364 Electrical Power Systems Technology
copper losses are relatively high. However, the advantages outweigh this
disadvantage for certain applications. Since there are no brushes and com-
mutator, motor life is limited mainly by the bearing. With proper lubrica-
tion, a brushless DC motor can be used for an indefinite period. Also, the
motor frequency, and thus the speed, can be adjusted by varying the oscil-
lator circuit.
DC Stepping Motors
DC stepping motors are unique DC motors that are used to control
automatic industrial processing equipment. DC motors of this type are
found in numerically controlled machines and robotic systems used by
industry. They are very efficient and develop a high torque The stepping
motor is used primarily to change electrical pulses into a rotary motion
that can be used to produce mechanical movements.
The shaft of a DC stepping motor rotates a specific number of me-
chanical degrees with each incoming pulse of electrical energy. The amount
of rotary movement or angular displacement produced by each pulse can
be repeated precisely with each succeeding pulse from the drive source.
The resulting output of this device is used to accurately locate or position
automatic process machinery.
The velocity, distance, and direction of movement of a specific ma-
chine can be controlled by DC stepping motors. The movement error of
this device is generally less than 5 percent per step. This error factor is not
Figure 14-10. A brush less DC motor circuit