Designing Hands and Wrists for Manufacturing
A recurrent theme in this thesis is that many manufacturing tasks can be broken into fine motion and gross motion subtasks, and therefore it is appropriate to develop a manipulation system consisting of separate “modules.” In the case of assembly, the operation can be decomposed into gross motions that move the peg in the direction of the hole, and fine accommodations about the central axis of the hole. If a robot is to assemble parts, it suffices to have an arm with the required reach and speed to pick the parts up, move them roughly into position, and push them toward each other, while a compliant RCC wrist takes care of the fine accommodations and keeps the parts from jamming. In other tasks, such as grinding, the fine and gross motion elements are not entirely independent; a change in the velocity along the surface changes the amount of material removed and alters the apparent “hardness” of the surface. Still, it is possible to use a separate arm, wrist and hand provided that they communicate with each other. If the tasks displayed a large amount of interdependence between fine and gross motions, it would become more convenient to treat the wrist and hand as the last few joints at the end of an arm. In the present case, it suffices to work in cartesian coordinates, transmitting deflections or forces sensed at the wrist and hand, and locations reported by the robot. It is not necessary to directly couple, say, the third wrist sensor with the fourth arm actuator.
KeywordsActive Hand Fine Motion Extrinsic Muscle Active Wrist Manufacturing Task
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