OPC Integrates the Factory Floor

Manufacturing has been given the challenge. Enable smaller lot sizes, allow flexible options in products going down the same manufacturing line in random order, allow customers to make changes until just before actual production, communicate seamlessly with all suppliers and customers. Do all this and hold, or even decrease, costs, and just maybe the company will survive for a little whil...

01/01/2001


KEY WORDS

 

  • Human-machine interface

  • Software and information integration

  • OPC

  • PC-based control

Manufacturing has been given the challenge. Enable smaller lot sizes, allow flexible options in products going down the same manufacturing line in random order, allow customers to make changes until just before actual production, communicate seamlessly with all suppliers and customers. Do all this and hold, or even decrease, costs, and just maybe the company will survive for a little while longer.

DVT (Norcross, Ga.) president Bob Steinke states, 'The ultimate Smart Factory would be a living, breathing, coordinated enterprise where maximum output is available on demand, communications are precise and instantaneous; where all systems are focused on the desired result, and no effort is wasted on extraneous activities. The Smart Factory is a holistic approach to enterprise management.'

The fact is every manufacturing business leader wants to emulate the success of Dell. This personal computer manufacturer blends marketing strategy with manufacturing and web technologies to create great customer ordering and service experiences.

What can control engineers to do to achieve this? The first response was to adopt open standards. One reason is that openness only exists if various software and hardware components are interoperable. Further, open standards foster communication. Users, OEMs, and system integrators all win in this open world by gaining the ability to use best-in-class components in a system with ever-decreasing hassle in putting it together. Interestingly, suppliers also win by opening up their products because new opportunities are created.

Hardware standards have evolved into either PC-based components or standard communication ports in 'proprietary' hardware. Networks are evolving into a few standards for which most, if not almost all, manufacturers provide ports.



OPC is a software communications technology enabling many different devices to communicate with each other and with the enterprise.

Software interoperability

Software interoperability has evolved into the tedious task of writing drivers. Drivers provide the interface between the application and devices and/or other software.

Dennis Hayes, senior software engineer at Raytek Automation Products Division (Santa Cruz, Calif.), puts it this way: 'For system integrators and control engineers, the old multiple proprietary driver format required trying to find ways to transfer data between, or send control information to, an ever-changing cacophony of devices. This could include loading a driver, trying to find a compatible device, writing their own drivers, reading/writing shared files, or, in the worst case, just not using the device. The amount of effort needed to create and maintain all these proprietary drivers cannot be overestimated.'

Enter OPC. The acronym stands for OLE for Process Control, with OLE (the acronym within the acronym) being Microsoft's Object Linking and Embedding. As Don Holley, National Instruments' (Austin, Tex.) industrial marketing manager and marketing director for OPC Foundation, explains, OPC is the glue that binds industrial applications together into a cohesive whole.

First, a little history. When Microsoft came out with Windows and its ability to open multiple applications on one desktop, users and developers wanted a method for these applications to share data. Enter Dynamic Data Exchange (DDE). This early technology enabled data communication. It is still used today, but mostly in legacy applications. This technology was one foundation of Wonderware's (Irvine, Calif.) then-risky strategy of using PCs for SCADA/HMI applications in place of more expensive Unix workstations. DDE works, but has drawbacks of slow speed and still requires drivers. That strategy worked very well for Wonderware. Carl Hoffman, product marketing manager, points out its latest products incorporate OPC, XML, and VML (Vector Markup Language for representing graphics).

Representatives of several companies met to try to improve on DDE. They figured that if there were a vendor-neutral standard that all agreed to and used, then users and suppliers alike would benefit. Thus was born the OPC Foundation, one of the most successful initiatives in the industry.



OPC and XML provide the 'glue' to hold different manufacturing applications together to accomplish the e-manufacturing goal.

OPC Foundation born

Along with this developing Microsoft Windows standard came the C++ programming language. This language supports 'objects'-reusable pieces of code consisting of private data structures that may include functions and interfaces, so the object may be called by other functions.

Object Linking and Embedding was a Windows technology that, for example, allowed a user to encapsulate part of an Excel spreadsheet as an object and link it to a Word document. Whenever data in the spreadsheet changed it was reflected in the Word document. The technology grew and Microsoft, as it often does, renamed it 'ActiveX.' Today, ActiveX objects can be found almost everywhere.

Another technology, based in C++, is Component Object Model (COM). This is a standard method of defining interfaces as separate from programming classes that implement them. Distributed COM (DCOM) allows calling the object over a network. COM and DCOM are basic technologies for OPC.

What OPC Foundation members did was specify a common interface for control objects and devices. This enabled anyone with an OPC client (the computer requesting information) to request and accept data from an OPC server no matter whose client or server it was. Not only did this eliminate the driver problem, but it also speeded up data exchange.

GE Fanuc's (Charlottesville, Va.) Mark Preiss, product marketing manager, explains, 'The communication interface of an OPC Server is made available to other programs by use of COM and DCOM. This makes its existence known to other programs, called Clients, that may want to connect. Within the OPC Client 'driver' one can browse the network, much like Window's Network Neighborhood, to find what OPC Servers are currently running and enable connections.'

Jim Thompson, eMation (Mansfield, Mass.) product marketing manager, says, 'One of OPC's milestones was the decision early on to limit the scope of the standard to strictly reading and writing real-time data so that they could release something quickly that would still be useful.'

Technology evolves

These new technologies are sometimes promoted to users and integrators as the greatest thing since sliced bread-maybe the last technology you'll ever need. It is better to understand them as a step in the evolution of ever improving technologies.

Karsten Newbury, Siemens Energy & Automation's (Alpharetta, Ga.) business manager, Manufacturing Execution Systems, advises, 'Open systems are increasingly beginning to provide benefits in real-world applications. It is important to consider the technologies as simply enabling technologies. There is still a need for knowledge of the technology and each implementation within a manufacturer's product. Standards-based open systems place more of the burden for integration on the user.'

How can users be sure a supplier complies with OPC standards? Al Chisolm, Intellution's (Foxborough, Mass.) co-founder and technical director of OPC Foundation, notes, 'OPC for COM was extremely successful because it is vendor-neutral and lots of people bought in to it. OPC Foundation has compliance testing to assure new servers will work when users implement them. We have 'interoperability sessions' where many vendors come, set up their products, and test them.

'One issue we have seen is with DCOM's Remote Procedure Calls. These just don't work as well as the calls within a machine and they are a little harder to set up. That's why we're looking into XML. It isn't a solution looking for a problem, but something that customers are very interested in. An XML protocol is more straightforward than COM and can be quite flexible. The committee is trying to wrap existing COM servers in XML, but we're not tied to it, so that it can be eventually used in operating system-agnostic platforms.'

XML expands integration

XML (eXtensible Markup Language) is a world-wide open standard in evolution sponsored by the W3C organization (see Control Engineering July 2000, p. 12, 'Technology Update'). Like it's cousin, HTML, it is a language based on ASCII, so it's operating-system neutral. Where HTML describes how to layout a page, XML tags data on a page. If there is agreement on what a tag means, for instance &TEMPERATURE>, then a client can request that tag and the data sent between the tags, &TEMPERATURE>90&/TEMPERATURE> , can be interpreted and used in a function or saved in a database.

Intrinsyc's (Vancouver, British Columbia, Canada) Graham Rowbotham, senior software developer and member of the OPC Foundation Working Group on XML, explains, 'The OPC XML specification lowers the barrier for achieving interoperability in situations where high performance is not an overriding requirement. Deployment is not constrained to platforms that support COM/DCOM. Under the specification, all client-server interactions are via the exchange of XML documents. A client requests to read one or more data items, and the corresponding server replies or callbacks. The specification does not mandate the underlying transport protocol. The initial version of the specification when re-leased will include sample code providing an example implementation using SOAP (simple object access protocol). SOAP is currently being investigated for adoption by W3C, which will transport it over HTTP.'

Mike Rothwell, Advantech Automation's (Cincinnati, O.) division manager, defines SOAP: 'It is an XML-based protocol consisting of an envelope that describes what is in a message and how to process it; a set of encoding rules for expressing instances of application-defined data types; and a convention for representing remote calls and responses. For example, imagine a component that lives somewhere on the Internet that implements a notification and generates a problem report interface. This method would be invoked when an alarm acknowledgement is received.'

Using standard, web-based technologies will further enhance the amount of functions available. In fact, engineers will be freed even more to think about their processes, rather than the technologies needed to implement them. For instance, existing web technologies can enable exposure of XML data to a styled web page on a browser.

XSL displays data

John Baier, director of software fusion at Rockwell Software (Mayfield Heights, O.), says, 'XSL (eXtensible Style Sheets) will apply visualization. XML combined with XSL provides supervisory human-machine interface where timing is not as critical. WML (Wireless Markup Language) exposes XML data over wireless networks. For instance, alarm data can be sent to a cell phone. These technologies enable just the amount of information each user needs in the form needed.'

Tom Burke, Rockwell Software's technical evangelist and president of OPC Foundation, adds, 'At the same time we're looking at XML, we are also wrestling with how to move complex data from intelligent de-vices with data structures or templates. Meanwhile, XML looks good for moving things like alarms and batch information. With a defined XML schema, a server can say what a batch looks like when communicating to the client. XML is far more than putting data on a web page.'

Karl Rapp, Machine Tool Industry branch manager at Rexroth Indramat (Hoffman Estates, Ill.), believes, 'XML is preferred in the future since it allows dynamic data access in screens and therefore affords easier integration. There will be some standard for scripts in production applications, so that a plug-and-play interface will be possible in place of OPC's tag lists.'

What kinds of real benefits can control engineers expect from these technologies? Dave Gee, Steeplechase Software's (Ann Arbor, Mich.) vp of technical marketing, thinks that, 'Because XML includes semantic information along with the data, receiving applications know what the sender meant without an intimate knowledge of the sender. This frees control engineers to become less concerned with minutiae of app-to-app messages and more focused on how delivery of information can affect the company's profitability.' Steeplechase was recently acquired by Schneider Automation (North Andover, Mass.)

Dave Quebbemann, Omron Electronics' (Schaumburg, Ill.) industrial automation marketing manager, agrees, 'The continued acceptance of these software and hardware standards is making it a lot easier to extract data.

'Since OPC does not require special communications software, problems of keeping versions in sync from control stations up through enterprise machines is minimized. OPC can be a savior in installations with a variety of machines from a variety of vendors.'

Expand control horizons

To expand the concept beyond just one machine or small process in a factory, think about the need to integrate the enterprise so your company can compete in this new economy. Andy McMillan, marketing director for Think & Do Software (Ann Arbor, Mich.) says experiences in e-manufacturing reveal the possibility of using control application software solely as a transport to move OPC data directly from the device to a SQL database.

Does XML really work to move real-time data? Well, yes. Benson Houghland, director of technical marketing for Opto 22 (Temecula, Calif.), reports a working application in food service using straight XML from 250 I/O points to point of sale terminals with no interfaces or drivers. Mr. Houghland further notes that many full PCs now used can be replaced with smaller devices like cell phones or PDAs.

With many companies devoting resources to implementing these technologies, there is no doubt control engineers will have an answer that will warm the heart of the coldest general manager when asked to support the company's e-manufacturing initiative.






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