Stratégies de planification et d'ordonnancement. Quel modèle pour l'industrie des produits frais laitiers ?

Abstract

Scheduling in the food processing industry. This article analyses the problem of production scheduling in the dairy product industry where variety and sell-by date constraints have to be taken into account. Using the formalization of priorities as a basis, we shall attempt to demonstrate that a thorough understanding of the relation between a formai scheduling model and its implementation permits one to grasp the profound changes in industrial processing Systems at present. The analysis presented does not daim to represent a generai theory of scheduling in the dairy industry, taking into account ail the industrial aspects, but a departure point for highlighting basis issues which will no doubt prepare future industrial Systems. The formalization of priorities gives a clear indication of the knowledge of those involved in scheduling. In practice these actors strive continually to find a schedule combining the different constraints to devise a programme based on compromise. This "savoir-combiner", or skill in combining, is in fact closely related to the state of productive facilities. Production managers structure the resolution of a priority problem by using a few rules to break it down into several smaller independent problems. This enables them to reduce the number of possible combinations and then to find a schedule in stages. Their calculation takes into account firm orders and stocks, the state of the workshop's resources, the sequence and assignment of products to lines according to the size of orders and in the light of past experience. It is their experience which leads them to consider certain workshop configurations as potentially more efficient than others. This experience also leads them at the start of production to favour highly decentralized scheduling and consequently to simplify combinations which leads, in the end, to a certain succession of batches. The search for a compromise between multiple objectives based on both previous situations in the workshop and on a decentralization of scheduling seems to favour the development of skills in combining, which closely follow changes in the productive system it self as is shown below. With this analysis new representations of possible changes can be created and the idea of a transformation of work organization based on a new form of production management can be developed. Other ways of adapting to this new organization of production and simplification of scheduling now exist and concern mainly investment in production capacity. Some industries over-size and specialize their plants to deal with intense efforts during peak periods. They must however also convince the operators and the workers of the necessity of going from normal to flexible hours during the year.