In brief
In an automated miniload warehouse one storage and retrieval machine per aisle serves every level in three axes. In a shuttle system, vehicles on each level handle horizontal transport and a lift handles vertical transport. Every further difference in throughput, scalability, availability and effort follows from that separation.
The one difference everything else follows from
Both designs store light unit loads in standardised load carriers — totes, trays, cartons. The difference is structural, and it shapes every figure:
- In an automated miniload warehouse (AKL), one storage and retrieval machine serves every level of an aisle. VDI 3630 characterises these systems by machines controlled in three axes as a rule. Horizontal and vertical movement therefore sit in the same machine.
- In a shuttle system under VDI 2692 Part 1, vehicles on each level handle horizontal transport and a lift handles vertical transport. The two movements are decoupled.
Decision criteria compared
| Criterion | Miniload | Shuttle system |
|---|---|---|
| Movement principle | One machine per aisle, three axes | Vehicles per level plus lift, decoupled |
| Throughput | Limited by the cycle time of one machine | Scales with the number of vehicles |
| Height versus performance | More height lengthens the cycle | Height and throughput largely independent |
| Machine failure | The whole aisle stops | One level stops, the rest keeps working |
| Control | Manageable, one machine per aisle | More demanding: traffic, priority, handover |
| Maintenance | Few large units | Many vehicles, dedicated maintenance concept |
| Investment | Lower at moderate throughput | Rises with vehicle count |
The application case comes before the design
VDI 3630 names two typical applications for the miniload, and the distinction bears directly on sizing: order picking system or buffer system. A buffer is sized against throughput peaks, a picking system against lines per hour. Leave that question open and you are comparing two quotations that solve different problems.
The same order applies to the design decision: required performance over time first, design second. A shuttle system that only matches the peak of a miniload costs more without delivering more.
Underestimated effort on each side
With the miniload, the coupling of height and cycle time is underestimated. Every additional metre lengthens the cycle and reduces throughput — storage capacity grows, performance does not. The failure risk is underestimated too: if the machine stops, the aisle stops.
With the shuttle system, control, power supply and maintenance are underestimated. VDI 2692 Part 1 devotes separate sections to power supply, communication, control concept and system maintenance — not out of thoroughness, but because that is where the effort sits. The lift adds to it: it becomes the new bottleneck when many levels must retrieve at once.
Five questions for the direction
- What is the required peak performance — and how often does the peak occur?
- Picking or buffering? Doing both calls for a separate calculation.
- How much height does the building allow, and how much of it converts into performance?
- What does an aisle outage cost in operation — in hours and in orders?
- Who will operate the system later, and under which maintenance concept?
Basis
VDI 3630 "Automatic miniload warehouses (AKL)", 2006-08, and VDI 2692 Part 1 "Shuttle systems for small load carriers", 2015-03. Both editions were confirmed against the VDI guideline list on 5 September 2026.