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Pneumatics Packs a Gentle Punch

May 14, 2008
A key to high packaging production rates is to use pneumatics for speed without the shock and impact that often accompanies high speed.

Buying a packaging machine can seem a lot like buying a laptop computer. Those on a tight budget might go for an entry-level machine that performs basic functions. But you can add options to enhance operation or move up to a premium model that may be lighter, smaller, faster, and with more standard features. Whether it’s a computer or packaging machine, many customers are willing to pay for higher speed and smaller size.

Pearson's BI18 Bag Inserter uses a rodless cylinder to operate the insertion axis that lines cases with poly bags for bulk filling of product. Click image for larger view.

With all else equal, the price of a packaging machine increases with cycle rate and smaller footprint. Customers are willing to pay a premium for machines with a smaller footprint because floor space at most packaging plants comes at a premium.

Pearson Packaging Systems, Spokane, Wash., makes a wide variety of case erectors, case sealers, bag inserters, robotic case packers, and other equipment in a variety of standard sizes with options to match the specific needs of customers. The end result is a machine with features designed for a specific application but at a fraction of what it would cost to build a custom-designed machine.

Pneumatics for operation

Mike Johnson, new product development engineer at Pearson, says that pneumatics technology is used throughout most of the machines they manufacture. Pneumatics powers air cylinders, grippers, vacuum cups, and other actuators that manipulate the carton, case, or other work piece. However, he points out that most of their higher-end machines use electric servodrives to perform functions requiring closed-loop motion control or frequent changes to operating parameters. In most cases, electromechanical and pneumatic drives work in concert to accomplish the task at hand most effectively.

The pneumatic system of all Pearson machines starts with a lockout-tagout valve to prevent accidents when the machine is being serviced. When a mechanic or technician will be working on a machine, the lockout-tagout valve blocks incoming compressed air. The valve also accommodates a padlock to physically lock the valve in the closed position. The only way for the machine to be pressurized is if the padlock is removed so the valve can be opened.

With the lockout-tagout valve open, compressed air then flows through a filter-regulator assembly to a dump valve, which is also standard on Pearson machines. Johnson explains that all packaging machines meeting industry standards are equipped with a lockout-tagout valve, but Pearson provides the dump valve as an additional safety feature.

As with all packaging machines conforming to industry standards, Pearson’s machines contain a lockout-tagout valve to ensure worker safety whenever maintenance is performed on a machine. In addition, Pearson also provides a dump valve on all machines to ensure smooth pressurization. Click on image for larger view.

As with most OEMs Pearson limits the number of vendors for products and services. Norgren, Littleton, Colo., is a major source of pneumatic and other automation components. Pearson also works closely with Norgren’s local distributor, Warren Fluid Dynamics, also in Spokane. Charlie Jett, of Warren Fluid Dynamics, explains, “The dump valve is what we call a soft-start, quick exhaust valve. It is a normally closed 3-way valve that blocks incoming pneumatic flow and routes any downstream compressed air to atmosphere. Once all the machine’s interlocks and switches are closed, an electric signal energizes the valve’s solenoid. The solenoid energizes a pilot circuit that shifts (opens) the valve. With the valve open, compressed air flows to the machine’s system.

“The dump valve’s air pilot operation contains an adjustable needle valve to provide gradual pressurization of the machine’s pneumatic system,” continues Jett. “Without the needle valve, the sudden rush of compressed air into the machine’s pneumatic system would produce a sound similar to that of an impact.”

Smooth and quiet

Pearson prides itself on having machines that operate smoothly and quietly, so the air piloted dump valve prevents the sudden surge of compressed air that otherwise would occur when energizing the machine’s pneumatic system. Engineers apply this rule of smooth, quiet operation throughout the Pearson product line.

Pearson uses extended cushioning on cylinders with long strokes as another means of producing smooth, quiet operation. Because cylinders must extend and retract rapidly to maximize throughput, pistons can reach high velocity when long strokes are involved. Extended cushions provide controlled deceleration to reduce shock and noise. For example, the Pearson Multi Packer contains a 1-in. bore, 36-in. stroke tie-rod cylinder for the machine’s load ram. Rather than limit the speed of this cylinder, which would extend cycle time, extended cushions decelerate the piston smoothly at the end of extension and retraction strokes.

“The cylinders themselves can take a pounding without getting damaged. But to an operator, the loud noise and heavy shock can give the appearance that the machine is tearing itself apart. It’s not, but the perception may be that it is. So we reduce the end-of-stroke shock so the machine runs smoother and quieter without sacrificing any machine cycle time to speak of.”

Johnson says he specifies non-repairable cylinders primarily in short stroke applications. “When you have a cylinder that strokes only a couple inches or less, it takes many thousands of cycles before the seals show any substantial wear. By that time, it’s more economical to just replace the cylinder, rather than repair it. On the other hand, a cylinder with a stroke of, say, 6 in. or more can wear out three times faster than a cylinder with only a 2-in. stroke. So we’ll specify a (Norgren) Round Line tie-rod or other repairable type of cylinder on a case-by-case basis according to the application.”

Putting vacuum to work

Pneumatic cylinders are used in concert with vacuum generators and vacuum cups for the case forming action, allowing for opposing vacuum to be established on each side of the case for reliable and consistant case forming. Click on image for larger view.

In addition to their extensive use of valves and cylinders, most Pearson packaging machines also contain multiple vacuum generators and vacuum cups. Johnson continues, “We’ll use the most effective type of device for the application. Sometimes this will be a set of grippers. Other times, it might be mechanical fingers. But when all you have to grip is a smooth surface, nothing beats vacuum cups.

“We’ll often use two sets of vacuum cups to create opposing vacuum to erect a carton. A stationary set holds the carton in place, while a second set — actuated by a cylinder, for example — pulls on the carton to open it. This feature provides our customers with a more reliable approach to case forming then alternative designs. Depending on the weight and size of the box, each set might contain four or more vacuum cups. Each cup within a set is usually served by a line branching out from a single vacuum generator. Once a valve shifts to route compressed air to the vacuum generator, a slight delay occurs before the generator pulls its rated vacuum. But we know this, so we program the machine’s PLC to shift the valve that energizes the vacuum generator before the vacuum cups actually contact the carton. Once they’ve contacted the carton, the cups quickly achieve their rated vacuum to pull and erect the carton.

Johnson concludes, “Packaging machines used to use a centralized vacuum system with a mechanical vacuum pump. But for many years we’ve found vacuum generators to be much more practical and economical.”

For information on Pearson Packaging Systems, visit www.pearsonpkg.com. For information on Norgren’s pneumatic and other automation components, visit www.norgren.com.

Click here to see a video of Pearson's MP50 Multipacker in action.

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