Automation of small parts logistics Stacker crane, shuttle or AutoStore-AKL?

You want an efficient solution for the storage of your containerized small parts?

Then the question of the degree of automation usually arises. This is because the dynamics of the markets, also driven by e-commerce, as well as rising personnel costs are increasingly ruling out intralogistics solutions that function according to the "person-to-goods" principle. When planning an automated solution with foresight, it is therefore necessary to clarify: Which goods-to-person system best covers my individual requirements and targets in terms of performance and efficiency in the long term? Whether storage and retrieval machines (SRM), shuttles or AutoStore - the choice is vast. Anyone who has ever visited a logistics trade fair such as LogiMAT or HMI is probably "flattened" by the variety of technologies on offer.

But the decision for an individually suitable solution needs to be well considered. After all, the investments to be made must ultimately pay for themselves and the technology should still be suitable for the range of articles and orders in 10 or 20 years. To put it in a nutshell: Each solution naturally has its advantages and disadvantages, which must be weighed up in the light of strategic considerations. You can find initial information that may be helpful at this point in this article.

The most important questions at a glance:

"Goods-to-Person" (WzP) refers to the fact that requested items - for example in containers - are supplied to assigned picking locations from a warehouse. After picking, the staging unit is transported back to the warehouse. Walking distances are eliminated and picking performance is increased.

An automated small parts warehouse (AS/RS) is used for the compacted and dynamic storage of small-volume goods in totes, cartons and/or on trays. It is operated via storage and retrieval machines (SRM) or shuttle vehicles. An AS/RS can be designed for single- or multiple-deep storage. With the help of multiple load handling devices, weights of up to 300 kg can be picked up and transported per tour.

A storage and retrieval machine (SRM) is a fully automatic mast vehicle that travels in an aisle between the rows of racks, usually guided by rails, and performs the storage and retrieval operations. Shuttles usually handle the horizontal movements into the X-axis of the rack aisle. In this case, the vertical movements of the storage bins into the Y-axis are performed by separate bin lifters.

Definition & classification of miniload systems with storage and retrieval machines (SRM)

Automated small parts warehouses (AS /RS) with stacker cranes (SRM) in the aisles are a "classic" in intralogistics and have been tried and tested thousands of times worldwide. Storage and retrieval machines (also called "rack vehicles") consist of a chassis, one or two masts, a hoist unit and one or more load handling devices. Containers, cartons and/or trays can be used as load carriers. With most manufacturers, heights of up to approx. 25 meters can be realized and their use is possible for almost all ambient temperatures (also use in deep-freeze areas down to -30oC).

Definition & Classification Shuttle AKL

Shuttle systems for automated small parts warehouses (AS/RS) are also no longer new, but have been installed since the 2000s. The difference compared to an AS/RS with stacker cranes is that lifting and travel movements are decoupled from each other. In addition, the vehicles (shuttles) are smaller and usually transport only one tote (or carton) at a time. However, several shuttle vehicles can then travel simultaneously in each aisle or level. They are able to switch between these aisles or levels in parallel. The lift is performed by vertical lifters. Heights of up to 25 meters are possible, similar to those of miniloads.

Definition & Classification AutoStore

AutoStore is a development of the Norwegian company of the same name, which is offered worldwide through sales partners (system integrators). This solution is a robotic compact storage system that does not require rack storage or aisles. The containers are simply stacked, with the stacks separated by aluminum profiles. This saves space. The robots travel along the top of a rack lattice structure (grid) in both longitudinal and transverse directions and store and retrieve the totes. As a rule, however, AutoStore systems are only designed for construction or stacking heights of up to approx. 5 meters.

Comparison between the three systems

In favor of RBG solutions is the fact that a high storage density is achieved through good use of the space volume in the vertical direction and the option of double- to multiple-deep storage. In addition, the technology is robust, proven over decades and works reliably. Companies that do not expect major changes in terms of throughput to be achieved are well served by an AS/RS solution. However, their scalability (depending on the design) is limited to some extent, as you usually only use one or two vehicles per aisle. It is also important to reserve space in the planning phase - as far as possible - where additional aisles can be installed if required.

As with an AS/RS-operated miniload, shuttle applications also require a corresponding lead time. They are also characterized by high storage density and good performance values, but are more flexible in their approach. This means that additional shuttle vehicles can be "sent in" to the plant if required due to increased order volumes. Shuttle lifters (elevators) also make it possible for shuttles to change levels, so that the vehicles are always deployed where they are needed at the moment to handle the order load. Depending on the design of the shuttle system, a higher throughput rate can usually be achieved than with a "classic" miniload with stacker cranes (with the same number of storage locations). However, shuttle solutions are usually more expensive than comparable AS/RS systems.

AutoStore systems can also be integrated into existing halls with low ceilings with comparatively little effort. Despite the limited overall height, the storage density - converted to a square meter of space - is very high. Similar to the shuttle, the solution is easily scalable. However, only standard containers are suitable and only about ten percent of the stocked range is directly accessible. A dedicated ABC classification is therefore indispensable. Of course, the larger the number of storage containers, the greater the space required for the solution, as the warehouse tends to expand in width and cannot take advantage of the height benefits as with RBG-AKL or Shuttle. And there may also be restrictions in terms of throughput requirements, if only because of the necessary stock transfers (as soon as you have to reach the "lower" bins). However, if the basic conditions of article and order structures as well as line requirements fit, AutoStore is a fast and inexpensive acquisition that is becoming increasingly popular among logistics companies.

Which system is suitable for which application?

Automated goods-to-person solutions based on SRM, shuttle and AutoStore are always a good solution when growing order volumes need to be handled efficiently with ever smaller order sizes. The savings in space and personnel are additional arguments in favor of the automated systems. The personnel-intensive nature of conventional warehouses has been felt in particular by companies that are active in e-commerce or have expanded their activities. This share of total sales has again recorded significant growth rates since the outbreak of the pandemic at the latest. These growth rates will also stabilize at a high level after the pandemic. In principle, however, these systems can be profitable wherever high throughput rates with a minimized error rate are required.

However, important parameters that ultimately determine the prioritization of one of the three solutions for the storage of totes are also of a technical and economic nature. This can have a restrictive effect in existing halls. Shuttle warehouses and AutoStore solutions, on the other hand, can be dimensioned more flexibly, as they can still demonstrate their advantages even at low room heights. They are also more energy-efficient than moving heavy-duty SRMs. If a vehicle or piece of equipment fails, no aisle comes to a standstill, unlike in the case of AS/RS-AKL, and the remaining shuttles continue to work reliably instead. However, miniload systems with stacker cranes are also characterized by the fact that they are a widespread, standard market technology that can be evaluated on a manufacturer-neutral basis. This means that there is not necessarily any dependence on specific individual manufacturers for the selection of suppliers, for operation, and also for maintenance and spare parts.


Conclusion and a look at the costs

As is so often the case with comparisons: There is not THE one solution to be preferred. For low ceiling heights, both shuttles and AutoStore are suitable, which are basically more flexible than RBG-AKLs. In contrast to AutoStore, which is only suitable for standard containers, shuttles and SRM-AKLs can be equipped with load handling devices that can also safely handle varying container sizes. Furthermore, shuttles and SRM-AKLs are selected for high throughput performance requirements where there are limitations with AutoStore solutions. For very high performance requirements, shuttle solutions are more likely to be found.

Those who also favor shuttle solutions for reasons of possible better performance must also provide for higher initial investments in addition to the operating costs. However, whether the selected system will actually deliver the performance desired in the course of order processing in the future also depends on the extent to which additionally required modules are conclusively coordinated with it. In addition to the conveyor system connection and the connected picking workstations, this applies in particular to the material flow control software (WMS, MFC) that is used. And for SAP customers, of course, also the controllability and compatibility with SAP EWM.

More information on the different types of warehouse technology can be found at