Design, Modeling and Evaluation of a Hybrid Driven Knee-Ankle Orthosis with Sma Actuators

This paper demonstrates the mechanical design, analysis, and evaluation of a knee-ankle orthosis (KAO) for lower limb rehabilitation, including shape memory alloy (SMA) actuators and DC brushless motor actuators. First, the mechanical structure of the KAO is detailed, including the actuator system, transmission mechanism, monitoring device, and processing method of SMA actuators. Next, based on the thermal constitutive model of SMA, the dynamic model of SMA spring actuators in the process of phase transition is established. In addition, the dynamic output response of the knee joint under three working states is analyzed, and the rotation angle of SMA soft actuator during bending is described by pseudo rigid body model. Finally, the output of SMA actuator is preliminarily evaluated through experiments. The experimental results show that the maximum displacement of SMA spring actuator is 46.10mm, the maximum error between the experimental and theoretical displacement is 11.82mm, the maximum restoring force during phase transformation is 4.14N, and the maximum rotation angle of SMA soft actuator is 44.04 °. The experimental results are consistent with the theoretical model