Control of nonholonomic systems with extended base space dynamics

This paper extends certain results in Reference 1 to a more general class of nonholonomic systems with extended base space dynamics. This extension is important in applications for which control actuator dynamics are significant. These nonlinear control systems are referred to as nonholonomic control systems owing to certain nonintegrability assumptions which are made. The class of systems considered in this paper are characterized by general nonlinear base space dynamics that are input-output decouplable. Controllability results for this class of nonholonomic control systems are presented.     

一类非完整系统的全局镇定

当非完整系统只能局部转换为链式形式时, 由于存在变换奇异点集合, 针对链式系统所设计的全局反馈控制律只能局部镇定原非完整系统, 而且当期望状态接近奇异点时, 闭环系统的吸引区很小. 本文针对一类可局部转换为链式系统的非完整系统, 首先利用吸引区是状态空间中的一个不变集且与变换奇异点集不相交的条件导出了一个吸引区的不变子集, 然后给出了将系统状态从任意点驱动到吸引区不变子集内的开环控制算法, 最后结合开环控制和闭环控制得到一种混合控制算法. 该混合控制算法可以保证任意不在变换奇异点集合内的期望状态是全局渐近稳定的. 对平面两转动关节空间机器人的仿真结果证实了算法的有效性.     

基于输出反馈的非完整链式系统跟踪控制研究

针对非完整链式系统设计了基于输出反馈的全局跟踪控制律. 首先, 利用时变坐标变换和非自治系统的级联控制方法构造了状态观测器;然后对于时变坐标变换以后的误差系统继续利用非自治系统的级联控制方法设计了输出跟踪控制律. 区别于已有文献对于非完整链式系统跟踪控制问题的研究, 设计得到的输出跟踪控制律放松了参考轨迹所必需满足的不趋于零条件或持续激励条件. 结论表明在非完整链式系统跟踪控制问题 的研究中, 参考轨迹所必须满足的不趋于零的条件或者持续激励条件是不必要的. 最后的仿真结果验证了所给控制方法的有效性.     

Study of the internal dynamics of an autonomous mobile robot

The requirement of ideal rolling without sideways slipping for wheels imposes nonholonomic (non-integrable) constraints on the motion of the wheels and consequently on the motion of wheeled mobile robots. From the control point of view, the dynamics of nonholonomic systems can be divided in two parts: external and internal dynamics. The dimension of the external dynamics of nonholonomic systems depends on the number of inputs to the system and the dimension of the internal dynamics depends on the number of independent nonholonomic constraints. For different motion control problems of nonholonomic systems, a smooth (model based) state feedback control law only deals with the system external dynamics; therefore, the system internal dynamics must be examined separately and its stability has to be analyzed and proved.In this paper, the internal dynamics of a three-wheel mobile robot with front wheel steering and driving is investigated. In particular, its internal dynamics stability is analyzed for two different situations, when the mobile robot is moving and when it is stationary.     

Planning and control of under-actuated mobile manipulators using differential flatness

Mobile manipulators are intrinsically nonholonomic systems since the mobile base is subject to nonholonomic constraints that result from no-slip constraints on the wheels. The highly nonlinear dynamic coupling between the mobile base and the manipulator arm, in addition to the nonholonomic constraints at the base, makes these systems difficult to plan and control. If the system is under-actuated, the problem becomes even more difficult.     

Partial-state Feedback Stabilization for a Class of Generalized Nonholonomic Systems with ISS Dynamic Uncertainties

In this paper, the problem of global stabilization control via partial-state feedback is addressed for a class of uncertain nonholonomic systems with the disturbed virtual control directions. The investigated nonholonomic system has the input-to-state stable (ISS) dynamic uncertainties. The small gain theorem and the changing supply function technique are employed to derive a global stabilization controller. Additionally, we develop a switching control strategy in order to get around the smooth stabilization burden associated with nonholonomic systems. The simulation results illustrate the efficacy of the presented algorithm.     

Discontinuous control of nonholonomic systems

The problem of asymptotic convergence for a class of nonholonomic control systems via discontinuous control is addressed and solved from a new point of view. It is shown that control laws, which ensures asymptotic (exponential) convergence of the closed-loop system, can be easily designed if the system is described in proper coordinates. In such coordinates, the system is discontinuous. Hence, the problem of local asymptotic stabilization for a class of discontinuous nonholonomic control systems is dealt with and a general procedure to transform a continuous system into a discontinuous one is presented. Moreover, a general strategy to design discontinuous control laws, yielding asymptotic convergence, for a class of nonholonomic control systems is proposed. The enclosed simulation results show the effectiveness of the method.     

Stabilization of Hamiltonian systems with nonholonomic constraints based on time-varying generalized canonical transformations

This paper is concerned with the stabilization of nonholonomic systems in port-controlled Hamiltonian formulae based on time-varying generalized canonical transformations. A special class of time-varying generalized canonical transformations are introduced which modify the kinetic energy of the original system without changing the generalized Hamiltonian structure with passivity. Utilizing these transformations, time-varying asymptotically stabilizing controllers for the nonholonomic Hamiltonian systems are derived. Since the proposed method is a natural generalization of passivity based control for conventional holonomic systems, it is expected that the tools developed for conventional systems will be applicable to nonholonomic systems based on the proposed method.     

Output‐feedback control strategies of lower‐triangular nonlinear nonholonomic systems in any prescribed finite time

In this paper, output‐feedback control strategies are proposed for lower‐triangular nonlinear nonholonomic systems in any prescribed finite time. Specifically, by employing the input‐state–scaling technique, the controlled systems are firstly converted into lower‐triangular nonlinear systems, which makes it possible to study such systems using the high‐gain technique. Then, by introducing a scaling of the state by a function that grows unbounded toward the terminal time and proposing a high‐gain observer–prescribed finite time recovering the system states, the output‐feedback regulation control problem in any prescribed finite time is firstly achieved for nonlinear nonholonomic systems with unknown constant incremental rate. Moreover, by designing another time‐varying high gain, the output‐feedback stabilization control problem in any prescribed finite time is then achieved for nonlinear nonholonomic systems with a time‐varying incremental rate. Finally, a numerical example is introduced to show the effectiveness of proposed control strategies.     

Finite‐time tracking control of uncertain nonholonomic systems by state and output feedback

This paper studies the finite‐time tracking control of nonholonomic systems in chained form with parameter uncertainties, unknown output gains, and mismatched uncertainties. To achieve the finite‐time tracking control of uncertain nonholonomic systems, we propose 2 types of controllers by state and output feedback, respectively. Both of the proposed 2 types of controllers can achieve the finite‐time output tracking control of the nonholonomic systems even in the presence of mismatched uncertainties and/or unknown gains. The effectiveness of our proposed controllers are illustrated with simulation examples.