How To Shop for AS/RS and VNA Systems

There have been significant improvements in both automatic storage and retrieval systems and very-narrow-aisle turret trucks. Both offer significant benefits for the right applications.

by Howard Zollinger, P.E., president, Zollinger Associates Inc.

The need for storage has moved from large inventories to managed inventories that provide staging, whether it is in manufacturing or in distribution channels. How do you choose the best material handling solution where space is at a premium?

First, understanding your needs and requirements. Second, understanding the attributes of the potential solutions. Third, matching and evaluating the system benefits to your requirements.

The objective of this article is to present useful information and appropriate methodology for the application of AS/RS or VNA technology to your requirements. Automatic storage and retrieval machines work in very narrow aisles of high-rise racks. VNA turret trucks are manually operated in a very-narrow-aisle configuration of standard, industrial, post and beam pallet racks.

Given the right circumstances, the “VNA concept” can be the most justifiable solution to many storage applications. The same applies for the “AS/RS concept.” This article is not written to prove one concept is better than the other. It is to provide information leading you to the best solution for your requirements.


The crane-in-aisle type of AS/RS has become faster and faster for both the miniload and the unit load systems. The miniload has gone from 65 dual cycles per hour to 130. That is 130 x 2 loads per hour handled. The unit load has gone from 30 dual cycles per hour to 48.

The miniload machines have added storing and extracting capability for different types of loads (totes or cartons).

The variable-speed AC drives have added programmed acceleration and deceleration to move short or long distances within absolute minimum time.

Unit load and miniload machines have demonstrated the advantages of two or three loads on one carriage for greater throughput. Today’s logic systems have made this feasible in a number of applications.

The AS/RS concept has a number of advantages:

• The S/R machines are automatic;

• Reliability is higher than other storage systems, i.e., > 99.5% up time;

• Standard PC-based inventory control provides excellent functions;

• Security of goods is very high due to fencing and height;

• Less product damage than other systems;

• Automatic machines don’t take breaks.

Typical AS/RS applications:

• Manufacturing discrete parts;

• Machining centers;

• Manufacturing heavy industry parts;

• Manufacturing and assembling of electronic family;

• Warehousing and distribution with high throughput.

Favorable operational conditions:

• Two- or three-shift operation;

• Critical inventory levels;

• Staging for production flexibility;

• Joint storage of parts and tools;

• Dual cycle throughput, 10 to 35 per hour (20 to 70 loads moved per hour);

• High land cost;

• Soil — 3000 psi or greater;

• Where building height restrictions are not limiting;

• Skilled technicians availability;

• High-value parts or assemblies;

• Medium number of SKUs;

• Existing site space to avoid moving.

Favorable environments:

• Cold storage;

• Frozen foods;

• Strict item tracking.


The unit load turret truck type of VNA has become faster for both the man-up and man-down systems. The unit (pallet) load has gone from 10 dual cycles per hour to 14. That is 14 x 2 loads per hour handled.

A few turret truck manufacturers have gone from only manually operated machines to operator-less. This is not commonplace, so for this article I will describe only the manual VNA systems.

The variable-speed AC drives have added programmed acceleration and deceleration to move efficiently for short or long distances and have replaced hydraulic drives on a number of manufacturer’s equipment. The controls have become more capable and provide greater performance when the load or operator is up in the air.

With the advent of encoders, exact height is provided to make a man-down machine more efficient. Also, the drives and control techniques have permitted a 60 percent reduction in wiring on the machines.

The VNA concept has a number of advantages:

• Turret trucks can easily service two or more aisles;

• Operators can provide greater flexibility;

• With multiple machines for equal throughput, there is less loss with one machine down;

• Gains the benefit of reduced building cost per volume of storage;

• Easy to add another machine for greater throughput;

• Management comfort with manual operation vs. automatic.

Typical applications:

• Warehousing and distribution with modest throughput;

• Warehousing of bulky spare parts;

• Warehousing of bulky items;

• Manufacturing a wide variety of parts;

• Storage associated with manufacturing bulky parts;

• One-shift operation;

• Wide seasonal demands;

• Wide variation in load footprint;

• Low labor cost;

• Semi-critical inventory levels;

• Dual-cycle throughput three to 10 per hour (six to 20 loads moved per hour) per aisle or multiple aisle.

Favorable environments:

• Moderate to low land cost;

• Soil — 2000 psi or less;

• Where building height restrictions are limited to 35 to 50 feet;

• Limited skilled technicians availability;

• Low-value parts or assemblies;

• Medium to high number of SKUs;

• Abundance of site space;

• Management that prefers manual operation.

We hope this article helps you arrive at the best solution for your requirements. The guidelines are general, but they should lead you to a concept you can explore in greater depth. Once you arrive at that point, there is literature available that will show how to make a detailed comparison for your specific applications. For more information, visit, the Web site of the Material Handling Industry of America, and, the Web site of the Industrial Truck Association.

About the Author

Howard Zollinger is the founder and president of Zollinger Associates Inc., material handling consultants created specifically to help clients achieve the most effective combination of information, movement and storage in manufacturing and distribution systems. Howard is using his knowledge as a leader, an innovator and a teacher in this field to simplify the application of operations enhancement and/or simplification solutions. He is a registered professional engineer and winner of the prestigious MHIA Reed/Apple Award. He can be reached at (906) 482-1400, or e-mail him at