Design of ankle rehabilitation robot with antagonistic nitinol wire actuators

Foot drop is a major symptom suffered by stroke patients. Annually, there are millions of the individuals affected by this condition. Treating stroke is expensive and labour intensive. Over the years, robots have demonstrated their effectiveness in rehabilitating foot drop. However, these robots are bulky and generate a sudden burst of power, which can be undesirable in a rehabilitation setting. A Nitinol wire is known for its high power-to-weight ratio and ability to generate smooth and gentle motion. Therefore, this work uses the Nitinol wire as the mechanical energy source to create a portable and human movement mimicry platform type ankle rehabilitation robot. Unlike other actuators that utilise spring or external load as the bias force, which can be linear or erratic; this robot uses a pair of Nitinol wire actuators to work antagonistically to provide foot dorsiflexion and plantarflexion motions during rehabilitation exercise. Results showed that the robot can generate smooth nonlinear motion, and seamless activation and transition between the two actuators, thus reducing the risk of an ankle injury. They also demonstrated the prospect of Nitinol wire as an alternative source of mechanical motion for a rehabilitation robot.