A stacker crane is a core storage and retrieval device in an Automated Storage and Retrieval System (AS/RS). It travels along the rails inside a storage aisle and uses horizontal movement, vertical lifting, and a load handling device to store and retrieve pallets, totes, or other unit loads.
Stacker cranes can be classified by mast structure, operating height, load type, support arrangement, and storage depth. Common configurations include single-mast stacker cranes, double-mast stacker cranes, high-bay stacker cranes, pallet stacker cranes, and miniload stacker cranes.
Classification by mast structure
Single-mast stacker cranes
A single-mast stacker crane has one vertical mast connected to upper and lower structural beams. These components form the main supporting and guiding frame.
Its main characteristics include:
Relatively simple structure: The single-mast design generally results in a lower machine weight and can be suitable for projects with restrictions on equipment weight and installation space.
Light to medium load applications: These cranes are commonly used to handle pallets or totes. Their actual load capacity depends on mast dimensions, material, structural stiffness, and operating conditions.
Compact equipment arrangement: The structure can be designed to occupy less space while meeting the required strength and stability conditions.
Single-mast stacker cranes are often used in low- and medium-bay warehouses, although they can also be designed for some high-bay applications. Their load capacity should not be restricted to below 1,500 kg, nor should their lifting height be limited to 16 m as a general rule. The available range varies by manufacturer and product series. Selection should be based on the rated specifications and project requirements.
Double-mast stacker cranes
A double-mast stacker crane uses two vertical masts connected by upper and lower beams. The load carriage moves vertically along the mast guidance system.
Compared with a single-mast design, its main characteristics include:
Higher structural stiffness: The two masts form a supporting frame that helps improve overall structural stiffness and operating stability.
Higher load capacity potential: The design can handle heavier pallet loads and can be fitted with forks and hoisting mechanisms selected for the required application.
Suitability for taller warehouses: The machine can be engineered for different rack heights and structural requirements, including high-bay storage projects.
Double-mast stacker cranes are commonly considered for heavier loads, greater lifting heights, or applications with demanding stability requirements. However, a rated capacity of 5 tonnes is not a universal specification. The actual capacity depends on load center, mast design, fork extension, and duty classification.
Classification by operating height
Based on rack height and equipment design range, stacker cranes are generally available in low-bay and high-bay configurations.
Low-bay stacker cranes
A low-bay stacker crane is designed for automated warehouses with relatively low rack heights. Its mast height, hoisting mechanism, and operating parameters are selected according to the number of storage levels and the dimensions of the unit loads.
These cranes generally have a relatively compact structure and less demanding installation requirements. Typical applications include small and medium pallet warehouses, production line buffer areas, and general automated storage systems.
High-bay stacker cranes
A high-bay stacker crane is designed for warehouses with taller rack structures. It must maintain adequate structural stiffness, positioning accuracy, and operating stability over longer travel and lifting distances.
Important design considerations include:
High-strength mast structure: The masts and beams are designed according to machine height, rated load, and operating conditions to control structural deflection.
Load carriage lifting system: The hoisting mechanism moves the load carriage along the mast guidance system to reach different rack levels.
Position detection and control: Encoders, barcode positioning sensors, or optical distance sensors may be used to determine machine position, depending on the control system.
Safety protection: Travel limiters, overspeed protection, overload protection, anti-collision devices, and other safety components can be configured according to the machine design.
A high-bay stacker crane can have either a single-mast or double-mast structure. The term "high-bay" describes its operating height and product range, rather than a separate mast configuration.
Classification by load type
Pallet stacker cranes
A pallet stacker crane is designed to handle palletized unit loads. It is commonly equipped with telescopic forks or other load handling devices for single-deep or double-deep storage.
Typical applications include manufacturing raw material warehouses, finished goods warehouses, food and beverage storage, and distribution centers. Fork design must match the pallet dimensions, load weight, and rack storage depth.
Miniload stacker cranes
A miniload stacker crane handles smaller unit loads such as totes, bins, and containers.
Compared with pallet stacker cranes, miniload equipment generally uses a load carriage and handling device designed for smaller loads. It can be integrated with tote conveyors, automated sorting systems, and goods-to-person picking systems.
Typical applications include electronic component warehouses, pharmaceutical storage, retail distribution centers, and small-parts storage in manufacturing facilities.
Special-load stacker cranes
A special-load stacker crane handles loads other than standard pallets and totes.
The load handling device is designed according to the shape, dimensions, and support requirements of the goods. Depending on the application, the machine may use dedicated clamps, carriers, rods, vacuum grippers, or other handling equipment. Long workpieces, cylindrical materials, and special industrial components may require custom load handling arrangements.
Classification by support arrangement
Floor-running stacker cranes
A floor-running stacker crane is supported and driven by a travel mechanism running on rails installed on the warehouse floor. Guide devices are generally installed at the upper part of the machine to control lateral movement and prevent excessive tilting.
This is a widely used arrangement. The machine can be designed for different warehouse heights and rated loads.
Suspended stacker cranes
A suspended stacker crane runs beneath an overhead rail installed in the upper part of the aisle. The upper rail supports and guides the machine.
The design must account for the load-bearing capacity of the building structure and the arrangement of the lower guide system. This configuration is used in specific warehouse projects where the structural and load requirements can be met.
Rack-supported stacker cranes
A rack-supported stacker crane runs on a rail installed at the top of the storage rack, with the rack structure providing the main support.
The rack must therefore meet not only the requirements for storing goods but also the strength and stiffness requirements associated with stacker crane movement and operating loads.
Classification by storage depth
Single-deep stacker cranes
A single-deep stacker crane serves rack locations with one unit load position in the depth direction.
Each load can be accessed directly, making this arrangement suitable for warehouses with many SKUs and frequent access to individual storage locations.
Multi-deep stacker cranes
A multi-deep stacker crane can access two or more unit load positions in the depth direction of a rack lane.
This arrangement can reduce the number of aisles or increase the number of storage positions within a given floor area. However, inventory access and retrieval planning are more complicated. Depending on the fork design and system configuration, an auxiliary satellite shuttle may be required to handle loads stored deeper in the rack.
Other stacker crane configurations
Stacker cranes can also be classified by travel path, operating method, and working environment.
By travel path: Straight-travelling and curve-travelling stacker cranes are available, depending on the rail arrangement and warehouse layout.
By operator arrangement: Cranes can be classified as manned or unmanned. Unmanned stacker cranes normally perform storage and retrieval tasks through an automated control system.
By control mode: Configurations can include manual control, offline automatic control, online automatic control, and maintenance mode.
By working environment: Low-temperature, cleanroom, and explosion-protected stacker cranes are designed for warehouses with specific temperature, cleanliness, or explosion protection requirements.
How to select a stacker crane
The selection should not be based only on whether the machine has one or two masts. The following factors also need to be considered.
Load weight and dimensions
Determine the maximum unit load weight, external dimensions, center of gravity, and pallet or tote specifications. These parameters affect rated capacity, fork design, load carriage dimensions, and mast sizing.
Warehouse height and aisle layout
The rack height, aisle width, travel rails, and building structure determine the required mast configuration and operating range. For high-bay warehouses, structural stiffness, operating vibration, and positioning accuracy also require attention.
Inbound and outbound throughput
Handling capacity depends not only on horizontal travel and lifting speeds but also on fork extension time, individual storage and retrieval cycles, load location distribution, and conveyor capacity. The required number of inbound and outbound load units per hour should be calculated for the actual operating pattern.
Storage depth and load access
A single-deep configuration may be suitable when individual storage locations need to be accessed frequently. A multi-deep arrangement can increase storage density, but the project must also account for retrieval sequence and any auxiliary handling equipment.
Working environment and maintenance
Cold storage, cleanrooms, and special industrial environments may require suitable electrical components, lubricants, protective structures, and safety devices. Maintenance access and spare parts availability should also be considered.
Single-mast and double-mast stacker cranes differ mainly in frame structure and load-bearing design. Low-bay and high-bay models are defined by operating height and product configuration. Pallet, miniload, and special-load stacker cranes are selected according to the goods being handled. These classification dimensions can be combined to define the machine configuration required for a particular warehouse.
In addition to precision mechanical components for automated warehousing equipment, Hansheng Automation provides custom precision machining services for other industrial applications, including tobacco packaging machinery, food filling equipment, yacht components, and remote-controlled racing cars. We manufacture non-standard precision components according to customer-supplied drawings and support individual parts and small-batch production.
