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Design and Control of the Compact Cable-driven Series Elastic Actuator Module in Soft Wearable Robot for Ankle Assistance

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Abstract

For assisting the daily lives of the elderly or patients with abnormal walking by hemiplegia, wearable robots which are constructed with relatively soft materials such as cable-driven method are being actively developed and partially commercialized. The main advantage is that the flexible power transmission system could distribute the inertia of the distal area, which is essential for stabilizing the gait balance. However, in flexible power transmission system, it has disadvantage that it cannot directly measure the tension applied to the patients. Therefore, tension measurement device on the assisting point is required for generating precise assistance on the patients. But adding the tension measuring device is challenging because it increases complexity and inertia. The main factor for inaccurate force transmission is the unpredictable friction from the transmission cable’s varying curvature in human motion. In this paper, a methodology of design and control of reaction force-based series elastic actuator is proposed to generate the precise assistive force at the actuating module while maintaining the overall weight small. The mechanical elements of Series Elastic Actuator are designed with the optimal specifications required for stroke patient assistance. The compactness and weight reduction are also guaranteed by designing the mechanical elements with optimal specifications, which enables assisting the patients with minimal gravitational load. Furthermore, periodic friction compensation is done through experiments by using feedforward compensator, which adjusts the corresponding loss, linked with the estimated gait phase. Therefore, even in the presence of friction loss in the cable, application of precise torque at the end-effector became possible.

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Correspondence to Kyoungchul Kong.

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Conflict of Interest

The authors declare that there is no competing financial interest or personal relationship that could have appeared to influence the work reported in this paper.

Sumin Lee received his B.S. degree in mechanical engineering from Pusan National University (PNU), Busan, Korea, in 2020 and an M.S. degree in mechanical engineering from Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 2022. He is working toward a Ph.D. degree in mechanical engineering. His research interests include wearable robotics, actuator design, mechanism design, and design optimization.

Sanguk Choi received his B.S. (cum laude) degree in mechanical engineering from Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 2020. He is currently working toward an integrated M.S. and Ph.D. degrees in mechanical engineering. His research interests include wearable robotics and system control.

Chanyoung Ko received his B.S. degree in mechanical engineering from Yonsei University in 2021. He is currently working toward an M.S. degree in mechanical engineering from Korea Advanced Institude of Science and Technology (KAIST), Daejeon, Korea. His research interests include wearable robotics and mechanical control.

Taeyeon Kim received his B.S. and M.S. degrees in mechanical engineering from Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 2019 and 2021, respectively. He is currently working toward a Ph.D. degree in mechanical engineering. His research interests include hardware design and system control of wearable robots for assistance.

Kyoungchul Kong received his B.Eng. (summa cum laude) degree in mechanical engineering and a B.S. degree in physics from Sogang University, Seoul, Korea, in 2004, an M.S. degree in mechanical engineering from Sogang University in 2006, and a Ph.D. degree in mechanical engineering from the University of California at Berkeley, Berkeley, CA, USA, in 2009. In 2011, he joined the Department of Mechanical Engineering, Sogang University, as an assistant professor and moved to Korea Advanced Institute of Science and Technology (KAIST) as an associate professor. He has authored or co-authored more than 200 technical articles in journals and conference proceedings in the wide area of control applications and robotics, including locomotive robotics and human-robot interactive systems. His current research interests include design, modeling, and control of mechatronic systems with an emphasis on locomotion and mobility of humans. Dr. Kong received the Commendation by the Prime Minister of Korea in 2019, the Best Innovation Award from the President of Korea in 2017, the Commendation by the Minister of Commerce, Industry and Energy in 2017, the Bronze Medal of Cybathlon in 2016, the Gold and Bronze Medal of Cybathlon in 2020, the Young Researcher Award from the IFAC Mechatronics TC in 2016, and many others.

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This research was supported by a grant of the Korea Health Technology R& D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Korea (grant number: HJ20C0007).

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Lee, S., Choi, S., Ko, C. et al. Design and Control of the Compact Cable-driven Series Elastic Actuator Module in Soft Wearable Robot for Ankle Assistance. Int. J. Control Autom. Syst. 21, 1624–1633 (2023). https://doi.org/10.1007/s12555-022-0098-4

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