Workflow Simulation Scheduling Model with Application to a Prototype System of Cigarette Factory Scheduling Xingquan ZUO*, Yushun FAN**, Huiping LIN**, Yimin SHEN**, Hongjun SUN** * School of Information Engineering, Beijing University of Posts and Telecommunications, Beijing, 100876, P. R. China (E-mail:
[email protected]) ** Automation Department, Tsinghua University, Beijing, 100084, P. R. China Abstract Production scheduling is very significant for improving the enterprise efficiency and reducing the production supply periodicity. The scheduling problems have become more and more complex in recent years, and how to model the complex scheduling problems is a key problem. This paper uses a workflow simulation scheduling model to model the complex scheduling environment of cigarette factory. Then, a heuristic algorithm is designed that is integrated with the model to allocate resources for each active of the multi-process model. Based on the scheduling model and the heuristic algorithm, a prototype system of cigarette factory scheduling is developed. The system can well model the practice scheduling environment and generate feasible scheduling schemes successfully. KEY WORDS; Production scheduling. Workflow technology. Scheduling model, Cigarette factory. Heuristic algorithm
models first collect data through the simulation on a practice scheduling system, and then uses those data to analysis (or evaluate) the performances of a scheduling scheme. But the traditional simulation model is not a universal model, and a special simulation model is needed to be developed for each practice scheduling problem. So the cost of developing a simulation model is too high [2]. Workflow technology is a new information technology that is developed rapidly along with the maturation of computer, internet and data base technology [3]. Workflow technology has been successfully applied to the areas of library, hospital, bank and insurance company etc. Workflow model is a kind of process model that can describe complex production processes roundly, and has a clear and distinct modeling structure
Introduction Production scheduling is very significant for improving the enterprise efficiency and reducing the production supply periodicity [1]. The scheduling problems have become more and more complex in recent years, and how to model the complex scheduling environment is a key problem. Scheduling problems can be modeled by analytic models or simulation models. Analytic models are based on mathematical methods, including programming equations, disconnected charts and Petri net methods; however, analytic models are very difficult to describe a complex practice scheduling problem because of its large complexity. The simulation models of scheduling problems can well describe a practice complex scheduling environments. The
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that can be understood by customers easily, so it has nice capability of modeling complex manufacture processes [4]. In this paper, we use workflow models to model complex scheduling environments, and a workflow simulation scheduling model is introduced. The model is applied to modeling complex scheduling environment of cigarette factory. A heuristic algorithm is designed to integrate with the model to generate scheduling scheme. Based on the workflow simulation scheduling model and the heuristic algorithm, a prototype system of cigarette factory scheduling was developed. The system can well model the practice scheduling environment and generate a feasible scheduling scheme successfully.
Resource model Resource model defines resource entities used in a manufacturing process, and is used to describe the resource restriction of a scheduling problem. The resource entities mainly include manufacture devices, transportation devices, and storage devices etc. Two kinds of resources are defined, i.e., resource entities and resource pools. The resource entities refer to real equipments and a resource pool is a classification of resource entities that has some same functions. The resource model is related to the process model by the mapping between the actives in the process model and the resource entities in the resource model. Transaction model Jobs are considered as transactions. According to transaction model, the scheduling system generates transactions and enables process instances to execute on the workflow simulation scheduling system.
Workflow Simulation Scheduling Model The workflow simulation scheduling model (WSSM) [5], utilizing workflow model to describe scheduling problems, has nice conversional and is capability of describing all kinds of scheduling problems. The model is composed of process model, resource model, transaction model and workflow controlling data.
Workflow controlling data The workflow controlling data is used to identify and control the states of each process or active instance, and select the next process or active instance that should be executed. Hence, the workflow controlling data controls the execution of process instances and realizes the navigation of actives.
Process model The process model consists of multi-processes that are independent one another. Each of these processes describes the manufacturing procedures of a classification of jobs, and the process model defines the manufacturing procedures of all classifications of jobs. The process model can define job shop scheduling, flow shop scheduling, and hybrid scheduling problems easily, so the workflow simulation scheduling model is a universal model. Each process of the model has several actives, and an active is defined as an operation of a job. The logic relationship of actives in a process, i.e., the restriction of processing order of the job, is defined by the process.
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Figure 1 Workflow simulation scheduling model The four models above compose the workflow simulation scheduling model, which is shown in Figure 1. The model has some merits, such as clear model structure.
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powerful describing capability, and fitness for modeling large scale scheduling problems.
primary processing line can be easily expended to tow primary processing line, and the cut tobacco silos and cigarette making machines can be configured arbitrarily; (2) Powerful model description capability. The model can describe the cigarette factory scheduling environment expediently and intuitionally, and has powerful model description capability. The WSSM utilizes a multi-process workflow model to describe the practice scheduling process of cigarette factory. The workflow simulation engine uses this model to drive instances to simulate and run. During the simulation, there are resource conflict phenomena, and resource allocation algorithm is needed to solve these conflicts. Hence, the cigarette factory scheduling problem is converted into a resource allocation problem of workflow simulation on the multi-process model.
Modeling the Scheduling Problems of Cigarette Factory by the WSSM In this part, we use the workflow simulation scheduling model to model the complex scheduling problems of cigarette factory, i.e., describe the process of transporting and processing of cut tobacco on the primary processing line, cut tobacco silos, shaking discs and cigarette making machines. We briefly introduce the process model and resource model of the WSSM used to model the cigarette factory scheduling. Process model The process model describes the manufacturing process of cut tobacco. There are several process models, and the number of shaking discs used in a batch plan is considered as the number of processes. Each of these processes consists of two kinds of actives. The first active is "cut tobacco entering cut tobacco silo", and the resource used is primary processing line; the second active is "cigarette making machine processing cut tobacco", and the resources used are cigarette making machines.
A Heuristic Algorithm Integrated with the WSSM Heuristic algorithms are also called dispatching rules [6], and are used in engineering practices widely. The cigarette factory scheduling problem is modeled by WSSM, and a workflow simulation engine uses this model to simulate. During the simulation, a designed heuristic algorithm is used to allocate the resources for each active in the multi-process of the model. So a feasible scheduling scheme can be generated. The cigarette factory scheduling problem has there decision points. The designed heuristic algorithm is given as follows to make decision on the three decision points. (1) The processing order of cut tobacco on the primary processing line: a) If a cut tobacco silo is empty, then the kind of cut tobacco that should enter into the silo is arrayed on the primary processing line. b) If there are several empty cut tobacco
Resource model There are two kinds of resources in the resource model, i.e., primary processing line and cigarette making machines. The resource model adheres to process model through the mapping between actives and resource entities. The resource model is composes of the states and attributes of each resource entity, especially the sharing states for the resources of cigarette making machines. The WSSM based cigarette factory scheduling model has some characteristics and merits: (1) Model flexible and easy to expand. One
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relation between shaking discs and cigarette making machines. The system can generate a feasible and optimal scheduling scheme automatically according to a given batch scheduling plan. By using the obtained scheduling scheme, the system can give a vivid simulation of scheduling process.
silos, and each silo correspond to a kind of cut tobacco. The kind of cut tobacco that has the most uncompleted cut tobacco should be arrayed on the primary processing line. c) If there are several empty cut tobacco silos, and the uncompleted cut tobacco for each silo is similar, then the kind of cut tobacco whose silos has the quickest output speed is arrayed on the primary processing line. (2) Which cut tobacco silo should the cut tobacco enter: a) If there are several empty cut tobacco silos, then the kind of cut tobacco should enter the silo that has the most uncompleted cut tobacco. b) If there are several empty cut tobacco silos, and the uncompleted cut tobacco for each silo is similar, then the kind of cut tobacco should enter the silo whose output speed is quickest. (3) From which shaking disc should the cut tobacco processed on the cigarette making machine come. If a cigarette making machine connects two shaking disc, then the cut tobacco processed on the cigarette making machine is determined by following rules: a) If a kind of cut tobacco is completed, then the cigarette making machine processes the cut tobacco from the other shaking disc. b) The cigarette making machine should process the kind of cut tobacco whose uncompleted amount is the most.
Simulation E)einonstration and performance index
Collect and analysis data
Scheduling problems
Workflow simulation model
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Workflow simulation
Resource allocation algorithm (Scheduling algorithm) Workflow simulation
Figure 2 The prototype system of cigarette factory scheduling based on WSSM The input and output of the prototype system In cigarette factory, the annual production plan is decomposed into month production plans. Further, each month plan is divided into several batch production plans. A batch plan includes the production plans of several cigarette brands. The prototype system is to decide how to schedule and process a batch plan.
Prototype System of Cigarette Factory Scheduling Based on the WSSM of cigarette factory scheduling and the designed heuristic algorithm, a prototype system was developed, which is shown in figure 2. This prototype system can configure the cigarette factory scheduling environment easily, for example, setting the number of cut tobacco silos; setting the connection
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Figure 3 The simulation demonstration of the scheduling scheme obtained
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The input of the prototype system is a batch plan (time is about 5-15 days). The output of the system is a table of scheduling scheme including the decision information. By using the table, the Gantt chart for each device, the statistic performance indexes and simulation demonstration for the scheduling scheme can be illustrated.
Conclusion In this paper, a workflow simulation scheduling model is used to model cigarette factory scheduling problems, and a heuristic algorithm is designed to integrate with the model to generate scheduling scheme automatically. Based on the model and algorithm, a prototype system of cigarette factory scheduling was developed. The system has some merits, such as nice capability of configuring scheduling environment, clear and friendly interfaces, and nice expanding capability. Acknowledgements This work was granted financial support from the National Natural Science Foundation of China (No. 60504028)
Figure 4 The scheduling scheme table of the primary processing line
References 1. Brucker, P., Scheduling Algorithms. Berlin, Heidelberg: Springer-Verlag, 1998. 2. Chin, S. C, Appa, 1. S., Robert, G, Simulation-based Scheduling for Dynamic Discrete Manufacturing, Proceedings of the 2003 Winter Simulation Conference, 2003, pp.1465-1473. 3. Fan, Y. S., Luo H. B., Lin H. P., Workflow Management Technology Foundation. Beijing: Tsinghua University Press, Springer-Verlag, 2001. 4. Li, J. Q., Fan, Y. S., Zhou, M. C, Performance Modeling and Analysis of Workflow, IEEE Transactions on Systems, Man, and Cybernetics-Part A: Systems and Humans, 2004, 34-2, pp. 229-242. 5. Lin, H. P, Fan, Y. S., Loiacono, E. T., A Practical Scheduling Method Based on Workflow Management Technology, international Journal of Advance Manufacture Technology, 2004, 24-11, pp. 919-924. 6. Shutler, P. M. E., A Priority List Based Heuristic for the Job Shop Problem: Part 2 Tabu Search, Journal of Operational Research Society, 2004, 55-7, pp. 780-784.
Figure 5 The performance indexes of the scheduling scheme The interfaces of the prototype system A batch plan can be inputted in the input interface. Then a heuristic algorithm is used to generate a feasible scheduling scheme automatically. Utilizing the scheme, the prototype is capable of performing visual simulation to demonstrate the obtained scheduling scheme (see Fig.3). The generated scheduling scheme can also be illustrated in the form of table shown in Fig.4. In order to evaluate the performances of the scheduling scheme, the statistical performance indexes can be given in Fig. 5.
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