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GLENTEK Inc. 208 Standard Street, El Segundo, California 90245, U.S.A. (310) 322-3026
SMA7215 MANUAL
Figure 2.3
Brush type and Brushless type Motors
2.4 Brushed Motors vs. Brushless Motors:
There are two basic types of motor design that are used for high-performance motion
control systems: brush type PM (permanent magnet), and brushless type PM. As you can
see in figure 2.3, a brush type motor has windings on the rotor (shaft) and magnets in the
stator (frame). In a brushless type motor, the magnets are on the rotor and the windings are
in the stator.
To produce optimal torque in a motor, it is necessary to direct the flow of current to the
appropriate windings with respect to the magnetic fields of the permanent magnets. In a
brush-type motor, this is accomplished by using a commutator and brushes. The brushes,
which are mounted in the stator, are connected to the motor wires, and the commutator
contacts, which are mounted on the rotor, are connected to the windings. As the rotor turns,
the brushes switch the current flow to the windings which are optimally oriented with respect
to the magnetic field, which in turn produces maximum torque.
In a brushless motor there is no commutator to direct the current flow through the
windings. Instead, an encoder, hall sensors or a resolver on the motor shaft senses the rotor
position (and thus the magnet orientation). The position data is fed to the amplifier which in
turn commutates the motor electronically by directing the current through the appropriate
windings to produce maximum torque. The effect is analogous to a string of sequencing
Christmas lights: the lights seem to chase each other around the string. In this case, the
magnets on the rotor "chase" the magnetic fields of the windings as the fields "move" around
the stator.
The relative advantages and/or disadvantages of a brush type motor/amplifier
combination vs. a brushless motor/amplifier combination can be significant. On the next
page is a summary of advantages and disadvantages of brush type motor/amplifiers and
brushless type motor/amplifiers to help you decide which type to select for your applications.
Содержание SMA7215
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