A Distributed Object Based Integrated System for Material Requirement Planning and Job Shop Simulator Liao Qiang, Tham Chen Khong, Chris Choy Laboratory for Concurrent Engineering & Logistics (LCEL) Department of Mechanical Engineering National University of Singapore 10 Kent Ridge Crescent, Singapore 119260 E-mail:
[email protected] Abstract The paper presents an enterprise application that integrates material requirement planning (MRP) with job shop simulator using distributed object technology. The application aims to realize an integrated system that has rapid response to changing requirements and capability to integrate heterogeneous manufacturing facilities. At first, the application accepts the customer’s order and performs material requirement planning. Then MRP dispatches daily planned order to job shop that carries out real-time scheduling and production. At the same time, MRP sends order to supplier for purchasing raw materials. After completing production task, the job shop returns the relevant information about finished parts. Once the customers add or modify orders, MRP system will update data automatically to respond to the changes of customer requirements rapidly. MRP subsystem uses Enterprise Java Beans (EJB) deployed in a J2EE compliant application server to perform Business-toCustomer transactions and MRP logic, while the job shop subsystem uses Common Object Request Broker Architecture (CORBA) specification as communication platform.
1. Introduction Due to the customized production, shorter product life cycle and frequent process reengineering, today’s global business competition is imposing special requirements to manufacturing enterprises, such as rapid response to changing requirements, reduction in both time and cost of the product realization process. In addition, most of the manufacturing enterprises are often heterogeneous with respect to computer platforms, operating systems, network capabilities, and custom and commercial software. Further, it may be geographically distributed across a wide area. The information architecture itself must be scalable, interoperable and
reconfigurable. Internet technology, electronic data exchange, and industry standards for interoperability will be core to the infrastructure [1]. The application developed in this paper aims to realize an integrated system which has rapid response to changing requirements and capability to integrate heterogeneous manufacturing facilities. The application consists of two subsystems as follows: •
Web-Based Material Requirement Planning (MRP) The paper utilizes several emerging technologies such as Enterprise Java Beans (EJB) as well as Extensible Markup Language (XML) technology to establish a webbased MRP system that considers the process that begins when an order is placed by a customer and ends with the production of the corresponding item. All works are done on server-side. Three kinds of users, i.e. customer, administrator and supplier may access this system through web browser from anywhere and at anytime in the world. •
CORBA-Based Job Shop Simulator. To simulate the real heterogeneous manufacturing environment, the paper use CORBA as communication platform to develop a job shop simulator in which CORBA objects represent corresponding manufacturing devices. After receiving the customer’s order, MRP system performs material requirement planning. Then MRP dispatches daily planned order to job shop that carries out real-time scheduling and production. On the other hand, MRP sends purchased order to supplier for needed raw materials. After completing production task, job shop returns finished parts to MRP. Once the customers add or modify orders, MRP system may update data automatically so as to rapidly respond to change of customer requirement.
The paper describes how to use distributed object technology to develop modularized, distributed, configurable and maintainable enterprise application. First, section 2 presents the architecture of overall system. Then section 3 focuses on MRP subsystem, including MRP logic, three-tier architecture. The section 4 introduced CORBA-based job shop object model. The section 5 describes the communication means between MRP with Job Shop. The section 6 presents implementation and evaluation of the application. At last, the summary and conclusions are presented in section 7.
Figure 2 illustrates the web page of order input. The major components of the MRP are the Master Production Schedules (MPS) and the Bill of Materials (BoM), which will be discussed in this section.
2. Overall System Architecture The application consists of two subsystems: MRP subsystem, and job shop simulator subsystem. The overall system architecture is shown in Figure 1. At first, the application accepts the customer’s order through the B2C web front. In the backend, material requirement planning will be performed. Then MRP dispatches daily production jobs to job shop that carries out real-time scheduling and production. On the other hand, MRP sends purchased order to supplier for needed raw materials. After completing production task, job shop returns finished parts to MRP that may adjust some initial parameters like lot size, lead time to meet requirement of order from customer. The overall system architecture is shown in Figure 1. Database
Supplier Internet
Customer
MRP
Figure 2: Input of Customer Order
3.1 MPS Logic The MPS is a time-phased statement that contained numerous fields for each time unit called a “bucket”. One bucket is one day in this paper. Each time bucket consisted of the following fields – gross requirement, scheduled receipt, on-hand inventory and planned order release. Gross requirement is total actual demand for that item at that time. Scheduled receipt indicates the expected units that will be completed at that time. Planned order release indicates the suggested amount of units to order from the job shop. With the knowledge of time-phased gross requirements, scheduled receipts and other MPS parameters, the rest of the MPS can be filled out. An MPS snapshot from the application is shown in Figure 3.
Job Shop Model
Figure 1: Overall System Architecture
3. MRP System MRP is a computer modeling technique that allows for demand-driven production plans to be made. It determines what to produce, when to produce and how much to produce. We implement a MRP system that considers the process that begins when an order is placed by a customer and ends with the production of the corresponding item.
Figure 3: An MPS Snapshot from the System
Explosion of requirements in MRP programs flows down through component levels following the linkage specified in the BoM structure. The planned order release of a parent item multiplied by the quantity of the child item that goes into the making of one parent item, become the gross requirement of the component required at the next level. Explosion of requirements can be viewed as a recursive procedure, whereby the same process is done for each item, whose parent item’s production schedule has undergone a change. Once the BoM is detected to have zero components, the item is recognized a purchased item and no further explosion took place [2].
Presentation Tier
Entity Beans Session Beans Servlets
Web Browser
Web Server
Application Server
Figure 4: Application 3-Tier Architecture
4. Job Shop Object Model
In this paper, MRP is a web-based and server-side application that is partitioned into three-tier in terms of application logic. Each layer has a different responsibility in the overall deployment, and within each layer there can be one or more components.
4.1 Job Shop Architecture
•
The layer partitioning is as follows: Presentation Layer contains components dealing with user interfaces and user interaction. The presentation layer of a web-based deployment could use HTML pages, Java Server Pages, and/or Java Applets. Business Logic Layer contains components that work together to solve business problems. In this paper, these components are Servlets as well as Enterprise Java Beans (EJB) that include Session Beans and Entity Beans.
Database
Session Beans
3.2 Three-Tier Architecture of MRP System
•
Data Tier
Business Logic Tier
The job shop simulator is developed using the objectoriented paradigm. Petri Nets is used to model the job shop. Its various components such as Place, Transition and Tokens are developed as generic Java objects in the simulator and they serve as the building blocks for the job shop model. In addition, each of them are further categorized into different types and having different functions. A complex job shop consisting of a central storage, several workstations and a material handling system is shown in Figure 5. In this paper, four workstations are used. As such, the shop floor network that is simulated consists of 6 distributed modules including the central storage module and the material handling system module. Workstation 1
•
Data Layer that is used by the business logic layer may persist state permanently. Central to the data layer is one or more databases that house the stored state.
The advantage to partition the application into these logical layers is to isolate each layer from the others. For example, it should be possible to plug in a different view (i.e., change the presentation layer) while minimizing impacts on the business logic or data layers. It should similarly be possible to plug in a different set of business rule component implementations within your business logic layer, or to plug in a different database in your data layer, with relatively minor effects on the other layers [4]. In this paper, the three-tier architecture is shown in Figure 4.
Arrival Process
Central Storage
Material Handling System (Input)
Workstation 2
Material Handling System (Output)
. . . Workstation n
Figure 5: Job Shop Architecture
4.2 CORBA-Based Communication Platform Three main distributed object services are available today: CORBA, Java RMI, and DCOM. Each of these services uses a different Romote Method Invocation (RMI) network protocol, but they all accomplish basically the same thing: location transparency.
DCOM is primarily used in the Microsoft Windows environment and is not well supported by other operating systems. Its tight integration with Microsoft products makes it a good choice for Microsoft-only systems. Java RMI is a Java language abstraction or programming model for any kind of distributed object protocol. Java RMI may be used with almost any distributed object protocol, but in practice Java RMI has traditionally been limited to the Java Remote Method Protocol (JRMP) – known as Java RMI over JRMP – which can only be used between Java applications. CORBA is neither operating-system specific nor language specific and is therefore the most open distributed object service of the three. On the other hand, a CORBA client can be written in any language, including C++, Smalltalk, Ada, and even COBOL, so it’s an ideal choice when integrating systems developed in multiple programming languages [6]. As a platform-independent and language-independent distributed object protocol, CORBA is often thought of as the superior of the three protocols discussed here. In addition, CORBA’s object-oriented property can make application development or integration reusable and extensible. At the same time, CORBA is evolving towards a standard as component bus where software components and applications can be ‘plug & play’ into the object request broker just as what has realized in the hardware bus. This property will cause the revolution in software development, especially in heterogeneous distributed computing environment like the enterprise network. In our job shop model, all devices are modeled as CORBA objects, and these objects can be dynamically added to or deleted from manufacturing system network with CORBA technology. An object not only acts as a client, but also as a server. For example, when workstation request service to Central Storage, it acts as client, but when Central Storage request service to Material Handling System, it acts as server. CORBA Object model is shown in Figure 6.
customer orders. We design a thread that can monitor the change of customer order. Once the customers add or modify orders, this monitoring thread will invoke MRP system to update data automatically. Then MRP system initiates a CORBA client object that communicates with CORBA server object residing in the job shop system to send jobs for processing. When order is completed , the CORBA client residing in the job shop will communicate with CORBA server residing in MRP system to return finished jobs to MRP system. Then the CORBA server residing in MRP system sends relevant data to database or other objects. The communication interface is shown in Figure 7.
Central Storage Object Workstation Object
Workstation Object
Object Request Broker (ORB)
Workstation Object
Workstation Object
Material Handling Object
Figure 6: CORBA Object Model of Job Shop MRP
Job Shop
Monitor Thread
Input of Customer Order Servlet
SendJob CORBA Client
CORBA Server
ReturnFinishedJob CORBA Server
CORBA Client
Database
Figure 7: Communication between MRP System with Job Shop
6. System Implementation and Evaluations 5. Communication Between MRP and Job Shop After accomplishing MRP computing, MRP system needs to send the daily planned order to the job shop. In addition, because customers may add, modify orders with web browser at any time, the computing results of MRP system should be updated to reflect the changes of
Based on above analysis and design, a complete system has been successfully developed at the Laboratory for Concurrent Engineering and Logistics, National University of Singapore. The iPlanet Web Server and Application Server are used as platform of the application. The Visibroker ORB is used as the CORBA ORB for the job shop simulator. The experiment shows that the integrated system can rapidly respond to Customer’ order.
On the other hand, the MRP system can effectively collaborate with Job Shop to meet requirement of production.
7. Summary and Conclusions In this paper, an enterprise application is developed to integrate MRP system with job shop simulator by using distributed object technology. The promising Enterprise Java Beans specification is presented. In addition, several emerging technologies such as EJB, CORBA are introduced. According to the testing results of the application, it shows that the proposed system has good performance in terms of response to customer.
References [1] Whiteside, R.A., Pancerella, C.M., Klevgard, P. “A CORBA-based manufacturing environment”. System Sciences, Proceedings of the Thirtieth Hwaii International Conference, Hwaii, 1997, vol.1, pp. 34-43. [2] George Plossl. Orlicky’s Material Requirement Planning. New York: McGraw-Hill, Inc., 1995. [3] J.P. Morgenthal, Bill la Forge. Enterprise application integration with XML and Java. Upper Saddle River, N.J.: Prentice Hall PTR, 2000. [4] Ed Roman. Mastering Enterprise JavaBeans. New York: John Wiley & Sons, Inc, 1999. [5] Richard Monson-Haefel. Enterprise Java Beans. Sebastopol, CA: O’Reilly & Associates, Inc., 2000. [6] Jon Siegel. Corba 3 fundamentals and programming. New York: John Wiley & Sons, Inc, 2000. [7] Daniel Sipper, Robert Bulfin. Production: planning, control, and integration. New York: The McGraw-Hill Companies, Inc., 1997. [8] Meng Chu Zhou, Kurapati Venkatesh. Modeling, simulation, and control of flexible manufacturing systems: a Petri Net approach. Singapore: World Scientific, 1997. [9] Andreas Drexl, Alf Kimms. Beyond Manufacturing Resource Planning (MRP II): advanced models and methods for production planning. New York: Springer, 1998. [10] Darryl V. Landvater and Christopher D. Gray. MRP II standard system: a handbook for manufacturing software survival. New York: Wiley, 1989. [11] Erin Callaway. Enterprise resource planning: integrating applications and business processes across the enterprise. Charleston, SC: Computer Technology Research, 1999. [12] Andreas Vogel, Keith Duddy. Java programming with CORBA. New York: John Wiley & Sons, Inc, 1998. [13] Fan-Tien Cheng, Meng-Tsang Lin, Rong-Shean Lee. “Developing a Web-enabled Equipment Driver for Semiconductor Equipment Communications”. Proceedings of the 2000 IEEE International Conference on Robotics & Automation San Francisco,CA, April 2000, vol.3, pp. 2203-2210. [14] Hori, M.; Kawamura, T.; Okano, A. “OpenMES: scalable manufacturing execution framework based on distributed
object computing”. Systems, Man, and Cybernetics, 1999. IEEE SMC '99 Conference Proceedings, vol.6, pp. 398403. [15] Zhonghua Yang; Guangbin Huang; Guan, R.L.Y.; Gay, R. “CORBA as object-oriented infrastructure for factory communication and control”. Communications, 1999. APCC/OECC '99. Fifth Asia-Pacific Conference and Fourth Optoelectronics and Communications Conference, 1999, vol.2, pp. 1083-1086. [16] R. Kolluru, S. Smith, P. Meredith, T. Chambers, G. Seetharaman, T. D’Souza. “A Framework for the Development of Agile Manufacturing Enterprise”. Processding of the 2000 IEEE International Conference on Robotics & Automation San Francisco, CA. April 2000, vol.2, pp.1132-1137.
