Viscous pump for highly backdrivable Electro-Hydrostatic Actuator

It is widely acknowledged that the actuator´s intrinsic backdrivability is important in realizing a force sensitive behavior. It is desirable to realize such actuator with electric motor that is advantageous from power-to-weight ratio and controllability point of view. Electro-Hydrostatic Actuator is a type of hydraulic actuators that can realize high backdrivability by reducing transmission friction and by providing dynamics decoupling with an implicit serial damper. To farther enhance the backdrivability of a EHA, a pump with minimum static and Coulomb friction is necessary. In this paper, we introduce an EHA with viscous screw pump that minimizes static and Coulomb friction by eliminating the mechanical contact between pump components. Viscous screw pumps also have the advantage that there is no pulsation in pressure due to the continuity of the force transmission from the rotor to the fluid. The property of the actuator, including pulsation performance and impedance control performance were evaluated on a prototype of EHA with a viscous screw pump.