The superposition strategy for arm trajectory modification in robotic manipulators

This work deals with the problem of end-effector trajectory modification for a robot manipulator when it must respond to unexpected changes in target location. Trajectory modification and corrections are particularly important in dealing with dynamic tasks. In this paper, we present and discuss the superposition strategy derived from the study of arm trajectory modification in human subjects. According to this strategy, the motion toward the initial target location continues unmodified as planned from its beginning to its end even after the target location has unexpectedly changed. However, a trajectory leading from the first target to the final one is added vectorially to the initial one to yield the combined modified motion. A method for choosing the temporal parameters of this trajectory modification scheme is suggested so as to minimize the total travelling time under existing kinematic constraints (including both joint and hand space constraints). Then, a variant of this strategy is presented, dealing with trajectory modification in the case that the targets (both the initial and final ones) specify the desired end-point orientation rather than position.