Modeling and control of two DOF shape memory alloy actuators with applications

In this research, we developed several two degree of freedom actuators using shape memory alloy (SMA) springs. We tested these actuators in various applications like: mobile holder, and bio-inspired: fish body, and fish tail. In such applications the actuator weight and size are very important requirements as these requirements impact the overall design performance and cost. This SMA actuator consists of two groups of SMA springs: one group is to rotate the roll angle and the second group is to rotate the pitch angle. Each group has two elements: one SMA spring and another antagonistic SMA spring. An inertial measurement unit (IMU) sensor is used for angles feedback. We modeled and simulated the SMA spring in order to estimated the resultant spring force. The SMA spring mechanical characterization has been studied experimentally at various SMA temperatures. Also, we executed several experiments in order to control the orientations angles (roll and pitch) of the 2-DOF actuator simultaneously. We designed a PID controller and compared it experimentally with nested fuzzy controller. Moreover, preheating period is also considered to reduce the delay time, and rise time. Then, we studied the effect of cooling the SMA in order to obtain relatively higher frequencies (12 cycles/min).