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：被称为HASEL致动器的软体电液致动器因其卓越的动态性能和高输出功率而引起了广泛的研究兴趣。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，不仅解释了直流电压下位移的下降现象，还预测了交流方波电压下具有振荡的相对稳定位移。该数学模型通过实际位移验证了模型预测的趋势而得到确认。为了平滑交流电压引入的位移振荡，引入了串联弹性元件，形成了SE-HASEL致动器。采用比例积分算法的反馈控制使SE-HASEL致动器能够消除顽固的位移迟滞现象。我们的研究结果表明，通过所提出的方法，SE-HASEL致动器能够实现稳定且平滑的位移，并同时具备吸收外部冲击干扰的能力。基于SE-HASEL致动器开发了一个旋转关节，以证明其在广泛机器人应用中产生常见旋转运动的可能性。更重要的是，本文还提出了一种可用于MRI引导手术的高精度穿刺活检机器人。总体而言，我们实现了能够输出稳定平滑位移的交流驱动串联弹性电液致动器。