Modeling and High-Definition Control of a Smart Electroadhesive Actuator: Toward Application in Rehabilitation

Smart actuators with tunable dynamical characteristics have shown significant potential to improve the performance of physical human-robot interaction systems, such as exoskeletons. In this regard, electroadhesive clutches, which function based on a controllable dry kinetic friction between the discs, have attracted a great deal of interest for semi-passive actuation that has a high force-to-weight ratio and low power consumption. However, the complex dynamical behavior of such an actuator has limited the potential application in dynamic tasks. This paper, for the first time, presents a robust nonlinear control law for torque-adjustable rotary electroadhesive clutches in order to guarantee smooth, agile, and stable behavior in the presence of significant unmodeled dynamics. For this, a nonlinear Lyapunov-redesign approach is proposed based on a partially-identified model, which can guarantee convergence and robustness to unmodeled dynamics. The performance of the proposed algorithm is validated through a comprehensive set of experiments, including active-resistive and coordination-assisted rehabilitation using an elbow exoskeleton designed based on the rotary electroadhesive clutch. The proposed approach shows potential for application in dynamic scenarios such as those involving assistive and wearable robots.