Conventional actuators are not proper to construct a small manipulator because they have complex, large mechanical structure, and complicated power transmission. In this study, we propose a controller for a SMA(Shape Memory Alloy) which is very useful to make a multi- degree of freedom small mechanism. We describe a design procedure of a controller for SMA actuators which drive a small-sized, eye-like mechanism. We develope a model of a SMA actuator and verify it by experiments. The performance of the overall system is shown by experimental results.
To balance the control complexity and number of controlled positions, a novel multi-step SMA actuator is proposed that has multiple controlled positions and can be actuated by sensor-less and open-loop control. The proposed multi-step SMA actuator is constructed so that several electrical taps are connected to one SMA wire and the sections between the taps are all the same length. The controlled positions then vary stepwise according to the number of actuated sections. To control the multi-step SMA actuator, a PWM(pulse width modulated) voltage with an appropriate duty ratio is applied to designated sections while considering the resistance value of the sections, as well as the recommended current for the given SMA wire. To verify the effectiveness of the proposed multi-step SMA actuator, experiments were performed using a single nitinol wire actuator with a bias spring mechanism and electronic control system.