Customizing to User Functional Electrical Stimulation of Walking: Optimal Control

An improved planar biomechanical model of a human leg has been developed to investigate automatic control for Functional Electrical Stimulation (FES). The model comprises three body segments (trunk, thigh and shank-foot complex) and two joints (hip and knee). The actuators of the system were assumed as two antagonistic muscles acting at each of the joint. Each equivalent muscle (flexor and extensor) is modeled by a three component multiplicative model (driving force), a two component multiplicative passive visco-elastic model (opposing force) with exponential limiters representing the ligaments and other tissues at boundary positions. The complexity of model was driven by the needs that the model parameters must be estimated for an eventual individual with disability. The model was simulated in the MatLab environment. The simulation used dynamic programming to resolve the problem of redundancy. This model is suitable for off-line testing of the FES system.