Abstract

In this paper we discuss scheduling of semi-cyclic discrete-event systems, for which the set of operations may vary over a limited set of possible sequences of operations. We introduce a unified modeling framework in which different types of semi-cyclic discrete-event systems can be described by switching max-plus linear (SMPL) models. We use a dynamic graph to visualize the evolution of an SMPL system over a certain period in a graphical way and to describe the order relations of the system events. We show that the dynamic graph can be used to analyse the structural properties of the system. In general the model predictive scheduling design problem for SMPL systems can be recast as a mixed integer linear programming (MILP) problem. In order to reduce the number of optimization parameters we introduce a novel reparametrization of the MILP problem. This may lead to a decrease in computational complexity.

Highlights

  • Scheduling is the process of deciding how to allocate a set of jobs to limited resources over time in such a way that one or more objectives are optimized (Leung 2004; Pinedo 2001)

  • The contribution this paper is that by considering switching max-plus linear (SMPL) systems the performance of the scheduling procedure can be improved by using the properties of SMPL models and dynamic graphs, such as detecting bottlenecks and using reparametrization of the mixed integer linear programming (MILP) problem based on max-plus expressions to reduce the number of optimization parameters

  • In this paper we have shown that various semi-cyclic discrete-event systems can be modeled as switching max-plus linear (SMPL) systems and that dynamic graphs are a useful tool in the modeling and analysis process

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Summary

Introduction

Scheduling is the process of deciding how to allocate a set of jobs to limited resources over time in such a way that one or more objectives are optimized (Leung 2004; Pinedo 2001). Many flow shop scheduling problems can be solved very well by considering a class of cyclic discrete event systems (DES), namely the class of max-plus linear systems (Baccelli et al 1992; Heidergott et al 2006), which is capable of representing job and resource unavailability. The contribution this paper is that by considering SMPL systems the performance of the scheduling procedure can be improved by using the properties of SMPL models and dynamic graphs, such as detecting bottlenecks and using reparametrization of the MILP problem based on max-plus expressions to reduce the number of optimization parameters.

Max-plus algebra
Max-plus linear systems
Switching max-plus linear systems
Dynamic graphs
Examples of switching max-plus-linear systems
Production system
Classification of switching max-plus-linear systems
Fixed or variable route
Input type
Due date or time table
Scheduling and SMPL models
Routing in MPL systems
Ordering operations on resources in MPL systems
Synchronization of operations in MPL systems
Combined A matrix
Reference and input signal
Final SMPL model
Analysis of SMPL systems using dynamic graphs
Model predictive scheduling
The optimization problem
The mixed-integer programming problem
Reparameterizing the MILP
Reparametrization with max-plus functions
Reparametrization of the routing variables
Reparametrization of the ordering variables
Parameter reduction
Conclusions
Full Text
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