Project Aims

Poor production scheduling in large scale process industries such as steel mills, aluminum processing plants, etc., are responsible for a high proportion of non value adding waste in those industries in the form of excess inventories and lost sales due to late deliveries. Generic scheduling systems have had comparatively little success in solving this problem due to

• the large amounts of domain-specific and sometimes subjective human knowledge that is usually involved in constructing a satisfactory schedule which cannot be represented generically
• the lack of attention generally paid to the reactive as opposed to the predictive aspects of schedule construction
• the inadequate ability of the user to participate in the schedule construction process and to interact with the schedule in a satisfactory way to input their subjective preferences for such factors as technological sequencing constraints, due date preferences etc., and to explore interactively the possible trade-offs between different schedule effectiveness criteria.

Advances in object oriented programming techniques, with the associated concepts of extendible, re-usable objects and frameworks are starting to provide potential ways of overcoming the problems of configuring a generic scheduling system to specific industrial environments. Additional research on the specific problems of reactive scheduling, including the use of fuzzy temporal constraint representation to assess reasonable cut-off limits for the extent to which unexpected events will propagate down a schedule are likewise providing possibilities for developing scheduling systems that have a substantive capability for reaction to contingencies. Research on the representation, manipulation and combination of subjective preferences, combined with graphical methods of exploring multiple criteria trade-offs are allowing the possibility of more effective forms of user interface to the schedule.

Technical Objectives

To extend the existing framework with the following components:

• a fuzzy temporal constraint representation and propagation component for constraining the computations on the effects of schedule disturbance to zones where event timings can be predicted with sufficient precision , rather than over the whole schedule,
• a component for filtering and monitoring the relevant data of the application / simulation,
• a component for evaluating schedules against multiple performance criteria including robustness, stability, and nervousness,
• a repair-based scheduling algorithm to react in a generic way to unanticipated events on the shop floor in real-time, and
• a graphical user interface for exploring the trade-offs between different criteria and monitoring the dynamic production process.

To develop a generic simulation package with the following components:

• a language interpreter to describe a wide range of scheduling problems
• a component to generate benchmarks randomly
• a simulation capability allowing the exploration of the effectiveness of different types of scheduling policies in alternative future production scenarios,
• communication capability for a wide range of reactive scheduling systems.

To develop a prototype scheduling system with the framework for the specified scenario, and to compare this system

• with dynamic dispatching rules and
• with the OPIS-system.

Project Results

The output of this project will be:

• an extended scheduling software framework that can be easily adapted to specific plant requirements in terms of the different types of managerial and technological preference constraints, and which can use a wide range of different scheduling techniques.
• a simulation tool that can be used to evaluate the realized scheduling system as well as other reactive scheduling systems.
• a set of performance benchmarks for reactive scheduling of a wide range of flow-shop scenarios. This set will facilitate evaluation of scheduling strategies in the simulation package.
• a scheduling system communicating with the simulation model and solving the reactive scheduling benchmarks.
• a reuse manual describing how the existent framework can be reused in other applications.

The scheduling framework and systems built with the framework are likely to result in a long term increase in the competitiveness of the industries which use it, particularly with regard to reduced throughput times, inventory reductions, and better customer due date performance.