Pallet Stacker Crane

If a tote-type stacker crane can be described as a nimble “light cavalry,” then the pallet stacker crane (Unit Load Stacker Crane) is the “steel giant” responsible for handling heavy-duty materials. It is the core equipment of automated high-bay warehouses (AS/RS), specifically designed for standard pallets (such as 1200mm × 1000mm) or large containers. The typical load capacity per pallet ranges from 500kg to 1500kg, and in some cases even higher.

Structural Types: Single Mast vs Double Mast

According to the mast structure, pallet stacker cranes are mainly divided into two configurations:

Single Mast Structure:

Features:
Simple structure, lightweight design, and relatively low manufacturing cost.

Application:
Suitable for warehouses below 15 meters in height with moderate load requirements. However, its rigidity is weaker than the double-mast type, making it less suitable for ultra-high speed or heavy-load applications.

Double Mast Structure:

Features:
Composed of two vertical masts and a crossbeam forming a rigid “portal” frame structure. It offers extremely high stability and strong torsional resistance.

Application:
Suitable for high-bay warehouses exceeding 15 meters in height, heavy loads (typically above 1500kg), or high-speed operation scenarios. The double-mast structure effectively suppresses vibration during rapid acceleration and deceleration, ensuring smooth operation.

Drive System and Operating Parameters

The dynamic performance of a pallet stacker crane directly determines the overall throughput of the warehouse.

Traveling drive:

Typically uses an AC variable-frequency motor combined with a gearbox to drive the bottom wheels along rails. High-end models adopt synchronous belt or rack-and-pinion transmission to achieve higher positioning accuracy.

Lifting drive:

Uses steel wire ropes or plate chains to lift and lower the load platform. For heavy-duty models, a dual-rope anti-drop system is standard; even if one rope fails, the other can immediately lock the system.

Operating speed:

Traveling speed can reach up to 4 m/s, and lifting speed up to 1.5 m/s. Through S-curve motion control, smooth acceleration and deceleration are achieved to prevent pallet tipping or cargo displacement.

Load Platform and Telescopic Fork

The load platform is the base structure that carries the forks and loads, requiring both strength and precision.

Telescopic fork:

Usually designed for double-deep or triple-deep storage. The fork consists of inner, middle, and outer stages, driven by chains or synchronous belts to achieve extension and retraction.

Alignment device:

To prevent pallet displacement due to inertia, mechanical guide rollers or pneumatic side push devices are installed on the platform to ensure the pallet remains centered during movement.

Anti-fall mechanism:

Safety hooks or wedge-type locking devices are installed on both sides of the platform. In case of lifting failure, the system immediately locks onto the guide rails to prevent falling.

Positioning and Navigation: Laser vs Barcode

In ultra-high aisle environments, stable positioning is critical for safe operation.

Laser positioning (absolute addressing):

A laser distance sensor installed on top of the stacker crane measures the distance to reflective plates at the end of the aisle. This method requires no extensive physical coding strips, offers high precision, and requires low maintenance.

Barcode positioning (incremental addressing):

Barcode strips are installed along the aisle floor or walls. A scanner reads the barcode to determine position. This method is cost-effective but requires regular cleaning and recalibration after power loss.

Safety Protection: Multi-layer Defense

Safety is a top priority in pallet stacker crane design, requiring multiple redundant protection systems.

1. Hard limit protection:
   Physical bumpers and limit switches are installed at both ends and extreme positions of the aisle to force emergency stop.

2. Overspeed protection:
   The system continuously monitors speed; once overspeed is detected, power is cut off and mechanical braking is activated immediately.

3. Slack rope / rope break protection:
   A weight or cam mechanism monitors rope tension. If slack or breakage occurs, the system stops instantly.

4. Obstacle detection:
   Photoelectric sensors under the platform detect whether pallets or obstacles are present, preventing “rack penetration” accidents.

5. Emergency stop system:
   Red mushroom emergency stop buttons are distributed across the equipment, allowing operators to stop the system from any position.

Typical Application Scenarios: High-Bay Heavy-Duty Warehouse

Pallet stacker cranes are standard equipment in industries such as tobacco, power utilities, mechanical manufacturing, and cold chain logistics.

For example, in cold storage warehouses, stacker cranes must operate in extreme environments such as -18°C or even -25°C. This places strict requirements on electrical components:

• Servo motors require low-temperature lubricants

• Cables must be cold-resistant types

• PLC and frequency converters must be installed in heated electrical cabinets to prevent condensation-induced short circuits

Additionally, low-temperature environments reduce metal toughness, requiring more conservative fatigue strength design margins.

Selection Guidelines: Key Technical Parameters

When selecting equipment, automation engineers typically focus on the following key parameters:

• Rated load: maximum pallet weight (e.g., 1000kg, 1500kg)

• Aisle dimensions: clear width and total rack height, which determine structural type and stability requirements

• Throughput demand: number of pallets handled per unit time, which determines speed class

• Operation mode: simple storage or integration with conveyors and complex sorting workflows

The pallet stacker crane is a foundational component of warehouse automation. With proper configuration and precise installation, it can significantly improve space utilization while ensuring safe and efficient handling of heavy materials in modern logistics systems.