Can Pallets Be Automatically Stacked Where The Product Is Unstable?

Some product types better lend themselves to automated palletising than others.  One of the best types of products for automated palletising is boxes.  However, not everything comes in boxes! Some products need to be packed in other ways such as bags or sacks. These are usually just as easy as boxes to automatically palletise, but depending on their properties, can sometimes be more complex to automatically stack onto pallets due to the nature of the product inside them or the material the bags/sacks are made of.

Typically, automated palletising of bags or sacks is not an issue at all.  When the bag or sack being palletised is made of paper or similar, the bags don’t tend to slip once they’ve been placed onto the pallet so a neatly formed stack can be created without any special measures needing to be used.  Similarly, where the product inside the bag is fairly stable and doesn’t move around, the bag can be run through a bag flattener, or over square rollers on a conveyor, to even out the distribution of the product in the bag before it is picked and placed onto the pallet.  Once the product is evenly distributed through the bag, the gripper will be able to pick and place the product with minimal disturbance to the bag and it will result in a neatly stacked pallet.  Depending what the bag being palletised contains, the bag gripper may be programmed to drop the bag onto the stack, as the dropping height can actually help to form the product into place and improve the stack quality. Where bags are likely to slip when placed on top of each other, a vacuum bag gripper will usually be used. This is a large vacuum cup in a ring with soft foam around the edges which can pick many different types of bags and place them in place very neatly without dropping them.  Alternatively, where a bag gripper or vacuum gripper are not suitable then an underneath gripper can be used. An underneath gripper will slide underneath the bag, and then delicately place the bag onto the pallet by pushing it off a sliding plate. All of these methods have their own benefits and it is often best to talk to a specialist and arrange for a free trial to determine which method is best suited to your products.

The video below shows a bag palletiser in action.

However, when bags or sacks are loosely filled with product, or the outer bag is plastic, additional methods will likely need to be used to ensure the pallet is neatly stacked. This is because when a bag is loosely filled, the product inside the bag is not evenly distributed throughout the bag, and once you have multiple bags that are unevenly filled placed onto a pallet you can very quickly end up with an unevenly stacked pallet.  There can also be issues when the bags or sacks are plastic as they can start to slide away from the position that they’ve been placed on the pallet and then create an uneven stack.  Without correcting or eliminating these issues, you very quickly end up with an unstable pallet that is very likely to suffer from transit damage.

There are several different methods that can be used to help eliminate these issues. A couple of the more commonly used methods are to shrink wrap the pallet as it is stacked to stop product movement, or to stack into a cardboard sleeve pallet case as this prevents product from slipping off the edge of the pallet. Both of these methods help to minimise movement of the product as it is being stacked and keep the pallet stable, thus reducing the risk of transit damage.  Another method that is sometimes used is a former that slides up the pallet stack to help it hold its shape as the pallet is stacked.

When automating the palletising process of unstable products, the most commonly used method is to palletise directly onto a pallet that is placed on a wrapper.  This allows the robotic palletiser to place a certain amount of product onto the pallet, then the pallet can be wrapped, before placing the next layers. This helps to keep the product in position as the stack is formed and therefore creates a stable pallet.

Whether or not your pallet stacking process can be automated will depend entirely on the product being palletised.  In most cases it is possible for unstable product to be automatically palletised but there are a few cases where it may not be possible.  Areas that may need to be considered when automating palletising of unstable products include:

  • Is the product being palletised into a cardboard sleeve?
  • Does the product have to be held in place whilst the next product is placed on top?
  • Does the pallet need to be shrink wrapped as the pallet is stacked to stop the product from slipping off the pallet?
  • Is the product uneven in shape?
  • Do the bag contents move around as the bag is picked up?

As you can see, it is very rare that unstable product can’t be automatically palletised. If you would like to know more about what products can be automatically palletised, or would like to arrange a free trial of your product on a palletiser, please contact us on 01223 499488 or contact us at

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