Electrode Shifts Estimation and Adaptive Correction for Improving Robustness of sEMG-Based Recognition

Abstract

In sEMG-based recognition systems, accuracy is severely worsened by disturbances, such as electrode shifts by doffing/donning. Traditional recognition models are fixed or static, with limited abilities to work in the presence of the disturbances. In this paper, a transfer learning method is proposed to reduce the impact of electrode shifts. In the proposed method, a novel activation angle is introduced to locate electrodes within a polar coordinate system. An adaptive transformation is utilized to correct electrode-shifted sEMG samples. The transformation is based on estimated shifts relative to the initial position. The experiments acquisition data from ten subjects consist of sEMG signals under eight gestures in seven or nine arbitrary positions, and recorded shifts from a 3D-printed annular ruler. In our extensive experiments, the errors between recorded shifts (as the reference) and estimated shifts is about <inline-formula><tex-math notation= LaTeX >$-0.017\\pm 0.13$</tex-math></inline-formula> radians. Eight gestures recognition results have shown an average accuracy around 79.32%, which represents a significant improvement over the 35.72% (<inline-formula><tex-math notation= LaTeX >$p< 0.0001$</tex-math></inline-formula>) average accuracy of results obtained using nonadaptive models, and 60.99% (<inline-formula><tex-math notation= LaTeX >$p< 0.0001$</tex-math></inline-formula>) results of the other method iGLCM (an improved gray-level co-occurrence matrix). More importantly, by only using one-label samples, the proposed method updates the pre-trained model in an initial position. As a result, the pre-trained model can be adaptively corrected to recognize eight-label gestures in arbitrarily rotary positions. It is proven a highly efficient way to relieve subjects’ re-training burden of sEMG-based rehabilitation systems.