Picking strategies and equipment

One of the most cost areas within the picking operation is that the movement between pick locations. Depending on the operation, this can account for up to 50 per cent of a picker’s time. The aim is to reduce the amount of travel.
Congestion at the pick face is also an issue as it can convert travel time into waiting time. This section examines the different methods of picking and the equipment utilized to attain these goals of reduced travel and waiting time.
There are variety of dimensions to the picking process. These include how and when the orders are presented, how the particular items are picked and therefore the equipment required. These dimensions are shown in Figure 5.1.
What we can see from Figure 5.1 is that there are many interrelationships and many options. For example, if we choose a picker-to-goods operation this will either be done by, for instance , picking individual orders, batch or cluster picking, utilizing trolleys or pallet trucks and a choice of paper, voice or scanning.
The first point to say here is that in terms of picking there's no ‘silver bullet’ or ‘one size fits all’ solution.

According to an Aberdeen Group report (2009), 46 per cent of best-in-class companies are more likely than all others to use advanced pick methodologiessuch as batch, zone and cluster picking as opposed to individual-order picks.
However, each company has different requirements and these strategies might not suit everyone.
A picking operation may require full-pallet picks, pallet-layer picks, outercarton picks, inner-carton picks or individual-item picks.
Many managers see advanced technology and automation as the silverbullet where picking is concerned; however, they may well be overlooking basic improvements that can be introduced to enhance order picking efficiency and also the potential lack of flexibility that accompanies automation in certain operations.
During many of the warehouse management courses I run I tend to seek out that the bulk of attendees don't use ABC analysis and order profiling. There are many opportunities therefore to enhance basic pick operations before introducing automation. Companies are likely to work variety of various order-picking strategies and techniques counting on the character of the merchandise , the number of things  to be picked and the size of order.
There are usually four sorts of pick requirement within a warehouse. However, they do not always occur individually and can be included on the same order. These are as follows:

piece, each, unit, item or broken-case pick;

• full-case or carton pick;
•  layer pick; and
• full-pallet pick.

In the following sections we'll check out each of the pick strategies successively and discuss their interrelationships.
Pick strategies can be split into three categories. These are:

• picker to goods;
• goods to picker; and
• automated picking.

Picker to goods
The majority of warehouses still operate with minimal automation and picker-to-goods operations prevail.

Pick to order

Here the picker takes one order or a part of an order (assignment) and travels through the warehouse either on foot with a cage or trolley or with a pallet using a pallet jack or fork lift truck, collecting items until the entire order or assignment is completed. Orders are often for individual items, full cartons, full pallets or maybe a mixture  of these.
All order lines are picked in sequence for a selected customer order. Depending on the size of the items, piece pick items are likely to be stored on shelf locations, in carousels or on flow racks for example. Full cartons can be stored on pallets in pick locations, on shelving or in flow racking.
The advantage of picking individual orders is that the minimum amount of handling involved because the product moves from store to dispatch in one handling movement.
This remains the most common method of picking. However, orders with multiple SKUs and long distances between picks are often very labour intensive.
There can also be a requirement for a second person to check the order before it is despatched. This requirement for checking is discussed in greater detail in the chapter on despatch.

Batch picking

Batch picking is where operators pick products for variety of orders at an equivalent time. This is almost like cluster picking however instead of have a cluster of separate orders, these orders are consolidated into one pick list and once picked are later weakened into their constituent orders. Pickers are often sent to the reserve cargo area to select full pallets or layers of pallets to satisfy the order quantities.
There are two alternatives: pick by line and pick to zero. Pick by line may end in excess items being returned to stock where full pallets or cartons are picked. For example, a batch of 10 orders may require 100 units to be picked in total. A full pallet holds 120 units and is brought to the order consolidation area. Once the 100 units are picked the extra 20 units are returned to the reserve cargo area or possibly transferred to the forward pick area. In the case of pick to zero the right number of things (the 100 units during this case) are picked and allocated to customer orders until the lines and units are exhausted. This is also termed bulk picking.
Advantages include less travel and potentially increased accuracy as two people are involved within the pick and allocation process. The disadvantage is that it is a two-stage process and cannot easily manage time-sensitive orders.
Batch picking can significantly increase the amount of lines picked per hour; however, you furthermore may need to take under consideration the collation of the things .
The system are often utilized within a cross-dock operation where products are often picked and allocated on arrival at the warehouse. This removes the putaway and replenishment aspects of the operation and increases throughput and accuracy. Orders can be batched in a number of different ways. For example, mail order or e-commerce operations could batch by single order lines or single items. A typical usage is in televised home shopping like the QVC channel.
Different products are promoted at certain times of the day and orders are placed for them. This results in a large number of orders for a single product. Each order is probably going to be for potentially one or two units. It makes sense to consolidate these orders into one pick list and pick large quantities of the product in one pass. It is then simply a case of attaching a shipping label onto each item for despatch.
Orders containing similar items also can be batched together. Finally orders are often split, supported where the products are within the warehouse.
Batching orders together are often done manually; however, most warehouse management systems (WMSs) today have this capability. Technology like put-to-light systems are often wont to help ensure accuracy.
As the bulk picked products are delivered to the sorting or consolidation area each line is scanned successively and lights will indicate what percentage of every product should be placed into a tote or container for shipment. This can be used successfully for multiple mercantile establishment delivery with each store having its own cage, tote or despatch area.

Zone picking

In zone picking, products are picked from defined areas within the warehouse and every picker is assigned to a selected zone or zones and only picks items from within those zones. The level of activity will determine the amount of zones/pick locations allocated to each picker.
Orders are moved from one zone to subsequent as each zone completes its pick.
This movement are often undertaken by a cage, trolley or pallet being passed from one operator to a different but is more commonly done by conveyor. The conveyors could also be powered or use rollers or gravity to maneuver the cartons or totes between the zones.
Orders are often picked simultaneously within the zones and consolidated later or they will be picked sequentially. Separate pick instructions are produced by the WMS for every zone for simultaneous picking. A single pick list travels with each order for sequential picking.
The volume of orders sent to every zone must be controlled in order that each sector has the same amount of picks. The potential for bottlenecks are often high with staff having to attend for orders to arrive. Zones are usually sized to accommodate enough picks for one or two order pickers. A picker may take care of two zones or more if the volumes are reduced on a specific day.
Zone picking are often effective in operations with large numbers of SKUs, multiple orders and low to moderate picks per order. DVD and computer games retailers are typical examples.
The most popular picking method utilized within the zones is pick by light. As an operator scans subsequent order to arrive within the zone, variety of lights illuminate within the section. A digital display denotes the number of items to be picked. Once the pick is completed the sunshine is turned off and therefore the picker goes to subsequent illuminated location. Some companies also will scan the barcode on the merchandise before placing it within the tote to make sure that the right item has been picked.
Advantages include the reduction in travel and a rise within the speed of pick as multiple lines are often picked at an equivalent time compared with pick by order.
This system can be used by companies where there are different zones for product families such as pharmaceuticals, hazardous items and food items.


Wave picking

In wave picking, orders are combined and released at specific times during the day or to associate them with vehicle departures, replenishment cycles, shift changes, product locations, product commonality, value-adding service
requirements and priorities. The use of wave picking can also balance workload by time or by area by logically grouping and releasing orders. Orders can be released at different times to different zones based on how long it takes to pick the orders. The drawback is the requirement for a further step in the process, having to bring the partial orders back together. However, as discussed with batch and zone picking, it does allow for a second check on product codes and quantities.