Because each controller was proprietary, communication among the three machines was anything but optimal, not to mention the fact that supporting proprietary controllers is costly.
Now Triangle is replacing proprietary controllers in its scale/bagger/cartoner installations with Allen-Bradley ControlLogix™ integrated controllers from Rockwell Automation. One governs the combination scale and the bagger directly beneath it, while a second controls the cartoner. The controllers are “integrated” in that they handle both logic and motion-control functions.
”With off-the-shelf, open-architecture controllers in place of proprietary controllers,” says Steve Bergholt, chief engineer at Triangle, “all three machines can communicate freely with each other along an Ethernet connection. That brings real flexibility to our customer. Suppose he wants to add an output for a diverter or an infeed synchronizer or whatever. Or suppose he needs to move the scale and put it over a different bagger. No programming is required. Just add the output or move the scale and go.”
Another key benefit to the Triangle cartoner is greater overall simplicity.
“There’s one less programming language for operators and maintenance technicians to learn,” says John Nesi of Rockwell Automation. “The implications for maintenance people are also important. Rather than having to call Triangle for service on a proprietary scale system, he can call a local A-B distributor for a replacement if something breaks.”
As much as Triangle’s Bergholt appreciates the connectivity, simplicity, and flexibility that Triangle can now bring to a scale/bagger/cartoner installation, he says the use of a PLC to control the combination scale is also a noteworthy breakthrough.
“PLC processors and their ladder logic programming haven’t been powerful enough to make the thousands of calculations that are needed as a combination scale picks the right combination of weigh buckets to empty with each fill cycle,” says Bergholt. “So makers of combination scales have always relied on their own proprietary controllers, often something based on a pentium processor chip or something like it.”
So why is it that now all of a sudden the ControlLogix controller, which is more PLC than PC, is up to the task? Nesi says it’s a matter of PLCs and PCs converging into something that is better described as neither PC nor PLC but rather PAC: Programmable Automation Controller.
“The bottom line is that today’s controllers resemble PCs in many characteristics,” says Nesi. “They’re supposed to handle far more than sequential ladder logic and can now also handle calculations having to do with motion, weighing, and process control. You’re looking at PC characteristics in a PLC frame.”
