Modeling and Identification of Electrically Stimulated Muscles for Wrist Movement

The modeling of electrically stimulated muscles is of great importance for the tremor suppression via functional electrical stimulation (FES) approach. In this paper, with fully consideration of the characteristics of wrist muscles, a four input two output wrist muscle model with Hammerstein structure is proposed, by which the four-channel functional electrical stimulation signals can simultaneously stimulate the wrist muscles of flexor carpi radialis (FCR), extensor carpi radialis (ECR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) to realize 2 degrees of freedom (DOF) wrist movements. Then, we use the recursive least squares identification algorithm to identify the parameters of the pre-existing four input and one output system. Simulation results show that the least recursive squares identification algorithm of two-step method is advantageous in convergence and identification accuracy.