Problem solution: Separating workpieces that are stuck together
Problem definition:
Separating adhering stacked workpieces
Flat workpieces stacked in magazines or sheet feeders, such as sheets of paper, cardboard, plastic sheets, foils, metal sheets and similar materials, are often difficult to separate automatically.
They are unstable, adhesive, sometimes moist, statically charged, burrgy and simply stubborn.
Separating these automatically and processing them individually is often an impossible task for the designer.
Video: The separation process in slow motion (duration 38 sec.)
Solution:
The process-safe way to separate stacked flat parts by using vacuum lifting cylinders
Pre-separation through precise lateral introduction of blast air
Compressed air is blown into the side of the stack using one or more blowing nozzles.
The air flow causes the workpieces on top to fan out separately and float on top of each other without contact.
To achieve this effect, it is important that the air flow has the right distance to the stack and the right flow velocity.
If the blowing nozzle is too close to the stack and the air flow is too directed, a rapid laminar flow develops between the workpiece, which holds the workpieces together.
Care should therefore be taken in the design to ensure that the distance and flow rate of the nozzle(s) can be adjusted. The correct distance is created at the boundary between laminar and turbulent flow. The air volume and speed, i.e. the energy of the flow, is responsible for the reliable separation or pre-separation of the workpieces.
The uppermost workpieces should float fanned out above the stack, but not lift off in an uncontrolled manner.
Precise and repeatable positioning of the blowing nozzles is easily achieved by using our manually operated positioning units, which can also be combined into multi-axis systems and thus enable adjustment in all degrees of freedom.
Picking off the top workpiece with a vacuum cylinder without compressing the air cushion again
After the workpiece floating on top has now been separated from the workpieces below, it must be picked off while floating on the air flow without the part below sticking again by compressing the air cushion.
Our vacuum lifters were developed precisely for this purpose.
The unique mode of operation of the lifting suction cup (also known as a vacuum lifting cylinder or trailing suction cup) enables the
Picking or picking the workpiece from the stack. The vacuum lifting gripper reverses the direction of the vertical movement at lightning speed before it compresses the air cushion between the workpieces and the materials stick together again.
The workpiece is lifted out via the magazine and can then be fed into the machine.
Optional support of the process with position enquiry
It is also possible to query the retracted end position of the lifting cylinder using a magnetic field sensor.
Vacuum on + sensor activated = workpiece gripped and lifted
We offer a magnetic field sensor and suitable mounting clamps for correct positioning on the lifting cylinder as accessories.
Attention: This option is only possible for lifting cylinders with anti-rotation protection!
1. adjusting the air nozzles
2. separating the workpieces with blast air
3. gripping the workpiece and automatic direction reversal
4. lifting of the workpiece
The separation process summarised
1.
Arrangement in basic position
2.
Pre-separation by lateral injection of compressed air
3.
Sensitive picking of the floating workpiece with lifting suction cup
4.
Workpiece separated and lifted
Multiple use of vacuum lifters for large, unstable workpieces
For larger workpieces, several vacuum lifters can be connected to one vacuum generator and used synchronously.
To ensure optimum parallel connection and synchronised operation, the same line lengths and the shortest possible distance from the vacuum generator to the vacuum lifters should be selected.
When releasing the workpieces by switching off the vacuum, it is essential to use a blow-off or ejector pulse so that the workpiece is safely and quickly separated from all lifting suction cups simultaneously by the air blast.
This principle is often the only way to separate statically charged, moist, adhesive or burred workpieces from each other without scratching.
Blown air separation in combination with vacuum gripping usually works more reliably than mechanical peeling.
Thanks to its unique mode of operation, the lifting suction cup enables lifting out of magazines and picking from different or changing stack levels.
