Jan 222011
 
MagLev Train
Image by Burns! via Flickr

TRAINS that float on air may be the most famous objects borne by magnetic fields.

But magnetic forces can also support other, less visible objects: the spinning shafts, for example, hidden at the mechanical core of industrial equipment like pumps, generators, motors and compressors.

Electromagnets surround these rotating shafts and keep them suspended in the air — with the help of sensors and computer algorithms that adjust the position of the shafts thousands of times a second, keeping them centered.

Magnetic bearings may play an increasingly important role in future industrial systems, including environmentally friendlier ones. The low-friction technology of these bearings eliminates the need for lubrication to keep a system operating smoothly.

“With magnetic bearings, there’s no oil in the shaft, no grease, no ball bearings,” said David Trumper, a professor of mechanical engineering at the Massachusetts Institute of Technology.

Despite their advantages, magnetic bearings have been slow to catch on widely in industry, said Eric Maslen, a professor of mechanical and aerospace engineering at the University of Virginia in Charlottesville. One reason, he said, has been the complications involved in installing the control system that runs the electromagnets. That system is typically housed in a bulky cabinet far from the rotating shaft.

A company called Synchrony Inc., in Salem, Va., has miniaturized the control system — which often includes dozens of cables, digital processors and power amplifiers, as well as other electronics — and tucked it into the housing of the magnets themselves. That eliminates the need for extensive cables or separate cabinets and may thus simplify installation. The control system detects and then adjusts the position of the shaft about 15,000 times a second by redistributing the current to the electromagnets.

The compact systems, Dr. Maslen said, are an important innovation. “This is a way to make magnetic bearings an off-the-shelf technology,” he said.

At present, companies that want to use magnetic bearings typically must give detailed information about their machines to the vendor, which then makes customized bearings.

But magnetic forces can also support other, less visible objects: the spinning shafts, for example, hidden at the mechanical core of industrial equipment like pumps, generators, motors and compressors.

Electromagnets surround these rotating shafts and keep them suspended in the air — with the help of sensors and computer algorithms that adjust the position of the shafts thousands of times a second, keeping them centered.

Magnetic bearings may play an increasingly important role in future industrial systems, including environmentally friendlier ones. The low-friction technology of these bearings eliminates the need for lubrication to keep a system operating smoothly.

“With magnetic bearings, there’s no oil in the shaft, no grease, no ball bearings,” said David Trumper, a professor of mechanical engineering at the Massachusetts Institute of Technology.

Despite their advantages, magnetic bearings have been slow to catch on widely in industry, said Eric Maslen, a professor of mechanical and aerospace engineering at the University of Virginia in Charlottesville. One reason, he said, has been the complications involved in installing the control system that runs the electromagnets. That system is typically housed in a bulky cabinet far from the rotating shaft.

A company called Synchrony Inc., in Salem, Va., has miniaturized the control system — which often includes dozens of cables, digital processors and power amplifiers, as well as other electronics — and tucked it into the housing of the magnets themselves. That eliminates the need for extensive cables or separate cabinets and may thus simplify installation. The control system detects and then adjusts the position of the shaft about 15,000 times a second by redistributing the current to the electromagnets.

The compact systems, Dr. Maslen said, are an important innovation. “This is a way to make magnetic bearings an off-the-shelf technology,” he said.

At present, companies that want to use magnetic bearings typically must give detailed information about their machines to the vendor, which then makes customized bearings.

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