Research On Kinematics Calibration Method Of XYZ-3RPS Six-axis Hybrid Machining Equipment

With the rapid development of ship industry,the machining level of propeller is required with high precision and high efficiency.Two sets of the same XYZ-3RPS six-axis hybrid machining equipment are symmetrically arranged on both sides of the propeller to be machined to carry out double-knife double-sided machining,which can effectively solve the vibration,interference,secondary clamping and other problems existing in the machining process of large propeller,and improve the machining precision and efficiency of propeller.The end precision of hybrid mechanism is the bottleneck that restricts its wide application in the field of complex curved parts machining.As an economical and effective means to improve the end precision of the mechanism,the kinematics calibration has been widely studied by scholars at home and abroad.The kinematics analysis of XYZ-3RPS six-axis hybrid machining equipment was carried out.The structural characteristics of the hybrid equipment were analyzed.Based on the decoupling of the motion parameters of the 3RPS parallel mechanism with less degrees of freedom,the forward and inverse kinematics models of the hybrid equipment were established.The kinematics model of the parallel mechanism was verified by the virtual prototype technology of ADAMS.The error models of the serial and parallel mechanisms were established by using the idea of separate calibration.The mapping model between the actual displacement of the end of the equipment and the actual movement direction of the X,Y and Z three directional platform of the series mechanism was established.Based on the spatial closed-loop vector method and perturbation theory,the mapping model between 6-dimensional pose errors of the terminal of the 3RPS parallel mechanism and its 30 geometric error elements was established,and the error source separation was realized.Numerical simulation verified the effectiveness of the error model of the parallel mechanism.The analysis results of the end pose error analysis showed that the extreme values of the end 6-dimensional pose error are all distributed at the edge of the workspace.The parameter identification model and error compensation strategy of the hybrid equipment were studied.Based on the end position information,the parameter identification models of the series and parallel mechanisms were established respectively.By adding constraint conditions,the full rank of the parameter identification matrix of the parallel mechanism was achieved.Taking the reciprocal of the condition number of identification matrix as the observability index O,the observation configurations of parallel mechanism were optimized by using local convergence and tabu search methods.The Tikhonov regularization method was used to optimize the robustness of parameter identification of the parallel mechanism.The errors of controllable DOF direction of the parallel mechanism were compensated by modifying its own input,and the residual end position errors were compensated by modifying the geometrical parameters of the series mechanism.The effectiveness of parameter identification method and error compensation strategy were verified by the numerical simulation.Calibration experiment and compensation effect test were carried out on the prototype of the hybrid machining equipment.The binocular vision measurement system for three-dimensional coordinates was established,and the stereo calibration of binocular vision was completed.Based on the end position measurement information,the zero calibration of the initial configuration of the equipment was completed.The parameter identification of XYZ series mechanism was realized by uniaxial motion.Using the calibrated series mechanism to reversely adjust the nominal displacement of the end at calibrated configurations,the calibration experiment of the 3RPS parallel mechanism was completed.The test results showed that the end absolute pose error of the equipment prototype is effectively reduced after compensation.