Anterior-Posterior Center of Pressure Analysis for the DIP/VIP Balance Maintenance model: Formalization and Preliminary Results

Double-link inverted pendulum (DIP) represents a consistently descriptive model of the kinematics of the human sway in quiet stance. Recently it has been used to simulate human-like sway patterns by an intermittent controller (IC) that actively acts at the ankle and generates motor command based on the sway angle of the DIP center of mass. This virtual internal pendulum (VIP) and its outer redundant structure constitute the DIP/VIP human balance maintenance model. In this work the center of pressure (COP) for a DIP structure is mathematically derived and used with the DIP/VIP model to evaluate whether the latter is able to reproduce human COP characteristics. This was found under the critic time metric (Tcr) of the stabilogram diffusion analysis, and for different IC parameterizations. In particular, IC proportional (P) and derivative (D) terms allowed plausible T_cr~1s [1] only in specific regions of the P- D grid. Thus, the present work suggests the use of the DIP/VIP model in studying humanlike balance control and its functional rearrangement through parametric changes.