IBM 1627 Manual page 23

functional circuits. Inputs to the recorder from the
system consist of drum up and drum down, carriage
left and carriage right, and pen up and pen down
pulses. These three groups of signals are generally
referred to as the X-axis, Y-axis, and Z-axis sig-
nals' respectively.
Drum Control
The X-axis signals from the system are applied to
separate 1. 5 ms single shots, which in turn control
the action of a reversible ring counter, through
suitable diode gating circuits. The ring counter
consists of three stages, each of which supplies
current to one pair of stator coils in the drum step
motor. The design of the ring counter is such that
only one pair of coils receives current at any given
time. When an incoming pulse fires one of the sin-
gle shots, the ring counter changes state. The
direction of change depends upon whether the in-
coming pulse is a drum up or a drum down signal.
When the ring counter changes state, the step
motor current is switched from one pair of coils to
an adjacent pair. This causes the motor to rotate
1/12 of a revolution clockwise or counterclockwise.
The drum step motor is connected to the drum
through a reduction gear train that causes the drum
to move 1/100" for each step of the motor.
Manual positioning of the drum is provided by
two front panel controls that allow the drum to be
advanced up or down in single steps, or continuously
at the rate of 120 steps per second.
Carriage Control
The Y-axis signals from the system are applied to
the carriage control circuit. This circuit and the
carriage step motor are identical to the drum con-
trol circuit and step motor described above. Front
panel controls are also provided for manual posi-
tioning of the carriage.
Pen Control
The Z-axis signals from the system control a pen
solenoid which, when energized, lifts the pen off the
chart. The incoming pen up and pen down pulses
are applied to a trigger. The trigger acts as an
electronic switch that controls current to the pen
solenoid through the suitable control stages and a
current driver. Manual control of the pen solenoid
is provided by means of a front panel switch.
3.2
Chart Take Up Motors
The remaining functional circuits of the 1627 are the
chart take up motors and power supply. The chart
motors operate in a stalled condition to maintain
proper tension on the chart spools. A front panel
ON/OFF switch is provided to allow the chart motors
to be disabled when single sheets of graph paper are
used in place of the continuous roll. (See Operating
Instructions in Section 1).
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Power Supply
The power supply consists of a silicon bridge recti-
fier and filter divider components. The supply pro-
vides two positive and three negative output voltages,
referenced to a circuit ground that is isolated from
the 1627 chassis. The output voltages from the
power supply are:
+ 3. 0 volts DC
+ 1. 5 volts DC
- 7. 5 volts DC
- 9. 0 volts DC
-24. 0 volts DC
CIRCUIT DESCRIPTIONS
The drum, carriage and pen solenoid control circuits
are contained on a single printed circuit board.
Because of this, ALDs are not available for the 1627.
In place of ALDs, the printed circuit board is pre-
sented in schematic form in Figure 3-4.
Step Motors
A simplified schematic diagram of the drum step
motor is shown in Figure 3-2. The motor consists
of a stator with three pairs of poles arranged sym-
metrically around a 4-pole soft iron rotor. Each of
the three pairs of poles has a separate current
winding that is controlled by a transistor current
driver. The motor advances 1/12 of a revolution
each time the current is switched off in one stator
winding and switched on in another winding. The
direction of rotation is determined by the sequence
in which the windings are energized.
For illustrative purposes, the three pairs of
stator windings, shown in Figure 3-2 are numbered
1, 2, and 3. The four poles of the roter are desig-
nated a, b, c, and d. Assume that transistor Q5 is
conducting. The circuit is designed so that when