سیستم مدیریت جریان کار مبتنی بر شبکه پتری برای کنترل فرایند در یک نیروگاه پردازش های پلاستیکی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|21729||2003||8 صفحه PDF||سفارش دهید||4137 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Journal of Materials Processing Technology, Volume 139, Issues 1–3, 20 August 2003, Pages 302–309
To manage a complex system, an operation model is proposed for evaluating the effectiveness and efficiency of each possible plan. During the planning process, an easy-to-use modeling system for operation modeling could be very useful for assisting the shop floor manager to understand and predict the performance of operation plans. In this paper, the Petri Net is used as a tool to realize the proposed modeling concept. Derived from the basic Colored Petri Net (CPN) language, a Modular Colored Petri Net (MCPN), composed of a number of CPN Modules (CPNMs), is proposed for this adaptive modeling approach. The CPN in each CPNM represents the discrete event logic of the corresponding operation. Despatching rules of the material and activities are modeled by the components and functions of the CPNs in these CPNMs, and the dynamics of the system can be modeled by the transition firing and connections amongst them. In this way, the time and cost for the development and maintenance of the shop floor operation model can be reduced. The application of the system in in-process control in a plastic processing plant is illustrated in the paper.
1.1. Workflow management A workflow management system (WMS) is defined as a system that completely defines, manages, and executes workflow through a software application where the order of execution is driven by a computer representation of the workflow logic . The basic functions of a WMS, including the definition of tasks and procedures, are discussed in . Management of workflow covers the manipulation of information involved in controlling, monitoring, optimizing and supporting a business process. Since workflow management develops a systematic foundation to specify and manipulate information, it can be adopted to solve many communication problems in production management. With an effective WMS in the system, business policies and practices can be automatically deployed, implemented, monitored, measured and, if necessary, improved. Moreover, with an in-depth understanding and a well-defined formal definition of the business processes in an organization in the development and operation of a WMS, the flow of business processes can be continuously improved through systematic analyses. Adoption of an effective WMS can also foster better tracking of business processes and enhance the reliability of the operation system. A typical plastic processing routing involves a large number of steps in complex sequences in various stages of the operation, such as planning, preparation, forming, finishing, decoration and recycling. Examples of some common steps are given in Table 1.These complex sequences of tasks involve various types of resources such as machines, operators and their skills, etc. It is found that since each step requires only its specific resource, other resources are usually in an idle state. In order to optimize the productivity of the resources, the allocation of work to them must be carefully planned and managed. A workflow system for a material processing environment to speed up its work by eliminating non-value work both within and between operations and to balances the overall work load to improving the overall efficiency is required. It is used as a tool to assist different levels of executives, engineers and clerical staff to improve their productivity. For effective planning of a complex system, an operation model has to be constructed for evaluating the effectiveness and efficiency of each proposed plan during the planning process. However, owing to the complexity of such a model, the development process using traditional methods is usually time-consuming and error-prone. To overcome these problems, which are mainly due to the ill-organized and partitioned structure of the specification of operation and its components, a more systematic and structural methodology is required. Objects and events to be handled in a workflow system in a plastic process plant cover a wide range of tasks at different levels of aggregation. However, a number of basic types of primitive elements of a workflow model were categorized in  as shown in Table 2.1.2. An example: an injection molding workshop This example describes an injection molding workshop with three injection machines, Machine_1001 to 1003. Several workers with specific skill types and levels on different jobs, such as mold setting and hopper cleaning, are working in the shop. In this example, a range of product models in different types of plastic material, which require different preparation work, such as handling and pre-dry time, will be produced. Changeover of the product model or material happen frequently, consuming extra setup time and operator resources. In order to control the workflow on this shop floor, a workflow model is developed. Since the production requirements change frequently from one model to another or from one material to another, an adaptive approach is required. It is expected that such production requirements changes cause minimum disruption to the model.
نتیجه گیری انگلیسی
To ensure the efficiency of the flow of material and information within complex manufacturing systems, effective workflow systems require models which can truly reflect their complicated behavior. The design and development of such complex models are usually time-consuming and error-prone. This paper presents a MCPN-based modeling method for constructing workflow models in a more systematic way. The above case example used here provides an illustration of the proposed method to model complex production system. The dynamics of the operation is reflected by the change of the marking and the tokens’ colors in the model in a way that can be understood and verified easily. The approach described in this paper focuses on the representation of the workflow of an application system. In order to further extend the functionality of this modeling approach, it is suggested that the temporal feature can be implemented to the places of activity to represent the duration of tasks to be carried out in the process to be modeled. With the added temporal feature, the model can be further used to evaluate the performance of the workflow of a proposed operation with different alternative business logics by means of simulation; thus to assist system planners to select the most suitable plan for their requirements. In short, this proposed MCPN-based modeling method suggests a systematic way to support an adaptive approach which can thus reduce the time and cost for the development and maintenance of the shop floor operation model. As a result, a more flexible and versatile production system can be obtained.