When you're hot, you're hot. And when you're not, you're not.

That phrase says a lot about the automatic guided vehicle (AGV) industry during the past 30 years.

During the 1970s and '80s, few materials handling technologies were hotter, especially in manufacturing environments.

Unfortunately, too many systems were installed in the wrong applications. After some large early users replaced their AGVs with lift trucks, interest in the technology cooled.

In 1991, the industry booked 100 new AGV systems. Five years later, AGV suppliers booked just 39 new systems.

Today, AGVs are making a comeback. Why now?

In part, it's that users and suppliers alike have gotten smarter about using AGVs. What's more, the systems are better. 'The basics of AGVs haven't changed,' says Bruce Boldrin, corporate accounts manager for SK Daifuku Corp. 'But there is a lot more reliability under the hood.'

Improvements include quick charging battery systems; reliable radio frequency (RF) communications; more onboard intelligence; and flexible guidance systems.

The suppliers are also more reliable. 'In the past, many of the sales pitches were better than the vehicles,' says Randy Winger, AGV product manager for HK Systems, Inc. 'The suppliers still in the business today know what they're doing.'

An AGV consists of battery-driven, unmanned vehicles with programming capabilities for path selection and positioning. Vehicles come in different configurations depending on the application, and are guided by either wires buried in the facility's floor or non-wire guidance systems. Communication between the vehicles and a host computer is by radio frequency.

Tow vehicles, also known as tuggers, are simple and inexpensive. They can pull a trailer with capacities of up to 60,000 pounds. Add multiple trailers, and you can move more loads at one time than with a single fork truck.

Unit load vehicles carry pallets, cartons, or subassemblies. The vehicle decks may be equipped with lifts that can raise or lower the deck; powered or non-powered conveyor to interface with other equipment; or multiple compartments to carry two, three or four pallets at one time.

There are also vehicles with forks that lift, lower and carry loads just like lift trucks but without the driver.

Regardless of vehicle type, there are three principal methods of guiding the vehicles.

Early AGV systems were navigated by an RF signal transmitted from a wire buried in a slot below the floor. A sensor under the vehicle detected the signal and adjusted its position.

While wire-guided systems have a relatively attractive initial purchase price, nearly 80% of the systems booked last year were for non-wire-guided systems. That's because non-wire-guided systems are easier to reconfigure when requirements change. Simple software changes reroute these AGVs, eliminating the need to remove and then relay the guidance wire in the floor to create the new path.

Laser-guided vehicles are the most common non-wire-guided navigation system. An onboard laser reflects off of targets that are mounted above the floor on columns, walls, machines, or posts approximately 25 feet apart. The system automatically measures the distance and angle of the reflected light to calculate and adjust the AGV's position on the preplanned guide paths.

AGVs with an inertial or gyro navigation system rely on an onboard gyroscope that senses very small deviations in the AGV direction of travel. Instead of reflective targets, small magnets or passive RF tags are installed in the floor approximately every 25 feet to serve as position points.

Choosing between non-wire-guided navigational systems ultimately comes down to personal preference. 'Inertial and laser systems each have their pluses and minuses,' says Gary Koff, AGVS technology manager for Siemens Dematic. 'But they both do the job.'

There are at least four reasons to use an AGV.

First, they solve the problem of finding, training, and retaining good labor.

AGVs reduce the damage to facilities caused by inattentive lift truck drivers. 'We were recently in an auto plant with a crew of five workers whose sole job was to fix things that had been damaged by lift trucks,' says Mark Longacre, marketing manager for FMC Technologies.

AGVs arrive when they're supposed to arrive and can be precisely positioned in critical operations. And with automated battery charging, they can operate 24/7. Those are key selling points for just-in-time operations.

Finally, AGVs are flexible. If your facility needs change, it's quite simple using advanced software to reroute an AGV.

Although some automotive installations rely on dozens of vehicles, a typical AGV installation today uses four to six vehicles. Applications vary from a short pick-up and delivery arrangement on a manufacturing line to more complex layouts with vehicles that automatically interface with other automated manufacturing and storage equipment.

Guided vehicles are particularly suited to moving large, heavy, and unwieldy loads, like paper rolls, over long distances. They are also strong in hazardous environments and clean rooms.

Most systems still go into manufacturing plants: last year, less than 15% were intended for pure distribution facilities or non-industrial settings.

Throughput and flexibility are often the determining factors for using AGVs. 'Typically, you look first at whether you can save money through automation,' says John Hayes, system sales manager, AGV Products, Inc. 'Then you choose between traditional solutions like conveyor or AGVs. If flexibility is important, an AGV has the edge. If high throughput is important, conveyors.'

Likewise, if there's a great deal of variability between loads, a lift truck may be a better choice.

AGVs shine in medium throughput, repetitive applications: picking up product at the end of a machine, and delivering it to a palletizer, a stretch wrapper, or the delivery dock, for instance.

One emerging trend is use of AGVs to integrate manufacturing and warehousing. 'That's an area that is just now being tapped into,' says Bob Jurcago, account manager, Mentor AGVS. 'Users are replacing lift trucks that were on a milk run. The labor savings justifies the cost.'

AGVs are also beginning to show up on distribution center receiving docks. 'We're installing AGVs to pick up pallets at a staging area on the dock and then deliver them to aisles for receiving, or to cross-dock them,' adds Paul Roche, director of logistics systems sales for Swisslog.

While the basic functionality hasn't changed, AGVs suppliers are improving their systems. Many of these improvements are aimed at making AGVs more versatile and affordable.

An automatic guided cart, for instance, is designed as an alternative assembly platform for low-to-medium volume assembly lines and loads of up to 2,000 pounds. The carts can also be adapted to order fulfillment operations in a warehouse or distribution center. 'We've experimented with installing a pick-to-light system on the cart to identify which carton inventory should be placed in for order fulfillment,' says Earl Raynal, sales manager, for Control Engineering.

A new vehicle from FMC Technologies combines AGV technology with walkie lift trucks capable of handling loads up to 4,000 pounds. At a workstation, an operator positions a load for pick up or drop off as with a manual pallet jack. Then the AGV is automatically routed to its destination.

Many AGV manufacturers have replaced mechanical bumpers with 'virtual' laser bumpers. A laser field in front of the vehicle senses when an object is near and slows down or stops a vehicle before impact. 'By creating a virtual bumper, we can extend the field out as far as we need to still stop in a safe distance,' says Brian Keiger, manager of systems business and sales, Transbotics Corp. 'That allows the vehicles to travel faster, especially in open areas.'

Those safety zones can also be extended above the vehicle to protect it from traveling into the path of an overhead crane.

New software solutions allow users to reconfigure the guide paths for laser and inertial-guided vehicles and download the changes to the vehicles without calling in a vendor to reprogram the computer.

Thanks to improved RF communications, today's systems can communicate in real time with host computer systems. 'The information flow today is as important as the material flow,' says Boldrin of SK Daifuku. 'With its information component, the AGV system allows movements to be tracked precisely. And because it communicates with the host system in real time, you have the ability to support just-in-time delivery to machines or work stations.'

You can learn more about AGVs, their applications, and the industry by visiting the AGV production section at the Material Handling Industry of America Web site.

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