Models for human postural regulation that include realistic delays and partial observations

The quietly standing human is modeled by a two-segment inverted pendulum controlled by an ankle torque. Both the control and the observations are significantly delayed and corrupted by exogenous noise, as they are in reality. Three controllers of this plant are derived and compared. The first is an MPC-based controller that approximately optimizes a performance criterion that is quartic in the state and quadratic in the control. The second is an LQG optimal controller. The third is a PID controller proposed by Peterka. The controllers are shown to exhibit several of the experimentally observed phenomena related to sway.