A Novel Underactuated End-Effector for Planar Sequential Grasping of Multiple Objects

We propose a serpentine type tendon driven underactuated end-effector design with a closing mechanism that is triggered upon contact with an object. This end-effector can grasp objects without knowing the size a priori and is able to grasp a new object while securing another one previously grasped, and so grasp multiple objects sequentially with a single DOF actuation. Design parameters based on the object dimensions are proposed. A low-cost prototype demonstrates two implementations (radius estimation and autonomous grasp of circular objects by torque control, and sequential grasps of multiple objects) of the end-effector through several experiments. A method for estimating applied internal forces is also proposed. This end-effector can benefit robotic manipulation in tasks such as fetching applications, industrial pick-and-place of single or multiple objects and human-robot hand-off interactions.