{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,25]],"date-time":"2026-09-25T04:59:13Z","timestamp":1790312353296,"version":"4.1.0"},"reference-count":26,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T00:00:00Z","timestamp":1789948800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["25K17531"],"award-info":[{"award-number":["25K17531"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"award":["25K17531"],"award-info":[{"award-number":["25K17531"]}],"id":[{"id":"https:\/\/ror.org\/00hhkn466","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Soft actuators capable of flexible motion have been actively studied and developed. Soft actuators that can extend and bend have been developed; however, soft rotary actuators have rarely been reported. In our previous studies, a soft rotary actuator (SRA) that generates rotational motion by constraining extension-type soft actuators (EFPAs) in a spiral shape was developed. However, the SRA had the limitation of rotating only in one direction, either clockwise or counterclockwise. In this paper, we aim to develop a symmetric bidirectional soft rotary actuator (SB-SRA) that achieves comparable rotational performance in both clockwise and counterclockwise directions while maintaining the flexibility of polymeric materials, such as rubber, and allowing static hysteresis adjustment. In particular, arranging several EFPAs so that they do not interfere with each other during extension enables the SRA to generate both clockwise and counterclockwise rotational motion. Unlike previously reported unidirectional soft rotary actuators, and unlike rigid antagonistic bidirectional joints that require bearings and a dedicated brake, the proposed SB-SRA achieves symmetric bidirectional rotation with a bendable rotational axis and enables static hysteresis compensation using only the opposing actuators. The results show that the maximum rotation angle and torque of the SB-SRA are approximately 105\u00b0 and 0.51 Nm, respectively, under an input pressure of 500 kPa. The maximum directional differences between clockwise and counterclockwise operation were 3.3% for the rotation angle and 2.4% for the torque, demonstrating approximately symmetric output characteristics. In addition, static hysteresis adjustment can be achieved by varying the supply pressures applied to the opposing EFPAs.<\/jats:p>","DOI":"10.3390\/s26185978","type":"journal-article","created":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T10:21:48Z","timestamp":1790072508000},"page":"5978","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["A Symmetric Bidirectional Soft Rotary Actuator with a Bendable Shaft Driven by Extension-Type Pneumatic Actuators"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-1598-3254","authenticated-orcid":false,"given":"So","family":"Shimooka","sequence":"first","affiliation":[{"name":"Faculty of Environmental, Life, Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shunsuke","family":"Mori","sequence":"additional","affiliation":[{"name":"Faculty of Environmental, Life, Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tetsushi","family":"Kamegawa","sequence":"additional","affiliation":[{"name":"Faculty of Environmental, Life, Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2000128","DOI":"10.1002\/aisy.202000128","article-title":"Soft Actuators for Soft Robotic Applications: A Review","volume":"2","author":"Mishra","year":"2020","journal-title":"Adv. Intell. Syst."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1038\/s41578-021-00389-7","article-title":"Soft actuators for real-world applications","volume":"7","author":"Li","year":"2022","journal-title":"Nat. Rev. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"251","DOI":"10.20965\/jrm.2024.p0251","article-title":"Fluid-Driven Soft Actuators for Soft Robots","volume":"36","author":"Nakamura","year":"2024","journal-title":"J. Robot. Mechatron."},{"key":"ref_4","unstructured":"Noritsugu, T. (2005, January 7\u201310). Pneumatic Soft Actuator for Human Assist Technology. Proceedings of the 6th JFPS International Symposium on Fluid Power, Tsukuba, Japan."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"2100140","DOI":"10.1002\/aisy.202100140","article-title":"Soft Actuators and Robotic Devices for Rehabilitation and Assistance","volume":"4","author":"Pan","year":"2022","journal-title":"Adv. Intell. Syst."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"59442","DOI":"10.1109\/ACCESS.2022.3179589","article-title":"Soft Pneumatic Actuators: A Review of Design, Fabrication, Modeling, Sensing, Control and Applications","volume":"10","author":"Xavier","year":"2022","journal-title":"IEEE Access"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"204","DOI":"10.1089\/soro.2017.0044","article-title":"Design of a Lightweight Soft Robotic Arm Using Pneumatic Artificial Muscles and Inflatable Sleeves","volume":"5","author":"Ohta","year":"2018","journal-title":"Soft Robot."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"nwab048","DOI":"10.1093\/nsr\/nwab048","article-title":"Muscle-Fiber Array Inspired, Multiple-Mode, Pneumatic Artificial Muscles through Planar Design and One-Step Rolling Fabrication","volume":"8","author":"Zou","year":"2021","journal-title":"Natl. Sci. Rev."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"123301","DOI":"10.1115\/1.4065522","article-title":"Optimized Design of a Soft Actuator Considering Force\/Torque, Bendability, and Controllability via an Approximated Structure","volume":"146","author":"Yang","year":"2024","journal-title":"J. Mech."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Yang, W.T., Stuart, H.S., K\u00fcrk\u00e7\u00fc, B., and Tomizuka, M. (2024, January 15\u201319). Nonlinear Modeling for Soft Pneumatic Actuators via Data-Driven Parameter Estimation. Proceedings of the 2024 IEEE\/ASME International Conference on Advanced Intelligent Mechatronics, Boston, MA, USA.","DOI":"10.1109\/AIM55361.2024.10637145"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"113222","DOI":"10.1016\/j.sna.2021.113222","article-title":"A pneumatic rotary actuator for forceps tip rotation","volume":"333","author":"Fukushima","year":"2022","journal-title":"Sens. Actuators A Phys."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"527","DOI":"10.1089\/soro.2017.0040","article-title":"A new spiral-type inflatable pure torsional soft actuator","volume":"5","author":"Yan","year":"2018","journal-title":"Soft Robot."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"10","DOI":"10.5739\/jfpsij.12.10","article-title":"Improvement of home portable rehabilitation device for upper-limbs","volume":"12","author":"Shimooka","year":"2019","journal-title":"JFPS Int. J. Fluid Power Syst."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"114603","DOI":"10.1016\/j.sna.2023.114603","article-title":"A soft rotary actuator with a flexible shaft using flexible pneumatic actuators","volume":"361","author":"Shimooka","year":"2023","journal-title":"Sens. Actuators A Phys."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Hawkes, E.W., Christensen, D.L., and Okamura, A.M. (2016, January 16\u201321). Design and implementation of a 300% strain soft artificial muscle. Proceedings of the 2016 IEEE International Conference on Robotics and Automation, Stockholm, Sweden.","DOI":"10.1109\/ICRA.2016.7487592"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Skorina, E.H., Rahbar, N., Luo, M., Oo, W.Y., Tao, W., Chen, F., Youssefian, S., and Onal, C.D. (2018). Reverse pneumatic artificial muscles (rPAMs): Modeling, integration, and control. PLoS ONE, 13.","DOI":"10.1371\/journal.pone.0204637"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"111623","DOI":"10.1016\/j.sna.2019.111623","article-title":"Development of the extension type pneumatic soft actuator with built-in displacement sensor","volume":"300","author":"Azami","year":"2019","journal-title":"Sens. Actuators A Phys."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1359","DOI":"10.1016\/j.bbe.2020.08.002","article-title":"Simulation analysis for optimal design of pneumatic bellow actuators for soft-robotic glove","volume":"40","author":"Guo","year":"2020","journal-title":"Biocybern. Biomed. Eng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"112578","DOI":"10.1016\/j.sna.2021.112578","article-title":"Flexible push pneumatic actuator with high elongation","volume":"321","author":"Fracczak","year":"2021","journal-title":"Sens. Actuators A Phys."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Ito, F., Itsuno, T., and Nakamura, T. (2024). MD-LUFFY: Massively Deformed Linearly-elongation-actuator Using Flexible Fiber and Yarn-Fundamental Characteristics on Elongation\/contraction and Expansion rate. 2024 IEEE International Conference on Advanced Intelligent Mechatronics, Boston, MA, USA, 15\u201319 July 2024, Institute of Electrical and Electronics Engineers (IEEE).","DOI":"10.1109\/AIM55361.2024.10637060"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"9828","DOI":"10.1038\/s41598-026-40604-5","article-title":"Design, manufacturing, and testing of a novel omnidirectional soft sleeve actuator","volume":"16","author":"Abboodi","year":"2026","journal-title":"Sci. Rep."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1800429","DOI":"10.1002\/admt.201800429","article-title":"Vacuum-Powered Soft Pneumatic Twisting Actuators to Empower New Capabilities for Soft Robots","volume":"4","author":"Jiao","year":"2019","journal-title":"Adv. Mater. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"395","DOI":"10.1089\/soro.2021.0185","article-title":"Origami-Inspired Soft Twisting Actuator","volume":"10","author":"Li","year":"2023","journal-title":"Soft Robot."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"550","DOI":"10.1177\/02783649241273662","article-title":"A New Design and Analysis of Low-Profile Soft Rotary Pneumatic Actuator for Enhanced Rotation and Torque","volume":"44","author":"Lee","year":"2025","journal-title":"Int. J. Robot. Res."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"031003","DOI":"10.1115\/1.4026629","article-title":"Pneumatic Torsional Actuators for Inflatable Robots","volume":"6","author":"Sanan","year":"2014","journal-title":"J. Mech. Robot."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"8584798","DOI":"10.1155\/2021\/8584798","article-title":"Study on the Structure and Performance of an Antagonistic Pneumatic Bidirectional Rotary Joint","volume":"2021","author":"Liu","year":"2021","journal-title":"Math. Probl. Eng."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5978\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,25]],"date-time":"2026-09-25T04:10:51Z","timestamp":1790309451000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5978"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,21]]},"references-count":26,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["s26185978"],"URL":"https:\/\/doi.org\/10.3390\/s26185978","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,21]]}}}