Kinematic Parameter Calibration Of Vertical Six-joint Industrial Robot

With the continuous development of the robot industry in China,the application of robots has become more and more extensive,robots are gradually participating in more and more complicated tasks.The demand for high-performance industrial robots is increasing.Accuracy is one of the important parameters that reflects the robot's performance,many aspects of robot applications such as off-line programming,visual servoing,and laser cutting require robots to have high absolute positioning accuracy.The kinematic calibration of industrial robots can reduce the end-position errors of the robot and improve the robot's positioning accuracy by recognizing the parameter deviation of the kinematic model of the industrial robot and compensating for the robot's end positioning errors.At present,a large number of researches on kinematics calibration of robots have been conducted at home and abroad,and a large number of robot kinematics modeling methods and parameter identification algorithms have been proposed.However,most of the scholars use laser trackers to measure the end-position of robot.The actual end-position of the robot.Due to the relatively high requirements of environmental factors such as temperature,humidity,and dust during the use of the laser tracker,the high price of the laser tracker is not conducive to the use of small and medium enterprises.This paper uses a robot position measurement system consisting of draw-wire sensor to measure the actual end-position of the robot.Combined with the robot's desired position and the differential error model of the robot,the least squares method is used to identify the parameter deviation of the robot's kinematic model,and then the Cartesian space compensation method is used to compensate the robot's terminal positioning error to improve the positioning accuracy of the robot.Firstly,this paper uses the ER3A-C60 industrial robot of EFORT,Anhui,as the experimental object of the calibration experiment,and uses the MD-H modeling method to establish the kinematics model of the robot for some disadvantages of the standard D-H model;The differential error model of the robot is established according to the robot's MD-H model,and the constraint equation between the parameter deviation of the robot's kinematics model and the end-position errors of the robot is obtained;The least squares method is used to identify the parameter deviation of the robot's kinematic model,using the Cartesian space compensation method to compensate for the end-position errors of the robot based on the identified parameter deviation of the kinematic model of the robot.The kinematics calibration algorithm of the robot was simulated and the correctness of the calibration algorithm was verified.Then,this paper designed a robot position measurement system consisting of draw-wire sensor to measure the actual end-position of the robot.A robot end drawstring universal join is designed to make the extensions of the four draw-wire sensor drawstrings intersect at one point.This point is combined with four draw-wire sensors to form a quadrangular pyramid;The CIFX104-CO communication interface card from Hilscher is used to read the pull rope length of the draw-wire sensor;The length of the quadrangular pyramid is calculated according to the pull rope length of the draw-wire sensor,and the position coordinate of the measuring point in the coordinate system of the robot position measuring system is calculated by the four-line method.Since the calculated position coordinates of the measurement point are the position coordinates in the coordinate system of the robot position measurement system,the base coordinate system of the robot needs to be determined,and the position coordinate of the measurement point is converted into the position coordinate in the robot base coordinate system.The least square fitting method is used to determine the origin of the robot base coordinate system and the orientation of each axis.Then enough sampling points are selected in the robot's work space and the position coordinates of these sampling points in the robot's base coordinates are measured.Finally,according to the kinematics calibration algorithm of the robot and the measured actual position coordinates of the sampling point in the robot base coordinate system,the parameter deviation of the kinematic model of the ER3A-C60 robot is identified,and the endposition error of the robot is compensated using the Cartesian space compensation method.Comparing the end-position errors of the robot before and after calibration,the effectiveness of the robot kinematics calibration algorithm and the robot position measurement system composed of a pull rope displacement sensor was confirmed.