This thesis is aimed toward the development and evaluation of a novel active ankle foot orthosis (AAFO) based on shape memory alloy (SMA) actuators. This device intends to fill the gap in the existing research aimed at helping patients with drop foot muscle deficiencies as well as rehabilitation activities. To examine the feasibility of this idea, the current study focuses on the dynamic behavior of the ankle joint. A SMA manipulator with a similar dynamic behavior is experimentally evaluated. Nonlinear behavior of SMA wires requires nonlinear control techniques such as Sliding Mode Controller (SMC) for tracking the desired ankle angle. Simulation results of several different techniques are compared (PID, SMC, SMC-PID and Adaptive PID) and finally the experimental result of an Adaptive PID is used to check the stability of walking. This results shows that an Adaptive PID controller as a robust and precision control can be used to track the desired position of the ankle. However for frequencies more than 0.25 Hz (time cycle less than 4 seconds), the walking conditions will be unstable due to slow cooling process.

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