Cooperation of legged robots is useful to transport autonomously a large-sized object on irregular terrain such as steps or slopes. In this research, we propose the cooperative transportation method by quadruped robots in 3-dimensional environment.

   The legged robot vibrates its body during walking and so does the object on it (Fig. 1). Then the following two points must be considered; (a) internal force on the object and (b) vibrating ingredients of sensed values, the object position and orientation. These values include the ingredient of the object’s deviation from the normal position and that caused by the vibration of the robots. Therefore, it is impossible to feed back these values directly to the control system like the case of controlling wheeled robot. In this study, we do not deal with how to control the robot body completely without vibration, but tackle with construction of a motion control method of cooperation system with vibration.

   The approach is detailed as follows; Firstly (1) we decide how to suitably distribute the object’s degree of freedom to two quadruped robots. Secondly (2) we create the vibration model for the periodic gait of the quadruped robot. This model enables us to estimate the deviation of an object on the robot and the vibration parameters of the other robot (Fig. 2). Then, (3) we create the unresponsive section of the robot velocity for a little deviation of the object that is close to zero. This makes the transporting system robust against vibration. The effectiveness is verified by experiments using two quadruped robots equipped with the end-effectors (Fig. 3).

   Keywords: Cooperative Transportation, Quadruped Robot, Multiple Mobile Robots

References

1. Y. Aiyama, et al.: "Cooperative Transportation by Two 4-legged Robots with Implicit Communication", 4th International Symposium on Distributed Autonomous Robotic Systems, pp131-140, 1998.
2. M. Hara, et al: "System of Cooperative Transportation by Two Legged Robots on Irregular Terrain", In Proceedings of. the 4th Japan-France / 2nd Asia-Europe Congress on Mechatronics, pp.304-309, 1998.