Structurally variable control of time-varying Lurie systems

This poses and solves the problem of structurally variable control synthesis for time-varying Lurie systems, which has both theoretical and engineering significance. A theorem on absolute stability of a set related to Lurie systems solves the problem. The theorem is basic for proving control algorithms that ensure absolute stability of a sliding subspace or its stability with finite reachability time. Moreover, they ensure the attraction in the whole of the zero equilibrium state of the whole control system of the plant on N(L). The selection of the sliding subspace can be such that the system nonlinearity does not influence the sliding motion.     

Cooperative Mobile Robotics: Antecedents and Directions

There has been increased research interest in systems composed of multiple autonomous mobile robots exhibiting cooperative behavior. Groups of mobile robots are constructed, with an aim to studying such issues as group architecture, resource conflict, origin of cooperation, learning, and geometric problems. As yet, few applications of cooperative robotics have been reported, and supporting theory is still in its formative stages. In this paper, we give a critical survey of existing works and discuss open problems in this field, emphasizing the various theoretical issues that arise in the study of cooperative robotics. We describe the intellectual heritages that have guided early research, as well as possible additions to the set of existing motivations.     

一类欠驱动系统的控制方法综述

近年来欠驱动系统已经成为机器人与自动控制领域的研究热点之一,本文对一类欠驱动系统(欠驱动连杆系统)的控制方法的研究状况进行了综述.首先给出了欠驱动系统的动力学模型,并介绍了2种基本控制模式;随后,对其主要的控制方法,包括最优控制方法、运动规划法、部分反馈线性化方法、能量(无源)方法、变量降维法、分级控制设计方法及智能控制方法,展开了分析与讨论;在此基础之上,对欠驱动连杆控制系统设计存在的抗干扰性、实用性及快速性等主要问题进行了简要分析,并就今后的研究方向进行了展望,如鲁棒策略、饱和控制与有限时间控制等.     

A Paradigm for Dynamic Coordination of Multiple Robots

In this paper, we present a paradigm for coordinating multiple robots in the execution of cooperative tasks. The basic idea in the paper is to assign to each robot in the team, a role that determines its actions during the cooperation. The robots dynamically assume and exchange roles in a synchronized manner in order to perform the task successfully, adapting to unexpected events in the environment. We model this mechanism using a hybrid systems framework and apply it in different cooperative tasks: cooperative manipulation and cooperative search and transportation. Simulations and real experiments demonstrating the effectiveness of the proposed paradigm are presented.     

非线性组合系统基于状态观测器的分散镇定

讨论了一类非线性相似组合系统的基于估计状态反馈的分散控制问题。构造了非线性渐近状态观测器,并证明了状态误差按指数收敛到零。同时,给出了组合系统经估计状态向量的反馈控制可实现分散镇定的一个充分条件。     

Switched model predictive control for performance enhancement

This article presents a switched model predictive control (MPC) algorithm for non-linear discrete time systems where the weights on the state and control variables in the cost function to be minimised depend on the current value of the state. In so doing, with a reduced computational burden one can easily include, in the problem formulation, a number of control specifications, such as the requirement to avoid critical regions in the state space or to reduce as much as possible the use of some actuators in other zones of the state space. The proposed MPC method has stability properties and is applied for control of a thermal system. The reported simulation results witness its favourable characteristics with respect to a standard MPC implementation.     

High Precision Formation Control of Mobile Robots Using Virtual Structures

A key problem in cooperative robotics is the maintenance of ageometric configuration during movement. To address this problem, theconcept of a Virtual Structure isintroduced. Using this idea, a general control strategy is developedto force an ensemble of robots to behave as if they were particlesembedded in a rigid structure. The method was instantiated and testedusing both simulation and experimentation with a set of 3differential drive mobile robots. Results are presented thatdemonstrate that this approach is capable of achieving high precisionmovement that is fault tolerant and exhibits graceful degradation ofperformance. In addition, this algorithm does not require leaderselection as in other cooperative robotic strategies. Finally, themethod is inherently highly flexible in the kinds of geometricformations that can be maintained.     

On the potential contributions of hybrid intelligent approaches to Multicomponent Robotic System development

The area of cognitive or intelligent robotics is moving from the single monolithic robot control and behavior problem to that of controlling robots with multiple components or multiple robots operating together, and even collaborating, in dynamic and unstructured environments. This paper introduces the topic and provides a general overview of the current state of the field of Multicomponent Robotic Systems focusing on providing some insights into where Hybrid Intelligent Systems could provide key contributions to its advancement. Thus, the aim is to identify prospective research areas and to try to delimit the field from the point of view of the following essential problem: how to coordinate multiple robotic elements in order to perform useful tasks.     

Robust Sliding Control of Robotic Manipulators Based on a Heuristic Modification of the Sliding Gain

A task space robust trajectory tracking control is developed for robotic manipulators. A second order linear model, which defines the desired impedance for the robot, is used to generate the reference position, velocity and acceleration trajectories under the influence of an external force. The control objective is to make the robotic manipulator’s end effector track the reference trajectories in the task space. A sliding mode based robust control is used to deal with system uncertainties and external perturbations. Thus, a sliding manifold is defined by a linear combination of the tracking errors of the system in the task space built from the difference between the real and the desired position, velocity and acceleration trajectories in comparison with previous works where the sliding manifold was defined by the desired impedance and the external force. Moreover, the ideal relay has been substituted by a relay with a dead-zone in order to fit in with the actual way in which a real computational device implements the typical sign function in sliding mode control. Furthermore, a higher level supervision algorithm is proposed in order to reduce the amplitude of the high frequency components of the output associated to an overestimation of the system uncertainty bounds. Then, the robust control law is applied to the case of a robot with parametric uncertainty and unmodeled dynamics. The closed-loop system is proved to be robustly stable with all signals bounded for all time while the control objective is fulfilled in practice. Finally, a simulation example which shows the usefulness of the proposed scheme is presented.     

Lyapunov vector function method in the motion stabilisation problem for nonholonomic mobile robot

In this paper we propose a sampled-data control law in the stabilisation problem of nonstationary motion of nonholonomic mobile robot. We assume that the robot moves on a horizontal surface without slipping. The dynamical model of a mobile robot is considered. The robot has one front free wheel and two rear wheels which are controlled by two independent electric motors. We assume that the controls are piecewise constant signals. Controller design relies on the backstepping procedure with the use of Lyapunov vector-function method. Theoretical considerations are verified by numerical simulation.