Pallets for automated storage and retrieval systems (AS/RS)
A pallet in an automated warehouse has just one key task: never to bring the line to a halt. Any deviation in dimensions, weight or rigidity—even by a single millimetre—will sooner or later trigger a system alarm, cause the stacker crane to stop and result in costly machine maintenance.
What is an automated storage and retrieval system (AS/RS)?
Automated storage and retrieval systems (AS/RS) are state-of-the-art logistics environments in which autonomous stacker cranes, shuttle systems or miniload systems – controlled directly via warehouse management systems (WMS) and PLCs – are responsible for the transport, storage and retrieval of goods.
For these systems, the pallet serves as the direct ‘mechanical-logistical interface’. It must therefore have absolutely reproducible dimensions, a constant weight and unchanging structural rigidity, as the entire automated system operates with tolerances in the millimetre range. Unlike a traditional high-bay warehouse, which is operated by forklift drivers, there is no room for even the slightest deviation from the norm in AS/RS systems. A single warped board, a broken skid or a protruding nail can block the forks of the stacker crane or the optical sensor, thereby paralysing the operation of the entire distribution centre.
What is the most important factor when it comes to pallets for automation?
We can identify five key features that a transport vehicle must have in warehouse automation:
1. Absolute dimensional repeatability
In automated warehouses, it is essential that every pallet has identical dimensions (the Euro standard: 1200 × 800 × 144 mm). Stacker cranes and shuttle trolleys are designed for a fixed format. Plastic pallets, produced using injection moulding, guarantee identical dimensions for each unit, eliminating sensor reading errors and the risk of collisions.
2. No nails, splinters or loose parts
Protruding nails or splinters of wood are the most common cause of mechanical damage to roller and belt conveyors. What is more, small splinters and wood dust contaminate photoelectric cells and safety sensors. Control systems interpret them as obstacles on the route, which generates false alarms and forces a manual restart of the line. A plastic pallet is completely uniform and free of metal components.
3. High structural rigidity
A pallet designed for automated handling must not bend or twist under the weight of the cargo – particularly when stored on cantilever racks. Excessive deflection shifts the load’s centre of gravity, which means that advanced vision systems and automated grippers may incorrectly identify the pallet’s position, rejecting it to the error station.
4. Clean, uniform and stable runners
Any defects in the runners, unevenness or damp patches on wooden pallets cause slippage, increase rolling resistance on the rollers and result in uneven loading of the electric drives. The smooth, consistent surface of the plastic pallet’s runners ensures smooth movement and stable operation of the entire transport system.
5. Controlled and consistent kerb weight
The algorithms that control warehouse automation are based on precise calculations of the permissible weight: load weight + pallet weight. The weight of traditional wooden pallets can vary by as much as several kilograms, depending on their moisture content. Plastic pallets have a constant tare weight, which facilitates the calibration of system scales and overload protection mechanisms.
Shelf load capacity certified to ISO 8611
In AS/RS warehouses, the key parameter is the racking load capacity, i.e. the ability of the load-bearing structure to rest safely on the crossbeams under maximum load without exceeding the permissible deflection.
When selecting a medium for automation, one must not rely solely on marketing claims. It is essential to have certified parameters obtained from laboratory tests conducted in accordance with the international standard ISO 8611. Only objective destructive and load tests in accordance with ISO 8611 guarantee that a pallet placed in an automated racking system will maintain the required rigidity and will not cause a system failure.
Wood vs plastic in AS/RS warehouses – A summary of the differences
Any flaw in a wooden pallet could potentially bring logistics operations to a standstill, whereas a plastic pallet eliminates these risks right from the warehouse design stage.
Libra Partners’ dedicated automation pallets
Our plastic pallets in the standard Euro size (1200 × 800 × 144 mm) have been specifically designed to meet the stringent requirements of AS/RS systems. Their geometry and high racking load-bearing capacity (confirmed by tests in accordance with ISO 8611) ensure they work perfectly with stacker cranes, shuttle trolleys and conveyor systems. All pallets in this series are identical from the perspective of optical sensors and laser pallet profile scanners.
The introduction of plastic pallets from Libra Partners eliminates breakdowns caused by wood contaminating the line, reduces the number of false detections and minimises the need for maintenance intervention. As a result, the overall equipment effectiveness (OEE) of the entire AS/RS system increases significantly.
FAQ – Frequently Asked Questions
Is every Euro pallet suitable for AS/RS warehouses?
Definitely not. Warehouse automation requires pallets with very tight dimensional tolerances, excellent rack stability and flawless skid quality. A standard, randomly selected wooden Euro pallet very often fails to meet these criteria and is rejected by the so-called contour inspection stations (inbound scanners).
Why do inspection stations so often reject wooden pallets?
As a natural material, wood is constantly changing – it swells when exposed to moisture, shrinks or warps during use. For the sensors and measuring lasers in the automated warehouse, these changes mean that permissible limits are exceeded, resulting in the pallet being automatically stopped and removed from the line.
Won’t a plastic pallet be too slippery for the machine’s metal rollers?
No. The design of plastic pallets intended for AS/RS systems takes this into account. The skids of the carriers feature a specially designed material structure and optional rubber anti-slip elements. This ensures an optimal coefficient of friction and guarantees safe, stable movement on the rollers, as well as preventing slippage during sudden braking of the stacker cranes.
How can I be sure that the plastic pallet I’ve chosen will meet the requirements of my system?
The pallet specifications (dimensional tolerances, weight, deflection and load-bearing capacity, as confirmed by ISO 8611) must be consulted and verified with the AS/RS system integrator (technology supplier). Compliance with the integrator’s guidelines is also essential for maintaining the full warranty on the automated equipment.
Does switching from wooden pallets to plastic ones require any changes to the software or hardware?
In most cases, this does not require any mechanical or programming changes. All that is needed is to enter the pallet’s fixed geometric parameters into the WMS system and carry out tests on the production line. Thanks to their perfect dimensional and weight consistency, plastic pallets make it much easier to calibrate the entire system.
Summary: Are you implementing or designing a state-of-the-art automated warehouse and want to eliminate the risk of costly downtime and losing your integrator’s warranty? Contact the experts at Libra Partners. We will help you select the optimal plastic pallet model and deliver a free trial batch directly to your production line.
Rafał Szarzała Centrum Produkcyjno-Handlowe “Szarpol”
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