A Novel Method to Assess Angle Sensor Performance for Wearable Exoskeletal Joint Kinematics

Full range of motion (ROM) at a joint is necessary for efficient and adaptive movement; as such, it is an essential clinical evaluation measure for assessing an individual's motor function, which can be affected by any number of musculoskeletal injuries and neuropathies. Measurement of joint ROM in the clinic has classically been accomplished statically through the use of a manual goniometer. More recent efforts in the fields of prosthetics and orthotics have demonstrated the potential utility of wearable systems (e.g., exoskeletons, orthoses) designed to control joint motion(s) and instrumented with sensors capable of capturing joint angle data dynamically. This paper presents a novel methodology to assess the performance of a variety of angle sensors in the context of wearable joint angle measurement, particularly for use in articulated ankle-foot orthoses (AFOs). Dynamic and static errors are considered, and a cost-benefit analysis of a variety of off-the-shelf and custom-built sensors is reported to provide comparative data for selecting a sensor to measure joint motion in wearable exoskeletal systems. All of the sensors considered reported angular errors below 5. across all tests, though the optical encoder consistently demonstrated the highest accuracy (< 0.7 degrees) and precision, and both the resistive potentiometers exhibited the highest error in the dynamic tests (1.5 degrees to 4 degrees). The anisotropic magnetoresistive (AMR) sensor demonstrated the highest performance-to-cost ratio.