Commercial-Off-the-Shelf (COTS) Wearable Elbow Joint Angle Measurement System

Measuring joint angles is crucial for kinematic analysis of human movement. The measurement of range of motion (ROM) is particularly essential for evaluation of a patient's joint function in physical therapy and rehabilitation. Physical therapists and physicians typically use a mechanical goniometer to measure joint angles in clinical settings. However, this measurement is often limited by low accuracy, limited resolution, and observation error. This study presents a commercial-off-the-shelf (COTS) wearable elbow joint angle measurement system, which would enhance the measurement accuracy. The accuracy of the system was evaluated in two test setups: 1) desktop test setup without human subjects and 2) wearable test setup with human subjects. In the test without human subjects, the angle measurement was repeated for five times at the angles varied from 60° to 180° by 10° increments. In the test with human subjects, nine healthy human subjects participated in the experiment. Three representative elbow joint angles between 60° and 180° were measured for 10 times at each subject (60°, 120°, and 180°). The average error of the measured angle was 0.52±0.34 % (AVR±STE) at the desktop test without human subjects. The average error of the measured angle at the test with nine human subjects was -0.29±0.10%. These results indicate that the presented system can measure the elbow joint angle in high accuracy and consistency.