Battle Royal for Machining Center Control

Engineers Wrestle With CNC and PLC, but the Application Still Dictates the Choice

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By Jim Romeo

When it comes to controller architecture, PLCs, PACs and PC-based controls are all players. However, CNC machining centers still play a viable role. Because machining varies by industry and application, so does the efficacy of controller. Many different permutations of control are integrated with machining for different applications.

So where is this element of control architecture heading? Opinions differ. Some believe there is a clear trend in integrating advanced control into CNC machining. While CNC may still be the dominant choice, the use of other controllers is becoming an increasingly visible consideration, often due to the need to integrate the machining center with other systems.

“CNC control of machine tools was, and still is, a breakthrough technology,” says Robert Page, and engineer with Milltronics, a machine builder in Waconia, Minn. “CNC makes it possible to cut angles, arcs and complex 3D shapes that were either impossible or difficult on manual machines tools. Many modern efficiencies are the direct result of CNC machine tool technology.” Page appreciates CNC’s extensive user interface, making the coordinated motion of several axes possible, but the only constant is change.

“The only trend clear to me is the growing use of PC-based devices,” says Page. “The growth of PC-based devices is a natural because in the past 10 years PCs have become vastly more powerful and capable, and also more reliable while their cost has been going down.”

Did He Just Say, “PC”?

PC-based controls are undoubtedly becoming more prevalent in the industry, says Kevin Bevan, president of GBI Cincinnati, a Tier 1 international distributor and the exclusive master distributor for Cincinnati Lamb’s high-end aerospace and transfer-line products.

“Back in the mid-’90s there was a strong push for more open architecture controls,” he says. “Customers felt that the standard control offerings were too closed and did not provide the end-user flexibility to customize the functionality as needed. Control builders tend to prefer a closed or more proprietary approach to the product they sell.”

Bevan contends that not much has changed since the mid-’90s. He feels that some companies have developed PC-based controls and have performed well in niche markets such as die/mold and medical, noting also that the term “PC-based” can be misleading. Ten years ago, the term made many wary that a standard PC may not be reliable enough. “With the changes that have taken place, today’s PCs are far more robust with extremely low failure rates,” adds Bevan.

GBI’s Revolution line uses computing technology in the development of its MTI CV control. This proprietary control architecture uses tool path algorithms that have a read speed of more that 50,000 blocks/sec and up to 50% cycle reduction, says Bevan. The result is a constant-velocity machining center that is fast, constant and without acceleration and deceleration, he claims. “With the leap in technology, we actually run on a dual kernel platform,” explains Bevan. “This means that the machine is being controlled by one platform that maximizes the efficiency in the cutting operation, while the secondary kernel performs all the PC functions in a Windows environment. The only time the two kernels communicate is in the loading of part programs.”


PLC/PC Controls
Figure 1: PLC/PC controls can be expanded by integrating CNC controls and then can replace the CNC functionality previously hard-coded in dedicated hardware.

The Windows environment also is appealing to Russ Jacobsmeyer, chief technology officer for Sunnen, a vertical honing machine builder in St. Louis. He feels that the PC-based controls are easier to use and program, largely because many who use them are already familiar with a Windows environment. “This has been something we have had success with, or received constructive feedback from the market on,” says Jacobsmeyer. “The demand is global and in large and small shops. I believe productivity is driving the demand. In speaking with a customer we have in Germany when I was there in the fall, he had nothing but wonderful things to say about the operating system on our new PC-based equipment. He found it easy, intuitive, flexible, and ultimately most productive or efficient for him. We have also written our software to be easily translated into the local language of interest. I think this has been a plus for us.”

Softly, as in an Integration

Dario Doko, a sales engineer with B&R Industrial Automation also sees integration of traditional CNC with PLCs, PACs and PC-based controls as a definite trend. Doko attributes the trend to two factors: a better and easier CNC integration and a lower price for hardware, software and engineering.

From Doko’s vantage point, typical users are OEMs who would like to seamlessly integrate their standard machine control to the CNC feature (Figure 1).

“The standard PLC/PC controls can be expanded by integrating dedicated CNC controls in its software for easy CNC controls, data share between PLC and CNC components in a machine and future upgrades,” says Doko. “This way, a dedicated and expensive CNC controller is not required any more, but instead standard and well-known PLC/PC controls can be used.”

Doko explains that in the past CNC functionality was often hard-coded in a dedicated hardware. “We can extend the standard PLC runtime with a ‘soft’ CNC,” says Doko. “This means that the customer can use the same hardware for controlling, visualization, standard motion and CNC just by adding software components." But he explains that for some applications, standard dedicated controllers are still better. “The reason for that is not in the better technology they possess, but rather in well-developed software components that these dedicated CNC controllers historically have,” says Doko. “Over the time, this gap will be smaller and smaller. CNC on standard PLC/PC platform is a very young topic indeed.”

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