Kinematic Calibration Of Parallel Robot Based On The Rotary Angle Errors Of End-effector

This dissertation deals with the key issues relevant to mechanism,error measuring and parameter identification of a 4-DOF parallel robot(Cross-IV robot)with a goal to establish a kinematic calibration method which can ensure the geometric accuracy of the robot.The following contributions have been accomplished.With aid of the closed-loop vectorial chain and the first-order perturbation technique,a systematic approach is proposed by modeling geometric error of one limb and then promoting to all limbs.The established error models allow the source errors affecting the compensatable and uncompensatable pose accuracy to be separated in an explicit manner,and then an error model only including errors that can compensate is established,enabling the processes of kinematic calibration to be integrated into a unified mathematic framework.By the decomposition of the error transfer matrix and measuring the rotary angle errors by the rotary encoder,a fast error identification model is constructed.To further maximize the measure efficiency and improve the robustness of the identification matrix,an optimized selection scheme of the measure points is proposed.Detailed simulation verifies the robustness and correctness of this scheme.The measuring instrument is cheap and the calibration method is simple and effective.Consider about the random error,a mapping model between the complete geometric errors and the output errors is established.Establishes mathematical models of Least Squares(LS),Truncated Singular Value Decomposition(TSVD),Principal Component Analysis(PCA),Kalman Filter(KF)and Ridge Regression(RR)and Liu-estimation etc.is proposed.Certifies the KF,RR and Liu-estimation algorithms have high accuracy and strong robustness by simulation.The three algorithms have good effects of error compensation and apply to the system that has many parameters and bad identification matrix.Experiment show that the kinematic calibration method satisfies to realize fast measurement and accurate compensation in the engineering practice.Linear compensators are developed for the real time implementation.A hierarchical strategy is then used via rough calibration by the identification of active arm initial corner errors as well as the fine calibration by that of all possible source errors.The experimental results show that a volumetric/rotational accuracy of 0.250 mm/1.382° of the end-effector can be achieved after calibration.