Switching fuzzy tracking control for mobile robots under curvature constraints

In this paper a switching fuzzy logic controller for mobile robots with a bounded curvature constraint is presented. The controller tracks piece-wise linear paths, which are an approximation of the feasible smooth reference path. The controller is constructed through the use of a map, which transforms the problem to a simpler one; namely the tracking of straight lines. This allows the use of an existing fuzzy tracker deployed in a previous work, and its simplification leading to a 70% rule reduction. Simulation results and a comparison analysis with existing trackers are also presented along with some stability considerations on the impulsive error dynamics which emerge.     

Image-based fuzzy trajectory tracking control for four-wheel steered mobile robots

A four-wheel steered mobile robot is fit for a higher power or improvement in the movement speed of a robot than a two-independent wheeled one. Since a steered mobile robot that slips very often cannot apply a popular dead-reckoning method using rotary encoders, it is desirable to use external sensors such as cameras. This paper describes a method to trace a straight line for four-wheel steered mobile robots using an image-based control method. Its controller is designed as a fuzzy controller and evaluated through some simulations and real robot.     

改进QPSO算法的移动机器人轨迹跟踪控制方法

分析了智能群体的决策机制,发现在智能群体决策过程中,个体粒子参与决策的权利根据个体的优劣程度是不同的,提出了在量子粒子群优化（QPSO）算法中引入线性权重算子进一步提高QPSO算法的搜索效率及优化性能。分析了移动机器人轨迹跟踪控制的滑模变结构控制器设计方法,并采用指数趋近律和幂次趋近律相结合的方法,设计了新的滑模跟踪控制律,使用PSO算法、QPSO算法和改进算法优化了滑模跟踪控制器中的参数,通过两个实例验证了优化后的跟踪控制器的设计效果;设计效果的分析和比较表明了设计的跟踪控制器能够控制机器人实现对既定轨迹的跟踪,仿真结果显示改进QPSO算法能够在轨迹跟踪控制器的参数优化中取得更好的优化效果。     

A nonlinear trajectory tracking controller for mobile robots with velocity limitation via fuzzy gains

This paper proposes a fuzzy controller for trajectory tracking with unicycle-like mobile robots. Such controller uses two Takagi–Sugeno (TS) fuzzy blocks to generate its gains. The controller is able to limit the velocity and control signals of the robot, and to reduce the errors arising from its dynamics as well. The stability of the developed controller is proven, using the theory of Lyapunov. Experimental results show that the use of the proposed controller is attractive in comparison with the use of a controller with fixed saturation function.     

Robust formation tracking control of mobile robots via one-to-one time-varying communication

We solve the formation tracking control problem for mobile robots via linear control, under the assumption that each agent communicates only with one ‘leader’ robot and with one follower, hence forming a spanning-tree topology. We assume that the communication may be interrupted on intervals of time. As in the classical tracking control problem for non-holonomic systems, the swarm is driven by a fictitious robot which moves about freely and which is a leader to one robot only. Our control approach is decentralised and the control laws are linear with time-varying gains; in particular, this accounts for the case when position measurements may be lost over intervals of time. For both velocity-controlled and force-controlled systems, we establish uniform global exponential stability, hence consensus formation tracking, for the error system under a condition of persistency of excitation on the reference angular velocity of the virtual leader and on the control gains.     

A learning fuzzy algorithm for motion planning of mobile robots

A sensor-based fuzzy algorithm is proposed to navigate a mobile robot in a 2-dimensional unknown environment filled with stationary polygonal obstacles. When the robot is at the starting point, vertices of the obstacles that are visible from the robot are scanned by the sensors and the one with the highest priority is chosen. Here, priority is an output fuzzy variable whose value is determined by fuzzy rules. The robot is then navigated from the starting point to the chosen vertex along the line segment connecting these two points. Taking the chosen vertex as the new starting point, the next navigation decision is made. The navigation process will be repeated until the goal point is reached.In implementation of fuzzy rules, the ranges of fuzzy variables are parameters to be determined. In order to evaluate the effect of different range parameters on the navigation algorithm, the total traveling distance of the robot is defined as the performance index first. Then a learning mechanism, which is similar to the simulated annealing method in the neural network theory, is presented to find the optimal range parameters which minimize the performance index. Several simulation examples are included for illustration.     

A linear-interpolation-based controller design for trajectory tracking of mobile robots

This work presents a novel linear interpolation based methodology to design control algorithms for the trajectory tracking of mobile robotic systems. Particularly, a typical nonlinear multivariable system—a mobile robot—is analysed. The methodology is simple and can be applied to the design of a large class of control systems. Simulation and experimental results are presented and discussed, demonstrating the good performance of the proposed methodology.     

Adaptive observer-based trajectory tracking control of nonholonomic mobile robots

In this paper, an adaptive observer-based trajectory tracking problem is solved for nonholonomic mobile robots with uncertainties. An adaptive observer is first developed to estimate the unmeasured velocities of a mobile robot with model uncertainties. Using the designed observer and the backstepping technique, a trajectory tracking controller is designed to generate the torque as an input. Using Lyapunov stability analysis, we prove that the closed-loop system is asymptotically stable with respect to the estimation errors and tracking errors. Finally, the simulation results are presented to validate the performance and robustness of the proposed control system against uncertainties.     

Modeling and hierarchical tracking control of tri-wheeled mobile robots

After exploring the structure of the dynamics derived by using the Appell equation, we propose a hierarchical tracking controller for a tri-wheeled mobile robot in this paper. With appropriately chosen privileged variables, the reduced equations are decoupled from the kinematic equations associated with the underlying nonholonomic constraints. This special character of the system makes it possible to separate the design into three levels: motion planning, kinematic, and dynamic. In the proposed scheme, a fuzzy inference engine in the kinematic level is used to update the desired trajectory computed in the motion-planning level. An adaptive sliding-mode controller is then adopted to track the new reference values of privileged variables in the dynamic level, which subsequently drives the nonprivileged variables. Simulation results show the effectiveness of such a tracking-control scheme, which concurrently takes kinematics and dynamics into consideration. All system variables can be tracked asymptotically to their desired values, which are assured by the skew-symmetric property of the Appell equation.     

加入临时路径的移动机器人路径跟踪模糊控制

对含不确定性的移动机器人系统设计了路径跟踪模糊控制方法。该方法引入临时路径,使机器人先从初始位置出发沿临时路径行进,当移动到期望路径附近时,再让机器人跟踪期望路径。整个控制过程只需要一个模糊控制器,极大地减少了工作量,并引进积分环节以消除稳态误差。仿真和实验结果验证了该方法的有效性。     

Bounded controllers for global path tracking control of unicycle-type mobile robots

This paper presents a design of bounded controllers with a predetermined bound for global path tracking control of unicycle-type mobile robots at the torque level. A new one-step ahead backstepping method is first introduced. The heading angle and linear velocity of the robots are then considered as immediate controls to force the position of the robots to globally and asymptotically track its reference path. These immediate controls are designed based on the one-step ahead backstepping method to yield bounded control laws. Next, the one-step ahead backstepping method is applied again to design bounded control torques of the robots with a pre-specified bound. The proposed control design ensures global asymptotical and local exponential convergence of the position and orientation tracking errors to zero, and bounded torques driving the robots. Experimental results on a Khepera mobile robot verify the proposed control controller.     

基于模糊控制的移动机器人FPGA实现

针对轮式移动机器人寻线行走的跟踪控制要求,提出一种通用的移动机器人行走模糊控制设计方法,并以FPGA为核心器件,通过硬件描述语言(VHDL)实现移动机器人模糊控制系统,充分发挥模糊控制及可编程逻辑器件的优点。实验表明,该移动机器人具有自动纠偏、寻线准确、高集成度和高可靠性的特点。     

A hybrid control approach to action coordination for mobile robots

In this paper, the problem concerning how to coordinate the contributions from concurrent controllers, when controlling mobile robots, is investigated. It is shown how a behavior based control system for autonomous robots can be modeled as a hybrid automaton, where each node corresponds to a distinct robot behavior. This type of construction gives rise to chattering executions, but it is shown how regularized automata can be used to solve this problem. As an illustration, the obstacle-negotiation problem is solved by using a combination of a robust path-following behavior and a reactive obstacle-avoidance behavior that move the robot around a given obstacle at a predefined safety distance.     

Precise trajectory tracking ofmecanum-wheeled omnidirectional mobile robots via a novel fixed-time sliding mode control approach

This paper proposes a novel fixed-time sliding mode control approach for trajectory-tracking tasks of a mecanum-wheeledomnidirectional mobile robot. First, the idea of two-phase attractors is introduced into the domain of sliding mode control,and a new fixed-time sliding surface is proposed. Then, according to this sliding surface, a new type of nonsingular fastterminal sliding mode control algorithm is designed for the omnidirectional mobile robot, which can realize a fast fixed-timeconvergence property. The stability of the control system is proven scrupulously, and a guideline for control-parameter tuningis expounded. Finally, experiments are implemented to test the trajectory-tracking performance of the robot. Experimentalresults demonstrate the superiority of the proposed sliding surface and the corresponding control scheme in comparison withbenchmark controllers.     

Unified nonsingular tracking and stabilization controller design for unicycle-type wheeled mobile robots

A unified, singularity-avoidant controller which enables simultaneous trajectory tracking and posture stabilization of unicycle-type wheeled mobile robots is proposed. The design scheme is based on phase portrait analysis, dynamic feedback linearization and sliding mode control. Path planning via phase portrait analysis plays a key role in choosing the control parameters and the initial value of the extended state in avoiding any singularity. Simulation results on posture stabilization as well as an eight-shaped trajectory tracking are presented to demonstrate the performance of the proposed controller.     

移动机器人的免疫非时间参考路径跟踪控制

针对移动机器人非时间参考控制方法的不足之处,借鉴生物免疫反馈响应过程的调节规律,提出了移动机器人的免疫非时间参考路径跟踪控制方法。该方法既有不依时间规划调节输出控制的特性,而且充分考虑到机器人机械结构与电机力矩特性的要求,实现了在误差较大时对控制量的限幅;通过选取合适参数,还能减小系统的超调量,进一步改善整个控制系统的性能。对于动态事件,采用插入算法,提高机器人对动态环境适应能力,使控制方法更适宜实际应用。仿真与实物实验,验证了该方法的有效性。     

EP-based kinematic control and adaptive fuzzy sliding-mode dynamic control for wheeled mobile robots

This paper proposes a complete control law comprising an evolutionary programming based kinematic control (EPKC) and an adaptive fuzzy sliding-mode dynamic control (AFSMDC) for the trajectory-tracking control of nonholonomic wheeled mobile robots (WMRs). The control gains for kinematic control (KC) are trained by evolutionary programming (EP). The proposed AFSMDC not only eliminates the chattering phenomenon in the sliding-mode control, but also copes with the system uncertainties and external disturbances. Additionally, the convergence of trajectory-tracking errors is proved by the Lyapunov stability theory. Computer simulations are presented to confirm the effectiveness of the proposed complete control law. Finally, real-time experiments are done in the test field to demonstrate the feasibility of real WMR maneuvers.     

Model-based PI–fuzzy control of four-wheeled omni-directional mobile robots

The purpose of this study is to suggest and examine a PI–fuzzy path planner and associated low-level control system for a linear discrete dynamic model of omni-directional mobile robots to obtain optimal inputs for drivers. Velocity and acceleration filtering is also implemented in the path planner to satisfy planning prerequisites and prevent slippage. Regulated drivers’ rotational velocities and torques greatly affect the ability of these robots to perform trajectory planner tasks. These regulated values are examined in this research by setting up an optimal controller. Introducing optimal controllers such as linear quadratic tracking for multi-input–multi-output control systems in acceleration and deceleration is one of the essential subjects for motion control of omni-directional mobile robots. The main topics presented and discussed in this article are improvements in the presented discrete-time linear quadratic tracking approach such as the low-level controller and combined PI–fuzzy path planner with appropriate speed monitoring algorithm such as the high-level one in conditions both with and without external disturbance. The low-level tracking controller presented in this article provides an optimal solution to minimize the differences between the reference trajectory and the system output. The efficiency of this approach is also compared with that of previous PID controllers which employ kinematic modeling. Utilizing the new approach in trajectory-planning controller design results in more precise and appropriate outputs for the motion of four-wheeled omni-directional mobile robots, and the modeling and experimental results confirm this issue.     

Finite-time tracking control for multiple non-holonomic mobile robots based on visual servoing

This paper investigates finite-time tracking control problem of multiple non-holonomic mobile robots via visual servoing. It is assumed that the pinhole camera is fixed to the ceiling, and camera parameters are unknown. The desired reference trajectory is represented by a virtual leader whose states are available to only a subset of the followers, and the followers have only interaction. First, the camera-objective visual kinematic model is introduced by utilising the pinhole camera model for each mobile robot. Second, a unified tracking error system between camera-objective visual servoing model and desired reference trajectory is introduced. Third, based on the neighbour rule and by using finite-time control method, continuous distributed cooperative finite-time tracking control laws are designed for each mobile robot with unknown camera parameters, where the communication topology among the multiple mobile robots is assumed to be a directed graph. Rigorous proof shows that the group of mobile robots converges to the desired reference trajectory in finite time. Simulation example illustrates the effectiveness of our method.