Abstract：This paper presents a hierarchical fuzzy controller for mobile robot navigating from an initial position to a target point through unknown environments.Eight sonar sensors are mounted on the robot to detect obstacles so that the mobile robot can navigate safely.Sonar data and target information are processed by the two-stage fuzzy system to generate the control commands.Firstly,the danger fuzzy controller(DFC) is used for each sonar sensor to judge the danger degree of the detected obstacles.Then,all the outputs of the inference engine are analyzed and normalized by the combination behavior.Finally,the danger information as well as the fuzzified target information is induced by the velocity fuzzy controller(VFC) and the rotation fuzzy controller(RFC) respectively to determine the motion of the robot.Maximum defuzzification method is used to solve the "symmetric hesitation" problem.Simulations and experiments validate the performance and effectiveness of the proposed approach.
 Borenstein J, Koren Y. Error eliminating rapid ultrasonic firing for mobile robot obstacle avoidance[J]. IEEE Transactions on Robotics and Automation, 1995,11(1):132-138.  Ramirez-Serrano A, Boumedine M. Real-time navigation in unknown environments using fuzzy logic and ultrasonic sensing[A]. Proceedings of the 11th IEEE International Symposium on Intelligent Control[C]. USA:IEEE, 1996. 26-30.  Marref H, Barret C. Sensor-based fuzzy navigation of an autonomous mobile robot in an indoor environment[J]. Control Engineerring Practice,2000, 8(7):757-768.  Beom H R, Cho H S. Sonar-based navigation experiments on mobile robots in indoor environments [A]. Proceedings of the 15th IEEE International Symposium on Intelligent Control [C]. USA:IEEE,2000. 395-401.  Thongchai S, Kawamura K. Application of fuzzy control to a sonarbased obstacle avoidance mobile robot[A]. Proceedings of the 2000IEEE International Conference on Control Applications[C]. USA:IEEE, 2000. 425-430.  孙多青,霍伟,杨枭.含模型不确定性移动机器人路径跟踪的分层模糊控制[J].控制理论与应用,2004,21(4):489-494.  Hani A. Hagras. A hierarchical type-2 fuzzy logic control architecture for autonomous mobile robots[J]. IEEE Transactions on Fuzzy Systems,2004,12(4):524-539.  Teiner M, Rojas I, Goser K, et al. A hierarchical fuzzy steering controller for mobile robots [A]. Proceedings of the IEEE International Symposium on Computational Intelligence for Measurement Systems and Applications[C]. USA:IEEE, 2003. 7-12.  孙增圻,张再兴,邓志东.智能控制理论与技术[M].北京:清华大学出版社,1997.