A Compact Transmitted-force-sensing Series Elastic Actuator with Optimized Planar Torsional Spring for Exoskeletons

Series elastic actuator (SEA), which enables torque-based control, is widely used in human-robot interaction applications such as exoskeletons. However, it is not yet widely used due to the trade-off between size and control performance. In this study, a compact transmitted-force-sensing SEA (TFSEA) module is introduced, applying a cycloid reducer and a planar torsional spring(PTS). A novel spring design with the optimal circumferential profile, which can maximize the length and the radius of curvature, is proposed and quantitatively compared to the previously studied profiles using finite element analysis. The proposed spring design showed a higher deformation when the same torque was applied. Low hysteresis and symmetry of the deformation are verified by experiment. Also, high-frequency torque control performance is evaluated by a reference-tracking experiment using a feedback controller.