{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,4]],"date-time":"2026-04-04T18:35:46Z","timestamp":1775327746768,"version":"3.50.1"},"reference-count":29,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2021,9,30]],"date-time":"2021-09-30T00:00:00Z","timestamp":1632960000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>With the emerging of wearable robots, the safety and effectiveness of human-robot physical interaction have attracted extensive attention. Recent studies suggest that online measurement of the interaction force between the robot and the human body is essential to the aspects above in wearable exoskeletons. However, a large proportion of existing wearable exoskeletons monitor and sense the delivered force and torque through an indirect-measure method, in which the torque is estimated by the motor current. Direct force\/torque measuring through low-cost and compact wearable sensors remains an open problem. This paper presents a compact soft sensor system for wearable gait assistance exoskeletons. The contact force is converted into a voltage signal by measuring the air pressure within a soft pneumatic chamber. The developed soft force sensor system was implemented on a robotic hip exoskeleton, and the real-time interaction force between the human thigh and the exoskeleton was measured through two differential soft chambers. The delivered torque of the hip exoskeleton was calculated based on a characterization model. Experimental results suggested that the sensor system achieved direct force measurement with an error of 10.3 \u00b1 6.58%, and torque monitoring for a hip exoskeleton which provided an understanding for the importance of direct force\/torque measurement for assistive performance. Compared with traditional rigid force sensors, the proposed system has several merits, as it is compact, low-cost, and has good adaptability to the human body due to the soft structure.<\/jats:p>","DOI":"10.3390\/s21196545","type":"journal-article","created":{"date-parts":[[2021,10,8]],"date-time":"2021-10-08T21:26:20Z","timestamp":1633728380000},"page":"6545","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Differential Soft Sensor-Based Measurement of Interactive Force and Assistive Torque for a Robotic Hip Exoskeleton"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3905-4770","authenticated-orcid":false,"given":"Sun\u2019an","family":"Wang","sequence":"first","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, No. 28, Xianning West Road, Xi\u2019an 710049, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1170-8640","authenticated-orcid":false,"given":"Binquan","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, No. 28, Xianning West Road, Xi\u2019an 710049, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2266-5778","authenticated-orcid":false,"given":"Zhenyuan","family":"Yu","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, No. 28, Xianning West Road, Xi\u2019an 710049, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6510-798X","authenticated-orcid":false,"given":"Yu\u2019ang","family":"Yan","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, No. 28, Xianning West Road, Xi\u2019an 710049, China"}]}],"member":"1968","published-online":{"date-parts":[[2021,9,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1109\/TNSRE.2016.2521160","article-title":"State of the Art and Future Directions for Lower Limb Robotic Exoskeletons","volume":"25","author":"Young","year":"2017","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"668","DOI":"10.1126\/science.aav7536","article-title":"Reducing the metabolic rate of walking and running with a versatile, portable exosuit","volume":"365","author":"Kim","year":"2019","journal-title":"Science"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12984-020-00663-9","article-title":"The exoskeleton expansion: Improving walking and running economy","volume":"17","author":"Sawicki","year":"2020","journal-title":"J. Neuroeng. Rehabil."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12984-016-0180-3","article-title":"Robot-aided assessment of lower extremity functions: A review","volume":"13","author":"Maggioni","year":"2016","journal-title":"J. Neuroeng. Rehabil."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"775","DOI":"10.1007\/s12369-020-00662-9","article-title":"Development of Active Lower Limb Robotic-Based Orthosis and Exoskeleton Devices: A Systematic Review","volume":"13","author":"Kalita","year":"2020","journal-title":"Int. J. Soc. Robot."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12984-021-00906-3","article-title":"Review of control strategies for lower-limb exoskeletons to assist gait","volume":"18","author":"Baud","year":"2021","journal-title":"J. Neuroeng. Rehabil."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Seo, K., Lee, J., Lee, Y., Ha, T., and Shim, Y. (2016, January 16\u201321). Fully autonomous hip exoskeleton saves metabolic cost of walking. Proceedings of the 2016 IEEE International Conference on Robotics and Automation (ICRA), Stockholm, Sweden.","DOI":"10.1109\/ICRA.2016.7487663"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Zhu, H., Doan, J., Stence, C., Lv, G., Elery, T., and Gregg, R. (June, January 29). Design and validation of a torque dense, highly backdrivable powered knee-ankle orthosis. Proceedings of the 2017 IEEE International Conference on Robotics and Automation (ICRA), Singapore.","DOI":"10.1109\/ICRA.2017.7989063"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"103514","DOI":"10.1016\/j.robot.2020.103514","article-title":"A robust phase oscillator design for wearable robotic systems","volume":"128","author":"Fuente","year":"2020","journal-title":"Robot. Auton. Syst."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Zhu, H., Nesler, C., Divekar, N., Peddinti, V., and Gregg, R. (2021). Design Principles for Compact, Backdrivable Actuation in Partial-Assist Powered Knee Orthoses. IEEE\/ASME Trans. Mechatron.","DOI":"10.1109\/TMECH.2021.3053226"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1186\/s12984-015-0062-0","article-title":"Effects of a wearable exoskeleton stride management assist system (SMA\u00ae) on spatiotemporal gait characteristics in individuals after stroke: A randomized controlled trial","volume":"12","author":"Buesing","year":"2015","journal-title":"J. Neuroeng. Rehabil."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1016\/j.robot.2014.08.012","article-title":"A survey of sensor fusion methods in wearable robotics","volume":"73","author":"Novak","year":"2015","journal-title":"Robot. Auton. Syst."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1521","DOI":"10.1109\/JBHI.2016.2608720","article-title":"Toward Pervasive Gait Analysis With Wearable Sensors: A Systematic Review","volume":"20","author":"Chen","year":"2016","journal-title":"IEEE J. Biomed. Health Inform."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"4271","DOI":"10.1109\/JSEN.2019.2895289","article-title":"A Two-Dimensional Feature Space-Based Approach for Human Locomotion Recognition","volume":"19","author":"Chinimilli","year":"2019","journal-title":"IEEE Sens. J."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"120","DOI":"10.1016\/j.robot.2014.09.032","article-title":"Review of assistive strategies in powered lower-limb orthoses and exoskeletons","volume":"64","author":"Yan","year":"2015","journal-title":"Robot. Auton. Syst."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1573","DOI":"10.1109\/TNSRE.2020.2989481","article-title":"Performance Evaluation of Lower Limb Exoskeletons: A Systematic Review","volume":"28","author":"Torricelli","year":"2020","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"ref_17","first-page":"027836492096145","article-title":"A hip\u2013knee\u2013ankle exoskeleton emulator for studying gait assistance","volume":"40","author":"Bryan","year":"2020","journal-title":"Int. J. Robot. Res."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Choi, H., Seo, K., Hyung, S., Shim, Y., and Lim, S.C. (2018). Compact Hip-Force Sensor for a Gait-Assistance Exoskeleton System. Sensors, 18.","DOI":"10.3390\/s18020566"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"95","DOI":"10.1109\/MRA.2018.2815083","article-title":"A Lower-Back Robotic Exoskeleton: Industrial Handling Augmentation Used to Provide Spinal Support","volume":"25","author":"Zhang","year":"2018","journal-title":"IEEE Robot. Autom. Mag."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1109\/MCS.2018.2866605","article-title":"On the Design and Control of Highly Backdrivable Lower-Limb Exoskeletons: A Discussion of Past and Ongoing Work","volume":"38","author":"Lv","year":"2018","journal-title":"IEEE Control Syst."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Beil, J., Ehrenberger, I., Scherer, C., Mandery, C., and Asfour, T. (2018, January 1\u20135). Human Motion Classification Based on Multi-Modal Sensor Data for Lower Limb Exoskeletons. Proceedings of the 2018 IEEE\/RSJ International Conference on Intelligent Robots and Systems (IROS), Madrid, Spain.","DOI":"10.1109\/IROS.2018.8594110"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1269","DOI":"10.1109\/JSEN.2018.2882796","article-title":"Soft Fabric-Based Pneumatic Sensor for Bending Angles and Contact Force Detection","volume":"19","author":"Cheng","year":"2019","journal-title":"IEEE Sens. J."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Choi, B., Lee, Y., Lee, J., Lee, M., Lim, B., Park, Y.J., Kim, K., Kim, Y.J., and Shim, Y. (2019, January 3\u20138). Development of Adjustable Knee Assist Device for Wearable Robot based on Linkage and Rolling Joint. Proceedings of the 2019 IEEE\/RSJ International Conference on Intelligent Robots and Systems (IROS), Macau, China.","DOI":"10.1109\/IROS40897.2019.8967826"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Araromi, O.A., Walsh, C.J., and Wood, R.J. (2017, January 24\u201328). Hybrid carbon fiber-textile compliant force sensors for high-load sensing in soft exosuits. Proceedings of the 2017 IEEE\/RSJ International Conference on Intelligent Robots and Systems (IROS), Vancouver, BC, Canada.","DOI":"10.1109\/IROS.2017.8205994"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Zhang, B., Wang, S., and Zhou, M. (2021, January 12\u201316). A Novel Control for Gait Assistance and Resistance with a Robotic Hip Exoskeleton Using Compact Soft Force Sensors. Proceedings of the 2021 IEEE\/ASME International Conference on Advanced Intelligent Mechatronics (AIM), Delft, The Netherlands.","DOI":"10.1109\/AIM46487.2021.9517371"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Winter, D.A. (2009). Biomechanics and Motor Control of Human Movement, John Wiley & Sons, Inc.. [4th ed.].","DOI":"10.1002\/9780470549148"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"103842","DOI":"10.1016\/j.robot.2021.103842","article-title":"An adaptive framework of real-time continuous gait phase variable estimation for lower-limb wearable robots","volume":"143","author":"Zhang","year":"2021","journal-title":"Robot. Auton. Syst."},{"key":"ref_28","unstructured":"Seo, K., Hyung, S., Choi, B.K., Lee, Y., and Shim, Y. (2015, January 26\u201330). A new adaptive frequency oscillator for gait assistance. Proceedings of the 2015 IEEE International Conference on Robotics and Automation (ICRA), Seattle, WA, USA."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1068","DOI":"10.1109\/JSYST.2014.2351491","article-title":"Lower Limb Wearable Robots for Assistance and Rehabilitation: A State of the Art","volume":"10","author":"Huo","year":"2016","journal-title":"IEEE Syst. J."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/19\/6545\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:08:02Z","timestamp":1760166482000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/19\/6545"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,9,30]]},"references-count":29,"journal-issue":{"issue":"19","published-online":{"date-parts":[[2021,10]]}},"alternative-id":["s21196545"],"URL":"https:\/\/doi.org\/10.3390\/s21196545","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,9,30]]}}}