Motion control in the support phase for a one-legged hopping robot

In this paper, the method of determinating the leg length and the leg angle at touchdown is proposed. With this method, the robot can track the soft-landing trajectory, considering the torque limits of the joints. Suppressing impact force in the landing phase remains as a big issue to be resolved for hopping robots. This paper applies the soft-landing trajectory which was proposed before in order to minimize impact force of landing. Regarding hopping as an extended function of walking robots, they would have rotary joints instead of prismatic joints. Considering torque limits of joints, the relationship between the tip position from the COG (center of gravity) and the COG velocity at touchdown is determined so as to track the soft-landing trajectory. In addition, the vertical velocity of the COG is estimated from the duration of the aerial phase. Consequently, even if a floor level varies, the hopping robot can select a proper landing position of the tip without getting over the torque limit at landing. Numerical results verify the proposed method.