Research On The Key Issue Of Robot Calibration Based On Laser Tracker

With the high-speed development of economy and the rapid development of science and technology,the industrial robot gradually becomes an indispensable tool to improve productivity and it plays an important role in the manufacturing industry.Increasing product quality requirements and new application fields have put forward higher requirement for the accuracy,reliability and performance of the robot.The improvement of repeated positioning accuracy and absolute positioning accuracy of industrial robots has become a key problem in the development of robot technology.It is very important to carry out the research of robot calibration technologyThe nominal kinematic model of a 6R series industrial robot is calibrated based on laser tracker using LM algorithm.The main contents are as follows(1)The influence factors,the components and the practical applications of laser measurement system are analyzed.The performance of Leica AT901-MR laser tracker for robot calibration is presented in this paper.The measurement principles about IFM,ADM and orientation measurement of laser tracker are studied.The powerful graphical SA measurement softwar is introduced(2)The mathematical basis and the D-H parameter method for describing the kinematics of the robot are introduced.D-H kinematic model is established for UR3 robot The forward kinematics of the robot is analyzed,and the Jacobian matrix is derived.The concept of dimensional constraint type is introduced,and the motion characteristics of robot joints are grouped according to dimensional constraint type.Motion characteristics of the robot end-effector is analyzed(3)The error sources of the robot end-effector are analyzed and classified.The principle of LM algorithm with adaptive step size,the convergence condition and the implementation step of the algorithm are analyzed.Aiming at the calibration precision of UR3 robot,pose calibration methods and the experimental schemes are proposed.A series of pose data of the measurement points are measured using laser tracker,and 24 geometric parameters of the UR3 robot are estimated.Aiming at solving that the measurement data of the pose leads to the increase of the power exponent in the robot calibration technology,observability index is a selection index based on the singular value decomposition of the Jacobian matrix.It can greatly reduce the amount of computation.The step of parameter identification in robot calibration technology is studied.In order to realize specific application of robot,the calibration mode of the combined joints is proposed.The robot combined joints move separately,and the pose of robot end-effector is measured by laser tracker.The geometric figures fitting by the data are analyzed.The sensitive parameters affecting the precision of the robot end-effector are obtained.The target function of LM algorithm according to the sensitive parameters is estimated(4)According to the robot calibration methods,the calibration experiment platform of UR3 robot is built.The robot base coordinate system is established by laser tracker in the SA software.According to the ISO 9283:1998 standard,the pose accuracy evaluation of robot end is carried out.The pose data of 115 measurement points are measured by laser tracker.According to the calibration methods,the parameters are estimated and calculated,and the nominal kinematic model of the robot controller is modified.The pose accuracy of the robot after calibration is tested,and the effectiveness of the calibration methods are obtained.In this paper,the reliability of the calibration methods is verified by the robot calibration experiment.It has theoretical significance and practical value.