Elbow Angle Monitoring and Error Analysis Using a Wearable PDMS Embedded FBG Sensor

Elbow flexion and extension are necessary movements for daily tasks. Elbow joint impairments can be brought on by aging, accidents, and repetitive motions making the monitoring of elbow angles critical. In this work, a sensor for elbow angle monitoring during bending and extension using a fiber Bragg grating (FBG) embedded in polydimethylsiloxane (PDMS) with a wearable band is proposed. Two methods for measuring elbow angles, wearable and platform-based sensing are investigated. The wearable sensor-based measurements are consistent over different trials with a linear variation of Bragg wavelength with flexion/extension angle up to 90 degrees. The sensitivities for flexion and extension are 0.0029 and 0.0037 nm/degrees, respectively. Further, the factors contributing to error in the measurement of elbow angle such as tightness of wearable band, spatial and angular misalignment of the sensor, and the removal and replacement of sensor are studied. The findings show that the error is maximum for an angular misalignment followed by tightly bound sensor and spatial misalignment. The desirable configuration for elbow angle measurement is a tightly bound sensor at the mean position for high mean sensitivity with a tolerable level of error and a left/right-aligned sensor with moderate tightness for minimum error at a low sensitivity. The PDMS-embedded FBG-based wearable sensor, in an optimal configuration, can be used for monitoring elbow angles.