基于样条插值的模糊控制算法

利用三次样条插值函数,直接由控制输入输出数据对建立了控制输入与控制输出之间的映射关系,得到了一元三次样条插值控制算法和二元双三次样条插值控制算法,并将二者分别用于单输入单输出系统和双输入单输出系统的仿真控制.仿真结果表明,上述方法是可行的,并且基于三次样条函数的模糊插值控制,具有响应快,无超调,稳态误差极小等很好的控制效果.其设计简单,不需要过多规则,对稀疏规则库条件下的控制器设计尤为适用.     

Autonomous control of complex systems: robotic applications

One of the biggest challenges of any control paradigm is being able to handle large complex systems under unforeseen uncertainties. A system may be called complex here if its dimension (order) is too high and its model (if available) is nonlinear, interconnected, and information on the system is uncertain such that classical techniques cannot easily handle the problem. Soft computing, a collection of fuzzy logic, neuro-computing, genetic algorithms and genetic programming, has proven to be a powerful tool for adding autonomy to many complex systems. For such systems the size soft computing control architecture will be nearly infinite. Examples of complex systems are power networks, national air traffic control system, an integrated manufacturing plant, etc. In this paper a new rule base reduction approach is suggested to manage large inference engines. Notions of rule hierarchy and sensor data fusion are introduced and combined to achieve desirable goals. New paradigms using soft computing approaches are utilized to design autonomous controllers for a number of robotic applications at the ACE Center are also presented briefly.     

Numerical methods for the stability of time-periodic hybrid time-delay systems with applications

This paper extends two numerical methods for the stability analysis of a class of time-periodic hybrid time-delay systems. In particular, the pseudospectral tau and spectral element methods are extended to hybrid systems. The analyzed delay-differential equation involves delayed terms with both continuous and piecewise constant arguments, in other words, it involves delays both without and with zero-order hold, respectively. The analyzed class of hybrid systems can be used to describe time-periodic hereditary processes subjected to digital feedback control. The proposed numerical algorithms are applied to the mathematical models of haptic systems and milling processes subjected to digital feedback control.     

The delay approximation of discrete control in higher-order systems

Physical machinery of high mathematical order operating in industry increasingly nowadays requires the replacement of early analog controllers by imbedded digital systems. Using a 7^th-order longwall shearer as the motivating case-study, the paper examines the possibility of easing the digital control system design process by substituting a continuous transport-delay for the digital sample-hold operation. Based on first- and second-order models, this is shown to produce a design procedure that is pessimistic (i.e., safe) in the main and to a practically acceptable degree. Similar response speeds are generated by the discrete- and delay-models. By simulation, the technique is shown to carry over well to the higher-order case study aforementioned. This provides confidence in the delay-for-sampler substitution, the advantages of which are that the need to generate multiple z-transform models for a range of sampling intervals and the difficulties of interpreting z-plane plots (compared to those of familiar Nyquist diagrams and root loci) are avoided.     

高性能模糊控制研究

针对常规模糊控制器的本质及其缺陷,设计了一种规则简单、控制量论域可变的模糊控制制器,实现快速响应、小的超调以及较高的控制精度,具有较强的通用性及应用前景。     

轴向数控磁力轴承系统的研究

本文建立了轴向磁力轴承的动力学方程和数学模型 ,阐述了基于数学模型分析的数字控制系统的设计方法 .介绍了本课题设计的新型数字控制系统 .试验表明该系统具有较好的控制稳定性和运转稳定性 ,具有较强的承载力 .     

The optimal control of just-in-time-based production and distribution systems and performance comparisons with optimized pull systems

In just-in-time (JIT) production systems, there is both input stock in the form of parts and output stock in the form of product at each stage. These activities are controlled by production-ordering and withdrawal kanbans. This paper discusses a discrete-time optimal control problem in a multistage JIT-based production and distribution system with stochastic demand and capacity, developed to minimize the expected total cost per unit of time. The problem can be formulated as an undiscounted Markov decision process (UMDP); however, the curse of dimensionality makes it very difficult to find an exact solution. The author proposes a new neuro-dynamic programming (NDP) algorithm, the simulation-based modified policy iteration method (SBMPIM), to solve the optimal control problem. The existing NDP algorithms and SBMPIM are numerically compared with a traditional UMDP algorithm for a single-stage JIT production system. It is shown that all NDP algorithms except the SBMPIM fail to converge to an optimal control.Additionally, a new algorithm for finding the optimal parameters of pull systems is proposed. Numerical comparisons between near-optimal controls computed using the SBMPIM and optimized pull systems are conducted for three-stage JIT-based production and distribution systems. UMDPs with 42 million states are solved using the SBMPIM. The pull systems discussed are the kanban, base stock, CONWIP, hybrid and extended kanban.     

INVITED PAPER: Some mathematical aspects of security in the automated business environment

In the automated business world, personal contact and paper-basedtransactions are being replaced by digital electronic communications.This transition raises many new security issues, and has seenthe emphasis of cryptography broaden from secrecy to includemessage integrity, user verification, digital signature, andaccess control. In this paper, we consider some of the waysin which mathematics is playing a crucial role in securing theautomated business environment. We begin with a brief introduction to cryptography and the principlesupon which the design of cipher systems is based. We then considerstream ciphers and block ciphers in turn, discussing their respectiveuses, design requirements, and crypt-analysis. Here statisticalmethods are of prime importance, as well as algebraic methodsfor generating and combining bit strings and blocks. The section on public key systems includes a discussion of severalmathematical techniques that provide one way functions. Theseare functions that are easy to perform but difficult to invert,often based on some difficult mathematical problem, and areat the heart of public key systems. Two public key systems (RSAand El Gamal) are described, and the status of algorithms forsolving the difficult problems upon which they are based factoringand discrete logarithms is reviewed. Finally we discuss applications of digital-signature and user-verificationtechniques. These are becoming of increasing importance in today'sautomated business world.     

On queuing systems with failures and several types of input flows

In this paper two models of queuing systems with failures and several types of input flows are considered. These models can simulate the functioning of cellular communications networks under various control regimes. For stationary probabilities of service process (including failed ones) the closed form and the effective calculating algorithms are obtained. The results are used to control the input flows in an optimal way. This research was supported by the INTAS (grant 96-0828).     

Number-theoretic interpretation and construction of a digital circle

This paper presents a new interpretation of a digital circle in terms of the distribution of square numbers in discrete intervals. The number-theoretic analysis that leads to many important properties of a digital circle succinctly captures the original perspectives of digital calculus and digital geometry for its visualization and characterization. To demonstrate the capability and efficacy of the proposed method, two simple algorithms for the construction of digital circles, based on simple number-theoretic concepts, have been reported. Both the algorithms require only a few primitive operations and are completely devoid of any floating-point computation. To speed up the computation, especially for circular arcs of high radii, a hybridized version of these two algorithms has been given. Experimental results have been furnished to elucidate the analytical power and algorithmic efficiency of the proposed approach. It has been also shown, how and why, for sufficiently high radius, the number-theoretic technique can expedite a circle construction algorithm.     

一类MIMO非线性系统的稳定自适应模糊控制

针对一类 MIMO不确定非线性系统 ,基于一种修改的李亚普诺夫函数并利用 I型模糊系统的逼近能力 ,提出一种分散自适应模糊控制器设计的新方案。该方案不但能够避免现有的一些自适应模糊 /神经网络控制器设计中对控制增益一阶导数上界的要求 ,而且能够避免控制器的奇异问题。通过理论分析 ,证明闭环控制系统是全局稳定的 ,跟踪误差收敛到零。仿真结果表明了该方法的有效性。     

组合型自适应模糊控制器的设计与分析

充分利用被控对象与控制行为的知识,为一类非线性系统设计一个组合型自适应模糊控制器。它的主要特点是设计一个自适应补偿器来减小建模误差和参数估计误差对系统性能的影响。在不要求最优逼近误差平方可积和上界已知的条件下,证明闭环系统全局渐近稳定,所有信号有界且跟踪误差收敛到零。     

Counteracting the dynamical degradation of digital chaos via hybrid control

Chaotic systems would degrade owing to finite computing precisions, and such degradation often seriously affects the performance of digital chaos-based applications. In this paper, a chaotification method is proposed to solve the dynamical degradation of digital chaotic systems based on a hybrid structure, where a continuous chaotic system is applied to control the digital chaotic system, and a unidirectional coupling controller that combines a linear external state control with a modular function is designed. Moreover, we proof rigorously that a class of digital chaotic systems can be driven to be chaotic in the sense that the system is sensitive to initial conditions. Different from the existing remedies, this method can recover the dynamical properties of system, and even make some properties better than those of the original chaotic system. Thus, this new approach can be applied to the fields of chaotic cryptography and secure communication.     

Efficient algorithms for generalized algebraic Bernoulli equations based on the matrix sign function

We investigate the solution of large-scale generalized algebraic Bernoulli equations as those arising in control and systems theory. Here, we discuss algorithms based on a generalization of the Newton iteration for the matrix sign function. The algorithms are easy to parallelize and provide an efficient numerical tool to solve large-scale problems. Both the accuracy and the parallel performance of our implementations on a cluster of Intel Xeon processors are reported.      

The achievable region method in the optimal control of queueing systems; formulations,bounds and policies

We survey a new approach that the author and his co-workers have developed to formulate stochastic control problems (predominantly queueing systems) asmathematical programming problems. The central idea is to characterize the region of achievable performance in a stochastic control problem, i.e., find linear or nonlinear constraints on the performance vectors that all policies satisfy. We present linear and nonlinear relaxations of the performance space for the following problems: Indexable systems (multiclass single station queues and multiarmed bandit problems), restless bandit problems, polling systems, multiclass queueing and loss networks. These relaxations lead to bounds on the performance of an optimal policy. Using information from the relaxations we construct heuristic nearly optimal policies. The theme in the paper is the thesis that better formulations lead to deeper understanding and better solution methods. Overall the proposed approach for stochastic control problems parallels efforts of the mathematical programming community in the last twenty years to develop sharper formulations (polyhedral combinatorics and more recently nonlinear relaxations) and leads to new insights ranging from a complete characterization and new algorithms for indexable systems to tight lower bounds and nearly optimal algorithms for restless bandit problems, polling systems, multiclass queueing and loss networks.     

输入采用标准模糊分划的模糊控制系统性质及稳定性分析

具体定义模糊控制系统输入变量的标准模糊分划，研究和证明输入采用标准模糊分划的模糊控制系统的有关性质。在此基础上，采用Lyapunov直接法研究该类模糊控制系统的稳定性，提出一个判定模糊控制系统稳定性的充分条件。该条件将以往方法要在所有的子系统中寻找一个公共的正定矩阵满足Lyapunov不等式，放宽为在各最大交叠规则组内分别寻找公共的正定矩阵，从而减小稳定性判定的保守性和难度。     

FLOATING QUANTIZATION EFFECTS ON MULTIRATE SAMPLED-DATA NONLINEAR CONTROL SYSTEMS

In this article,floating quantization effects on multirate sampled-data control systems are studied.It shows that the solutions of multirate digital feedback control systems with nonlinear plant and with floating quantization in the controller are uniformly ultimately bounded if the associated linear systems consisting of linearization of the plant and controller with no quantization are Schur stable.Moreover,it also shows that the difference between the response of multirate digital controllers without quantizers and the same plant with floating quantization in the controllers can be made as small as desired by selecting proper quantization level.     

一类死区非线性输入系统的自适应模糊控制

针对一类具有死区非线性输入的非线性系统,基于滑模控制的基本原理,利用II型模糊逻辑系统对未知函数进行在线逼近,提出了一种具有监督器的自适应模糊滑模控制方法。该方法通过监督控制器保证闭环系统所有信号有界,并通过引入最优逼近误差的自适应补偿项来消除建模误差的影响。通过理论分析,证明了跟踪误差收敛到零。     

非线性时滞系统的直接自适应模糊控制

针对一类具有摄动的严格反馈非线性时滞系统,基于后推设计方法,利用第一类模糊系统的逼近能力,提出了一种新的直接自适应控制方案。该方案避免了虚拟控制增益符号已知的假设。设计中引入连续鲁棒项对系统的摄动部分进行抑制。通过理论分析,证明了闭环系统是半全局一致终结有界的,跟踪误差收敛到一个小的残差集内。