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Why we use...composite disk couplings. (Just One More).

Letting the chips fall where they may is not acceptable policy at Robert's Packaging, Battle Creek, MI. They produce machines that, in a single line, form and fill the currently-popular pouch package with food products such as potato chips, rice, candy, nuts and pet food at a rate of 220 pre-made contoured shaped pouches per minute. Servomotor-powered indexing stations in automated pouching systems require accurate registration as the pouches are stood up, filled and heat sealed.

Keeping motion control under control in these systems is a key design consideration because of the high-speed, intermittent motion of thin, flexible polypropylene film, the raw material for the pouches. In a machine consisting of a series of automated forming and filling stations, intermittent motion is especially critical at the sealing station. The system's servo motor draws the preprinted film forward through a series of rubber-covered rollers, stopping to heat seal a completed pouch, then instantly restarting to repeat the cycle. An indexing cycle occurs every 0.3333 sec., with approximately half of that required for film advance and the remaining 0.1666 sec. used in the sealing operation. This timing is significant since pouch travel for each sealing and cutoff cycle ranges from 4 in. for the smaller pouches to 12 in. for the largest pouches, depending on machine model (pouch width is either 4- to 12-in.).

"We have a zero-backlash requirement for the indexing operation in our pouching systems," reports Scott Risnes, senior engineer for Robert's Packaging. "Any backlash or improper hesitation in the drawing cycle can cause misalignment of the film for the heat sealing operation." His company's machine uses an integrated servomotor/coupling combination, which provides rapid start/stop film advance while preventing misalignment problems before they occur. The motor draws the film smoothly, in-register while the CD coupling dampens any backlash forces, thereby eliminating any chance of a misfeed of the system's polypropylene film. The system's pouch forming accuracy is monitored each indexing cycle by an optical reader, which, Risnes says, "hits a tiny target spot on the pouch face without fail every time." There are two such stations in a typical pouching system.

Well-suited for this packaging application, a CD coupling has many of the best features of other coupling designs. While the CD coupling transmits torque similar to any conventional coupling, it does a better job of dampening backlash and shock without the coupling fatiguing which can occur in a fast-moving system. It accomplishes the task through a patented unique open arm disc design made of highly durable composite disc material. This design absorbs and cushions any tendency for backlash from the servomotor's intermittent motion. Another benefit the company found using the CD coupling was that it allowed for the use of a single flex, single disc model, which is less costly and does the work of most other metal double disc designs, while using less space with greater misalignment capability.

The clamp style hub model used -- a Zero-Max .Model 6A37C single flex CD coupling with clamp style hubs connected directly to a Yaskawa servo motor -- allows for fast installation by tightening just one screw on each hub of the coupling. For this application, the servo motor's 35 mm shaft diameter dictated the choice of the Model 37 size coupling, according to Risnes, which proved more than adequate for the system.

As for coupler performance, Risnes reports, "We have several systems in the field that are six years old and the CD's continue to operate 24/7, stopping only for 2 minutes to load new film every 2 hours or so. In fact, I knew of one connected to a gearbox where the gearbox failed but the coupling continued performing satisfactorily. We never considered any other coupling design for our servo motors but the CD coupling."

Circle 145--Roberts Packaging, or connect directly to their website via the Online Reader Service Program at www.rsleads.com/302df-145

Circle 146--ZeroMax, or connect directly to their website at www.rsleads.com/302df-146
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Publication:Designfax
Date:Feb 1, 2003
Words:662
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