Highly Underactuated Radial Gripper for Automated Planar Grasping and Part Fixturing

Grasping can be conceptualized as the ability of an end-effector to temporarily attach or fixture an object to a manipulator-constraining all motion of the workpiece with respect to the end-effector's base frame. This seemingly simplistic action often requires excessive sensing, computation, or control to achieve with multi-fingered hands, which can be mitigated with underactuated mechanisms. In this work, we present the analysis of radial graspers for automated part fixturing and grasping in the plane with a design implementation of a single-actuator, 8-finger gripper. By leveraging a passively adaptable mechanism that is under-constrained pre-contact, the gripper conforms to arbitrary object geometries and locks post-contact as to provide form closure around the object. We also justify that 8 radially symmetric fingers with passive locking are sufficient to create robust form closure grasps on arbitrary planar objects. The underlying mechanism of the gripper is described in detail, with analysis of its highly underactuated nature, and the resulting form closure ability. We show with a wide variety of objects that the gripper is able to acquire robust grasps on all of them, and maintain maximal quality form closure on most objects, with each finger exerting equal grasp force within ±2.48 N.