In this paper, we develop a small-scale hip exoskeleton by utilizing double acting artificial muscle comprised of shape memory alloy (SMA) springs arranged in hexagonal architecture. This exoskeleton enables both hip extension and flexion motions by selectively heating the corresponding group of SMA springs. The prototype has an operational range spanning from −20° to 200°. Thermo-mechanical characterization experiments were conducted to evaluate the performance of the SMA springs, while an inertial measurement unit (IMU) provided feedback on the hip angles. Temperature measurements of each SMA spring group were obtained using thermocouples, facilitating control actions. Furthermore, system identification and PID tuning techniques were employed to enhance the proportional-integrator-derivative (PID) controller, enabling trajectory tracking of the hip angle and temperature. Experimental results demonstrate the successful tracking of desired trajectories by the hip joint prototype. |
