A PID Model of Balance Keeping Control and Its Application to Stability Assessment

The aim of this study is to establish a PID model of balance keeping control during static upright standing to elucidate the possible mechanism of body sway, and to apply this to balance stability assessment especially concerning the roles of pelvis and its muscles. The dynamic model includes five joints, i.e. two ankles, two hips and one lumbosacral joint makes up a multi-link system, and is driven by two pairs of muscles, the psoas major (PM) and glutaeus medius (GM). Ankle and lumbosacral joint sway in almost the same amplitude, whereas, their phase difference being approximately equal to pi. The result suggests that the trunk is maintaining its stance perpendicular to horizon. By applying human physical parameters to the model the body sways and its spectral response can be simulated. The simulated results are quite agree with the experimentally recorded both in body sway and in spectral response. It is suggest that balance keeping in upright standing can be fulfilled on this PID controller, and this model can be applied to individual body stability assessment