An Integrated Frameless Motor Gerotor Pump for Hydraulic Actuation of Soft Robots

Abstract

Abstract. This work presents a novel geometry for a gerotor hydraulic pump integrated into the rotor of a brushless, direct-current, frameless motor. The design eliminates excess dynamic seals and produces a pump that is more compact, more efficient, higher bandwidth, and capable of greater pressure and flow performance than any servopump previously presented at this scale. Two pumps are presented, with one capable of achieving pressures in excess of 2.9 MPa, flows up to 1.6 L/min, output power levels of 31.5 W with 25% efficiency, and operation at bandwidths up to 37 Hz in a compact form weighing 265 g. Due to its compact size and high output, the proposed design achieved a peak power density of 119 W/kg. Variations of the second produced pressures up to 2500 kPa, flows over 4.5 L/min, hydraulic power of 25 W, and weighed 410 g. The proposed design was quiet in operation, with a maximum sound pressure level at 1 m of 55.8 dBA. Because the proposed design contains no external moving parts, a simple fabric wrap reduced pump noise to a maximum of 47.7 dBA. The pump was evaluated for positional-feedback control of representative systems via integration into two setups: one driving standard rigid hydraulic pistons and one driving a soft robotic actuator. The pump was able to control these setups with positional accuracy on the order of 1 mm and angular accuracy of 2 deg, respectively.