Compliant motion control for a compliant rehabilitation system

In the previous study [1], an arm exoskeleton was proposed to be worn across the elbow joint of an amputee's residual limb using a pneumatic circuit. The pneumatic circuit provides not only the elastic element in a series elastic actuator (SEA), but also a flexible power transmission. The use of a customised cylinder on the off-grounded exoskeleton, however, imposes restrictions on the range of motion and reducing weight. In this study, a simple and light rotary pneumatic transmission is developed to be replaced with the cylinder. This device increases the range of motion. Also, control strategies for the pneumatic system is analyzed, focusing on compliance. Based on the positive effect of impedance control augmented with dynamics compensation on further reducing the driving-point impedance, an impedance controller for the system is proposed. The controller is model-free, robust, and simple to implement. A simulation study is provided to validate the efficacy of the impedance controller for the pneumatic circuit system for an elbow exoskeleton.