Research on Ultra-Wide Joint Bending Angle Detection Based on Transparent Tubing Structure

The design of a bending angle sensor consisting of plastic optical fibers (POFs) embedded in transparent tubing is proposed for the detection of the angle of human joints. Highly sensitive sensing is achieved by the bending of the transparent tubing between the two fiber end faces which is functioning as a hollow-core optical fiber with the air inside the tubing as the core and the tubing as the cladding. Simulation results based on the ray tracing method show that when the transparent tubing was bent, both end-face coupling and internal reflection mechanisms coexisted in the beam transmission process, with reflection in the tubing being the main mechanism at a large bending angle. A motor-driven angle measurement system is constructed to achieve accurate control of the bending angle. Experimental results show that the sensor can achieve ultra-wide-angle detection ranging from 0° to 180° with a high sensitivity of 0.136 dB/° and a linear regression coefficient (
$\text{R}^{{2}}{)}$
of 0.997. Finally, the dynamic response characteristics of the sensor are tested on both motor-controlled bending and joint bending, and the results show fast response, good repeatability, and stability of the proposed sensor.