Position-Based Lateral Balance Control for Knee-Stretched Biped Robot

This paper discusses a lateral balance controller for a biped robot with both legs fully extended. In a conventional position-controlled legged robot, a balance control with stretched knees is an open problem since the mechanical singularity prevents the direct control of the floor force distribution. To control forces indirectly, we introduce an additional acceleration of the center of mass and a ZMP modification as control inputs. The lateral balance controller is designed as a state feedback system by using a data driven approach. The proposed lateral controller was merged with a sagittal controller based on the Spatially Quantized Dynamics (SQD), then it helped our humanoid robot HRP-2Kai to achieve laterally well balanced, knee-stretched, and long stride gait.