A study of scheduling problem in agro-food manufacturing systems

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Abstract

This paper identifies and characterizes specificities of agro-food production systems. We focus on the features which represent hard constraints that must be met by the scheduling problem. So synchronization with the stock state must be integrated. Next, we suggest a real time scheduling approach based on some preference and priority rules that allow us to take into account the majority of constraints and to consider the unforeseen events that can eventually occur. The two main objectives of the generated scheduling are the minimization of the cost of expired products and the minimization of the time interval between the finishing date and the expedition date in order to handle storage cost and avoid the discount imposed by the distribution sector. Such work is new both in terms of the production systems studied and in terms of the criteria considered. This work will contribute to the knowledge of production and operation management in agro-food systems.

Introduction

During the last decade, agro-food industries have reached an important economic position. The food and drink market has become very dynamic and very competitive. There is a very wide range of agro-food products corresponding to the large diversity of consumer tastes and consumption trends. To address the challenges of the new market, as well as to adapt business process to the changing conditions and regulations of this industry, more effort should be focused on new methods aimed at monitoring all levels in the production system so as to better handle flow control problem.

Today many developments and technological innovations are being made to improve efficiency and to increase productivity of workshop stations. However, very few results have been obtained in the literature. So the flow control part must be considered jointly. Many approaches have been, already, proposed to solve this problem and especially scheduling problem. But it seems that the majority of these solutions are fairly generic and not particularly helpful in the agro-food industries context. Indeed, the environment of these industries is very dynamic due to primary and end-products which often have short production processing and especially brief life-cycles. It has to be noticed that available methods suggest a solution for a static scheduling problem whereas, in practice, many unforeseen events and disturbances may occur in agro-food manufacturing context.

In this paper, we aimed firstly to identify specificities of the agro-food production system and the particularities of its environment. At first, we focus on the features which represent hard constraints that should be met by the schedule. Secondly, we attempt to propose a real time scheduling approach in which primary products have use-by dates and end-products, to be processed, which have brief life-cycles and due dates.

The classical scheduling problem is described in Section 2. Section 3 analyses and identifies the specific characteristics of agro-feeding industries. Section 4 is devoted to a detailed presentation of the different scheduling approach steps.

Section snippets

Characteristics of general scheduling problems

Many basic data are needed to characterize a scheduling problem [4], [6]. These data are as follows:

  • end-products defined by the production plan;

  • resources required to carry out the end-products;

  • constraints describing the processing conditions in the workshop which have to be met by the schedule;

  • criteria or objectives to be reached via the scheduling procedure.

Characteristics of agro-food scheduling problems

Effective scheduling algorithms for agro-food system can help to shorten the production lead times. As quick response to customer orders is essential for today’s agro-food manufacturers to survive in the very competitive global market, reducing production lead times has become a major goal in the make-to-order production. Similarly to all industries workshops, in agro-food manufacturing we manipulate products characterized by release and due dates. However, these products have other

Scheduling approach

In the dynamic environment of agro-food manufacturing workshops, scheduling should be as a real time decision process [1], [2], [5], [6], [9], [10]. Indeed, modeling all constraints and objectives of the problem is unrealistic in most practical situations. We attempted to generate an approach aimed to:

  • propose, at each decision time, a set of actions compatible with the constraints to be handled. This approach allow us to choose the best action considering the main criterion and hard constraints

The monitoring of production

In agro-food products process, once launched, the mixture must be supervised during all its processing duration. In fact, in some case, it cannot evolve normally because of the difference between the biological characteristics of its components. For example, the fermentation or the maturation cannot evolve normally, the degree of acidity is very high. So the resulting mixture cannot be immediately convoyed on the next step of production. Many different actions having different and particular

Conclusion and perspectives

Scheduling problems have constituted a very active area of research for about four or five decades, and many theoretical results are still to be found in the frameworks. The cooperative scheduling has, particularly, strongly emerged during the last decade. Man–machine interaction has become essential in real time scheduling. The continuous evolution and the dynamic characteristics of industrial workshops, particularly those of agro-food shops, impose the generation of a real time decision

Acknowledgements

This work is integrated in the group “optimization of scheduling and manufacturing systems” of a regional program entitled “GRAISyHM” (“Groupement de Recherche en Automatisation Intégrée et Systèmes Hommes/Machines”—“research group on integrated manufacturing and man–machine systems”). This program is supported by the “Conseil Régional du Nord Pas de Calais” and the “FEDER” and it involves several laboratories in the north of France. One of the goals of this program is to increase the

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