Hendersonville, NC--A pick-and-place unit was needed to position cardboard slip sheets on pallets of varying heights prior to stretch wrapping. Stretch wrapping and conveying operations were already automated, using PLC control.
The most obvious solution, says Larry Orr, president of Automated Designs, Inc., would have been to expand the current PLC control to include the additional pick-and-place function. Doing so would have required another PLC, I/O cards, software, and various electrical components.
Engineers developed a simpler solution that uses a pneumatic rodless cylinder, rotary actuator, vacuum, and an all-pneumatic "Quickstepper" sequencing unit from Festo Corp. It can control as many as 12 inputs and 12 outputs from a single module. "Using an all-pneumatic subsystem saved the company almost 30% on initial costs by eliminating electronic/pneumatic integration" says Mark Miller, the Festo engineer who designed the circuit.
The pick-and-place sequence consists of removing a large cardboard cover sheet from a magazine and placing it on top of pallets of product. There is no need for the flexibility associated with PLC control. If personnel at Automated Designs need to alter the sequence, they can make the changes by reconnecting tubing to fittings on the Quickstepper's removable backplane.
The height of the pallets and the level of sheets in the magazine can vary. To accommodate these factors, a six-foot-long Festo "DGP"rodless cylinder provides vertical motion. It can deal with a stacked pallet height ranging from 36 to 100 inches, and does so within its own length, reducing overall machine height. Further, the extruded aluminum cylinder serves as a structural element, eliminating the cost, weight and labor associated with using external struts.
It's necessary to limit the cylinder extension according to the height of the pallet. A simple, pneumatically actuated, spring-loaded roller-lever sensor device--mounted in the center of the vacuum pick-and-place arm--performs this function. The sensor extends below the arm's four vacuum suction cups. It depresses the floppy cardboard sheet, forming a convex surface when the sheet is held on four sides by the suction cups. This approach ensures that the system picks up only one sheet at a time.
During a pick-and-place sequence, cardboard slip sheets stacked in a magazine are picked up by a venturi-generated vacuum and bellows-style suction cups attached to a strut extending from the rodless cylinder. Next, the cylinder lifts the sheet to the top of the unit. A rotary actuator turns the sheet approximately 100 degrees, and then lowers it into position on the pallet. When the slip sheet is over the pallet, a pneumatic sensor, attached to the base of the rotary actuator, signals the Quickstepper to lower the rodless cylinder. The roller-lever sensor then trips, sending a signal to the stepper unit to stop the cylinder.
Mounted to the suction cups, the vacuum generators provide quick pickup and re-lease. The bellows-style cups allow approximately ¾ inch of motion before bottoming out. This range allows sufficient time to stop the cylinder without hitting the pallet.
* Assembly lines
* Pneumatic sequencing systems
If the magazine is empty when the vacuum pickup arm reaches bottom position, the lack of a signal from a vacuum switch stops the sequence, initiates an alarm, and raises the vacuum arm to its top position. After an operator refills the magazine, the sequence can resume without resetting the Quickstepper. When the system completes the sequence, a pneumatic signal sent to a pneumatic/electric converter signals the PLC on the stretch-wrapper system conveyor to move the next pallet into position.
Additional details...Contact Richard Day, Pneumatics Marketing, Festo Corp., 395 Moreland Rd., Hauppauge, NY 11788, (516) 435-0800