Brian Huff

Structured models and dynamic systems analysis: the integration of the IDEF0/IDEF3 modeling methods and discrete event simulation

The role of modeling and simulation is receiving much press of late. However, the lack of practice in employing a link between the two is alarming. A static model is used to understand an enterprise or a system, and simulation is used for dynamic analysis. Generally, most models are considered static, whereas simulation is really a dynamic model. Static models are useful in achieving understanding of the enterprise. Simulations are useful in analyzing the behavior of the enterprise. Most enterprises develop and even maintain multiple types of models for different purposes. If a single model can be used to drive other modeling purposes, then model maintenance and development could be reduced. This paper describes the procedure necessary to use a static representation as the primary input for an animated simulation. It presents the additional steps necessary to annotate a static model for input to a dynamic model. Two commercial suites, WorkFlow Modeler™ to ServiceModel™ and ProSim™ to WITNESS™, are compared and contrasted based on the respective ease of conversion from the static model to the dynamic model. Any user who purchases these products can follow the steps described in this paper for either of these product suites to generate a simulation from a static model. Finally, some general observations of using an existing IDEF (0 or 3) model to create a working simulation are presented along with conclusions.

Commercial simulation over the Web

Modeling and simulation provide objective analysis tools for many fields including manufacturing. This paper presents the requirements and describes the usefulness of a Web-based interface to discrete-event simulation. A description of related efforts is first presented and an approach is then described. The approach develops a Web-based interface to use commercial discrete-event commercial tools.

On the Use of Enterprise Models

This paper presents the results of a field study designed to determine how enterprise models are used. The paper begins with an introduction to enterprise models then provides an overview of the survey method used. No known empirical studies have been conducted to determine how enterprise models actually are used by industry. The research is designed to answer this question. A screening sample and complete web-based survey of 72 enterprise modelers was conducted. The primary research question of this survey was on the use of enterprise models, with particular focus on the three dimensions of living models: scope, enactment, and dynamicity. Half the respondents claim that their enterprise models were of their entire division, multiple divisions, and even multiple enterprises. It is encouraging to see that enterprise models are used on such a wide scope. The enactment of the enterprise models was not as large as was expected. Of the respondents, 75% claimed that their models did not receive information from the enterprise more frequently than quarterly. The same was true for how often the models provided information to the enterprise. Seventy-five percent did not update their models more than five times (although, 32% did update the model three to five times). Finally, additional areas of research are proposed.

A computer based production scheduling architecture suitable for driving a reconfigurable manufacturing system

Abstract In order to address the time constraints and increased flexibility requirements which will be placed on manufacturing activities in the 1990s, manufacturing must shift its focus from the specific products it produces to the process resources required for their production. Reconfigurable manufacturing systems must be developed which are capable of tailoring their configuration to meet the resource demands of an ever changing mix of products. A corresponding scheduling architecture must also be developed to control these systems. This architecture will be based on the concept of scheduling manufacturing processes as opposed to manufactured products. The proposed scheduling architecture outlined in this paper has a hierarchical structure and utilizes opportunistic scheduling techniques. The structure of this scheduling system is directly determined by the configuration of the production system and as a result must be as dynamic as the manufacturing resources it controls.

The Needs and Issues Associated with Representing and Integrating Multiple Views of the Enterprise

A critical component of any information infrastructure is a common understanding of the enterprise. Enterprise models enable this common understanding. The enterprise model can provide a comprehensive understanding of the environment the information infrastructure is designed to support. Models are typically developed from one of five perspectives or views. The different model views are presented and a comparison of these views is discussed. These five views are: business rule, activity, business process, resource, and organization views. The primary concern in this research is the identification of the issues of multiple views of an enterprise or system. Most project managers do not consider the issues pertaining to a multiple view model of a system. These managers develop and even maintain multiple types of models for different purposes. These multiple types of models are generally developed on an ad hoc basis. By understanding the issues relating to maintaining multiple views of an enterprise, the benefits of multiple views can be realized while minimizing its difficulties. Three approaches to integrating multiple views are explained and their relative shortcomings are discussed.

A Sensor Calibration Methodology for Evidence Theoretic Unmanned Ground Vehicle Localization

We present a novel sensor calibration methodology that is suited to an evidence theoretic unmanned ground vehicle (UGV) localization system. The proposed procedure for sensor calibration employs a series of designed experiments with the objective of creating parametric calibration models and forming a mass assignment table for a Dempster-Shafer belief system. Sensors calibrated include custom built magnetic encoders positioned at the rear wheels of the UGV, an accelerometer, a solid-state rate-gyro, a digital compass, and a global positioning system (GPS). The estimated parameters together with a mass assignment table are presented. This table is created for the GPS unit based on the factors that significantly impact the accuracy of the readings using an experimental procedure. We conclude with a brief summary of the main results.

Construction of an obstacle map and its realtime implementation on an Unmanned Ground Vehicle

This paper presents the development of an obstacle mapping system based on the concept of a Probabilistic Threat Exposure Map (PTEM). The paper also discusses the realtime embedded implementation of this obstacle mapping system on a small Unmanned Ground Vehicle (UGV) to support realtime obstacle avoidance. These activities are a part of a larger effort to establish a theoretical foundation for autonomous and cooperative multi-UxV guidance solutions in adversarial environments.

η-Filter: An Evidence Theoretic Approach to Unmanned Ground Vehicle Localization

In this paper, we present a novel evidence theoretic fusion filler, and its application to the Unmanned Ground Vehicle (UGV) localization problem. The various components of the sensor fusion framework such as the adaptive pre-processing unit, the evidence extraction and combination unit, and the extended Kalman filter are described in detail. The crux of this architecture is the evidence extraction and combination unit that employs a two-pronged approach, one to switch between parametric models, and another to adaptively vary the measurement noise covariance matrix. The process of evidence extraction using fuzzy-type or rule-based techniques, and their subsequent combination using the Dempsters rule for combination are detailed. An experiment is conducted to demonstrate the merits of this UGV localization approach. Finally, we conclude with a brief summary of the results.

Simulation modelling for a bus maintenance facility

The Greyhound Lines Dallas maintenance facility was congested during peak operating periods. A stochastic model of this facility was developed to determine the resource requirements needed to provide adequate service during periods of peak demand. The structure of the simulation model is described. A representative sensitivity analysis is presented to discuss how this model was used to support facility sizing decisions. Based on our simulation experiments, we concluded that the existing site, with appropriate modifications, could accommodate peak traffic with some room for growth.

The Dynamically Reconfigurable Assembly System

Abstract An essential element of World Class Manufacturing is the existence of small, focused factories in which a variety of products can be made. Unfortunately, classical approaches to assembly automation result in systems which are difficult to reconfigure; i.e., to reprogram, refixture and retool. The Dynamically Reconfigurable Assembly System (DRAS) is a project at the Automation & Robotics Research Institute to address the issues involved in introducing more flexibility into assembly systems by making them able to be dynamically reconfigured for new products. Both hardware and software standards and architectures are being developed to facilitate the reconfiguration of DRAS in minutes instead of the usual weeks. The requirements for such a system and the hardware and software architecture will be described.