Development of compact revolute electro-hydrostatic actuator module and evaluation of its backdrivability and internal leakage

AbstractActuators of a robot that physically interacts with objects or human require backdrivability to obtain force controllability, impact resistance and compactness. An electro-hydrostatic actuator (EHA) is a servo pump type hydraulic system that has a potential to satisfy backdrivability. However, the previous mechanical design of a revolute EHA did not achieve compact design compared to the other actuators. The hydraulic pump and vane motor were separately located, which made the size of EHA system larger. To solve this problem, we propose a design methodology of a revolute EHA using a frameless motor. Commercially available frameless motor is suitable for actuating the hydraulic pump. Moreover, the pump can be built in the hollow space of the frameless motor, and this design makes the EHA downsized. We present a prototype design based on the formulation of the output power. Through the experimental validations, we show that developed EHA has higher backdrivability than the comparable harmonic drive, and obtain the knowledges on design factors that are crucial to the EHA with high power-to-weight ratio.Keywords: Electro-hydrostatic actuatorsbackdrivabilityinternal leakagemodularized design Disclosure statementNo potential conflict of interest was reported by the author(s).Notes1 http://store-en.tmotor.com/goods.php?id=8592 https://www.maxongroup.co.jp/maxon/view/content/ec-4pole-motors3 https://www.hds.co.jp/english/Additional informationFundingThis work was supported by the joint research of the University of Tokyo and Nachi-Fujikoshi CORP. titled ‘Research and development on the mechanism, control, and application of modular electro-hydrostatic actuators with high power-to-weight ratio’.Notes on contributorsMitsuo KomagataMitsuo Komagata received his BEng, MEng, and PhD degrees in Mechano-Informatics from the University of Tokyo in 2014, 2016, and 2020, respectively. He was Project Researcher at the University of Tokyo in 2020 and Project Assistant Professor at the Department of Mechano-informatics, University of Tokyo in 2020–2023. Since 2023, he works in OMRON Corporation. His research interests include actuations and mechanical design. He is a member of RSJ.Takahiro NakanishiTakahiro Nakanishi received his master degree in Mechano-Informatics from the University of Tokyo in 2021. His research interests include mechanical design of hydraulic actuators.Ko YamamotoKo Yamamoto received the PhD degree in mechano-informatics from the University of Tokyo, Tokyo, Japan, in 2009. He is an Associate Professor with the Department of Mechano-informatics, University of Tokyo. He was a Postdoctoral Research Fellow with the Tokyo Institute of Technology in2009–2012, and an Assistant Professor with Nagoya Universityin 2012–2014. He joined the University of Tokyo as an Assistant Professor in 2014, and was a Project Lecturer with the Department of Mechanical Engineering in 2016–2017. He was also a Visiting Assistant Professor with Stanford University, Stanford CA, USA, in 2012. His research interests include mechanical design, dynamics computation and motion control of humanoid robots and soft robots, biomechanical analysis based on human musculo-skeletal model, and modeling and control of swarm robots and pedestrian crowds. Dr. Yamamoto isa Member of the Japan Society of Mechanical Engineers, the Robotics Society of Japan and IEEE.Yoshihiko NakamuraYoshihiko Nakamura received Ph.D. degree in mechanical engineering from Kyoto University. He is Professor Emeritus and Project Researcher of University of Tokyo, and Cofounder/CEO of Kinescopic, Inc. He held faculty positions at Kyoto University and University of California Santa Barbara before joining University of Tokyo. His fields of research are humanoid robotics, human digital twin, and their computational algorithms. He is a recipient of JSME Medal for Distinguished Engineers in 2019, Pioneer Award of IEEE Robotics and Automation Society in 2021, and Tateisi Prize Achievement Award in 2022. Dr. Nakamura is Foreign Member of Academy of Engineering Science of Serbia, TUM Distinguished Affiliated Professor of Technische Universitat Munchen, Life Fellow of IEEE, and Fellow of Japan Society of Mechanical Engineers; Robotics Society of Japan; and World Academy of Art and Science.