Pole-placement in discrete systems by using single and multirate sampling

This paper deals with closed-loop pole-placement in discrete, linear systems under single and multirate sampling. The technique is extendable to hybrid systems, i.e. those involving both continuous and discrete substates. The sampling rates for the state, input and output components are used as a controller design technique to achieve closed-loop pole-placement since the controller, which is also discrete or hybrid in the general case, can be periodically reparametrized, the main useful effect of which being the availability of multiple design gains whose number and value are under the designer's choice. The key design factor in the multirate sampling design is that once the closed-loop running sampling period (i.e. that defining the closed-loop dynamics and thus the controller reparametrization periodicity) has been chosen, one can use freedom in the choice of smaller sampling periods for the various plant input and output components as well as for those of the controller state. All these sampling periods are chosen as submultiples of the closed-loop running sampling period.     

Practical finite-time command filtered backstepping control of MPCVD reactor systems with uncertainties

A practical finite-time command filtered backstepping control method is proposed in this paper for a microwave plasma chemical vapor deposition (MPCVD) reactor system. The MPCVD reactor system is modeled as a coupled nonlinear system with unknown control direction functions and unknown nonlinearities. To address the unknown nonlinearities, novel practical finite-time command filters are proposed to construct the estimations of such nonlinearities. On the other hand, an equivalent augmented system of the reactor system is proposed to address the design challenges that posed by the system unknown control direction functions. Additionally, it can be concluded that the proposed control method ensures practical finite-time stability of the reactor system tracking errors by using the practical finite-time Lyapunov stability criterion. Finally, the effectiveness of the approach is demonstrated through the simulation results.     

A graph structured text field index based on word fragments

An indexing technique for text data based on word fragments is described. In contrast to earlier approaches the fragments are allowed to be overlapping and are linked in a directed graph structure reflecting that many fragments (“Superstrings”) contain other fragments as substrings. This leads to a redundant free set of primary data pointers. By classifying the set of Superstrings belonging to a fragment according to the position of the fragment in the Superstring, one gains a novel possibility of supporting exact match-, partial match-, and masked partial match-retrieval by an index. The search strategies for the various retrieval cases are described.     

In search of insights into the generation of techno-economic trends: Micro- and macro-constituencies in the microprocessor industry

In the field of technology policy, few challenges are more intriguing than understanding the nature of technical and market trends. This paper deals with this problem by using the sociotechnical constituencies approach in order to integrate the treatment of “micro”/“macro” issues — from product to industry. The case study is that of the microprocessor industry where at present a Risc (reduced instruction set computer) technology is emerging in a field where a powerful and far-from-exhausted Cisc (complex instruction set computer) technology tends to occupy almost every segment of the market. The analysis reveals how emerging product-constituencies do implement pro-active trend-creating strategies in order to establish themselves as industrial trends, and, by so doing, they simultaneously re-define the existing content of the “macro” industrial level. The study also reveals the important role of the nature and maturity of microprocessor technology in conditioning the constituency-building strategies implemented by different players. Microprocessor technology is specifically characterised as an architectural, codified-knowledge component with indirect network externalities and weak appropriability regime. Finally, the paper also highlights the potential risks of both fragmentation and complete proprietary control of technology in technological processes involving strongly competitive situations.     

A measure of “efficiency factor”— Communication theory applied to document selection systems

An imperfect document selection system is represented as the analogy of a system in which symbols are selected and transmitted through a noisy channel. Provided that transmission reception uncertainties and not meaning are considered, it is suggested that one of Shannon's equations is applicable, and a single figure measure of system efficiency, H_t, is proposed.Values obtained using this new yardstick are compared with Recall/Precision values obtained for a typical system. Further research is required to test whether system “improvements” resulting in higher values of H_t are perceived as such by users.     

PID pitch attitude control for unstable flight vehicle in the presence of actuator delay: Tuning and analysis

In the realm of flight control, proportional–integral–derivative (PID) control is still widely used in practice due to its simple structure and efficiency. The robustness and dynamic performance of PID controller can be evaluated by stability margins. Based on the empirical knowledge about the unstable flight dynamics, the analytical tuning formulas of the PID pitch attitude control with actuator delay are derived with the help of several proper approximations. These tuning formulas can meet the increasing gain and phase margins (iGPM) requirement and avoid time-consuming trial-and-error tuning process. The feasible iGPM area is established in 2-D plane subject to several conditions, especially taking the decreasing gain margin into account, wherein the numerical polynomial solving approaches are employed. The relationship between an existing PD tuning scheme and the proposed PID tuning method is also revealed. The applicable area of the tuning rule is then investigated on the basis of a crucial assumption. Furthermore, the achievable decreasing gain and phase margins (dGPM) area is obtained when the decreasing gain margin is critical; and another tuning rule is derived according to the dGPM specifications. The effect of the actuator delay on the achievable GPM area is demonstrated in a straightforward manner such that the reasonable criteria can be specified. Finally two numerical paradigms are presented to validate the proposed method; and the robustness and dynamic performance of the PID control are also reexamined for unstable flight dynamics.     

What determines technological hits?: Geography versus firm competencies

The centrality of firms vis-à-vis regions underlines a general contrast between two models of producing innovations. This paper uses a new database composed of 4262 European chemical patents applied by 693 firms during 1987–1996 to compare the relative effect of firm and regional characteristics on the production of technological “hits” (highly cited patents). By using extensive controls, the main finding of the paper is that technological hits in the “traditional” chemical sectors are explained only by R&D intensity at the firm level and the scale of the research projects. Firm competencies, particularly technological specialisation, are still important in biotechnology. However, the distinct feature of the biotechnology model is that localised knowledge spillovers also matter.     

Querying the French yellow pages: Natural language access to the directory

ERLI was asked by the French TELECOM to develop a specific system to query the professional headings of the French Yellow Pages directory. Approximately 4 million end users now have access (via their “Minitel” terminals) to some 6 million professionals registered under 2500 different headings. (A second application has also been developed using a similar system: the Minitel Applications Directory, which gives information on all the available applications in the Minitel network.)Although the retrieval of a heading is a necessary step in accessing data, it is of no real interest to the user, who wishes only to retrieve the phone number of a given professional or tradesperson.The general aims of the Natural Language System (NLS) are to facilitate access to headings by intelligent query processing (or even to bypass completely the necessity of choosing between headings).This is done through: • The association of a specific knowledge base to the list of headings, • The construction of a “grammar” ensuring a consistent interpretation of the queries.ERLI's system is as an alternative to the existing one, which is based on a key-word indexing technique. The weaknesses and insufficiencies of such a technique are well known, especially in this context, where queries are expressed by unqualified users, who are unfamiliar with the data (i.e., the headings of the directory).Finally, it is important to note that the NLS was developed with regard to industrial considerations (in particular, the minimizing of the average processing time per query). The system is not a prototype. Extensive on-side testing is scheduled to begin in July 1988 and a complete installation will be carried out at the end of the year.     

Step7中PID模块采样时间的正确使用

西门子PLC在工业自动控制过程中得到了越来越广泛的应用,其过程控制的PID功能同样被大量使用,但PID模块调用时的参数并非被大家能完全正确的使用,其中以CYCLE(采样时间)尤为突出.以PID控制理论为基础,分析采样时间如何对PID运算产生影响,以此来正确理解和使用CYCLE参数,这使工程技术人员能更好地理解其实质,从而更好地应用PID模块及其参数设置,以快速有效地完成工程.     

Reachable set synthesis for singular systems with time-varying delay via the adaptive event-triggered scheme

This work is concerned with the problem of reachable set synthesis for a class of singular systems with time-varying delay via the adaptive event-triggered scheme. Compared with the static event-triggered mechanism, the adaptive event-triggered mechanism can save the communication resources more effectively. By virtue of Lyapunov stability theory, sufficient conditions are given to guarantee the stability of the closed-loop system and that the reachable set of the resulting system is bounded by the obtained ellipsoid. In addition, by using linear matrix inequality technique and free-weighting matrix method, the weighting matrix of event-triggered condition and proportional-derivative (P-D) feedback controller gains are obtained. The effectiveness and superiority of the developed control approach are substantiated by a numerical example and two practical examples.     

基于模糊控制的PID控制器研究

在工业控制过程中,由于被控对象具有时变、非线性、不确定等因素,常规PID控制算法难以满足控制要求。本文设计了一种模糊PID控制器可实现对该类工业对象的控制,利用模糊推理在线整定PID控制器的3个参数Kp、Ki、Kd。通过仿真实验,表明该控制器取得了较好的快速性和稳定性。     

Variable-structure PD controller for satellite attitude: Stability analysis and design for optimal performance

A novel variable structure controller is investigated for satellite attitude control. This novel controller does not lead to a sliding mode, which avoids the chattering problem, making it suitable for practical implementation. Detailed formulation of the controller is presented along with analytical stability analysis for a second order system. The system having this nonlinear controller is homogeneous, which leads to a similar response at large and small deviations from the equilibrium. A procedure for tuning homogeneous controllers for all initial conditions is proposed. A detailed model of the satellite attitude dynamics, actuator dynamics, and delays in the system is utilized to optimize controller gains numerically. A comparative analysis shows the superiority of the proposed controller over a conventional PID controller in terms of better transients and lower energy consumption.     

Quadrotor stabilization under time and space constraints using implicit PID controller

In this paper, the quadrotor stabilization under time and state constraints is studied. The objective is to design a nonlinear controller under time and state constraint for quadrotor. The nonlinear quadrotor model is built by the Euler-Lagrange approach while ignoring the Coriolis terms, hub moment and force. Based on quadrotor’s dynamic model, a nonlinear feedback controller is designed for the quadrotor stabilization under time and state constraints. This feedback is an implicit PID controller where the feedback gains are obtained from LMIs (Linear matrix inequalities). LMI system characterizing the system stability and convergence properties is built based on convex embedding approach and implicit Lyapunov function method. To demonstrate the application prospects of implicit PID controller, robustness analysis is provided to show the property of implicit PID controller under external disturbance. The key novelty of this paper is that the implicit PID controller is proven feasible for applying to the quadrotor under time and state constraints, which is also the main outcome.     

Delay-dependent stochastic stability and H∞ analysis for time-delay systems with Markovian jumping parameters

This paper studies the problem of the stochastic stability and H_∞ disturbance attenuation for linear continuous-time time-delay systems that possess randomly Markovian jumping parameters. A delay-dependent sufficient condition on the stochastic stability with given H_∞ performance is proposed using the stochastic Lyapunov–Krasovskii stability theory. The conditions are formulated as a set of coupled linear matrix inequalities.     

Observer-based output-feedback control of large-scale networked fuzzy systems with two-channel event-triggering

This paper concerns data transmissions for large-scale T–S fuzzy systems with event-triggering control, where each subsystem communicates its information via a two-channel network. We propose an event-triggering scheme in which two event-triggering mechanisms are used to verify the data transmissions. At first, a novel model transformation is presented, where the event-triggered control system is reconstructed as a constant-delay system with extra inputs and outputs. By using a relaxed Lyapunov–Krasovskii functional (LKF) without the requirement of positive definiteness for all Lyapunov matrices, and the scaled small gain (SSG) theorem, the co-design problem of desired observer and controller gains, event-triggering parameters, and the sampling period is resolved in the form of linear matrix inequalities (LMIs). It will be shown that the solution guarantees the stability of closed-loop fuzzy control system and the reductions of data communications in both the sensor-to-controller and controller-to-actuator channels. The proposed method is validated by using a numerical example.     

Intelligent information retrieval: diagnosing information need. : Part I. The theoretical framework for developing an intelligent IR tool

The research examines the notion that the principles underlying the procedure used by doctors to diagnose a patient's disease are useful in the design of “intelligent” IR systems because the task of the doctor is conceptually similar to the computer (or human) intermediary's task in “intelligent information retrieval”: to draw out, through interaction with the IR system, the user's query/information need. The research is reported in two parts. In Part II, an information retrieval tool is described which is based on “intelligent information retrieval” assumptions about the information user. In Part I, presented here, the theoretical framework for the tool is set out. This framework is borrowed from the diagnostic procedure currently used in medicine, called “differential diagnosis”. Because of the severe consequences that attend misdiagnosis, the operating principle in differential diagnosis is (1) to expand the uncertainty in the diagnosis situation so that all possible hypotheses and evidence are considered, then (2) to contract the uncertainty in a step by step fashion (from an examination of the patient's symptoms, through the patient's history and a physical (signs), to laboratory tests). The IR theories of Taylor, Kuhlthau and Belkin are used to demonstrate that these medical diagnosis procedures are already present in IR and that it is a viable model with which to design “intelligent” IR tools and systems.     

Event-based control for networked T-S fuzzy cascade control systems with quantization and cyber attacks

This paper investigates the event-based control for networked T-S fuzzy cascade control systems with quantization and cyber attacks. In order to solve the problem of limited communication resources, an event-triggered scheme and a quantization mechanism are adopted, which can effectively reduce the burden of communication and save the network resources of the system. By considering the influence of cyber attacks, a newly quantized T-S fuzzy model for networked cascade control systems (NCCSs) under the event-triggered scheme is established. By using the Lyapunov stability theory, sufficient conditions guaranteeing the asymptotical stability of networked T-S fuzzy cascade control systems are obtained. In addition, the controller gains are derived by solving a set of linear matrix inequalities. Finally, a numerical example is presented to verify the validity of the proposed method.     

A modified PID controller (PIIσβD)

The purpose of this study is to modify the traditional PID controller in order to improve its performance (stability and tracking) by changing the length of integration interval. The performance of the traditional PID controller was improved by changing the length of integration interval to make the most of the returns of the PID and PI_σD controllers. The asymptotic stability domain, in terms of the feedback gains, is derived for systems of second order using the modified controller which will be identified as PII_σ^βD. Comparing this controller with the traditional PID controller and PI_σD controller proposed in [1], it proves that it is more accurate and more stable. For illustration and comparison, two examples have been simulated to evaluate the performance of the modified controller. All simulation results indicate that the modified controller is better than the traditional PID controller and the PI_σD controller from the accuracy and stability point of view.     

Delayed proportional-integral control for offshore steel jacket platforms

This paper is concerned with the problem of delayed proportional-integral control of an offshore platform subject to self-excited nonlinear hydrodynamic force. By using current and distributed delayed states, a delayed proportional-integral controller is designed to stabilize the offshore platform. Under such a controller, the closed-loop system of the offshore platform is modeled as a nonlinear system with discrete and distributed delays, which allows us to employ the Lyapnov–Krasovskii functional method to analyze its asymptotic stability. Since an affine Wirtinger-based inequality is exploited to estimate the derivative of the Lyapunov–Krasovskii functional, a new stability criterion for the closed-loop system is derived, based on which, suitable control gains can be designed provided that a set of linear matrix inequalities are feasible. It is found through simulation results that the proposed control scheme can improve the control performance remarkably. Moreover, (i) compared with the existing delay-free controllers, the proposed controller can reduce the required control force and the oscillation amplitudes of the platform significantly; and (ii) compared with several delayed controllers, the proposed controller requires less control cost.     

Independent force and position control for cooperating manipulators

The problem of independent force and position control of multitask cooperating manipulators is studied. Each manipulator is in a non-singular configuration and the object can be driven by the contact forces exerted by the end effectors of the manipulators. The design requirement is to control each coordinate of the position of the object as well as each component of the “rest” forces, except the moving forces that are determined uniquely from the object's position. The present design requirement has been proved to be always satisfied together with asymptotic and BIBO stability. A class of controllers solving the above simultaneous problem is analytically determined. The proposed state feedback controller does not depend upon the specific object dynamics and thus the resulting closed-loop multimanipulator system performs as required, not only when handling various objects but also when the dynamics of the objects are unknown or hard to compute or disturbed by external forces.