Page 656 - Mechatronics with Experiments

642 MECHATRONICS
8.4.1 Operating Principles of DC Motors
There are three major classes of brush-type permanent magnet DC (PMDC) motors:

1. iron core armature,
2. printed-disk armature,
3. shell-armature DC motors.
Iron core armature PMDC motor is the standard DC motor where the stator has a permanent
magnet and rotor has wound conductors (Figures 8.21a, 8.22, 8.23). The other two types
are developed for applications which require a very large torque to inertia ratio, and hence
the ability to accelerate and decelerate very fast (Figure 8.21). The use of the printed-disk
and shell-armature type motors has significantly reduced in recent years since comparable
or better torque to inertia ratios can be achieved by low inertia brushless DC motors with
better reliability (Figures 8.21b, 8.24).
Brush-type DC motors have the permanent magnet as the stator (typically two pole or
four pole configuration) and the windings on the iron core rotor (Figure 8.22). The rotor is
supported by two ball bearings inside the housing. The ends of the housing are covered by
the end plate and face mount plate. Small washers are placed between the bearings and the

Disc-armature "printed" motor Motion
Iron-cored motor Stator
magnets

Rotor
windings
Permanent magnet
(8 pole)
Brushes
Commutator Shell-armature motor Magnet pole
_ Air gap
+
Motion

Armature Core Flux path
(Hollow club shaped
conductor array)
(a) Brush-type

S

N Magnets N

S
windings
Lamination

(b) Brushless type
FIGURE 8.21: Permanant magnet DC motor types : (a) brush-types (iron-core, disc-armature,
shell-armature) (b) brushless type.