Design of a Lightweight SMA Driven Parallel Gripper for Collaborative Robots

For a given use case of a collaborative assembly station, a gripper is needed that can handle workpieces with varying geometries. Existing electric robotic grippers are heavy and expensive, while pneumatic alternatives are noisy, inefficient and need stiff tubes and additional valves. A gripper driven by shape memory alloys (SMA) is by design silent and lightweight, purely electric, can be controlled in an energy efficient way and is predestined for collaborative applications due to the soft actuator behavior. The challenges of the development of such a system are given by the requirements for the use case at hand. They are jaw opening stroke and high forces combined with a short cycle time. In this paper the design process of a normally closed parallel gripper prototype driven by SMA wires featuring 14 N maximum gripping force and 30 mm opening stroke is discussed. Thin NiTi wires with a diameter of 76 mu m are used to ensure a fast cooling. With this measure a cycle time of 1 second and below can be reached. A two-stage telescopic mechanism having overall 96 wires in parallel drives the gripper jaws by means of a lever mechanics. The power consumption is around 48 W and the gripper is designed to work with the electrical industry low voltage standard of 24 V and 2 A.