Design of Crawling Motion for a Biped Walking Humanoid with 3-DoF Rigid-flexible Waist

In order to be applied in complex environment, humanoid robots are desired to have the ability of both biped walking and quadruped crawling. Crawling is a multi-contact motion. If the mechanism is completely rigid, there will be a closed kinematic chain of robot which is likely to cause damage to robot joints. Therefore, the robot needs to have some flexibility in mechanism. However, biped walking requires highly rigid mechanism to maintain walking stability. Consequently, it is a crucial issue to study crawling motion and biped walking motion in case of rigid-flexible mechanism. In this paper, firstly a 3-DoF rigid-flexible waist is proposed. The waist has rigidity when walking and flexibility when crawling. Then a crawling pattern generation algorithm based on CPG is presented, which solves the problem of difficult to plan crawling motion of robot with rigid-flexible mechanism. Finally, the validity of the proposed method is confirmed by experiments.