自治飞艇直接自适应模糊路径跟踪控制

针对具有模型不确定和未知外部干扰的自治飞艇, 提出了直接自适应模糊路径跟踪控制方法. 该方法由路径跟踪控制和自适应模糊控制两部分组成. 首先基于飞艇的平面运动模型设计路径跟踪控制律, 包括制导律计算、偏航角跟踪和速度控制3 部分; 然后构造直接自适应模糊控制器逼近路径跟踪控制律中的不确定项. 稳定性分析证明所设计的控制律能使飞艇跟踪给定的期望路径, 跟踪误差收敛到原点的小邻域内. 仿真结果验证了所提出方法的有效性.

     

自治飞艇动力学建模及反馈控制

在Kirchhoff方程和Newton-Euler理论基础上,推导出一种通用符合实际的、带有气囊和压块的飞艇六自由度动力学模型,并对该模型实施了状态量和控制量的非线性反馈变换,同时利用最小相位系统特性,构造飞艇反馈线性化动力学系统.在此基础上,分别研究了飞艇在纵向平面内的平衡飞行可行性和稳定性,以及平衡航迹的镇定和期望输出的跟踪.仿真结果和样机试飞都验证了理论分析的正确性和可靠性.     

Finite-time path following control for a stratospheric airship with input saturation and error constraint

This paper addresses the finite-time path following control problem for an under-actuated stratospheric airship with input saturation, error constraint, and external disturbances. To handle the adverse effect of input saturation, anti-windup compensators are employed and finite-time convergence of the saturated control solution is established. Error constraints of airship position and attitude are handled by incorporating a tan-type barrier Lyapunov function (TBLF) in guidance and attitude control schemes. Backstepping design is presented with the anti-windup compensators, the TBLF, and nonlinear disturbance observers which estimate the external disturbances. Stability analysis shows that the tracking errors of the airship position converge into a small set around zero within finite-time, the constrained requirements on the airship position and attitude are not violated during operation, and all closed-loop signals are guaranteed to be uniformly ultimately bounded. Compared with the conventional control scheme, simulation results illustrate that the proposed finite-time controller offers a faster convergence rate and a higher path following accuracy for the stratospheric airship.     

A review of path following control strategies for autonomous robotic vehicles: Theory,simulations, and experiments

This article presents an in-depth review of path following control strategies that are applicable to a wide range class of marine, ground, and aerial autonomous robotic vehicles. From a control system standpoint, path following can be formulated as the problem of stabilizing a path following error system that describes the dynamics of position and possibly orientation errors of a vehicle with respect to a path, with the errors defined in an appropriate reference frame. In spite of the large variety of path following methods described in the literature we show that, in principle, most of them can be categorized in two groups: stabilization of the path following error system expressed either in the vehicle's body frame or in a frame attached to a “reference point” moving along the path, such as a Frenet-Serret (F-S) frame or a Parallel Transport (P-T) frame. With this observation, we provide a unified formulation that is simple but general enough to cover many methods available in the literature. We then discuss the advantages and disadvantages of each method, comparing them from the design and implementation standpoint. We further show experimental results of the path following methods obtained from field trials testing with under-actuated and over-actuated autonomous marine vehicles. In addition, we introduce open-source Matlab and Gazebo/ROS simulation toolboxes that are helpful in testing path following methods before their integration in the combined guidance, navigation, and control systems of autonomous vehicles.     

Underactuated ship tracking control: Theory and experiments

We consider complete state tracking feedback control of a ship having two controls, namely surge force and yaw moment. The ship model has similarities with chained form systems but cannot directly be transformed in chained form. In particular, the model has a drift vector field as opposed to the drift-free chained form systems. It is shown here that methods developed for tracking control of chained form systems still can be used for developing a tracking control law for the ship. Through a coordinate transformation the model is put in a triangular-like form which makes it possible to use integrator backstepping to develop a tracking control law. The control law steers both the position variables and the course angle of the ship, providing exponential stability of the reference trajectory. Experimental results are presented where the control law is implemented for tracking control of a model of an offshore supply vessel, scale 1:70. In the experiments the ship converges exponentially to a neighbourhood of the reference trajectory, and stays close with errors depending on factors as unmodelled dynamics, parameter uncertainty, measurement noise, thruster saturation, waves, currents and position measurement failures.     

Adaptive tracking control of manipulators: Theory and experiments

This paper considers the trajectory tracking problem for uncertain robot manipulators and proposes two adaptive controllers as solutions to this problem. The first controller is derived under the assumption that the manipulator state is measurable, while the second strategy is developed for those applications in which only position measurements are available. The adaptive schemes are very general and computationally efficient since they do not require knowledge of either the mathematical model or the parameter values of the manipulator dynamics, and are implemented without calculation of the robot inverse dynamics or inverse kinematic transformation. It is shown that the control strategies ensure uniform boundedness of all signals in the presence of bounded disturbances, and that the ultimate size of the tracking errors can be made arbitrarily small. Experimental results are presented for a PUMA 560 manipulator and demonstrate that accurate and robust trajectory tracking can be achieved by using the proposed controllers.     

A path following control for unicycle robots

In this work we present a new path following control for unicycle robots that is applicable for almost all the possible desired paths and whose analysis is very straightforward. First we select the path following method that consists of two steps: choosing a “projection” that relates the actual posture to the desired path and imposing a “motion exigency” to ensure that the robot advances. A “projection” that considers all the error coordinates is selected and closed equations are obtained for it. The uniqueness projection is carefully analyzed and a necessary and sufficient condition is also presented. This condition shows that a slight bound on the curvature derivative of desired paths must be imposed to preserve uniqueness. It is remarkable that the selected path following is applicable for paths containing zero‐radius turns, a problem that has never been resolved as far as we know. In addition, an asymptotically stable control law is found using the closed form equation of the proposed path following and the second Lyapunov method. Finally, we show the behavior of the path following and the control law through several simulated and experimental results, using a computerized wheelchair built at our research facility. © 2001 John Wiley & Sons, Inc.     

Output synchronization control of ship replenishment operations: Theory and experiments

A leader–follower synchronization output feedback control scheme is presented for the ship replenishment problem where only positions are measured. No mathematical model of the leader ship is required, and the control scheme relies on nonlinear observers to estimate velocity and acceleration of all ships to realize the feedback control law. The scheme yields semi-global uniform ultimate boundedness of the closed-loop errors. The bound is a function of the main ship acceleration, and under the assumption of zero main ship acceleration the closed-loop errors are semi-globally exponentially converging. The results are verified through experiments on a model-scale ship.     

Non-linear control of advanced direct drive robots: Theory and experiments

Direct drive robots are widely used to perform high precision positioning, and advanced control algorithms are applied to attain the desired performance. Small direct drive manipulators are widely used in aerospace, biotechnology, instrumentation, medicine, micro manufacturing, high-density integrated circuits and VLSI fabrication, etc. This paper studies non-linear modelling, analysis and control of direct drive robots to guarantee the desired level of performance. We are particularly interested in the physical laws to model mechanical-electromagnetic phenomena and effects, and the integration of electric motors is a key factor to design high performance direct drive robots. The non-linear mathematical model, found using the Lagrange equations of motion, is applied in non-linear analysis and design. The design method is described and validated. The design concept uses the Hamilton-Jacobi and Lyapunov theories to synthesize robust tracking controllers. It is illustrated that minimizing a non-quadratic performance functional, a bounded control law is analytically designed using necessary conditions for optimality. The sufficient conditions for robust stability are examined using the criteria imposed on positive-definite return functions. Results indicate that the reported method allows one to guarantee robust accurate tracking and disturbance attenuation. A two-degree-of-freedom prototype of direct drive manipulator is described, and the achieved performance is documented and discussed.     

基于观测器的轮式移动机器人路径跟踪控制

研究基于状态观测器的轮式移动机器人的路径跟踪控制问题.首先简要回顾了基于状态反馈的移动机器人的路径跟踪控制问题;进而通过适当的状态变换将移动机器人模型转换为合适的形式,并在移动机器人的位置可以测量的情况下设计了一种可保证状态观测误差指数收敛的状态观测器;最后结合状态反馈路径跟踪控制器和所设计的观测器得到了一种基于观测器的路径跟踪控制器,该控制器可以保证移动机器人的运动轨迹指数收敛到期望路径上.仿真结果证实了所提出的基于观测器的路径跟踪控制器的有效性.     

带拖车移动机器人全局路径跟踪控制

研究带拖车移动机器人的前向路径跟踪控制和倒车路径跟踪控制问题.首先建立系统的运动学模型,并进行系统的运动特性分析;然后基于Lyapunov方法提出一种新的单体移动机器人全局路径跟踪控制器,并将其引入带拖车移动机器人的前向路径跟踪控制;再后通过运动学变换,实现了拖挂任意节拖车的系统的倒车路径跟踪控制;最后针对三车体系统的两种路径跟踪控制进行仿真,结果表明了该方法的有效性.     

Nonlinear model predictive control for path following problems

This paper presents a general nonlinear model predictive control scheme for path following problems. Path following problem of nonlinear systems is transformed into a parameter‐dependent regulation problem. Sufficient conditions for recursive feasibility and asymptotic convergence of the given scheme are presented. Furthermore, a polytopic linear differential inclusion‐based method of choosing a suitable terminal penalty and the corresponding terminal constraint are proposed. To illustrate the implementation of the nonlinear model predictive control scheme, the path following problem of a car‐like mobile robot is discussed, and the control performance is confirmed by simulation results. Copyright © 2014 John Wiley & Sons, Ltd.     

Formation path following control of unicycle-type mobile robots

This paper presents a control strategy for the coordination of multiple mobile robots. A combination of the virtual structure and path following approaches is used to derive the formation architecture. A formation controller is proposed for the kinematic model of two-degree-of-freedom unicycle-type mobile robots. The approach is then extended to consider the formation controller by taking into account the physical dimensions and dynamics of the robots. The controller is designed in such a way that the path derivative is left as a free input to synchronize the robot’s motion. Simulation results with three robots are included to show the performance of our control system. Finally, the theoretical results are experimentally validated on a multi-robot platform.     

Autonomous UAV path planning and estimation

Unmanned aerial vehicles (UAVs) have shown promise in recent years for autonomous sensing. UAVs systems have been proposed for a wide range of applications such as mapping, surveillance, search, and tracking operations. The recent availability of low-cost UAVs suggests the use of teams of vehicles to perform sensing tasks. To leverage the capabilities of a team of vehicles, efficient methods of decentralized sensing and cooperative path planning are necessary. The goal of this work is to examine practical control strategies for a team of fixed-wing vehicles performing cooperative sensing. We seek to develop decentralized, autonomous control strategies that can account for a wide variety of sensing missions. Sensing goals are posed from an information theoretic standpoint to design strategies that explicitly minimize uncertainty. This work proposes a tightly coupled approach, in which sensor models and estimation objectives are used online for path planning.     

固定双桨驱动的无人水面艇自主直线路径跟踪系统

针对直流电机驱动固定双桨的无人水面艇,介绍了一种自主直线路径跟踪系统,该系统由岸基监控系统和艇载控制系统组成,具有自主航行和遥控航行两种工作模式,可在自主航行出现危险时切换到遥控模式,保证航行安全。岸基监控系统通过数传电台与艇载控制系统通信,向艇载控制系统发送控制命令,接收并显示其传回的状态信息;艇载控制系统以工控机为主控单元,进行数据采集与解算,与岸基监控系统通信,并为直线路径跟踪控制算法提供程序接口;GPS双天线高精度测向定位系统为直线路径跟踪控制算法提供位置和航向信息,直线路径跟踪控制算法根据距离偏差和航向偏差计算出左右两侧电机电压,进而控制无人水面艇航行。实验分别采用了PID、模糊控制和模糊PID三种控制方法,系统实际水上实验表明,在风力2~3级,晴到多云天气条件下,无人水面艇对目标路径的最大跟踪误差小于0.6 m。     

Autonomous learning of sequential tasks: experiments and analyses

Presents a learning model CLARION, which is a hybrid model based on the two-level approach proposed by Sun. The model integrates neural, reinforcement, and symbolic learning methods to perform on-line, bottom-up learning (i.e., learning that neural to symbolic representations). The model utilizes procedural and declarative knowledge (in neural and symbolic representations, respectively), tapping into the synergy of the two types of processes. It was applied to deal with sequential decision tasks. Experiments and analyses of various ways are reported that shed light on the advantages of the model.     

欠驱动飞艇平面路径跟踪控制

针对欠驱动飞艇模型,提出一种基于制导向量场的平面路径跟踪控制方法.首先,基于牛顿-欧拉方程建立欠驱动飞艇动力学模型;然后,基于向量场理论构造制导向量场以获得期望偏航角,结合反步法设计路径跟踪控制律,并通过稳定性分析证明所设计的控制律能够使路径跟踪误差收敛到零而且闭环系统状态有界;最后,通过仿真对比了所提出方法与已有方法的控制效果,仿真结果验证了所提出方法的有效性和优越性.     

Autonomous ground vehicle path tracking

Autonomous ground vehicle navigation requires the integration of many technologies such as path planning, position and orientation sensing, vehicle control, and obstacle avoidance. The work presented here focuses on the control of a nonholonomic ground vehicle as it tracks a given path. A new path tracking technique called “vector pursuit” is presented. This new technique is based on the theory of screws, which was developed by Sir Robert Ball in 1900. It generates a desired vehicle turning radius based on the vehicle's current position and orientation relative to the position of a point ahead on the planned path and the desired orientation along the path at that point. The vector pursuit algorithm is compared to other geometrical approaches, and it is shown to be more robust, resulting in more accurate path tracking. © 2004 Wiley Periodicals, Inc.     

离轴式拖车移动机器人的任意路径跟踪控制

离轴式拖车移动机器人属于非完整系统,当车头线速度随时间变化且过零变号时,难以用一个控制器实现系统对期望路径的跟踪.本文研究离轴式拖车移动机器人系统的任意路径跟踪问题.首先由系统和虚拟小车的运动学方程得到误差状态模型,线性化后用坐标变换将其化为标准型,然后基于Lyapunov方法构造出一种跟踪控制律.只要车头的运动线速度有界且不趋于零,其导数有界,则所设计的控制律就可以保证系统跟踪任意的期望路径,且跟踪误差最终一致有界,最终界的大小与期望路径的曲率变化率成比例.当期望路径的曲率变化率为零或趋于零时,所设计的控制律可以保证拖车移动机器人指数收敛到期望路径.仿真结果证实了控制律的有效性.     

基于事件触发的无人驾驶汽车路径跟随预测控制

研究存在有界扰动的非线性无人车辆模型的路径跟随问题,提出一种基于事件触发的模型预测控制算法,与现有的基于时间周期的模型预测控制算法相比,可以在保证车辆对参考轨迹跟随准确性的同时减少跟随过程中求解优化问题的计算量,降低在线实时优化的计算负担.最后给出无人车运动学模型的仿真结果,对比所提出的控制算法与传统算法,验证了其有效性.