The Role of Inertial Stabilization in Walking Patterns

Impedance control has been often proposed as a stable control strategy for human walking. On the other hand, the continuous control of stiffness in human is energetically expensive. It has been shown that systems with unstable equilibrium points can be stabilized using inertial effects. A Kapitza’s pendulum shows that it is possible to stabilize an inverted pendulum by making its base oscillate vertically. This work provides a set of simulations that show how an impedance control strategy can be used for dynamic stabilization. The simulations presented are based on experimental data extracted from publicly available videos depicting the self-paced walking pattern of an unimpaired human and a that of a NAO humanoid robot. In both cases, the average lower limb stiffness can be maintained under the minimum level of stability if its modulation induces vertical oscillations on the trunk with frequencies compatible with human locomotion. The results reiterate the possibility of integrating the intermittent control of human balance under the umbrella of impedance control.