{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,27]],"date-time":"2026-03-27T19:30:47Z","timestamp":1774639847455,"version":"3.50.1"},"reference-count":31,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2021,3,25]],"date-time":"2021-03-25T00:00:00Z","timestamp":1616630400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Alchemist Project, Ministry of Trade, Industry and Energy","award":["20007014"],"award-info":[{"award-number":["20007014"]}]},{"DOI":"10.13039\/501100003701","name":"Korea Institute of Machinery &amp; Materials","doi-asserted-by":"publisher","award":["NK224F"],"award-info":[{"award-number":["NK224F"]}],"id":[{"id":"10.13039\/501100003701","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This study proposes a soft inductive coil spring (SICS) strain sensor that can measure the strain of soft actuators. The SICS sensor, produced by transforming a shape memory alloy (SMA) wire with the same materials as that of an SMA spring bundle actuator (SSBA) into a coil spring shape, measures inductance changes according to length changes. This study also proposes a manufacturing method, output characteristics of the SICS sensor applicable to the SSBA among soft actuators, and the structure of the SICS sensor-integrated SSBA (SI-SSBA). In the SI-SSBA, the SMA spring bundle and SICS sensor have structures corresponding to the muscle fiber and spindle of the skeletal muscle, respectively. It is demonstrated that when a robotic arm with one degree of freedom is operated by attaching two SI-SSBAs in an antagonistic structure, the displacement of the SSBA can be measured using the proposed strain sensor. The output characteristics of the SICS sensor for the driving speed of the robotic arm were evaluated, and it was experimentally proven that the strain of the SSBA can be stably measured in water under a temperature change of 54 \u00b0C from 36 to 90 \u00b0C.<\/jats:p>","DOI":"10.3390\/s21072304","type":"journal-article","created":{"date-parts":[[2021,3,25]],"date-time":"2021-03-25T21:09:45Z","timestamp":1616706585000},"page":"2304","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["Soft Inductive Coil Spring Strain Sensor Integrated with SMA Spring Bundle Actuator"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4869-4000","authenticated-orcid":false,"given":"Kyungjun","family":"Choi","sequence":"first","affiliation":[{"name":"Department of Robotics and Mechatronics, Korea Institute of Machinery &amp; Materials, Daejeon 34103, Korea"},{"name":"Department of Mechatronics Engineering, Chungnam National University, Daejeon 34103, Korea"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5806-044X","authenticated-orcid":false,"given":"Seong Jun","family":"Park","sequence":"additional","affiliation":[{"name":"Department of Robotics and Mechatronics, Korea Institute of Machinery &amp; Materials, Daejeon 34103, Korea"},{"name":"Department of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea"}]},{"given":"Mooncheol","family":"Won","sequence":"additional","affiliation":[{"name":"Department of Mechatronics Engineering, Chungnam National University, Daejeon 34103, Korea"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7942-7311","authenticated-orcid":false,"given":"Cheol Hoon","family":"Park","sequence":"additional","affiliation":[{"name":"Department of Robotics and Mechatronics, Korea Institute of Machinery &amp; Materials, Daejeon 34103, Korea"}]}],"member":"1968","published-online":{"date-parts":[[2021,3,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1798","DOI":"10.1109\/TMECH.2019.2928881","article-title":"Shape memory alloy-based spring bundle actuator controlled by water temperature","volume":"24","author":"Park","year":"2019","journal-title":"IEEE\/ASME Trans. Mechatron."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"4056","DOI":"10.1109\/JSEN.2013.2272320","article-title":"Design and characterization of a soft multi-axis force sensor using embedded microfluidic channels","volume":"13","author":"Vogt","year":"2013","journal-title":"IEEE Sens. J."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2711","DOI":"10.1109\/JSEN.2012.2200790","article-title":"Design and fabrication of soft artificial skin using embedded microchannels and liquid conductors","volume":"12","author":"Park","year":"2012","journal-title":"IEEE Sens. J."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1748","DOI":"10.1177\/0278364914543793","article-title":"Wearable soft sensing suit for human gait measurement","volume":"33","author":"Park","year":"2014","journal-title":"Int. J. Rob. Res."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"5440","DOI":"10.1002\/adma.201103406","article-title":"High-strain sensors based on ZnO nanowire\/polystyrene hybridized flexible films","volume":"23","author":"Xiao","year":"2011","journal-title":"Adv. Mater."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1770","DOI":"10.1021\/acsami.6b12415","article-title":"Highly stretchable, hysteresis-free ionic liquid-based strain sensor for precise human motion monitoring","volume":"9","author":"Choi","year":"2017","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Zhang, K., Shi, X., Chen, J., Xiong, T., Jiang, B., and Huang, Y. (2021). Self-healing and stretchable PDMS-based bifunctional sensor enabled by synergistic dynamic interactions. Chem. Eng. J., 412.","DOI":"10.1016\/j.cej.2021.128734"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Wang, A., Wang, Y., Zhang, B., Wan, K., Zhu, J., Xu, J., Zhang, C., and Liu, T. (2021). Hydrogen-bonded network enables semi-interpenetrating ionic conductive hydrogels with high stretchability and excellent fatigue resistance for capacitive\/resistive bimodal sensors. Chem. Eng. J., 411.","DOI":"10.1016\/j.cej.2021.128506"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Wang, S., Fang, Y., He, H., Zhang, L., Li, C., and Ouyang, J. (2021). Wearable Stretchable Dry and Self-Adhesive Strain Sensors with Conformal Contact to Skin for High-Quality Motion Monitoring. Adv. Funct. Mater., 31.","DOI":"10.1002\/adfm.202007495"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Nguyen, T., Chu, M., Tu, R., and Khine, M. (2021). The effect of encapsulation on crack-based wrinkled thin film soft strain sensors. Materials, 14.","DOI":"10.3390\/ma14020364"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1002\/admt.201900908","article-title":"Strategies for Designing Stretchable Strain Sensors and Conductors","volume":"5","author":"Wu","year":"2020","journal-title":"Adv. Mater. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"519","DOI":"10.1016\/j.compositesa.2018.01.031","article-title":"Ink-jet printed stretchable strain sensor based on graphene\/ZnO composite on micro-random ridged PDMS substrate","volume":"107","author":"Hassan","year":"2018","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"478","DOI":"10.1089\/soro.2019.0064","article-title":"Experimental Investigation into the Dynamics of a Radially Contracting Actuator with Embedded Sensing Capability","volume":"7","author":"Dang","year":"2020","journal-title":"Soft Robot."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Devaraj, H., Giffney, T., Petit, A., Assadian, M., and Aw, K. (2018). The development of highly flexible stretch sensors for a Robotic Hand. Robotics, 7.","DOI":"10.3390\/robotics7030054"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1002\/admt.201700136","article-title":"Batch Fabrication of Customizable Silicone-Textile Composite Capacitive Strain Sensors for Human Motion Tracking","volume":"2","author":"Atalay","year":"2017","journal-title":"Adv. Mater. Technol."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Wang, H., Totaro, M., and Beccai, L. (2019, January 27\u201330). Development of fully shielded soft inductive tactile sensors. Proceedings of the The 26th IEEE International Conference on Electronics Circuits and Systems (ICECS), Genova, Italy.","DOI":"10.1109\/ICECS46596.2019.8964922"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1678","DOI":"10.1002\/adfm.201504755","article-title":"Stretchable, Skin-Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review","volume":"26","author":"Amjadi","year":"2016","journal-title":"Adv. Funct. Mater."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Kim, D., Kwon, J., Jeon, B., and Park, Y.-L. (2020). Adaptive Calibration of Soft Sensors Using Optimal Transportation Transfer Learning for Mass Production and Long-Term Usage. Adv. Intell. Syst., 2.","DOI":"10.1002\/aisy.201900178"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1821","DOI":"10.1021\/nl204052z","article-title":"A highly elastic, capacitive strain gauge based on percolating nanotube networks","volume":"12","author":"Cohen","year":"2012","journal-title":"Nano Lett."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1016\/j.sna.2017.03.005","article-title":"Highly stretchable printed strain sensors using multi-walled carbon nanotube\/silicone rubber composites","volume":"259","author":"Giffney","year":"2017","journal-title":"Sens. Actuators A Phys."},{"key":"ref_21","first-page":"346","article-title":"Thermal drift characteristics of capacitive pressure sensors","volume":"11","author":"Beddiaf","year":"2016","journal-title":"J. Eng. Sci. Technol."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Guo, X., Huang, Y., Cai, X., Liu, C., and Liu, P. (2016). Capacitive wearable tactile sensor based on smart textile substrate with carbon black \/silicone rubber composite dielectric. Meas. Sci. Technol., 27.","DOI":"10.1088\/0957-0233\/27\/4\/045105"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"6185","DOI":"10.1039\/D0TC00373E","article-title":"Highly stretchable and sensitive strain sensors based on carbon nanotube-elastomer nanocomposites: The effect of environmental factors on strain sensing performance","volume":"8","author":"Nankali","year":"2020","journal-title":"J. Mater. Chem. C"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Sareh, S., Noh, Y., Li, M., Ranzani, T., Liu, H., and Althoefer, K. (2015). Macrobend optical sensing for pose measurement in soft robot arms. Smart Mater. Struct., 24.","DOI":"10.1088\/0964-1726\/24\/12\/125024"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2333","DOI":"10.1109\/LRA.2020.2970984","article-title":"Optically Sensorized Elastomer Air Chamber for Proprioceptive Sensing of Soft Pneumatic Actuators","volume":"5","author":"Jung","year":"2020","journal-title":"IEEE Robot. Autom. Lett."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"3424","DOI":"10.1109\/JSEN.2012.2212883","article-title":"Wearable low-cost system for human joint movements monitoring based on fiber-optic curvature sensor","volume":"12","author":"Stupar","year":"2012","journal-title":"IEEE Sens. J."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Silva, A.S., Catarino, A., Correia, M.V., and Fraz\u00e3o, O. (2013). Design and characterization of a wearable macrobending fiber optic sensor for human joint angle determination. Opt. Eng., 52.","DOI":"10.1117\/1.OE.52.12.126106"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Wu, C., Liu, X., and Ying, Y. (2021). Soft and Stretchable Optical Waveguide: Light Delivery and Manipulation at Complex Biointerfaces Creating Unique Windows for On-Body Sensing. ACS Sens.","DOI":"10.1021\/acssensors.0c02566"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1268","DOI":"10.1109\/TMECH.2016.2642588","article-title":"Self-sensing of deflection, force, and temperature for joule-heated twisted and coiled polymer muscles via electrical impedance","volume":"22","author":"Smit","year":"2017","journal-title":"IEEE\/ASME Trans. Mechatron."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Kim, H., Han, Y., Lee, D.Y., Ha, J.I., and Cho, K.J. (2013). Sensorless displacement estimation of a shape memory alloy coil spring actuator using inductance. Smart Mater. Struct., 22.","DOI":"10.1088\/0964-1726\/22\/2\/025001"},{"key":"ref_31","unstructured":"Package, T.R. LVDT Signal Conditioner AD598, Analog Devices."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/7\/2304\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:41:10Z","timestamp":1760161270000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/7\/2304"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,3,25]]},"references-count":31,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2021,4]]}},"alternative-id":["s21072304"],"URL":"https:\/\/doi.org\/10.3390\/s21072304","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,3,25]]}}}