Seeing the light
Light-directed picking brings improved efficiencies, greater throughput, and increased accuracy to distribution operations.
By -- Modern Materials Handling, 8/1/2000
People have always looked to sources of light for direction.
Wise men followed a star, eastbound sailors steer toward the sunrise, and today's commuters follow the guidance of traffic signals.
Likewise, light is an important source of direction at many of today's most successful distribution operations. Tied to an effective warehouse management system (WMS), light-directed picking can come very close to attaining the magical 100% accuracy that puts smiles on the faces of operations managers.
Just as the term implies, light-directed picking uses lights to guide workers to the proper storage locations of items needed to fill customer orders. These may include flow racks, carousels, shelving, or carts. In most systems, the WMS determines the required stock keeping unit (SKU), then notifies the pick-to-light system to illuminate a light next to the storage space of the SKU. Typical systems also have a pick-quantity display that indicates exactly how many of each SKU should be pulled, based on cases, boxes, packs, or individual items.
"The advantage of pick-to-light versus other systems is that both hands are free for picking," says George King, president of Real Time Solutions. "With the light and quantity displayed, the person only needs to be able to count. They don't even have to know the product to pick it."
This means that training is simplified for workers.
"It's just 'follow the bouncing light,'" says Ed Romaine director of marketing for Remstar. "It tells a person where to pick, what to pick, and where to put it. It forces them not to have to make any crucial decisions."
Pick to light systems additionally offer high throughputs of a wide range of items, permit flexible balancing of workloads in pick zones, and offer high accuracy rates.
The right pick-to-light
Efficient picking requires that the equipment match the need. Light-directed units can be used with most common storage systems. Many facilities utilize several types, designed according to product and pick frequency.
"All picking systems can complement each other," Romaine says. "The trick is to create a work station that takes advantage of all possibilities."
Carousels for instance, are among the most common systems using pick-to-light. They are ideal for holding a large number of SKUs. As product is needed, the pods on a carousel spin to the correct location. Under software control, the light next to the storage shelf illuminates, indicating the SKU and the quantity to select.
Flow racks are ideal for fast movers in facilities. Again, lights and quantity-displays illuminate to direct picking from the racks. Bin shelving also works in a similar manner, but is generally used for slower moving SKUs.
Rolling carts may additionally be outfitted with a combination of pick-to-light and radio frequency data communication (RFDC) technology. These carts contain a number of compartments where items for individual orders are accumulated. In one scenario, a worker pushing the cart passes shelving equipped with display lights. As a pick is required, a light illuminates on the shelf, directing the worker to that SKU. A light on the cart also turns on along with a quantity indicator to direct the picking into a specific order compartment.
Systems may use a combination of RF terminals, voice systems, or printed pick tickets that tie into a WMS.
Much of the success of light-directed picking is due to the dedicated software that manages the operations. Not only does it control what and how much of each item gets picked, but the software must easily interface with the WMS to ensure a smooth product flow. Some pick-to-light suppliers partner with leading WMS providers to eliminate interface problems.
Additionally, software should be designed to make it easier for the worker to interact with the system.
"We've gone out of our way to make certain that the software interface is very instinctive and easy to use," says Kevin Reader, vice president of marketing for Diamond Phoenix. "This allows training to be minimized and carries efficiencies and benefits when the worker does not have to interact with a computer terminal."
Adaptable picking
Light-directed picking can easily adapt to a wide range of order-filling applications. Batch picking is often used with pick-to-light. In this method, a number of orders are picked simultaneously and later divided into individual orders.
Most carousel workstations are designed to easily accommodate batch picking. Many contain a "sort bar" where 8-16 order totes are staged. Items needed for several orders are pulled together from the carousel as directed by the lights at each storage location. Lights corresponding to each of the staged totes then illuminate to indicate the amount of the SKU to place into each tote needing that item.
Individual orders are also picked-by-light. Many facilities use a pick-and-pass conveyor to deliver a tote to several picks zones holding required product. When the tote reaches a zone with a needed item, a light illuminates to direct a worker to pull it from flow rack or shelving. Once all picks in a zone have been completed, the tote is routed to the next area containing product.
Put it here
Just as the lights on a cart are used to gather items for individual orders, carousels and racks are also being used for order accumulation. Known as a "put system," the technology used is similar to picking, but in reverse.
In this type of order processing, each shelf or storage location is assigned to an individual order. Items are pulled from other storage areas as batch picks and placed into totes. The totes then travel to the carousel or racks and are scanned upon arrival. This notifies the WMS that the pulled SKU is available for assignment. The WMS next illuminates lights and quantity indicators adjacent to each of the order accumulation shelves that require that SKU. The worker simply pulls items from the tote and puts them into the designated locations.
Picks/hour | System |
|---|---|
25 - 100 | Shelving |
75 - 150 | Cart |
200 - 600 | Flow Rack |
100 - 800 | Carousels |
Pick numbers depend on SKU, product size, and system design. | |
Source: Industry Experts |
Full range of pick-to-light at Texas grocer
San Antonio-based HEB Grocery is well acquainted with light-directed picking. The company uses a wide range of systems (Real Time Solutions, 510-985-6300, www.easypick.com) in its San Marcos, Texas retail support center. Each day, the facility distributes 150,000 health and beauty products and non-prescription medications to its 230 stores.
Ten foot flow racks combine with light-directed picking for the 11,000 fastest-moving stock keeping units (SKUs), such as cough medicine, foot care products, school supplies, hair care items, and first aid products.
Two carousels house 5,000 higher-value SKUs, including cosmetics. Each carousel has a 12-tote put station. The light-directed system guides workers to picks in the carousels and also indicates which of the staged totes need items to fill orders.
Store supplies also pass though the distribution center. Many of these, such as labels, saw blades for the meat departments, and hairnets, are picked from 5 ft flow racks into carts equipped with radio-frequency receivers (RF). Each cart contains four sections.
"The biggest advantage of the carts is that they can hit picks for four stores at a time, plus they have high accuracy," says Gene Valdovieso, operations manager.
The warehouse management system indicates by RF which of the 2,000 SKUs in this area need to be picked. A worker pushes the cart to the proper rack and scans a location label. A light and quantity indicator then illuminates on the cart next to the section that requires that SKU.
"We used to pick with labels. That involved a lot of thinking and seeking," says Mark Richardson, general manager for health and beauty aids. "Now we just look for the light. Being hands free also us gives total flexibility. We have 50% higher productivity with the pick to light."
While light-directed picking from carousel storage is used by thousands of distribution centers around the nation, a few innovative companies have used the technology in reverse. Instead of picking from the carousels, they use them to accumulate orders in what is known as a "put system."
Hot Topic is one such company. This retailer of apparel, accessories, and home furnishings operates 270 specialty stores and has experienced an increase in productivity while decreasing labor by using this technology. Eight carousels (White Systems, 908-272-6700, www.whitesystems.com) in the company's City of Industry, Calif. distribution center are used to gather the merchandise destined for each store.
"Each of the 384 spaces in the carousel system is a unique store location," says Sue McPherson, division vice president of distribution.
Product is received at the dock and is immediately unpacked according to stock keeping unit (SKU) into individual totes - one SKU per tote. No storage is done at this facility, as items are immediately assigned to stores.
Each tote is given a unique license that is married to the SKU it contains. It is next sent to the carousels, where the license plate is scanned. The software system determines which stores require that SKU and spins the carousel pods. Lights next to each required location illuminate along with a quantity indicator directing workers to place items from the tote into a carton staged in the location. Once the carton is full, a worker pushes it off onto a takeaway conveyor.
Prior to using the carousel system, workers staged cartons on the floor and manually placed outbound orders into them. It took 15 people to do this. Hot Topic installed the first four carousels in 1997, and was so pleased with the productivity of the system that the other four were added last year.
Four workers can now do the job, and throughput has more than doubled from 500 to 1,200/hour. The carousel software also records the contents of every carton that leaves the facility and can additionally track the productivity of every worker, eliminating the need for additional productivity software.
"The big advantage for us is that we can handle our growth without needing more distribution space," says McPherson. "It is a very flexible tool for us."
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