On the benefits of head stabilization with a view to control balance and locomotion in humanoids

The estimation of the gravitational vertical is a fundamental problem faced by locomoting robots and animals alike. We describe a technique to address this problem that involves a damped inclinometer, an inertial measurement unit mounted on an actuated orienting platform, that is a robot head, so-to-speak. Simulations show that a nonlinear observer based on Newton´s method to solve the full dynamics of the system given inertial sensor data gives accurate verticality estimates even in the presence of highly dynamic perturbations that include large fictitious force terms. Moreover, when the sensor platform is servoed to the estimate of the gravitational vertical to provide for horizontal stabilization, the accuracy of the estimate is improved by almost two orders of magnitude. Similar gains of performance are observed even in the presence of noise and parameter uncertainty.