Synthesizing two-fingered grippers for positioning and identifying objects

Most industrial grippers now in use are two-fingered. Among them the parall el-jaw gripper is the simplest. It can partially remove the pose uncertaint y of an object through grasping, such as the orientation uncertainty. This paper addresses a new type of grippers with the finger configuration of fou r circles instead of two parallel lines. It has a number of important advan tages. Especially, it achieves form-closure and confines the object to a lo cally unique pose, so as to remove the pose uncertainty completely. It allo ws the gripped object to reach this pose freely without loss of required fr iction in the direction perpendicular to the grasping plane. More informati on can be acquired for identifying the object and its grasp mode. As a resu lt the identification can be performed at one grasp. The key parameter of a symmetric four-pin gripper is the distance (span) between two pin centers on each finger, which depends upon the object shape and impacts the closure property. Based on a new approach to the grasp geometry, selection and lim itations of the span are illustrated.