A 3-Phase Electrostatic Clutch with Variable Mechanical Impedance Control for Soft Robotic Systems

Various studies have explored mechanical impedance control strategies in soft actuators to enhance stability and precision, as the nonlinear characteristics of soft materials frequently lead to unwanted oscillations. Among these approaches, electrostatic (ES) clutches have shown promise for achieving friction-based mechanical impedance control; however, conventional ES clutches are limited by issues such as residual charge accumulation and stick-slip behavior, which compromise force stability and reliability over time. To address these limitations, this study introduces a 3-phase ES clutch with variable mechanical impedance control, designed to enable continuous friction modulation and thereby reduce force degradation and oscillatory motion. Experimental validation was conducted through tensile tests and mechanical impedance applications in an MCK (Mass-Damper-Spring) vibration system, where the 3-phase ES clutch demonstrated stable friction characteristics without performance loss over repeated activations. When incorporated into a wearable assistive device, the clutch effectively delivered torque assistance for lower-limb movements, demonstrating its potential to achieve precise control of mechanical impedance in wearable systems. These findings suggest that the proposed 3-phase ES clutch offers a robust and adaptable solution for friction modulation and mechanical impedance in soft robotic and wearable systems, effectively addressing the key limitations of conventional ES clutch technology.