
D.C. Motor Drives 137
look briefly at how this is achieved. Later (in Chapter 8) we
will see that the stepping motor provides a simpler open-
loop alternative method of position control.
In the example shown in Figure 4.13, the angular position
of the output shaft is intended to follow the reference volt-
age (0
re
f)> but it should be clear that if the motor drives a
toothed belt linear outputs can also be obtained. The
potentiometer mounted on the output shaft provides a feed-
back voltage proportional to the actual position of the out-
put shaft. The voltage from this potentiometer must be a
linear function of angle, and must not vary with tem ...