Parametric Excitation Walking for Four-linked Bipedal Robot

In the bipedal walking, mechanical energy needs to be restored because of energy lost by heel strike collisions. Harata et al. have applied parametric excitation method to a kneed bipedal robot, and have shown that sustainable gait is generated with only knee torque. In this paper, we propose the method that combines the parametric excitation method for swing-leg with that for support-leg to improve the gait efficiency. To do this, we first extend the three-link bipedal robot to four-link bipedal robot by adding a support-leg knee, and then apply the parametric excitation method to the support-leg. Consequently, parametric excitation method for swing-leg and support-leg restores energy twice a step, and gait of the proposed method grows in efficiency. In the method proposed by Harata et al., the robot has large shin masses to restore much energy and has large semicircular feet to decrease the energy lost by heel strike. These features are unfavorable because common bipedal robots do not have such features. By simulation, we show that the bipedal robot with small shin masses or small feet can walk sustainably because the proposed method increases the quantity of restored energy. For example, the ratio of shin mass to thigh mass is one and the foot radius is reduced to one fifth of the previous method.