Workspace of planar cooperating robots with rolling contacts

Abstract

In multifingered grippers and multiarm manipulation systems it is possible to manipulate a grasped object by rolling the object along the contacting links. This affords greater versatility, a potentially larger workspace and the ability to adapt to external loads without regrasping. The reachable workspace, or the set of points that can be reached by a reference point on the object, is an important measure of performance. The functional workspace, a subspace of the reachable workspace in which the object can be held in a force-closed grasp, is also an important design consideration. In this paper, the reachable and functional workspaces and methods to determine their boundaries are studied. The basic idea is to determine extreme configurations using screw system theory and obtain the locus of the reference point as the system is moved through these configurations. Although this procedure has been used in an earlier paper, the modeling of rolling contacts and consideration of joint limits require a different treatment. Examples of planar grasps with two manipulators are used to illustrate the application of the theory.