In this paper, the kinematic accuracy problem caused by geometric errors of a 2(3HUS+S) parallel manipulator is described. The kinematic equation of the manipulator is obtained by establishing a D–H (Denavit–Hartenberg) coordinate system. A D–H transformation matrix is used as the error-modeling tool, and the kinematic error model of the manipulator integrating manufacturing and assembly errors is established based on the perturbation theory. The iterative Levenberg–Marquardt algorithm is used to identify the geometric errors in the error model. According to the experimentally measured attitudes, the kinematic calibration process is simulated using MATLAB software. The simulation and experiment results show that the attitude errors of the moving platforms after calibration are reduced compared with before the calibration, and the kinematic accuracy of the manipulator is significantly improved. The correctness and effectiveness of the error model and the kinematic calibration method of the 2(3HUS+S) parallel manipulator for simulation of hip joint motion are verified.

An ultra-precision integrated robotic system is developed, which integrates a passive robotic measurement system (shadow system) with an industrial robot. The shadow system is built almost ideal. In a working process, when the end-effecter of integrated robot is driven to a target with errors which are caused by degrading factors associated with the robot, the shadow system will independently detect the end-effecter frame instantly with ultra-precision kinematic accuracy. A scheme of approach control is then established to drive the end-effecter of the integrated robot to compensate the error step by step until the desired target is achieved with ultra-precision positioning accuracy.