Inside Logistics

Materials Handling: Warehouse automation

A Primer: Part II


December 30, 2015
by Dave Luton

Dave Luton

Dave Luton is a consultant in the Greater Toronto Area.

In this column we will look at storage, starting with dynamic storage systems, and outbound processes including order selection.

Dynamic storage systems are designed to handle full unit loads. The same basic principal is used in carton flow order selection systems. In general, the storage system is loaded from one side—the charge side—and the product is automatically conveyed to the other side—the discharge side—for offloading.

Because the storage system itself conveys the product it achieves high-density storage without aisles. The pick-face product access makes for efficient loading and unloading, unlike high-density storage systems where the operator has to maneuver in narrow tunnels.

These systems automatically achieve FIFO, but like all high-density storage, are generally restricted to high volume usage with a limited number of SKUs. This is because product cannot be mixed in individual lanes.

Carton selection systems have been further automated with pick-to-light systems. The pick-to-light system is a methodology to select orders without pick documents.

Orbital shuttle systems achieve many of the same results of dynamic storage systems but use a different methodology to achieve in-lane pallet conveyance. In dynamic storage systems pallets use gravity to automatically index the remaining pallets from the charge side to the discharge side when a pallet is removed.

Orbital shuttles are high-density storage systems that consist of specially designed storage channels. Into these an in-channel shuttle vehicle, an orbiter, is used. This is combined with a channel docking station that is placed at the end of the channel by a forktruck as an integrated unit. They use a common discharge and charge aisle. Each channel is equipped with a console that centres the channel docking station.

Once placed in the channel, the orbiter conveys a pallet to the end and then returns to the docking station. The forklift operator starts putaway by placing inbound pallets on the docking station/orbiter. The orbiter then operates independently of the forktruck allowing the forktruck operator to do other tasks while the shuttle completes the putaway. Instructions to the shuttle vehicle are given by wireless remote.

Order picking works in a similar fashion and the shuttle is directed to select a pallet in storage and bring it to the docking station for pickup by the forktruck operator.
Automated storage systems for unit loads also include AS/RS (automated storage and retrieval systems) in which the product is not touched by human hands once it is placed in a pickup and dispatch area. Stacker cranes convey it to the storage area and select it when needed. Unlike dynamic storage systems or shuttles, these allow for greater product selectivity. They function like traditional warehouse storage systems because of the improved product access.

These systems are custom designed, and in their extreme form—rack-supported building—the entire structure is designed around the storage system.

The same general principle can be found for smaller volumes stored in trays or totes in a mini-load AS/RS. For case or less-than-full case order selection, many automated systems use a principle of bringing the stock to the picker. For smaller-quantity orders automated alternatives consist of: horizontal carousel, vertical carousel, and VLM (vertical lift module).

Horizontal carousels operate on the same basic principle as the automated systems you see in a dry cleaning store. By eliminating aisles they are space efficient, and operating them in banks permits an operator to pick from one while the system is indexing stock for the next pick or putaway.

The limitation is vertical cube efficiency because of the height restriction imposed by the pickers’ need to access the stock. For slower moving stock this has been partially resolved using lift tables or multilevel picking stacked carousels.

To solve the vertical cube issue and use limited space, vertical carousels rotate in the vertical dimension, not unlike a ferris wheel. Vertical lift modules provide many of the same benefits as vertical carousels:
•    Improved order selector productivity. The software queues orders, and introduces enhancements like batch picking. Then it does the work of finding, and with the hardware, delivering the product to the order selection pick face. Resulting productivity is several times that of traditional shelf picking.
•    Improved ergonomics. VLMs and vertical carousels present the product at convenient height with a built-in counter. This eliminates the bending and reaching encountered with traditional shelving or horizontal carousels.
•    The efficient use of vertical cube saves floor space. Overhead space is often wasted and these systems convert them into usable storage space.
•    Enhanced dust protection and product security. These systems are enclosed and can be locked up. For valuable items like computer chips this provides both product quality and security benefits.