Shuttles or stackers?

MOST FIRMS that have to move quantities of palletised goods moving in, out or through a warehouse are familiar with that old stalwart – the stacker crane. Indeed it is no exaggeration to say that in many cases the warehouse is designed and built around the craneage.

The downsides of stacker cranes

However, in terms of operational efficiency stacker cranes are far from ideal. They are undeniably chunky. They consume a lot of material in their construction, and a lot of energy moving all that mass around. Partly as a result they require significant upfront capital investment, which is a particular challenge for smaller businesses with budget constraints.

They are also very wasteful of available, expensive, floor area. They require generous aisle space to work in which reduces the overall storage density within the warehouse. They are not well suited to more space-efficient deep storage. They require the site to be all on one level, which for a warehouse of any magnitude often means building on a flood plain. 

Perhaps most fundamentally, warehouse systems built around a stacker crane concept are fundamentally inflexible. The specific configuration of locations, aisles and cranes places a fixed limit on the maximum throughput of the facility: increasing throughput is likely to require a fairly large scale and expensive redesign and rebuild.

Shuttles and space 

Stacker cranes still have their place but for many palletised warehouse operations there is an increasingly attractive and viable alternative in the form of shuttle systems.

Pallet shuttles are small vehicles with a low height, and with a footprint essentially that of the pallet they are moving. They move on rails within the storage lanes of the racking system to bring pallets to and from a loading/unloading end aisle which can also be used to transfer pallets between storage lanes. Shuttles operate in two dimensions in each ‘layer’ of the racking system, but can be transferred vertically as well as between lanes. The latter is carried out automatically, through the management system and, unlike some earlier systems, without the use of a forklift truck to effect the transfer. Movu Atlas shuttles, for example, can carry pallets of 1 m x 1 m, or 1 m x 1.2 m, weighing up to 1,500 kg. 

No limits on vertical height

Besides greatly reducing the amount of ‘wasted’ aisle space required, this approach has a number of advantages. There is no particular limit to vertical height – 18 metres is commonplace, and we have one client whose racking extends to an eye-popping 46 metres. Odd-shaped pockets of the site, whether this is in the plans or because of uneven ground, can be brought into use economically simply by using some shorter lanes. And because shuttles, unlike stacker cranes, in no sense fixed, it is relatively straightforward and economical to reconfigure the racking if needs be – the racking itself is of modular design.

Integrating with Autonomous Mobile Robots (AMRs), picking arm robots or with other forms of automation permits a high degree of automation that can yield further sustainability benefits. These can support areas of a warehouse that does not have to support regular human labour so can be run ‘lights out’ or with reduced heating. Cold store operations, meanwhile, can be made more energy efficient – Movu equipment, for example stands out as capable of working in temperatures down to -25° C.

Shuttles offer a flexible, scaleable, modular approach to automation. Systems are quick to install, even in existing buildings and on awkward sites, simple to integrate, and easy to reconfigure or expand with minimal impact on ongoing operations. 

Stefan Pieters is CEO of Movu Robotics 

For more information: 

www.movu-robotics.com