A Novel Exoskeleton Neuromuscular Interface Based on Motor Unit Action Potential Model Using High-Density sEMG

The topical and noninvasive measurement of high-density surface electromyogram (HD-sEMG) signals enables the estimation of human motor unit action potentials (MUAPs) as crucial motor function indicators for human-robot interaction. In this paper, we present a two-dimensional (2D) high-density microneedle electrode array using the potassium hydroxide (KOH) bulk etching technique and the flexible printed circuit (FPC). To determine the optimal configuration of the 2D electrode array, we propose an accurate and efficient neuromuscular analytical model for HD-sEMG that comprehensively analyzes the effects of the micro-needle electrode size, inter-electrode distance, and location. The experiment was conducted to demonstrate the feasibility and performance of the proposed micro-needle-based high-density electrode array for the sEMG-based upper-limb exoskeleton's elbow joint angle estimation, specifically in comparison with a commercial wet electrode. The experimental results showed that the proposed micro-needle electrode with high spatial resolution was comparable to the wet electrode (Wilcoxon rank sum test, p > 0:05). On average, the correlation and root mean squared error (RMSE) of the micro-needle electrode array with high space utilization were 7:56% and 19:83% better than those of the wet electrode, respectively. The 2D high-density micro-needle electrode array based on the proposed HD-sEMG model facilitates a novel neural-machine interface for intuitive control of upper-limb exoskeletons.