Variable Frequency Drives Combat Shrink-Wrapping Delays
Product spacing concerns solved by a variable frequency drive
Deb Kling, Contributing Editor -- Design News, February 3, 2008
When it comes to shrink-wrapping, space, cutting processes and speed are crucial concerns. A sudden change in load can cause a conveyer belt to slow down, disrupting the entire operation.
But, a variable frequency drive (VFD) can solve that problem, by noting weight and adjusting the belt’s speed.
“We needed to choose a VFD that would deliver the level of performance we — and our customers — demand and would do so at the right price,” says Mike Laurin, an Extreme Packaging Machinery Inc. engineer. “We wanted to maintain consistent spacing between the products to get good results on the wrapping and cutting process.”
The company began manufacturing shrink-packaging equipment in 1990.
EXTREME shrink-wrappers, known for their longevity, straightforward operation and simple maintenance, were introduced by the company in 1999.
“What’s important to our customers ends up in the blueprint,” says Laurin.
As the EXTREME team was studying VFD products from several manufacturers, they found Applied Mechatronics, a Valley Center, CA firm specializing in automation solutions. Sandor Gyetvai, a company spokesman, recommended the use of an open-loop vector drive from Lenze-AC Tech. “I was convinced that the engineers at Extreme could increase the speed and maintain better control without any cost increase by using the open-loop vector control capabilities of the TCF VFD,” says Gyetvai.
He says the target speed for the belt was 100 ft per min. Using a tachometer to measure it, in non-vector mode the speed would seem to fluctuate one to two ft per min. In vector mode, however, the speed would only fluctuate ½ ft per min. “Clearly, we could all see that with the vector mode we were getting excellent speed control, economically and with no complications, so the decision became rather obvious,” says Gyetvai, whose experience with the advantages offered by different motion control technology options was an important reason behind the final choice.
At the End of the Day
Are the VFDs keeping up to their initial performance? “Absolutely,” says Laurin, who reminds us the core of the robust EXTREME Packaging Equipment systems is its built-in efficiency, so all the components used in its design must be equally dependable. “These machines are flexible, cost-effective and easy to use; they are designed to perform in a wide range of wrapping applications at different speed requirements and they offer years of reliable service.” Laurin says items as different in size and weight as toys, paper goods and home improvement products can be economically packaged using these versatile wrappers.
Open-Loop or Closed-Loop Vector?
A closed-loop vector drive delivers outstanding performance — at a price. Since it relies on the use of a motor fitted with an encoder to monitor speed and position, comparing and correcting speed dynamically as needed, it requires additional expense. Needless to say, it adds complexity to the system.
An open-loop vector drive, on the other hand, is simpler, less costly and can also deliver excellent performance.
How does it work?
An open-loop vector drive uses a standard “off-the-shelf” ac induction motor. The drive creates an internal “model” of the motor. The model is based on motor specs input by the user and by an auto calibration function whereby the drive calibrates itself specifically to the applied motor during commissioning. The motor model, as well as high performance current sensing circuitry built into the drive, create a system that delivers near closed-loop performance while using a very economical drive and a standard ac motor.
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