information, and compare the torque command absolute difference value to a counting threshold, wherein, when the torque command absolute difference value is smaller than the counting threshold, the gain adjustment module maps the position absolute difference value to a gain mapping curve to obtain a current gain value and updates the current gain value to the control loop.
9 . The control system of claim 8 , wherein, when the torque command absolute difference value is greater than or equal to the counting threshold, the gain adjustment module activates a counter to count, wherein, when a counting time of the counter is greater than two seconds, the counter is reset and the position absolute difference value is obtained, wherein, when the counting time of the counter is less than or equal to two seconds, the counter keeps counting, wherein the counting threshold is 0.5 times a rated torque of the joint motor.
10 . The control system of claim 8 , further comprising: a current controller, coupled to the joint motor, the gain adjustment module and the speed controller and configured to control a position of the joint motor according to the current gain value and a torque absolute difference value; and a speed calculator, coupled to the position encoder and the speed controller and configured to generate an actual speed information according to the actual position information received from the position encoder, wherein the torque absolute difference value is an absolute difference value between an updated torque command information generated by the speed controller according to a speed absolute difference value and the current gain value, and a current torque information of the joint motor sensed by a current sensor of the robotic arm, wherein, the speed absolute difference value is an absolute difference value between a speed control information provided by the controller according to the current gain value, and the actual speed information generated by the speed calculator.
11 . The control system of claim 10 , wherein the gain mapping curve comprises: a first gain interval, a second gain interval and a third gain interval generated by the gain adjustment module; a gain dead zone position, a gain center position and a gain recovery position generated by the gain adjustment module according to a resolution of the position encoder; and a mapping relation between the first gain interval, the second gain interval and the third gain interval, and the gain dead zone position, the gain center position and the gain recovery position.
12 . The control system of claim 11 , wherein a gain magnification of the first gain interval is 5, a gain magnification of the second gain interval is 80, and a gain magnification of the third gain interval is 1, wherein a number of position pulses at the gain dead zone position is 3, a number of position pulses at the gain center position is 0.00005 times the resolution, and the gain recovery position is 0.00025 times the resolution.

Description

This application claims the benefit of Taiwan patent application Serial No. 113142084, filed Nov. 4, 2024, the subject matter of which is incorporated herein by reference. TECHNICAL FIELD The disclosure relates in general to techniques of control method and control system of robotic arm, and more particularly, to techniques of control method and control system of joint motor in robotic arm. BACKGROUND Currently, with the development of automated production, the demand for robotic arms has increased. The performance of robotic arms, such as control techniques of robotic arms, has also attracted the attention of various manufacturers. For improving the control accuracy of the robotic arm, the conventional method adjusts the control gain according to the angular velocity. For example, when the angular velocity is less than a threshold value, the gain is reduced linearly or in a curve to achieve the purpose of control. However, such conventional techniques cannot handle the state of the robot arm when it is running at an extremely low speed, moving in small steps, or at static state. Because in these states, the torque output by the joint motor will be affected by the friction force, causing the robot arm to swing back and forth or move suddenly, resulting in reduced accuracy and performance of the robotic arm, which may cause the robotic arm to accidentally reach the safety threshold and may cause the manufacturing line to stop. Thus, there are needs for techniques of improving performance and accuracy of static state or small movement of robotic arms. SUMMARY According to techniques of control method and control system of robotic arm provided by the implementations of the present disclosure, by comparing the absolute difference of the torque command between the current torque command information and the prior torque command information with the counting threshold, and substituting the absolute difference of the position between the command position information and the actual position information into the gain mapping curve, the current (new) gain value is obtained and updated to the controller. In this way, when the robotic arm is at static state or moves slightly, the control accuracy of the joint motor is improved, thereby improving the performance of the robotic arm and reducing the problems of shutdown or manufacturing line being stopped caused by the movement state of the robotic arm accidentally reaching the safety threshold. In addition, due to the improved control ability of friction, the influence of the variability of the joint motor and the mechanical components of the robotic arm can be reduced. The first aspect of the present disclosure features a control method of a robotic arm. The control method includes outputting, by a driver, a first driving force to control the robotic arm located in a first position. The control method also includes outputting, by the driver, a second driving force to control the robotic arm located in a second position. The first position is different to the second position, and the first driving force and the second driving force respectively include an anti-friction force and a kinetic force smaller than the anti-friction force. The control method also includes adjusting, by using a control loop, the first position and the second position, the second driving force to control the robotic arm. The first position and the second position are related to a friction force of the robotic arm. The second aspect of the present disclosure features a control system of a robotic arm. The control system includes a driver, configured to output a first driving force to control the robotic arm located in a first position and output a second driving force to control the robotic arm located in a second position. The first position is different to the second position, and the first driving force and the second driving force respectively include an anti-friction force and a kinetic force smaller than the anti-friction force. The control system also includes a control loop configured to adjust the second driving force to control the robotic arm according to the first position and the second position. The first position and the second position are related to a friction force of the robotic arm. The details of one or more disclosed implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a function block diagram illustrating an example of robotic arm and control system, according to some implementations of the present disclosure. FIG. 2 is a diagram illustrating a gain mapping curve graph of control system, according to some implementations of the present disclosure. FIG. 3A is a diagram illustrating a moving speed comparison between conventional joint motor and the joint motor according to some implementations