Parallel Robot Calibration by Working Mode Change

The positioning accuracy of robotic manipulators can be enhanced by identification and correction of the geometry parameters of the controller model in a way that it best matches the real physical robot. This procedure, denoted as kinematic calibration, is performed by analyzing the difference between conflicting information gained by the kinematic model and corresponding redundant measurement information. Most traditional robot calibration approaches require extra sensors or special constraint fixtures in order to obtain redundancy. This paper proposes a new calibration method that does not require any special calibration equipment, thus being very economical. The presented technique which is designed to be applied to parallel robots is based on a working mode change and incorporates special knowledge about serial singularities. Exemplarily the approach is verified by means of simulation studies on a 3-RRR-structure.