Real-time step edge estimation using stereo images for biped robot

A state-of-the-arts biped robot can take foot-steps such that its heels always overhang corner edges while ascending stairs, as humans naturally do. The overhanging footstep is advantageous in terms of relaxation of restrictions on gait planning. However, in a man-made environment without geometry information, the overhanging footstep requires the estimation of the exact step-edge position in real-time. In this paper we propose a real-time method for estimating step edge positions using stereo images. We find a straight edge line, which divides a view area into two regions representing the upper and lower step-able planes at the target edge. The edge line is obtained by minimizing a cost function composed of pixel-value-difference images, which are computed from the two stereo images and the geometry parameters of the planes, estimated by an efficient direct method in high precision. The validity of the proposed method is demonstrated through online experiments using stereo cameras mounted on the body of a biped robot traversing real stairs.