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Zhong et al. Soft Sci. 2025, 5, 3 Soft Science
DOI: 10.20517/ss.2024.52

Research Article Open Access

Calibration-free optical waveguide bending sensor

for soft robots

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Liang Zhong , Xiaoqing Tian , Ji-Yong Wang , Jian-Xiang Wang , Zhanguo Nie , Xueyin Chen , Yuxin
Peng 1,*
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Institute of Exercise Science and Health Engineering, Zhejiang University, Hangzhou 310058, Zhejiang, China.
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School of Mechanical Engineering, Hangzhou Dianzi University, Hangzhou 310018, Zhejiang, China.
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School of Electronic and Information, Hangzhou Dianzi University, Hangzhou 310018, Zhejiang, China.
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Authors contributed equally.
* Correspondence to: Prof. Yuxin Peng, Institute of Exercise Science and Health Engineering, Zhejiang University, Yuhangtang
Road 866, Hangzhou 310058, Zhejiang, China, E-mail: yxpeng@zju.edu.cn
How to cite this article: Zhong, L.; Tian, X.; Wang, J. Y.; Wang, J. X.; Nie, Z.; Chen, X.; Peng, Y. Calibration-free optical waveguide
bending sensor for soft robots. Soft Sci. 2025, 5, 3. https://dx.doi.org/10.20517/ss.2024.52
Received: 19 Oct 2024 First Decision: 27 Nov 2024 Revised: 10 Dec 2024 Accepted: 17 Dec 2024 Published: 16 Jan 2025
Academic Editor: Xing Ma Copy Editor: Pei-Yun Wang Production Editor: Pei-Yun Wang

Abstract
Soft robots have become increasingly popular due to their compliance, deformability, and adaptability. Soft
sensors, particularly bending sensors, play a crucial role in providing essential posture and position information for
these robots. However, current soft bending sensors encounter difficulties in accurately measuring joint bending
angles and directions under different curvatures. To address these challenges, we propose a novel dual-colored
layer structured (DCLS) bending sensor based on the optical soft waveguide. The DCLS sensor is constructed using
polydimethylsiloxane (PDMS) as the clear core, with red and blue layers on each side. The sensor’s performance is
evaluated through experiments involving bending, compression, and impact conditions. The DCLS bending sensor
exhibits excellent calibration-free properties, allowing it to effectively monitor bending angles and directions of
joints of varying sizes without requiring any additional calibration. The sensor is successfully integrated into various
soft robots, including a fruit sorting robot, a fish-inspired robot, and a hand orthotic exoskeleton robot, showcasing
its versatility and potential for different applications.

Keywords: Optical waveguide, bending sensor, soft robots, calibration-free

© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0
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