Vertical lift storage modules: Advances drive growth
Building on their excellent use of the cube, vertical lift storage modules are being enhanced to extend their storage/retrieval and inventory management capabilities.
By Staff -- Modern Materials Handling, 10/1/1998
In the world of powered storage equipment, vertical lift storage modules (VLSMs) are a relative newcomer.When VLSMs debuted about 12 years ago, horizontal and vertical carousels as well as automated storage and retrieval systems (AS/RS) were well established. And for several early years there was one supplier of these small footprint, high-density storage systems.
Today, there are seven suppliers (see box) and annual sales of VLSMs will exceed $70 million this year, according to the market research firm Frost & Sullivan. In fact, the researcher projects an annual growth rate of 8% to nearly $115 million for VLSMs through 2004, making it the fastest growing category of powered storage equipment.
That growth is driven by use of VLSMs, which typically cost $30,000 to $40,000 each, to support production and in tool rooms in the aircraft, automotive, telecommunication, and semiconductor industries, to name four. VLSMs are also used in low-volume distribution operations at medical, communications, and electronics companies.
Such broad appeal is due to the unique storage and retrieval capabilities of VLSMs. Compared to single-level horizontal carousels, they require much less floor space to store comparable inventory quantities. And compared to vertical carousels, VLSMs offer more storage flexibility for a changing mix of inventory.
The end-result is an ability to store large quantities of parts at their point-of-use. Floor requirements are minimal and use of the cube excellent. Heights of 30 ft or greater are standard. The modularity of VLSMs means new storage capacity can be added adjacent to existing units with minimal disruption of established operations. In addition, VLSMs can be networked with remote database and order management systems to maximize inventory management efficiencies.
Several recent developments extend the capabilities of VLSMs. The majority of the activity has focused on optimizing storage/ retrieval cycles and increasing load capacity of the units.
How VLSMs operate
In its basic configuration, a VLSM operates more like an AS/RS than it does like a vertical or horizontal carousel.
As the drawing shows, inventory is stored in trays stacked vertically in fixed locations on either side of a central, open lane. An extractor travels up and down this lane storing trays in and retrieving them from their fixed locations. The extractor receives its directions from a terminal mounted on the VLSM next to the front access window where trays are picked up and deposited. Operators and/or software provide the necessary input to the terminal.
When a new tray is deposited at the window, an operator slides a previous tray onto the extractor for putaway. During that operation and subsequent retrieval of another tray, picking can be done at the access window and the tray readied for pickup and putaway.
Typically VLSMs are installed in groups of two or more, allowing simultaneous putaway/retrieval and operator activities at the units. However, the operator must move from one access window to the next to perform required tasks with the delivered inventory.
A new variation on this arrangement was introduced this year. One supplier has joined two VLSMs and uses a single extractor to service trays in both structures, increasing accessibility to more inventory without the added cost of a second extractor.
This design allows the extractor to store and retrieve trays in either or both units while an operator works from a tray. If needed, a second operator can be working at the unit's second access window.
There are other approaches being tried to optimize inventory accessibility.
One is to increase the extractor's vertical travel speed. At this point, speeds are in the 65-138 ft/min range. However, at least two suppliers offer speeds from 150 ft/min to 175 ft/min.
Another approach uses software to optimize cycle times for picking trays. Several packages assign locations for the fastest movers closest to the window and slow movers more distant.
At least two packages include programmable acceleration/deceleration speed routines. This allows users to assign different travel speeds to different inventory types-faster for rugged items and slower for fragile or spillable items, for instance.
A third type of software written improves productivity of VLSMs. While all units direct putaway/ retrieval activity locally, there are new packages that connect with a remote database on a host computer or on a client/server network. By directly downloading order requirements to the VLSM, the software facilitates continuous order processing without operator intervention.
On the capacity side of recent VLSM developments, there have been advances in the maximum payload of the modules.
Only a couple of years ago, the maximum payload for a VLSM was 44,000 lb. Last year it was upgraded to 66,000 lb by at least one supplier who subsequently upped the limit to 88,000 lb earlier this year. At presstime, another supplier was ready to announce a 132,000 lb capacity VLSM.
These developments and others will make VLSMs increasingly versatile in the future.
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