RBG

What is a storage and retrieval machine?

A storage and retrieval machine (SRM) is an automatically controlled machine that travels on floor rails within a racking system and is equipped with a lifting mast and load handling attachment. It moves along a racking aisle, raises the lifting carriage to the required height, and stores or retrieves load carriers – pallets, containers, trays or cartons – in a fully automated manner. Communication with the higher-level warehouse management system (WMS) takes place in real time, typically via Wi-Fi or data bus, enabling transport orders to be dynamically prioritized and processed.

SRMs are the backbone of automated high-bay warehouses (HBW) and automated small-parts warehouses (AS/RS). Depending on design and application, a distinction is made between single-mast and double-mast machines, as well as between single cycles and dual cycles. In a dual cycle, the SRM simultaneously stores and retrieves within a single cycle, significantly increasing throughput compared to single cycles.

How does an SRM work in practice?

The WMS transmits a transport order to the SRM specifying the source and destination location. The machine travels horizontally to the target aisle while simultaneously raising the lifting carriage to the target height – on modern machines both axes run synchronously to minimize travel time. The load handling attachment – for example a telescopic fork, belt conveyor or shuttle carriage – picks up the load carrier and moves it into the storage location or onto the transfer station.

The control system continuously monitors the weight, contour and position of the load carrier. If a value deviates from the specified range, the SRM stops and reports a fault to the supervisory control system. Modern machines automatically log maintenance intervals, axis wear and braking distances, enabling predictive maintenance.

• Single-mast SRMs are lighter and faster, suited for small-parts warehouses and lighter loads up to approx. 500 kg.
• Double-mast SRMs handle heavy loads of several tonnes and are used primarily in pallet warehouses.
• Shuttle SRMs combine a horizontal carrier vehicle with autonomous shuttle units that travel deep into the rack depth.

What matters when selecting a system?

Planning an SRM system involves several interdependent parameters: aisle length, warehouse height, required throughput in storage and retrieval cycles per hour, and the type and weight of the load carriers. Whether one SRM per aisle or multiple machines make sense depends on the required throughput. Redundancy is a frequently underestimated planning aspect: if one SRM fails, the entire aisle comes to a standstill – a second aisle or a bypass concept can safeguard the availability of the overall system.

Integration with the warehouse management system must be specified at an early stage, as the data interface – often based on standardized protocols or vendor-proprietary APIs – has a significant impact on throughput capacity. Energy regeneration during braking and lowering of the lifting carriage is available on most modern machines and noticeably reduces energy consumption. The actual savings achievable depend on the individual load profile and cannot be stated as a blanket figure.