Linear Quadratic control for restoring paralyzed muscles to standing through Functional Electrical Stimulation in paraplegic patients

A Linear Quadratic (LQ) optimal controller is proposed in combination with a Functional Electrical Stimulation (FES) system to regulate the quite standing for paraplegic subjects. The lower part of the body (i.e., legs, knees and ankles) is modeled through a double inverted pendulum with user-specific parameters and is driven by two pairs of muscles acting around the ankle and knee joints. For each joint, indeed, extensor and flexor muscles are inserted and their contraction dynamics is described through a three-factor muscle model as in [1]. Trunk, arms, head, hips and pelvis, instead, are described by a point-wise mass placed at the top of the thigh segment. In this study, we present simulation results achieved through a control law based on the linearized dynamics of muscles, joints and body during quite standing.