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Kinematic Calibration of Industrial Hydraulic Manipulators

SUMMARY A novel off-line technique for automatic calibration of kinematic parameters for hydraulic manipulators is presented. Hydraulically actuated manipulators have joints which are always powered and, unlike conventional robots, may not have conventional joint sensors to exploit in the calibration procedure. Instead, our approach employs an external three-dimensional linkage, termed “the calibrator”, which has sufficient number of joints with corresponding sensors. One end of the calibrator is grasped by the manipulator's end effector while the other end is attached to a passive spherical joint fixed to the world coordinate system. The mobile closed kinematic chain thus formed has the added advantage of eliminating the explicit measurement of the manipulator's endpoint location. A sequential identification technique that uses a least squares numerical search algorithm has been developed based on link-by-link movement of the manipulator. Simulation and experimental calibration results on a typical mobile hydraulic manipulator are reported in this paper, which show that the proposed technique is globally stable, and potentially fast, inexpensive, and easy to apply on site.