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Print Emitter and Print Emitter Pickup
The print emitter
B
is a stationary board with a land
pattern and a 4.25 MHz oscillator
a.
The land pattern
simulates the primary winding of an air core transformer.
The print emitter pickup
II
is mounted on the bottom
of the print carrier" and slides along the length of the
print emitter. The pickup consists of 4 separate land
patterns and associated amplifier detector trigger
circuits. The land patterns of the print emitter pickup
simulate the secondary windings of an air core
transformer.
Land patterns denoted by
II
and
II
are at right angles
to the patterns denoted by •
II
and
II.
When the
print emitter pickup enters the left margin area, land
pattern
II
of the print emitter pickup moves directly
underneath land pattern
II
of the print emitter. As a
result of this alignment, energy is coupled from the
primary winding of the print emitter into the secondary
winding of the print emitter pickup and causes a level
change at the output of the amplifier detector trigger
circuit. This level change signals the microprogram that
the print head is in the left margin area.
The amplifier detector trigger circuit of patterns.
II
and
II
is set to trigger at the null position (where
minimum energy is coupled from the print emitter
winding). The null position occurs at the maximum
misalignment of the land patterns of the print emitter
and land patterns of the print· emitter pickup. When the
print emitter pickup is moved left or right, land patterns
• II
and
II
each produce an output pulse every
0.762 mm (0.030 inch) of print head travel. When the
pulses from the 3 circuits are ORed, a pulse is produced
4-34
every 0.254 mm (0.010 inch) of print head travel.
This illustrates the null position of the print emitter land
pattern. The land pattern of the print emitter pickup is
shown with dotted lines.
r-----.
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I
r-,
I
I
I
I
I
I
I
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I
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I
I
I
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I
I
I
I
I
I
I
I
I
I
I
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I
I
I
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L.J
I
LJ
L ---
I
I
II
I L-t
L_.,
Because character spacing is 10 characters per inch,
there is 2.54 mm (0.100 inch) for each character. With
the 7 dot positions for each character and 3 positions
between characters, there is 0.254 mm (0.010 inch)
between dot positions and an emitter pulse for each
position.
Outputs of the amplifier detector trigger circuits are
'-left margin', '-print emitter 1', '-print emitter 2', and
'-print emitter 3'. The print emitter pickup moving from
left to right produces a sequence of emitter pulses-D
II
and
II;
from right to left produces a sequence of
emitter pulses-B
II
and
II.
The' -left margin' signal
and the emitter pulses provide the microprogram with
enough information to determine:
• The firing time for the wires
• Where the print head is on the print line
• Which direction the print head is moving
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