When General Motors Powertrain upgraded its manufacturing facility in Toledo, Ohio, speed was a critical element. GM plans daily production of 2,200 GF6 transmissions for its Chevy Malibu and Cruze lines, so every machine has to operate quickly with a high level of synchronization and precision.

That’s a high volume for complex six-speed transmissions, which contain many components. Networked automation is a key to the process, as GM strives to cut costs and press defects to ever-lower levels. This automation program begins by delivering workpieces with autonomous guided vehicles. The workpieces are tracked by radio-frequency identification (RFID) tags placed on each pallet. Model number, serial number and build status information are all contained in the tags.

While speed is a key factor for automotive production, quick changes are also critical. To meet the demands of GM’s flexible automated assembly system, all hardware and software is designed with a deterministic functionality. After a detailed deterministic study, GM opted to employ a high-level Ethernet protocol, Profinet, in which all the control elements for every assembly operation and test station would be fully integrated.

Third-party software package provider Elite Engineering Inc., of Rochester Hills, Mich., teamed up with the Siemens Automotive Center of Competence in nearby Troy, Mich., to devise a networking and production program that would meet these demands. Their networking selection highlights the growing role of deterministic Ethernet in demanding applications.

Profinet gives GM a deterministic network with no special hardware required, cutting costs. Further cost cutting was achieved by eliminating a safety network. All safety devices are now networked over Profisafe protocol, a certified safety network, eliminating time-consuming and difficult-to-maintain traditional hardwired safety connections.

The combination of determinism and safety shine the spotlight more directly on the real-time variations of Ethernet. When these networks handle multiple critical data sets, the importance of their speed and timing is matched by the need for reliability.

Once engineers determine which version of Ethernet best meets their demands, their design challenges shift to the topology. This choice will determine performance traits, as well as reliability, as it is critical to ensure that devices remain connected when a cable is disconnected or cut.

“Most of the time, these networks also require fault tolerance. Developers want to ensure that data gets there even if there’s some sort of break,” says Martins Jansons, network consultant at Siemens Industry Inc., the Alpharetta, Ga.-based automation supplier.

The networking topology will play a key role in determining the level of fault tolerance. It will also be a factor in costs. Some architectures require duplicate cabling, while others require some additional hardware. Selecting a topology is not a simple decision.

“We spend a lot of time with customers trying to determine which topology they need,” says Nate Holmes, Product Manager for Motion and EtherCat at National Instruments Corp. (NI), a test and automation supplier headquartered in Austin, Texas. “We usually break out six to 10 characteristics that will help them pick a topology. But it’s not always apples to apples; there are a number of lemons that make it hard to say this approach will work best in this environment.”

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