Stations in the warehouse

An inside look at a storage facility

Modern warehouses are equipped with all sorts of technical equipment that enables goods to be efficiently stored. This equipment includes operator-less conveyor systems that move through various warehouse zones as though they were guided by an invisible force or stock pickers who select products from the pick locations in racks based upon instructions they receive on headsets from a central computer. The following graphic and detailed explanations provide insights into the most important processes in a warehouse.

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From receiving to shipping

Goods that arrive in the warehouse are accepted by receiving and prepared for storage. This includes unloading and identifying incoming goods. Identification is usually done by scanning a barcode Barcode attached to the good. However, new innovative technologies like RFID Radio frequency identification allow for contactless scanning of goods. As a result, the contents of a whole pallet Pallet can be read at once by the radio signal emitted by RFID chips as soon as the shipment passes a gate or similar checkpoint. But this method of identification is relatively more expensive than the barcode and is less used.
After being inspected at receiving, the goods are prepared for storage. In this process, they may be placed onto the appropriate load-carrying device such as pallets Pallet or into parts containers or repacked. The time the goods spend at receiving should be as short as possible. The receiving area for incoming shipments where goods that will be stored are processed is often called the I Point, or information point.
In theory, there are two types of warehouses: single-line stores and order-picking warehouses – but in reality, many warehouses combine these two activities.
Single-line stores are designed to store and retrieve identical units of the same type of good. For instance, a pallet of goods will be placed in storage, and the complete pallet will be retrieved again. Due to the great similarity of activities, single-line stores can be highly automated. Since movement processes are greatly simplified, space can be used very efficiently. The single-line store is also called a reserve warehouse if units are not sent directly to shipping but are placed in an order-picking warehouse instead. Reserve warehouses are used to store large volumes and units of goods for a relatively long time.
In general, small quantities and units of goods are stored for shorter periods in the order-picking warehouse. This warehouse area carries out movement processes that are used to consolidate or break down the flow of goods, the picking. This means the goods do not leave the storage area in the state in which they were stored. To keep the time required for manual picking to a minimum, efficient picking procedures and short transport routes must be considered in the organization of the order-picking warehouse. Order-picking warehouses also frequently rely on modern technologies such as pick-by-light Pick-by-light and pick-by-voice Pick-by-voice , which not only make the order picker’s job easier but also increase productivity and accuracy.
In the packing station, the picked order is consolidated into a unit for shipment, which can also involve a transfer to another internal station.
Shipping involves both the dispatch of goods to the recipient and delivery-related activities. This includes receipt of the goods from the packing station, set-up of interim storage sites that extend back to pick-up, arrangements for pick-up vehicles and loading. Transport-related processes are the primary job of shipping. Goods stay in shipping for lengthy transition periods only in extraordinary cases.
In addition, warehousing and means of conveyance used in the warehouse must be directed and coordinated. This is the job of the warehouse management, which forms the interface between the logistics subsystem warehouse and the logistics subsystem order processing Order processing [1].

Warehouse technology

Business trends have a strong impact on intralogistics Intralogistics , i.e., the material flow within a business operation and, thus, the technology associated with the warehouse. These trends include the accelerating pace of innovation, the increasing individual nature of customers’ requirements, the growing diversity of product variations and the extreme volatility of the order inflow.
The main task of conveyor technology is to transport, store, pick and handle goods. Increasingly, discussions are centering on solutions that can combine all conveyor equipment and systems in an efficient way that uses a minimum amount of time. This will enable conveyor technology to be flexibly adapted to different types of shipped goods.
Ground conveyors Ground conveyor are used today in many industries. Their flexibility allows them to be adjusted to the appropriate job with little effort. They are much easier to adapt to configuration changes or system expansion than automated conveyors [Conveyor] [2].
But the basis for these systems remains the warehouse technology with its storage racks, means of conveyance and picking systems.

Storage racks

Products can be stored in all sorts of ways in modern warehouses. Key criteria that apply here are not only which product is to be stored but also how quickly it must be available again. Shelf-type racks Shelf-type rack and space-saving storage carousels Storage carousel are frequently used for such things as non-palletized small parts, while pallet-racking systems [pallet-racking system] are particularly suited for large quantities of items.
Here, just like drive-in racks Drive-in rack and drive-through racks Drive-through rack , transport-related processes for storing heavy, bulky goods are used. A distinction is also drawn among drive-through racks that are primarily used for picking. Push-back racks Push-back rack are designed for infrequently needed products, and high-bay racks High-bay rack are frequently employed by industrial and retail companies [1].

	Rackings Rackings are frequently used to store non-palletized goods, small parts or bulky items. Generally speaking, they are suited for storing small to medium quantities of goods involving a large number and wide array of items.
	Pallet racks Pallet racks store pallets or stillages. They are used to store small to large quantities involving a large number of goods or assortments of goods.
	Drive-in racks Drive-in racks are used to store large quantities involving a small number of heavy items. They are also suited for fragile goods and non-stackable load units.
	Drive-through racks Just like drive-in racks, drive-through racks are used to store large quantities involving a small number of heavy items - as well as fragile goods and non-stackable load units.
	Flow-through racks Flow-through racks are frequently used for picking in distribution warehouses. Medium quantities involving small and intermediate-range numbers of items are stored on the racks.
	Push-back racks Push-back racks are primarily used to store items that are infrequently needed. Special areas of use are archiving records, documents or electronic data carriers. Medium quantities involving intermediate-range and large numbers of items are stored in push-back racks. They are also frequently used in freezer warehouses.
	Storage carousels Storage carousels are frequently used for small-parts storage systems, replacement-parts storage, tool storage, pharmaceuticals storage or document storage. Small to medium quantities involving intermediate-range to large numbers of items are stored in storage carousels for picking purposes.
	High-bay racks High-bay racks are most frequently found at industrial and retail companies. They store small to large quantities involving large numbers of items or assortments.

Storage racks
Source: Materialflusssysteme. Förder- und Lagertechnik | Hompel / Jünemann 2007

Means of conveyance

Various work-saving means of conveyance can be used to efficiently move products in the warehouse as well as to store and retrieve products. On one hand, these means of conveyance include permanently installed systems such as overhead conveyor systems Overhead conveyor system , cranes [cran], wheel conveyors [Wheel conveyor] and electric trolley conveyors [Electric trolley conveyor]. On the other hand, they encompass such unattached means of conveyance as forklift trucks Forklift truck , forklifts Forklift and automatic-guided transport systems [Automatic-guided transport system]. Special storage and retrieval equipment is also available. It simplifies warehousing and retrieval in things like pallet-rack, high-bay-rack or tank-rack storage.

	Overhead conveyor system Overhead conveyor systems are frequently used in machinery and installation manufacture and in fashion warehouses. They transport items between production segments and can perform jobs in the manufacturing process as well - including cooling and drying. They can also be used as safety stocks.
	Wheel conveyor Wheel conveyors are used widely because of their simple design, their robustness, and their low investment and operating costs. They are only suited for the transport of goods that have a solid, even surface. Otherwise, operations cannot be carried out smoothly. Wheel conveyors are frequently used at the front end of the warehouse, and in production for jobs related to the loading and unloading of road vehicles, rail cars, ships and airplanes.
	Crane Cranes are used to serve warehouses and to supply and dispose of equipment and facilities used in production. Typical tasks are warehouse operations and transport of goods.
	Electric trolley conveyor Electric trolley conveyors can be used in all areas of a company, from the receiving area, warehouse and picking area to shipping. Their main area of use is for short trips requiring little to mid-range throughput that can be covered quickly. They are frequently used in the electronic, textile and food industries as well as in vehicle-body assembly in the automotive industry.
	Forklift trucks Forklift trucks facilitate ground transport of horizontally stacked goods throughout a business operation. They are particularly suited for short trips and mid-range transport frequency. Favored areas of use are between workstations and in confined spaces - including the loading and unloading of containers, trucks and rail cars.
	Forklifts Forklifts combine the horizontal transport of goods with stacking jobs. They are used to move goods onto load-carrying devices like pallets, wire-mesh boxes or individual parts. Favored areas of use are storing and retrieving pallets in rack storage.
	Operatorless transport system Operatorless transport systems are frequently used to move large loads and trailing loads with a low to medium throughput over short to medium distances. In such facilities as production operations and product distribution centers, they are used in irregular horizontal and vertical transports in the areas of receiving, production, warehousing, the front end of the warehouse and shipping.
	Storage and retrieval system Storage and retrieval systems are used in pallet-rack, high-bay-rack or tank-rack warehouses to store and retrieve goods placed on load-carrying devices that have been standardized to the largest extent possible, including pallets, wire-mesh boxes and containers.

Means of conveyance
Source: Materialflusssysteme. Förder- und Lagertechnik | Hompel / Jünemann 2007

Picking systems

The question that arises especially in large warehouses is: Where is a specific item located among the maze of shelves? Modern order-picking systems assist stock pickers by showing them the location of the goods. The systems include the use of light signals (pick-by-light Pick-by-light ) or even information transmission by headset (pick-by-voice Pick-by-voice ).
In this process, the information “Row 14, Position 2” is passed to the picker over the headset. As a result of this communication, the worker learns about the optimal path to the pick location and the pick list [pick list]. He then identifies the storage shelf and parts of the EAN code EAN code for the items stored there, possibly including the code’s last two digits. If the item number matches, this system then informs the picker over the headset how many items need to be picked. The picker takes the goods from the shelf, checks the quantity and receives an “OK.” This procedure is repeated until the prescribed stack height is reached or an order is completely filled.
A new addition to this order-picking system is pick-by-vision Pick-by-vision . With this technology, the picker receives information through data goggles. This system is only in the prototype phase at the moment.

	Picking list The picking list is the traditional management and information instrument used in manual picking processes.
	Pick-by-light Pick-by-light is frequently used to pick fast-selling items. The system is especially useful to companies with small product quantities.
	Pick-by-voice Pick-by-voice is primarily used for picking. The system is also useful in quality control as well as in packing and shipping - e.g., for communicating the carton size to be used. These systems are well suited for those areas where workers need to be able to use both hands for picking purpose due to safety concerns.
	Pick-by-vision Pick-by-vision is only a research prototype at the moment. Application areas are picking of fast- and slow-selling items. The system is an alternative to pick-by-voice and pick-by-light.

Picking systems

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References

[1] Logistiksysteme | Pfohl 2004
[2] Die Fördertechnik | Günthner / Boppert 2004. In: Entwicklungspfade und Meilensteine moderner Logistik | Prockl / Bauer / Pflaum / Müller-Steinfahrt (Hrsg.)

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An inside look at a storage facility

From receiving to shipping