Driving the open bus

Harrisburg, PA--If you've spent 18 years designing automation systems, you should know what works. And for Mark Stremmel, president of Device Bus Integration, open bus systems make a lot of sense for all sorts of machines, including packaging, converting, assembly, or materials handling.

"Two years ago, if I talked to 25 customers a week, maybe one or two would consider an open bus system," says the Penn State-educated engineer. "Now, most people want to go to an open bus, though many still need some help in making this shift."

Stremmel's career includes broad experience with PLC vendors, as well as seven years of engineering work with Hershey Foods during which he helped design and implement automation systems worth $500 million. Now his mission is to help engineers simplify their automation setups. About 75% of his customers are OEM machine builders.

The kind of situation he encounters often with OEM customers is an application that involves a PLC, IO, an operator interface that can be a PC running some software, and perhaps another PC-based controller to handle motion. All of this is hard-wired together between IO or perhaps linked by some type of proprietary bus structure. Result: the customer ends up with three different boxes, three different data bases, and often a maintenance nightmare--especially when you add demands for links to a local area network.

What DBI offers to handle all the above functions is what Stremmel calls a "flattened solution." He uses one PC to integrate all these functions. "Any PC-based controller worth its salt will offer at least three and better still all five of the IEC 1131-compliant languages. And, increasingly, people want motion control integrated within this same box. So you end up with one box, and one shared data base--and you plug in the open bus for IO."

The adoption of open bus systems goes hand-in-hand with PC-based controls, says Stremmel, but he recommends that companies first implement the open bus structure. "Don't try to do too much too soon," he cautions, "especially these days when busy OEMs are strapped for engineering staff." In the U.S., the most prevalent open bus system Stremmel sees among his customers is DeviceNet, followed by Profibus DP.

What is driving the move to open bus systems? Stremmel cites these factors:

- Open systems can cut controls costs, typically from 10% to 40%. Says Stremmel: "You don't need a long conveyor line to make an open bus system pay for itself. Even a short line with dense clusters of IO lends itself to an open bus system, which cuts costs by eliminating point-by-point hard wiring and reducing connections and cabinets."

- Built-in diagnostics eases maintenance headaches. With open buses, interface cards in the controller tell which nodes are down or need attention.

- Open systems answer the demand for flexible automation, letting manufacturers add new plug-and-play modules.

- Finally, open buses allow engineers to use the best available components, rather than being locked into products dictated by proprietary systems.

DBI itself has prospered right along with the move toward open systems. Since establishing his firm two years ago, Stremmel's company has grown to 20 people in his main Harrisburg office, plus a new branch office in Detroit. More often than not, the OEM engineers he encounters are not "controls gurus" but find themselves with the responsibility of upgrading to new automation systems that need to be faster, more productive, and more flexible.