Brushed DC motors, featuring simple design and easy control, are widely used to open and close disk trays. In cars, they are often used for retracting, extending, and positioning electrically-powered side windows. The low cost of these motors makes them suitable for many uses. One drawback, however, is that brushes and commutators tend to wear relatively quickly as a result of their continued contact, requiring frequent replacement and periodic maintenance.
A stepper motor is driven by pulses; it rotates through a specific angle (step) with each pulse. Because the rotation is precisely controlled by the number of pulses received, these motors are widely used to implement positional adjustments. They are often used, for example, to control paper feed in fax machines and printers—since these devices feed paper in fixed steps, which are easily correlated with pulse count. Pausing can also be easily controlled, as motor rotation stops instantly when the pulse signal is interrupted.
With synchronous motors, rotation is synchronous with the frequency of the supply current. These motors are often used to drive the rotating trays in microwave ovens; reduction gears in the motor unit can be used to obtain the appropriate rotational speeds to heat food. With induction motors, too, the rotation speed varies with frequency; but the movement is not synchronous. In the past, these motors were often used in electric fans and washing machines.
There are various types of motor in common use. In this session, we look at the advantages and applications of brushless DC motors.