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May 2012

An Attractive Solution

Magnetic technology has the potential to give detachable lifts greater flexibility, easier maintenance, and longer life.

Written by Chuck and Jeff Peterson, Tramway Engineering | 0 comment

The linear synchronous motor (LSM) could be the next big technical innovation in detachable lifts. The technology, used in a variety of industries, has the potential to provide a simpler, low-maintenance way to move carriers within the top and bottom terminals, and provide greater flexibility in carrier loading and spacing. As such, LSM-powered terminal conveyance systems could not only enhance new lifts, but have the potential to upgrade older lifts and extend their useful life by 20 years.


In a linear synchronous motor (LSM), a series of electromagnets (in the yellow channel, above) push/pull a carrier, topped by a magnetic pad (black in the illustration), through the terminal.


LSMs have already proven themselves in a variety of other applications. They can drive maglev (magnetic levitation) trains, automate pallet movement, power ropeless high-speed elevators, and launch planes off aircraft carriers.

LSMs have already revolutionized the roller coaster, which has several similarities to detachable lifts. Ever since the roller coaster made the first person scream with excitement, chains have been used to pull the coaster to the top of the crest hill before allowing gravity to take over. The potential energy of the coaster train is then converted into kinetic energy as the coaster speeds around the track at a decreasing speed until it eventually coasts back into the station.

The old chain lifts—which are similar to the chain-driven conveyance systems of many detachables—took too long on the lift hill, were expensive to maintain and limited the potential thrill. In 1997, coaster engineers begin using magnetic propulsion (LSMs and linear induction motors, LIMs, which are similar) to catapult the coaster trains out of the station and up the lift hill. Today, there are more than 50 magnetic propulsion coasters operating around the world. They use LSMs to not only accelerate the coaster to 70 mph in under 4 seconds, but to enforce speed control along the coaster path, and brake the coaster as it returns to the station. The similarities to terminal conveyance needs are obvious.


How It Works
With current technology, LSM control systems can precisely control the movement and positioning of individual permanent magnets along the path of travel. A magnetic “wave” pushes and pulls a moving part along its path. A linear synchronous motor is simply a rotating squirrel cage induction motor opened up flat. Instead of producing rotary torque, it produces linear forces.

All electric motors consist of stators and rotors. In an LSM, the stators are a line of electromagnets along the path of the linear motion. The rotors are permanent magnets that are attached to the moving part, such as coaster trains or lift carriers. The stators are controlled to create multiple traveling magnetic waves—in the case of a lift carrier, one wave per carrier. The permanent magnet is attached to the moving part, which travels at the same speed (synchronous) as the moving electromagnetic wave.

LSMs themselves have some major advantages: no moving parts, silent operation, energy efficiency, reduced maintenance, compact size, ease of installation, and precision positioning.

In the lift industry, we don’t need the power to accelerate a 10-ton coaster train to 70 mph, but the operational requirements and the standards for passenger safety are similar. LSMs can accelerate and decelerate a carrier in a controlled manner, convey it through the terminal, and provide greater flexibility than existing systems.

The physical layout of an LSM lift terminal is identical to the current design. The stationary stators of the LSM would replace the current tire/belt/pulley mechanical system. The existing friction plate on the grip, which provides traction for the wheels, would be replaced with a permanent magnetic array (see schematics).

Once detached from the haul rope, the carrier would be decelerated by the LSM stators and begin to travel around the terminal’s running rails.

For the first time, carrier movement would no longer be directly tied to the rope speed. Individual carrier deceleration, movement within the terminal and acceleration are under software control. If it is necessary to slow a carrier by two seconds to allow riders more time to board, for example, the control system would have the flexibility to create a buffer zone that would allow the operator to stop or slow a carrier at the loading area without having to stop the entire lift.

Carrier spacing would no longer have to be adjusted with clutches and within defined limits. Instead, the on-line carrier spacing could vary, and carrier spacing could be adjusted within either of the terminals. Independent control of each carrier means that real-time switching could allow for multiple carrier paths in the terminal; that could allow for double loading and unloading positions, to increase the lift’s capacity. The use of LSM opens up possibilities for new lift designs.

But perhaps the most important use of LSMs will be in retrofitting older detachables. The continued operation of the aging detachable fleet is becoming an urgent issue. The oldest detachable lifts are now more than 25 years old. Because of cost constraints, the detachable fleet will continue to operate well past its intended life cycle. But that leads to escalating maintenance time and costs.

The two systems that present the most maintenance problems are the grips and terminal conveyance systems. The conversion of an existing lift to LSM technology would address both of these issues and extend the life of the lifts for perhaps 20 years. An LSM-retrofitted lift could utilize the existing terminal structure, running rails, towers, line equipment, drives and carriers. The tire/ pulley/belt conveyance machinery would be replaced with the stators, and the grips would be replaced or retrofitted with a magnetic array in the place of the friction plate.

This idea is not really so far-fetched as it might sound. Fifteen years ago, the roller coaster industry was using the same old lift chain mechanical system. The industry turned to new LSM designs and adapted existing technology to meet their needs. The roller coasters are now faster, safer and more thrilling.

Like the roller coaster industry, the lift industry can benefit from new technology. While there are still some wrinkles to work out, we feel that the remaining obstacles can be solved in the next year or so. We are working with Leitner-Poma to set up a test bed at its facilities in Grand Junction to refine the technology. The benefits are many, and well worth the effort needed to make them a reality.

These schematics show that an LSM-driven terminal conveyance system would look a lot like current designs, except the usual tires, belts, and pulleys would be replaced by magnets.



The View from the Front Lines

Is the lift maintenance community open to the idea of radical change? It seems so. Phil Patterson, lift maintenance manager at Beaver Creek, Colo., has been talking with the Petersons about the LSM terminal conveyance system, and he has high hopes for it. “The potential is huge,” he says. “This is the next big advancement in terminals.”

With the Centennial Express ferrying guests out of the main Beaver Creek base area, Patterson knows all too well the amount of maintenance older terminal conveyance systems require. This 1986 Dopplemayr detachable has hundreds of mechanical parts involved in terminal conveyance. “Few of the individual maintenance items are very expensive,” he notes, but there are a lot of them—more than 80 tires and pulleys, double the number of belts, plus clutches and drive lines. And like every mechanical system, these parts are subject to failure that can shut down the lift. “The greater the mechanical complexity, the higher your failure rate,” Patterson says. So he appreciates the lack of moving parts in an LSM system, and its potential for creating a more reliable and low-maintenance terminal. To him, it makes sense to invest in a new LSM type of lift, or to spend what could easily be $1 million to retrofit an older lift and extend its life by 20 years or more.

But will LSM lifts be economical? Will resorts want to retrofit older detachables in high-profile and high-capacity roles? Those questions remain to be answered.