Current-pressure-position triple-loop feedback control of electro-hydrostatic actuators for humanoid robots. (17th December 2018)

• Record Type: Journal Article
• Authors: Ko, Tianyi; Kaminaga, Hiroshi; Nakamura, Yoshihiko
• Is Part Of: Advanced robotics. Volume 32:Number 24(2018)
• Page Start: 1269
• Page End: 1284
• Publication Date: 2018-12-17
• Subjects: Actuator -- EHA -- hydraulic -- force control -- backdrivability; Robotics -- Periodicals; Robotics -- Japan -- Periodicals; Robotics; Japan; Periodicals; 629.89205
• DOI: 10.1080/01691864.2018.1555880
• Languages: English
• ISSNs: 0169-1864

Abstract

ABSTRACT: To overcome the tradeoff between torque density and response of the backdrivable actuators, actuation by electro-hydrostatic actuators (EHA) is effective. While their backdrivability and energy efficiency was shown in the previous studies, their closed-loop dynamic behavior was not discussed in detail. In this paper, we present the analysis and experimental evaluation of the force control performance of the electro-hydrostatic actuator for the humanoid robot 'Hydra'. We first present a simplified model of EHA and show that EHA can be simplified as a mass-spring-damper model if all values such as pump torque/velocity and fluid pressure/flow-rate are expressed in the equivalent value seen from the actuator. We also show the comparison between the model and experimentally acquired open-loop dynamic behavior. Then, the evaluation on the force measurement and control performance is shown. The static friction on the rod-seal was 0.46% of the maximum piston force, and with additional strain gauge information, the error can be reduced to 0.28% of the maximum force. We also show that our developed EHA has a pressure control bandwidth of 100 Hz in the fixed piston configuration, which is higher than other state-of-the-art series elastic actuators. In the last of paper, the joint level position and torque control performance of Hydra is examined. GRAPHICAL ABSTRACT: