IBM 1627 Manual page 24

RI3
os
07
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Collector
04
Collect~o-r--I
Circuit
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Collector
Figure 3-2. Step Motor Drive Schematic
05
Q5 conducts, Q8 and Qll are cut off. Current
therefore, flows only in stator winding number 1.
This current creates a magnetic field that holds
poles a and c of the roter in alignment with the
number 1 stator poles. If transistor Q5 is switched
off and Q8 is switched on, the rotor turns until one
pair of its poles is aligned with the poles of stator
winding number 2. Because poles b and d are the
closest to the number 2 stator poles, the rotor steps
counterclockwise.
In the above example, if transistor Qll is
switched on instead of Q8, the rotor steps clockwise
until poles b and d are in alignment with the poles
of stator winding number 3.
If the current is continuously switched between
windings in a clockwise sequence (i. e., 1-2-3-1-2-
3, etc ,) the rotor steps counterclockwise. Con-
versely, if the switching sequence is counterclock-
wise, the rotor steps clockwise.
The rotor shaft of the drum step motor is
coupled to the drum through a reduction gear train.
The gear train consists of a 9-tooth pinion on the
rotor shaft which engages a 75-tooth gear in the
primary gear box on the motor assembly. A 12-
tooth pinion mounted on the same shaft as the 75-
tooth gear rotates at the rate of one revolution per
100 steps of the motor. The 12-tooth pinion drives
a 225-tooth gear fastened to the end of the drum.
The mechanical and electrical design of the
carriage step motor and its associated circuit are
identical to that of the drum step motor, except
that the 12-tooth pinion on the carriage step motor
drives a 156-tooth gear on the carriage drive pulley.
On both motors, the 12-tooth pinion in the primary
gear box is mounted off center. This permits the
backlash between the pinion and the drum or carriage
gear to be adjusted to zero. Resistors R15, Rll
and R16, shown in Figure 3-4 are current limiters.
A suppression diode is connected across each of the
three windings in both step motors to damp out the
high counter-emf generated by the decaying magnetic
field when the current is switched off.
3.3