Sit-to-Stand movement assistance using an actuated knee joint orthosis

Sitting down and standing up from a chair are pre-requisite activities for any upward moving activities such as standing, walking, climbing stairs, etc. They are performed many times in a single day by elderly and dependent people with the help of external aids. In this context, we present a prototype of wearable orthosis device designed to help and assist the movements of dependent persons for the standing activity. A person in sitting/standing position is modeled by a triple inverted pendulum with both feet fixed to the ground. Human body consists of shank, thigh and HAT (Head-Arms-Trunk) segments. Dynamic model of the human body-orthosis is presented and its parametric identification is performed using different techniques. Known for its robustness with respect to external disturbances and model uncertainties, a Second order Sliding Mode Controller (SoSMC) is used to drive the orthosis. Experimental results are performed with a healthy subject during standing up movements. Robustness of the controller in terms of external disturbances is also shown.