3m Long Electrohydrodynamic Fiber Pumps for Powering Soft Fluidic Actuators

Electrohydrodynamic (EHD) fiber pumps consist of a soft tube in which two helical copper wires are embedded, such that the wires are in electrical contact with the dielectric liquid (e.g. Novec 7100). When a voltage of several kV is applied between the two wires, charge injection EHDs lead to fluid flow. In prior work [1], we achieved flow rates of 0.9 mL/s and pressures of 100 kPa/m for pumps 20 to 80 cm long with a 1.5 mm inner diameter. Those pumps generated pressures between 20 and 80kPa. However, fully inflating a typical McKibben muscle requires pressures in the order of 600 kPa. Using such EHD fiber pumps to drive such fluidic actuators therefore calls for a) longer fibers, and b) higher performance. We report here 3 m long pumps, generating pressures up to 380 kPa/m, with 10-fold higher fluidic output per meter than our earlier work. We lift 2 kg loads using such pumps.<br/><br/>We developed a manufacturing tool to fabricate multi-meter long EHD fibers. Our previous methods involved winding copper and thermoplastic polyurethane (TPU) threads on a metal rod and then fusing the TPU filaments in an oven, a process limited by the oven's size. Our new machine works in a reel-to-reel manner, winding the copper wires and TPU filaments around a 20 m long flexible Teflon tube, using an inline heater to fuse the TPU in a continuous process. The Teflon tube is easily removed from the final fiber pump.<br/><br/>After fabrication, to remove an oxide layer that likely formed on the copper during the heating process, we fill the pumps with glacial acetic acid, wait 10 minutes, rinse with DI water, and dry the pump. The 1 m to 3 m long pumps made with the reel-to-reel process had performance in line with our earlier work.<br/><br/>Pump performance was then improved by reducing the spacing between the copper wires from 0.8 mm to 0.4 mm. This modification increased the electric field strength and enabled the generation of pressures of 380 kPa/m and flowrates of 2.5 mL/s—a tenfold increase in power output per meter. The efficiency at maximum power increased to 4%, doubling the previous result.<br/><br/>We use a 1.3 meter-long EHD pump to drive a 68 cm long, 5 mm diameter McKibben actuator. This EHD-powered actuator could lift a 2.1 kg load by 15 cm in 15 seconds. Our EHD fibers now generate sufficient pressure to fully contract standard McKibben actuators, allowing us to. replace traditional compressors with soft pumps. In the future, both the EHD fibers and McKibben actuators will be integrated into a textile so that they can be easily incorporated into a wearable exo-suit.