On the Synthesis of Constraint Systems for Stable Workholding

During a robotic materials handling operation, the position and orientation of the workpiece must remain fixed with respect to the coordinate frame of the gripper when the robot arm moves from one point to another. This is achieved if all degrees of freedom of the workpiece relative to the gripper are eliminated by placing appropriate constraints on its movements. Deciding how to constrain an object forms an important part of the design of gripping devices. In this paper, the rules for analysing the state of constraint of an object are reviewed. This is followed by a discussion of a procedure for synthesizing stable constraint configurations for a wide variety of object shapes. Finally, examples are provided to illustrate the application of the proposed procedure in the case of two simple objects.