Adaptation of kinematic model of a six-axis robot for improving volumetric error compensation

: To improve the three-dimensional (3D) positioning accuracy of a six-axis industrial robot, many researchers have studied the model-based error compensation. Our research group has proposed a new kinematic model containing Denavit-Hartenberg (DH) parameters and angular positioning deviations of all the rotary axes as error sources. In this model, the DH errors and rotary axis angular positioning deviations are identified by the circular test for each rotary axis, where a nominally circular 3D position trajectory of the end effector is measured by using a laser tracker, as each rotary axis is indexed at the given constant interval over the prescribed angular range. Although this model showed a significantly better prediction performance than the conventional DH model, depending on the paths, it can still have a significant prediction error. We consider that it is due to the influence of the gravity-induced elastic deformation that results in the change in the position and orientation of rotary axis average lines. This paper proposes a new method to “adapt” the DH parameters, identified from the circular test of an individual axis, by using the positioning error profiles measured on actual working paths. The DH parameters are re-tuned so that the prediction performance on the working paths is optimized, while the prediction performance over the entire workspace is preserved by incorporating with the conventional circular tests as well. It is experimentally verified that the proposed scheme significantly improves the prediction accuracy of the present model on the actual working path.