Fast bipedal walk using large strides by modulating hip posture and toe-heel motion

Typically most humanoid robots walk with relatively small strides even on the level ground, and consequently their walking speed is fairly slow compared to humans. One reason is that the constraint of the constant COM (Center of Mass) height, which is for decoupling the frontal and lateral motion, produces the characteristic bent knee feature of walking robots and requires higher motor torques. The other reason is the feet trajectory limitation which demands the feet remain parallel to the ground. The parallel foot placement feature, using no toe-off and heel-strike motions, means that robots have to lower their hip height to perform large strides. This paper studies a trajectory generation method that enables fast bipedal walking with large strides. We address this issue by formulating a hip pattern generator and a feet trajectory generator with toe-off and heel-strike motions, based on the preview control. This scheme is applied to a dynamic simulation of the child humanoid “iCub”, which demonstrates successful gaits in large strides at the average speed from 1.08 km/h to 2.52 km/h.