May 1, 2009
equipment & applications | Pick to Light

Get more bang from your pick-to-light buck

Here's how to get the most out of your pick-to-light investment.

By Susan K. Lacefield

You know that pick-to-light technology can boost picking accuracy and accelerate throughput. But times are tight, and these systems aren't cheap. How can you make sure you'll see a quick return on your investment?

With most technologies, the answer is simply to go out and find as many applications for the new system as possible. But that's not the case with pick to light. In fact, order fulfillment experts—including some who sell pick-to-light equipment—strongly advise against it. With pick to light, they say, the key is to use the technology selectively, reserving it for applications that meet very specific criteria (and finding alternate picking methods—like radio frequency (RF), voice, or even paper—for those that don't).

Although that might seem unduly complicated, this type of blended approach is the key to a smooth-running picking operation, according to the experts. "No one solution meets 100 percent of everybody's needs," says Ed Romaine, vice president of marketing for Remstar International, a manufacturer of automated storage and retrieval systems (AS/RS) that use pick to light. At the same time, pick to light's advocates also maintain that virtually any operation can benefit from the technology. "I do believe there is a limited number of SKUs within every DC that pick to light really makes the most sense for," says Lance Reese, group manager, sales support for FKI Logistex, which makes automated material handling solutions.

The need for speed

Since their emergence several decades ago, pick-to-light systems have become a fixture in DCs around the globe. Designed to promote efficiency, the systems use lighted beacons, usually mounted on storage racks, to direct order picking activity. In a typical pick-to-light operation, warehousing software electronically "reads" order pick tickets, determines the best picking sequence, and transmits signals to the light modules on the racks. Flashing lights then guide workers to the items they need and indicate the quantity needed. When the worker is finished, he or she presses a button so the computer can verify that the correct item has been picked.

So where does pick to light provide the biggest bang for the buck? To answer that question, you have to look at the items being picked in a given zone, how they're picked, and the method of storage, says Richard Gillespie, senior project engineer for TriFactor, an integrator of material handling systems. Are the stockkeeping units (SKUs) in the zone fast or slow movers? Are they picked individually or in case or pallet quantities? Where are they stored—on shelving? on flow racks? in carousels?—and how far apart are the pick locations?

Because pick to light's advantage over competing systems is speed, it stands to reason that it's best suited to fastmoving items. But how fast is fast moving? Reese of FKI Logistex considers an item to be fast enough for pick to light if it moves at a rate of 300 to 1,100 lines per hour.

Remstar's Romaine takes a somewhat different approach to determining if an item qualifies as a fast mover. "I have a very scientific test," he says. "I walk up to a rack, and I run my finger over the second or third line of items. If there's dust a quarter of an inch thick, then it's not a high-activity item."

Just how many SKUs will fall into the "fast movers" category? Although the answer varies from one operation to the next, usually the 8020 rule applies, says Dave Broadfoot, managing partner of pick-to-light manufacturer Lightning Pick. That is, about 80 percent of all orders will "hit" 20 percent of the SKUs. The zones containing these SKUs will benefit most from pick to light.

What makes pick to light a good choice for fast movers is its ability to provide picking instructions for several items simultaneously. With voice and RF systems, order pickers must wait for the computer to tell them what their next pick is, according to Gillespie. With pick-to-light systems, the wait time is eliminated. All of the displays for items needed for an order can be illuminated at once, so the picker can tell at a glance where the next pick location is.

Prime picks
Another key factor in determining whether a zone is a good fit with pick to light is the picking method used. Generally speaking, pick to light is best suited to splitor brokencase picking applications, in which items like single bottles of wine or power cords are picked as "eaches."

Still, there are plenty of companies that have used pick to light successfully for fullcase picking operations. Lightning Pick has one customer, for instance, that decided that voice wasn't providing the speed it was looking for in its fullcase picking operation. The company is now in the process of switching to pick to light.

The type of storage system used in a zone will also enter into the decision. Most experts agree that pick to light works best for items stored in carton flow racks, with replenishment taking place at the back end and picking occurring at the front end. Pick to light can also be used with static shelving, although that will keep the operation from taking full advantage of the technology's speed.

Carton flow racks and shelving aren't the only storage media that are good candidates for pick to light, however. For medium-velocity SKUs that might not warrant carton-flow racks, Remstar's Romaine recommends using AS/RS pod technology (which incorporates pick to light). These systems bring the items to the pickers, instead of requiring the pickers to travel to the pick location. For example, a pod may consist of two horizontal carousels that are integrated into a pick-to-light system. The carousels automatically turn so that the correct item is in a position for picking, and the light tree indicates what carousel to pick from, what shelf to pick from, which cell on the shelf, and the number of items to be picked.

Whatever the type of storage used, however, it's important to take travel distances into account. For pick to light to make sense, pick locations must be relatively close to one another; lengthy travel distances will offset the technology's speed. "Even though you may have a very high-velocity item, if you've got to travel six feet in between picking locations, then pick to light may not provide the best payback," says Reese.

The non-starters
Just as there are characteristics that make a zone a good candidate for pick to light, there are others that essentially rule it out. What's not a good fit? To begin with, zones with bulky items and items that are being picked from a pallet. "Any place where you have a worker aboard a forklift truck picking pallet quantities, pick to light does not make sense; it's almost impossible to get off a forklift truck and push a light," says Broadfoot.

The same goes for zones where throughput volume is extremely low or extremely high. David Remsing, system sales manager for Innovative Picking Technologies Inc. (IPTI), says IPTI receives many inquiries about the technology from companies that only have two pickers. "In those cases, you just don't have enough volume to justify it," he says. To be a good candidate, he says, the operation needs at least 10 pickers.

At the same time, Remsing warns against using pick to light for extremely high-volume operations. For those applications, he says, a mechanized solution like a mechanical sorter or an A-frame would probably be a better choice.

Other non-starters include what Broadfoot calls "grocery store setups" that contain 10,000 to 100,000 SKUs and where travel distances between picking locations can be several pallet-lengths long. Still, these aren't hard and fast rules. Sometimes, there are operational considerations that make pick to light the best choice for a zone that wouldn't otherwise fit the profile. An example would be a zone that doesn't contain any fast movers but would nonetheless benefit from improved picking accuracy.

Broadfoot adds that in some instances, the need for consistency will override all other considerations. "If you find that you have 100 SKUs that need to be managed by pick to light but you have a total of 300 SKUs, then let's just put lights on all 300 SKUs," he says. "That way, the business process will be the same for everyone involved."

The price is right?
Inevitably, any discussion of how to get the most from pick to light will turn to costs. With the lights alone costing around $50 a pop, according to Gillespie, pick to light isn't cheap. But there are ways to economize.

One is to stay away from the "extras" when choosing a system. Most manufacturers offer a base package that doesn't include all of the bells and whistles (like reporting capabilities and labor tracking), and some offer models designed specifically as low-cost alternatives (like IPTI's Pick-MAX Micro). These solutions can provide a good entrée into the technology without breaking the bank.

Another option is leasing. Broadfoot reports that some smaller companies—say, those with around 100 pick locations—have found leasing to be an affordable choice.

There are also opportunities to save money at the installation stage. "One of the shortcomings of pick to light is that it requires a light for every pick location, which can be relatively expensive," says Gillespie. "You can eliminate some of the costs by having a light share multiple pick locations or a light for one whole bay, but then you lose some of the accuracy."

Remsing adds that some customers have kept costs down by handling some of the installation work themselves. They provide most of the labor and have just one or two people from the manufacturer participate as supervisors.

Companies sometimes try to save money by installing RF or voice systems in areas that are more suitable for pick to light, but they're fooling themselves, says Gillespie. Although people often assume pick to light is the highest-priced option, he says, that's not always the case. "If you have a [small] number of SKUs and a [large] number of pickers," he says, "then RF and voice picking are generally going to cost more [than pick to light]."

Rather than focusing on initial cost alone, says Romaine, DC managers would do better to take a hard look at how the technology fits with the company's strategic goals. If pick to light emerges as the logical choice from the standpoint of productivity, space constraints, and accuracy, it will likely prove to be the economical choice as well.

About the Author

Susan K. Lacefield
Editor at Large
Susan Lacefield has been working for supply chain publications since 1999. Before joining DC VELOCITY, she was an associate editor for Supply Chain Management Review and wrote for Logistics Management magazine. She holds a master's degree in English.

More articles by Susan K. Lacefield

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