Development of Backdrivable Servovalve with Feedback Spring for Enhanced Electro-Hydraulic Torque Actuator

This letter proposes a novel backdrivable servovalve to implement a torque-controlled electro-hydraulic actuator. The proposed backdrivable servovalve simultaneously contains the characteristics of a flow-control servo valve (=feedback spring) and a pressure-control servovalve (=pressure feedback port). Consequently, the torque control performance of electro-hydraulic torque actuators (EHTAs), which consist of the backdrivable servovalve and rotary vane-type hydraulic actuators, can be enhanced. First, the effective torque bandwidth, which represents the region where the torque output remains constant within a 90 degrees phase lag, is improved. Second, torque-based control algorithms developed for electric motors are realized in a wide frequency region. Finally, although the effect of viscous friction increases, the effect of static friction is reduced. With these advantages, we achieved an enhanced EHTA with calculated torque output of -372 similar to 355 Nm; this could facilitate in the development of a high-performance interactive robot system. The proposed backdrivable servovalve and enhanced EHTA were evaluated through experiments.