Implementation of time-optimal path-tracking control on palletizing robots

It is not easy to apply the algorithms for time-optimal trajectory planning in practice because they rely on the exact dynamic models of the system. In this paper, the authors propose a simplification of the time-optimal path-tracking control algorithms. The proposed algorithms are based only on the kinematic constraints. Such simplifications can be justified in cases when the actuators are never pushed to their torque limits and when the task gives the constraints for the optimal trajectory. One of the practical applications of these simplified algorithms are palletizing robots. For these robots, the gripping force is one of the key factors. If the dynamic forces are to high, the gripper may lose the load. Assuming that the payload is constant during the motion, the dynamic properties in the task space are not changing, and the maximal allowable accelerations can be determined from maximal gripping force. The acceleration and velocity bounds are then used in the trajectory planning algorithm. Although the the simplifications reduce the computational complexity, the trajectory has still to be precalculated offline. The proposed algorithm has been implemented in the authors' PC-based robot controller which is used to control a palletizing robot. Experimental results confirm that the proposed algorithms assure the end-effector motion in the prescribed bounds.