Dead reckoning of biped robots with estimated contact points based on the minimum velocity criterion

A novel technique of dead reckoning for biped robots, which could be utilized for agile motion controls, is proposed. A complementary filter combines the estimations of the position of robot body from both the kinematic computation and the acceleration information, where the former is relied on in the lower frequency domain and the latter is done on in the higher domain. Even though the supporting foot of the robot happens to roll and rotate on the terrain, the estimation accuracy of the kinematics is improved by taking such movements into consideration. We suppose that the contact point moves with respect to the ground at the instantaneously minimum velocity, and thus name it the instantaneous minimum velocity point (IMVP), which is estimated by an optimization. IMVP can be computed for each foot, so that the weighted sum of them by the magnitude of reaction forces on each foot is adopted as a candidate of the contact point under an assumption that the contact condition is more steady when a larger reaction force is applied. Finally, it is merged with the twice-integrated acceleration through the complementary filter, where the crossover frequency is also determined by the reaction forces. Hence, it is robust against the change of contact conditions. Results of computer simulations will show that the proposed method reduces the estimation error comparing with the conventional methods.