KINEMATIC CALIBRATION OF INDUSTRIAL HYDRAULIC MANIPULATORS

A novel off-line technique for automatic calibration of kinematic para meters for hydraulic manipulators is presented. Hydraulically actuated manipulators have joints which are always powered and, unlike convent ional robots, may not have conventional joint sensors to exploit in th e calibration procedure. Instead, our approach employs an external thr ee-dimensional linkage, termed ''the calibrator'', which has sufficien t number of joints with corresponding sensors. One end of the calibrat or is grasped by the manipulator's end effector while the other end is attached to a passive spherical joint fixed to the world coordinate s ystem. The mobile closed kinematic chain thus formed has the added adv antage of eliminating the explicit measurement of the manipulator's en dpoint location. A sequential identification technique that uses a lea st squares numerical search algorithm has been developed based on link -by-link movement of the manipulator. Simulation and experimental cali bration results on a typical mobile hydraulic manipulator are reported in this paper, which show that the proposed technique is globally sta ble, and potentially fast, inexpensive, and easy to apply on site.