T. Govindaraj

Research in object-oriented manufacturing simulations:an assessment of the state of the art

Object-oriented programming (OOP) has been revolutionizing software development and maintenance. When applied to simulation of manufacturing systems, OOP also provides an opportunity for developing new ways of thinking and modeling. In this paper, we identify existing large-scale, persistent OOP-based research efforts focusing on manufacturing system simulation, and present an integrating framework for discussing the associated modeling abstractions, implementation strategies, common themes, and distinctive features. The goal is to identify the fundamental research and application issues, assess the current state of the art, and identify key research needs.

The effectiveness of supervisory control strategies in scheduling flexible manufacturing systems

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. >

Knowledge organization in intelligent tutoring systems for diagnostic problem solving in complex dynamic domains

Turbinia-Vyasa is a computer-based instructional system that trains operators to troubleshoot and diagnose faults in marine power plants. It is implemented on Apple Macintosh 11 computers. The simulator, Turbinia, is based on a hierarchical representation of subsystems, components, and primitives. Vyasa is the computer-based tutor that teaches the troubleshooting task using Turbinia. The simulator, an interactive, direct manipulation interface, and the tutor (with its expert, student, and instructional modules) comprise the architecture for the instructional system. In this paper, we discuss the details of knowledge organization that supports the functions of the three major elements of the intelligent tutoring system. Graphical interfaces, Knowledge representation, Fault diagnosis, Training, Maintenance, Intelligent tutoring systems, Intelligent computer assisted instruction, Interactive learning environments, Marine power plants, Simulation.

A specification environment for configuring a discrete-part manufacturing system simulation infrastructure

A well-designed graphical environment that supports model specification has the potential of enabling the modeler to make better use of the modeling constructs and architecture. We describe on-going research in creating a graphical environment that supports model specification in OOSIM (Object-Oriented Simulation in Manufacturing), a high fidelity manufacturing system simulator.<<ETX>>

Decision models for aiding FMS scheduling and control

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

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.

Object-oriented simulation to support operator decision making in semiconductor manufacturing

The authors describe research on the development of a high-fidelity simulator using the object-oriented programming paradigm. The simulator models the complex interactions in reentrant flow manufacturing facilities. In addition to potentially providing better estimates on throughput, work-in-progress levels, and bottleneck resources in the modeled system, the simulator serves as a platform to investigate issues of operator cross-training, decision aiding, and the effect of operator decisions in such manufacturing facilities. The authors describe the class hierarchy of objects required for modeling and analysis of semiconductor and thin films fabrication, and discuss their approach to modeling complex supervisory control decisions in reentrant flow lines.<<ETX>>

An ICAI architecture for troubleshooting in complex, dynamic systems

Ahab, an intelligent computer-aided instruction (ICAI) program, illustrates an architecture for simulator-based ICAI programs to teach troubleshooting in complex, dynamic environments. The architecture posits three elements of a computerized instructor: the task model, the student model, and the instructional module. The task model is a prescriptive model of expert performance that uses symptomatic and topographic search strategies to provide students with directed problem-solving aids. The student model is a descriptive model of student performance in the context of the task model. The instructional module coordinates information presented by the instructional media, the task model, and the student model so that each student receives individualized instruction. Concept and metaconcept knowledge that supports these elements is contained in frames and production rules, respectively. The results of an experimental evaluation are discussed. >

Object-oriented modeling and simulation of automated control in manufacturing

The object-oriented modeling of manufacturing systems as used in the development of a high-fidelity simulator is described. The separation of control and plant resources in the model allows explicit representation of the factory control system. Different control strategies can be readily tested within the simulation. The application of this approach to deadlock detection and resolution within a flexible manufacturing cell is discussed. The simulator also serves as a platform to investigate the integration of human resources and automated equipment in advanced manufacturing facilities, and to study supervisory control issues in automated systems.<<ETX>>

An intelligent tutor for diagnostic problem solving in complex dynamic systems

An intelligent tutoring system (ITS) is discussed that helps to organize system knowledge and operational information, including symptom-cause relationships, to enhance operator performance. The ITS incorporates the structure, function and behavior of the controlled system in an appropriate form that achieves cognitive compatibility with the operators. In addition, the ITS contains a normative task model that provides it with the ability to infer the trainees misconceptions. The example system considered is an intelligent tutor to be used for training operators to troubleshoot large dynamic systems.<<ETX>>