Safe High Stiffness Impedance Control for Series Elastic Actuators using Collocated Position Feedback

Physical human-robot interaction applications re-quiring safety and compliance characteristics usually employ mechanical devices as series elastic actuators (SEAs). Impedance control schemes for SEAs have been investigated to overcome the limited displayable stiffness at the end-point, represented by the stiffness of the physical spring, in a passive way. SEAs usually mount two encoders on both motor and load sides for position measurements. However, in many applications, the installation of a load-side encoder is not trivial, both for cost and manufacturing issues. In this scenario, a Kalman Filter (KF) based on MEMS accelerometers has been proposed for external force and load side quantities estimation. A novel impedance control scheme exploiting this approach is proposed, to effectively overcome the stiffness of the physical spring while maintaining passivity at the end-point. Compared to conventional load side encoder-based impedance control schemes, the proposed one presents comparable performances, as shown by simulation and experimental results.