Analysis and Optimization of Closed-loop Manipulator Calibration with Fixed Endpoint

This paper investigates a calibration method where the manipulator end-effector is constrained to a single contact point using a fixture equivalent to a spherical joint. The required fixture has the advantage of being inexpensive and compact when compared to pose measuring devices required by other calibration techniques, such as theodolites. By forming the manipulator into a mobile closed kinematic chain, the kinematic loop closure equations are adequate to calibrate the manipulator as it executes self-motions, without the need of endpoint measurements or precision points. Adding a wrist force sensor allows for the calibration of elastic effects due to endpoint forces and moments. A performance index is introduced to calculate the optimal location of the calibration device. The method is evaluated experimentally on a Schilling Titan II manipulator. The results show that the calibration method is able to effectively identify and correct for the errors in the system.