Note: Descriptions are shown in the official language in which they were submitted.
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1 METHOD FOR ADAPTIVELY USING A PRINT RIBBON
IN AN IMPACT PRINTER
The invention relates to a method for adaptively
using a print ribbon in an impact printer such as a
typewriter or dot matrix printer, for example.
Generally, in impact printers two types of print
ribbon are used. The first may be called a singleuse
ribbon, where the colouring material, such as carbon,
at the impact location is completely transferred to the
record carrier, thus leaving a noncolouring area on the
ribbon substrate, so that after one complete pass of
its entire length for successive printing the ribbon
has to be discarded, save any provisions for repleting.
The second type of ribbon, in contrast, may usually be
passed back and forth several times in front of the
printing station since after each impact and ensuing
removal of dye from the impact location, sufficient
time is provided as the ribbon is further advanced, and
later reversed, for the dyestuff to "bleed" into
depleted areas from the neighbourhood so as to maintain
a reasonable though continuously degradating print
quality over several reversals of the transport
direction of the ribbon. These print ribbons as well as
their transport mechanisms are so commonplace that it
appears unnecessary to list references for their
description.
As was pointed out before, with the second type of
ribbon one has to accept that the print quality
gradually decreases until it reaches a minimum
tolerance level at which the ribbon has to be replaced.
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l This is very simple in the case of a singlecolour
ribbon but complex if a multicolour ribbon is employed
because not all of the colours will be used with the
same frequency. It may happen, therefore, that red, for
example, was frequently used for printlng pictures and
is accordingly rather depleted after some time, while
yellow was rarely used and thus stays fresh.
Another point to consider is the smudging of the
ribbon through takeup thereby of dust and dirt which
may cause ribbon areas unwilling to print although
enough colourant is available, or which leads to
undesirable obscuring or changing of colours.
Swiss Patent 474 757, assigned to W.H. Howson
Ltd., describes method and device for measuring the
density of the printing ink in a multicolour printer. A
current sample of the printing ink of each colour is
compared with a standard of the respective colour in
that light is shone through the inks under
investigation and directed onto photosensitive means
for electronic comparison.
That same Swiss Patent 474 757 refers to
conventional apparatus for determining the density of
printing colours employing complementary colour
filters.
This state of the art does not address the
economics of print ribbon use, in particular no
provisions have been proposed to permit an
appropriately fresh portion of the print ribbon to be
made available at the printing station in case a high-
quality printing job is to be performed. The present
invention aims at proposing a method for adaptively
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l using the print ribbon, i.e. provide undepleted ribbon
if high quality printing is desired but leave the
ribbon just as it happens to be if no special quality
requirements have been signalled.
The method in accordance with the present
invention for adaptively using a print ribbon, be it in
singlecolour or multicolour impact printers is
characterized by transporting in forward and reverse
directions, during printing operation, one subsection
of predetermined length of the ribbon, continuously
monitoring the condition of the printing colour or
colours in said one subsection, until the condition of
said colour or of any one of the colours in said one
subsection has reached a predetermined lower tolerance
level, and then advancing the ribbon so as now to
expose at the printing station the subsequent, fresh
subsection of the ribbon, regardless of the condition
of the possibly remaining colours in said one
subsection, for repeating the procedure until the
entire ribbon is used up.
With this method it will be possible to
immediately advance to a fresh ribbon subsection
through manual intervention by the operator in case a
printing job is signalled to require highquality
printing.
Details of the method in accordance with this
invention will now be described with reference to the
attached drawings in which:
Fig. 1 shows the essential components of a wire
matrix printer;
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1 Fig. 2 shows a multicolour ribhorl wi-th its spools
and lift fork;
Figs. 3 and 4 depict the degradation of the ribbon
quality over time;
Fig. 5 schematically shows an optical ribbon
quality monitoring device;
Fig. 6 refers to minimum and typical lengths of
ribbon subsections;
Fig. 7 represents the interconnections between the
components of a ribbon quality monitor;
Figs. 8 and 9 show flow diagrams for the interrupt
and ribbon advance routines, respectively;
Fig. 10 is a schematical diagram of the counter
circuitry of Fig. 7.
Besides typewriters which account for the greater
part of all impact printers in use today, there is an
increasing number of dotmatrix impact printers which
serve as output printers for digital computers, in
particular in applications where alphanumeric charac-
ters and pictures are to be printed. In most previous
cases impact printers have used singlecolour ribbons
but as the art of colourimage reproduction advances,
the multicolour dotmatrix impact printer is gaining
importance for producing sharp, accurate colour images
for graphics applications.
While the method of the present invention is
considered applicable to both, singlecolour and multi-
colour impact printers, the explanation of the
invention will be made by way of example with reference
to a multicolour dotmatrix printer the functioning of
which will now briefly be reviewed.
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1 Referring to Fig. 1, the printer 1 comprises a
platen 2 which carries a record carrier such as a sheet
of paper 3. Platen 2 is supported in frames 4,5 and
indexed via belt 6 and pulleys 7 and 8 by a stepper
motor 9. Slidingly supported on rods 10 and 11 is a
print head 12 which may be escaped along the print line
by a belt 13 slung around drums 14 and 15 and driven by
a stepper motor 16.
Print head 12 contains, e.g. seven wires ~not
shown~ arranged at equal mutual distances in a column,
the tips of the wires directed against platen 2 and
their ends connected to electromagnets which may be
selectively energized via a flexible cable 17 connected
to appropriate control apparatus as is known to those
skilled in the art. Printing of alphanumeric characters
and symbols is through composition of single dots in a
7x5 matrix arrangement, i.e. after the parallel
energizing of the appropriate number of wires the print
head has to be advanced by one fifth or less of a
character width whereupon the selective energization
for the then actual print position will be made, and so
forth until a character is completed and an
intereharaeter eseapement is aecomplished.
The wires impact actually against a print ribbon
18 arranged between platen 2 and print head 12 and
extending between two spools 19 and 20. The latter are
supported by means (not shown) for movement in both
directions under control from a control unit to be
described below. Print ribbon 18 (Fig. 2) has four
parallel colour bands 21 through 24, for example, with
yellow (21), magenta (22), cyan (23) and black (24)
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1 inks, respectively. These inks permit printing in a
total of seven different colours by superposition in
accordance with the subtractive primary colour system
which is, for example, explained in European Patent
Publication No. 0 011 722. Print ribbon 18 may alter-
natively be dedicated to a different system of colours
such as the one disclosed in Swiss Patent 610.825 which
prefers golden yellow, carmine, violet and turquoise.
Still another system might comprise the positive
primary colours red, yellow, blue and black, the black
always being used to enhance contrast.
The colour band to be presented at the print
station for printing is selected by a print control
unit which either controls the lifting of a
conventional ribbon fork 25 or of said ribbon spools 19
and 20. The differently coloured inks are composed such
that every two inks impregnated on adjacent bands are
mutually repelling so that their mixing (bleeding) is
prevented and no degradation of one ink by its
neighbour can occur.
Printers of the type described above presently can
perform up to a speed of 5000 imprints per second. The
limitation in speed is mainly dictated by the
mechanical parts which must be moved, viz. the print
wires and their associated electromagnets. With a
further reduction of mass of the wire/electromagnet
assemblies and with improvements in the materials used
in the print head, still higher speed will certainly be
possible soon.
Attainable printing speed and recent advances in
LSI technology bring the introduction of image
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1 processin~ systems on the basis of dot matrix impac-t
printers closer to reality. ~lowever, the high density
of multicoloured dots necessary for accurate image
printing accents the need for precise, clear, clean
dots from a print head/ribbon assembly. As a ribbon
begins to age, it commences to produce faded, blurred
dots which make an exact image reproduction impossible.
In the printers of the prior art, the entire
ribbon is treated as one unit assumed to have the
uniform deterioration characteristics as shown in
Fig. 3. When the ribbon is new, its quality is, of
course, very high, but with use the quality decreases
until a 1ower quality threshold is reached at which
replacement of the ribbon is required. Uniformity of
wearing is achieved by escaping the ribbon by a small
increment after each printing impact until the entire
supply of new ribbon is used up and then reversing the
direction of transportation several times until said
lower quality threshold is reached.
There are several problems with this method which
make it unsuitable for high-resolution colour
printing. The primary problem is that multicolour
ribbons cannot be made to wear uniformly across all co-
lours. Invariably, part of the ribbon will become
smudged or faded, or one of the lighter colours
collects black or just dirt. Accordingly, one or more
of the colour bands may have reached their
predetermined lower quality level while others have
not, yet the ribbon continues to be used since part of
it is still usable. Obviously, images printed with a
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1 ribbon in this state will have blurred, faded or
otherwise corrupted sections.
Another problem with prior art printers is that
there is no reliable method for monitoring ribbon
quality. The surest sign that a ribbon needs replaciny
is a poor colour print. And it is indeed difficult to
set a lower quality threshold since printing jobs may
have different quality requirements. If a job requires
high quality, with prior art printers the operator is
forced to replace the ribbon although it may not yet be
worn down.
The method of the present invention remedies these
problems by partitioning the entire ribbon into several
subsections of essentially equal length and employing
those subsections for printing sequentially until each
one reaches its individual lower quality level and then
switching to a fresh subsection. Fig. 4 shows this for
a colour ribbon partitioned into six subsections
Sl..S6, with the life of the subsections varying with
the parameters of the colour images printed, such as
frequency of colour changes, colour dot density,
printer speed, degree of resolution, etc. The
comparatively fast deterioration of subsections S2 and
S5 may be due to dark colour overprint causing a
lighter colour band to fade or a high frequency of
colour variation causing streaks on the ribbon,s colour
bands. Because in accordance with this method one
subsection is completely exhausted before the printer
switches to the next, the faster deterioration of
subsections S2 and S5 in the example of Fig. 4 is not
allowed to harm the overall picture quality.
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1 To advantageously employ the inventive method, it
will be necessary to continuously monitor the quality
of the ribbon subsection currently in use. The
following three schemes are contemplated to do this:
The first monitoring scheme employs discrete
counters to count the number of times the individual
colour bands in a ribbon subsection are struck by the
wires of the print head to produce a dot. Each colour
is assigned its own empirically determined maximum
count. When the number of dots produced from a
particular colour exceeds the maximum count for that
colour, the monitor will issue a signal causing the
ribbon transport mechanism to advance the ribbon to its
next subsection. In presetting the maximum number of
counts, the quality requirements of the printing job
can be balanced against ribbon longevity.
The second monitoring scheme as shown in Fig. 5 is
basically optical and comprises a light source 26 and a
photodetector 27. The idea here is that a streaked,
smudged or faded ribbon can be detected by the
intensity of light its emits. The photodetector is
mounted adjacent print head 12, and as the latter is
escaped, the detector scans ribbon 18. Light from
source 26 passes through a short length of each colour
band of ribbon 18 to a bank of optical filters 28
through 31. Each filter suppresses every colour except
the one of the colour band directly in front of it. For
example, light shone through the magenta band 22 is
passed through corresponding filter 29. The filtered
light is then passed to a string of photosensitive
elements 32 through 35 which convert the intensity of
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1 the colour received from their associated filter 28
through 31 to electrical signals which they feed to
individually connected integrators 36 through 39. Each
integrator adds the signals received over time to the
previous output of the respective photosensitive
element 32 through 35 and supplies its output signal to
one of comparators 40 through 43 which have one of
their inputs commonly connected to a threshold voltage.
Separate adjustment facilities may be provided at the
comparators so as to permit the threshold for each
colour to be preset individually.
If after a specified time, which may, e.g.
correspond to one sweep, the voltage output from one
integrator is below the threshold for the colour
concerned, then detector 27 signals via OR gate 44 that
one of the coulour bands in the current subsection is
corrupted. Ribbon 18 is then advanced to the next,
fresh subsection.
The third scheme simply involves a manual advance
option. When for any reason, the operator desires to
proceed to a fresh subsection of ribbon 18, e.g. for a
printing job requiring high quality, this option may be
used. The ribbon then advances to the next subsection
regardless of the state of the current subsection.
The length of the ribbon subsections can be set by
the operator prior to printing. The minimum practicable
length corresponds to the distance the print head 12
can travel across platen 2 between the left and right
stops 45, 46 (Fig. 1 and 6). Typically, the length QL
of a subsection should extend on both sides beyond said
travel distance. In the latter case, to ensure uniform
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1 aging)wearing of the entire subsection, ribbon 18
should be advanced by a tiny fraction ~x of the
subsection length ~L for every couple of print head
carrier returns.
Implementation of the method so far described is
best done on a microprocessorbased system having the
necessary degree of functionality. A block diagram for
such a system is shown in Fig. 7. For the purpose of
the following description, the operation of the system
is divided into three phases" powerup, normal
operation, and power down.
During the power-up cycle, microprocessor 47 runs
through some checkout routines and then reads the
operating parameters pertaining to the previous
operation out of a nonvolatile memory 48 and into the
appropriate units, such as a random access memory 49~
Into specific areas of memory 49 are read the maximum
count for the wire impacts on the ribbon for each
colour band 22...25, the length ~L for the ribbon
subsections, the current count for ~x, and the maximum
count for ~x. The previous values of the counters
(which were saved in memory 48) are rounded off, e.g.
to the nearest 102 and read back into the counters.
When this is complete, microprocessor 47 commences
normal operation by causing the printer to print.
During printing operation, the number of impacts
the print wires perform on ribbon 18 is counted
separately for each colour. Simultaneously, photo-
detector 27 is swept across ribbon 18 to discover any
faded or smeared colour bands. When the impact count
for any colour exceeds the preset value or a corrupted
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1 colour band is found, or lf the manual Rihbon Advance
button 50, Fig. 7, is pushed, a flipflop 51 is set to
be read later by processor 47. When a return of the
print head carrier is signalled by printex 1, an
interrupt signal is generated, and microprocessor 47
enters an interrupt routine (Fig. 8). In block 52 first
the RESET button 53 is checked. Since the mechanism is
preferably designed such that hitting RESET button 53
does not have any effect while printing is in progress,
reset flipflop 51 is assumed to be reset. Therefore,
the operation proceeds to block 54 decrementing the
current carrier count which is representative of the
number of carrier returns performed since the last time
the ribbon was advanced. When the current carrier count
reaches zero (block 55), said count is reloaded from
memory 48 and the ribbon is advanced by Ax (Fig. 9).
When microprocessor 47 determines that ribbon 18
should be advanced, it checks first on the direction of
advancement, i.e. foreward, backward or not at all, as
would be the case if the length ~L of a ribbon
subsection was chosen to be equal to the distance of
carrier travel. The processor will look at the number
of times the ribbon was previously advanced by ~x by
asking whether the current ~x count has reached zero
(block 56). If the answer is NO, i.e. the ribbon has
not reached the end of the current subsection, the
processor reads the direction flag stored in memory 48
(block 57). If the answer to the question of block 56
is YES, the processor asks the direction flag at which
end of the subsection the ribbon is. If the ribbon is
at the left end of the subsection, (block 58) it just
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1 reverses direction and begins to progress to the right
end of the subsection. If the ribbon is at the right
end of the subsection, the processor checks (block 60)
the status of flipflop 51 ( which may be set by the
counters 59, the photodetector 27 or by manual advance)
to decide whether to go to the next subsection or go
back over the preceding one. If either photodetector 27
or counters 59 signal that the ribbon is worn, or
manual advance button 50 indicates ribbon transport
regardless of ribbon condition, processor 47 reloads
the counters 59 and signals the advance into the new
subsection (blocks 61, 62). Otherwise, processor 47
toggles the direction flag, reloads the Ax count for
the subsection and begins to go back over the preceding
subsection (blocks 63, 64).
If the minimum length for the ribbon subsection is
chosen (~L), the subsection is only long enough to
cover the carrier, the ribbon does not get advanced by
any ~x. Processor 47 implements this by noticing at
powerup that ~Lmin was chosen, and computes a zero for
the ~x count (block 65). This zero value is continually
loaded for the ~x count and so the ribbon never
advances in any direction (block 66).
In summary, the length of each ribbon subsection
(~L) is set by the operator during a powerup or RESET
operation. While the printer is printing,
microprocessor 47 is supervising the uniform wearing of
the ribbon subsection by slowly moving the ribbon back
and forth by small increments (~x) every few carrier
returns. When a ribbon advance is signalled, the
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1 processor causes the ribbon to be transported to the
next subsection and repeats the process.
The only other incident which can cause an
interrupt to microprocessor 47 is the pushing of the
RESET button 67 by the operator. This causes
microprocessor 47 to enter the interrupt routine of
Fig. 8, loading new parameters (~L, counter limits)
into storage ~blocks 66 and 68). When RESEI' button 67
was pushed, processor 47 assumes that a new ribbon has
been installed. Therefore, the printer must be offline
when this happens.
A DEFAULT button 69 may be provided which has
essentially the same conse~uences when pushed as RESET
button 67, except that the new parameters are read from
a default list stored in the nonvolatile memory 48.
Fig. 10 shows the design principle for the
counters 59 of Fig. 7. The purpose of the counters is
to determine the actual number of impacts performed on
each of the colour bands of ribbon 18 and to cause
ribbon advance to a new ribbon subsection when the
predetermined maximum number of impacts is surpassed.
As mentioned before, print head 12 is assumed to
have seven print wires and, accordingly, there will be
seven control lines 70 for activating the print wire
magnets. These control lines 70 are also connected to a
discrete logic unit 71 which also receives vertical
position control signals over lines 72 from the ribbon
transport mechanism 73. A clock signal from system
clock 74 via line 75 synchronizes logic unit 71 with
the rest of the printer. Depending on which colour band
21 through 24 is selected, logic unit 71 enables the
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1 appropriate one of counters 76 through 79 which then
decrements by the number of ti~es the associated colour
band is impacted by a print wire. The counters 76
through 79 may be implemented as binary counters, with
the proviso that each counter comprises two sections
(a) and (b), respectively counting the least and most
significant bits. The input to counters 76 through 79
as well as the most significant bits are continuously
mapped in map section 80 of memory 48 so as to permit
the system to remember after a powerdown which were the
latest counts for each of the colour bands 21 through
24.
At powerup either the maximum count predetermined
for each colour will be set into its associated
counter, if the ribbon subsection is fresh, or the
current count reached at the last powerdown will be
set, if the subsection was already used for printing.
As one of the counters is decremented to zero,
processor 47 will notice and cause a fresh ribbon
subsection to be brought in printing position.
The human interface to the printer can vary widely
with the kind of printer used. The essential elements
of the human interface are shown in Fig. 7 and comprise
ribbon advance button 50, RESET button 67, ~EFAULT
button 69, a visual display 81 for displaying a
numerical output from microprocessor 47, this display
might, e.g. use light emitting diodes, a ~L button 82,
and a set of microswitches 83 or the like for entering
said predetermined counts for each one of the colour
bands into microprocessor 47. An alternative to those
microswitches 83 would be an appropriate setup mode
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l preprogrammed so as to write the values direct into
random access memory ~9.
The mechanisms described above can be implemented
on existing and future systems in a variety of
different ways all leading to the performance of the
method in accordance with the invention. It will be
obvious to those skilled in the art that the ribbon
subsection control described can be implemented as a
separate unit interfacing the printer at the power
supply, the print control lines and the ribbon
transport mechanism. It may also be fully integrated
into a host printer, if the printer is run from a
microprocessor. In this case, besides the addition of a
few components, the program code for the host
microprocessor will have to be modified. In printers
without a keyboard the human interface of Fig. 7 may be
used. Where there is a keyboard on the printer, the
entire human interface could be integrated into the
setup mode of the printer. The availability of a
microprocessor offers the additional advantage to
monitor and remember the quality status of all
subsections of the ribbon at the time an advance to a
fresh subsection was made so as to enable a possible
return to those subsections which still would permit
printing in a quality commensurate with the quality
then required.
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