Preserving balance during unsupported standing using synergistic combination of discrete sliding predictive and adaptive controllers

Abstract

We suggest a decentralized control method which is based on the synergistic combination of a discrete sliding predictive and an adaptive controllers. In this study, the FES control of plantar flexor and dorsiflexor muscle groups is used to control balance. For this purpose, first, the inverted pendulum model is used for modeling of the skeletal section of the human body. Second, center of pressure and velocity of center of pressure are defined with the help of this model. Third, because of using the discrete controllers, the inverted pendulum will become discrete. Finally, suitable designs of controllers are used to stabilize the upright posture. Center of pressure and velocity of center of pressure are considered as two inputs for each controller. Studies show that under normal conditions each of the inputs is in their own basin of attraction, so in this study, the purpose of the control is to reach these two variables to their own basin of attraction. Because center of pressure and velocity of center of pressure have been commonly used as two indexes of balance and quality level of balance during standing, respectively. The control approach reaches these two variables to their suitable basin of attraction which results in maintaining both balance and quality level of balance. The results of this study show that the proposed control strategy is an effective method in paraplegic subjects using functional electrical stimulation.