Progressive Series-Elastic Actuation with Magnet-based Non-linear Elastic Elements

We present the design and development of a non-linear series-elastic element based on repelling magnets. Progressive stiffness offers the transparency advantages of a low-stiffness elastic actuator at low load levels, and the high torque tracking bandwidth of a high-stiffness actuator at high loads. The design space of this magnet-based concept is thoroughly analysed, for both box- and arc-segment magnets. A proof-of-concept prototype is presented which is experimentally validated. A gain-scheduled torque controller is used to exploit its non-linear dynamics. Simulation and experimental results demonstrate the viability of the concept.