CONTREX CXB2040 - Manual (Page 17)

CXB1525 and CXB2040 MANUAL
8900 Zachary Lane N., Maple Grove, MN 55369 U.S.A. 14
CHAPTER 2: THEORY OF OPERATION
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.
Figure 2.3
Brush-type and Brushless-type Motors