Page 658 - Mechatronics with Experiments

644 MECHATRONICS
Flying lead terminations: flying
leads w/ MS connector at end and
motor mounted MS connector are
standard termination options Primary feedback
device
High voltage
insulation rating
Secondary feedback
device-optional encoder

Rugged TENV, IP65
washdown construction

English or metric
dimentions
“O” ring prevents rotation
of outer bearing race for
longer bearing life

Optional shaft
configurations
Overtemperature-
protection thermistor
Medium-inertia rotor;
neodymium-iron-boron
rotor magnets
FIGURE 8.24: Brushless DC motor cross-sectional view showing the permanent magnet rotor,
stator winding, and position sensor. The rotor has the permanent magnets glued on its
periphery. In high speed and/or high temperature applications, a steel sleeve may be fitted over
the magnets to hold them in place securely. The rotor may be manufactured from laminations
fitted onto the solid shaft. The stator is made of laminations and houses the windings.
Reproduced with permission from Parker Hannifin.

Almost identical mechanical components exists in the brushless DC motors with
three exceptions:

1. there are no commutator or brushes since commutation is done electronically by the
drive,
2. the rotor has the permanent magnets glued to the surface of the rotor and the stator
has the winding,
3. the rotor has some form of position sensor (i.e., Hall effect sensors or encoder are the
most common) which is used for current commutation.

In order to understand the operating principle of a permanent magnet DC (PMDC)
motor, let us review the basics of electromagnetism (Figure 8.25). A current carrying
conductor establishes a magnetic field around it. The electromagnetic field strength is
proportional to the current magnitude, and the direction depends on the current direction
based on the right hand rule. The magnetic field shape can be changed by changing the
physical shape of the current carrying conductor, that is form loops of the conductor as in
the case of a solenoid winding. When the current passes through the winding of a solenoid,
the magnetic field inside the coil is concentrated in one direction, which in turn temporarily
magnetizes and pulls the iron core of the solenoid. This is an example of electromechanical
power conversion for linear motion.
Let us consider that a current carrying conductor is placed inside a magnetic field
established by two permanent magnet poles (or the magnetic field can be established by a
field-winding current in the case of field-wound DC motors). Depending on the direction of