Kinematic calibration of a six-axis serial robot using distance and sphere constraints

This paper describes a kinematic calibration method developed to improve the accuracy of a six-axis serial industrial robot in a specific target workspace, using distance and sphere constraints. A simulation study demonstrates the ability of the calibration approach to identify the kinematic parameters, regardless of measurement noise. Experimental validation shows that the robot's accuracy inside the target workspace is significantly improved by reducing the mean and maximum distance errors from 0.698 to 0.086 mm and from 1.321 to 0.127 mm, respectively. The experimental data are collected using a Renishaw precision touch probe mounted on the flange of a FANUC LR Mate 200iC and a special triangular plate with three datum 2-in spheres 300 mm apart. The calibration method uses an optimization model based on fitting several probed positions on spheres and minimizing the residual of the spheres' center-to-center distances.