Grasping Without Grasping: A Sweeping-Based Pickup Strategy Using Planar Fingers

Conventional object pickup strategies utilize multi-point contact by grippers or an enveloping grasp by multi-finger hands, both of which require as high a number of degrees of freedom (DOFs) as possible, in addition to precise control to maintain the equilibrium between the fingers and the object while handling it. This paper describes a novel object pickup strategy for a foldable robotic hand. The robotic hand, which was previously proposed by the authors, is based on the operational characteristics of the human hand, which applies force at a point or surface when handling an object. This unique configuration allows an object to be picked up in a manner fundamentally different to that for conventional multi-point contact or enveloping grasp strategies. In this paper, the details of the hardware and control system for the robot are described. A theoretical analysis is used to derive a suitable posture for the fingers to handle cylindrical objects using the proposed method. Experiments are conducted using various cylindrical objects, a sphere, and flat plates to demonstrate the effectiveness of the method. The results show that the proposed sweeping-based strategy can achieve object pickup using a low-DOF hand without the need for complex force sensing and with less dependence on friction than that for conventional friction-based gripping.