Equipment Buying Guide: Carousel basics

When space, convenience and throughput are a priority, horizontal and vertical carousels and vertical lift modules fill the bill.

By Bob Trebilcock, Editor at Large -- Modern Materials Handling, 8/1/2008

Mention automated storage technology and most people think automated storage and retrieval systems (AS/RS) and mini-load automated storage. Carousels, however, are another class of automated technologies for high-density storage in manufacturing and distribution environments.

There are three automated technologies in this space: horizontal carousels, vertical carousels, and vertical lift modules (VLMs).

While each has its own unique characteristics and applications, three things are common:

By employing dense storage technologies, carousels can save up to 85% of floor space compared to conventional floor- and rack-storage methodologies.
By bringing the work or items to the operator, carousels eliminate the walking and searching associated with traditional picking technologies, reducing man hours by up to 66%.
Finally, because carousels deliver parts to the operator at an ideal ergonomic height, they reduce the potential for injuries associated with bending and reaching to pick items from pallet or carton shelving.

Horizontal carousels

Horizontal carousels are ideal for distribution environments, especially those with an emphasis on small parts and piece picking, according to Bob Rienecke, vice president of sales for Diamond Phoenix (207-784-1381, www.diamondphoenix.com).

“The interest today is coming from customers who have seen increases in the number of SKUs. They are managing and an increase in the number of single-line items they are picking,” says Rienecke. “When you increase your storage density with a carousel, you can slot your products more effectively and your picking efficiency can go up tremendously.”

Horizontal carousels consist of a series of bins or carriers that rotate horizontally around a track like a merry-go-round.

Software manages the putaway and picking activities. An operator enters order information into a station at the front of the system. The carousel then rotates until the right bin is at the operator station. That reduces the travel time needed for an operator to retrieve the parts in a static shelf environment.

Traditionally, a typical carousel has between 20 and 60 bin locations measuring up to 36-inches in width and 6 to 8 feet in height. Newer systems feature bin locations measuring up to 48-inches wide. Each bin location can have multiple shelves to increase the storage density.

Bins can handle loads of up to 1,500 pounds. What's more, carousel systems can be stacked on top of one another to create even more storage in the same footprint. Output from the upper levels can be accessed from a mezzanine, or delivered by conveyor to a workstation below.

Companies often create a pod with two to four carousels for batch picking. While the operator is retrieving a part from one carousel, another system in the pod is retrieving the next pick. Depending on how the carousel is slotted, you can get 200 to 400 line picks per hour from a pod configuration. If you stack the carousels and use an inserter/extractor, you can achieve carton pick rates of 4 cartons per minute from each unit.

Multi-carousel pods are flexible, says Ed Romaine, vice president of marketing for Remstar (800-639-5805, www.remstar.com). “During peak order picking, a floor manager can use software to reconfigure the pods to add pickers and increase throughput,” says Romaine. “During down periods, one picker may be able to operate all of the units in a pod and keep up with demand.”

Vertical carousels

If a horizontal carousel resembles a merry-go-round, then a vertical carousel is like a ferris wheel. The whole unit rotates elliptically to deliver the right shelf or pan to the operator.

These systems bring together high-density, vertical storage and retrieval technology in a small footprint. “The sweet spot for a vertical carousel is incredibly dense storage for fast-moving items that are consistent in size,” says Romaine. “While they can go as high as 60 feet, they are really efficient in areas with a low ceiling height.”

Vertical carousels are often used to store documentation, tools or raw materials on a manufacturing floor and spare parts in a maintenance, repair and overhaul operation. Even high-value small items, like jewelry, can be handled securely in a distribution environment because access to the unit can be restricted.

Romaine is also seeing vertical carousels employed to store and test finished goods at the end of a manufacturing line. “We have one customer that uses a vertical carousel to do an electronic test burn-in,” says Romaine. “Each shelf has an electrical outlet, which allows us to plug in the product when it's stored. The software knows when the product was plugged in, how long it has to be tested, and where it's stored.”

Despite these advantages, vertical carousels have design limitations, especially when applied to heavy parts. Because the whole unit rotates, parts must be stored evenly to prevent an imbalance. For that reason, vertical carousels are most often used for lightweight products, like components in the electronics industry.

Vertical lift modules

From the outside, a vertical lift module, or VLM, resembles an enclosed vertical carousel.

There are similarities. Both systems take advantage of high ceilings: VLMs have been built up to 90 feet tall. And like a vertical carousel, stored inventory can be accessed from multiple windows on multiple floors. Also like a vertical carousel, a VLM can safely store high-value items.

The systems, however, are very different inside. While the whole vertical carousel rotates to make accessible the right bin location, a VLM uses an automatic extractor, much like an AS/RS, to putaway and retrieve one tray at a time. That allows the VLM to make more efficient use of the storage space inside the unit. Before putting away a tray, the cartons are scanned, and the system figures out the optimal space to put them in. To further maximize space, the systems can automatically and optimally rescan and reposition the inventory stored inside the unit during down periods.

Since only the tray required for putaway or picking is moving, there is less vibration with a VLM than a vertical carousel, which makes it appropriate for highly sensitive or fragile parts, like electronic components. The system can even be programmed to handle different parts at different speeds.

“With a VLM you get the benefit of vertical storage space, but the ability to use multi-bay technology to increase storage density,” says Rienecke. “With two storage bays and two access windows you can get better pick rates than you can from a vertical carousel.” That's because one picker can be picking from one bay while another picker can access the other. “That concept also allows you to replenish the unit while you're picking,” says Rienecke.

Company	Web site	Telephone number	Horizontal carousel	Vertical carousel	Vertical lift module (VLM)
Diamond Phoenix	www.diamondphoenix.com	888-233-6796	x	x	x
Hanel	www.hanel.us	412-787-3444		x	x
Kardex	www.kardex.com	800-234-3654		x	x
Modula	www.modula-us.com	732-469-4300			x
Remstar	www.remstar.com	800-639-5805	x	x	x
SSI Schaefer	www.ssi.schaefer-us.com	704-944-4500	x
Stanley Vidmar	www.stanleyvidmar.com	800-523-9462			x
White Systems	www.whitesystems.com	908-272-6700	x	x	x

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