Inkjet printers are printers that traditionally sweep a carriage back and forth across the media as printheads mounted M the carriage deposited printing fluids onto the media. The media is advanced after each swath of the image is printed onto the media. After all the swaths are printed the media is ejected from the printer. Printing fluid is any fluid deposited onto media to create an image, for example a pre-conditioner, gloss, a curing agent, colored inks, grey ink, black ink, metallic ink and the like.
Newer inkjet printers have a page wide array (PWA) of printheads that stretch across the full width of the media. The media is moved underneath the stationary printheads while the printheads deposit printing fluids across the full width of the media.
A page wide array (PWA) of printheads use multiple printheads in an staggered line of overlapping printheads that stretch across the width of the media.
Each printhead 104 may have one or more rows of nozzles for each color.
In a staggered line of overlapping printheads, for example a PWA, each printhead overlaps adjacent printheads by a number of nozzles.
When printing an image, the nozzles in the overlap region are used in three different ways. A first set of nozzles on each row are fired at 100% utilization. A second set of nozzles on each row are fired at less than 100% utilization. And a third set of nozzles are not fired (i.e. 0% utilization). In this example, for row A, the nozzles in region 322 are fired at 100% utilization, nozzles 318A and 320A are fired at 50% utilization and the nozzles in region 324 are not used. For row B, the nozzles in region 324 are fired at 100% utilization, nozzles 318B and 320B are fired at 50% utilization and the nozzles in region 322 are not used. The nozzles in each row that are not in the overlap region are fired at 100% utilization. This would include all the nozzles in row A to the left of the overlap region and all the nozzles in row B to the right of the overlap region.
In this example there are two blending nozzles on each row. In other examples there may be more or fewer blending nozzles. A blending nozzle is a nozzle that is used to blend the image between the two overlapping printheads. A blending nozzle is utilized at less than 100%. In this example, the two blending nozzles on each row, nozzles 318A and 320A on row A and nozzles 318B and 320B on row B, are fired at 50% utilization. When a drop of ink for an image needs to be deposited on the media at the location of nozzle 318A along the nozzle axis, either nozzle 318A or nozzle 318B can be used. At 50% utilization, half the time the drop is deposited by nozzle 318A and half the time the drop is deposited by nozzle 318B.
In other examples the blending nozzles on one printhead may have a different utilization than the blending nozzles on the adjacent printhead. The sum of the utilization of the blending nozzles on one printhead plus the utilization of the corresponding blending nozzles on the adjacent printhead will equal 100%. For example, the blending nozzles on one printhead may have an 80% utilization and the blending nozzles on the adjacent printhead may have a utilization of 20%. In some examples the blending nozzles in one row of one printhead may have different utilizations. For example, when there are 4 blending nozzles in each adjacent printhead, the utilization for the 4 blending nozzles in the first printhead may be 20%, 40%, 60% and 80% respectively. The utilization for the 4 corresponding blending nozzles in the adjacent printhead may be 80%, 60%, 40% and 20% respectively.
The nozzle to nozzle spacing is the same for each row of nozzles. Nozzle 340A is the last nozzle in nozzle row A utilized at 100%. Nozzle 322B is the last nozzle on nozzle row B utilized at 100%. The distance between nozzle 340A and nozzle 322B is distance D1 Distance D3 is equal to 3 times the nozzle to nozzle spacing.
Due to manufacturing tolerances, the nozzles in one printhead may not be aligned along the nozzle axis with the nozzles in the adjacent printhead.
In this example there are two blending nozzles on each row of nozzles. In other examples there may be more or fewer blending nozzles. A blending nozzle is a nozzle that is used to blend the image between the two overlapping printheads. A blending nozzle is utilized at less than 100%. Nozzles 442B and 444B are the two blending nozzles on nozzle row B.
There are two sets of two nozzles on nozzle row A that may be used as the two blending nozzles. Nozzles 442A and 444A make up the first set of nozzles and nozzles 444A and 446A make up the second set of nozzles. When using the first set of nozzles (442A and 444A) in row A as the blending nozzles, nozzle 440A is the last nozzle in nozzle row A utilized at 100%. Nozzle 446B is the last nozzle on nozzle row B utilized at 100%. The distance between nozzle 440A and nozzle 446B is distance D3.
When using the second set of nozzles (444A and 446A) in row A as the blending nozzles, nozzle 442A is the last nozzle in nozzle row A utilized at 100%. The distance between nozzle 442A and nozzle 446B is distance D4. Distance D3 is equal to 3.5 times the nozzle to nozzle spacing. Distance D4 is smaller than distance D3 and is equal to 2.5 times the nozzle to nozzle spacing.
The distance between the last nozzle in row A utilized at 100% and the last nozzle in row B utilized at 100% when the nozzles in the two rows are aligned (see
When using the second set of nozzles in row A as the blending nozzles when the nozzles between the two rows are not aligned, the distance between the last nozzle in row A utilized at 100% and the last nozzle in row B utilized at 100% is equal to 7.5 times the nozzle to nozzle spacing. This is smaller than the nozzle to nozzle spacing when the nozzles are aligned. This creates a darker area in the image printed by the blending nozzles between the two printheads.
This defect due to misaligned nozzles along the nozzle axis between the two printheads is known as thin die to die boundary banding (TDBB). Depending on which set of nozzles are selected to be used as the blending nozzles, the image between the two printheads will either be too light or too dark. One way to correct this problem is to make sure the adjacent printheads are physically aligned to each other. Unfortunately, this would increase the cost of the print engine.
In one example, the printer will modulate the ink amount used by the blending nozzles. The ink modulation will be increased when using the first set of nozzles in row A (i.e. when the image printed by the blending nozzles is too light) and the ink modulation will be decreased when using the second set of nozzles on row A (i.e. when the image printed by the blending nozzles is too dark). The amount the ink modulation is scaled will be determined using a calibration routine. The calibration routine will print a target in the overlap region of each set of adjacent printheads. Light or dark streaks in the thin die to die boundary region will be located. The density difference between the light or dark streaks and the average density value of the target will be used to scale the ink modulation of the image printed with the blending nozzles.
In one example a target will be printed with different ink modulation amount used for the blending nozzles. The printed images will be scanned and light or dark streaks will be located in the overlapped region. The difference delta (Δ) between the average printed density of the targets will be compared to the density of the light or dark streaks. The ink modulation amount for the blending nozzles can be determined using A.
There is an overlap area between each adjacent set of dies where the nozzles from the first die overlap the nozzles from the adjacent die. The overlap area between die0 and die1 is area 550. The overlap area between die1 and die2 is area 552. The overlap area between die2 and die3 is area 554. In each overlap area there is a portion of the image printed by the blending nozzles in the two adjacent dies. The image printed by the blending nozzles between die0 and die1 is area 562. The image printed by the blending nozzles between die1 and die2 is area 564. The image printed by the blending nozzles between die2 and die3 is area 568.
The image printed by each die is a constant density target, in this example a mid tone grey level. In other examples other colors or densities may be used, for example a 70% magenta target. In this example the target is shown as being printed across the full width of each die/printhead. In other examples the constant density target may only be printed by a small set of the nozzles on each side of the blending nozzles, for example 40 nozzles on each side of the blending nozzles. The number of nozzles in the small set of nozzles will be selected such that an accurate value for the background level of the constant density target can be measured.
Each row (rows 1-5) in the target has a different amount of ink modulation used for the portion of the image printed with the blending nozzles between the adjacent dies/printheads. Row 1 has +20% modulation, row 2 has +10% modulation, row 3 has 0% or the default modulation, row 4 has −10% modulation and row 5 has −20% modulation. When the nozzles from two adjacent dies are aligned, the image area printed by the blending nozzles will be the same density as the constant density image in row 3. This is because the image printed by the blending nozzles in row three use the default modulation used by the rest of the nozzles in each of the dies.
In this example the nozzles in die 1 are aligned with the nozzles in die 2. As can be seen, the image area printed by the blending nozzles between dies 1 and 2 (area 564) in row 3 have the same color/density as the image areas printed adjacent to area 564 (i.e. the surrounding area). Image area 564 is a different intensity than the adjacent printed area in rows 1, 2, 4 and 5. In rows 1 and 2 with a 20% and 10% increase in ink modulation respectively, area 564 is darker than the surrounding area. In rows 4 and 5 with a 10% and 20% decrease in ink modulation respectively, area 564 is lighter than the surrounding area.
The nozzles in die 0 are miss-aligned with the nozzles in die 1. Area 562, printed by the blending nozzles of dies 0 and 1, is darker that the surrounding area in rows 1, 2 and 3. Area 562 is almost the same color/density as the surrounding area in row 4. Area 562 is lighter than the color/density as the surrounding area in row 5. By measuring the density of area 562 and the surrounding area in each row, the difference in density Δ compared to the surrounding area vs. the modulation amount can be determined. The density of the printed target can be measured using a scantier or one or more sensors in the printer. The scanner can be a standalone scanner or may be incorporated with the printer as a multi-functional peripheral (MFP).
The difference Δ vs. the modulation amount can be plotted and the intercept point where the modulation amount causes the density of area 562 to match the density of the surrounding area can be determined (see
Because all the rows of nozzles on each printhead are created on the same die, the alignment between all the rows on a first printhead will be the same for all the rows on an adjacent printed. Therefore if the target is printed using only one color of ink, for example black, the ink modulation amount calculated for the black ink nozzles between each set of adjacent printheads may be used for all the nozzles for each color for that pair of adjacent printheads. In other examples, an ink modulation amount will be determined for each color in each set of adjacent printheads.
The nozzles in dies 1 and 2 are aligned with each other (in the nozzle axis) and the plot of the line 564 intersects the horizontal axis at zero. Therefore the blending nozzles will print the same density as the nozzles on either side without any ink modulation. The nozzles between dies 0 and 1 are not aligned. The plot intersects the horizontal axis at point 376 which is about 3.3% modulation. Therefore during operation the image printed with the blending nozzles for die 0 and 1 will be modulated at 3.3% to produce the same printed image density as the nozzles on either side. The nozzles between dies 2 and 3 are not aligned. The plot intersects the horizontal axis at point 378 which is about −7.5% modulation. Therefore during operation the image printed with the blending nozzles for die 2 and 3 will be modulated at −7.5% to produce the same printed image density as the nozzles on either side.
In one example the modulation amount for each set of adjacent printheads may be entered into the printer by a user during a calibration routine. The user may use the printer's user interface, for example a touch screen, to enter the values. In another example, a scanner integrated with the printer as part of a multi-functional peripheral (MFP) may scan the target and automatically send the modulation amounts to the printer.
The slope of the plotted lines in
The print modulation is a scaling amount for the image printed with the blending nozzles. In one example the scaling can be done for all the ink channels at the same time by scaling the density of the image when the image is in LAB color space. In another example the density for each color channel is scaled separately when the image data is in contone-linear ink space. In one example an image to be printed has the following ink densities in contone-linear ink space: 50%, 50%, 10%, 0% for the cyan, yellow, magenta and black inks respectively. The nozzles on either side of the blending nozzles would print the image using these densities/ink amounts. In this example the blending nozzles are miss-aligned such that a 12% increase in ink modulation is needed to print the image with the same density as the surrounding nozzles. In this case the image data for the blending nozzles would be modified by 12% such that the blending nozzles would print using the following ink densities: 56%, 11.2% and 0%. In one example the ink modulation scaling is done in the data pipeline before the image is halftoned.
I/O module 866 is used to couple printer to other devices, for example the Internet or a computer. Printer has computer executable code, typically called firmware, stored in the memory 864. The firmware is stored as computer readable instructions in the non-transitory computer readable medium (i.e. the memory 864). The processor generally retrieves and executes the instructions stored in the non-transitory computer-readable medium to operate the printer and to execute functions. In one example, processor executes code that adjusts the ink modulation of blending nozzles in adjacent printheads, for example as shown in
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PCT/US2014/033251 | 4/8/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/156770 | 10/15/2015 | WO | A |
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20170028717 A1 | Feb 2017 | US |