Terrain-adaptive control to reduce landing impact force for human-carrying biped robot

Many researchers have studied on walking stability controls for biped robots. Most of them are highly accurate acceleration controls based on the mechanics model of the robot. However, the control algorithms are difficult to be used for human-carrying biped robots due to modeling errors. In the previous report, we proposed the landing pattern modification method, but it had a problem that a foot landing impact increased when a walking cycle was short. So, we propose a new terrain-adaptive control reducing a landing-impact force. To increase a concave terrain adaptation, we set a target landing position beneath a reference level. To reduce the landing-impact force, we change the position gain control value to a small value at a swing phase. Moreover, we set landing-foot speed at zero when the foot landing is detected by the force sensor mounted on a foot. To follow uneven terrain, a virtual spring is applied along the vertical direction after detecting a foot-landing on a ground, and a virtual compliance control is applied to the roll and pitch axes. In a stable walk while carrying a 65 kg human on uneven terrain, the new control method decreased the landing-impact force than the previous terrain-adaptive control.