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The Ceiling's The Limit
February 29, 2008

In modern warehouses it can be challenging to find efficient ways to store and handle smaller items. One solution can be found by looking up. As land prices for warehouses soar, it is wise to make the most of the cube.

Traditional static shelving is only practicle up to about eight feet high for ground-level picking. This wastes over two-thirds of the available cube in a low-rise modern warehouse with a height of 27 feet.

There are two tactics to make better use of vertical space. The first is a multi-level mezzanine, which increases the number of floors in a building. The second is high-bay storage, which uses mobile equipment to elevate the picker to high-level racking, or automated systems to bring items to the ground.

Using A Mezzanine

Mezzanine storage systems can be installed using a few different designs, usually selected for the nature and movement of the product being stored. For medium and faster moving items, a multi-story pick tower is often best. A pick tower usually consists of several vertical levels with pallet or carton flow racking, fed by conveyors (powered and non-powered) in the centre. Sometimes there is static shelving on the top level for slower-moving items.

Mezzanines can also accomodate traditional paper-based picking. For 'pick-and-pass' order-picking of broken-case items, an order travels to lower levels in sequence, with items being added to a case in each picking zone. Usually this technique is combined with a wave system, in which orders are organized by factors like common destination. Orders can also be combined for batch picking to improve efficiency. Automatic conveyors then direct the full cases or totes into lanes for consolidation.

Static shelving in a mezzanine can work well for slower-moving items.

In bigger systems with more SKU's, items are often picked into totes on carts. The totes then travel by conveyor for colsolidation.

Using High-Bay Storage

Another way to make the most of warehouse height is to have high-bay shelving, which can extend as high as the ceiling. Pickers are generally elevated up to the desired height using a man-up stockpicker.

Often with this type of shelving the picker travels to the storage slot and then makes the order selection. But another method is to bring the stock to the picker using an automated system.

Automated systems have integrated technology that downloads orders directly to the controlling system. Such paperless picking is much more efficient than paper-based systems. It is usually used for faster-moving items, for which gains in picking productivity can justify the higher cost.

Automated Assistance

Automated vertical systems that can maximize height usage included:

  • Stacked horizontal carousels
  • Mini-load automated storage and retrieval systems
  • Vertical carousels
  • Vertical lift modules (VLM's)

Stacked horizontal carousels are quite simply traditional horizontal carousels stacked on top of each other. Upper levels are picked either from a lift table or from a mezzanine with a takeaway conveyor.

A mini-load system uses specialized equipment that extracts trays via an automated storage and retrieval device and brings them to a ground-level station for order selection and packing. These can consist of several aisles, depending on the size of the application. In comparison to other approaches, these systems tend to be expensive.

A vertical carousel is a self-contained storage lift that rotates vertically to bring a picking slot to a work station.
VLMs are enclosed vertical storage lifts comprised of two row of rack-mounted trays and a robot-driven tray extractor carriage. The carriage travels between the two rows of rack-mounted trays and a robot-driven tray extractor carriage. The carriage travels between the two rows of racking, extracting the trays and bringing them to a workstation. The workstation is run by the operator, who receives instructions from a controlling computer.

Initially, a vertical carousel appears to be similar to a VLM. Each has many advantages over traditional tall shelving. Both can make efficient use of high spaces and allow for items to come to the point of use. Both can be secured against theft. Both allow for ergonomic handling, with no bending or climbing.

One disadvantage of a VLM is that it tends to have slower retrieval speeds than a carousel. This makes it better for items like spare parts than for faster-moving applications.

Still, the VLM is often a better option. It tends to cost less, and is usually safer for sensitive small items that may be damaged by the constant motion of a carousel. It also offers greater configuration flexibility, allowing different-sized products to be handled in the same unit.
Choosing to go 'up' for smaller-item storage can be cost-effective and cube-efficient. Whether you choose a manual or high-tech system depends on what works for your warehouse.

 * Written By: Dave Luton. Materials Management & Distribution Magazine. January/February 2008 issue
Norpak Handling currently has a VLM on display at their head office in Port Hope, ON. Norpak is the Canadian Distributor for Diamond Phoenix who is a world class manufacturer of material handling equipment, including Vertical and Horizontal Carousels, Vertical Lift Modules and Pick to Light Systems. They are technology leaders in order picking and order fulfillment solutions for the e-commerce, distribution and in-line manufacturing markets.
Please contact us for an appointment to come a check out the latest techonology. or call us at 1-800-854-6054.