Compliant physical interaction to enhance rehabilitation training of a parallel ankle robotic system

Isotonic exercise is an effective way to improve the ankle joint complex's (AJC) muscle strength, and a contracting muscle shortens against a constant load during the process, or in other words, the muscle maintains equal tone while shortening. In order to change the physical human-robot interaction into the reciprocating motion of the parallel ankle rehabilitation root (PARR), to improve its compliance and enhance muscle strength training, we implement the admittance-based isotonic exercise strategy on our PARR. The mechanical design of the PARR and the admittance-based isotonic exercise to change the physical human-robot interaction torque into the angle movement were described at first. Then, an adaptive law of the admittance parameters was further proposed to adaptively adjust the compliance. Experiments with neurologically intact subjects were conducted, and the experimental results showed good trajectory tracking performance and excellent practicability, which can improve muscle strength training safely.