ادغام - کلیدی برای یکپارچه سازی برنامه ریزی تولید و برنامه ریزی

In this paper we suggest an integrated planning and scheduling framework with a special emphasis on the link between these control levels. Our planning model is generated automatically by performing aggregation on de facto standard product and technology related data in the dimensions of time, resource capacities and operations. The method addresses make-to-order production environments. An industrial case study is also presented, demonstrating how our algorithms work on large-scale problem instances.

Production planning and scheduling (PPS) map the load of a factory to its capacities on different time horizons and levels of detail. Planning and scheduling problems differ in their timescale, the granularity of resource and activity models and in their optimization criteria. The two levels of PPS are strongly coupled since planning sets the goals as well as the resource and temporal constraints for scheduling. On the other hand, scheduling is responsible for unfolding a plan into detailed resource assignments and operation sequences. No scheduling strategy can improve much on an inadequate plan, whereas a bad scheduling strategy that wastes resources may inhibit the fulfillment of a good plan. All this makes PPS extremely complex and hard to solve. At the same time, PPS calls for efficient decision support methods and intuitive, flexible models with fast, reliable solution techniques that scale-up well to large problem instances Departing from detailed product, resource and production technology related information, aggregation connects the two levels by composing distinct resources and operations into larger units. Thereby aggregation reduces the complexity of production planning when deciding over the flow of materials and the use of resources on a longer horizon. Aggregation addresses also the various uncertainties of production: it does not allow generating detailed plans for a future that will certainly be different from what we anticipate now. Note that this principle applies well not only in PPS but also in the early stage of product design [I] and engineering [2]. The idea of aggregate production planning was introduced almost fifty years ago, just with the motivation to respond to fluctuations in product orders by means of a clear-cut mathematical model that used a common measure of work required by the different orders [3]. A number of theoretical models followed: they merged discrete operations requiring the same resources into distinct aggregate activities [4]. However, if the parts loop over the same resources several times, this method may result in very complex temporal interdependencies of the activities. Consequently, temporal patterns used by planning could hardly be filled in with technological data [5] [6], and planning disregarded most temporal relations [4]. In practice, so-called materiahanufacturing require- ments planning systems (MRP/MRP II) do work with precedence relations, but assume that components and complete products can be produced with fixed lead times, without any direct regard to capacities and the actual load. None of these assumptions is realistic in make-to- order production environments that respond to fluctuating orders. No wonder that plans generated this way can barely be refined to executable detailed schedules.

In this paper we have emphasized the role of aggregation as the primarily link between the models of production planning and scheduling. We have pointed out that aggregation is a representation problem whose solution has a great impact both on the quality of the production plans and the feasibility of the detailed schedules. The proposed methods enable PPS to work on common product, resource and production technology data. Our experiences support the claim that proper aggregation is a major prerequisite for using advanced PPS methods successfully.