AC Square Wave Voltage-Driven Series Elastic Electrohydraulic Actuator With Stable and Smooth Displacement Output for Robotic Applications

Soft electrohydraulic actuators, also known as hydraulically amplified self-healing electrostatic (HASEL) actuators have attracted widespread research interest due to their outstanding dynamic performance and high output power. However, the displacement of electrohydraulic actuators usually declines with time with a constant dc voltage, which hampers its prospective application. In this article, a systematic model is first established to not only explain the inconsistent behaviors in the displacement of electrohydraulic actuators with dc voltage but also predict the relatively stable displacement with oscillation with ac square wave voltage, with further experimental validation. To smooth the displacement oscillation introduced by ac voltage, a serial elastic component is incorporated to form a series elastic HASEL (SE -HASEL) actuator. A feedback control with a proportion-integration algorithm enables the SE-HASEL actuator to eliminate the obstinate displacement hysteresis. The results revealed that, through the proposed methodology, the SE-HASEL actuator can simultaneously provide stable and smooth displacement. Furthermore, to demonstrate the potential applications, this article also proposes a highly accurate needle biopsy robot and a rotary robotic joint based on the SE-HASEL actuator. Overall, this study has achieved ac voltage-driven series elastic electrohydraulic actuators that can output stable and smooth displacement.