Computer Science

D-dissertation (10 p)

2004:06

Kjell Olofsson

An investigation into production scheduling

systems

This report is submitted in partial fulfillment of the requirements for the

Masters degree in Computer Science. All material in this report which is

not my own work has been identified and no material is included for which

a degree has previously been conferred.

Kjell Olofsson

Approved, 2004-12-09

Opponent: Thijs Holleboom

Advisor: Donald Ross

Examiner: Anna Brunstrm

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Abstract

Production scheduling consists of the activities performed in manufacturing companies to

manage and control the execution of the production process. The basic task is to perform the

production as planned while at the same time trying to satisfy the overall goals of the

company. This is an important part of the management of a company since it directly affects

the performance of the enterprise. There exists much interest from industry in using software

systems to support the scheduling process but the application of such systems has shown to be

problematic.

This dissertation is an investigation into the area of production scheduling and production

scheduling systems. The purpose of the study is to determine which requirements there are on

a scheduling system and what functionality such a system should provide. The aim has been

to maintain a practical focus and try to find requirements that are important in reality when a

system is used in a company.

The investigation has been performed through literature studies and by performing a case

study in a company that use a scheduling system. From the information gathered in the

investigation, a design of a scheduling system framework has been proposed and a prototype

of the most important parts of this framework has been implemented. The results so far show

that scheduling systems satisfying the requirements elicited from the investigation can be

developed using the proposed framework.

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Contents

1 Introduction ....................................................................................................................... 1 1.1 Production scheduling, a brief introduction............................................................... 2

1.2 ComActivity .............................................................................................................. 2

1.3 The scope of this dissertation .................................................................................... 3

1.4 Dissertation layout ..................................................................................................... 3

2 Manufacturing planning and control from a scheduling perspective .......................... 5 2.1 Introduction................................................................................................................ 5

2.1.1 The difference between planning and scheduling .................................................................... 5 2.2 Material requirements planning................................................................................. 6

2.2.1 A general model ....................................................................................................................... 6 2.2.2 The evolution of material requirements planning .................................................................... 8 2.2.3 Shortcomings of material requirements planning..................................................................... 9

2.3 Terminology ............................................................................................................ 10

3 Production scheduling .................................................................................................... 13 3.1 Characteristics of production environments ............................................................ 14

3.1.1 Production resources .............................................................................................................. 14 3.1.2 Orders and operations ............................................................................................................ 15 3.1.3 Materials and subparts............................................................................................................ 16

3.2 Scheduling objectives .............................................................................................. 16

3.3 Organization and information flow ......................................................................... 17

3.4 Schedule evaluation and comparison....................................................................... 17

3.5 Scheduling methods................................................................................................. 18 3.5.1 Deterministic and stochastic scheduling methods.................................................................. 19 3.5.2 Dispatching rules.................................................................................................................... 20 3.5.3 Advanced scheduling methods............................................................................................... 21

3.6 Scheduling in practice.............................................................................................. 26 3.6.1 Practical modeling and handling of uncertainties .................................................................. 26 3.6.2 Human factors ........................................................................................................................ 27

4 Scheduling theory............................................................................................................ 29

4.1 The scheduling problem .......................................................................................... 29 4.1.1 A problem formulation........................................................................................................... 30

4.2 Solution methods ..................................................................................................... 31 4.2.1 Problem solving ..................................................................................................................... 31

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4.2.2 Dispatching rules.................................................................................................................... 33 4.2.3 Bottleneck based methods...................................................................................................... 34 4.2.4 Local search methods............................................................................................................. 34 4.2.5 Constraint programming ........................................................................................................ 37

4.3 Summary.................................................................................................................. 38

5 Software systems for manufacturing planning and control ........................................ 39 5.1 Enterprise Resource Planning systems .................................................................... 39

5.2 Scheduling systems.................................................................................................. 39 5.2.1 Complete systems .................................................................................................................. 39 5.2.2 Scheduling components ......................................................................................................... 40

5.3 Manufacturing execution systems ........................................................................... 41

6 A Case-Study ................................................................................................................... 43 6.1 Production environment........................................................................................... 43

6.1.1 General description ................................................................................................................ 43 6.1.2 The job shop and order structure............................................................................................ 44 6.1.3 Organization........................................................................................................................... 45

6.2 The scheduling process............................................................................................ 47 6.2.1 The process for an order......................................................................................................... 47 6.2.2 Scheduling.............................................................................................................................. 48

6.3 Scheduling objectives .............................................................................................. 49

6.4 Scheduling tasks ...................................................................................................... 50

6.5 Scheduling algorithm............................................................................................... 51

6.6 Discussion................................................................................................................ 52

7 A scheduling system framework .................................................................................... 55 7.1 Requirements .........................................................................................................