Fuji Technology Press Ltd. Acta Medica Okayama 1883-8049 37 1 2025 Fan-Shaped Pneumatic Soft Actuator that Can Operate Bending Motion for Ankle-Joint Rehabilitation Device 43 53 EN So Shimooka Faculty of Environmental, Life, Natural Science and Technology, Okayama University Hirosato Yokoya Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masanori Hamada Department of Rehabilitation Medicine, Okayama University Hospital Shun Shiomi Department of Rehabilitation Medicine, Okayama University Hospital Takenori Uehara Department of Orthopaedic Surgery, NHO Okayama Medical Center Takahiro Hirayama Department of Emergency, Critical Care and Disaster Medicine, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Tetsushi Kamegawa Faculty of Environmental, Life, Natural Science and Technology, Okayama University Nowadays, owing to declining birthrates and an aging population, patients and the elderly requiring rehabilitation are not getting enough physical activity. In addressing this issue, devices for rehabilitating them have been researched and developed. However, rehabilitation devices are almost exclusively used for patients who can get up, rather than those who are bedridden. In this study, we aim to develop a rehabilitation device that can provide passive exercise for bedridden patients. The ankle joint was selected as the target joint because the patients who have undergone surgery for cerebrovascular disease remain bedridden, and early recovery in the acute stage is highly desirable. We proposed and tested a fan-shaped pneumatic soft actuator (FPSA) that can expand and bend stably at angles when supply pressure is applied as an actuator for a rehabilitation device to encourage patient exercise. However, the previous FPSA’s movement deviates from the arch of the foot owing to increased supply pressure. In the ideal case, FPSA should push the arch of the foot in an arc motion. This study proposes and tests the FPSA that can operate a bending motion to provide passive exercise to the ankle joint using tensile springs and a winding mechanism powered by a servo motor. The proposed FPSA has a significant advantage of exhibiting no hysteresis in its pressure-displacement characteristics. The configuration and static analytical model of the improved FPSA are described. No potential conflict of interest relevant to this article was reported.