Experimental validation of nonlinear PID model for human standing with large body sway

Human generates very slow (<;1[Hz]) and large (>20[mm]) body sway. This sway is considered to reflect the characteristic of human neural control. We propose a human control model with nonlinearlity and the effect of nonlinearlity is considered by mathematical analysis and simulation. As a result, we found that the proposed model has bifurcation structure with the magnitude of control gain. We consider that body sway is caused by this bifurcation structure. In order to verify the existence of such a nonlinear nature in human, we performed human experiment with two floor environments: fix and rotate floors. As a result, we verified the existence of nonlinearlity in human body sway and showed the potential existence of bifurcation structure.