At the beginning of the Denver Airport automated baggage-handling project, Federico Pe˜na, Denver Mayor from 1983-1991, said “I hope it will be said of our effort, when history sits in judgment, that we reached out beyond our borders and helped shape the world’s aviation future.” (At press time, Mr. Pe˜na was still Secretary of Transportation in the Clinton administration).

Reach, they certainly did. But after a year’s delay in opening, the result was a heavily downsized baggage-handling system that cost slightly over $200 million. To put it kindly, initial judgments say the Denver project has not helped shape aviation’s future. Instead, it may have dampened the use of linear-motion-based baggage handling systems. Which is a shame, because this technology works. There are three major installations successfully operating and one planned to begin operation in 1998.

After Denver’s three failed attempts at opening the airport, however, blame centered on the computerized, digitally coded vehicle system — a trackmounted car propelled by linear induction motors. Some “authorities” claimed the problem was wayward power surges that shorted the linear motors. But technical problems were not the fault of linear-motor technology. They were a result of too little time, little or no planning, no project management, no development of teams, and politics.

Why use linear motor technology?

In Denver’s case, it was to move luggage faster, reduce maintenance, and resolve political situations.

As the distance between an airline’s gates to the terminal increases and as each airline attempts to handle more traffic, new ways are needed to move baggage efficiently and quickly, into, out of, and between concourses and gates. Cars powered by linear motors can move luggage faster than traditional belt conveyor systems. One of the newest belt systems, for example, at the new Pittsburgh terminal, has a total speed of 1,000 fpm. The plan at Denver was to have linear- motor propelled cars move luggage at 19 mph, or over 1,600 fpm.

Linear-motor-based, baggage-handling systems work. “They are an application of the future,” said Howard Zollinger, president of Zollinger Associates Inc., a consulting firm for the Oslo Hovedflyplass airport project. “They can lower maintenance costs and offer higher system performance over conventional cart-tug and conveyor systems.”

Properly implemented, the cars pick up and unload bags when called by a PC. Otherwise, they wait in a holding area. This reduced movement on a track means less wear on the wheels and other sections of the car, which reduces maintenance.

As for politics, one cannot underestimate the importance of a major carrier’s, such as United Airlines, desire to have automated cars. Its gates were going to be a mile from the terminal, and it hoped to have airplanes land, disembark passengers, unload luggage, replenish fuel and supplies, load in new luggage, take in new passengers, and fly out of the airport in 35 min.

The linear-motor car system

As with most linear motors, the stator is a flat linear section of electrical iron with coils wound in it such that ac waves travel down the stator. The rotor is a piece of aluminum or copper backed by steel.

The early implementations all have a flat stator segment as the fixed element, embedded in the track in the floor. The flat rotor is on the underneath side of the moving car. Benefits of this arrangement are that it eliminates the need for collector shoes and the need to put power to the moving devices. The same interaction of magnetic fields that turns an induction motor propels these cars equipped with linear motors.

The cars have wheels that ride the track and keep the air-gap between stator and rotor of 4 to 7 mm.

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