Study on the force myography sensors placement for robust hand force estimation

Abstract

Force Myography (FMG) is a method of tracking functional motor activity using volumetric changes associated with muscle function. With comparable accuracy and multiple advantages over traditional methods of functional motor activity tracking, FMG has shown a promising potential in terms of applications in human-machine interfaces, tele-operation and healthcare devices. This paper provides a study that explores the effect of the spatial coverage and placement of the Force Myography (FMG) measurements on the accuracy and predictability of the machine learning models of isometric hand force. Five participants were recruited in this study and were asked to exert isometric force along three perpendicular axes while wearing custom built FMG devices. During the tests, the isometric force was measured using a 6 degree-of-freedom (DOF) load cell whereas the FMG signals were recorded using a total number of 60 FSRs, which were embedded into four bands worn on the arm. General Regression Neural Network (GRNN) model was employed in this study for predicting the hand force in three axes from the recorded FMG signals. The regression model was trained using all possible band combinations to find the optimal placement for the FMG measurements. The results showed that the accuracy significantly improved when increasing the spatial coverage from 1 FMG band to 2 or 3 bands for all axes. While the accuracy slightly improved when the 4 bands used instead of 3. Specifically, the average R2 across all subjects and axes are 0.68 ± 0.12, 0.84 ± 0.04, 0.91 ± 0.02 and 0.95 ± 0.01 using single, double, triple and four bands combination, respectively, in 5-fold cross-validation evaluation. The knowledge generated from this work aims serve as a guide towards the development of portable FMG based technology for widespread deployment in the general population.