Manufacturers that need materials moved along fixed paths have several handling systems to choose from. Each of these has an advantage and is therefore preferred by one industrial customer over another. What follows is an up-to-date sketch of fixed-path handling systems and the industries that use them.

For the auto industry, conveyors are still king. Ever since Henry Ford introduced the chain-driven conveyor in the early part of last century, conveying systems have been the most popular way of moving materials for the purpose of automobile assembly. Keeping with this trend, DaimlerChrysler Corp. utilizes over 10 miles of overhead and floor conveyor systems. Before one of their Jeep Cherokees ever hits the pavement, it spends a day and a half on DaimerChrysler's conveyor system. Likewise, PACCAR builds trucks in its Montreal plant with both overhead and over-and-under systems. The main advantage to implementing the overhead conveyor system is a safer, and less cluttered, shop floor. Computer operated, both systems can sequence specific units to the manufacturing line.

For Howard Computers, a single powered roller conveyor, set up in a straight line, is the system of choice. According to Dan Lewis, vice president of manufacturing, "because the line's a straight shot, we have the visibility to see if we have any flow problems developing." Of course, if the assembly plan includes variable routing, a combination of both belt and roller conveyors might be best. At QSC Audio Products a main roller conveyor utilizes the "straight shot" concept, but then smaller belt conveyors branch off from the main line to allow the redirection of certain units.

Monorail systems provide another option for moving materials along a fixed path. This includes simple track and rail trolley systems as well as the more complex automated electrified monorail (AEM) systems. Though AEM systems have a reputation for being inflexible once they are installed, Harley Davidson, which relies on AEM, has modified its path system five times since 1990. This suggests that AEM systems can be adjusted to some extent. The advantage of AEM systems is that they allow assembly line workers 360-degree access to the work unit as it is being moved.

A third fixed-path option is the use of automatic guided vehicles (AGVs), which keep to fixed paths by following the guidance of rails, wires or tapes. The advantage AGVs have to offer is that they can traverse very narrow spaces that do not allow for operator error. Like other systems, AGVs have been traditionally restricted to moving units forward or backward along a path. But this limitation is becoming less and less the case. At the Seattle Times newspaper, for example, AGVs possess the additional flexibility of a traffic routing system which can "unlock" or "lock" a section of wire for movement by a specific AGV.

By assessing their manufacturing environment, and the configurations that their assembly methods demand, manufacturers can choose the ideal type of fixed path system. As the material handling needs of manufacturers change, fixed path technology has enough flexibility to adapt along with them.

Source: Following a Fixed Path
Tom Feare
Modern Materials Handling, Sept. 1,2000
http://www.manufacturing.net/magazine/mmh/archives/2000/mmh0901.00/mmh0901equip.htm