The majority of warehouses continue to operate with minimal automation and therefore picker-to-goods operations prevail.
Pick to order
The picker takes one order and travels through the warehouse either on foot with a cage or trolley or with a pallet or fork truck, collecting items until the whole order is picked. Orders can be for individual items, full cartons or even full pallets. The picker follows a route designated by reading a paper pick list, reading instructions on a radio data terminal or following voice commands.
All order lines are picked in sequence for a specific customer order. Depending on the size of the items, these will be stored on shelf locations, in carousels or on flow racks. Full cartons can be stored on pallets in pick locations or in flow racking. The advantage of picking individual orders is the minimum amount of handling involved. This remains the most common method of picking. However, orders with multiple SKUs and long distances between picks can be very labor intensive. There is normally a requirement for a second person to check the order before it is dispatched.
Cluster picking
In order to reduce overall travel time, operators can take a number of orders out into the warehouse and pick into individual compartments on their trolleys or cages. Some operations will utilize powered pallet trucks that can carry two pallets at a time or utilize tugs or tractors that can move multiple pallets through the picking aisles. Cluster picking can also be used with conveyors, where a tote diverts into a pick zone. As the tote passes a barcode reader its unique ID is read and all the picks for the current tote are displayed on the individual pick-to-light terminals.
Each terminal indicates both the quantity to be picked and the location where it is to be placed. A pick of eight pieces into the B compartment would be displayed as B8. When all picks for all compartments in the current zone are complete, the tote is returned to the conveyer belt and it proceeds to the next zone, where additional picks for any compartment are required. The number of orders per cluster will depend on the number of lines, units per order, total cube and the capacity of the totes, cages or trolleys.
The correct number of items are picked and allocated to customer orders until the lines and units are exhausted. This can also be termed bulk picking. Advantages include less travel and potentially increased accuracy as two people are involved in the pick and allocation process. The disadvantage is that it can be a two-stage process and it doesn’t always take into account time-sensitive orders. Batch picking can significantly increase the number of lines picked per hour; however, you also have to take into account the collation of the items. The system can be utilized within a cross-dock operation where product can be picked and allocated on arrival at the warehouse. This removes the put-away and replenishment aspects of the operation and increases through-put and accuracy. Orders can be batched in a number of different ways. For example, mail order or e-commerce operations may well batch by single order lines or single items. Orders containing similar items can also be batched together. Finally orders can be split, based on where the products are in the warehouse. Batching orders together can be done manually.
Zone picking
In zone picking, products are picked from defined areas in the warehouse and each picker is assigned to a specific zone or zones and only picks items from within those zones. The level of activity will determine the number of zones allocated to each picker. Orders are moved from one zone to the next as each zone completes its pick. This movement can be undertaken by a cage, trolley or pallet being passed from one operator to another but is more commonly done by conveyor. The conveyors may be powered or use rollers or gravity to move the cartons or totes between the zones.
The volume of orders sent to each zone needs to be controlled so that each sector has an equivalent amount of picks. The potential for bottlenecks can be high with staff having to wait for orders to arrive. Zones are usually sized to accommodate enough picks for one or two order pickers. A picker may look after two zones or more if the volumes are reduced on a particular day. Zone picking can be effective in operations with large numbers of SKUs, multiple orders and low to moderate picks per order.
Some companies will also scan the barcode on the product prior to placing it in the tote to ensure that the correct item has been picked. Advantages are the reduction in travel and the speed of pick as multiple lines can be picked at the same 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 released at specific times during the day. This can be hourly or morning or afternoon. The idea is to associate them with vehicle departures, replenishment cycles, shift changes, etc. 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.
