Table of Contents
Advertisement
4.5.1 Principles of Printing (285 Ipm)
The belt printer has 132 hammers, one hammer
for each print position. The print operation is
separated into these functions:
• Subscan.
A subscan is the time required to
option every fifth print position to every
second belt position. Five subscans make
one print scan.
• Print scan.
A print scan is the time required
to option one character to all print positions.
• Print line.
A print line is 48 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 4-84.
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. 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
m
sensing the missing timing
mark
m
that identifies the home position. 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 synchronism of the
home pulse with the belt position counter.
The subscan pulses are generated by the transducer
detecting the raised timing marks on the type belt.
Two subscan pulses are developed from each
timing mark.
1
The 64-character set takes 64 print scans. The 96-charac-
ter set takes 96 print scans.
Because the printer has a continously moving type
belt, the attachment must determine when to fire
a hammer to print the specified character. Using
the illustration
II
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 position
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 position 1 is compared to
the character aligned at position 1. During this
first subscan, every fifth position (1,6,11,16,
21,26,31, etc) is compared with its-respectively
aligned character (every second belt character). If
the character specified and the character aligned
compare equal, the hammer is fired at the begin-
ning of the next subscan. This sequence, starting
at print position 1, is called subscan 1.
At the end of subscan 1, the type belt movement
aligns the character B with print position 3, as
shown in the illustration
m.
Print optioning
now continues with print position 3 and proceeds
through every fifth print position until the charac-
ter aligned with print position 128 is optioned.
This sequence, starting with print position 3, is
called subscan 2.
Belt movement has now aligned the character C
with print position 5, as shown in the illustration
II.
Print optioning continues for every fifth
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 optioning
with print position 2 and every fifth position
through print position 127. Subscan 5 starts
optioning with print position 4 and every fifth
position through print position 129. These five
subscans make the first print scan.
4-82
During this first print scan, each of the print
positions was optioned to print one character,
but only those hammers are fired that had the
aligned character compare equal with the speci-
fied character.
The first print scan started with the character A
aligned at print position 1. Now, the character B
is aligned with print position 1 to start the second
print scan.
After the second five subscans, all positions are
now optioned to print a second character. To
option the 46 remaining characters to each print
position, 46 more print scans are taken.
Hammers are fired for the optioned print positions
that compare equal on each succeeding subscan.
To reduce the hammer power requirements, 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 print scans, an additional print scan
(49) is taken to fire hammers selected during
subscan 5 of print scan 48.
Advertisement
Table of Contents
