Detection of Lower-Limb Motion Using a Kneepad Sensor Based on Textile Strain Sensor

The monitoring of the knee joint angle during lower-limb motions is crucial for knee disorders patients and their rehabilitation. However, commonly used methods for lower-limb motion detection, such as inertial measurement units (IMUs) and motion capture systems, have limitations such as drift and high cost. To address these issues, we developed a wearable kneepad sensor using textile resistive strain sensors to measure knee angle during lower-limb motion. The strain sensors change in resistance signals caused by their deformation of them when the knee joint bends. To improve the accuracy of knee angle measurements, an encoder was integrated with kneepad sensor onto a prosthetic limb and used linear mapping method to calibrate the kneepad sensor with the encoder data as the ground truth. The calibrated kneepad sensor achieved an R$^{2}$ value of 0.956, MAE of 6.15°, and MSE of 64.35 while detecting the knee angle. It was demonstrated that the ability of the kneepad sensor to measure knee angles during two types of lower-limb motions, sit-to-stand (STS) and knee extension. It is shown in this work that this comfortable, wearable kneepad sensor can help detect knee angles during lower-limb motions in various environments and has broad applications in healthcare and robotics.