Biped robots have good mobility and can move in various environments such as rough terrain, up and down slopes, or regions containing obstacles. But since almost of them are high order nonlinear dynamic system, their walking pattern, stability and control method, etc are important problems.
In this paper, the new type biped walking robot which is composed of the minimum number of links just for walking and its appropriate gaits are proposed. The proposed new gaits for this robot are four - crossing, crawling, standing and turning gait. In designing the biped robot, we propose the Performance Index which means the needed torque per a moving distance and generate foot trajectories by 3rd order spline interpolation. Among those, numerically we find the optimal conditions which minimize the Performance Index. Dynamically stable walking of the biped robot is realized by satisfying the stability condition of ZMP (zero moment point), which is related to maintaining the ZMP within the stable region of the supporting foot during the single leg support phase. We determine the region of mass center from the stability condition of ZMP and plan joints' trajectories which track the mass center moving with constant velocity or being stationary in the center of supporting foot where the stability margin is largest. We find out that ZMP trajectories of the obtained joints' ones also satisfy their stability condition. Finally we implement the gaits statically tracking the original planned trajectories and the backlash-compensated trajectories using PD control method. And experimental walking test results are described.