Accuracy analysis and calibration of a parallel guidance device for minimal invasive spinal surgery

In this paper a medical robot based on a 3-RPS parallel platform is presented for providing correct screw path in transpedicular fixation surgery. For improving the accuracy of the robot, a calibration approach for 3-RPS with CMM (Coordinate Measuring Instrument) data is developed. Sensitivity analysis of the error source had been done with Monte-Carlo techniques. The results show that the length errors of the joint-links are main contribution to the output error of the 3-RPS parallel manipulator; and the secondary factor is the radius error of the static and the moving platform. Based on above analysis, the calibration model of the inverse kinematics was established and the mono-branched calibration method was used. The presented method has high identification accuracy for length error of the chain. Based on the identification parameters, the results show that the method can improve the 3-RPS output accuracy.