Screw pump for Electro-Hydrostatic Actuator that enhances backdrivability

Force sensitivity and backdrivability are vital functionality of actuators to be used in robots that physically interact with humans. Electro-Hydrostatic Actuator (EHA) is a type of a hydraulic actuator with backdrivability. To improve backdrivability of an EHA, reduction of friction, especially static friction is important. This, however, is difficult because most of the hydraulic pumps require sliding contacts between mechanical components. A viscous screw pump is a variation of a viscous pump that transfers mechanical kinetic energy to fluidic kinetic energy with viscous friction of the fluid. Since this class of pumps does not require mechanical contacts between the rotor and the stator, they are pumps with least static friction. In this paper, design and development of a screw pump targeted for use in an electro-hydrostatic actuator to improve the backdrivability of the actuator system is presented. Pressure-Flow discharge performance of the developed pump and backdrivability performance when combined with a vane motor were evaluated.