On the Calibration, Fault Detection and Recovery of a Force Sensing Device

Ground reaction force information, which includes the location of the center of pressure (COP) and vertical ground reaction force (vGRF), has various applications, such as in the gait assessment of patients post-injury or in the control of robot prostheses and exoskeleton devices. At the beginning of this work, we introduce a newly developed force-sensing device for measuring the COP and vGRF. Then, a model-free calibration method is proposed, leveraging Gaussian process regression (GPR) to extract COP and vGRF from raw sensor data. This approach yields remarkably low normalized root mean squared errors (NRMSEs) of 0.029 and 0.020 for COP in the mediolateral and anteroposterior directions, respectively, and 0.024 for vGRF. However, in general, learning-based calibration methods are sensitive to abnormal readings from sensing elements. To improve the robustness of the measurement, a GPR-based fault detection network is outlined for evaluating the sensing state within the fault in individual sensing elements of the force-sensing device. Moreover, a GPR-based recovery method is proposed to retrieve the sensing device's function under the fault conditions. In validation experiments, the effect of the scale factor of the threshold in the fault detection network is experimentally analyzed. The fault detection network can achieve over 90% success rate with a lower than 5 seconds delay on average in detecting the fault when the scale factor is between 1.68 and 1.90. The engagement of GPR-based recovery models under fault conditions demonstrates a substantial enhancement in COP (up to 85.0% improvement) and vGRF (up to 84.8% improvement) estimation accuracy.