Unified Balance Control for Biped Robots Including Modification of Footsteps with Angular Momentum and Falling Detection Based on Capturability

Abstract

In this paper, we propose walking balance control based on Caputurability. The proposed method consists of five strategies: (i) moving Zero Moment Point (ZMP) in the support polygon (ii) landing position modification (iii) landing timing modification (iv) angular momentum control (v) falling detection and fall control. Walking pattern generation calculates the ZMP so that the Capture Point (CP) reaches the position of the supporting foot at the end of the double support phase. Owing to the asymmetry of the reachable landing region, landing timing modification is different in the sagittal and lateral planes, and the step time is extended in the lateral plane depending on the direction of disturbances. The torque around the center of gravity to avoid falling is realized through whole-body inverse kinematics with constraints on the angular momentum. In addition, we propose falling detection considering the reachable landing region. We verified the effectiveness of the proposed method through experiments in which the biped robot was disturbed by pushing during tether-free walking. The robot could prevent breakdown by detecting possible falling and performed knee bending motions to suppress damage.