Compact, backdrivable, and efficient design of linear electro-hydrostatic actuator module

Abstract

An electro-hydrostatic actuator (EHA) has high backdrivability and is suitable for robots that interact with the environment, including human. However, the challenging problem in its mechanical design is that it is difficult to achieve compact size and high power transmission efficiency, compared with standard gear reducers. To tackle this problem, this study presents the design method by macro- and micro-scale designs. A linear-type EHA consists of a cylinder and a hydraulic pump. The former includes cylinder parameters that are dominant in the total size, and the latter includes gap width in the gear pump that is important for reducing power loss. We propose the hierarchical design to determine these parameters. In the macro-scale design, we determine the cylinder radius and differential pressure to maximize the efficiency-to-volume ratio. Based on the result of the macro-scale design, the micro-scale design determines the width of internal gaps to minimize the power loss in the gear pump. We derive mathematical formulations for the designs and develop the EHA by utilizing modular design and 3D printing. Moreover, we evaluate the fundamental properties of the developed EHA module, focusing on its power transmission efficiency and backdrivability.