Does size really matter?

It's an age-old question. When it comes to storing and handling small and large parts it turns out there is a difference that goes beyond the fact that small parts are, well, smaller than big parts.

'In a manual system, the manpower to pick small parts can be greater than picking full cases,' says Dave Gealy, systems consultant with Forte Industries (513-398-2300, www.forte-industries.com). 'Inventory accuracy is also a challenge. So is the replenishment of active pick locations. These are all important considerations.'

If you look beyond traditional static solutions, like shelves and drawers, the choice for moving small parts usually comes down to four automated technologies: horizontal carousels, vertical carousels, vertical lift modules (VLM) and mini-load automated storage and retrieval systems (AS/RS).

Each has its own unique characteristics and works in a different application.

Horizontal carousels are ideal for distribution environments.

These oval units consist of a series of bins or carriers that rotate horizontally around a track much like a merry-go-round does.

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 go get the parts in a static shelf environment,' explains Bob Rienecke, vice president, sales, Diamond Phoenix (207-784-1381, www.diamondphoenix.com).

A typical carousel has between 20 and 60 columns of storage locations that circulate on a track. Each column is generally 36 inches in width and 6 to 8 feet in height. Stacked within each column are multiple bins or baskets, maximizing storage density. Bins can handle loads of up to 1,500 pounds. What's more, horizontal carousels can be stacked on top of one another to create even more storage in the same footprint.

Horizontal carousels can also be grouped tightly together in pods for efficiency of picking. Pods frequently consist of 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 you slot the carousel, you can get 200 to 400 line picks per hour from a pod configuration,' Rienecke says. 'If you stack the carousels and use an automatic inserter/extractor, you can achieve carton pick rates of 4 cartons per minute from each unit.'

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

These systems combine high-density, vertical storage and retrieval technology in a small footprint. That makes them ideal for point-of-use storage of components and parts in manufacturing operations with high ceilings and limited floor space. 'The higher the ceiling, the more density you can get in storage,' explains Dave Simon, director of product marketing, FKI Logistex White Systems (800-275-1442, www.whitesystems.com).

It is not uncommon for vertical storage systems to reach 40 feet tall, and some systems are 60 feet with pick windows on multiple floors.

Since many designs are enclosed, vertical carousels are also ideal for safely storing high-value inventory. As appropriate, the system can be secured to prevent theft.

Despite these advantages, vertical carousels have design limitations, especially when applied to heavy parts. Because the entire unit rotates, parts must be stored evenly to prevent an imbalance. 'If you have a 30 pan unit, you can't arbitrarily have one side full and one side empty or the unit will become unstable,' Simon says.

For that reason, vertical carousels are most often used for lightweight products, like components in the electronics industry.

However, heavy-duty, open systems have been designed to handle larger parts, adds Tony Mariani, marketing manager with J&D Associates (800-444-4532, ww.jdstorage.com). 'We have supplied vertical carousels that hold up to 1,050 pounds on a pan and up to 30,000 pounds in a unit,' Mariani says.

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

And the similarities don't stop there. Both systems take advantage of high ceilings: VLMs have been built up to 90 feet tall, although most are 15–20 feet tall. And like a vertical carousel, stored inventory can be accessed at pick windows from multiple floors.

'We have designed systems where inventory is putaway at the floor level; organized into kits at the second level; and delivered to a manufacturing workstation on the third level,' says Ed Romaine, marketing director, Remstar International (800-639-5805, www.remstar.com).

And like a vertical carousel, a VLM can safely store high-value items.

On the inside, however, VLMs more closely resemble an AS/RS than a vertical carousel. While the entire vertical carousel rotates to bring the right bin to the picking window, storage locations in a VLM are stationary and an automatic inserter/extractor performs putaway and retrieval one storage tray at a time, much like an AS/RS. 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's software figures out the optimal space to put it in,' Romaine says.

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 suitable for highly sensitive or fragile parts. 'The system can be programmed to handle different parts at different speeds too,' Romaine says.

A mini-load system is an automated storage and retrieval system designed to handle cartons and totes instead of pallet loads of material in high-density manufacturing and distribution settings. Mini-load systems typically handle totes or containers measuring two feet by four feet in a variety of heights with loads of 250 to 750 pounds.

'The totes or containers can often be subdivided into smaller compartments for better utilization of space or for grouping kit components,' says Mike Kotecki, senior vice president, HK Systems (800-424-7365, www.hksystems.com)

A computer-controlled storage/retrieval (S/R) machine travels the length of an aisle between stationary storage locations holding trays, bins or totes. The S/R machine's inserter/extractor retrieves and puts away loads in the computer-selected storage location, and delivers them to a workstation typically located at one end of the system. Generally, one S/R machine is dedicated to each aisle of the system, maximizing throughput.

Mini-load systems are most often used to replenish picking stations. 'A common application involves the goods to the person principle,' explains Ken Ruehrdanz, business solutions manager, Siemens Dematic (616-913-7275, www.siemens-dematic.us). 'The mini-load retrieves a tray/container from a location in the AS/RS and delivers it to a person who will pick items from that tray/container. When the pick is complete, the mini-load system returns the load back to storage.'

Another typical application for mini-load AS/RS is handling slow-moving stock keeping units (SKU) in a distribution or production environment. 'Slow-moving items are kept in the mini-load AS/RS thereby reducing warehouse space requirements,' Ruehrdanz says. 'When a slow mover is required, the mini-load retrieves that item and creates a temporary pick face for it.' That eliminates a pick face in the warehouse for each slow mover, freeing up valuable space.

While each of the four technologies solves the problem of handling and storing small parts, one size doesn't fit all.

'Storage and picking systems should not be limited to a single technology,' says Bruce Boldrin, corporate account manager, Daifuku America (614-863-1888, www.daifukuamerica.com). 'A hybrid solution using one or more technology is going to provide the best solution.'

The trend today is to mix a combination of small parts handling solutions, matching traditional methods of storage like flow racks and static shelves and drawers, with automated technologies, based on the movement of parts and requirements of the job.

Most often, that means putting the fastest moving SKUs in flow racks outfitted with pick-to-light systems, which might be replenished by a mini-load AS/RS. Next to that might be a pod of horizontal carousels for batch picking, while the slowest moving items are reserved for vertical storage in a carousel or VLM.

'Every category of movement has a sweet spot,' Boldrin adds. 'Once you look at your SKU profiles and determine the picks per hour and the cubic feet required for storage, you can put together a warehouse with a combination of sweet spots. That gives you the greatest value with the minimum space requirements.'

Click on the icon to learn how Sheetz uses horizontal carousels to optimize deliveries. (Sheetz takes control of its distribution destiny - April 2004)