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4.1.1 Principles of Printing
(50, 100, and 155 Ipm)
The belt printer has 66 hammers, one hammer
for each two print positions. Therefore, to
print one line of 132 positions, each hammer
is fired twice. The print operation is separated
into these functions:
• Subscan.
A subscan is the time required to
option every tenth print position to every
fourth belt position. Five subscans make
one print scan.
• Print scan.
A print scan is the time required
to option one character to all odd print posi-
tions or all even print positions.
• Print line.
A print line is 48 odd print scans
and 48 even print scans for a 48-character
set
l
(standard). That is, every character on
the set is optioned to every print position.
Each print position can print only one character
per print line (when the print position is optioned
and the character specified for that position is
equal to the character aligned at that position).
See page 4-4.
During a subscan, the hammers selected for
firing are buffered in the attachment, and they
are gang-fired at the start of the next subscan.
Odd or even print scans are stopped early if all
optioned hammers are fired.
To synchronize the type belt to the attachment,
two types of pulses are required-a home pulse
and the subscan pulses.
The home pulse is generated from the type belt
by the transducer
a
sensing the missing
timing mark
II
that identifies the home posi-
tion. The home pulse occurs one subscan before
the first character of each character set is aligned
to print in position 1. Sensing the first home
pulse initiates a continuing check of the synchro-
nism of the home pulse with the belt position
counter.
1
The 64-character set takes 64 odd print scans and 64
even print scans. The 96-character set takes 96 odd
print scans and 96 even print scans:
The subscan pulses are generated by the trans-
ducer detecting the raised timing marks on
the type belt. Two subscan pulses are developed
from each timing mark.
Because the printer has a continuously moving
type belt, the attachment must determine when
to fire a hammer to print the specified charac-
ter. Using the illustration
m
as a reference,
observe the relationship between the moving
type belt and the hammer positions. This
shows the character A aligned with hammer 1
in print position 1.
Print optioning can start when a character is
aligned with print position 1. The belt posi-
tion counter keeps track of what character is
aligned to print in print position 1. This value
is set into the scan register at the beginning of
each print scan. During the first hammer
option cycle, the character specified for posi-
tion 1 is compared to the character aligned at
position 1. During this first subscan, every
tenth position (1, 11, 21, 31,41, etc) is com-
pared with its respectively al igned character
(every fourth belt character). If the character
specified and the character aligned compare
equal, the hammer is fired at the beginning of
the next subscan. This sequence, starting at
print position 1, is called subscan 1.
At the end of subscan 1, the type belt move-
ment aligns the character B with print position
3 and hammer 2, as shown in the illustration
II .
Print optioning now continues with
print position 3 and proceeds through every
tenth print position until the character aligned
with print position 123 is optioned. This
sequence, starting with print position 3, is
called subscan 2.
Belt movement has now al igned the character
C with print position 5, as shown in the illus-
tration
m .
Print optioning continues for
every tenth position until the character aligned
with print position 125 is optioned. This
sequence, starting with print position 5, is
called subscan 3.
Subscans 4 and 5 follow the same pattern (illus-
tration
Ii
and
m).
Subscan 4 starts op-
tioning with print position 7 and every tenth
position through print position 127. Subscan 5
4-2
starts optioning with print position 9 and every
tenth position through print position 129. These
five subscans make the first odd print scan.
During this first odd print scan, each of the odd
print positions was optioned to print one char-
acter, but only those hammers are fired that had
the aligned character compare equal with the
specified character.
The first print scan started with the character
A aligned at print position 1. Now, the char-
acter B is aligned with print position 1 to start
the second print scan.
After the second five subscans, all odd positions
are now optioned to print a second character.
To option the 46 remaining characters to each
odd print position, 46 more odd print scans are
taken.
Hammers are fired for the optioned print posi-
tions that compare equal on each succeeding
subscan. To reduce the hammer power require-
ments, only five hammers are allowed to fire
on one subscan. If more than five optioned
print positions compare equal, optioning starts
again with 48 new print scans. Scanning starts
again at print position 1 and positions not
printed are optioned again.
After the 48 odd print scans, there is a delay
(18 dummy subscans) to allow the hammers to
fire and settle. Then the even positions are
scanned starting with the first character in print
position 2 and every tenth position through
print position 132 on subscan 1. Subscan 2
starts with print position 4 and every tenth
position through print position 124. Subscan
3 starts with print position 6 and every tenth
postion through print position 126; subscan 4
starts with print position 8 and every tenth
position through print position 128; subscan 5
starts with print position 10 and every tenth
postion through print position 130. This
sequence continues through 48 even print scans
to option every character on the type belt to
every even print position. An additional print
scan (49) is taken to fire hammers selected
during subscan 5 of print scan 48.
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