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1 2004

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Komputerowo wspomagane planowanie realizacji zlecenia w przedsiębiorstwie wirtualnym

Pisz I.

Zarządzanie Przedsiębiorstwem

2004

Vol. 7, nr 1

35-44

In recent years the market conditions have been changing. The customers demand more specialized products. The enterprises have to tailor their offers according to individual customer wishes. In order to decrease complexity and increase flexibility enterprises employ the core competence strategy. It means that they concentrate on what they can do best, they specialize in certain areas. They joint their core competencies in a value chain to exploit fast changing opportunities. The set of core enterprises built the virtual enterprise that the form of this organization is temporary. The stakeholders of the contract-order are in alliance/consortium, they share costs and skills in delivering process of the goods to the market. In order to decide whether a new work order can be executed in a given production system - in the structure of the potential virtual enterprise the producer capabilities and the customer needs have to be taken into account. This paper addresses an issue of decision-making support for small and medium size enterprises gathered in virtual enterprise. The objective is to find a computationally effective method of planning the production flows in a virtual enterprise. The considered problem regards of finding a feasible schedule that follows the constraints imposed by duration order and price given by customer and by the time-constrained resources availability. In other words it is looking for the answer whether a given work order can be accepted for processing in virtual enterprise. The following problem can be now formulated. Consider a manufacturing system providing a given production capability while processing some other work orders. That means that only a part of the production capability (specified by in the time-restricted resources availability) is available for use in the system. Given work order is represented by an activity-on-node network where the nodes and the arcs represent the activities and precedence relations, respectively. The work order is specified by project duration deadline, which is equivalent to a presumed completion time as well as a total selling price. Each activity may be executed in one out of the set of system resources. Also, each activity may not be pre-empted and the mode once selected may not be changed. Considering a time horizon that is an upper bound on the project's makespan, there is an available amount of units of renewable resource in period considered. The cost of using the unit of the resource is specified in the map of accessible of renewable resources. The problem considered regards of finding of a makespan - feasible schedule that follows the constraints imposed by the precedence relations and by the time-constrained resources availability. The objective is to find an answer for the following question: whether there exist a potential virtual enterprise which is able to do the work order in agreement with enterprise technical capacities and the client s requirements? In order to cope with this problem authors proposed a heuristic method. The method bases on the branch and bound scheme. The searching procedure is driven by an upper bound evaluation policy. In order to avoid costly exhaustive enumeration of possible schedules the cases explored are limited first of all to the ones possessing the lowest margins of cost and time. In other words first of all the cases those could lead to an unfeasible schedule are considered. Of course, the proposed way the eases are explored can be treated as searching aimed at proving that a feasible schedule docs not exist. The proposed method includes four resources allocation heuristics. The heuristics are based on estimation the value of resource capability and the average of the resource cost usage in the given period. The heuristics proposed are following: - the smallest resource capability heuristic, - the biggest resource capability heuristic, - the smallest average resource cost heuristic, - the biggest average resource cost heuristic. The presented method has been implemented in a software package Simulator of Virtual Project. The package permits to respond to a question whether a given work order can be completed for processing in a virtual enterprise? A positive response for the question provide a feasible schedule as Gantt's chart and report of the project cost. The package permits the user to investigate the effect of a new work order in a given manufacturing system. The user can find the answer whether a given work order can be accepted for processing in a given structure of a virtual enterprise. The method proposed can be useful for the project-driven production flow management in small and medium size enterprises and for prototyping of the virtual enterprise structure. It provides a good platform for consistency checking between the work order requirements (client requirements) and enterprise capabilities offered (a virtual enterprise or a single enterprise).