Research ArticleSymmetric caging formation for convex polygonal object transportation by multiple mobile robots based on fuzzy sliding mode control

- Three processes are presented to cage and transport an object, including forming a symmetric caging formation process, heading consensus process, and transporting an object process.
- A* algorithm is used so that mobile robots can move to the proper points in shortest paths, without collisions.
- Artificial potential field method is used to avoid obstacles, where robots and the object are regarded as a rigid body.
- Fuzzy sliding mode control method is applied for tracking control of the nonholonomic mobile robots.

In this paper, the problem of object caging and transporting is considered for multiple mobile robots. With the consideration of minimizing the number of robots and decreasing the rotation of the object, the proper points are calculated and assigned to the multiple mobile robots to allow them to form a symmetric caging formation. The caging formation guarantees that all of the Euclidean distances between any two adjacent robots are smaller than the minimal width of the polygonal object so that the object cannot escape. In order to avoid collision among robots, the parameter of the robots radius is utilized to design the caging formation, and the A⁎ algorithm is used so that mobile robots can move to the proper points. In order to avoid obstacles, the robots and the object are regarded as a rigid body to apply artificial potential field method. The fuzzy sliding mode control method is applied for tracking control of the nonholonomic mobile robots. Finally, the simulation and experimental results show that multiple mobile robots are able to cage and transport the polygonal object to the goal position, avoiding obstacles.