Joseph J. Talavage

Complexity in manufacturing systems, Part 1: Analysis of static complexity

This paper studies static complexity in manufacturing systems. We enumerate factors influencing static complexity, and define a static complexity measure in terms of the processing requirements of parts to be produced and machine capabilities. The measure suggested for static complexity in manufacturing systems needs only the information available from production orders and process plans. The variation in static complexity is studied with respect to part similarity, system size, and product design changes. Finally, we present relationships between the static complexity measure and system performance.

A Tradeoff Cut Approach to Multiple Objective Optimization

There is a need to develop user-oriented math programming techniques for resolution of decision problems in which several objectives must be considered. One approach, the Geoffrion-Dyer-Feinberg algorithm, allows interaction between the computer and the decision maker during the solution process. The interactive approach is adopted in this paper. However, our approach focuses on reducing the feasible region of the decision space rather than improving the stored image of the overall preference function. In so doing, the problem is reduced to a series of pairwise tradeoffs between the objectives. This obviates the need for any type of choice among vectors on the part of the decision maker and stays reasonably within his capability to supply necessary information for problem solution.

A transient-based real-time scheduling algorithm in FMS

Real-time scheduling in flexible manufacturing systems (FMS) is a difficult problem because of the complexities and dynamic behaviour of FMS. In this paper, a transient-based real-time scheduling algorithm which selects a dispatching rule dynamically for a next short time period in order to respond to changes of system state is proposed. In this algorithm, the scheduling interval associated with the selected dispatching rule is defined based on the system transient state as predicted by discrete event simulation. Simulation is also applied to evaluate the performance of the candidate dispatching rules for the next scheduling interval.

INTELLIGENT DISPATCHING FOR FLEXIBLE MANUFACTURING

Abstract A decision rule for real-time dispatching of parts, each of which may have alternative processing possibilities, has been developed and tested in a simulated flexible manufacturing system. A part, upon completion of an operation, is not routed to a specific machine, but is, in effect, sent to a general queue. Thus, a machine has a global option for choosing parts which in turn may be processed on alternative machines. For effective use of the systems routeing flexibility under these circumstances, the machine needs an intelligent part-selection strategy (rather than shallow heuristics represented by the conventional dispatching rules) that takes into account the current state and trends of the system. The proposed intelligent reasoning procedure has been found to achieve better shop performance than some of the popular dispatching rules, the improved performance being due to the ability to respond to changing circumstances.

A mixed dispatching rule approach in FMS scheduling

Short-term scheduling in flexible manufacturing systems (FMSs) is a difficult problem because of the complexities and dynamic behavior of FMSs. To solve this problem, a dispatching rule approach is widely used. In this approach, however, a single dispatching rule is usually assigned for all machines in a system during a given scheduling interval. In this paper, a mixed dispatching rule which can assign a different dispatching rule for each machine is proposed. A search algorithm which selects an appropriate mixed dispatching rule using predictions based on discrete event simulation is developed for this approach. The search algorithm for the mixed dispatching rule is described in detail. The effectiveness (in meeting performance criteria) of the mixed dispatching rule and the efficiency of the search algorithm relative to exhaustive search (complete enumeration) is demonstrated on an FMS model. The mixed dispatching rule approach performs up to 15.9% better than the conventional approach, and is 4% better on average. The statistical significance of the results is dicussed.

The strategic value of flexibility in sequential decision making

Abstract This paper formalizes the notion of flexibility in sequential decision making and investigates conditions under which the use of flexibility as an additional criterion may be justified. The correlations between flexibility and value, and flexibility and risk, are studied under various assumptions of uncertainty and information. A number of approaches to constructing a multiple objective decision criterion are discussed. In particular, characteristics of a dual-objective value function, that accounts for both expected value and flexibility, are described. The usefulness of these results is illustrated by applying them to decision processes in discrete part manufacturing. Relationships between flexibility and manufacturing performance are shown and implications to part flow control are discussed.

A multiple-objective planning methodology for information service managers

Abstract The problem of allocation of scarce resources in an organization is frequently complicated by the presence of multiple, often conflicting, managerial objectives and a high degree of ambiguity in the definition of the organizations purpose. This is particularly true within the operating environment of many public and privately operated information centers and special libraries. In recent years, the managers of such centers have been pressed by both the funders and the users of their services to improve the efficiency of their operations. Although techniques are available for determining and evaluating various measures of the performance of these centers, relatively little has been accomplished with respect to the more fundamental decision making problem of allocating resources in order to optimize the achievement level of the various objectives of the decision maker. The problem addressed in this research is the extension of existing techniques to more adequately deal with the resource allocation problem in an ambiguous environment. The technique known as goal programming is extended and a new methodology, termed goal-range programming, is presented. The goal-range programming methodology is related to the information center planning environment through examples derived from the interaction of the authors with several centers.

A spreadsheet model approach for integrating static capacity planning and stochastic queueing models

This paper proposes a manufacturing system modelling approach using computer spreadsheet software, in which a static capacity planning model and stochastic queueing model are integrated. Most stochastic performance measures such as throughput time or work in process as well as deterministic measures can be captured directly from the proposed model. Several special manufacturing features such as machine breakdown and batch production can be included in the model. The performance of the proposed model is evaluated by comparing its results with those obtained from other existing approaches.

The effect of routeing and machine flexibility on the performance of manufacturing systems

Abstract The effect of routeing and machine flexibility on the performance of manufacturing systems is investigated. The results obtained indicate that in a variable environment, a positive correlation between flexibility and several measures of performance may indeed exist. These measures include part mean flow time and waiting time, flow time and waiting time variance, and mean and variance of work-in-process inventory. The significance of the effect of routeing and machine flexibility is shown to increase with increases in either the degree of variability in the system or in the level of system loading. In addition, the relationship between flexibility and performance is found to be of the diminishing return type. That is, most of the performance improvements are achieved at relatively low levels of flexibility. It is also shown that the effect of part flow control policies (e.g. dispatching rules) diminishes with increases in routeing and machine flexibility. The benefits of flexibility are found, how...

A pattern-recognition-based method for controlling a multi-loop production system

The control of an equipment-intensive production system in the electronics industry is a very complicated task due to the complex process flow, especially the necessity for several loop sequences of the same processes. This paper describes the development of a pattern-recognition-oriented control-decision support system (CDSS) in order to set the best control strategy and an application for a circuit board fabrication system. The CDSS has been designed to be flexible to adapt to a change of market demands. This procedure is based on the state table concept. A combined discrete-event/process-interaction simulation model for the production system has been developed in order to provide basic data for the CDSS. The simulation analysis evaluates the alternatives of the control strategy on the efficiency performances, such as throughput and WIP.