Development of a Novel 2-DoF Wearable Ankle Angle Sensor With an Adjustable Rotation Center

This article presents a novel fiber Bragg grating (FBG)-based sensor for precise 2-degree-of-freedom (DoF) ankle angle monitoring. The proposed sensor primarily comprises two symmetric torsion springs, a planar spring, and three FBG-embedded optical fibers. Symmetric torsion springs are used to measure plantarflexion/dorsiflexion (PF/DF) rotation, while a planar spring targets inversion/eversion (INV/EVE) motion, effectively minimizing cross-axis interference due to their distinct stiffness characteristics. Crucially, the sensor’s high in-plane compliance accommodates the physiological shift of the ankle’s rotation center, enabling enhanced wearing comfort. Moreover, a symmetric differential fiber configuration compensates for rotation-axis variations and ensures high measurement accuracy. Structural optimization was conducted to maximize sensitivity and minimize crosstalk. Experimental results demonstrate high sensitivities of 37.09 pm/° (PF/DF) and 224.70 pm/° (INV/EVE) over ranges of ±55° and ±23°, respectively. The structural decoupling is validated by a low maximum crosstalk of 3.56%. Furthermore, the sensor maintains accuracy against rotation center offsets, with sensitivity deviations kept below 2.8% under a 2-mm misalignment. Dynamic tests at 50°/s and 300°/s yielded maximum root-mean-square errors (RMSEs) of 2.47° and 1.27° for PF/DF and INV/EVE, respectively. Finally, on-body validation, including seated range-of-motion (ROM) tests, squat-to-stand exercises, and level walking, confirmed the sensor’s ability to capture high-fidelity kinematic profiles for rehabilitation applications.

• Publication year

  2026

• Venue

  IEEE Transactions on Instrumentation and Measurement

• Publication date

  Unknown publication date

• Fields of study

  Not labeled

• Identifiers
  DOI 10.1109/TIM.2026.3660402
• External record

  Open on Semantic Scholar

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  Semantic Scholar

• No claims are published for this paper.

• No concepts are published for this paper.

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