Communication in Low-Cost CIM Systems A New Approach

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Communication in Low-Cost CIM Systems A New Approach

N. Girsule and R. Probst Institute of Handling Devices and Robotics University of Technology, Vienna, Austria

Abstract: Computer Integrated Manufacturing is based on computer communication. Data exchange is done by connecting workstations, manufacturing cells, machine tools, robots, etc. by networks. Many protocols and standards are defined to ensure safety and reliability of communication. Usually one problem arises in CIM: software costs ex-plode, because ClM solutions almost are specialised programs for one distinct emironment. A second problem in automation are the hardware requirements for CIM-software. Software developers assume, that appropriate hardware is present. Many software packages are available only for workstations and mainframes, which are much more ex-pensi\'e than simple PCs. In most cases small or medium sized enterprises do not have the financial power to buy large computers and sophisticated software packages. They do not really need all the options and processing speed of these solutions. What they need are flexible, small programs, which can be adapted and supplemented easily and fast without external help. This paper presents an unusual approach to organise communication in small CIM systems: Microsoft Windows 3.x Dynamic Data Exchange (DOE) combined \\;th NetBIOS handle all data exchange and sessions. Both systems use the client/server architecture and work together properly. MS-Windows is in use world-\\;de. NetBIOS is available for most of the common networks today. Using a small MS-Windows application for DOE-routing full DDE-communication is possible. For ex1emal databases or ex1emal LANs with different protocols some gateway applications can be designed, which are used as database or communication servers. Users can easily program new applications by hand of the various, really simple programming tools for MS-Windows. Keywords: CIM, Computer communication, Distributed databases, Networks

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CAM consumes work plans, NC-programs, and production data as manufacturing tools.

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CAQ designs and uses various data from CAD, CAP, and CAM for quality management.

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OCA detennines the current state of production and reports it to the controlling system.

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CAO uses drawings and statistical information from CAD, CAM, and OCA to generate reports, public relations material, employee remuneration base data, etc.

INTRODUCTION

CIM as Computer Integrated Manufacturing needs computer communication. Central databases are accessed from various applications. The main groups of CIM-c:omponents generate and consume a lot of data which must be interchanged between different applications running on different computers: •

PPS-systems design workplans, manufacturing orders and tool or material reservations.

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CAD-stations create large drawings and piecelists which are used in other modules.

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CAP uses dra\\;ngs and technological data to develop work plans, manufacturing and assembly suppon tools.

All these data must be transponed and controlled by communication services. Today normally Local Area Networks (LAN) are used to connect the different areas of the factories.

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Laver

Name

Function

7

Application Layer

Common application service elements like connect, abon, and transfer data and specific application senice elements for particular application services

6

Presentation Layer

Transformation of local data representations into those agreed upon for interchange between nodes

S

Session Layer

Connection negotiation, establishment, and release as well as duplex data transfer

4

Transpon Layer

Guaranteed delivery, message sequencing, and full error detection

3

Network Layer

Routing of messages from source to destination through intermediate systems

2

Data Link Layer

Medi.a access: protocol to control access to the shared medium (CSMAlCD or Token) Logical link control: connectionless, connection oriented, or immediate ackno\\ledge service

I

Physical Layer

Electrical and mechanical characteristics of the network Table 1: The ISO/OSI reference model

Various vendors sell various LAN products which use more or less different techniques and standards. Applications use LAN services by specially adapted drivers. The common problem in integration of autonomous CIM-components are different standards of LAN access and incompatible data formats. This situation results from the history of the CIM-modules. Most of them initially were designed as isolated islands with few external communication. Various vendors offered CIM-modules based on their internal standards. The next step was connect applications of the same kind. Basical standards for each kind of application were defined. But no respect to other modules within design, planing, and manufacturing was given. When CIM was introduced in a large frame these quasi-standards 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 SlaDdards for CIMintegration.

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COMMUNICATION STANDARDS

The ISOIOSI Reference Model

The International Standards Organisation (ISO) introduced the Open Systems Interconnection (OSI) in 1983. The ISO/OS1 reference model 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. The ISO/OSI model divides the complex communication procedure in 7 layers. Each layer has well defined tasks. While communication between to network consumers each layer is used by the layer above in hierarchy. Between the different layers vertical protocols are defined. Inside the layers peer-to-peer protocols handle the communication between the two systems (horizontal protocols). The 7 layers can be classified in two general groups:

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layer 1 to 4 realise the transpon of data,

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layer S to 7 coordinate and process application data.

The tasks of the layers are shown in table 1. The Manufacturing Automation Protocol (MAP)

In 1980 General Motors staned a project to standardize communication between machinery coming from a wide variety of vendors. Many other enterprises were involved in this project. The ISO/OSI reference model was used as a base for communication standards. In 1988 MAP 3.0 was introduced. Table 2 shows the specification of the 1S0/0S1 layers in MAP 3.0.

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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 an MAP definitions. Otherwise not all the possibilities of MAP and the subsets of definitions are reany used in sman and medium sized enterprises. Normany 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 en\;ronment which uses many elements of MAP.

Laver

COMMUNICATION IN MS-WINDOWS 3.X 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 (Dynami~ Data Exchange) communication standard from MS-Windows 3.x. NetBIOS

NetBIOS was introduced by IBM in 1984 with the IBM PC Network adapter card. This first NetBIOS implementation based on the CSMAlCD access method with IEEE 802.3 Ethernet. Since this time many variations of NetBIOS were developed worldwide. This communication interface is available for most of the commercially available networks using protocols like IPXlSPX, TCPIIP or MAP. As sho\\ll in figure 1 NetBIOS resides between layer 5 (session layer) and layer 6 (presentation layer) of the ISOIOSI reference model. Four categories of commands are supponed (table 3). Name suppon and session suppon make NetBIOS a Function

Name

Application Program Interfaces (AP1) 7

Application Layer

IS0-MMS DP 9506 ISO-rTAM DIS 8571 ISO ASCE DIS 8649/1-2

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ISO ASCE DIS 8650/1-2 MAP Directory Services MAP Network Manaiement 6

Presentation Laver

ISO Presentation DlS 8823

S

Session Layer

ISO-Session Kernel IS 8327 dUDlex

4

Transport La,'er

ISO-Transport Class 4 IS 8073

3

Network Layer

ISO-Connectionless Internet DIS 8473

2

Data Link Layer

ISO Logical Link Control DIS 8802/2 Type 1 (for Broadband) Type 3 (for Carrierband) ISO Token Bus DIS 8802/4

1

Physical Layer

ISO Token Passing Bus DIS 8802/4 Broadband (10 Mbitlsec) or Carrierband (5 Mbitlsec) Table 2: The IS010S1 layers in MAP 3.0

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MS-Windows 3.x

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DIIIUnl

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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. The according messages and their meanings are shown in table 4.

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Application, topic, and item are referenced by names.

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Figure 1: NetBIOS in the ISO/OSI layers

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CONNECTION BETWEEN ODE AND NETBIOS

very efficient and flexIble tool for creation of distributed systems.

Name Support

Add Name

DDE and NetBIOS both use a client/server architecture and sessions for communication. The

WM_DDE_ACK

General message for acknowledgement. This message uses various parameters to report receipt and processing of other DDE-messages.

WM_DDE_ADVISE

Request to a server application to supply an update for a data item whenever it changes.

WM_DDE_DATA

Send a data item from the client to the server or report availabilitv of data.

WM_DDE_EXECtJTE

This message forces a Server to execute a command posted as string.

Add Group Name Delete Name Data2ram SuPPOrt

Receive Datagram Receive Broadcast Datagram Send Datagram Send Broadcast Datagram

Session Support

Call Listen Send Send No-Ack Chain Send Chain Send No-Ack

. WM_DDE_INlTIATE

initiates a DDE conversation for a topic with an application.

WM_DDE-'OKE

Request to the server to acceot unsolicited data.

WM_DDE_REQUEST

Request to server to provide the value of a data item.

WM_DDE_UNADVlSE

Termination of a WM_DDE_ADVISE session.

Receive Receive-Am' Hang Up ·Session Status General Commands Reset Cancel Adapter Status Unlink Table 3: NetBIOS commands

Table 4: MS-Windows messages related to DOE

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NC-Data

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r:J:l1

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..11 l§

1..1.

01

NC-programs locations

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mm.

Group Control System

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~ NC-Data-9t'0up

NC-Data-Oroup

NC~Data-Updater

Group Control System

NC -Programmer

Figure 2: Example for DDE and NetBIOS communication MS-Windows application NetBWin designed to convert ODE requests and sessions into NetBIOS fonnat 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.

Only valid versions of NC programs can be used. ®

In this system two servers are installed for this task. They only have rights to read the central -database file. Both servers receive the request and one of them looks up for the requested data in the central database (e.g. MS-EXCEL sheet).

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Location and filename are sent back 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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At the same time the NC programmer changes another NC program at his station. After c:ompletition 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 central database as above. This request is sent to the server with the unique name NC-Data-Updater.

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The NC-Data-Updater has rights to write to the database file. After performing the update an acknowledgement is sent back to the client.

Figure 2 shows a small example of communication in this environment:

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The client receives the acknowledge and tenninates the session.

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This simple example shows the mechanism behind this communication method.

Based on NetBWin MS-Windows applications are installed as servers on the net~\'ork. Each server can solve a special task like updating a small MSEXCEL database or looking up in reference tables. Clients call data via DOE by sending topic and item to NetBWin. Results are presented on the same way. Depending on traffic at one PC two or more servers can be installed. 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 c:ommunication between the members of one group. Large files are exchanged only by sending filename and location on the c:ommon fileserver. There is no need to send the whole file.

A NC machine tool needs a NC program. The Group Control System requests location and filename of the NC program from the group NC-Data-Group. The request is done by sending a piece number and machine type.

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Each single task is implemented in a special MS-Windows application. They are referenced

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by unique or group names "ia the DOE to NetBIOS interface NetBWin.

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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 spJined up into small and easy to be updated files or spreadsheets. Access can be done by world-\\ide available programs like MS-EXCEL. 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 sometimes do not have the possibility to realise a complete MAP system. 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' DOE communication standard combined \\ith the common NetBIOS definition.

Via NetBIOS a remote-DOE communication is implemented and any MS-Windows application can exchange data with any other application. REFERENCES

Schwaderer. W,D. (1988). C Programmer 's Guide 10 NetBIOS. Howard W. Sams & Company, Indianapolis. Tangne)', B., and D. O'Mahony (1988). Local Area . Networks and Their Applications. Prentice Hall, Herdfordshire. Petzold, Ch. (1990). Programming Windows. Microsoft Press, Redmond, Washington. Scholz-Reiter, B. (1991). CIM-Schnillstellen . Oldenbourg, Munchen. Nonon, P. and P. Yao (1992). Windows 3. Markt & Technik, Haar bei Miinchen. Kopacek, P., N. Girsule, J. HOlzl (1992). A low cost modular CIM concept for small companies. Proceedings of the IFAC-Symposium on Information Control Problems in Manufacturing Technoloy - INCOM '92,

Toronto.