Development of a gripper using SMA wire

A gripper actuated by shape-memory-alloy (SMA) wire was designed and fabricated. The design took the advantage of the small linear displacement of the SMA wire to convert it into angular movement of the gripping jaws. The SMA actuation is provided by pulsing electric current from a driving circuit. With this method, the risk of the SMA being overheated can be reduced, yet providing sufficient power for the useful gripping task. This ensures that the gripper has long and lasting actuation. Testing experiments were conducted using the prototype to evaluate its working responses and reliability, including the generated force, level of excitation, reaction time, its characterization and cyclic performance. The gripping force achieved was in the range of 70–500 mN, ideal for micro-applications. This force can be varied by changing the driving current through a variable resistor. In terms of reliability, millions of gripping cycles were accomplished without any deterioration in performance. This proves that the concept of the design is feasible and the gripper is able to support a continuously long operation before any replacement of parts is required. The actuator (SMA wire) costs only US$ 0.7, much less-expensive than other actuators such as piezoelectric actuators.