Performance Analysis of a Lower Limb Multi Joint Angle Sensor Using CYTOP Fiber: Influence of Light Source Wavelength and Angular Velocity Compensation

This paper presents the analysis of an intensity variation polymer optical fiber (POF)-based angle sensor performance, i.e., sensitivity, hysteresis and determination coefficient ([Formula: see text]), using cyclic transparent optical polymer (CYTOP) fiber. The analysis consisted of two approaches: influence of different light source central wavelengths (430 nm, 530 nm, 660 nm, 870 nm and 950 nm) and influence of different angular velocities ([Formula: see text] rad/s, [Formula: see text] rad/s, [Formula: see text] rad/s, [Formula: see text] rad/s and [Formula: see text] rad/s). The first approach aimed to select the source which resulted in the most suitable performance regarding highest sensitivity and linearity while maintaining lowest hysteresis, through the figure of merit. Thereafter, the analysis of different angular velocities was performed to evaluate the influence of velocity in the curvature sensor performance. Then, a discrete angular velocity compensation was proposed in order to reduce the root-mean-square error (RMSE) of responses for different angular velocities. Ten tests for each analysis were performed with angular range of [Formula: see text] to [Formula: see text] , based on knee and ankle angle range during the gait. The curvature sensor was applied in patterns simulating the knee and ankle during the gait. Results show repeatability and the best sensor performance for [Formula: see text] nm in the first analysis and show high errors for high angular velocities ([Formula: see text] rad/s) in the second analysis, which presented up to [Formula: see text] angular error. The uncompensated RMSE was high for all velocities ([Formula: see text] to [Formula: see text]), whereas the compensated RMSE decreased up to [Formula: see text] ([Formula: see text] to [Formula: see text]). The compensated responses of application tests showed maximum error of [Formula: see text] and minimum of [Formula: see text] , presenting a decrease of mean angular error up to [Formula: see text] when compared with uncompensated responses.