Picking

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Picking is the compilation of certain partial quantities ( articles ) from a total quantity made available ( assortment ) based on orders . This can be a sales order or a production order. The employee who puts the order together is known as the order picker, picker or gripper.

Origin of goods

Picking can be differentiated depending on the origin of the goods:

  • Removal of the goods from a standard warehouse (common)
  • Removal of goods from a picking warehouse (improved picking)
  • Removal of the goods directly from production (called: Just in time )
  • Removal of the goods from a stationary shop (for example with Click and Collect )

Picking methods

Customer orders often consist of several items. In practice, a variety of picking methods are used to process these customer orders smoothly and without errors. Below are three basic methods and their variants. They differ in their information and material flows as well as in their organization.

Order-oriented, serial picking

The orders are processed one after the other in the various storage areas. All storage zones can be passed through by a single order picker per order, or by one order picker per storage zone. This is a frequently practiced method of picking, as it ensures easy familiarization, can quickly determine responsible persons and requires little organizational preparation. However, the associated long order throughput times, the long picking routes and the problem of handing over an order to the picker in the next storage zone are problematic.

Order-oriented, parallel picking

Each customer order is separated into partial orders according to the storage zones so that picking can take place in parallel in the individual storage zones. The partial orders are then merged. Although the order processing times are significantly shorter here, the problem arises of a complex order division and consolidation, as well as an uneven load on the individual picking areas.

Series-oriented, parallel order picking

The incoming orders are grouped into series and distributed within a series to the positions of the individual storage areas. In this way, an article that is available in several orders can be removed collectively. The individual articles are then reassigned to the individual orders.

  • Remove in series - merge order by order
    The main advantage is that a storage location only has to be accessed once per series and not per customer order. However, there are still relatively long order throughput times as well as complex preparation and consolidation of orders, which cannot be managed without the use of IT.
  • In general, the picking routes can be shortened by the access aisle strategy, i.e. H. all articles with high circulation are stored close to the dispatch point. Articles that are rarely used are stored further back on the shelf.
  • Another way to save time during order picking is to use pick lists that are optimized for the route. The orders whose storage locations are close to each other are summarized on the pick list. This saves the warehouse employees long walking distances.

Picking times

How quickly a customer or the production department receives the desired items or materials depends on the picking time. The picking time is made up of various individual times:

Base time
+ Travel time
+ Gripping time
+ Dead time
+ Distribution time
= Picking time

Explanations for the individual times

Base time

The base time includes the time for the organizational activities before and after the commission:

  • Record, read and organize the picking documents
  • Access to the picking device
  • Delivery of the picking device to a collection point
  • Searching for and provision of aids such as pallets, order picking trolleys, small containers
  • Handover of the container to the order collection point or a conveyor system

The high base time is mostly due to two causes:

  • incomplete, poorly readable, disordered picking documents
  • poorly organized provision of commission tools (search, repair, etc. required)

Travel time

The way time is the time for coping with the way between two withdrawals. It is usually recorded per position. In most cases, the travel time contains the largest proportion of the total picking time.

  • Start of the storage locations of all order items
  • Return to the starting point

The travel time can be reduced by

  • Avoidance of wrong ways due to poor knowledge of the storage locations
  • Increasing the article concentration (if the "frontal area" per article on the shelf is reduced, the distance between two articles decreases),
  • Storage of the most frequently requested articles (A-goods, bestsellers) at the beginning of the shelf (aisle strategy)
  • Combining several partial orders for a picking tour
  • Use of order picking vehicles. The higher speed of the vehicles compared to people walking, however, only has an effect on long distances between the individual withdrawals
  • Use of flow racks.

Gripping time

The gripping time (removal time, picking time) includes the activities:

  • Take items off the shelf, d. H. Reach, grab, take out
  • Place the item in the container

The gripping time depends on:

  • from the handle height
  • from the depth of the handle
  • the weight, volume and sensitivity of the items removed
  • the type of delivery (container, conveyor belt)
  • on the amount of items to be removed

Dead time

The dead time, also called secondary time, includes:

  • Search for the storage location of the article
  • Form dawn
  • Check, count, compare
  • Make labeling (e.g. entry in warehouse card )

The dead time can usually only be shortened slightly by suitable measures:

  • good shelf labels for quick finding
  • automatic counting processes
  • Refrain from handing in parts, only handing over prepackaged quantities
  • Pre-packing in different quantity units (e.g. 1, 5, 10, 20, 50, 100 pieces)

Preparatory:

  • Search for the storage location
  • Compare the position with the item in the compartment
  • possibly formation of the crack
  • Counting the quantity removed

Follow-up:

  • Checking, counting and weighing of the removed items
  • Acknowledging the removal

Distribution time

The distribution time records the time in which there is no productive work. These include:

  • personal distribution times, e.g. B. go to the toilet, blow your nose, do fake work
  • factual distribution time, e.g. B. Break due to lack of work, waiting for the means of transport or for information

The distribution time can be shortened by:

  • better workplace planning
  • Employee motivation
  • a good working atmosphere
  • Introduction of a bonus wage system that takes quantitative and qualitative aspects into account
    (quantitative: time per order unit; qualitative: error rate per order).

However, it is particularly important that the employee contributes to shortening the distribution times through his own will.

Picking systems

A distinction is made between automatic and manual order picking systems:

Mechanical order picking systems

  • Picking machines

In order picking machines, goods are in shafts that are attached to the left and right of a conveyor belt. Each good has its own shaft. For the execution of a picking order, a container that is already assigned to the order via a barcode at the system entrance runs over the conveyor belt. The shaft opens at the right moment and the goods to be picked are fed into the container via an ejector.

  • Picking robot

Picking robots receive the order data such as order number, coordinates of the storage location, number of items and weight of the goods automatically from the warehouse computer. You are able to drive to the shelf and remove the goods from the shelf with the help of a gripping system consisting of suction cups and place them in a container that is carried along. The gripper itself is equipped with an image processing system that recognizes the goods in the warehouse. The correct withdrawal amount is determined by weight.

Manual picking systems

Goods-to-person workstation with pick-by-light displays
  • Goods-to-person systems; so-called dynamic provision = dynamic picking
  • Person-to-goods systems; so-called static provision = static picking

Picking process

Picking using picking slips

Using the picking slip (also known as picking list or picking list), which contains the storage location, item number and quantity, the picker removes the specified quantity and then ticks it off.

The feedback in the warehouse management system takes place after processing the picking list. Incorrect locations, inventory errors, picking errors etc. result in picking errors that on the one hand hinder the following processes (e.g. production) and lead to inventory differences. Therefore, various methods of automatic identification and data acquisition are used to guide the warehouse worker to the correct location as well as to ensure that the correct material is removed.

Picking with mobile data acquisition (MDE)

The picking list is displayed here on an MDE . Articles removed are confirmed on the MDE; Shortages can be entered. The current status of the picking can be continuously tracked through the mostly direct connection of the MDE to the warehouse management system . Inventory data can be updated without additional data entry. MDEs are often combined with barcode scanners or RFID readers in one device, which enables additional checking of the removed item.

Order picking with barcode scanner shelf storage
Order picking with barcode scanner shelf storage

Picking by barcode

With the pick-by-scan process, the pick list is displayed on a PDA . When goods are removed and stored, the barcode of the article and that of the storage location are scanned. On this basis, the storage location and article are correctly assigned. This method can therefore also be used in the context of dynamic storage. The pick-by-scan process can also be used when assigning the goods to orders and, as a control instance, helps prevent incorrect deliveries.

There are also mixed forms of order picking. Some manufacturers combine the pick-by-scan process with the picking process using a pick list. In this case, the scan serves as a control and is intended to help the order picker remove the correct item from the storage location.

Warehouse navigation in narrow aisles

Modern order picking forklifts know the current rack aisle and their respective horizontal position within the rack aisle. This is z. B. realized with the help of RFID transponders laid in the floor , which are read by the vehicle and check the vehicle's internal distance measurement for plausibility. In addition, the current height of the picking cabin that can be raised in these vehicles is permanently determined. The picking orders from the warehouse management system are now not only displayed on a terminal ( MDE ) on the vehicle, but also transmitted directly to the vehicle control system. Based on the known actual and destination coordinates, the vehicle control system determines the most economical approach to the destination. The operator of the order picking vehicle now initiates the target approach and is automatically directed to the desired storage location. When the target position is reached, the order picker will find the appropriate storage compartment z. B. signaled by a spot attached to the side of the picking cabin. The feedback to the warehouse management system takes place manually, with barcode scanners or RFID readers. The optimal picking sequence is determined by the warehouse management system.

Advantages and disadvantages

advantages disadvantage
  • Keep your eyes open when approaching your destination
  • optical display and illumination of the correct storage location
  • fewer picking errors
  • no searching for storage locations, no wrong trips
  • significantly higher picking performance
  • Storage topology is unimportant for the operator
  • The warehouse management system provides the most efficient picking sequence
  • Illuminance in the warehouse can be reduced
  • currently only available with guided order picking vehicles (rail or guide wire guided)
  • High acquisition costs

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