Design of a modular add-on compliant actuator to convert an orthosis into an assistive exoskeleton

In an ageing population many people with muscle weakness may benefit from an assisting exoskeleton to improve their mobility. Recent developments in research labs around the world are often complex, not modular and expensive. This paper introduces a novel modular compliant actuator for use in assistive lower limb exoskeletons. It is a low-cost, light-weight, compliant actuator unit that can be easily mounted on commercially available orthoses. It has the versatility to assist hip-, knee- and ankle flexion/extension individually and/or in sit-to-stance or walking activities. An adjustable passive compliance is achieved by a design based on the MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) principle. The assisting output torque and the rendered range of compliance are simulated and experimentally demonstrated.