Modelling and Control of Paraplegic Subjects Walking Using Functional Electrical Stimulation

Walking stabilization of paraplegic patients by designing a controller in order to apply functional electrical stimulation (FES) to their muscles is still a challenging issue. In this paper, to analyze the paraplegic walking, at the first step, a model for human locomotion is presented and then, PID controllers arc designed in order to determine the activation patterns using FES to contract muscles of a patient that can walk like healthy persons. In this manner, a known walking musculoskeletal model is implemented, which comprises angles of feet, shanks, thighs and trunk. The model is a seven degree-of-freedom (DOF) rigid linkage in the sagittal plane. The model is specified by user-specific parameters consisting of lengths, masses and inertia. Reference trajectory for simulation are recorded from healthy subjects during walking. Here, by the use of muscle inverse model and seven independent PID controllers, controlling signals in the form of FES are calculated and applied to the corresponding muscles of the model such that they can contract and produce required torques for human walking, and therefore the angles of joints (feet, shanks, thighs and trunk) can finely trace the trajectory patterns of healthy subjects.