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Big Picture: A new take on unit-load storage

As end users optimize their facilities, high-density dynamic storage is getting a fresh look.
By Bob Trebilcock, Executive Editor
December 01, 2012

Four types of solutions
At least four types of high-density storage solutions are available on the market today. They include mechanical, semi-automated and automated solutions. All three combine high-density, flow-through rack storage with some type of technology to provide pallet movement.

Mechanical solutions: In this solution, pallets are loaded at one end of a lane and are retrieved from the other end. Pallet movement through the racks is controlled by air. Pallets rest on a rail on either side of the rack. Wheels or rollers are set atop an air hose in an inner channel on either side of the rail. When the pallet is at rest, the air hose is deflated. To move the pallets forward, the wheels or rollers are raised by the pulsation of air in the hose. When the channel rises, the load moves by gravity in a controlled manner. As the hose deflates and the inner channel is lowered, the load sets down on the rails for a soft braking. The solution can handle loads as light as 50 pounds and heavier loads from 4,000 to 10,000 pounds in the same lane. It will also operate in freezers as cold as -25ºF. “We’ve done projects as many as 20 pallets deep and the technology has been used in deeper lanes than that,” says Quinn of SafeFlo. The system works best in first-in/first-out applications, especially in buffer storage applications.

Radio-controlled shuttle technology: In this solution, radio-controlled shuttles or carts are used to move pallets. As with the mechanical solution, pallets are only moving forward or backward in a lane. A lift truck operator places a shuttle in a designated lane where work is about to take place. Once the cart is in place, the operator uses a radio transmitter to instruct the cart to perform the command. The operator may drive away to retrieve or deliver another pallet while the shuttle works on its own. “The beauty of a shuttle system is that you can match up the number of shuttles you need with the number of lift trucks working in an area,” says Grafe of PAS. He adds that a facility moving 16 to 18 pallets an hour with just a lift truck can move up to more than double that amount with a shuttle. “It’s best suited to high-volume, fast-moving product, especially at the receiving or shipping docks.”

Cable-driven shuttle technology: The shuttles and carts described above are moved from rack to rack by a lift truck operator. In a variation, pallets are moved using a combination of three technologies that allows for computer-controlled load sequencing in a deep-lane storage area. The process begins when a pallet is loaded by a lift truck or a conveyor onto a vertical transfer lift. This device delivers the pallet to different levels in the pallet rack. Each level of the rack system has a cross-aisle transfer vehicle that can move across all the lanes of storage on each level. The cross-aisle transfer vehicle deposits the pallet onto a cable-driven shuttle that slides forward and backward in the deep storage lanes. “Because the system has three axes of travel, we can configure the system based on how pallets are shipped and routed and not just on increasing throughput,” says Retrotech’s Beyer. “The software automatically places loads into optimal positions based on the order patterns. Fast movers are more accessible and slow movers are positioned out of the way.”

Automated shuttle technology: Automated shuttle technology is used to automatically store and retrieve pallet loads of product. Where a unit-load AS/RS uses a crane in each aisle to store and retrieve pallets, automated shuttle technology uses a vertical lift to deliver the pallet to the right level in the system. One or more shuttle vehicles on each level move pallets to a storage location within the lane, similar to the shuttle in a mini-load shuttle. In a deep-lane configuration, a second shuttle or roll cart can drive into the rack to deposit or pick up pallets. The primary advantage is the additional speed in high-throughput applications. “Shuttle-based systems for totes are meant to be faster than conventional mini-load AS/RS systems,” says Coyne of System Logistics. “Similarly, these systems are faster than unit-load handling AS/RS systems.”

New processes
High-density dynamic storage solutions were initially installed to provide very efficient reserve storage. Today, as the nature of storage changes, they are being applied as a complement to a conventional process such as work-in-process or shipping. They are also being combined with other highly automated technologies to create new order fulfillment processes.

“The concept, and what we’re working on, is a blending of automation and high-density dynamic storage techniques,” says Quinn. “The merge between the two has been slow to catch on, but we’re now seeing interest among the end user community in solutions that bridge that gap.”

As an example, Quinn’s company worked with Muratec to develop an alternative to a conventional unit-load AS/RS for a freezer application in the meat industry. A mechanical solution provides the dense deep-lane storage. Instead of dedicating a pallet-handling crane to service each aisle in the AS/RS, the system will be serviced by one crane that can automatically load pallets into the system and a second crane at the front of the unit to remove pallets from storage to fill orders. “The cost savings came from reducing the number of cranes required to automate the system,” says Quinn. “In addition, we’re reducing the amount of energy required to maintain the temperature in the freezer since you don’t have to light it, and you don’t have lift trucks going in and out of the temperature-controlled area.”

System Logistics is pairing mechanical technologies and automated shuttle systems with a case buffering and picking system to automatically sequence and build mixed-SKU pallets. “SKU proliferation is creating a much more labor-intensive picking process,” says Coyne. “If there are a limited number of SKUs coming off the line, we can put them in a mechanical system. If there are a lot of SKUs, we can put them in an automated shuttle system.”

The high-density storage systems feed a mini-load case buffering system that sequences cartons to the palletizing line as needed. “The flow rate we get with one of these high-density systems allows us to build a 20,000-case buffer instead of an 80,000-case buffer and still keep up with demand,” says Coyne.

On the shipping dock, the solutions are being used to reduce the amount of space required for staging and to speed up the truck-loading process. In a typical solution, the system will begin pulling pallets required for an order when the truck driver pulls into the dock. When the truck is ready for loading, “the lift truck driver is simply pulling a pallet from the end of the system and putting it directly into the truck,” says Retrotech’s Beyer. “In one of our installations, it’s only 15 feet from the end of the system to the back of the truck.

“As we deploy more of these systems, we’re finding more end users who can get many of the benefits of AS/RS without the heavy costs associated with an implementation,” says Frazier’s Garside. “These systems aren’t right for everyone, but there are a lot of possibilities for many industries.”

Companies mentioned in this article
Automha USA
Frazier Industrial
Interlake Mecalux
Power Automation Systems (PAS)
Muratec
Retrotech
SafeFlo Technologies
Smoov ASRV
http://systemlogistics.comSystem Logistics


HD/DS definition

More than a decade ago, the Material Handling Industry of America (MHIA) created a definition for the space:
“We define HD/DS (high-density dynamic storage) as a concept where multiple unit loads of the same SKU are sequentially stored in the same location or lane, (one in front of the other), with a minimum distance between loads, thus the item high density. The term dynamic storage implies moving storage, because a HD/DS system also has the ability to automatically or semi-automatically index or convey the loads from the load point to the unload point of the system. More realistically, [high-density dynamic storage] is a flow through rack, where loads pass through the rack toward their next point of use, as preceding loads are used or retrieved.”

About the Author

Bob Trebilcock
Executive Editor

Bob Trebilcock, executive editor, has covered materials handling, technology and supply chain topics for Modern Materials Handling since 1984. More recently, Trebilcock became editorial director of Supply Chain Management Review. A graduate of Bowling Green State University, Trebilcock lives in Keene, NH. He can be reached at 603-357-0484.


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