A stacker crane system for high-bay pallet warehouses should be designed from inventory data, required throughput, pallet quality, fire protection and maintenance access—not from rack height alone. This automated pallet warehouse design guide explains how to select an AS/RS stacker crane layout, calculate storage capacity, define warehouse automation interfaces and control operational risks. The key terms are high-bay storage, pallet handling, load unit, WMS, WCS and stacker crane. A suitable design can increase storage density, but an unsuitable one can create pallet jams, low crane utilization, difficult maintenance and unsafe recovery work.
Most projects begin with a practical problem: the warehouse has reached its floor-space limit, operators spend too much time traveling, pallet locations are difficult to control, or labor availability changes by shift. A stacker crane system addresses these problems by moving pallets automatically inside dedicated rack aisles.
However, automation does not automatically solve poor warehouse planning. The system must match:
Daily and peak pallet receipts and dispatches.
Number of stock-keeping units and pallet positions.
Pallet dimensions, weight and bottom-board condition.
Required storage temperature and humidity.
FIFO, FEFO or batch-traceability rules.
Fire protection requirements and local building regulations.
Available maintenance access and emergency procedures.
Interfaces between the WMS, WCS, PLC and material-handling equipment.
In a conventional warehouse, forklifts can often compensate for layout changes. In an automated high-bay warehouse, rack geometry, conveyor height, barcode position and software logic are interdependent. A change from a 1,000 kg pallet to a 1,500 kg pallet, for example, can affect rack beam loading, crane load capacity, acceleration settings and floor design.
Coca-Cola HBC has publicly documented automated logistics projects in Europe, including high-bay pallet storage and automated material flow. Public supplier and company material shows the typical design logic: production or receiving areas connect to pallet conveyors, the warehouse management layer controls inventory, and automated storage and retrieval equipment handles repetitive pallet movements.
The lesson is not that every beverage plant needs the same number of aisles or cranes. The verified lesson is that high-volume operations benefit when pallet identification, conveying, storage and dispatch sequencing are designed as one process rather than purchased as separate machines. Coca-Cola HBC case information is available through the company’s published automation and logistics communications and supplier case-study archives; project figures should be confirmed directly against the specific site before being used for budgeting.
Public case studies from suppliers such as SSI SCHÄFER, Jungheinrich, Dematic and Swisslog repeatedly identify pallet quality, barcode readability and standardized load units as prerequisites for reliable AS/RS operation. These are not cosmetic details. A damaged pallet can fail at the transfer station, become unstable in the rack or require a manual recovery intervention.
For a new project, the useful takeaway is measurable: define an acceptance standard for pallet flatness, broken boards, overhang, load height, wrapping and barcode placement before commissioning. Do not rely on a general statement such as “the warehouse uses standard pallets.” Specify the actual pallet type, tolerances and inspection method in the user requirement specification.
Important verification note: supplier case studies often report installed capacity or design throughput, not independently audited operating performance. Treat published figures as reference information, not as a guaranteed result for a new UNISTAR project or any other supplier installation.
Prepare at least 12 months of historical data if the operation already exists. If the warehouse is new, use signed sales forecasts, production plans and seasonal scenarios rather than a single average day.
| Data group | Required information | Why it matters |
|---|---|---|
| Inventory | Peak pallets, average pallets, SKU count, batch and expiry rules | Determines storage capacity and slotting logic |
| Flow | Inbound pallets/hour, outbound pallets/hour, peak 15-minute rate | Determines crane, conveyor and station capacity |
| Load unit | Pallet length, width, height, gross mass, overhang and pallet condition | Determines rack clearances and crane load rating |
| Building | Clear height, column grid, floor load, settlement, seismic conditions | Determines rack and crane feasibility |
| Operations | Shift pattern, order cut-off time, dispatch sequence and labor model | Determines buffering and operating windows |
| Safety | Fire strategy, evacuation routes, guarding and emergency access | Determines compliance and recovery design |
Warehouse layout in CAD or BIM format.
Inventory and transaction data in CSV or database export format.
Pallet specification sheets and photographs of typical damage.
Laser distance meter or verified building survey.
Floor flatness, levelness and load-bearing reports.
Fire engineering report and local authority requirements.
Electrical supply information and network architecture.
WMS interface documentation and ERP process maps.
Risk assessment based on applicable machinery and workplace safety rules.
Use standards applicable to the project location. Common references include EN 528 for rail-dependent storage and retrieval equipment, EN 15629 for specification of storage equipment, EN 15635 for use and maintenance of storage equipment, ISO 3691-5 where applicable to driverless industrial trucks, and local fire codes such as NFPA requirements in the United States. The final compliance list must be confirmed by the project engineer and the authority having jurisdiction.
Tools: pallet scale, tape measure, calipers, pallet inspection form and sample pallets.
Action: Record pallet length, width, total height and gross mass. Measure the highest product position, stretch-film overhang and any labels that may interfere with sensors. Inspect representative pallets from every supplier or production line.
Parameters: Define minimum and maximum pallet dimensions, maximum mass, center-of-gravity limits, allowable overhang and acceptable pallet damage. The crane, rack and transfer equipment should be rated for the maximum declared load, not the average load.
Check: Run a sample inspection using normal, borderline and damaged pallets. Confirm that the pallet remains stable on the conveyor and that the barcode is visible from the required scanner position.
Failure fix: If pallet dimensions vary beyond the proposed tolerance, separate the load classes, introduce a pallet repair or repalletizing station, or redesign the storage locations. Do not solve uncontrolled variation only through software.
Tools: inventory spreadsheet, demand forecast and slotting model.
Action: Calculate the required number of pallet positions using peak inventory and a documented reserve policy.
Parameters: A basic calculation is:
The reserve factor must come from the business plan. It should reflect seasonal growth, supplier variability and the time required to replenish or dispatch stock. Do not confuse pallet positions with pallets moved per day: capacity is a storage measure, while throughput is a movement measure.
Check: Test at least three scenarios: normal operation, seasonal peak and business-growth case. Verify that every SKU and batch rule can be stored without forcing incompatible products into the same location.
Failure fix: If the required capacity exceeds the building envelope, compare increased height, more aisles, narrower aisle pitch, external overflow storage or inventory policy changes. A taller rack is not automatically the lowest-cost solution because it may increase structural, fire and maintenance requirements.
Tools: transaction history, time study, crane cycle-time model and simulation software.
Action: Separate inbound, replenishment, internal relocation and outbound movements. Measure the highest demand interval, not only the daily average.
Parameters: A simple planning relationship is:
For each crane, consider travel distance, lift distance, acceleration and deceleration, load transfer time, empty travel, dual-command cycles and queueing. A single-cycle estimate is not sufficient if the crane performs combined storage and retrieval cycles.
Check: Verify that the crane is not planned at 100% utilization. The available operating time must account for planned maintenance, shift breaks, fault recovery, startup and traffic imbalance. The exact utilization target should be set through simulation and supplier guarantees.
Failure fix: If simulated queues occur at inbound or outbound stations, add stations, rebalance aisles, change wave release logic or add crane capacity. If only one aisle becomes overloaded, increasing total warehouse capacity may not solve the bottleneck.
Tools: rack-loading tables, structural calculations, CAD layout and building survey.
Action: Arrange single-deep or double-deep storage according to access requirements, SKU velocity and inventory rotation. Define rack height, storage levels, aisle pitch, end clearances and transfer-station locations.
Parameters: Include the maximum load mass, rack deflection limits, crane guide-rail tolerances, floor settlement, thermal movement and seismic loads where relevant. Double-deep storage can increase density, but it may reduce direct accessibility and complicate FIFO or FEFO execution.
Check: Confirm that the rack design supports the heaviest load at every affected level and that the building floor can accept concentrated column and rail loads. Review collision clearances at the crane mast, load-handling device and pallet positions.
Failure fix: If the floor or building structure cannot meet the design loads, reduce height, strengthen the slab, use an independent structural solution or revise the layout. Never compensate for structural uncertainty by reducing safety margins.
Tools: material-flow diagram, conveyor capacity calculation, barcode specification and ergonomic assessment.
Action: Map every pallet route from receiving to storage, storage to picking or production, and storage to dispatch. Identify inspection, weighing, wrapping, labeling and quarantine points.
Parameters: Define conveyor speed, pallet spacing, accumulation length, sensor positions, stop logic and maximum queue size. Specify whether each station supports one pallet type or several load classes.
Check: Conduct a physical walk-through using an empty pallet and a fully loaded pallet. Confirm that operators can safely reach labels, remove rejected pallets and perform inspection without entering guarded areas.
Failure fix: If a station becomes a bottleneck, increase the number of parallel lanes, separate quality inspection from normal flow or move labeling upstream. If pallets stop unexpectedly, check photo-eye alignment, sensor logic, pallet overhang and accumulation-pressure settings.
Tools: interface control document, state diagrams, test database and network diagnostic software.
Action: Define which system owns inventory, task creation, route assignment, equipment commands, alarms and recovery decisions.
Parameters: Document message fields such as pallet ID, SKU, batch, quantity, source location, destination location, priority, timestamp and status. Define acknowledgements, timeouts, duplicate-message handling and restart behavior.
Check: Test normal, delayed, duplicated, rejected and interrupted messages. Confirm that a pallet cannot be declared stored in the WMS until the physical location and load identity have been verified.
Failure fix: If inventory discrepancies appear, stop automatic reassignment, quarantine the affected pallet ID and reconcile the last confirmed physical state. Avoid manual database edits without an audit trail.
Tools: risk-assessment template, safeguarding drawings, lockout/tagout procedure and maintenance access plan.
Action: Define perimeter guarding, access gates, interlocks, emergency stops, safe speed zones, rescue provisions and isolation points. Provide access for inspection of rails, cables, sensors, brakes, drive systems and load-handling devices.
Parameters: The safety design must follow the machinery risk assessment and applicable local legislation. Separate normal operator access from controlled maintenance access. Provide a documented method for recovering a load after a crane fault.
Check: Test every gate switch, emergency stop, safety circuit, restart interlock and alarm under commissioning conditions. Confirm that an emergency stop removes hazardous motion while preserving the information needed for safe recovery.
Failure fix: If personnel can enter a hazardous zone without a controlled isolation process, suspend commissioning and correct the safeguarding design. Do not depend on warning signs or operator training as the only control.
Tools: commissioning checklist, calibrated test weights, barcode test set, network test tools and acceptance-test protocol.
Action: Commission in stages: mechanical inspection, electrical energization, safety circuits, empty travel, loaded travel, conveyor integration, WCS logic, WMS integration and production ramp-up.
Parameters: Record measured travel, lift and transfer performance, scan success, positioning accuracy, alarm response, recovery time and throughput under agreed test conditions.
Check: Run the agreed factory acceptance test and site acceptance test using representative pallets and real process rules. Include power interruption, network interruption, barcode failure, pallet rejection, crane fault and emergency-stop scenarios.
Failure fix: Classify defects as safety-critical, operational, software, documentation or cosmetic. Block production release for unresolved safety-critical defects and require evidence for every corrective action.
Problem: The daily average appears acceptable, but dispatch queues form during the final hours of a shift.
Solution: Analyze 15-minute or 30-minute transaction intervals. Model order waves, production release patterns and truck departure windows. Size the system around the agreed peak scenario and document the operating assumptions.
Problem: Broken pallet boards, excessive film or product overhang causes sensor faults and transfer failures.
Solution: Add a pallet inspection point, define rejection criteria and measure the rejection rate during the pilot. Repair or replace nonconforming pallets before they enter the automated storage area.
Problem: High-demand products are stored in locations that create excessive travel or aisle congestion.
Solution: Classify SKUs by movement frequency, order-line behavior, weight, batch restrictions and replenishment pattern. Review the slotting model after actual operating data becomes available.
Problem: A rejected pallet blocks the main conveyor because there is no controlled exception route.
Solution: Provide physically identified quarantine positions, a manual inspection station and software status codes for rejected, damaged, unknown and awaiting-release pallets.
Problem: The WMS knows inventory but cannot coordinate millisecond-level equipment sequencing, sensor states and conveyor interlocks.
Solution: Define the WMS-WCS-PLC architecture during concept design. The WMS should generally manage inventory and business orders, while the WCS coordinates material flow and the PLC executes equipment control, subject to the selected architecture.
Problem: The system performs well during demonstrations but loses availability when a pallet must be recovered from a high level.
Solution: Design recovery routes, lifting equipment, spare-parts storage, safe access and technician training before installation. Include fault recovery in acceptance testing rather than treating it as an emergency-only activity.
Problem: A project business case relies on a case-study figure that was measured under different pallet, shift and software conditions.
Solution: Request the test conditions, duty cycle, load profile, availability definition and maintenance assumptions. Convert the supplier’s claim into a project-specific acceptance criterion.
When comparing UNISTAR with other suppliers, use the same technical schedule for every bidder. The comparison should include:
Rated load and permitted load dimensions.
Single-deep or double-deep storage capability.
Travel and lifting performance under the project load.
Measured or guaranteed throughput conditions.
WMS and WCS interface responsibility.
Safety standards and conformity documentation.
Spare-parts availability and response time.
Preventive-maintenance intervals.
Manual recovery method and training scope.
Acceptance-test procedure and performance remedies.
Ask each supplier to model the same peak day, the same pallet mix and the same dispatch schedule. A meaningful comparison requires identical assumptions. Also separate capital cost from whole-life cost, including energy, maintenance labor, software support, spare parts, building modifications and planned downtime.
Start with the load unit and transaction profile, then design storage capacity, throughput, rack geometry, conveyors, controls and safety as one system. Validate the design with simulation and representative pallets before ordering equipment. Keep a clear distinction between documented facts, supplier claims and project assumptions. Public cases such as Coca-Cola HBC’s automated logistics projects demonstrate the importance of integrated pallet flow, while published AS/RS project experience consistently shows that pallet quality and control-system discipline affect operational reliability.
The most useful project deliverables are a user requirement specification, pallet acceptance standard, capacity model, peak-throughput model, layout drawing, WMS-WCS interface document, risk assessment, maintenance plan and site-acceptance protocol. With these documents in place, a stacker crane system for high-bay pallet warehouses can be evaluated on measurable requirements: automated pallet warehouse design guide assumptions, AS/RS stacker crane layout, high-bay storage, pallet handling, load unit, WMS and WCS performance.
