Mild market pressure convinced sheeter maker Marquip Ward United that PCs could control its machines as well as, or better than, PLCs. Now that the company has shipped more than two dozen dual rotary knife sheeters with PC controls, its customers are affirming the wisdom of that decision.
According to Jon Jahn, director of project management for the company's sheeting systems group, some of its users on the sheet goods side of the business were objecting to the barrage of nearly constant upgrades in PLC firmware and the fees that went along with them. PC control offered superior performance and reliability, since chips are made "by the gazillions," he says. Costs differentials ran 20-40 percent less for PC controls, too.
Yet, the perception that PCs were unstable and could compromise machine safety and uptime presented a barrier that Marquip engineers had to cross, Jahn says. It was the way in which Beckhoff Automation's PC control ran beside Windows, and not on top of it, that convinced those engineers that a stable solution could be found.
According to Beckhoff sales manager, Jeff Brown, TwinCAT software actually runs on the second of two Windows modes, the kernel mode, using the company's patented double-tick kernel extension to provide real time control in the 1-2 msec response range.
Although some experts say that PC controls will eventually sweep the industry, plenty of resistance to that change remains. Some of Marquip's larger customers have enough PLCs running in their plants that the expense of firmware upgrades can be spread over many units. For them, the savings of switching to PC control doesn't justify the risk, whether it's real or perceived.
Still, Marquip's sheet good customers have met the change to PC control favorably, Jahn says, rewarding the company's bold pursuit of the new.
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