A Rationale for Acceleration Feedback in Force Control of Series Elastic Actuators

Series elastic actuators (SEAs) have become fundamental components in robots that physically interact with unstructured environments and humans. Force control of SEAs is indeed an active area of research. This paper proposes a theoretical foundation for acceleration feedback (AF) in SEA force control. Even if AF already appeared in early works on SEAs, its advantages have not been properly highlighted in the literature. In particular, this paper formally motivates improved performance robustness and transparency exactly as if using a softer and lighter actuator. Taking advantage of AF, we propose a generic control architecture characterized by impressive performance robustness in spite of even high environment uncertainties. A comparison with state-of-the-art force control solutions such as disturbance observers and adaptive controllers is reported using a comprehensive set of simulations and experiments. As a result, AF methods exhibit the higher performance robustness and accuracy. Beside this outcome, AF controllers are extremely easy to implement and the rise of low-cost miniaturized accelerometers based on micro electromechanical systems (MEMS) represents an additional motivations for their use.