Move, But Don't Touch

The package was a thin, decorated plastic bag that was proving difficult to lift, open and fill in an end-of-line workstation.In the lifting stage, static charge and cling made conventional vacuum handling ineffective, often lifting two or three bags in addition to the one lifted by the vacuum fixture. In addition, the vacuum contact wrinkled or smudged the package. Plus, conventional blow opening could not be used to make the bag ready for product. Product specifications set a maximum particulate limit on the bag interior and using external, intermittent streams of air to open bags injected too much dust into the packages.Manual methods were considered. “Unfortunately,” says Gottfried Kaufmann, purchasing team member at Bürstenfabrik Ebnat-Kappel, “batch production dictated short runs at relatively high manufacturing rates, making automation a necessity.” The solution was a non-contact transfer (NCT) solution from Bosch Rexroth that employed the Bernoulli principle to create lift by blowing horizontally across the surface of the bag.In the simplest terms, Bernoulli’s principle states that there is an inverse relationship between the speed of a gas or liquid and its pressure – higher speed means lower pressure. Aircraft design exploits this by ensuring that the speed of air over the top of a wing is faster than air over the bottom. The resultant lower pressure above the wing creates lift. In the same way, the NCT tooling creates a laminar flow of air across the surface of the plastic bag, causing it to lift and move toward the surface of the NCT tool. Thus, the decrease in pressure from the accelerated air flow in effect “holds” the bag to the tool.In operation, two NCT modules are used in the automated, 5-10 second cycle. As an interdental flosser reaches the packaging station, the first NCT lifts and rotates a bag 90 degrees to vertical, without marring or creasing it. At that point the second, arm-mounted NCT swings in to open the bag, and a depositor drops the dental product into the bag. All air flows externally, so only minimal particulate enters the open bags. Valves then stop airflow to the first NCT as the arm with the second NCT swings to release the filled bag onto an outbound conveyor.The units are NCT60s, with a 60mm (2.36 in.) diameter delivering a 6 Newton (21 ounces force) lift at 5 bar (73 psi). The application is not the first for Ebnat-Koppel: “We first tested NCT with perforated, blister-pack cardboard, as well as with beakers for travel toothbrush sets,” Kaufmann says. “Standard vacuum lifters left slight marks on the smooth surface of the beakers, but the NCT left none. Follow-on testing showed we could successfully lift relatively heavy floor mops in a three-NCT fixture.”