A Fast Turning Method for Biped Robots With Foot Slip During Single-Support Phase

For a biped robot to have the capability to change the direction of locomotion fast without tripping itself is important in enhancing its mobility. This paper proposes a new method to realize a quick and natural turn, or to make an abrupt change in the walking direction of a biped robot by taking advantage of a foot slip, which is created intentionally between the sole of the foot and the ground. By using the slip at the supporting foot, the robot can turn its body, in a single step, beyond the kinetic limit of its yaw joint. Thus, the proposed method makes it possible for the robot to make a single turning motion during the single-support phase in order to achieve a change in the locomotion that would not be possible unless the robot takes multiple steps. This reduces the time and the amount of space needed for a biped robot to make a turn. The mathematical conditions for a foot slip to occur are derived based on a simplified 3-D dynamic model of a biped robot consisting of three parts: a swing leg, a supporting leg, and the rest of the body. Under these conditions, the desired translational and rotational trajectories for the swing foot and the main body are generated based on the expected floor surface condition. Computer simulations and experiments were carried out to prove the effectiveness of the proposed method for a quick and natural turn.