Sheeter Maker Swaps PLC for PC 20048

September 10, 2005

3 Min Read
Sheeter Maker Swaps PLC for PC

Mild market pressure convinced sheeter maker Marquip Ward United that PCs could control its machines as well as, or better than, PLCs did. 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—-who tend to run smaller operations than the company’s corrugated customers—-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. Faster speed, lower component counts, cheaper spares: these also buttressed the case for PC control.

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 millisecond response range. By Windows, Brown means NT, 4.0, 2000, or the XT versions—not Windows CE, which is a real-time operating system. 

The Marquip sheeters made good candidates for PC control because of their need to be able to divert sheets in real time. In the event Windows hiccupped, the machine could be halted at a safe position to give the system time to recover without the machine needing a long restart period. 

Although some experts say that PC controls will eventually sweep industry, plenty of resistance to that change remains. For some of Marquip’s larger customers, particularly those in the corrugated business, the economic case for switching over isn’t so readily made. Many of these users have enough PLCs running in their plants that the expense of firmware upgrades can be spread over many units. For them, the savings doesn’t justify
the risk, whether it’s real or perceived.
Still, Marquip’s customers on the sheet side have met the change to PC control favorably, Jahn says, rewarding the company’s bold pursuit of the new. 

Marquip Ward United’s Tom Miske stands beside the control console of a sheeter line. The familiar keyboard and Windows interface make the operator learning curve “steep and short,” according to director Jon Jahn.

Sheeting systems customers have grown fond of the PC controlled machines, and comfortable with their operation.


Resources
   See overview of Beckhoff Automation’s Industrial PC 

Read information on its TwinCAT software 

Read more on Marquip Ward United’s sheeter lines
    

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