A Double-differential Actuation for an Assistive Hip Orthosis

The population ageing implies an increasing need for support especially in terms of mobility. Actuated orthoses offer new possibilities to assist walking by compensating the diminished muscular force which occurs with age. In order to assist efficiently the user, the orthotic device needs to provide torque without constraining the voluntary movements. Transparency is therefore a critical characteristic. A first implementation of such a device using a conventional actuation is presented and its limitations are analyzed. The walking trajectory being a cyclic movement, the actuator often needs to accelerate and decelerate. Its dynamics is therefore crucial and can be problematic at the higher cadences. Dual-differential actuation is therefore presented as a profitable alternative to overcome these weaknesses.