Showing papers on "Supervisory control published in 1988"

On observability of discrete-event systems

Abstract: The observability of discrete-event systems is investigated. A discrete-event system G is modeled as the controlled generator of a formal language L m ( G ) in the framework of Ramadge and Wonham. To control G, a supervisor S is developed whose action is to enable and disable the controllable events of G according to a record of occurrences of the observable events of G, in such a way that the resulting closed-loop system obeys some prespecified operating rules embodied in a given language K. A necessary and sufficient condition is found for the existence of a supervisor S such that L m ( S/G ) = K . Based on this condition, a solution of the supervisory control and observation problem (SCOP) is obtained. Two examples are provided.

Supervisory control of discrete-event processes with partial observations

Abstract: Extends certain aspects of the work of P.J. Ramadge and W.M. Wonham (see SIAM J. Control Optimiz., vol.25, Jan. 1987) on the control of a class of discrete-event processes. The controlled process is described by a language L having strings that specify the sequences of events sigma /sub 1/ . . . sigma /sub n/ that the process can execute. The controller makes partial observations on the process events. Based on these observations the controller must enable or disable certain process events so that the resulting language generated by the closed-loop process is the specified sublanguage K contained in/implied by L. The case of decentralized control in which there are several controllers each of which makes partial observations and controls a subset of the process events is also studied. The results are illustrated for an example of communication protocols. >

Modular Supervisory Control of Discrete Event Systems

Abstract: We examine a modular approach to the synthesis of supervisory controls for discrete-event systems. Discrete-event systems are modelled by automata together with a mechanism for enabling and disabling a subset of state transitions. The basic problem of interest is to ensure by appropriate supervision that the closed loop behavior of the system lies within a given legal behavior. Assuming this behavior can be decomposed into an intersection of component restrictions we determine conditions under which it is possible to synthesize the appropriate control in a modular fashion.

Decentralized supervisory control of discrete-event systems

Abstract: A discrete-event system G is modeled as the controlled generator of a formal language L( G ) , in the framework of Ramadge and Wonham. In general a centralized global supervisory controller S for G can be defined which generates a suitable closed-loop languageL(S/G). The paper develops the idea of local supervisors Si whose concurrent operation results in the closed-loop language L( ΛS i /G ) . Conditions are obtained which guarantee that L( ΛS i /G ) = L( S/G ) , namely, distributed local supervision is equivalent to global supervision. For illustration a simple manufacturing system is discussed.

Finitely recursive process models for discrete event systems

Abstract: A class of discrete-event models called finitely recursive processes (FRP) is introduced. These models are motivated by problems in supervisory control, while some of the formal structure is based on C.A.R. Hoare's (1985) communicating sequential processes. Although only preliminary work is presented, it is believed that for many problems it offers a formalism that is superior to that of finite-state machines recently introduced in control theory. Simple examples illustrate the calculus of operators for FRPs. A more complex exercise is worked out to show how the formalism is used to construct a scheme for handling connections in a data network. This preliminary work needs to be extended in several directions, especially in directions that can assist implementation of real controllers based on the FRP formalism. Some specific suggestions towards this end are made. >

OFMspert: inference of operator intentions in supervisory control using a blackboard architecture

Abstract: The authors proposes an architecture for an expert system that can function as an operator's associate in the supervisory control of a complex dynamic system. Called OFMspert (operator function model (OFM) expert system), the architecture uses the operator function modeling methodology as the basis for the design. The authors put emphasis on the understanding capabilities, i.e. the intent referencing property, of an operator's associate. They define the generic structure of OFMspert, particularly those features that support intent inferencing. They also describe the implementation and validation of OFMspert in GT-MSOCC (Georgia Tech-Multisatellite Operations Control Center), a laboratory domain designed to support research in human-computer interaction and decision aiding in complex, dynamic systems. >

Task Allocation and Supervisory Control

Abstract: Publisher Summary This chapter discusses the concept of supervisory control. It discusses the characterization of 10 sequential functions of the human supervisor of a semiautomatic control system, together with a review of relevant research. For each function, a mental model is assumed and a computer decision aid is suggested. Some problems and models for human attention allocation in supervisory control are also presented in the chapter. The chapter discusses two factors that ultimately limit the ability to model human behavior in such situations. A first factor is that people worry that computers can do some tasks much better than they themselves can, such as memory and number crunching. A second factor is that supervisory control tends to make people remote from the ultimate operations they are supposed to be overseeing—remote in space, desynchronized in time, and interacting with a computer instead of the product itself. A third factor is that people lose the perceptual-motor skills that in many cases gave them their identity.

The effectiveness of supervisory control strategies in scheduling flexible manufacturing systems

Abstract: The results of an experimental study of the supervisory control of a simulated flexible manufacturing system (FMS) are discussed. A real-time simulator of an FMS, (Georgia Tech-FMS (GT-FMS)) was implemented and configured with data from a real manufacturing system. An experiment was run in which humans interacted with the automatic control system of GT-FMS with the goal of improving overall system performance by meeting due data while simultaneously minimizing inventory. Experimental results show that with human supervision both due data and inventory performance of GT-FMS can be improved. The results strongly support the idea of actively integrating humans into operational controls of automated manufacturing environments. >

Decision models for aiding FMS scheduling and control

Abstract: Control of flexible manufacturing systems (FMS) requires the complex interaction of two components: (1) computers to perform automated control and routing activities, and (2) humans to supervise the automation, to monitor system flows and outputs, and to intervene to diagnose and either correct or compensate for unanticipated events. Current academic FMS scheduling research has focused mainly on the first component in the control loop, development of scheduling algorithms for optimization and control. Here, the second component is included in both the definition of the FMS control problem and the corresponding control approach. A more realistic definition of the FMS control environment is presented using a supervisory control framework. Within this context, the concept of aiding a human operator who supervises the predominantly automated FMS operations is developed. >

A supervisory control paradigm for real-time control of flexible manufacturing systems

Abstract: Most of the current academic flexible manufacturing system (FMS) scheduling research has focused on the derivation of algorithms or knowledge-based techniques for efficient FMS real-time control. Here, the limitations of this view are outlined with respect to effective control of actual real-time FMS operation. A more realistic paradigm for real-time FMS control is presented, based on explicit engineering of human and automated control functions and system interfaces. To illustrate design principles within the conceptual model, an example of algorithmic and operator function models for a specific real-time FMS control problem are developed.

Design of a Self-Tuning Expert Controller for a Gasoline Refinery Catalytic Reformer

Abstract: The objective is to explore design concepts for self-tuning expert controllers. To accomplish this, two interacting rule based controllers for supervisory control and system optimization are constructed to control a gasoline catalytic reformer. The knowledge bases for the controllers are established from human operator experience and basic engineering knowledge about the process dynamics. Inference is provided by a fuzzy logic engine. After manual tuning of the expert controller scaling coefficients is accomplished, a crisp heuristic is developed for self-tuning. The performance of the self-tuning expert controller is tested against perturbations of a simulation model of the catalytic reformer.

Issues in human/computer control of dexterous remote hands

Abstract: Much research on dexterous robot hands has been aimed at the design and control problem associated with their autonomous operation, while relatively little research has addressed the problem of direct human control. While many of the issues in mixed computer/human control of dexterous hands parallel those found in supervisory control of traditional remote manipulators, the unique geometry and capabilities of dexterous hands pose many new problems. Among these are the control of redundant degrees of freedom, grasp stabilization and specification of nonanthromorphic behavior. An overview is presented of progress made at the MTI AI Laboratory in control of the Salisbury three-finger hand, including experiments in grasp planning and manipulation by controlled slip. The author also suggests how it might be possible to introduce human control into the process at a variety of functional levels. >

Supervisory control of discrete event processes with arbitrary controls

Abstract: An extended model for a class of discrete event systems is proposed. Based on the model formulated by Ramadge and Wonham [1], we introduce the notion of a nondeterministic supervisor and extend the definition of a controllable language [1]. Some results on the existence of deterministic and nondeterministic supervisors to achieve a given closed loop language are presented. We briefly discuss closure properties of controllable languages in the extended model.

Cooperative control in telerobotics

Abstract: It is argued that autonomous robotics is not yet feasible, and that instantaneous human control may be difficult because of communication delay and expensive because of labor costs. Therefore, it is argued, human supervisory control with cooperation between man and a partially autonomous distant robot is the most viable engineering solution. Model control of image processing enables efficient visual displays. Cooperative control in paired manipulators required rapid controller signal information to be passed over a cross-filter in a heuristic study. >

Supervisory control of discrete event systems: A survey and some new results

Abstract: We present an overview of the modeling of discrete event systems using formal languages. Some new results on the controllability of sequential behaviors are presented and a standard coordination problem for a product system is shown to be of polynomial complexity.

A Petri-net approach to the control of discrete-event systems

Abstract: In this paper we describe a theory for the synthesis of supervisory controllers for discrete-event systems such as computing, communication and manufacturing systems. The required behaviour of the system is specified by an invariant relation which must hold during operation of the system and a controller is derived which when combines with the system will ensure the required behaviour. The theory is based on viewing the Petri-net model of the system as a two-sorted algebra and the composition operation as a natural product between two such algebras.

Model-based low-level control in flexible manufacturing systems

Abstract: Low-level (supervisory) control of flexible manufacturing systems (FMS) assures conflict-free operation and enforces production requirements such as priorities. It forms a crucial link between medium and higher-level decision making, on the one hand, and the various machine-controllers and servomechanisms on the other. In the absence of a suitable control methodology, ad hoc development is the current practice and compromised results at high cost are far too common. Here we described a model-based framework for a new, systematic approach to supervisory control.

Group control elevator device

Abstract: PURPOSE: To enable analysis of a cause by determining a service car every time of generation of nonconformity phenomenon with relation to group supervisory control, and collecting car condition information and car allocation information to be constantly outputted to a first display means, and outputted to a second display means when necessary. CONSTITUTION: An allocation control computer 4 receives input of car condition information from each main control panel 1A-1H, and hall call from a hall call registration circuit 3, and determines a service car number. Every time of generation of nonconformity phenomenon with relation to group supervisory control, that is car call first arrival or forecast change, necessary information when the service car number is determined, and car condition information and car allocation information after determining the service car number to correspond to it are collected by an analysis computer 9, and they are constantly outputted to a RAM display part 12, and to a printer 13 when necessary. Causes for mis-forecast for cars in a building can thus be analyzed after actual operation.

Telerobotics: problems and research needs

Abstract: With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of 'telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA. >

11 – Pilot Control

Abstract: Publisher Summary This chapter focuses on the human aspects of the flight control problem. Flight control by human pilots is one of the most studied and well understood of human activities. Quantitative models have been developed to describe and predict human control performance and workload, and these have been applied to study a wide range of significant problems such as aircraft handling qualities, display and control system design and analysis, and simulator design and use. These models do not replace human-in-the-loop simulation as a development tool, but instead are complementary to simulation, flight testing, and to more conventional human factors analyses. Despite the high level of understanding of human control that has been attained and the accomplishments alluded to above, there are a number of challenging problems and areas for research that remain or are arising. The evolution of aircraft, control and display systems, and mission requirements are imposing new problems in control. The future concern most often raised in connection with modeling and understanding the pilot in the aircraft control loop is the changed and changing nature of the pilot's task owing to the introduction of substantial amounts of automation. Thus, the roles of flight management and supervisory control are becoming dominant in many pilot-vehicle-display applications. As might be expected, the data and models needed for understanding these roles are not at all up to the standards of those for manual flight control tasks and are clearly in need of further development.

The complexity of some basic control problems for discrete event systems

Abstract: We present a summary of some of the known results on the complexity of supervisory control of discrete event systems in the framework of [RW1]. In addition some recent results on the controllability of sequential behaviors and on the complexity of basic coordination problems are presented.

Knowledge-Based Approach to Real-Time Supervisory Control

Abstract: Increasing complexity of industrial plants necessitates the usage of advanced programming techniques in process control. Artificial Intelligence programming offers new opportunities in constructing complex software systems. This paper describes an approach which has been used to build Intelligent Process Control System (IPCS). IPCS expand the conventional process control systems with an additional, "knowledge-based layer", where declarative programming methods are used extensively. The knowledge-based components represent a model of the process from multiple viewpoints and the simulator, monitor, control, diagnostics and operator interface subsystems are coupled to a symbolic process database. A special architecture, the Multigraph Architecture has been used as a general framework for integrating symbolic and numeric programming techniques in a distributed environment. The knowledge-based components have been implemented as "Autonomous Communicating Objects". The application of concurrent programming techniques made possible the introduction of new approaches in the design of the monitoring and diagnostic system. A prototype IPCS has been implemented on a network of VAX computers.

Information technology and the control function of supervision

Abstract: The ability of computer systems to rapidly process and transmit large quantities of operating information over dispersed geographical areas has important implications for supervision and management control of the labour process (Child, 1984, p. 258). The characteristics of this technology provide management with the opportunity to incorporate into the machine elements of control associated with directing, monitoring and evaluating production operations (Edwards, 1979, pp. 18–162). Such an application of new technology may serve to reduce managements’ dependence on hierarchical control structures, and thereby alter the dimensions and combination of other control systems within the organisation (Thompson, 1983, p. 152). The options open to management include: devolving additional elements of control to the local level and enhancing the role of the supervisor; concentrating control at a higher level of management and eroding personal supervisory control mechanisms; replacing the traditional role of the supervisor with a computerised system of control (Dawson and McLoughlin, 1986). It has thus been suggested that computer technology may necessitate a reconstruction of line management (Buchanan, 1983, p. 79) and a redefinition of the supervisory function (Dawson, 1986a).