The aim of utilising movement strategies is to adhere to specified guidelines in warehouse operations and, at the same time, achieve the best possible throughput performance. The respective movement strategy determines in which arrangement stacker cranes are used for storage, transfer or retrieval of material.

Important: Movement strategies are not always compatible with possible allocation strategies.

Movement strategies are:

  • Double-cycle / Double-cycle strategy
  • Single-cycle / Single-cycle strategy
  • Transfer Strategy
  • Aisle change strategy
  • Feed strategy
  • Discharge strategy

Movement strategies: Double-cycle / Double-cycle strategy

The double-cycle or double-cycle strategy is a movement strategy within warehouse operations. The design combines storage and retrieval, and thus, storage and retrieval cycles are carried out.

Double-cycle procedure

The double-cycle strategy can be carried out for single orders as well as for a larger number of orders. For single orders, selection of the putaway tray near the picking tray occurs. By optimally selecting the storage bin, the storage and retrieval machine can switch to stock removal immediately after the material has been put away, and vice versa. With collective orders, a combination of orders takes place whose storage and retrieval bins are close to each other.

An optimized double-cycle strategy is, for example, the putaway in the outbound area of the storage bin or the picking in the outbound area of the storage bin. In the best-case scenario, this movement strategy can save the average travel time between storage and retrieval points.

Advantages and disadvantages of double-cycle

The advantage of the double-cycle is the route optimization of the operating device. Combined storage and retrieval increases efficiency in the entire value-added process of warehouse logistics. The strategic movement sequences ensure that the storage and retrieval machine avoids empty runs, stores and retrieves on its way and improves throughput performance by up to 10%.

The disadvantage is that individual movement sequences take a little longer. Furthermore, careful calculation in advance is mandatory.

Movement strategies: Single-cycle / Single-cycle strategy

The single-cycle strategy is a movement strategy within warehouse operations. It is a strategy in which only storage or retrieval takes place. Putaway and picking do not take place simultaneously or in combination.

Single-cycle procedure

In the single-cycle strategy, the stacker crane picks up a storage unit and moves it to the storage bin provided for it. The storage and retrieval machine then moves back again to transport the next storage unit. The individual cycles often start and end at buffer locations provided for this purpose. Depending on whether goods receipt or goods issue has priority, either stock placements or stock removals take place in single cycles.

Calculation of the single-cycle strategy

The time required for the single-cycle provides information about the handling performance of an automatic warehouse, such as a high-bay warehouse. The particular clearance time is calculated from the travel time of the storage and retrieval machine from the point of origin to the storage bin, the travel time for picking up the storage unit at the storage bin, and the travel time for transferring the container to the storage bin. The travel time of the stacker crane from the point of origin to the storage bin is multiplied by two since this route is included twice in the single lot. Once when moving the unit to the storage bin. Once again, when returning from the storage bin to the point of origin.

The advantage of a single-cycle is the increased performance in storage and retrieval.
The disadvantage is that longer empty runs of the storage equipment must be expected.

Movement Strategies: Stock Transfer Strategy, Stock Transfers

The stock transfer strategy (stock transfer) is another movement strategy within warehouse operations. A pending retrieval of concealed units usually triggers such a movement of goods.

The following characteristics of the storage device used are essential for the stock transfer performance of a storage system:

  • Construction
  • driving behaviour
  • gait-bound nature
  • load handling attachment
  • capacity

The number of storage devices used also plays a role.

The more a multiple bin warehouse fills, the more the number of twice occupied storage channels increases. The last, in turn, increases the probability of necessary stock transfers.

Four strategies are possible:

  • Random stock transfer
  • Relocation near outsourcing
  • Combined transfer and retrieval
  • Transfer to the next storage compartment

In the case of random stock transfer, selection of storage location happens randomly. However, this strategy usually takes up more lead time than the other stock transfer strategies. Random movements of goods are therefore rarely used in practice.

Relocation near outsourcing is an often-used strategy. The loading unit to be transferred should be stored as close as possible to the retrieval channel.

When double-width load handling attachments are available, combined transfer and retrieval is the obvious choice. The load unit to be transferred is picked up by the storage device and transported to the location where the load unit to be removed is to be picked up. The loading unit picked up for retrieval blocks one side of the storage device. Therefore, the loading unit to be transferred is put away opposite the unit to be removed from storage.

The transfer to the next storage compartment is a possibility when using several storage devices. Free storage devices are used as intermediate buffers and transfer the units to be transferred to the next storage bin.

Movement strategies: Aisle change strategy

The aisle change strategy is a method in which storage and retrieval orders are collected and only executed after a certain period.

Process of the aisle change strategy

To fulfil a picking order goods usually have to be picked from different storage bins, whereby the storage bins to be approached for an order can be located in different aisles. The aisle change occurs when all positions (of one picking order) in a warehouse aisle have been picked. The storage device then changes to the next aisle that holds items of the order. The reason for this may be that the previous order has not yet been completed or that items are being collected for the next order.

The aisle change strategy aims primarily at route-optimised picking. Since the aisle change requires relatively much time, storage and retrieval performance reduces significantly at a high aisle change frequency. The aisle change frequency is calculated using the formula vGW = 1/h, where h stands for the maximum storage and retrieval time, i.e. the specified cycle time.


To automatically operate a warehouse, storage devices must follow precise track guidance when changing aisles. This guidance can be mechanical, optical, acoustic or electronic. The aisle-bound nature of the storage devices is more or less dependent on the driving behaviour, the type of track guidance and the design of the devices. For aisle changes, it is usually necessary to use one of the following storage devices:

  • Aisle transferable storage devices
  • Aisle-independent storage devices

Aisle-transformable storage devices include, for example, storage and retrieval machines with transfer devices, while aisle-independent storage devices include, among others, pallet trucks and forklifts.
For a particular cycle, all storage and picking orders are initially stockpiled without processing further. The orders are then sorted according to specific warehouse aisles. The storage devices used in the aisles then execute the orders at regular intervals, i.e. after a fixed cycle time.

Advantages of the aisle change strategy

The advantage of the aisle change strategy is a possible continuous adaptation to the environment. Extended storage and retrieval times, which would hurt throughput, are to be avoided. The aisle change of the storage devices aims at minimising the loss of performance.

Movement strategies: Feed and discharge strategy

The feed and discharge strategies are both movement strategies in intralogistics.

Feed strategy

The feed strategy requires a so-called feed conveyor. There are two ways to use the method:

  • The loading units are allocated to the individual storage aisles according to set cycles.
  • The loading units are assigned in batches to the aisles between the racks where the feed conveyor has the lowest occupancy.

Discharge strategy

The discharge strategy needs a so-called delivery spur track. Guiding of the loading units takes place via the delivery branch line into the delivery section. Following the discharge strategy, the units that are most urgently needed are given priority and have the right of way.


Warehouse operations employ certain movement strategies. Depending on which movement strategies are used in the warehouse and subsequently executed by the storage devices, the arrangement of the stacker cranes for the storage, transfer or retrieval of material differs. In compliance with specified guidelines, it is the aim to achieve the highest possible performance in storage, retrieval and throughput. Movement strategies are not always compatible with possible allocation strategies.

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