The case for carousels

New storage and picking technologies are stealing the limelight, but horizontal and vertical carousels and VLMs still have a place in the tool kit.

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When it comes to automated storage and picking technologies, “no single size fits all requirements,” says Dan Boone, quality manager for Plasser American Corp., a manufacturer of maintenance equipment for the railroad industry. “We’re using the best tool for the job.”

Boone was referring to his selection of vertical lift modules (VLMs) and a pick-to-light order fulfillment solution to manage $16 million worth of service parts in a Chesapeake, Va., manufacturing and distribution facility (see below). New automated storage technologies like shuttles were likely on every distribution center manager’s wish list during the holiday season. Yet, when it comes to space and cost per storage unit, carousels still have a lot to offer in the right application.

“With the right product line, order profile and application, carousels should be considered as part of the solution in a blended system,” says Don Derewecki, a senior consultant with St. Onge Company.

Historically, the right application has been maintenance parts to support a production line; spare and service parts distribution; kitting; and put-to-light or pick-to-light order fulfillment in some retail applications. For instance, carousels have been effectively used to consolidate picking of slow-moving parts. Because they can be enclosed, carousels are a good choice in high-security applications. They can also be independently climate controlled for product that is sensitive to temperatures or humidity. Most importantly, they’re not a one-size-fits-all solution, but a component of a broader system.
Let’s make the case for carousels. 

Steady versus sexy: Carousels aren’t sexy, but they are steady. “Carousel technology has been perfected over decades,” says Ed Romaine, chief marketing officer for Integrated Systems Design. “They are relatively easy to maintain, and they now have the best of today’s controls.” What’s more, they work well in distribution environments where space and productivity are at a premium. “A horizontal carousel will take up 70% less floor space than conventional storage for the same amount of inventory,” says Romaine. “If you’re picking slow- to medium-movers, the sweet spot is 250 to 550 lines per hour.” That can be increased if you stack units or add multiple picking pods.

Keep it simple: Order fulfillment has become much more complex. However, applications where a simple, high-density, space-saving automated storage technology fits the bill still exist. “We do not see carousels in fast-moving e-commerce applications,” says Tim Archer, a sales training manager for Kardex Remstar. “However, carousels deliver an attractive cubic-foot-to-square-inch ratio, and it’s a simple storage method.” Hospitals, for instance, are adopting horizontal and vertical carousels in their central storage areas, where the value of the inventory is high and space is limited.

Balancing productivity gains against the cost of those gains: “In a typical Pareto distribution of slow-, medium- and fast-moving SKUs, you can often get the best bang for your buck with a horizontal carousel,” says Tom Coyne, CEO of System Logistics. “There may be a little more walking compared to a mini-load or shuttle system, but carousels eliminate the walking associated with a conveyor-based picking system.” On the other hand, a carousel doesn’t require a conveyor to deliver a tote to a workstation, which can reduce the cost of the solution. Why haven’t carousels gotten more love lately? Coyne attributes to the introduction of competing technologies, like shuttles, just as the carousel industry went through a shakeup. “As the new technologies are maturing, some customers are evaluating carousels versus shuttles and mini-loads,” Coyne says. “We could see a comeback of carousel technology.”

They can be highly automated: For end users looking for high degree of automation, horizontal carousels can be stacked on top of one another and equipped with extractors that automatically remove totes or cases and deliver them to a takeaway conveyor, much like crane-based technology. “There are cost/throughput issues to consider,” says Coyne. “An automated carousel system can provide better throughput than a mini-load. However, mini-loads are better at sequencing the delivery of product.”

Still drawbacks:  Carousels aren’t right for every application. Fast-moving SKUs are better suited to a shuttle or a pick-to-light mezzanine. What’s more, it’s not efficient to pick and replenish at the same time—something that can be readily done with conventional picking, a mini-load or a shuttle. But, as Derewecki says, if you do the analysis, “you should look at all the viable alternatives and in many cases, carousels are a viable alternative.” 

Companies mentioned in this article
Integrated Systems Design:
Kardex Remstar:
St. Onge Company:
System Logistics:

About the Author

Bob Trebilcock
Bob Trebilcock, editorial director, has covered materials handling, technology, logistics and supply chain topics for nearly 30 years. In addition to Supply Chain Management Review, he is also Executive Editor of Modern Materials Handling. A graduate of Bowling Green State University, Trebilcock lives in Keene, NH. He can be reached at 603-357-0484.

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