Staging/storing: up, down, and all around
Add horizontal carousels and vertical lift modules to automated storage and retrieval systems for powered handling of unit loads.
By Tom Feare, Senior Editor -- Modern Materials Handling, 2/1/2001
When it comes to staging and storing pallets or other unit loads in powered equipment and then very selectively retrieving them, the automated storage and retrieval system rules. AS/RS has done so for some time with good reason.
Benefits include improved control over materials, reduced levels of inventory, greater utilization of available floor space, less repetitive or unnecessary handling of staged/stored loads, and more efficient use of labor.
An AS/RS performs well, for example, under what are very harsh conditions for manned operations, as Kevin Thuet, director, advanced applications, Eskay, observes. Food storage applications of the automated technology at temperatures as low as -60 deg F illustrate how "we can take people out of having to work in this cold environment," Thuet adds.
An AS/RS also "definitely increases inventory control and minimizes handling," he continues. With this equipment, an end user can automatically sort pallets for sequentially loading them aboard an over-the-road trailer so there's less handling required at the unloading destinations.
Vertical space utilization is another key AS/RS benefit, as Thuet says. "We can go up to 120 feet high with an AS/RS." And systems with double-deep staging of unit loads further increase storage density compared to very-narrow-aisle or narrow-aisle rack systems with single-deep storage and manned industrial trucks for picking and putaway.
One recent trend, says Mike Perry, AS/RS product manager, Rapistan Systems, involves using these systems as "fully automatic pick modules." Distribution centers are replacing conventional pick modules with AS/RS for picking.
"In this concept," Perry explains, "pallet pick faces are on multiple levels, and the S/R machines replenish the pick faces automatically as pallets are depleted. Reserve pallet storage is strategically located near to the pick faces to optimize throughput."
Among the gains from applying this concept are reductions in personnel and manual equipment needed to move pallets, Perry says. With system heights up to 100 ft, less building square footage is required too. There's also flexibility to easily reconfigure pick face designations to accommodate slow moving and seasonal stockkeeping units (SKUs).
AS/RS technology also has improved, Perry maintains. Communication is by optical modems now and S/R cranes move by digital drives. "On-board PLCs and proprietary microprocessors have given way to off-board personal computers capable of controlling the movements of multiple S/R machines," he says.
Alternatives to AS/RS
There are other equipment options, however. Several U.S. materials handling suppliers–including one with a long history in AS/RS and another with extensive experience with carousel technology–now stand ready to offer end users powered equipment alternatives for storing and staging unit loads. In the right applications, these different approaches to load handling are expected to yield significant benefits.
Horizontal pallet carousels are now available from at least two U.S. vendors. And vertical lift modules (VLMs) with unit load capabilities now can be obtained from several U.S. suppliers. Moreover, at last year's CeMat show in Hannover, Germany, several companies displayed new VLMs with storage trays holding loads of 1 ton or more (see June 2000 issue ).
To be sure, these newer options for powered staging/storage of unit loads don't yet seem likely to displace the AS/RS from its leading position. But they do have as-yet-untapped potential in varied industrial applications.
A horizontal pallet carousel–like its cousins for handling cases, totes, small parts, and even dry-cleaned apparel–is a mechanized, rotating rack system. Electric drive motors power the rack system's bins or shelves horizontally around a stationary, floor-mounted loop. These carousels can be semi- or fully automated. Under the latter, computerized control software directs and keeps track of all staging and retrieving movements of loads.
A subsidiary of Jervis B. Webb is one of the U.S. suppliers offering horizontal pallet carousels (Webb-Triax, 440-285-4630, asrs-webbtriax.com ). Fred Cirino, sales manager, suggests a number of possible uses for the technology:
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Staging prior to shipping finished goods.
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Cross docking of materials in warehousing and distribution.
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Sequencing work-in-process in assembly line operations.
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Providing staging for timed periods for work-in-process (WIP) or product that needs to be cured, aged, or otherwise staged before subsequent processing or warehousing.
In Webb-Triax's design, the rotating carousel stages loads up to three or more pallets high. The unit has a total weight limit of 8,000 lb for each column of loads. Maximum height of the carousel is 30 ft.
An inserter/extractor, which can be customized for the particular application, stages or retrieves loads from the carousel. Or a standard lift truck can interface with the carousel for load transfers (photo).
At the loading dock, the carousel might be used to sequence trailer loading so loads go on the truck in a last-on, first-off order. Or the carousel might help assemble multiple pallet loads for loading aboard the same trailer to keep a multi-pallet shipment intact.
Another supplier now also offers unit-load horizontal carousels (Remstar, 800-639-5805, www.remstar.com ). These systems are an efficient and cost-effective alternative to the use of palletizers and gantry robots in building mixed pallet loads, says Ed Romaine, marketing director.
In addition, the carousels can be equipped with pick-to-light technology creating more efficient order selection. For applications in e-commerce order fulfillment, for uses in distribution for the pharmaceutical, food, beverage, and electronic components industries, and for assembly operations, the pallet carousel systems can significantly reduce order picking errors, Romaine says. Operator productivity and system throughput can improve by as much as 300% to 400%, the Remstar exec maintains.
Several of the pallet carousels can be configured together so they act as a "put" system for mixed pallet and split layer order building (see sidebar below).
In Remstar's system design, shelves rotate horizontally. They do so automatically in response to an operator's commands at a computer terminal. A carousel can have as few as 12 or as many as 100 pallet positions. Loads up to 3,000 lb per position, double-pallet high, can be placed into a system.
Compared to conventional shelving, these carousels can store more items and hold more weight, while using up to 60% less floor space and 80% less cubic space, according to Romaine.
Remstar also is introducing a vertical lift module designed to handle far larger loads than do conventional VLMs and vertical carousels.
A tray (or shelf) within this unit-load VLM can hold slightly more than 11,000 lb. Height on one of these VLMs can reach to 132 ft; one model of this system has a width of 12 ft. Thus, the technology packs a lot of staging/storing capability into a small footprint on the plant or warehouse floor. Pallets, sheet metal, bar, rod, and tube stock are among the larger loads these VLMs can hold.
Another VLM supplier (Hanel Storage Systems, 412-787-3444, www.hanelus.com ) has a number of Europallet VLM installations overseas, says national sales manager Michael Fanning. And in the U.S., the technology now provides full pallet storage for several users in industries such as aircraft manufacture and auto assembly, he explains.
These unit-load VLMs rise as high as 49 ft for useful loads to 2,200 lb, and to heights of 65 ft for loads to 1,100 lb. Pallet jacks and forklifts interface readily, says Fanning, with these high-density VLM storage units.
In addition, the entire load can be automatically extracted from the VLM by an integrated conveyor.
AS/RS: still the king
High storage density within a small footprint is also one of the key benefits and principles behind AS/RS. It's been one of the technology's major selling points over the years, helping it garner many powered unit load staging/storing success stories.
Unit loads, however, are stationary within the racking of one of these systems. Instead of the loads moving like they do in the carousels and VLMs just described, an in-aisle storage/retrieval (S/R) machine (also known as a stacker crane) moves horizontally and vertically within an aisle to pull or putaway a designated load.
Because loads are stationary and not moving, the height of an AS/RS can easily be designed so it rises to levels of a dozen or more load positions high. Often, these systems are housed in a rack-supported building.
AS/RS racking can also be designed so loads are positioned in single-deep or double-deep bays. With double-deep staging, even more unit load handling capability is created for the floor space and storage cube that are occupied compared to single-deep systems. However, accessibility is not as great as with single-deep systems.
AS/RS suppliers are prepared to provide users with customized load handling devices for the S/R machines working a system's aisles, moreover. Included are double-deep shuttles or forks, scissor lifts, rotating forks, and roll handling devices.
Except for these devices and the S/R machines they fit into, AS/R systems tend to be much like very-narrow- or narrow-aisle staging/storing rack systems.
Indeed, AS/RS and VNA or NA handling technology at times compete for the same applications.
Both AS/RS and VNA/NA systems feature tightly spaced racking, and thus very dense storage. They tend to differ in their level of automation, however. VNA or NA systems use turret trucks or other specialized vehicles to perform load staging and retrieving operations within a system's aisles. The "powered" part of these systems comes from the vehicle within the aisle.
While AS/R systems and their S/R machines are fully automated, the VNA or NA systems tend to be semi-automated, generally. Operator-aboard vehicles often run on wire or rail guidance, particularly so in the taller systems. But some manual intervention in load handling is still necessary. Yet in some VNA or NA systems, full automation can be achieved with unmanned vehicles.
Software control over all load handling steps and thereby computerized inventory management have been one of the strengths of AS/RS technology for years. High inventory accuracy and detailed tracking of all loads are benefits these systems readily deliver.
Book publishing and distributing is one of many kinds of businesses that have turned to powered, high-density staging of unit loads (see sidebar below).
Other powered systems
Meanwhile, France's second largest book distributor, Interforum, uses a powered staging technology somewhat different from AS/RS.
Staging of pallet loads of books occurs in two automated deep-lane systems at the firm's Malesherbes, France, DC. Instead of a high-masted S/R machine to pick or put away loads, low-profile, powered vehicles perform these staging steps. The vehicles move over a closed loop rail network and go from level to level within the system by means of vertical lifts (see International Report, June 2000 issue). Designed for this French publisher, the technology is also available in the U.S. (Retrotech, 716-924-6333, www.retrotech.com ).
Other system suppliers, in Europe and in Japan, notably, as well as in the U.S., have tried variations on the deep-lane system approach. In these systems, a "mole" vehicle generally accesses staged unit loads in racking and the vehicle stores or retrieves the loads.
Whether or not horizontal carousel, VLM, or "mole" systems move into territory long dominated by AS/RS is tough to call right now. But more importantly, end users now have more alternatives than ever. One of the technologies likely will prove to be just right for their plants or warehouses.
Penguin Putnam's high-bay 'bookstore'
Novels by best-selling author Tom Clancy are among the many popular books sold by Penguin Putnam Publishing. "But we don't hit a home run with every one of our titles," admits Don Cox, director of engineering services. Efficiently distributing slower-moving or seasonal books and also storing returned titles–the handful of books that come back from stores unsold - requires proper handling technology.
By installing an automated storage and retrieval system at its Kirkwood, N.Y. distribution center, Penguin Putnam found a good way to deal with order fulfillment and returns as well as business changes and growth.
"We were closing a 400,000 sq ft DC in Tennessee and consolidating," Cox says. "Nearly half of our business is in the Northeast. It is more economical to ship from Kirkwood," he explains.
The company needed a staging system with "the smallest footprint we could put on our property," Cox explains, yet still leave room for future expansions. Hilly terrain was a site factor too. Other system requirements included having sufficient pallet positions, achieving planned throughput rates, and controlling and adjusting inventory.
An architectural/engineering firm (McClier Corp., 312-373-7700, www.mcclier.com) designed a rack-supported AS/RS building for the site. McClier selected an AS/RS supplier (Swisslog's Munck Automation Div., 757-887-8080, www.swisslog.com/munck ) for the system.
The result is a six-aisle, double-deep, 13-levels-high (85 ft) AS/RS. Aisle-dedicated S/R stacker cranes work 30,264 pallet positions in a facility occupying 62,000 sq ft. Over a 24-hour, 3 shifts/day period, the 6 S/R cranes can pick or put away 250 to 500 loads.
With the AS/RS's software and graphic operator screens, "we have all kinds of information about system performance at our fingertips," Cox says. With a few mouse clicks one can determine which pallets were pulled, the percentage of orders filled, and the like.
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