In this article, leader-following formation control is investigated for nonholonomic mobile robots with inaccurate measurements of global positions and velocities. In many existing results, the leader robot's velocities are assumed to be precisely measured and transmitted to follower robots, and unmodeled parts of the kinematic model caused by inaccurate global position are often ignored. First, an error-based extended state observer (EBESO) for each robot is designed to counteract influence of the inaccurate global positions and velocities in real time. Then, an EBESO-based formation controller without the leader robot's velocities is proposed to guarantee the accurate formation tracking performances. Furthermore, both convergence of the EBESO and stability analysis of the closed-loop error system are provided, respectively. The superiority of the proposed method is verified and illustrated by experiments. K E Y W O R D Serror-based extended state observer, leader-following formation, multirobot systems, nonholonomic mobile robots INTRODUCTIONRecently, cooperative control of nonholonomic mobile robots has been an active research field of multiple unmanned vehicle systems. [1][2][3] Compared with a single robot, the cooperation of multiple robots shows some excellent performances, such as high efficiency, adaptability, and robustness. One of the key issues in multirobot systems is the formation control that aims at cooperating a group of robots to form up and maintain a desired geometric structure. Formation control of mobile robots has extensive applications in various fields, such as surveillance, 4 search and rescue operations, 5,6 cooperative transportation, 7,8 and military applications. 9 Many methods have been applied to the formation control of multiple robots, such as the behavior-based method, 10,11 the virtual structure approach, 12,13 the leader-following scheme, [14][15][16] the potential field method, 17 and consensus-based approach. 18,19 No matter which formation control method is adopted, the position information of robots comes from the local positioning (such as onboard cameras [20][21][22] ) or the global positioning (such as ultrawideband (UWB) sensors 23,24 ). It is pointed out that the local position information is precise but not comprehensive whereas the global position information is comprehensive but not accurate. In outdoor or complex situations, the local position information is usually limited, so the global position information is indispensable for formation control, path planning, and obstacle avoidance of robots. Unfortunately, the global positioning deviation is inevitable because robot's barycenter is difficult to be ascertained precisely in reality. Thus, how to control the formation of multiple robots in a high precision is a challenging work because of the global positioning deviation.
This article proposes an event-triggering mechanism (ETM)-based security control strategy for an uncertain networked control system (NCS) to cope with jamming attacks on multiple transmission channels. A structure of the system control block for the attacked uncertain NCS is constructed and a virtual system is designed to cope with the mismatched parametric uncertainty and derive both the optimal control gain and the virtual control gain. Under multiple wireless channels jamming attack, an optimal jamming attack strategy that maximizes the attack power from the attacker's point of view is engineered. Furthermore, an ETM-based control strategy with jamming parameters is designed to ensure the input-to-state stability of NCS under uncertainty and jamming attacks. Finally, the numerical simulation results show the effectiveness of the control algorithm in this article.
A novel distributed prescribed-time leader-follower tracking consensus control strategy is proposed for high-order nonlinear multi-agent systems (MASs) with lower triangular time-varying dynamic in directed communication topology. Firstly, a distributed prescribed-time state observer (DPTSO) is presented for follower to observe the leader’s state, transforming the consensus problem into a tracking control problem that the follower tracks the observations of the DPTSO. Then, a distributed prescribed-time controller is developed with the cascade control framework and dynamic control, which avoids differential explosion in traditional back-stepping control. Convergence time of both the DPTSO and the distributed prescribed-time controller is not only explicitly pre-specified but also determined regardless of the initial state of system and control parameters. Finally, it is demonstrated that the closed-loop systems realize prescribed-time full state leader-follower tracking consensus. Simulation results show that the method is effective and feasible.
This article studies a distributed consensus‐based estimation problem for discrete time‐varying non‐linear systems with missing measurements and Denial of Service (DoS) attacks. The probability of missing measurements is independent for each sensor. The communication link between sensor nodes is unreliable and subjected to DoS attacks. To achieve accurate state estimation against missing measurements, a local estimator with compensation mechanism is designed for each sensor node. A stochastic event‐triggered mechanism is used to lessen additional information transfer. Based on this, a distributed consensus‐based estimator is constructed by continually fusing local neighbours information matrixs and vectors. Moreover, the analysis of the designed estimator boundedness is presented. Finally, the effectiveness of the proposed algorithm is verified by three numerical examples.
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