POE Based Kinematic Calibration For Industrial Robots

In the applications of industrial robots, repeatability accuracy and absolute accuracy are important indexes of operation performance of the robots, precision error is generally required less than 2 mm. Due to defects of machining error and assembly error, industrial robots often does not meet the accuracy requirement, and with the development of industrial robot to the fields like welding, painting and other fields of high precision, high accuracy become the prerequisite of machining process, so calibration is significant enough. For the proposed calibration method based on D-H model which with more variables and constraints is also no guarantee on the reliability. Even the calibration method based on improved Product of Exponential(POE)could not consider the constraints, due to the redundancy, the error model is too complex and the algorithm has found slow convergence.To overcome the shortcomings of calibration method proposed. This dissertation presents geometric constraint matrix on the base of improved POE method, which could effectively express geometric constraints between adjacent joints, thus greatly reducing the identification of the parameters, the optimal error model makes the iteration fast convergence and the calibration process accurate. Through MATLAB simulation test, we verify the feasibility of calibration algorithm. At the same time in the process of actual operation, we found that the error of the reduction ratio and the coupling ratio could also produce certain effect in precisio n of the robot, so we joined the parameters of reduction ratio and coupling ratio into the calibration algorithm combining theory with actual.In the experiment part, the measurement method based on the laser tracker can guarantee accuracy reach micron grade which could ensure accuracy of data acquisition and can test and analyse of the accuracy of the robot before and after the calibration. Found in the experimental process, because the data of laser tracker coordinate could not accurate describe the space position of end point relative to the robot base coordinate, so we improved measuring method in the research. We have calibrated the manipulators like Yaskawa’s Motoman, Efort’s manipulator etc. Results show repeatability accuracy and absolute accuracy after the calibration of improved POE method have improved significantly, the space linear precision ca n be increased from 0.56 mm to 0.19 mm, robots after the calibration accuracy can completely meet the requirements of industrial and technological standards.