{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,19]],"date-time":"2026-05-19T01:30:49Z","timestamp":1779154249795,"version":"3.51.4"},"reference-count":25,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2022,4,22]],"date-time":"2022-04-22T00:00:00Z","timestamp":1650585600000},"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":["20K04240"],"award-info":[{"award-number":["20K04240"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001700","name":"Ministry of Education, Culture, Sports, Science and Technology","doi-asserted-by":"publisher","award":["Grant for the Promotion of Science and Technology in Okayama Prefecture by The Ministry of Education"],"award-info":[{"award-number":["Grant for the Promotion of Science and Technology in Okayama Prefecture by The Ministry of Education"]}],"id":[{"id":"10.13039\/501100001700","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A thin McKibben artificial muscle is a pneumatic actuator with an outer diameter of only 1.8 mm. We fabricated a string-shaped actuator called an \u201cactive string actuator,\u201d which achieves a high contractile displacement by accumulating thin McKibben artificial muscles. To control the displacement, the length of the active string actuator should be estimated. However, this is difficult because bulky and rigid sensors are unsuitable for the sensor element of the active string actuator. Therefore, in this study, we propose a new sensing method for estimating the length of an active string actuator. The proposed sensing system is simple and comprises only three components: a step-index multimode optical fiber, a light emitter, and a light receiver. A step-index multimode optical fiber was combined with the active string actuator, and the length was estimated from the change in the amount of light propagating in the optical fiber when the active string actuator was driven. Fundamental experiments were conducted in this study, and the results demonstrated that the optical fiber sensor value changed with the actuator length. This suggests that it is possible to estimate the displacement of an active string actuator using an optical fiber sensor.<\/jats:p>","DOI":"10.3390\/s22093232","type":"journal-article","created":{"date-parts":[[2022,4,24]],"date-time":"2022-04-24T00:45:21Z","timestamp":1650761121000},"page":"3232","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Displacement Sensing of an Active String Actuator Using a Step-Index Multimode Optical Fiber Sensor"],"prefix":"10.3390","volume":"22","author":[{"given":"Weihang","family":"Tian","sequence":"first","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5591-6161","authenticated-orcid":false,"given":"Shuichi","family":"Wakimoto","sequence":"additional","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Takefumi","family":"Kanda","sequence":"additional","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6870-5048","authenticated-orcid":false,"given":"Daisuke","family":"Yamaguchi","sequence":"additional","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,4,22]]},"reference":[{"key":"ref_1","unstructured":"Gaylord, R.H. 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