Pallet gripper: Lightweight, cost-effective and tough

• What was needed: drylin® R linear plain bearing
• Requirements: First and foremost, particularly lightweight and functionally reliable technology was needed that would also function without failure.
• Industry: Packaging technology
• Success for the customer: drylin® plastic bearings are light, inexpensive and yet very robust. They can withstand impacts and dirt as well as strong vibrations or extreme weather conditions. Krones has not yet had any complaints.

Krones AG has developed special packaging grippers for the beverage industry at its Rosenheim plant. They do not grip packs, but the intermediate layers of the pallet, but also, for example, pallets themselves, cover frames or snap-on lids. The grippers, which utilise the fin-ray effect, look like butterflies flapping their wings when gripping a layer pad, which is why they were given the name "butterfly gripper".
As the cardboard boxes are delivered in stacks, the individual layers are tightly packed together. This makes gripping more difficult. In the past, the intermediate layers were therefore cleanly separated using a brush magazine. They prevented the tightly pressed interlayers underneath from being moved when a layer was lifted. However, such brush magazines cost a lot of money.
The gripper head solves the task without the brush magazine: it lifts the pages upwards and the vacuum underneath is released.
But how does the gripper work technically? The entire assembly is pushed to the side using a tube as a guide. The butterfly function is created by the movement of slide bearings in a kind of pulling effect. Pneumatic cylinders move together and the distance between the individual links is reduced.
The technology is to be further improved in the future. It should be lighter and have an improved design thanks to the use of more plain bearings.
The gripper technology for packing aids must function one hundred per cent, otherwise the system will stop. The requirement is to build a reliable yet inexpensive system.

Today, plastic plain bearings play an important role in the movements of the grippers. Specifically, drylin® R linear plain bushings of type RJMP-01-25 are used here. They were favoured by Krones because they are made of plastic and are therefore light, inexpensive and yet very robust. This has proved very successful in practice: Krones has not yet had any complaints about the resistant bearings. They are robust against shocks or dirt and can also withstand strong vibrations or extreme weather conditions. Here again, it's the little refinements that count, such as the special segmented type of bearing. This special feature proves its worth in dusty environments. This is where the dust molecules that are pressed together normally accumulate on the guide shaft. As the dust layer increases day by day, the diameter of the shaft increases. As a result, the traversing movement becomes increasingly sluggish due to the strong friction.
Everything runs better in the plain bearing with the slots. The dust does not settle in the bearing, but is literally guided through the bearing without any significant changes in friction and wear behaviour.
In contrast, the Krones gripper specialists have had different experiences with the recirculating ball bearings used in the past. Even one collision could destroy such bearings. The balls have often pressed themselves into the shaft.
But 'conventional' packaging grippers from Krones also benefit from the plain bearings during operation. This is because the plastic plain bearings fit perfectly into the modular gripper system from Krones.