Communication in Low-Cost CIM Systems - A New Approach

Copyright © IFAC 12th Triennial World Congress, Sydney, Australia, 1993

COMMUNICATION IN LOW -COST CIM SYSTEMS - A NEW APPROACH N. Glrsule and R. Probst InsliluJe of lIandling Devices and Robolics, UniversilY of Technology, Vienna, Austria

Abstract: Usually elM-systems require powerful computers for sophisticated software which are too expensive for small or medium sized enterprises. They do not really need all the capabilities of these solutions. What they need are flexible, small programs, which can be adapted and supplementcd easily without external heIp. This paper presents an unusual approach to organise communication in small CIM systems: MS-Windows 3.x Dynamic Data Exchange (ODE) combined with NetE310S handle all data exchange and sessions. 130th systems use the client/server architecture and work together properly. A small MS-Windows application handles full DDEcommunication over the network. Keywords: CIM, Computer communication, Distributed databases. Networks

Resulting from the history of the CIM-modules as isolated islands with few external communication a common problem in integration of autonomous CIM-components arises. Different standards of LAN access and incompatible data formats are used. Various vendors offered CIM-modules based on their internal standards. On a higher level applications of the same kind were connected. Basical standards for each kind of application were defined with no respect to other modules within design, planing, and manufacturing. When CIM was introduced in a large frame these quasistandards were used anywhere. Both users and vendors had to invest very much money to override these imcompatibilities between the single islands. At this point it was necessary to create and publish international standards for CIM-integration.

I. INTRODUCTION ClM as Computer Integrated Manufacturing needs computer communication. Central databases are accessed from various applications. The main groups of CIM-components generate and consume a lot of data which must be interchanged between different applications running on different computers: Workplans, manufacturing orders and tool or material reservations from PPS-systems; large drawings and piece-lists from CAD-stations; drawings and technological data from and to CAP; workplans, NC-programs, and production data as manufacturing tools to CAM; various data from CAD, CAP, and CAM from and to CAQ; the current state of production from OCA; drawings and statistical information from CAD, CAM, and OCA to CAO. All these data must be transported and controlled by communication services.

1.2. Communication Standards The ISO/OSI Reference Model. The ISO/OSl reference model, introduced in 1983, defines communication standards for between open systems as well as inside closed systems. Closed systems use vendor specific communications protocols similar to the ISO/OSI model. Between these vendor specific protocols exist incompatibilities. Open systems base upon the ISO/OSI model. Interconnection between two open systems is possible without much adaption. 7 layers with vertical and horizontal (peer-to-peer) protocols are used .

1.1. Communication by LANs Today normally Local Area Networks (LAN) are used to connect the different areas of the factories. Various vendors sell various LAN products which use more or less different techniques and standards. Applications use LAN services by specially adapted drivers.

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As shown in Figure 1 NetBIOS resides between layer 5 (session layer) and layer 6 (presentation layer) of the ISOIOSI reference model. The facilities Name Support and Session Support make NetBIOS a very efficient and flexible tool for creation of distributed systems.

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Fig. 1. NetBlOS in the ISO/OSI layers

2.2. MS-Windows 3.x

The Manufacturing Automation Protocol (MAP). In 1980 General Motors started a project to standardize communication between machinery coming from a wide variety of vendors. Many other enterprises were involved in this project. The ISOIOSI reference model was used as a base for communication standards. In 1988 MAP 3.0 was introduced.

Microsoft presented version 3.0 of MS-Windows in 1990. The conception of this version is based on Intels 80386 processor. MS-Windows as an operating system shell offers a graphic user interface of high quality and multitasking. Between the single tasks the communication standard DDE is defined. DDE strictly uses the client/server architecture and includes full protocol and error detection. It is based on the internal message system of MS-Windows. Application, topic, and item are referenced by names.

Standards for small and medium sized enterprises. MAP as a common standard for communication in industrial environments is a suitable example to show that any CIM application should conform to the ISOIOSI standards. The Manufacturing Automation Protocol comes from large scaled factories. For small and medium sized enterprises some similar approach should be used. CIM systems in these factories should use as much as possible elements of MAP. But often some financial constraints prevent strict use of all MAP definitions.

A DDE communication for a topic with an application is initiated by a WM_DDE_INITIATE message. After the initialization of a communication WM_DDE_REQUEST can be used to request the server to provide the value of a data item. WM_DDE_ADVISE requests a server application to supply an update for a data item whenever it changes. This message establishes a session between two applications. The session is terminated by a WM_DDE_UNADVISE message. Availability of data is reported by a WM_DDE_DATA message. WM_DDE_DATA also sends a data item from the client to the server. The WM_DDE_EXECUTE message forces a server to execute a command posted as string. Unsolicited data are sent to the server by a WM_DDE]OKE message. Generally all DDE messages are acknowledged by WM_DDE_ACK. This message uses various parameters to report receipt and processing of other DDE-messages.

Otherwise not all the possibilities of MAP and the subsets of definitions are really used in small and medium sized enterprises. Normally cheaper computers are used, very often working under MSDOS with some LAN connection to a UNIX system. The authors developed a communication system for this special environment which uses many elements of MAP.

2. COMMUNICATION IN MS-WINDOWS 3.x AND NETBIOS

3. CONNECTION BETWEEN DDE AND NETBIOS

The new communication system is based on PCs under MS-DOS which are interconnected by a standard LAN. On top of LAN drivers NetBIOS must be installed. NetBIOS is used by the DDE (Dynamic Data Exchange) communication standard from MS-Windows 3.x.

DDE and NetBIOS both use a client/server architecture and sessions for communication. The MS-Windows application NETCOM designed to convert DDE requests and sessions into NetBIOS 876

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format enables all other MS-Windows applications to fully use NetBIOS communication facilities. This application handles adding and deleting names and group names, establishes NetBIOS sessions and advises the client about changes or results from the remote system (see Fig. 2).

only by sending filename and location on the common fileserver. There is no need to send the whole file.

NETCOM uses the NetBIOS commands Add Name, Add Group Name, and Delete Name for Name Support. The commands Call, Listen, Send, Chain Send, Receive, and Hang Up handle Session Support. For general tasks Reset, Cancel, and Adapter Status are used.

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The Group Control System requests location and filename of an NC program needed by a machine tool from the NC-Data-Server. The request contains a piece number and machine type. Only valid versions of NC programs can be used.

Based on NETCOM MS-Windows applications are installed as servers on the network. Each server can solve a special task like updating a small MSEXCEL database or looking up in reference tables. Clients call data via DDE by sending topic and item to NETCOM. Results are presented on the same way. Depending on traffic at one PC two or more servers can be installed.

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The NC-Data-Server receives the request and looks up for the requested data in the central database (e.g. MS-EXCEL sheet). The server sends back location and filename to the client (GCS). The client now opens the specified NC data file and copies the program into the NC machine tool.

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Meanwhile the NC programmer has finished to change another NC program at his station. He stores the new file on the fileserver and requests to update location and filename of the new version of this NC program in the same

Figure 3 shows a small example of communication in this environment.

Using group names large data traffic at one station can be avoided by splitting up requests to two or more stations of one group. Request handling is done by internal communication between the members of one group. Large files are exchanged 877

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central database as above. This request is sent to the NC-Data-Updater.

sometimes do not have the possibility to realise a complete MAP system.

The NC-Data-Updater has rights to write to the database file . After performing the update an acknowledgement is sent back to the client which receives the acknowledge and terminates the session.

This paper presents a suitable, cheap and easy to be realised way to fully integrate all single tasks in a manufacturing environment. The approach is to use MS-Windows ' DDE communication standard combined with the common NetBIOS definition. Via NetBIOS a remote-DOE communication is implemented and any MS-Windows application can exchange data with any other application.

This simple example shows the mechanism behind this communication method. D

Each single task is implemented in a special MS-Windows application. They are referenced by unique or group names via the DOE to NetBIOS interface NETCOM.

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Infrastructure of the Local Area Network is fully used for data storage, data exchange, and transmission.

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Large databases can be splitted up into small and easy to be updated files or spread sheets. Access can be done by world-wide available programs like MS-EXCEL.

5. REFERENCES Schwaderer, W.D. (1988). C Programmer's Guide to NetBlOS. Howard W. Sams & Company, Indianapolis. Tangney, B., and D. O 'Mahony (1988). Local Area Networks and Their Applications. Prentice Hall, Herdfordshire. Petzold, Ch. (\990). Programming Windows. Microsoft Press, Redmond, Washington. Scholz-Reiter, B. (1991). CIM-Schnittstellen. Oldenbourg, Mtinchen. Norton , P. and P. Yao (1992). Windows 3. Markt & Technik, Haar bei Mtinchen. Kopacek, P., N. Girsule, J. H6lz1 (1992). A low cost modular CIM concept for small companies. Proceedings of the IFII C-Symposium on Information Control Problems in Manufacturing Technoloy - INCOM '92, Toronto.

4. CONCLUSION Various standards were defined for communication in factory automation. For LANs the ISO/OSI reference model and the MAP 3.0 definitions are the best way to guarantee compatibility and stability. Small and medium sized enterprises 878