1. Keys to Fast & Flexible Factory Automation
BY D. CARO & C. RESNICK NOVEMBER 28, 2001 ARC INSIGHTS# 2001-052MD
KEYWORDS:
Factory Automation, PLCs, OPC, XML, Foundation Fieldbus, Ethernet/IP, Profibus
SUMMARY:
In recent years, the demands for increased productivity, more efficient processes, and
greater access to plant floor information have created a need for faster application devel-
opment and flexibility. These demands, however, often result in frustration with
existing control systems technology. In many applications such
In many industries such as material as material handling and packaging, processing speeds and
handling and packaging, processing throughput must be raised while simultaneously adding the
speeds and throughput must be raised
flexibility required for quick, continuous product changeovers
while simultaneously adding the
required for collaborative manufacturing. In applications that
flexibility required for quick, continuous
product changeovers required for require multiple control system elements, structured costs must
collaborative manufacturing. be lowered, system performance must be increased, and infor-
mation exchange must become easier.
ANALYSIS:
Delivering faster application development and flexibility to the factory floor involves a
multitude of factors. This Insight focuses on three areas, faster application development
for PLCs, integration of diverse Ethernet networks, and exchange of enterprise data.
A Roadmap for More Rapid & Efficient Application Development
The biggest problem in building a PLC application is the totally unstructured program-
ming environment. Programs become “write-only” and are difficult to modify.
Spaghetti-code is almost required by design. A well-integrated development environ-
ment for PLC programs is badly needed.
Programming Language Abbreviation Description
Relay Ladder Logic RLL Graphical interconnection diagrams of pushbut-
tons and relay coils and contacts
Function Block Diagrams FBD Graphical interconnection diagrams of
calculation objects
Sequential Function Charts SFC Graphical state machine diagramming
Structured Text ST A programming language similar to PASCAL
Instruction List IL Sequentially executed commands
ENTERPRISE AND AUTOMATION STRATEGIES FOR INDUSTRY EXECUTIVES

2. ARC Insights, Page 2
Build the state - machine logic The answer is almost at hand with IEC 61131-3 Program-
ming Languages for Programmable Logic Controllers. This
SFC
SFC
standard specifies four programming languages and a dia-
gramming language shown in the table.
RLL
RLL FBD
FBD ST
ST ARC takes this one more step, saying that SFC is the lan-
Logical & Workflow Workflow guage of the State Machine and all physical processes and
timed calculations,
calculations, calculations, machines must have all of their operating states defined by
interlocks function statements
blocks an SFC so that the State Transitions can be programmed.
Then, each state’s workflow and logic can be programmed in
Processes Are Defined with State-Machines,
and Coded in the Best Language for the the most appropriate language. RLL is ideal for interlocks
Application and pure timed sequences. FBD is ideal for complex data
flows, typical of regulatory loop control and motion control.
ST and IL are offered for those who prefer these methods of programming in statements
or commands respectively. So, begin first with the SFC and programs will become easier
to write, correct the first time, and much easier to modify in the future.
Integrating Diverse Ethernet Networks via an OPC DX Junction Box
One of the major barriers faced on the factory floor is the integration of various Ethernet
networks such as Foundation Fieldbus HSE, Ethernet/IP, and Profibus. The most prom-
ising method to overcome this barrier is OPC DX (Data eXchange.) OPC DX will allow
access to data for any of these networks by addressing its tag name independent of the
underlying network protocol. Naturally, each object will have its own data structure
based on the object type defined with an XML Schema. DX will support client/server,
producer/consumer, and publish/subscribe, which are the basic data transfer methods
used by these networks. The application will use the DX mechanism to “connect” with
the data source using a local OPC DX Client. Each OPC DX Server then translates the
request into its own network protocol, and ar-
ranges for delivery of the data. When the data
arrives at the DX Server for that network, it is
OPC DX
Client converted to DX protocol and supplied to the
DX Client. The one caution is that the OPC DX
OPC Foundation OPC EtherNet/IP OPC PROFIbus DX specification has yet to be released, so this is
Fieldbus DX Server DX Server Server
based on the promise of DX. However, once it
is released, a true “junction box” will be cre-
ated for tying together diverse Ethernet
networks on the factory floor.
© 2001 • ARC Advisory Group • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • ARCweb.com
USA • UK • Germany • Japan • India

3. ARC Insights, Page 3
Performing Enterprise Data Integration
Everyone wants to know how data can be bridged from the automation system to the
enterprise domain. Clearly, the Microsoft method utilizes their .NET framework based
on use of XML and SOAP operating in their BizTalk Framework. OPC DX will have
some options to be much simpler for just real-time use, but it will conform fully to this
Microsoft-centric view of the enterprise. There are several methods to get data to the
enterprise. One method is to let the enterprise software poll for the data when needed.
Another method is to push the data on a regular clock cycle, otherwise known as the
BAPI method used for SAP. Finally, another method is to push the data whenever it is
ready, otherwise known as the publish/subscribe method.
ARC believes that information derived from the manufacturing world will present itself
to the enterprise in the form of OPC DX, which will offer all three methods of data ex-
change conforming to BizTalk. ARC strongly prefers the Publish/Subscribe protocols
being used by Foundation Fieldbus and iDA, which are very close to the Pro-
ducer/Consumer protocol of Ethernet/IP. OPC DX will most likely mask these
differences since DX works both ways. When the enterprise planning software sets a
new production rate, the “production speed” target can be published by the planning
system with OPC DX, since the control system subscribes to the production rate target.
Likewise, when a manufactured unit rolls off the assembly line, all of its data can then be
published to the production tracking system and a transactional database both of which
subscribe to such data.
RECOMMENDATIONS:
• PLC application programming should be performed in a structured environment by
first using Sequential Function Charts so programs will become easier to write, cor-
rect the first time, and simpler to modify in the future.
• An OPC DX client should be looked upon as the future junction box that will elimi-
nate one of the major barriers faced on the factory floor by integrating various
Ethernet networks such as Foundation Fieldbus HSE, Ethernet/IP, and Profibus.
• Data should be bridged from the automation system to the enterprise domain by us-
ing the Publish/Subscribe options of OPC DX, which will make it simpler for real-
time use while conforming to the Microsoft .NET framework.
For further information, contact your account manager or the authors at rcaro@arcweb.com or
cresnick@arcweb.com. Recommended circulation: All MAS-D clients.
© 2001 • ARC Advisory Group • 3 Allied Drive • Dedham, MA 02026 USA • 781-471-1000 • ARCweb.com
USA • UK • Germany • Japan • India