"ASRS" covers a wider range of equipment than most people expect walking into the category. A carousel that spins slow-moving items to a picker, a crane that retrieves totes from a narrow aisle, and a robot that climbs through a cube-shaped structure are all technically automated storage and retrieval systems, and they solve different problems in different ways.
This is a field guide to where full 3D cube storage sits in that landscape: what the other major ASRS types do well, what they're built for, and where the mechanics of 3D robot movement set cube storage apart.
The Major ASRS Types
Automated storage systems generally break into three delivery methods: shelf or tray delivery (an entire shelf comes to the operator), bin or tote delivery (a container comes to the operator), and robotic delivery (a robot handles retrieval directly). Within those, eight common system types cover most of what's deployed today.
Vertical Carousel Modules (VCM)
A series of carriers rotate vertically around a track, similar to a Ferris wheel, delivering slow- to medium-velocity items to an operator. Standard throughput runs 100–400 lines per hour, with carrier capacity up to 1,430 pounds. It's a mature, reliable technology, well suited to slower-moving inventory in a compact footprint.
Horizontal Carousel Modules (HCM)
Dense storage bins mounted on an oval track rotate horizontally to bring items to an operator. Installed in pods, throughput can reach up to 600 lines per hour, with carrier capacity up to 2,000 pounds. HCMs offer strong space utilization for items and cases alike.
Vertical Lift Modules (VLM)
Two columns of trays with a center-mounted inserter/extractor deliver items to a waist-high pick window. VLMs handle 125–350 items per hour in standard configurations and dynamically store trays as close as one inch apart, which their manufacturers report can save up to 85% of floor space compared to static shelving. VLMs are the most adaptable of the shelf-based systems when inventory sizes change frequently.
Crane-Based Mini-Load ASRS
A crane-mounted load handler works a single, extremely dense rack aisle, delivering cases, totes, or trays to a workstation at the aisle's end. Single-deep configurations run 60–100 lines per hour; double-deep configurations reach roughly 120 putaways and picks per hour. Mini-load systems are a common choice above roughly 10,000 totes or 25,000 SKUs.
Vertical Buffer Modules (VBM)
A smaller-scale relative of the mini-load, built for operations under about 10,000 totes or 25,000 SKUs that don't need (or can't yet justify) a full mini-load system. A movable mast retrieves totes from an enclosed shelving system, and units can be linked by conveyor to remote picking stations.
Robotic Shuttle Systems
Independent shuttles travel level to level on rails within a rack structure, retrieving cases, totes, or trays weighing 35–110 pounds. Base throughput runs 200–700 lines per hour per aisle, and adding shuttles can scale throughput up to roughly 300–1,000 lines per hour. Shuttle systems are modular and can expand with minimal structural changes.
Robotic Cube Storage (Grid-Based)
Bins stack directly on top of each other inside a dense grid, with robots working at the top of the structure to shuffle, sort, and retrieve them for delivery to a port. This is the design AutoStore popularized, and it delivers strong density for small-item, high-SKU operations. Because robots operate from the top of the grid, retrieving a bin buried deeper in the stack can require temporarily moving the bins above it.
Floor Robots (AGVs/AMRs)
Mobile robots retrieve portable shelving units and bring them to an operator, rather than the operator or a crane going to fixed storage. Throughput runs 100–300 lines per hour depending on fleet size, with standard shelving capacity of 1,000 pounds (up to 3,000 pounds in heavy-duty configurations). AGVs follow fixed, marked paths; AMRs navigate freely using onboard mapping.
Where Full 3D Cube Storage Fits
Attabotics builds a variant of cube storage that differs mechanically from the grid-based design above. Instead of robots working from the top of a stacked grid, the Attabot™ robot moves both horizontally and vertically throughout the entire Cubic Storage Structure, at 2.7 meters per second, reaching any storage location directly.
That distinction matters because it removes the specific tradeoff grid-based cube storage carries: no bin has to be moved out of the way to reach one stored beneath or behind it, because the robot isn't confined to a single plane of travel. The result, per Attabotics' published figures:
- Direct access to any storage location in under 90 seconds
- Up to 85% reduction in warehouse space versus traditional racking
- No single point of failure: the system keeps running if one robot goes down
- Structure height up to roughly 12 meters (39'5"), depending on the facility
Comparing the Types at a Glance
| ASRS Type | Movement | Typical Throughput | Best Fit |
|---|---|---|---|
| Vertical Carousel Module | Carriers rotate vertically to operator | 100–400 lines/hr | Slow- to medium-velocity items, compact footprint |
| Horizontal Carousel Module | Bins rotate horizontally to operator | Up to 600 lines/hr | Items and cases needing high space utilization |
| Vertical Lift Module | Extractor retrieves trays from two columns | 125–350 items/hr | Frequently changing inventory sizes |
| Mini-Load ASRS | Crane works a single dense aisle | 60–120 lines/hr | 10,000+ totes or 25,000+ SKUs |
| Vertical Buffer Module | Mast retrieves totes in enclosed shelving | Scales with configuration | Under 10,000 totes or 25,000 SKUs |
| Robotic Shuttle | Shuttles travel level to level on rails | 200–1,000 lines/hr | Cases/totes needing high throughput per aisle |
| Robotic Cube Storage (grid) | Robots work top of a stacked bin grid | Varies by fleet size | High-SKU, small-item storage |
| Floor Robots (AGV/AMR) | Mobile robots bring shelving to operator | 100–300 lines/hr | Slow- to medium-velocity, flexible layouts |
| 3D Cube Storage (Attabotics) | Robots move in 3 dimensions throughout the structure | Direct access, any location, under 90 sec | High-SKU, mixed-item, each-pick operations needing direct access without reshuffling |
Choosing Between Categories
No single ASRS type is the right answer for every operation, and most large facilities end up running more than one technology matched to different inventory profiles. A few starting questions help narrow the field:
- How many SKUs, and how fast do they move? Slower-moving, lower-SKU-count inventory fits carousels and VLMs well. High-SKU-count, each-pick operations tend to outgrow those systems as complexity grows.
- Does reaching one item ever require moving others? Mini-load, VBM, and grid-based cube storage can require this in certain configurations. Robotic shuttle systems can require it in deep-lane setups. Full 3D cube storage, by design, doesn't.
- What does the building allow? Systems built around fixed aisles need a relatively regular footprint. Structures designed to work around existing walls and columns, like Attabotics', fit a wider range of buildings.
- How much does throughput need to scale, and how fast? Shuttle and floor robot systems scale by adding units to an existing structure. Cube storage systems scale by expanding the storage block itself.
FAQ
What's the difference between grid-based robotic cube storage and full 3D cube storage?
Grid-based systems, the design AutoStore popularized, have robots working from the top of a stacked bin grid, which can require moving bins to reach one stored deeper in the stack. Full 3D cube storage, like Attabotics' Cubic Storage Structure, has robots moving in three dimensions throughout the entire structure, reaching any location directly without needing to move other inventory first.
Which ASRS type has the highest throughput?
Among the types compared here, robotic shuttle systems report the widest published range, up to roughly 1,000 lines per hour with enough shuttles added to the system. Actual throughput for any system depends heavily on configuration, SKU profile, and fleet or robot count.
Is cube storage better than mini-load ASRS?
It depends on the operation. Mini-load systems are a strong fit above roughly 10,000 totes or 25,000 SKUs when throughput per aisle is the priority. Cube storage, particularly full 3D systems, tends to fit better when SKU variety and each-pick complexity are high and direct access to any single item matters more than aisle-based throughput.
Do all ASRS types require a purpose-built structure?
Most do, including carousels, VLMs, mini-load, and cube storage systems. Floor robot (AMR) systems are the exception, working with portable shelving on the existing floor rather than a fixed structure.
Can different ASRS types be combined in the same facility?
Yes, and it's common in larger operations. Matching different technologies to different inventory profiles, rather than forcing one system to handle everything, is a standard approach in facility design.
Conclusion
Every ASRS type trades off density, throughput, and flexibility differently, and the right one depends on SKU count, pick profile, and what the building can support. Full 3D cube storage sits at the high-density, high-flexibility end of that range, differentiated from grid-based cube storage specifically by removing the top-of-grid constraint that requires reshuffling. For operations with high SKU variety and each-pick complexity, that structural difference tends to be the deciding factor.
Sources
- Kardex — 8 Types of Automated Storage and Retrieval Systems (ASRS): A Deep Dive — category taxonomy, throughput and capacity figures for VCM, HCM, VLM, mini-load, VBM, robotic shuttle, grid-based robotic cube storage, and floor robots (AGV/AMR)
- Attabotics — Warehouse Automation Technology — Attabotics robot specs, structure specs, space reduction figure, FAQ
