If you are planning an automated warehouse and need to select the right stacker crane system, I will show you a practical specification process from storage analysis to final acceptance. By following these steps, you can define capacity, load dimensions, aisle layout, safety functions, software requirements, and service terms clearly—reducing design changes, installation delays, and long-term operating costs with a properly configured UNISTAR solution.
!
A stacker crane is not selected by lifting height alone. The correct system must match your throughput, pallet standard, rack configuration, load characteristics, warehouse management system (WMS), and future expansion plans. A detailed technical specification gives warehouse operators and equipment suppliers the same engineering reference before quotation and production begin.
The first step in How to Specify a Stacker Crane System for an Automated Warehouse is to document how the warehouse will operate in real conditions.
Prepare a load profile for every product or pallet type that the automated storage and retrieval system (AS/RS) will handle.
Record the following data:
Pallet or container dimensions, such as 1,200 × 1,000 mm or 1,200 × 800 mm
Maximum gross load and average operating load
Minimum and maximum load height
Load center of gravity
Pallet material and structural condition
Whether the load is stable, shrink-wrapped, boxed, or irregular
Product sensitivity to impact, vibration, temperature, or humidity
Required storage orientation and barcode position
For example, a pallet rated at 1,000 kg may not be suitable for a 1,000 kg load if the pallet deck is damaged or the center of gravity is offset. UNISTAR engineers should receive actual load drawings, photographs, and sample pallets before finalizing the fork or load-handling device.
Storage capacity and throughput are different design values.
Storage capacity describes how many pallet positions the warehouse requires. Throughput describes how many storage and retrieval cycles the equipment must complete within a specific time.
Specify:
Required pallet positions
Incoming pallets per hour
Outgoing pallets per hour
Number of single-deep or double-deep storage cycles
Peak-hour throughput
Average daily operating hours
Number of shifts per day
Required equipment availability
Future capacity increase
A useful initial calculation is:
Required cycles per hour = inbound cycles per hour + outbound cycles per hour
If a warehouse receives 30 pallets per hour and dispatches 40 pallets per hour, the stacker crane must support at least 70 combined cycles per hour during peak operation, subject to the final travel distance, lift height, storage depth, and control strategy.
Do not use only average throughput. A system designed for average demand may create queues during seasonal peaks. We recommend applying a realistic utilization target, often below 85%, so the crane has operational reserve for congestion, maintenance, and order surges.
Once the operating profile is clear, select the mechanical configuration that matches the building and storage strategy.
A single-mast stacker crane may be suitable for lighter loads and moderate lift heights. A double-mast design generally offers greater rigidity for high-bay storage and heavier payloads.
Important selection factors include:
Maximum lifting capacity
Maximum lifting height
Mast deflection
Travel speed and acceleration
Lift speed and acceleration
Load-handling device type
Required positioning accuracy
Earthquake or wind conditions
Cold-storage or cleanroom requirements
For heavy-duty applications, ask the supplier to provide mast strength calculations, wheel load data, rail reaction forces, and deflection limits. These calculations are especially important when rack-supported AS/RS structures are used.
A single-deep rack allows direct access to every pallet position and is easier to manage for high-SKU operations. Double-deep storage increases density but requires a telescopic fork or another specialized load-handling device.
Use single-deep storage when:
SKU variety is high
Direct pallet access is essential
Inventory rotation is complex
FIFO control is strict
Product dimensions vary significantly
Use double-deep storage when:
Pallet dimensions are standardized
Storage density is a priority
Inventory is managed in batches
The warehouse has sufficient buffer locations
UNISTAR should verify the fork stroke, pallet clearance, rack beam spacing, and load stability before approving a double-deep stacker crane system.
Vague statements such as “high speed” or “accurate positioning” are difficult to verify. A professional purchase specification should include measurable performance values.
| Parameter | Typical specification item |
|---|---|
| Rated load | 500–1,500 kg, according to application |
| Lift height | Defined by clear building height and rack geometry |
| Horizontal travel speed | Specified in meters per second |
| Lift speed | Specified under rated and unloaded conditions |
| Positioning accuracy | For example, ±5 mm or project-specific tolerance |
| Load-handling accuracy | Defined at pallet entry and withdrawal |
| Availability target | For example, ≥98% excluding planned maintenance |
| Inspection requirement | 100% functional inspection before shipment |
| Service response | Initial technical response within 24 hours |
| Control system | PLC, safety PLC, barcode or laser positioning |
| Communication | WMS/WCS interface using agreed data protocol |
| Safety standard | EN 528, ISO 13849-1, IEC 60204-1, as applicable |
The correct accuracy depends on the rack geometry, pallet tolerances, guide rails, and fork design. If your project requires positioning precision to 0.01 mm, confirm whether this refers to sensor resolution, encoder feedback, or actual load placement accuracy. These are not the same measurement.
For most pallet AS/RS applications, the specification should separately define:
Travel positioning accuracy
Lift positioning accuracy
Fork extension accuracy
Pallet detection accuracy
Barcode or RFID reading accuracy
A stacker crane system is a production asset, so the specification should include duty classification and expected service life.
Provide:
Cycles per hour
Operating hours per day
Operating days per year
Expected annual cycles
Design life in years
Motor starting frequency
Brake duty
Maintenance intervals
The supplier should select motors, gearboxes, brakes, chains, cables, bearings, and wheels according to the calculated duty cycle. Ask for a component list showing manufacturer, model, rated life, and replacement availability.
A stacker crane cannot be specified independently from the rack and building.
Before equipment design, verify:
Clear warehouse height
Floor flatness and levelness
Rail installation tolerance
Rack verticality
Rack deflection under load
Column and beam dimensions
Fire protection clearance
Sprinkler and smoke detection locations
Expansion joints
Seismic design requirements
Ambient temperature and humidity
Rack safety should be reviewed according to DIN EN 15635, where applicable. The crane aisle, rack structure, guide rails, and building slab must be treated as one integrated system.
For steel quality and mechanical testing, project documents may reference standards such as ASTM A370 for mechanical testing of steel products or the applicable EN/DIN material standard. The exact material standard should be agreed in the contract rather than assumed.
The floor and rail system directly affect crane stability and positioning. Ask UNISTAR to issue:
Wheel loads
Rail loads
Anchor bolt layout
Foundation requirements
Rail tolerance requirements
Floor flatness requirements
Installation datum points
Grouting and leveling method
A small rail alignment error can create vibration, wheel wear, noise, and positioning faults. Survey the installation area before delivery and complete a documented as-built check after installation.
Mechanical performance alone does not determine warehouse productivity. The control architecture must connect the crane with the warehouse management process.
A typical automated warehouse includes:
WMS for inventory and order management
Warehouse control system (WCS) for equipment coordination
PLC and safety PLC for machine control
Human-machine interface (HMI) for operation and diagnostics
Barcode, RFID, laser, or encoder-based positioning
Network infrastructure and industrial switches
The technical specification should define how inventory is assigned, how missions are released, and how exceptions are handled.
Important software functions include:
Automatic storage and retrieval commands
Pallet identity verification
Empty-location confirmation
Double-storage-depth management
FIFO or FEFO logic
Interlock with conveyors
Recovery after power failure
Manual retrieval mode
Fault history and alarm classification
Remote diagnostics
User access control
Production and availability reports
Before ordering, prepare an interface control document listing message names, data fields, acknowledgment rules, error codes, and response times. This prevents late integration problems between UNISTAR, the WMS provider, conveyor supplier, and warehouse operator.
Safety should be designed into the system rather than added during commissioning.
A compliant project may need to consider:
EN 528 for safety of storage and retrieval machines
ISO 13849-1 for safety-related control systems
IEC 60204-1 for electrical equipment of machines
DIN EN 15635 for application and maintenance of steel static storage systems
Local machinery, electrical, fire, and occupational safety regulations
The final standard list depends on the country, machine type, and project scope. We recommend asking UNISTAR to provide a compliance matrix showing each applicable requirement, design response, test method, and document reference.
Safety functions may include:
Emergency-stop circuits
Aisle access gates
Light curtains and safety scanners
Door interlocks
Overspeed monitoring
Anti-collision sensors
Slack-chain or rope detection
Load presence detection
Upper and lower travel limits
Safe maintenance access
Lockout/tagout provisions
Every safety function should be tested during factory acceptance testing (FAT) and site acceptance testing (SAT), with results recorded in a signed checklist.
A reliable supplier should provide verifiable quality records rather than only a product brochure.
A practical procurement package should include:
General arrangement drawings
Load data and cycle calculations
Electrical schematics
Pneumatic drawings, if applicable
Component datasheets
Motor and gearbox certificates
Welding procedures and inspection records
Surface treatment specifications
Calibration certificates
Factory inspection reports
Software backup
Operation and maintenance manuals
Spare parts list
Training records
FAT and SAT protocols
For structural welding, the applicable project may require visual inspection, dimensional inspection, or non-destructive testing. If radiographic, ultrasonic, or magnetic-particle testing is required, specify the method and acceptance criteria in advance.
A strong quality plan can include 100% inspection of critical safety devices, wiring continuity, sensor operation, fastener torque, and functional sequences before shipment. Dimensional checks should be recorded using calibrated instruments, with calibration traceability maintained.
The project becomes successful only when the equipment performs under operating conditions.
Follow this sequence:
Confirm building readiness and rail tolerances.
Inspect all delivered components against the packing list.
Install the rails, masts, cables, drives, forks, and safety devices.
Complete electrical wiring and network configuration.
Perform cold tests without loads.
Test travel, lift, fork extension, sensors, and emergency stops.
Test with empty pallets.
Test with rated loads.
Verify single-cycle and combined-cycle performance.
Integrate WMS and WCS mission commands.
Conduct FAT or repeat agreed site tests.
Train operators and maintenance personnel.
Complete SAT and sign the punch list.
Acceptance criteria should include throughput, positioning accuracy, load handling, alarm recovery, safety circuits, communication reliability, and availability.
Do not accept a system only because the crane moves. The equipment must demonstrate repeatable performance across the complete process, including pallet identification, storage confirmation, retrieval, conveyor handoff, and exception recovery.
Even a well-designed stacker crane system can face execution challenges.
Unstable or damaged pallets:
Use pallet inspection, pallet repair, or a pallet transfer station. Define allowable pallet deformation and maximum overhang.
Insufficient floor accuracy:
Complete a laser survey before installation. Correct the slab or use an approved leveling method before rail installation.
Throughput lower than expected:
Review travel distances, aisle congestion, crane acceleration, conveyor buffers, and WMS mission batching. Compare measured cycle time with the original calculation.
WMS integration delays:
Freeze the interface control document early. Test message simulation before the crane arrives.
Sensor contamination in cold or dusty environments:
Select appropriate protection ratings, heating systems, cleaning procedures, and spare sensors.
Maintenance access problems:
Design safe access platforms, isolation points, inspection lighting, and replacement routes for motors, drives, and sensors.
Limited spare parts availability:
Agree on a recommended spare-parts package and require a response commitment, such as technical support within 24 hours for critical faults.
When we evaluate a supplier for an automated warehouse, we look beyond initial equipment price. The better question is whether the supplier can convert operating requirements into a measurable, testable, and maintainable system.
Ask UNISTAR to provide:
A project-specific technical proposal
Cycle-time simulation or calculation
Rack and crane interface drawings
Safety and compliance matrix
FAT and SAT procedures
Preventive maintenance schedule
Recommended spare-parts list
Training plan
Warranty terms
Remote support process
Performance guarantees linked to defined test conditions
The strongest specification separates guaranteed values from design assumptions. For example, “throughput of 60 cycles per hour at a defined travel distance, load weight, and operating temperature” is more useful than “high-performance operation.”
Before requesting a final quotation, confirm these points:
[ ] Pallet dimensions and maximum gross load are documented.
[ ] Storage capacity and peak throughput are calculated.
[ ] Single-deep or double-deep storage is selected.
[ ] Travel, lift, and fork positioning tolerances are defined.
[ ] Building height, floor, rail, and rack interfaces are verified.
[ ] WMS, WCS, PLC, and communication responsibilities are assigned.
[ ] Applicable EN, DIN, ISO, IEC, ASTM, and local standards are identified.
[ ] FAT, SAT, and performance acceptance criteria are measurable.
[ ] 100% inspection requirements are defined for critical functions.
[ ] Maintenance access, spare parts, and 24-hour response expectations are included.
[ ] Future expansion and additional storage positions are considered.
By following this process, you can specify a stacker crane system that is technically compatible, operationally efficient, and easier to validate. A properly prepared How to Specify a Stacker Crane System for an Automated Warehouse plan also helps UNISTAR produce a more accurate quotation, reduce engineering changes, and deliver a system that supports dependable warehouse automation from commissioning through daily production.
