Research On Parameter Calibration Of Serial Robot Based On POE Formula

As essential mechatronics equipment in industrial production,industrial robots have been widely used in various industrial production fields.Motion accuracy is a vital parameter index to measure the comprehensive performance of industrial robots.At present,the absolute pose accuracy of industrial robots is low,which cannot meet the requirements of precision machining and manufacturing.The calibration of robot kinematics parameters is a crucial way to improve the accuracy of robot poses.This paper relies on the National Natural Science Foundation of China project“Research on Accuracy Compensation Method for Reconfigurable Robots Based on Errors Measuring and Decoupling Between Assembled Modules ”(Project ID:51605004).Aiming at the problem of low absolute pose accuracy of robots,this paper focuses on the kinematic parameter calibration method of serial robots,which is based on the product of exponentials formula.The main contents of the paper are as follows:1)Aiming at the problem that the inaccurate reduction ratio of the joint reducer leads to the reduction of the absolute pose accuracy of the robot,based on the linear relationship between the robot joint reduction ratio and the joint rotation angle,a comprehensive calibration method that takes into account the robot kinematic parameters and the joint reduction ratio is presented.Based on the product of exponentials formula,a robot kinematic model including kinematic parameters and reduction ratio parameters is established.According to the explicit expression of the exponential mapping differential formula,the linearized explicit expression of the robot pose error model is derived.The least-squares method is used to identify the parameter errors and correct the model parameters.The validity of the proposed calibration method is verified by the simulation test of the UR5 serial robot.2)Aiming at the problem of low parameter recognition accuracy and even divergence caused by the unreasonable weight of position and orientation data in the robot pose calibration model,a pose calibration method of serial robots based directly on the end position coordinate measurement is proposed,avoiding the influence of different levels of position and orientation data on the accuracy of parameter identification and also avoiding the need to measure the orientation of the robot’s endeffector during the calibration process.Using the product of exponentials method,a robot kinematics model containing three-point position information is established.By taking the differential of the kinematic model,the explicit expression of the mapping relationship between the position error of the robot end three points and the kinematic parameter error is derived by using the exponential mapping differential formula,and the parameter error identification method is given.The validity of the calibration method are verified by physical experiments on the UR5 serial robot.3)Aiming at the problem of parameter redundancy in the traditional kinematics calibration model based on the product of exponentials method,the physical meaning of parameter redundancy is explained based on the screw theory,by removing redundant parameters in adjoint transformation,a robot pose kinematic model with minimum parameters is established.A parameter identification method that separates and calibrates the position and orientation parameters is given.The linear mapping relationship between the robot’s position error and orientation error and the corresponding twist error is deduced through the differential kinematics model.The least-squares method is used to identify the orientation and position error parameters respectively,and the kinematic parameters are updated uniformly,which avoids the influence of the unreasonable weight of the position error and the orientation error in the identification model on the identification results caused by the different magnitudes of the position and orientation error units.The kinematic parameter calibration test is carried out with the UR5 serial robot,which verifies the validity of the calibration method.