To overcome labor shortages and reduce costs yet increase accuracy, productivity and service levels managers should follow these parameters to make the decision on which type of picking system and equipment should be used:
- The return on investment and payback periods for major capital investments will decide if automation should be taken or not.
- Ergonomic and green issues over energy usage and environmental friendly equipment is another area of importance
- Any relocation of the business, changes in product profile or distribution channel (ie the long term strategy) reflects that any investment in hard automation needs to be carefully considered.
By comparing picking solutions the simulation software is able to determine performance indicators such as operator pick rates and overall order throughput which are indicators of the most cost-effective method.
Picker to goods
This category involves the order picker travelling to the goods in order to pick them. Common picking equipment types, based on what the picker is picking to, are
- Trolleys and roll-cage pallets – With this method, the picker pushes the trolley (or roll-cage pallet) between shelving or pallet racking in order to access the goods. A trolley (also oft en known as a pick cart) normally has a shelf, or shelves, on which to place the goods or it may be in the form of a frame for holding plastic tote bins or cartons. Roll-cage pallets are normally taller and have wire mesh on three sides, with or without a mesh door on the fourth side.
- Powered order picking trucks – These are electrically powered trucks that have forks, often carrying two wooden pallets or three roll-cage pallets, on to which picked goods may be placed.
- Free-path high-level picking trucks – Goods may be picked from upper levels of racking, or from high-level shelving, by means of free-path high-level picking trucks.
- Fixed-path high-level picking trucks – These are similar to free-path trucks, except that they run on a bottom rail and are also guided by a top rail – thus being similar to an AS/RS crane operation.
- Pick cars – One problem with high-level picking trucks is that they need to return to the end of the aisle whenever the unit load (eg pallet) that receives the picked goods is full. In the case of picking to pallets, the full pallet is then normally placed at a pick-up and deposit (P&D) station at the end of an aisle and is collected by a reach truck or similar.
- Conveyors – A number of picking operations make use of conveyors.
Goods to Picker
It is inefficient for a picker to travel the whole length of a pick face if a relatively small proportion of the total product range is to be picked during that pick run. Various types of equipment have therefore been devised to bring goods to the picker, and which are
- Horizontal and vertical carousels – These are oft en arranged in modules of two or three carousels so that the picker can pick from one carousel while the other(s) is, or are, rotating.
- Miniloads – These may be used for full carton picking or for presenting cartons, or tote bins, to a picker for the picking of individual units.
- Totes-to-picker systems – These are oft en linked to miniload storage systems, with tote bins being extracted automatically by the miniload crane. The tote bins are then routed by complex conveyor systems to the individual picker requiring that SKU.
- Pallet-to-picker system – These may be based on AS/RS and typically operate similar to miniloads.
- Shelf modules-to-picker systems – A further system available is one that brings complete shelf modules (eg about one metre in length, comprising about two to five shelves) to the picker. This is undertaken by robotic drive units that move by computer control to beneath the required shelf module and then raise this and transport it to the appropriate pick station.
Automated Systems
There are automated picking systems available, as
- Layer pickers – Cases are normally stacked on to pallets in layers. a pallet is brought forward from the reserve pallet store (eg by AS/RS and conveyor) to a layer picking machine. This machine would lift the top layer off (eg by suction pads) and place it on to a pallet that is being assembled for the customer order.
- Dispensers – These typically comprise two lines of near-vertical magazines positioned over a conveyor in the shape of an ‘A’ – hence, the common name of A-frame dispensers. Each magazine contains a single SKU with the individual items or cartons stacked vertically.
- Robots – Robots are not commonly used for actually picking goods from pallets, cases or tote bins.
Sorting System
The sorting process including the requirement for a picking area, a storage area, replenishment of the picking area, and a sorter. This method uses automatic material handling system consisting of multiple conveyors and a number of sorting devices.
The items are placed on a conveyor in the storage area and the items are sorted for each particular order. The operator in the picking area collects the items that have been sorted for a customer order and processes that order. The efficiency is gained because the operator does not have to consume time collecting individual items.
Sortation may occur immediately after picking so that items can be assembled into the appropriate orders ready for packing or dispatch. Where there is a separate packing operation, sortation may also occur after packing so that the packed goods can be assembled into vehicle loads (or into postcode areas ready for postal deliveries).
Mechanized sortation can be undertaken as an integral part of conveyor systems. For example, a conveyor may sort to different packing stations by means of pop-up wheels that are raised when the required case goes past a conveyor spur. The wheels are then powered at that moment and the case is diverted down that spur.
However, for high-speed sortation, conveyors normally feed into specialist sorters. These are normally set out in a loop so that product (eg individual items or cases) move past numerous chutes or conveyors until they reach the one that they are destined for (eg representing a particular store or vehicle load). Product is normally identified by means of an automatic recognition system (eg bar code). Alternatively, there can be manual in-feed stations where goods are placed on to the conveyor and data concerning the SKU are fed in manually.
There are a number of sortation systems available, as
- Sliding shoe sorters – There are ‘shoes’ located at the edge of the conveyor. When the goods reach the appropriate destination point, the shoes slide across to divert the goods down that spur.
- Bomb-bay sorters – These hold goods in receptacles that have opening bottoms releasing the goods in the same way as a ‘bomb-bay’ on an aeroplane. These are suitable for goods that may be dropped vertically, for example, small packages into mail bags for postcode sortation.
- Tilt-tray sorters – Tilting conveyors are usually laid out in horizontal carousel configuration, with a series of tilting trays or slats fitted to a conveying chain, and capable of tipping loads off to left or right to branch conveyors or to off -take chutes. The slats can be tilted singly or in multiples according to sizes of load being handled.
- Cross-belt sorters – These comprise a series of mini-conveyor belts aligned at 90 degrees to the direction of travel. The appropriate mini-conveyor belt starts up when the item reaches the required off -take destination point.
Pick To Box
Pick to box is similar to the sorting solution as it uses the same elements; a picking area, a storage area, replenishment of the picking area, and a sorter.
The picking area is organized so that there are a number of picking zones connected by a conveyor system. The operator fills the box with the items on a customer order and the box moves to the picking zones until the customer order is complete and it is then ready for shipment to the customer.
The efficiencies are gained because the operator does not have to consume time collecting individual items, but the cost of the initial set-up of this solution could negate any cost benefits that the solution offers.
Choosing an order picking system depends on any number of requirements such as cost, complexity, the number of customer orders, size and number of items, etc.
Every company has a unique requirement and one order picking solution may suit one business and not another. Determining the requirements will ensure that the most efficient order picking solution is selected.
