Development of 6-DOF manipulator driven by ceramics reinforced hydrostatic actuators and its experimental evaluations on force control and payload abilities

Abstract

The purpose of the Hydracer project is to discuss the system performance of the EHAs (Electro-Hydrostatic Actuators) when integrated into robotic systems. We have developed EHAs focusing on compactness, light-weight, force controllability, and back-drivability. The requirements such as compactness and light-weight lead us to the adoption of high-pressure, which unfortunately contradicts with the other requirements, namely, force controllability and back-drivability. The contradiction indicates the necessity of study to find the balanced specification between them, which was the question we raised when we started the development of Hydracer, a 6-DOF manipulator driven by EHAs. The system design started following the specifications of an industrial standard of small-size manipulators. In the previous paper, we reported on the design and evaluation of actuators, namely, the linear EHA modules for the first three joints from the base and the ceramic-reinforced vane motors for the last three. We could also discuss the preliminary results of force control of the last three (wrist) joints. In this paper, we report on the performance of force-controllability and backdrivability of the first three joints of the manipulator after integrating force controllers and gravity compensation. It provides useful information about the total performance of manipulators driven by EHAs. The RMSEs (root mean square errors) of torques of the first three joints under the gravity compensation were 0.53, 1,7, and 1.2 Nm respectively, while the manipulator could carry 10 kg payload at the horizontally stretched configuration for 5 s.

GRAPHICAL ABSTRACT

Keywords:

• Hydraulic actuators
• manipulator
• flexible robots
• backdrivability

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 In Ordinance on Industrial Safety and Health, Article 150-4.

2 http://www.nachi-fujikoshi.co.jp/eng/rob/hand/mz04a.htm.

3 A force sensor is mounted only on the end-effector.

Additional information

Funding

This work was supported by the joint research of the University of Tokyo and Nachi-Fujikoshi CORP. titled ‘Development of an Electro Hydrostatic Driven Robot System (High-Pressure Drive System/Hand/Manipulator)’.

Notes on contributors

Mitsuo Komagata

Mitsuo 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.

Yutaro Imashiro

Yutaro Imashiro received his master degree in Mechano-Informatics from the University of Tokyo in 2021. His research interests include control of a robotic manipulator.

Ryoya Suzuki

Ryoya Suzuki received his master degree in Mechano-Informatics from the University of Tokyo in 2019. His research interests include mechanical design of hydraulic actuators.

Kento Oishi

Kento Oishi received his master degree in Mechano-Informatics from the University of Tokyo in 2022. His research interests include control of a robotic manipulator.

Ko Yamamoto

Ko 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, and also, Visiting Associate Professor with Stanford University in 2024. 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 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 is a Member of the Japan Society of Mechanical Engineers, the Robotics Society of Japan and IEEE.

Yoshihiko Nakamura

Yoshihiko Nakamura is Professor and Chair of Robotics Department, Mohamed bin Zayed University of Artificial Intelligence, Abu Dhabi, UAE. He is CEO of Kinescopic, Inc. He received Ph.D. degree in mechanical engineering from Kyoto University. He held faculty positions at Kyoto University, University of California Santa Barbara and University of Tokyo before joining MBZUAI in 2024. He is Professor Emeritus of University of Tokyo. Prof. Nakamura's fields of research are humanoid robotics, biomechanics, human digital twin and their computational algorithms. He received King-Sun Fu Memorial Best Transactions Paper Award, IEEE Transaction of Robotics and Automation in 2001 and 2002. He is also 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. He is Foreign Member of Academy of Engineering Science of Serbia, TUM Distinguished Affiliated Professor of Technische Universität München, Life Fellow of IEEE and Fellow of Japan Society of Mechanical Engineers, Robotics Society of Japan and World Academy of Art and Science.