While the future may hold some promise for standardization, machine network choices remain as much a political investigation as a technical one for OEMs and end users. Motion control protocols seem to be gravitating to SERCOS and FireWire, while the more I/O-intensive machine network decisions involve choosing among the usual suspects.
OEM Customers Want a Standard
Since there is no dominant networking protocol for motion control, suppliers try to influence users as to which of the existing protocols is the best candidate to be a standard. Though some end users have standardized on Ethernet for controller- to-controller communications, few have a motion control networking standard, and those who do tend to specify SERCOS. SERCOS is seen by many as a sound technology, but it’s adoption may be limited by its level of vendor support.
For an OEM customer, that’s no help. “From my perspective, vendor support is a marketing question and not a technical question,” responds Keith Campbell, director of automation and integration for Hershey Foods, a company that has standardized on SERCOS. “It does what we need and we don’t have any enhancements in mind. It’s up to the supplier community to respond.”
But it is still a problem. “We don’t go to an automation vendor and say we want SERCOS,” says Nabisco’s Don Boyle, senior director, process control systems. “We’ll listen to their presentation, but we would want to know why all the motion vendors haven’t adopted it as a primary communications protocol.”
Has Ethernet been considered as an alternative to SERCOS? “No, but FireWire has sparked my interest,” responds Procter & Gamble’s Rob Aleksa, corporate controls section head. FireWire, a fast network protocol, was originally created by Apple Computer. It is now an open standard under IEEE-1394, but, so far, only a few motion vendors support it.
What OEMs Are Saying
The important thing, of course, is what OEMs have learned from their experiences with the various networks available to them. And there are ample opinions, ably summarized by some OEMs who’ve worked with a number of the networks.
“For assembly automation, InterBus is not the fastest kid on the block, but I believe it’s the best because of its synchronicity, determinism, and safety, and it has standard interfacing specifications for a lot of applications,” says control engineer Rick Ahnen, Gilman Engineering, Janesville, Wis. “It also has easy setup and maintenance, good throughput for its baud rate, and seamless data transfer through fiberoptic, shielded, and inexpensive two-wire mediums. I just wish there were some more U.S. vendors to aid in competition and interest.”
Ahren rates DeviceNet second. “I’m a long-time DeviceNet user and have a love/hate relationship with it,” he says. “I love it because I know it well enough to comfortably employ it and there are a lot of U.S. vendors that interface to it.” That’s the good news. “I hate it for its cumbersome setup, EDS files, noncommittal interfacing specs that result in inconsistent I/O vendor products, and its management software,” he states.
Fogg Filler Co., Holland, Mich., is an OEM of rotary filling machines for flowable, non-carbonated liquids. “We use DeviceNet for our machine control, which involves motors and variable-frequency drives, along with some basic discrete I/O,” says Dan Winebrenner, electrical engineer. “We chose DeviceNet mainly for the wiring savings and because of the readily available component base provided by Allen-Bradley.” Winebrenner says Fogg started with DeviceNet and they understand it better than any other at the moment.
Winebrenner doesn’t feel any pressure from his customers to choose among the networks. “Probably 90% of our customers don’t care what control system decisions we make,” he says. “The cause of advancing new control ideas is more of a push from the OEMs rather than a pull from the customer base.”
Next comes Profibus for Ahnen because he finds it fast, with a significant number of I/O vendors, and it has large following in Europe. “However, it’s expensive and can be as big a pain as DeviceNet for setup,” he says.
Winebrenner is now working with Profibus for a special trade-show prototype. “We were forced to try Profibus because of certain specific component choices we wanted to make,” he says. “But I’m impressed by its straightforward configuration and implementation.” He found better support available this time compared to his initial experiences about two years ago.
Advanced real-time control of particles in his company’s semiconductor process equipment is the mission for Bill Shade, vice president, vacuum products, Pacific Scientific Instruments, Grants Pass, Ore. “Fieldbus use by OEMs in this industry is still pretty new, but Modbus TCP/IP over Ethernet is our choice,” he says. “It is already common in semiconductor manufacturing, and this makes is easy for customers to install and maintain.”
Sun Automation, Sparks, Md., builds highly automated four-color printing presses for the corrugated industry. For their network needs they chose to go proprietary and use GE Fanuc front-to-back, including a Genius/Ethernet network. “The applications engineers showed us that Ethernet would be a stronger backbone for this application and let us have operating interface monitoring and control, as well as modem-based diagnostics, with just one network,” says Jim Larson, electrical engineer at Sun. He says that while Genius is a capable product for GE Fanuc systems, Ethernet opens the system up to the outside world, allowing communication over the Internet with TCP/IP.
Remstar Intl. Inc., the U.S. sales and marketing arm of Kardex AG, Zurich, Switzerland, manufactures automated storage machinery in a wide spectrum of configurations. The system implementation was done with DeviceNet at the device and motion control levels. “Other networks we examined tended to have either a closed architecture or were more specific to off-shore groups of control manufacturers, says Greg Amos, director, systems engineering. “We viewed them as sort of islands of standardization.”
The need to close positioning loops in a real-time environment was important and DeviceNet facilitated this, according to Amos. “The ability to store and manipulate preset parameters on the more sophisticated elements such AC drives across the network was invaluable,” he adds.
For motion control applications, SERCOS works and has enough vendors on its bandwagon, thinks Ahnen. “And FireWire, because of growing and widespread commercial applications will become very inexpensive to employ,” he says. “As soon as they can package a version that isn’t so cable-sensitive, it should blow away any competition in the motion control marketplace.”
Automation Intelligence, Duluth, Ga., is a system integrator emphasizing motion control applications. For networks controlling I/O and OI, they mainly see DeviceNet and Profibus. “While there’s a lot going on to create Ethernet protocols for data sharing, you have to be dreaming to think it’s good for motion control,” says George Kaufman, president. “I would look for Ethernet to play a major role in machine control networking, but for standard motion networks, SERCOS is still the only motion network with an installed base and many suppliers of drives and controls,” he claims.
Adept Technology, San Jose, Calif., builds robots and says there are no right answers to the network debate. “The PLC manufacturers and their allied peripherals builders have great leverage in establishing what we call I/O-primary networks like DeviceNet or Profibus,” says Joe Campbell, vice president of marketing. “We’ve standardized on DeviceNet for I/O networking, and we support other protocols via third-party boards installed in our controller backplane or in a PC networked to our controller.” They also have Ethernet 10/100BaseT as a standard on all their controllers.
The Devil's in the Details
Vendor Speak
In terms of what they call proprietary networks, its own ModBus included, Square D, Palatine, Ill., rates DeviceNet as the leader because of Allen
Bradley’s installed based among major industrial companies. “The protocol Square D/Schneider Electric supports, Modbus, is simple, easy to implement, it’s free, and it’s been in use since 1977, so it’s well understood,” says Karl Meihofer, manager, automation marketing for Square D’s transparent factory.
Square D acknowledges that some people view Modbus as incomplete because it doesn’t define the device providing the data when it transmits. Other protocols go to greater lengths to describe the devices connected to the network.
So, Ethernet is what they’re pushing. “Previous barriers to Ethernet—determinism, speed, and the number of suppliers offering Ethernet I/O—have all been overcome,” says Meihofer. “Today you can buy Ethernet I/O from us, Opto 22, GE, National Instruments, and many others—and they all speak Modbus over Ethernet.”
CTC Parker Automation, Milford, Ohio, focuses their HMI business on OEMs. “Profibus-DP offers good performance, competitive cost per I/O point connection, and global market acceptance,” says Jerry Koch, software product manager. “DeviceNet supports intelligent devices and has wide U.S. market acceptance, and CANopen has growing strength in the European market.”
There’s perspective from the software world, as well. “As a PC-based control software vendor, we take a very neutral stance toward I/O networks,” says Dave Gee, vice president, technical marketing, Steeplechase Software, Ann Arbor, Mich.
“We see plain-old RS-232 used in far-and-away more installations than any other I/O driver.” Gee says that among drivers for actual I/O, Profibus, InterBus-S, and DeviceNet, in equal proportions, account for 75% of their installations.
Ormec, Rochester, N.Y., provides servo systems and networked solutions, and is a promoter of FireWire. “Ethernet TCP/IP and IEEE-1394 are becoming technologies of choice for OEM machine control networks,” says Al Presher, marketing manager. “Both of these technologies bring the advantages of open standards—namely industry-standard hardware, inexpensive cabling, and ease of use—along with top-of-the-line performance.”
David Smith, Profibus marketing manager at Siemens E&A, Alpharetta, Ga., wants OEMs to know AS-I has been gaining in the low-level areas of automation. He believes Ethernet will gain acceptance, but says there is still a lot of confusion and misinformation regarding Ethernet I/O. “Different proprietary application-layer protocols still abound, so various vendor solutions still represent highly proprietary solutions,” he states.
John Turner, Open System CNC Manager at GE Fanuc, Charlottesville, Va., says single-vendor networks are still most common in the machine tool market. “There is great interest in a standard servo drive interface bus, says Turner. “SERCOS has attempted to fulfill this need, but has made little progress outside of Indramat, although it has some success in general purpose motion control.” His warning: a SERCOS drive from one vendor won’t necessarily directly replace the SERCOS drive of another vendor.
Browsing For Savings
Remote diagnostics and troubleshooting via browsers are beginning to make their presence felt in OEM machines. Shade says he can’t over-emphasize the importance of Internet/intranet capability for remote troubleshooting and diagnostics. “It’s a competitive advantage for us because our customers are beginning to demand it to support the manufacturing of integrated circuits 24 hours a day,” he states. “Remote access and worldwide access are critical to meeting this demand.”
A view from the robot world defines the limits of browsers. “Control of robots via Web browser violates international safety standards, says Adept’s Campbell. “But Web-based monitoring of controls, control activity, software, and displays is a useful troubleshooting tool.” He sees a major limitation being the availability of Web connectivity on the typical manufacturing floor.
Remote diagnostics is an attractive capability that OEMs can leverage as a way to service end users without the travel expenses associated with on-site field service, agrees CTC’s Koch. “The use of the Internet for this purpose is intriguing, but we see many IS/IT managers still restricting access to their internal systems from outsiders (OEMS),” he warns.
Diagnostics for predictive maintenance can hold tremendous potential for increasing productivity. “For motion control, the SERCOS service channel can provide a wealth of diagnostic information on the motors and drives,” says motion provider Rexroth Indramat’s marketing manager, John Kowal. “This type of diagnostic information certainly can be presented via a browser.”
What About Proprietary?
Proprietary networks—those clearly the work of a single vendor with little or no capacity for interoperability—still represent a durable percent of the machine control system market.
Winebrenner sees Allen-Bradley’s proprietary Data Highway as easily the most popular network choice in his industry segment, and, because many of Fogg’s customers are not large companies with extensive plant floor data collection needs, he’s seen very little interest in Ethernet.
That sentiment is not easily accepted in some circles. “Proprietary protocols are only of interest to the vendors that supply them, curtly says Jim Fall, president of CNC software maker MDSI, Ann Arbor, Mich. “Now that there is an increasing number of open choices, the pressure on these proprietary vendors is mounting to open their systems.”
OEM Use of Device/Sensor Buses by Application
GE Fanuc’s Heitanen thinks it’ll be a while before proprietary network solutions go away, believing the industrial market has some segments that move quickly and others that move slowly. “Proprietary protocols will continue for some period of time due to their acceptance and the effort it requires to change,” he says. “We should remember that proprietary protocols also supply some features that standard protocols do not or will not.”
Emerging Trends
The network wars as we have known them are probably over. Manufacturers are now doing very similar things based on Ethernet. It’s a good bet that all network suppliers will make their components work with Ethernet, so the choice will be focused on how best to implement a system. “Ethernet cost and determinism is improving rapidly,” says Pacific Scientific’s Shade. “It will be the control network of the future.”
FireWire has support in the critical motion arena. “We’ve standardized on IEEE-1394 as the basis for all of our future motion control networking,” says Adept’s Campbell. “This protocol is unique in its ability to provide deterministic communications, which is a critical requirement to meet safety codes for industrial robots.”
“There is a migration of commercial communication technology, i.e., Ethernet, to industrial automation,” says Bill Moss, executive director of the Open DeviceNet Vendors Assn. (ODVA). “But today, Ethernet doesn’t deliver interoperability. Without a universally accepted application layer, Ethernet cannot describe data types, syntax, and operations and network visible behavior.”
Like many other OEMs, Ahnen sees an Ethernet future. “When PLC/PC manufacturers figure out they should put at least two independent Ethernet channels on the same platform, and an industrial Ethernet connector/cabling arrangement is finally standardized on, all we’ll need is a few more I/O vendors to get on board,” he says. “Then, Ethernet will be hard to beat.”
Thanks to David Newcorn, special projects editor, Packaging World, for his reporting contributions to this article.
Here's a selection of starting points for where to go to bore into the details of industrial buses.AS-Interface http://www.as-interface.comARCNet http://www.arcnet.comBitBus http://www.bitbus.orgController Area Network (CAN) http://www.canopen.comControlNet http://www.controlnet.orgDeviceNet http://www.odva.orgIndustrial Ethernet http://www.industrialethernet.comFoundation fieldbus http://www.fieldbus.orgFireWire http://www.ti.com/sc/1394HART http://www.fieldbus.com/hartInterbus-S http://www.ibsclub.comLocal Operating Network (LON) http://www.lonmark.orgModBus http://www.modbus.orgMotion and Control Ring Optical (MACRO) http://www.macro.orgProfibus http://www.profibus.comSafetyBus http://www.safetybus.comSemiconductor Equipment Communication Standard http://www.semi.orgSERCOS http://www.sercos.comSeriplex http://www.seriplex.orgSmart Distributed System http://www.honeywell.com/sensing/prodinfo/sdsUniversal Serial Bus http://www.usb.org
