Clutchable Fabric Actuator for Energy-Efficient Wearable Robots

Energy-efficient yet energy-dense soft actuators are essential for untethered wearable robots. This work reports a fabric-like actuator, combining shape memory alloy (SMA) springs and electrostatic clutches (ESClutches). The SMA springs provide high force density, with only 18 g of materials generating 40 N of force at actuation strains of over 35%, but requiring 78 W of power to hold that strain. The ESClutches cannot generate motion on their own, but can maintain the force and contraction generated by SMAs consuming only a few mW, thus allowing the SMAs to be turned off. By combining SMAs and ESClutches, a soft wearable fabric actuator is developed with force and stroke suited for an upper-limb soft exoskeleton, able to lock in any given position using negligible power. The design is scalable: the number and dimensions of the SMA springs and of the ESClutches can be chosen to meet size and actuator performance requirements. This work reports two wearable use cases, where the combined SMAs and ESClutches consume over 70% lower power than SMAs alone.