Optimal scheduling of batch industrial facilities
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r 2004 Operational Research Society Ltd. All rights reserved. 0160-5682/04 $25.00 www.palgrave-journals.com/jors
Optimal scheduling of batch industrial facilities AP Barbosa-Po´voa*1 and CMC Vieira2 1
Instituto Superior Te´cnico, Lisboa, Portugal; 2Polite´cnico Leiria, Morro do Lena, Leiria, Portugal
An increasing interest in batch processing has been evident in recent years. This renewed interest is explained by the inherent flexibility of such plants that permits a high level of response to uncertain market conditions and requirements. This level of response does require the use of efficient tools to help the decision-making process at the design and operational level. This paper presents a Mixed Integer Linear Program (MILP) model to optimise the scheduling of batch facilities subject to changeovers and distribution constraints so as to guarantee a pre-defined objective. Such an objective can be defined as the minimum orders’ total lateness or the maximum distribution units loading capacity, among others. A continuous-time representation is used as well as the concept of job predecessor and successor to effectively handle changeovers. Facilities having non-identical parallel units/lines, sequence-dependent orders, finite release times for units and orders, restrictions on the suitability of jobs to lines/units and different possible destinations to available distribution units are also considered. Based on these characteristics the proposed model is able to determine the optimal allocation of jobs to production lines/units, the sequence of jobs on every line/unit and the starting and completion production times of each order. Also, the usage and allocation of the distribution resources (eg trucks) to orders and destinations are obtained based on their availability and suitability to the orders. The model led to the development of a prototype information system that can be used as a tool to help the decision-making process at the operational plant level. Finally, the applicability of the proposed system/formulation is shown through the resolution of an industrial real case where the production of polymers is performed. Journal of the Operational Research Society (2004) 55, 116–122. doi:10.1057/palgrave.jors.2601522 Keywords: scheduling; optimization; integer programming; production; systems
1. Introduction The short-term scheduling of batch facilities appears as an important and often complex industrial problem. The activity of such plants can be described as the manufacture of a wide range of products that must satisfy given amounts and due dates. Operational restrictions such as pre-ordering, changeovers and maintenance constraints are often present and a nonregular production pattern is followed. Furthermore, within real plants, distribution restrictions (eg availability of trucks) influence the final orders due dates and should not be ignored when scheduling production. In the last two decades, a large number of papers has been published in the area of planning and scheduling of batch facilities. Extensive reviews
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