February 16,
1998
DESIGN APPLICATIONS
Direct-drive motor simplifies servo
applications
Eliminates gearboxes, pulleys,
belts, and other power transmission components
Charles J. Murray, Senior Regional
Editor
Lebanon, OH--Most
servo systems are complex. They typically contain motors,
drives, gearboxes, belts, pulleys, sensors, and power-transmission
shafts, often with right angle turns in them.
Not all applications require such complexity, however.
To simplify servo systems, Vickers Electronic Systems
(VES) now offers a direct-drive solution. With it, control
engineers can eliminate gearboxes, belts, pulleys, and
right angle shafts. The resulting servo systems are
therefore simpler to install and maintain. They also
generate less noise, are more compact, and cost less.
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Vickers FC direct-drive motors range in
power output from 1 to 9 kW.
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Key to the direct drive solution is a line of new permanent
magnet brushless servo motors. Originally created for
tire manufacturing applications in Europe, the motors
are designed for the specific needs of direct drive
applications. They supply sufficient torque and precise
rotation at relatively low speeds, overcome potential
problems due to torque harmonics, ensure accurate positioning,
and avoid mechanical resonances.
To accomplish all that, engineers incorporated several
unique features in the new design, known as VES FC High
Torque Low Speed Motor line. One of the keys is their
use of magnetics: They employed economical ferrite magnets,
then oriented them in such a way as to provide high
flux density. The rotor is also constructed in segments,
which helps to simplify manufacturing and reduce cost.
Equally important, the motor's designers incorporated
a high number of poles and armature slots, which enabled
them to reduce torque harmonics at slow speeds.
Engineers also paid special attention to thermal and
mechanical issues. The motor's armature is totally encapsulated
in thermally conductive material, thus enabling engineers
to reduce its volume. A special anti-resonance filter,
with adjustable frequency and amplitude, enables it
to deal with any potential mechanical resonance problems.
Although the new motor line was just recently introduced
to the U.S. market, engineers from VES say the technology
has had a wide variety of applications. The tire industry
used it for direct driving of variable diameter drums
for tire molding. The glass industry has employed it
for direct drive of spindle motors for making hollow
glass items. It has also seen use on bending machines,
particularly for bending of muffler components. Other
applications include plastic injection molding, printing
machines, and motion simulators.
Some advantages of the motor were unexpected, notes
Monte C. Swinford, a VES engineer. "Machines that
use the direct drive tend to be quieter, because the
motors operate at 600 to 1,000 rpm, instead of 3,000
rpm," he says. The elimination of gearboxes also
significantly reduces noise, he says.
Although Swinford recommends that users stick with
gearboxes for high bandwidth (above 400 Hz) applications,
he says that the direct drive concept offers far greater
simplicity for those applications where it best fits.
"If engineers are creative in their use of this
concept, they can eliminate ball screws, gearboxes,
couplings, and all kinds of other components,"
Swinford says. "This way, they can build a much
more compact machine than they could before."
Additional details?Contact Monte Swinford, Vickers
Electronic Systems, 1151 W. Mason-Morrow Road, Lebanon,
OH 45036, 513-494-5654,
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