Whether you're adding capacity to a crowded factory or trying to increase the throughput of a choked warehouse, floor space is valuable. That's when it's time to look up.

And that's where an overhead automated electrified monorail (AEM), also known as an overhead electric monorail system (EMS) fits in. Quietly, these AEMs move and buffer raw materials, components and finished parts between workstations and storage/staging areas well above the work floor fray.

Monorails are most widely used by the automotive industry. But they have also been pressed into service by several other industries to support manufacturing, distribution and time-pressured maintenance operations.

Monorails, however, are not inexpensive, typically costing substantially more per foot than alternatives such as overhead conveyor and power-and-free systems. And that is exactly what has kept monorails in the background when many are considering their overhead materials handling alternatives. But it doesn't have to be that way. The trick is to understand how this innovative technology suits your specific needs.

At its core, an overhead AEM is horizontal transportation device. Independent carriers, or trolleys, travel across a continuous extruded aluminum I-beam that hangs from the ceiling or other overhead support. The I-beam can include a single closed loop as well as spurs that connect to remote workstations or other destinations.

A pickup, or contact shoe, attached to the carrier collects power from a bus bar, or power rail, inside the I-beam. Each trolley has its own motor. Most importantly, this means a carrier is free to travel a unique path independent of other carriers, maximizing flexibility of the system. The motor can also be used to power loads while on the carrier or even at workstations where it picks up or deposits loads.

The path of each carrier is under the control of a central computer that communicates through the bus bar. Onboard intelligence allows the carrier to receive directions as well as communicate back, including new requirements input by a human operator. Intelligent communication also allows users to precisely track the location of carriers and work-in-process anywhere in the system. Due to its controls, AEMs can also stop precisely and position a part to within 1 millimeter where it can be worked on by a production employee or a robot. And if there's an operational problem, a carrier can notify the maintenance department to send an electrician.

Monorails routinely handle loads weighing less than 100 pounds in a warehouse and up to several tons in an automotive factory. What's more, monorail systems can easily handle inclines without assistance. At DaimlerChrysler AG's Bremen works, car doors for the Mercedes C-Class are transported by a monorail (Swisslog North America, 800-525-1841, www.swisslog.com) from a buffer area on the bottom floor to a hall three levels higher, with gradients of up to 90 degrees, without hoisting gears.

With speeds up to 600 feet per minute, monorails work well in facilities with long travel distances too. American Airlines uses an AEM (HK Systems, 800-HK SYSTEMS, www.hksystems.com) to shuttle parts to four repair hangars located one mile from a central parts warehouse.

For all of its strengths, overhead monorails are still a niche solution.

For instance, AEMs don't work well outside or in a caustic or harsh environment. Moisture, dirt and extreme temperatures can impede performance.

Furthermore, installations are relatively permanent. While carriers can follow unique paths on the track, it's no small task to change the track layout since the system is bolted in place.

But the biggest factor that limits monorail use is cost. Monorails have always been more expensive than alternative solutions even though cost continues to decline. One vendor estimates that systems that once cost $1,200 to $1,300 per foot now cost $800 per foot.

While that is beneficial to overhead AEMs, the cost of competing technologies, such as power-and-free, overhead conveyor or alternatives on the floor, have also come down in price on a relative basis, maintaining their less-expensive-than-monorails status.

With that in mind, the most effective way to ensure a successful monorail project, say the experts, is to use simulation and emulation software. That way the cost-benefit performance of the system is proven before the first foot of track is ever installed.

It's generally accepted that the sweet spot for monorail systems is the factory floor.

With precise positioning capabilities, AEMs allow manufacturers to easily accommodate a variety of products and sizes on the same production line. A manufacturer of outdoor sporting vehicles, for instance, uses a monorail system to manufacture all terrain vehicles and snowmobiles on the same line. By reprogramming the monorail (Eisenmann Corp., 815-455-4100, www.eisenmann.com), the carriers deliver the product to precisely the right location without reconfiguring workstations.

AEM is also making inroads in the electronics industry because it is both quiet and extremely clean.

In the warehouse and distribution center, monorails are emerging as a solution to automate non-value added processes, such as replenishing flow racks with high turnover items or delivering finished goods to an automated storage and retrieval system (AS/RS). Kodak, for instance, uses a monorail (HK Systems, 800-HK SYSTEMS, www.hksystems.com) to interface with an AS/RS to deliver and retrieve rolls of paper.

The basic concept behind monorail systems hasn't changed. But new developments promise to make them more efficient and cost effective.

As monorail systems increase in clean room environments, one new system includes a vacuum attached to the trolley to clean the track.

Another involves a trolley that can be programmed to automatically raise or lower the product it's carrying as it moves from one manufacturing station to another. That way, the part or product is always at the desired ergonomic height when it arrives at the next worker.

Going forward, however, the most broad-based development to emerge is a non-contact, or inductive, power system.

In traditional AEM systems, the track includes bus bars. Power and communication are available whenever shoes on the carriers contact the bus bars. That creates a maintenance issue since contact wears bus bars and shoes.

With these new systems, a single wire running inside the system replaces the traditional bus bar. The carrier is equipped with a "collector" that draws in, or induces, the power from the wire without coming in contact with the bar. Since there is no contact with a bus bar, there's no wear and tear, eliminating related maintenance issues.

Today, there are only a few installed monorail systems that use induction. But as the technology develops and the price comes down, vendors predict induction will be the technology of the future.

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