High-performance low-voltage soft electrothermal actuator with directly printed micro-heater

Abstract

Soft actuators are widely studied due to their high flexibility and adaptability. In this paper, a soft electrothermal actuator with directly printed microfilament heater was designed, fabricated, and tested. In this soft actuator, a polyimide (PI) film and a polydimethylsiloxane (PDMS) layer were selected as the two structural layers because of their distinct thermal expansion properties. Embedded between these two layers, a metallic microfilament heater that was made of low-melting-point metal alloy (i.e. Bi58/Sn42) was directly printed with custom-designed pattern using an electrohydrodynamic (EHD) printing process. The pattern of the microfilament heater and the thickness of the soft thermoelectric actuator were carefully designed towards the improved actuation capability. When an electric current was applied, the high temperature generated by the resistive heater causes large mismatch in the thermal expansion of the two structural layers, which bent the actuator. The fabricated soft actuator can achieve a maximum bending curvature of 1.0 cm−1 under an extremely low voltage about 3V. The soft actuator has been demonstrated for potential applications in soft robotics as a soft lifter and a soft gripper. At the full capability, the soft lifter provided a maximum actuation force about 3 mN, and was able to fully lift a load that was twice of its own weight. A four-finger soft gripper was designed and fabricated using four soft actuators to mimic humanoid motions and was implemented for pick-and-place operation for delicate objects.