Imagine the hundreds of science fiction movies you've seen, where sleek-looking trains float high above the ground, moving people from destination to destination. These high-tech railways may seem futuristic, but one company has brought them closer to reality with its magnetic levitation technology that represents an alternative to light rail and automated people movers.
MagneMotion, Acton, Mass., recently received a patent for its MagLev (magnetic levitation) system, which uses a single magnetic structure to provide suspension, guidance, and propulsion of vehicles on a guideway. Other levitation systems use two magnetic structures, one for suspension and guidance, and another for propulsion, which increases the weight of the system. Lighter vehicles require less power, which means less cost.
The system uses wide-gap Electromagnetic Suspension (EMS) and MagneMotion's QuickStick linear synchronous motor (LSM) technology, says Todd Webber, president and co-founder. Webber says the MagLev system can be used in any type of motion control system, such as material handling, assembly automation, and airport baggage carousels, and particularly in people movers.
LSMs are installed in a guideway between permanent magnet motors on a vehicle. Simply put, position sensors sense where the magnets are on the vehicle and communicate this knowledge to a central controller, which tells the vehicles when they can move. Controllers activate the coils and create a magnetic field for non-contact propulsion.
“LSM motors propel the vehicles while an electromagnetic suspension system levitates them. The vehicle floats on a magnetic field,” Webber says. “They ride the field like a surfer rides a wave.”
Windings on the steel guideway are energized in a controlled fashion to generate a synchronized magnetic field pattern that interacts with the permanent magnets on the vehicle. EMS systems use attractive force between permanent magnets on the vehicle and steel on the guideway to both suspend and guide the vehicle along the track.
MagneMotion's QuickStick LSM contains two ½-m long motors in a 1-m long package. Currents driven in the motor stator interact with permanent magnets on the vehicle to create thrust. Each QuickStick motor may interact with only one vehicle at a time.
Webber says the system operates like a Brio toy — the entire track system is a merge-to-verge electric system, allowing the vehicles to go straight or make left and right turns. Each section of track holds a LSM QuickStick module. Only one vehicle can be in this block at a time. “We designed this intelligent system so we know where all vehicles are in system at all times and if a vehicle can proceed to its desired destination,” Webber says. “This also acts as a built-in anti-collision system.”
Magnetic cushioning provides a smooth ride
Permanent magnets are attractive, not repulsive. They are drawn up to the suspension rail, and their natural tendency is to stick to it. The control coils actually counteract that field of attraction to achieve the levitation and maintain the gap at certain level.
Only a small amount of control power is needed to provide stable levitation due to the use of permanent magnets on the vehicle. The levitation control coils on the vehicle adjust the gap between the magnets on the vehicle and the steel on the guideway, maintaining a consistent force equal to the weight of the vehicle. Controls on the vehicle sense weight changes, as when passengers board or exit the vehicle, and adjust the magnetic gap accordingly, maintaining the equilibrium required for levitation. These same levitation control coils, coupled with the magnets on the vehicle and steel on the guideway, also provide mechanics-free guidance, dampen turbulence, and adjust for lateral movement during acceleration, deceleration, and travel through curves. The result is a stable and smooth ride through all kinds of weather and terrain.