Soft electrohydraulic actuators known as 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 under constant DC voltage, which hampers its prospective application. A mathematical model is firstly established to not only explain the decrease in displacement under DC voltage but also predict the relatively stable displacement with oscillation under AC square wave voltage. The mathematical model is validated since the actual displacement confirms the trend observed by our model. To smooth the displacement oscillation introduced by AC voltage, a serial elastic component is incorporated to form a SE-HASEL actuator. A feedback control with a proportion-integration algorithm enables the SE-HASEL actuator to eliminate the obstinate displacement hysteresis. Our results revealed that, through our methodology, the SE-HASEL actuator can give stable and smooth displacement and is capable of absorbing external impact disturbance simultaneously. A rotary joint based on the SE-HASEL actuator is developed to reflect its possibility to generate a common rotary motion for wide robotic applications. More importantly, this paper also proposes a highly accurate needle biopsy robot that can be utilized in MRI-guide surgical procedures. Overall, we have achieved AC-driven series elastic electrohydraulic actuators that can exhibit stable and smooth displacement output.

翻译：软电液致动器（HASEL致动器）因其优异的动态性能和高输出功率而受到广泛研究关注。然而，在恒定直流电压下，电液致动器的位移通常会随时间衰减，这阻碍了其潜在应用。本文首先建立了一个数学模型，该模型不仅能解释直流电压下位移的下降现象，还能预测交流方波电压下带有振荡的相对稳定位移。实际位移验证了模型所揭示的趋势，从而证实了该数学模型的正确性。为平滑交流电压引入的位移振荡，本文引入串联弹性组件，构成SE-HASEL致动器。采用比例积分算法的反馈控制使SE-HASEL致动器能够消除难以抑制的位移迟滞。研究结果表明，通过本文方法，SE-HASEL致动器可实现稳定平滑的位移输出，同时具备吸收外部冲击干扰的能力。基于SE-HASEL致动器开发了旋转关节，以验证其在广泛机器人应用中产生常规旋转运动的可行性。更重要的是，本文还提出了一种可用于磁共振引导手术的高精度穿刺活检机器人。综上所述，我们成功实现了交流驱动的串联弹性电液致动器，其可展现稳定平滑的位移输出。