Grasp synthesis for upper-extremity FNS

Publisher Website
Google Scholar
Abstract
Functional neuromuscular stimulation (FNS) has been used in upper extremity neuroprostheses to provide grasp and release for quadriplegic individuals. The goal of this project was to determine the electrode/muscle input/output characteristics with the greatest influence on the grasp output. This was evaluated by simulating the grasp synthesis procedure, using a model of the electrode/muscle output as a function of stimulus level and joint angle. The parameters of this model were determined from experimental data from 112 electrodes. The grasp output for 500 different modelled pairs of electrodes were analysed, with each pair consisting of a thumb flexor and a thumb extensor. The simulation results indicate that the most influential electrode input/output characteristics are the output stiffness, defined as the change in force output for a unit change in joint angle at a constant level of stimulation, and the length dependency mean-squared error. Recruitment gain was found to be of secondary influence on the grasp output, and the threshold, force direction and non-linearity of the stimulus level to force relationship were found to have little influence on the grasp output. These results establish criteria for electrode selection and implantation for use in upper extremity FNS.