Crane or Shuttle? Matching Pallet Automation to the Warehouse
In recent years, several warehouse technologies for automated pallet storage have become established. Stacker cranes (STCs), also known as storage and retrieval machines (S/R machines), have been proven solutions for more than 60 years. They are available in many configurations, depending on their field of application. Designs include single- or twin-mast versions, aisle-bound or aisle-changing configurations, and systems with heights of up to 50 meters (164 feet). In addition, different load-handling devices can be installed, in varying numbers.
Stacker Cranes: Proven Range and Payload
Single-deep telescopic forks provide direct access to each storage location and high handling capacity. Double-deep telescopic forks increase storage capacity and reduce costs by storing twice as many goods in the same space. While traditional telescopic forks are often limited to 1,500 kg (3,300 lbs), combining several forks allows a single stacker crane to handle payloads of up to 8,000 kg (17,500 lbs). This is crucial in industries such as paper and cardboard, wood, air freight, and steel.
Triple-deep telescopic forks were used for several years but have since been replaced by modern radio shuttles. These load-handling devices marked the first major shift in the approach to multi-deep pallet storage. Different types of stacker cranes could be equipped with up to three pallet shuttles at a time. Channel depths of up to 40 m (131 ft) improved space utilization, while modern PLC controls made it possible to manage multiple shuttles on a crane simultaneously, laying the groundwork for true system scalability.
To this day, automated storage and retrieval machines (CLD stacker cranes) remain a top choice for handling demanding goods and operating cost-effective, robust warehouses, thanks to their versatile design.
Mother-Child Shuttle Systems: Separated Axes
The need to make better use of space and scale throughput has contributed to the growing success of various shuttle system solutions. Building on existing radio shuttle technology, new compact transport carts were developed. These carts serve as an alternative to traditional stacker cranes and rapidly transport radio shuttles within the aisle. The radio shuttle itself continues to serve as the load-handling device for multi-deep storage. Lifts handle the vertical transport of pallets and goods. By separating the axes of movement, this approach created a new type of flexible, scalable warehouse design. These pallet shuttle systems are often called “Mother-Child” systems.
4-Way Shuttles: Independent Movement on Every Level
Modern energy storage and high-performance control systems have made it possible to combine multiple functions in a very compact space. The same vehicle can now move goods and travel between aisles and rack channels. These free-roaming shuttles operate independently on each rack level and can access all pallet locations. Lifts compensate for differences in elevation between shuttles or goods. These systems are often called 4-way shuttle or 2D pallet shuttle systems.
The shuttles’ new freedom of movement gives warehouse designers and operators new ways to scale throughput and make flexible use of space. The main challenges of shuttle systems lie in developing intelligent shuttle management software. Although all these systems are designed to automate the storage and retrieval of unit loads, they differ fundamentally in their applications. Each solution has its place. Stacker cranes offer the broadest range of applications, while Mother-Child shuttle systems are suited to extremely high throughput rates with a limited variety of items, as often found in the beverage industry. New 4-way shuttle systems offer the greatest flexibility in terms of scalability.
When selecting the right technology, choosing the right supplier is crucial. Manufacturers that offer all these technologies in their portfolio can provide an objective comparison of the available systems.
The author is Dr. Benjamin Thumm, Managing Director of DAMBACH Lagersysteme. The views expressed by the author do not necessarily represent those of The Supply Chainer.
