Continuous time representation for multi-stage plant scheduling: Formulation and case study

Abstract

The Operations Research literature provides a number of mathematical programming formulations of scheduling problems based on continuous time representation. This paper addresses the short term scheduling problem for continuous multipurpose/multi-product manufacturing plants. The continuous time representation model of Tahmassebi and Hindi for the single stage packing system, which accommodates sequence dependent changeovers and minimum run length, is extended to include making units, multipurpose storage and slave utility stations in a multistage plant setting. Scheduling of such plants is complicated by the presence of shared resources, which link the operation of the lines, and structural constraints linking the operation of different stages. The problem is formulated as a mixed integer program and solved to give as solution the exact starting and stopping of all events as well sequencing (making, storage and packing) at any time. The advantage of this formulation is that it is possible to use a standard solver which makes the approach very useful. Some preliminary results of a case study on a real factory, with relevant data are presented.