Flexible Wearable Joint Motion Sensor Based On Multi-Wire Displacement

The kinematic monitoring of human joint movements is beneficial in various applications, including biomechanics, rehabilitation, and wearable robotics. For consistent monitoring of human motions in different situations, a portable monitoring system with a compact form factor would be highly useful. However, most existing devices are susceptible to external disturbances or require a tedious and repetitive calibration process. In this paper, we propose a flexible and compact joint angle detection mechanism that allows for the estimation of the full configuration of the target joint, as well as the measurement of a flexion angle. The proposed approach incorporates a simple geometry, whereby the configuration of a two-dimensional rigid body can be determined by the lengths of three wires. A stand-alone device for the analysis of knee flexion based on the proposed mechanism is demonstrated and experimentally evaluated considering the in-plane assumption and the out-of-plane errors. The proposed sensor system estimates the flexion angle with root-mean-square errors of 3.96°, 4.23°, and 7.46° for an in-plane, a translated, and a rotated configurations, respectively. Finally the sensor was mounted on the knee of a human subject and estimated the knee flexion angle during walking.