Research On Formation Control Of Nonholonomic Wheeled Mobile Multi-Robot

Multi-robot cooperation and coordination is one of the hot topics in robotics and multi-agent fields.Multi-robot cooperation and coordination can accomplish tasks that cannot handle with only single one.The basis of multi-robot cooperation and coordination is formation control,which is also a hot research field at home and abroad.The so-called formation control refers to the multi-robots approached to target point in the process of sharing a unified rule to maintain a stable formation,and is bounded by the surrounding environment at the same time.We study the formation control of multi-robots under obstacles environment and obstacles-free environment separately.And the establishment of system model,designment of sliding mode controller,and the analysis of system stability are included.The main achievements are as follows:Firstly,the kinematics model and dynamic model of non-holonomic wheeled mobile robot are established under Cartesian coordinate,introduction to usual obstacle avoidance algorithm,the software of formation system control is built to lay the foundation for the following theoretical introduction and simulation experiments.Secondly,the virtual leader and the virtual leader formation control model is adopted for the question about nonholonomic wheeled mobile robots under obstacle-free environment.Aiming at the chattering phenomenon of traditional sliding mode control exists in multi-robot formation,the improved sliding mode surface is proposed.Using the integral sliding mode control method,and a new saturation function is adapted to suppress the occurrence of chattering.,the asymptotic stability of formation system is proved by Lyapunov function.And the simulation results show that the improved sliding mode control system can improve stability of whole formation system and suppress the chattering phenomenon well.Finally,the obstacle avoidance problem of nonholonomic wheeled mobile robots is studied taking account into real environment.This thesis presents an improved method of geometic obstacle avoidance with line-of-sight based on the defect of artificial potential field method.The obstacle is abstracted into its circumcircle model by using the distance sensor embedded in the mobile robot.The radius of circumcircle is the maximum range affected by the repulsive force,and then the geometrical-mathematical relation model is used to determine the direction of the obstacle to be avoided.Then the Lyapunov function is designed to prove the stability of the obstacle avoidance system.After determining the obstacle avoidance angle,the need for a certain buffer time to change its direction of motion.The thesis gives a concept of angular velocity rate,establishing minimum geometric obstacle avoidance surface to make sure the complement of obstacle avoidance.The simulation results show that the method of geometric obstacle avoidance based on line-of-sight under the artificial potential field successfully completes the obstacle avoidance promise that ensuring the formation integrity of the nonholonomic mobile robots formation.