Shape memory alloy actuators and their reliability

We have developed two types of shape memory alloy (SMA) actuator and estimated the long-term reliability of SMA microcoils. A tube type tip articulator consists of 4 sets of SMA microcoil (wire diameter: 0.125 mm, coil diameter: 0.5 mm) for driving source and super elastic alloy (SEA) microcoils (wire diameter: 0.1 mm, coil diameter: 0.5 mm) for bias springs, support plates and flexible outer tube. The tube type tip articulator was bent approximately 90 degrees in any directions when a 200 mA current was applied. The joint mechanism consists of base plate, universal joint, reflection plate (diameter: 170 mm), SMA microcoil springs (wire diameter: 0.1 mm, coil diameter: 0.9 mm) and bias spring. The joint mechanism showed good response for control values with maximum tilt angle of 3.2 degrees. We also estimated the thermal cycling behavior of SMA microcoil actuators with the resistance monitoring method. SMA microcoil actuators (wire diameter: 0.1 mm, coil diameter: 0.5 mm) were given 3.0% shear stress and heated by current. For 10,000 cycles, the force of SMA microcoil actuators was approximately constant and showed good long-term reliability. Since the results show good characteristics and reliability, SMA microcoil actuators can be used in a wide range of industrial and medical applications.