Standalone Thermopneumatic Micro Bellows Actuator using 3D Printing Technology

By adopting an independent battery-powered mechanism, typical pneumatic soft micro actuators can be manufactured without using heavy driving components such as pumps and power supplies. This paper presents manufacturing a thermopneumatically operated soft micro bellows actuator and its experimentally validated standalone operation. Thermopneumatic actuation is based on heating a cavity sealed by elastomer of the actuator to raise the pressure, which consequently leads to deflection of the elastomer. The bellows actuator was made by casting polydimethylsiloxane (PDMS) using a 3D-printed soluble mould process to avoid leakage, which is common in soft lithography due to individual layer bonding. To make a thermopneumatic actuator, a heater made separately from winding copper wire was inserted into the cavity of the bellows actuator. Combination of both 3D coil heater and bellows actuator allowed immediate heat transfer and free movement of the actuator in the intended direction, which is unachievable for conventional microfabrication. The fabricated actuator produced a stroke of about 2200 m, equivalent to 62% of its body length and exerted a force of approximately 90 mN at a voltage of 0.55 V. Instead of the conventional pneumatic operation, the thermopneumatic actuator was also able to demonstrate a repetitive standalone operation with the system consists of alkaline batteries and a control circuit.