Optimal control of elastic joints with variable damping

Viscoelastic joints with adjustable physical impedance have recently become very popular in robotics research. Making use of the energy stored in elastic elements and changing simultaneously their elastic properties, performance of these joints are shown to be substantially increased compared to their rigid counterparts of the same size. After our recent results on how to optimally alter a joint's elastic property to maximize its energy, we focus in this paper on elastic joints with controllable damping. In particular, we show the existence of optimal switching patterns, which follow a physical rule in terms of the obtained potential and kinetic energy similar to joints with adjustable elasticity. This insight complements our existing results and contributes to further understanding of elastic robot control.