Don Hommertzheim

Dynamic dispatching algorithm for scheduling machines and automated guided vehicles in a flexible manufacturing system

In this paper, an on-line dispatching algorithm is proposed for the FMS scheduling problem. The algorithm uses various priority schemes and relevant information concerning the load of the system and the status of jobs in the scheduling process. This information is organized into hierarchical levels. The scheduling decision process is hierarchical in the sense that different decision criteria are applied sequentially to identify the most appropriate part and the machine to be served. The algorithm schedules the jobs on a machine or an automated guided vehicle (AGV) one at a time as the scheduling decision is needed (or as the status of the system changes). Performance of the proposed algorithm is compared with several machine and AGV scheduling rules by using the mean flow-time and the mean tardiness criteria. Simulation results indicate that the proposed algorithm produces significant mean flow-time and mean tardiness improvements over existing scheduling rules for a variety of experimental conditions.

Experimental investigation of FMS machine and AGV scheduling rules against the mean flow-time criterion

Although a significant amount of research has been carried out in the scheduling of flexible manufacturing systems (FMSs), it has generally been focused on developing intelligent scheduling systems. Most of these systems use simple scheduling rules as a part of their decision process. While these scheduling rules have been investigated extensively for a job shop environment, there is little guidance in the literature as to their performance in an FMS environment. This paper attempts to investigate the performances of machine and AGV scheduling rules against the mean flow-time criterion. The scheduling rules are tested under a variety of experimental conditions by using an FMS simulation model.

Experimental investigation of an FMS due-date scheduling problem: Evaluation of machine and AGV scheduling rules

Although extensive research has been conducted to solve design and operational problems of automated manufacturing systems, many of the problems still remain unsolved. This article investigates the scheduling problems of flexible manufacturing systems (FMSs). Specifically, the relative performances of machine and automated guided vehicle (AGV) scheduling rules are analyzed against various due-date criteria. First, the relevant literature is briefly reviewed, and then the rules are tested under different experimental conditions by using a simulation model of an FMS. The sensitivity to AGV workload, buffer capacity, and processing-time distribution is also investigated to assess the robustness of the scheduling rules.

Expert simulation systems—recent developments and applications in flexible manufacturing systems

Abstract Flexible Manufacturing Systems (FMS), as a class of automated production systems, are being implemented to increase the flexibility and productivity of discrete part manufacturing. Today, as a result of on-going advances and developments in hardware, this technology is not only becoming more complex to control, but also presenting a number of decision problems to be solved, which, in turn, increases the pressure on both the researchers and practitioners to develop better software algorithms in order to use these extensive hardware systems efficiently. In the recent literature on FMS, planning problems are classified into strategic, tactical, and operational areas. Each area has been also studied extensively and several solution approaches have been proposed ranging from analytical techniques to simulation and expert systems. The objective of this paper is to review the recent developments in simulation and to discuss the role of Expert Simulation Systems (ESS) in FMS by identifying possible future research areas.

Experimental investigation of an FMS due-date scheduling problem: an evaluation of due-date assignment rules

Abstract This paper investigates the performance of due-date assignment rules in a flexible manufacturing system (FMS) Although emphasis is placed on a comparison of due-date assignment rules, machine and automated guided vehicle (AGV) scheduling rules are also evaluated under various experimental conditions using an FMS simulation model. The mean job tardiness is the measure of performance by which the rules are compared. The sensitivity to AGV workload, buffer capacity, and processing time distribution is also investigated to assess the robustness of the due-date assignment rules.

A knowledge-based model management system for aircraft survivability analysis

For the survivability analysis of a weapon system, an analyst has to consider and choose from a large number of available models the set of models that best fits the study requirements. This paper presents a knowledge-based approach for this Model Management System (MMS) problem. A hierarchical structure of the models is used in the MMS, where a lower level models output must match the input requirements of a higher level model. The search procedure for the appropriate model set is driven by the user defined weapon analysis requirements. This type of search procedure ensures that the final output of the selected models would provide the required information to the user and the set of selected models would be properly matched. A prototype of the knowledge system has been developed using a commercially available PC-based shell.

Expert systems and simulation in flexible manufacturing systems

Abstract Flexible Manufacturing Systems (FMS), as a class of automated production systems, are being implemented to increase the flexibility and productivity of discrete part manufacturing. Today, as a result of on-going advances and developments in hardware, this technology is not only becoming more complex to control, but also presenting a number of decision problems to be solved. Which, in turn, increases the pressure on both the researchers and practitioners to develop better sofware algorithms in order to use these expensive hardware systems efficiently. In the recent literature on FMS, planning problems are classified into strategic, tactical and operational areas. Each area has been also studied extensively and several solution approaches have been proposed ranging from analytical techniques to simulation and expert systems. The objective of this paper is to review the developments in simulation and to discuss the role of Expert Simulation systems (ESS) in FMS by identifying possible future research areas.

ESSEx - an intelligent advisor for expert system shell selection

Abstract This paper described an advisory system for selecting expert system software. Some background into the problems that an organization might face in the selection of expert system software will first be presented. After this, the methodology and architecture of the system will be reviewed. Finally, an example consultation session will be conducted. The purpose of this paper is to show how knowledge-based systems and database management systems can be linked to form a uniform information processing environment.

Computer usage in manufacturing systems

Abstract Flexible Manufacturing Systems (FMS), as a class of automated production systems, are being implemented to increase the flexibility and productivity of discrete part manufacturing. Today, as a result of on-going advances and developments in hardware, this technology is not only becoming more complex to control, but also presenting a number of decision problems to be solved. Which, in turn, increases the pressure on both the researchers and practitioners to develop better sofware algorithms in order to use these expensive hardware systems efficiently. In the recent literature on FMS, planning problems are classified into strategic, tactical and operational areas. Each area has been also studied extensively and several solution approaches have been proposed ranging from analytical techniques to simulation and expert systems. The objective of this paper is to review the developments in simulation and to discuss the role of Expert Simulation systems (ESS) in FMS by identifying possible future research areas.

Availability measures of human-equipment standby redundant data-flow system with application to NASA deep space station

Abstract This paper presents a mathematical model to evaluate availability and proportion degraded-performance of a two-unit standby data-flow system with three possible states of each unit; namely, normally operating, degraded, and failed. In addition to the operator involvement in system operation; the impact of the performance of a link-controller, as a second human component, is also incorporated into the model. The link-controller performance of the reconfiguration/link task allows for the assumption of noninstantaneous restoration of system operation. The system performance is analyzed stochastically using the theory of Markov Process. Steady-state availability and proportion degraded-performance measures have been derived and applied to an existing data-processing system. Selective graphs have also been developed to demonstrate the practical utility of the model.