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The amplifier detector trigger circuit of patterns
D , 0,
and
II
is set to trigger at the null posi-
tion (where minimum energy is coupled from the
print emitter winding). This occurs at the maxi-
mum misalignment of the land patterns of the
print emitter and land patterns of the print emit-
ter pickup. When the print emitter pickup is moved
left or right, land patterns
D, 0,
and
II
each·
produce an output pulse every
0.030
inch
(0.76
mm) of motion. When the pulses from the three
circuits are ORed, a pulse is produced every
0.010
inch
(0.25
mm) of motion.
Because character spacing is
10
characters per
inch, there is
0.100
inch
(2.54
mm) for each
character. With the seven dot positions for each
character and three positions between characters,
there is
0.010
inch
(0.25
mm) between print posi-
tions 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.
Motion of the print emitter
pickup moving from left to right produces a se-
quence of emitter pulses -
0, 0,
and
D;
motion from right to left produces a sequence of
emitter pulses -
0, 0, D.
The left margin
signal and the emitter'pulses provide the system
with enough information to determine
(1)
the
firing time for the wires,
(2)
where the print head
is on the print line, and
(3)
which direction the
print head is moving.
r
I
I
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L
r
l
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I
I
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I
I
I
I
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I
L
J
--
-
-- --
.,
r
-,
I
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L -1
I
I
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I
L-t
L--t
This illustrates the null position of the print emit-
ter land pattern. The land pattern of the print
emitter pickup is shown in phantom.
Print
Head
Moving
Left
to Right
Left Margin
The number of print emitter
1, 2, and 3 pulses depends on how
I~far
the print head is into left
margin.~
J
I
I
I
I
Printing starts (in character position 1)
on the next print emitter 3 pulse after
left margin goes inactive.
Print Emitter 1
?I------------------. . . . .
-----------IL-----------------t
1
I
I
Print Emitter 2
21_-: ,
--------L----------l'L----.a-----:.-----------IL----t
I
Print Emitter 3
~I-----------------------
....
---...IL---:----L..----'----~-___t
Note: The pulses become narrower as the speed
of the print head increases.
Serial Printer
9-5
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