Research On The Kinematic Accuracy And Parameter Identification Method Of Parallel Kinematic Machine

Parallel mechanism has been successfully applied in some fields, such as aviation manufacturing industry, automobile manufacturing industry, because its merit of high stiffness/weight ratio, good dynamic performance, high technical extro-value and so on. Hybrid machine tool, which combining advantages of serial mechanism and parallel mechanism, could satisfy the development tendency of high-speed and high-accuracy in manufacturing industry, and interest domestic and overseas experts. However, compared with serial machine tool, the accuracy of parallel kinematic machine (PKM) is still not high enough. The number of kinematic parameters is very large and their effect is nonlinear, so that the measurement, analysis and identification of kinematic parameter is complicated. Besides, the dynamic error caused by gravity, interia force and external load also limits the accuracy of machine tool. At present, the research on the kinematic accuracy and parameter identification method is still a research focus and challenge. From kinematic and dynamic perspectives, this dissertation researches on the geometric error analysis, kinematic calibration, dynamic parameter identification and so on. Mainly, the following research contents are carried out in this dissertation:(1) According to Denavit-Hartenberg method and closed-loop vector chain method, the geometric error models of serial mechanism, parallel mechanism and hybrid mechanism are separately built. An error modeling method is proposed to describe the distance errors between rotation axes in a composite spherical joint.(2) The geometric error analysis of 5-DOF PKM and 3-TPS hybrid machine tool is conducted. The effect on end-effector caused by single or several geometric error sources in parallel mechanism and constraint mechanism are separately analyzed and compared. The simulation result indicates that the geometrical error sources in constraint mechanism affect more on the pose of machine tool end.(3) According to quantum-behaved particle swarm optimization (QPSO) algorithm, the kinematic calibration of PKM is researched. The calibration procedure based on QPSO algorithm is designed, the parallel mechanism and constraint mechanism of 5-DOF PKM are calibrated through simulation and test, and the result shows that the accuracy of end-effector increased relatively obviously after calibration. As representative serial/parallel mechanism, two cases of serial mechanism and Stewart parallel mechanism are conducted to extend this calibration method to the application of other serial and parallel mechanisms.(4) An improved method of kinematic calibration is researched to further increase the identification accuracy of kinematic parameters. The step calibration procedure based on QPSO algorithm is built, the parallel mechanism of 5-DOF PKM are calibrated through simulation, and the simulation result indicates that not only the accuracy of end-effector is further increased, but the identification accuracy of kinematic parameters is also improved. Moreover, this step calibration method is also feasible for both serial mechanisms and parallel mechanisms.(5) The research on structure optimization and accuracy synthesis of 5-DOF PKM is conducted. The spherical joints in parallel mechanism are replaced with composite spherical joints, and the accuracy analysis of parallel mechanism before and after replacement is conducted. Besides, a weighted accuracy synthesis method is proposed to determine the component accuracy level in parallel mechanism.(6) The research on dynamic modeling and dynamic parameter identification of 5-DOF PKM is conducted. Based on Lagrange method, the dynamic model of 5-DOF PKM is built, and the dynamic parameter identification path is designed. Under the precondition of ignoring friction, dynamic parameter identification of 5-DOF PKM is simulated, the simulation result indicates that the identified dynamic parameters are relatively obviously accurate, and this lays the foundation for the future research on dynamic related issues and advanced control method.