Formation Control And Cooperative Transport Strategy For Multiple Mobile Robots In Unknown Environment

Multi-robot cooperation has a wide range of application in military, defense, industry and daily life after twenty years development. It demonstrates tremendous advantages in the application of formation patrol, environment exploration, production lines and storage industry. However, some specific application tasks, such as multi-robot cooperative map exploration, large object transportation and target grasping, require robot team to form particular formation structure, and keep the formation unchanged or alter the formation according to environment constraints. Therefore, multi-robot formation control attracts wide research attention and becomes one of the key technologies of multi-robot collaboration and coordination. The paper took cooperative object transportation as research background and made an intensive study on multi-robot environment perception, cooperative location, cooperative formation, formation obstacle avoidance and other key technologies.Location and environment perception are the basis and important issue in formation control study. In order to realize formation control, intelligent mobile robot in the team firstly needs to acquire its attitude through specific measures, understand and describe its working environment sufficiently. Therefore, a random obstacle group environment modeling method based on2-D laser ranger finder was proposed with respect to environment perception and modeling involved in multi-robot formation control technology. In the method, sensor data were stored in the form of polar vector and environment in the working space was modeled as random number obstacle groups, which saved storage amount of environment information; At the same time, a multi-robot cooperative location method based on relative observation model was presented, which combined information from external laser rangerfinder and vision sensor. The outstanding advantage of the method is that no global coordinate information of the robot is needed, precise relative cooperative location between every follower robot and its leader robot are achieved combining vision information and laser information only, which lays the foundation for the subsequent formation control and cooperaton task.A kinematic and fuzzy logic control combined cooperative formation control algorithm based on leader-follower formation control framework with respect to cooperative formation, which is the key problem in multi-robot formation control. The algorithm is mainly based on backstepping technology, and utilizes fuzzy logic controller based on Madani fuzzy model to control internal velocity loop, which makes actual velocity converge to designed one; meanwhile, kinematic controller makes robot attitude converge to designed one. The algorithm has shorter velocity error convergence time and improves real-time characteristic and control performance of the system.Multi-robot dynamic and optimized formation switching obstacle avoidance strategy is given in unknown obstacle environment. It percepts and acquires environment information autonomously via laser sensor on the leader robot and guides the robot team navigate obstacles autonomously. The strategy takes original formation of the robot team and environment constraints during obstacle avoidance process into consideration fully, and gets the optimum leader-follower topology being fit for the current environment most by making a selection between zero switching, isomorphic switching and isomeric switching; The strategy can both control the formation structure dynamically for the robot team carrying out formation tasks and be fit to the current environment constraints mostly. It has excellent performance of making robots in the team selecting the most optimum formation and is a new method in both theory and practice.On the foundation of formation control, multi-robot cooperative object transportation on flat environment is studied, and a multi-robot cooperativetransportation strategy based on L-VL-F formation control framework was proposed. The strategy transforms multi-robot transportation task into a two-stage formation control problem via seeing object needed to be transported as ‘Virtual Leader’. It realizes multi-robot object transportation tasks while avoiding obstacles in the environment.Ultimately, a great number of experiment studies were done on the self-developed multiple mobile robot experimental platform, including: formation generation along linear and circular trajectory, formation switching in static environment, dynamic and optimized formation switching in obstacle environment and multi-robot cooperative transportation experiment. Experiment results show that multi-robot can achieve formation control, formation obstacle avoiding and cooperative transportation tasks successfully, and validate the effectiveness of formation control algorithm and cooperative transportation strategy proposed in the paper.The paper takes multi-robot formation control as main line and cooperative object transportation as background, and makes studies on the following key technology in multi-robot formation control: environment perception, cooperative location, cooperative formation and formation obstacle avoidance. The paper gets a certain amount of theoretical results and experimental results. The study is importance complements to the multi-robot cooperation and coordination study and has a certain theoretical consequence and practical value...