Design and statistical validation of low-cost electrogoniometers for elbow orthosis applications

This study presents the design, implementation, and statistical validation of four low-cost electromechanical electrogoniometers for elbow joint angle measurement in orthotic applications. The proposed systems are based on distinct sensing principles: an infrared (IR) optical sensor, a calibrated IR optical sensor, a rotary potentiometer, and a slide potentiometer, all integrated into a custom mechanical structure that enables indirect measurement while reducing mechanical stress on sensing components. Experimental validation was performed using a controlled elbow motion simulator and human subjects, with measurements compared against a reference digital goniometer. Performance metrics included mean absolute error (MAE), repeatability, linearity (R²), and statistical agreement. A one-way ANOVA revealed significant differences among sensing modalities (p < 0.05), and Tukey's post hoc analysis confirmed that the IR-based system exhibited significantly higher errors than calibrated IRbased and both potentiometer-based systems. Bland-Altman analysis demonstrated strong agreement for calibrated IR-based and potentiometer-based designs, with minimal bias and narrow limits of agreement. The calibrated IR achieved the highest accuracy (MAE ≈ 2.78°), while the slide potentiometer provided a favorable balance between performance (MAE ≈ 4.72°) and mechanical integration. These results indicate that potentiometer-based electrogoniometers are suitable for wearable rehabilitation systems requiring reliable and realtime joint monitoring. The proposed designs offer cost-effective alternatives for biomechanical instrumentation and support the development of accessible assistive technologies.