Softly Stable Walk Using Phased Compliance Control with Virtual Force for Multi-Legged Walking Robot

Recently, although the researches on the terrain adaptability of multi-legged walking robot have been widely performed (D. Wettergreen & C. Thorpe, 1996; T. Kubota, et al., 2000; Q. Huang, et al., 2000; Q. Huang & K. Nonami, 2000; Q. Huang & K. Nonami, 2003; K. Nonami & Q. Huang, 2003), it has not been put to be more widely practical use. This is because there are still some problems in the stable walking of multi-legged robot that need to be solved. For example, when the swing legs of robot moves, because the COG, supported weight, and moment of inertia of body change dynamically, the posture of robot body becomes unstable; furthermore, with the switch between the swing leg and the support leg, there occur the collisions and slippage between the foot and the ground. Because of the above uncertain disturbances, the tiny vibrations occur when the robot is walking. Until now, we proposed a robust control of posture and vibration based on a virtual suspension model for multi-legged walking robot to decrease the tiny vibrations when the robot walks (Q. Huang, et al., 2004; Q. Huang, et al., 2007). However, how to decrease the impact force between the foot and the terrain has not been solved yet. When the robot walks on irregular terrain or it bumps against the obstacle, due to the influence from the impact force between the foot and the ground, it is a possibility that the mechanical parts of robot are destroyed; moreover, the vibration in the robot body occurs and arouses the instability of posture. Therefore, it is necessary to decrease the impact force for the walking of the multi-legged robot. Compliance control is one of the most effective control methods for the hand of manipulator to reduce impact force of contacting work (J. Huang, et al., 2002), because it can control relationship between the contact force and displacement of the hand. Recently, the compliance control was applied to biped walking robot (R. Quint, 1998). However, until now the compliance control is performed for decrease the vibration after impact force is generated, such as after the foot of the robot collides with the ground. It is impossible to reduce impact force perfectly as long as the compliance control is used after impact force is generated. So, counter measure which used the visual sensor to avoid object was proposed for manipulator in order to more effectively reduce the impact force (V. Mut, et al., 1998; X. Chen & H. Kano, 2005). And avoid action method that used virtual force to decelerate the 20