Note: Descriptions are shown in the official language in which they were submitted.
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DOT r~ATRIX PRINTER
Field of the Invention
This invention relates to impact printin~ and
in particular to impact line printers which employ
dot patterns in the printing operation to record
dots on a print medium to form characters, images,
symbols, lines or the like.
Background oE the Invention
Dot matrix printers may be of various diverse
types, such as, helical printers and band printers.
A dot-helix matrix printer, which is an enhancement
of the bar-helix printer, consists of a rotating
cylinder having rows of single raised dot print
elements formed in a helical pattern around the
peripheral surface. A plurality of print hamme~s
having a bar-shaped impact surface is provided. A
paper print medium is continuously fed between the
hammers and the cylinder. Actuators are provided
which selectively actuate the hammers to strike the
dot print elements against an ink ribbon and paper
whenever one of the dot elements is in position to
be printed to record printed dots o~ the paper.
Band matrix printers employ a single set of
raised dots distributed along a band or belt which
moves horizontally across the paper to be printed.
Another form is a drum printer which has raised dots
distributed in columns around a drum which rotates
around an axes parallel to the line to be printed.
In both cases, printing is achieved by impacting the
raised dot printing elements with a print hammer
which results in the raised dots impacting a printing
ribbon against paper and transferring ink or printing
dots at the position or the dots when the paper is
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contacted. Patterns are printed by striking the
hammers against the printing belt or drum whenever
one of the dot printing elements, which move along
the printing line, is in a position where a printed
dot is desired. In this way, any desired pattern is
formed by an array of dots which are printed along a
line. Subsequent lines are printed hy stepping the
paper vertically or normal to the printing line.
It is well known that one limitation on the
printing speed of impact printers such as impact
line printers i5 the cycle time of the print ha~mer
or maximum repetition rate of the pattern of the
print elements on a dot-helix cylinder or on a belt,
band or drum~ It became apparent that it would be
advantageous if the printer throughput could be
improved for a given hammer repetition rate.
Summarx_~f the Invention
The pre~ent invention makes use of multiple dot
patterns distributed on the cylinder, belt, band or
drum of a line printer to provide an improved
printing throughput for an all points addressable
line printer.
In a dot-helix matrix printer, different
arrangements of the dots are used which can be
?5 varied in position and spacing to increase printing
speed. By using a 1, 2, 1, 2, dot pattern, a 66~
printing speed and a 33~ power saving is realized
over the use of a single dot pattern. The use of a
1, 2, 1, 3, dot pattern results in a speed improve-
ment of 100~ over the single dot pattern.
On a belt, band or drum line printer, multipledot patterns are given a predetermined distribution.
More specifically, arrangements of dot~ are used
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which provide enhanced performance due to the fact
that they are determined by an analysis of the
statistical occurence of a particuLar dot pattern in
a character set. The higher statistical probahility
dot patterns are used more often on the belt, band
or drum. For example, assume pattern 1 consists of
a dot in the upper case position, pattern 2 consists
of a dot in the lower case position and pattern 3
consists of dots in both the upper and lower case
positions. If it is found that, for the character
set for a particular application, pattern 1 occurs
statistically more often than the other two patterns,
then pattern 1 can be used more often and distributed
- in more places on the belt, band or drum.
The above-described example included a pattern
with two rows (m=2) and one column (n=1) with three
possible patterns. The general case for any number
of rows and columns is 2mn- 1 possible patterns.
The particular patterns that are used and distributed
more often will depend on a statistical analysis of
whatever character set is to be employed.
Accordingly, a primary object of the present
invention is to provide a novel and improved dot
matrix printer.
Another object of the present inven-tion is to
provide a printer system having a plurality of
separate dot patterns marking elements to form a
character set and means for distributing the marking
elements on a printer according to a predetermined
distribution arrangement.
A further object of the present invention ls to
provide a matrix printer having a helical array of
embossed patterns of dots on a cylinder wherein
different arrangements of the dots can be used which
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are varled in position and spacing to increase the
printing spe~d.
A still further object of the present invention
is to provide a matrlx printer which makes use of a
band, belt or drum on which particular patterns of
embossed dots are used and distributed more often
depending on a statistical analysis of whatever
character set is -to be employed.
The foregoing and other objects, features and
advantages of the invention will be apparent from
the following more particular description of preferred
embodiments of the invention, as illustrated in the
accompanying drawings.
Brief Description of the Drawings
Fig. l is a diagrammatic view showing a basic
single dot pattern arranged in a helical array on a
cylinder of a dot-helix matrix printer.
Fig. 2 is a diagrammatic view showing the dot
matrix arrangement for the printed character "E".
Fig. 3 is a diagrammatic view showing a 1, 2,
1, 2, dot pattern arranged in a helical array on the
cylinder of Fig. 1.
Fig. 4 is a diagrammatic view showing a 1, 2,
1, 3, dot pattern arranged in a helical array on the
cylinder of Fig. 1.
Fig. 5 is a diagrammatic view showing a bar
pattern arranged in a helical array on the cylinder
of Fig. 1.
Fig. 6 is a diagrammatic view showing one
configuration of a single dot pattern on a belt of
a band matrix printer.
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Fig. 7 is a diagrar~atic view showing one
configuration of a vertical multidot pattern arrange-
ment on a belt of a band matrix printer.
Fig. 8 is a diagrammatic view illustrating the
3 vertical dot patterns shown in the arrangement of
~ Fig. 7.
Fig. 9 is a diagran~atic view illustrating the
dot patterns shown in the arrangement of Fig. 8 with
one of the dot patterns being used more frequently
than the others.
Fig. 10 is a diagrammatic view illustratin~ a
horizontal arrangement of 3 dot patterns on~a belt
of a band matrix printer.
Fig. 11 is a diagrammatic view illustrating a
horizontal arrangement of 2 of the dot patterns
shown in Fig. 10.
Fig. 12 is a diagrammatic view illustrating 7
dot patterns that could be arranged horizontally on
the belt of a band matrix printer.
Fig. 13 is a diagrammatic view illustrating a
horizontal arrangement of 4 of the dot patterns
shown in Fig. 12.
Description of Preferred Embodiments
_ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ . _
Referring to Fig. 1, there is illustrated a
rotating cylinder 10 of a dot-helix matrix printer.
- A row of single raised dot print elem~nts 11 is
shown formed in a helical pattern around the peripheral
surface of the cylinder. A plurality of similar
rows would be disposed along the cylinder, there
being one row for each character print position.
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A print hammer 12 having a bar-shaped impact surface
is provided for each row oE dot print elements. It
is not shown, but it is well known ~hat a paper
print medium is continuously fed vertically between
the rotating cylinder and print hammers. Magnetically
operated actuators are provided which selectively
actuate the hammers to strike the dot print elements
against an ink ribbon and paper whenever one of the
dot elements is in position to be printed to record
printed dots on the paper.
Taking the basic dot pattern shown in Fig. 1,
assume the print hammers repetition rate is fixed at
1 ms. and the vertical spacing between dots is .020
inches and the cylinder is rotating at a surface
speed of 20 in./sec. For a 5 by 7 character printing,
- it takes 6 ms to complete a horizontal row of dots
and 42 ms. to print a character. There are S dots
per character and 1 dot spacing between characters.
To print a S by 7 character "E", shown in Fig. 2,
will require the hammer to strike 18 times.
In accordance with the present invention, by
arranging different dot patterns on the cylinder,
the printing speed and power consumption can be
improved. One example is shown in Fig. 3 wherein
the dot elements are disposed in a 1, 2, 1, 2,
arrangement. The vertical spacing between dots is
maintained at .020 inches. With the hammer repetition
rate fixed at 1 ms. and the cylinder now rotating at
a surface speed of 60 in./sec., the dot pattern is
so arranged that the hammer is never required to
strike within 3 rows of dots (1 ms.). To print a S
dot row now requires 4 ms. instead of 6 ms., as is
the case for the pattern shown in Fig. 1. A printing
speed increase of 66~ is realized. To print the
character "E", shown in Fig. 2, requires only 12
hammer strikes instead of 18. This results in a
power saving of 33%.
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The printing speed can be further improved by
different arrangements of dot patterns. For example,
a 1, 2, 1, 3, pattern is shown in Fig. Ll. Assume
the same fixed parameters and the cylinder rotating
S at ~ speed of 80 in./sec. It now requires only 3
ms. to print a 5 dot line resulting in a 100~ speed
- improvement. To print the character "E", shown in
Fig. 2, now requires only 10 hammer strikes. Other
designs of dot patterns for different resolutions
can achieve similar printing speed improvements.
It will be understood that the embossed patterns
do not have to be in dot form~ They can be extended
to bar forms to further improve the print quality.
The bar pattern shown in Fig. 5 can be used.to
replace the dot pattern shown in Fig. 3. Solid line
printing can be achieved with overlapping dots or
bars.
In another embodiment of the present invention,
multiple dot patterns are distributed on A belt,
band or drum of a line printer to provide an improved
printing throughout for an all points addressable
line printer. Referring to Fig. 6, there is shown
one configuration of a "single dot" band printer in
which the ha~mer 13 can strike a single raised dot
~5 print element 14 at any one of seven locatlons
across the hammer. The dot print elements are
spaced at intervals of eight print positions along
the belt 15 so th~t no two dots are in front of a
print hammer simultaneously. The belt moves horizon-
tally across a paper print medium to be printed.Printing is achieved by impacting the raised dot
- print elements to a printlng ribbon against the
paper and transferring ink or printing dots at the
position of the dots when the paper is contacted.
Patterns are printed by selectively energizing
magnetic actuators to effect the striking of hammers
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against the printing belt or drum whenever one of
the dot print elements, which move along or across
the printing line, is in a position where a printed
dot is desired. The number of hammers employed can
vary and depends on the number of characters to be
printed per line and the spacing between dots. In
this way, any desired pattern is formed by an array
of dots which are printed along a line. Subsequent
lines are printed by stepping the paper vertically
or normal to the printing line.
Referring to Fig. 7, there is shown a simple
multidot belt pattern for the case m=2, n-1, where
m corresponds to the number of rows and n the number
of columns in the dot patterns distributed around
the belt. This pattern comprises dot P1 in the
upper case position, dot P2 in the lower case position,
and dots P3 in both the upper and lower case positions.
Fig. 8 shows the same pattern in shaded square form
for purposes of illustration. P1, P2 and P3 ~ould
be arranged around the belt as shown.
In order to pxint a line of characters where
each character consists of dots printed on an MxN
matrix and the print elements consist of dots distrl-
buted on an mxn matrix the printing time is given by
T = S x (M/m) x (N/n) x Tr + (M/m) x Tp
where Tr ~~ Hammer repetition rate
Tp = Paper advancing time
S = A function which varies dependent on
the initial position of the dot
patterns relative to the printed
information.
The factor 5 is unity for a single dot pattern
and S > 1 for a multidot band. It increases the
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urther the inltial position of -the required dot
pattern is from the position to be printed. In
order for the printing throughput to be better than
the single dot case, it is desirable that (S/mn)
decrease to less than one. If this ratio is less
than one, the multidot pattern will be definitely
better than the single dot pattern. Even if this
ratio is not less than one, if the ~M/n) Tp term
reduces the paper advance time to the extent that
the total time is less, then the multidot pattern is
s-till better than the single dot case. The fac-tor S
reduces if the belt speed is higher or if the statistics
or the multidot patterns are skewed. The latter is
the essence of the present invention, as described
later.
Considering the printing of an alphanumeric
character set as a 8x7 matrix with a single dot band
and a 3-patterns or m-2 7 n=1 band under conditions
of Tr = 1 msec and Tp = 5 msec. The single dot band
2Q requires 56 msec for the printing operation and 40
msec to advance the paper, for a total printing time
of 96 msec.
Now for the multidot case with m=2, n=1, the
average printing speed for all characters of the
25 alphanumeric set is 43.424 msec. This results in an
average improvement of 54.7%. However, it is
realized that this printing speed improvement
requires an eight fold increase in the belt speed
but an overall decrease in the number of actual
hammer firings per printed job. Further increase in
the belt speed will further increase the print
throughput. The essence is that even if the belt
speed is increased, the throughput will not increase
for the single dot belt.
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The approach described above is an extension of
the single dot band (belt, drum) printing concept to
multidot elements. What follows, however, is a
general description of methods which can be employed
to produce further overall printing throughput
increases. Methods which involve the use of the
statistics related to the desired printed character
set, the language to be printed and ultimately the
type of printing jobs. This exposition is not
exhaustive, but indicates the methods that are to be
employed when designing a multidot printer.
Considering a multidot belt printer as shown in
Figs. 7 and 8, with m=2, n-1, the number of independent
patterns on the belt is three. Considering the
entire character set described earlier the number of
times each pattern occurs is:
P1 = 231
P2 = 134
P3 = 111
It thus appears that for printing the entire alphanumeric
set when each character has an equal probability of
occurrence, a belt (band or drum~ which has a greater
number of patterns type P1 than P2 or P3 will give
greater printing throughput. Such a pattern is
25 shown in Fig. 9 as P1, P2, P1, P3.
Comparing a multidot printer m=2, n=1 which
does not employ the statistical distribution of the
patterns involved in the character set with a multi-
dot belt printer which does take into account this
fact, there is obtained for a sequenti~l printing
operation; i.e., characters printed from left to
right, the following printing speeds. Non-statistical
belt with three patterns P1, P2, P3 distributed
periodically around the beltO
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Average print speed: 24.424 msec/character
line
Worst case printing speed: 34.1Z5 msec/
character lines
Statistical belt with patterns distributed P1, P2,
- P1, P3 cyclically around the belt. The number of
cycle of 4 pattern positions is based on the length
of the belt.
Average Print 5peed: 23.878 msec/character
line
Worst Case Print: 34.125 msec/charcter line
For random printing, i.c , a pattern is struck as it
arrives at the correct printing position (no left to
right requirement), the printing speeds become:
Non-statistical belt: 21.47 msec average,
33.75 msec worst case
Statistical Belt: 21.114 msec average, 31.25
msec worst case
Further improvement may be possible by considering
the fact that not all characters are equally probably
used in any language. Also, the relative positions
of dot patterns on the belt (in any given dot
pattern cycle or between cycles) can influence the
overall printing speed through the statistical
probability of occurrence (i.e., dependent probabil-
ities) associated with a given dot pat~ern immedi-
ately preceding or following any other dot pattern.
Finally any statistical skew that my be associated
with a given type of printing operation (e.g.,
insurance, air lines, payroll, etc.) can also be
factored into the statistics of the dot pattern
distribu-tion.
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Referring to Figs. 10-13, pat~erns are shown
distributed in a horizontal row around the belt. In
the case of a horizontal distribu-tlon, the number of
patterns is 2n _ 1. For the case where n=2, there
are three patterns P1, P2 and P3, as shown in Fiy.
10. However, patterns P1 and P2 are redundant so
- that only patterns P1 and P3 need be used, as shown
in Fig. 11. Fig. 12 illustrates the seven patterns
P1-P7 which would be the case where n=3. In this
case, patterns 1 and 3, 4 and 6 are redundant and
only patterns P1, P4, P5 and P7 need be used, as
shown in Fig. 13.
It will be understood that the present invention
is not limited to the specific patterns shown and
described. These patterns ~ay be varied to meet the
requirements of dlfferent printing applications.
While the invention has been particularly shown
and descri~ed with reference to preferred embodiments
thereof, it will be understood by those skilled in
the art that various changes in form and details may
be made therein without departing from the spirit
and scope of the invention.
