Method and print chip for high speed single pass monochrome printing

Abstract

A method for printing an image from a printhead module having multiple horizontal nozzle columns, each nozzle column having a main column portion and a corresponding drop column portion vertically offset from the main column portion. The method includes determining a predetermined delay for the drop column portion based on the offset, the printing speed, and the printing resolution, assigning dot data for an image row to each nozzle column based on the printing speed and the printing resolution, transmitting first dot data for each main column portion and second dot data for each drop column portion to the printhead module, and firing nozzles from the main column portion and the drop column portion in a predetermined order. Each drop column portion is fired independently of, and delayed relative to, its corresponding main column portion by the predetermined delay.

Description

[Technical Field]

[0001] The present invention relates to a method for single-pass printing using multiple butting print tips and print tips designed for such printing. The invention was developed primarily to enable diverse print modes in ultra-high speed monochrome printheads with multiple nozzle rows. [Background technology]

[0002] Inkjet printers employing Memjet® technology are commercially available for many different printing formats and markets. Certain color printing technologies, such as the label printer described in U.S. Pat. No. 8,562,104 and the wide-format printer described in U.S. Pat. No. 8,480,221, employ color printheads configured to print CMYK inks from a single printhead. These color printheads have multiple print chips mounted on a manifold that distributes multiple ink colors to each print chip, as described in U.S. Pat. No. 7,475,976. More recently, monochrome printheads have been developed using Memjet® technology, particularly to meet the demands of high-speed digital printing machines, such as those described in U.S. Pat. No. 10,081,204, in which multiple monochrome printheads are aligned along a media feed path. These monochrome printheads have multiple print chips mounted on a manifold that supplies each print chip with a single ink color, as described in U.S. Pat. No. 9,950,527.

[0003] Both the color and monochrome printheads described above extensively employ Memjet® print chips 1 (FIG. 1), which are specially designed to allow multiple print chips to be tweezed together in a line along the printhead. Each nozzle column 3 of the Memjet® print chip 1 shown in FIG. 1 has its own drop column portion 7 at one end of the print chip, which is vertically offset from a corresponding main column portion 5 that contains most of the nozzles in that nozzle column. Typically, the vertically offset drop column portions 7 are arranged in a trapezoidal or approximately triangular shape (known in the art as a “drop nozzle area,” “displacement nozzle area,” or “drop triangle area”) and allow the print chips to be tweezed together while effectively maintaining a constant dot pitch throughout the combined area. FIG. 3 schematically illustrates an A4 page-width printhead 9 composed of eleven tweezed Memjet print chips 1 mounted on a substrate 10. Similarly, an A3 printhead can be constructed using 16 tweezed print chips.

[0004] The nozzles in a given drop nozzle section 7 of a nozzle column 3 are configured to fire at the same locations as the nozzles in the corresponding main column section 5 of that nozzle column. Because there is a fixed vertical spacing along the media feed direction between the nozzles in the drop nozzle region 11 and the nozzles in the main nozzle region 13, data sent to the nozzles in the drop nozzle region is delayed by a predetermined number of lines so that droplets fired from the nozzles in the drop nozzle region can seamlessly merge with droplets fired from the main nozzle region to form a single print line. Typically, for 1600 x 1600 dpi (i.e., 1 DP = 1 / 1600 inch) at maximum dot-on-dot printing speed (nominal 12 inches per second), there is a fixed spacing of 10 dot pitches ("DP") in the media feed direction between each drop nozzle section and its corresponding main nozzle section. Therefore, by delaying the data sent to each drop nozzle section by 10 print lines, seamless printing across merged regions can be achieved when printing at 1600 dpi in the media feed direction. A more detailed description of the Memjet® print chip with drop nozzle array can be found in US Pat. No. 7,290,852, the contents of which are incorporated herein by reference.

[0005] In principle, employing all nozzle rows of a single print chip to print one ink color should enable printing at higher print speeds for monochrome printing. However, problems arise with the drop nozzle compensation method described above when printing at a different print resolution and / or higher print speeds. First, the maximum firing frequency of each nozzle is fixed due to the time it takes for each firing chamber to refill with ink after droplet ejection. As a result, the duration of one firing cycle (i.e., the time allotted for all nozzles in a print chip to fire) is necessarily limited by the maximum firing frequency. Therefore, to print at higher speeds, inkjet nozzles cannot simply be fired more frequently—they are typically already operating at (or close to) their maximum firing frequency. Typically, the maximum firing frequency of Memjet® inkjet nozzles is approximately 15 kHz.

[0006] Second, for Memjet® printheads, the physical spacing between the drop nozzle area and the main nozzle area is nominally 10 / 1600 of an inch. th While remaining fixed at inch, when printing at lower print resolutions and / or higher speeds the printed dot pitch needs to be changed.

[0007] For example, if you want to print at 5 times the speed (nominally 60 inches per second) with a vertical print resolution of 1600 dpi, each nozzle column in the drop nozzle area should be 10 print lines (10 / 1600) less than its corresponding main nozzle column. thThe nozzles in the drop nozzle region 11 are offset by 1 / 1600 (inch ÷ 1 / 1600 = 10). Since 10 rows correspond to two firing cycles at 5x printing speed, the nozzles in the drop nozzle region 11 can seamlessly print dots that join rows of dots printed by the nozzles in the main nozzle region 13. The nozzles in each main column portion 5 and the corresponding drop column portion 7 of the same nozzle column 3 always fire simultaneously (or, more precisely, within the same column time), but the drop column portion is loaded with dot data from two rows after the main column portion is loaded with dot data. Similarly, for an 800 dpi vertical printing resolution, the drop nozzle region is offset by 5 print rows (10 / 1600 = 10), which corresponds to one firing cycle at 5x printing speed. th The nozzles in the drop nozzle region 11 can be seamlessly combined with the nozzles in the main nozzle region 13 because they are offset by 1 / 800 inch ÷ 5.

[0008] On the other hand, if you want to print at 5x speed when the vertical print resolution is 400 dpi, complete compensation by the nozzles in the drop nozzle area 11 is not possible. Here, the drop column portions 7 are separated from their corresponding main column portions 5 by 2.5 print lines (10 / 1600). th The drop column segments are offset by 7.5 print lines (10 / 1600 inch) from their corresponding main column segments. th Since the offset is 1 / 1200 (inch ÷ 1 / 1200 = 7.5), the same error occurs as when printing at 5x speed when the vertical print resolution is 1200 dpi.

[0009] Figure 4 shows the variation in error with a constant offset of the drop nozzle area relative to the main nozzle area for various print resolutions at 5x speed (monochrome) using the method described above. As explained above, the minimum error was achieved at 1600 dpi and 800 dpi resolutions, while the maximum error occurred when printing at 1200 dpi and 400 dpi. Since one dot pitch is nominally considered an acceptable amount of error, Figure 4 shows that there are many print modes in which acceptable print quality cannot be achieved. In practice, tolerance for certain artifacts may vary for different types of image content, such as contone images, line art, text, etc.

[0010] From the above, it can be seen that a relatively limited number of print modes are achievable when printing monochrome at high speeds using the drop nozzle compensation method described in U.S. Patent No. 7,290,852. Despite this limitation, the basic design of the print chips described in U.S. Patent No. 7,290,852, incorporating drop nozzle areas, remains a very attractive means for designing pagewidth printheads for high-speed printing. The drop nozzle areas allow the print chips to be tweezed together in a single row, thereby narrowing the print zone and avoiding positioning the chips in a relatively wide staggered array. A narrow print zone has the advantage of reducing demands on the media advance mechanism and generally achieving higher print quality than other pagewidth systems with relatively wider print zones.

[0011] It would therefore be desirable to provide a means by which print chips incorporating drop nozzle arrays can be used for high speed monochrome printing in a wider range of print modes. Summary of the Invention

[0012] In a first aspect, there is provided a method of printing an image from a printhead module having a plurality of horizontal nozzle columns, each nozzle column having a main column portion and a corresponding drop column portion vertically offset from the main column portion, the method comprising: identifying a printing speed; identifying a print resolution; determining a default delay for the drop train portion based on the offset, print speed and print resolution; storing a predetermined delay in a register of the printhead module; assigning dot data for an image row to each nozzle row based on a printing speed and a printing resolution, wherein each main row portion and its corresponding drop row portion are assigned dot data for the same image row; transmitting dot data to a printhead module, the dot data including first dot data for each main row portion and second dot data for each drop row portion; firing nozzles from the main row portion in a predetermined order based on printing speed and printing resolution; firing the nozzles from the drop train portions in the predetermined order, wherein each drop train portion is fired independently of its corresponding main train portion and is delayed relative to its corresponding main train portion by a predetermined delay stored in a register, such that the predetermined delay aligns drops fired from each drop train portion with drops fired from its corresponding main train portion.

[0013] Preferably, the first dot data is transferred to a first data latch corresponding to the main column portion, and the second dot data is buffered in a dedicated buffer of the printhead module.

[0014] Preferably, the buffered second dot data is transferred to a second data latch corresponding to the drop column portion based on a predetermined delay.

[0015] Preferably, the first data latch is positioned in a row along one side of the main column portion, and the second data latch is positioned in a row along the opposite side of the drop column portion.

[0016] Preferably, the default delay stored in the register is updated for different print jobs.

[0017] Preferably, the drop train portions have different lengths.

[0018] Preferably, the drop train portions are arranged together in a trapezoidal or triangular configuration.

[0019] Preferably, the printhead module comprises multiple ink planes, each containing one or more rows of nozzles supplied with the same ink.

[0020] Preferably, the printhead module includes multiple redundant ink planes.

[0021] Preferably, the printhead module is a monochrome printhead module in which all nozzle columns are supplied with the same ink.

[0022] Preferably, the dot data is sent to the printhead module row by row, and the same amount of dot data is sent for each nozzle row.

[0023] Preferably, the dot data contains a "1" for enabled firing nozzles and a "0" for non-enabled non-firing nozzles.

[0024] In a second aspect, a print chip is provided, the print chip comprising: an elongated silicon substrate defining leading and trailing longitudinal sides of the print chip; one or more circuit layers positioned on a silicon substrate; a MEMS layer positioned on the circuit layer, the MEMS layer comprising a plurality of parallel nozzle rows, each nozzle row comprising a plurality of inkjet nozzle devices arranged in a main row portion and a drop row portion offset from the main row portion; the circuit layer including data latches configured to provide dot data to the inkjet nozzle devices; a first column of data latches positioned adjacent to the leading column of the main column portion; The second column of data latches is positioned adjacent to the subsequent column in the drop column portion.

[0025] Preferably, a first set of conductive traces extends from the first column of data latches toward the main column portion, and a second set of conductive traces extends from the second column of data latches toward the drop column portion in an opposite direction to the first set of conductive traces.

[0026] Preferably, the drop column portions are arranged together in a trapezoidal shape.

[0027] Preferably, the trapezoidal shape has a leading nozzle row and a parallel trailing nozzle row, the trailing nozzle row being relatively longer than the leading nozzle row.

[0028] Preferably, the first and second sets of conductive traces are parallel to one another.

[0029] Preferably, in use, the leading side of the print tip is upstream relative to the media feed direction.

[0030] Preferably, in use, the trailing side of the print tip is downstream relative to the media feed direction.

[0031] Preferably, the circuit layer further comprises a command unit for receiving a row of dot data for the print chip.

[0032] Preferably, the command unit is positioned adjacent to the trailing nozzle of the main row portion.

[0033] Preferably, the command unit is configured to divide each row of the dot data into first dot data and second data.

[0034] Preferably, the circuit layer further includes a buffer, and the command unit is configured to route the first dot data directly to the first column of data latches and route the second dot data to the second column of data latches via the buffer.

[0035] Preferably, the buffer is configured to buffer the second dot data for a predetermined delay period before the dot data is sent to the second row of data latches.

[0036] Preferably, the command unit comprises a configurable register for storing the value of the predefined delay period.

[0037] Preferably, the buffer has a data capacity corresponding to the number of nozzles in the drop nozzle portion.

[0038] Preferably, the print chip further comprises an array of electrical pads positioned along one side of the print chip, the command unit being configured to receive the array of dot data via the electrical pads.

[0039] Preferably, the electrical pads are positioned along the trailing side of the substrate.

[0040] Preferably, each row of nozzles in the drop row portion is configured to fire its inkjet nozzles independently of the corresponding row of nozzles in the main row portion.

[0041] In a third aspect, there is provided a method of printing an image from a printhead module having a plurality of horizontal ink planes M supplied with the same ink, each ink plane having at least one row of nozzles, the rows of nozzles of all ink planes having vertically aligned nozzles, the method comprising: defining consecutive span groups along each nozzle row, each span group including N nozzles; assigning dot data for each image row of the image to a predetermined number of nozzles P in each span group of each nozzle column; sending dot data to the printhead module and firing nozzles from each of the M ink planes sequentially based on the dot data to print an image row of the image such that all ink planes contribute dots to the printed image row; Only one nozzle from each span group of the same nozzle row is fired at a time, N is an integer multiple of M, P is N divided by M.

[0042] Preferably, each ink plane has a pair of nozzle rows.

[0043] Preferably, a pair of nozzle rows are offset to print even and odd dots.

[0044] Preferably, the method is repeated to print all image lines of the image.

[0045] Preferably, the span groups of different nozzle rows have different firing nozzles.

[0046] Preferably, firing nozzles within a span group of consecutively fired nozzle columns are shifted horizontally by S nozzles, where S is preferably one.

[0047] Preferably, 1 / M of the image rows th is printable for each ink plane.

[0048] Preferably, the dot data contains a "1" for enabled firing nozzles and a "0" for non-enabled non-firing nozzles.

[0049] Preferably, based on the dot data, all aligned nozzle columns in the M ink planes are fired within one column time, where one column time is less than or equal to the period for firing all nozzles in a printhead module divided by the number of nozzle columns.

[0050] Preferably, one or more steps of the method are repeated to print all image rows of the image.

[0051] Preferably, dot data is assigned to a given nozzle column based on print speed and print medium position during successive firings of nozzles from each of the M ink planes.

[0052] Preferably, corresponding span groups of different nozzle columns are vertically aligned.

[0053] As used herein, the term "ink" refers to any jettable fluid and may include, for example, traditional CMYK inks (e.g., pigment-based and dye-based inks), infrared inks, UV-curable inks, fixatives, primers, binders, 3D printing fluids, polymers, sensing inks, biological fluids, etc. [Brief explanation of the drawings]

[0054] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0055] [Figure 1] FIG. 1 is a diagram illustrating a print chip having a drop nozzle area. [Figure 2] FIG. 2 is an enlarged view of the drop nozzle area. [Figure 3] FIG. 3 is a schematic diagram of a printhead having multiple tweezers and matching print tips. [Figure 4] FIG. 4 illustrates dot placement errors due to drop nozzle area artifacts in various print modes. [Figure 5]FIG. 5 is a diagram showing the logical distribution of dot data on a print chip. [Figure 6] FIG. 6 is a diagram illustrating the physical layout of selected features of a print chip. [Figure 7] 7A and 7B are simulated test prints using the printing methods described herein. DETAILED DESCRIPTION OF THE INVENTION

[0056] 1, the printing method described herein employs printhead modules, typically in the form of print chips, as described, for example, in U.S. Patent No. 7,290,852. Each print chip thus includes horizontal rows of nozzles extending parallel to the longitudinal axis of the print chip. Each nozzle row has a main row portion and a corresponding displaced ("drop") row portion vertically offset from the main row portion.

[0057] For convenience, a print tip is defined as having a nominal horizontal axis extending parallel to its length dimension and a nominal vertical axis extending perpendicular to the horizontal axis. As used herein, the terms "horizontal" and "vertical" are not intended to limit the orientation of the print tip or nozzle array during use. Furthermore, the term "drop" (e.g., "drop array portion," "drop nozzle area," etc.) is not intended to limit the orientation of the print tip relative to the media feed direction, and a "drop" array portion means that the array portion is displaced either upstream or downstream relative to the media feed direction of the corresponding main array portion.

[0058] The nozzles in the main row section extend along most of the length of the print chip, while the nozzles in the drop row section are positioned at one end of the print chip. The total number of nozzles in each main row section and corresponding drop row section is the same for all nozzle rows (e.g., 640 nozzles per row). However, the drop row sections each have different lengths and are arranged together in a generally trapezoidal shape in plan view, as shown in Figures 1 and 2. Collectively, multiple trapezoidally shaped drop row sections are referred to as the "drop nozzle region" of the print chip.

[0059] The print chip shown in Figures 1 and 2 includes five ink planes, all supplied with the same color ink for monochrome printing. Each ink plane includes two nozzle columns ("odd" and "even") offset horizontally by one dot pitch. Nozzles within the same nozzle column are spaced two dot pitches apart, so that odd and even nozzle columns within an ink plane can print odd and even dots in a single line of print. In the illustrated embodiment, odd and even nozzle columns within the same ink plane are vertically offset from each other by four dot pitches, while each drop column portion is offset by ten dot pitches (nominally at 1600 dpi) from its corresponding main column portion.

[0060] One embodiment is described herein with reference to a Memjet print chip that nominally prints at 1600 (horizontal) by 1600 (vertical) dpi, although it should of course be understood that the invention is not limited by print resolution or print speed.

[0061] As best shown in FIG. 2, each drop column segment is positioned to horizontally align with its corresponding main column segment so that a constant dot pitch is effectively maintained along the print chip and between adjacent print chips. In this way, the drop column segments can, in principle, compensate for printing at the junction area between adjacent print chips where nozzles are not manufacturable due to a lack of available silicon at the print chip edge. Nevertheless, due to the issues discussed above, the print chip described in U.S. Pat. No. 7,290,852 is not ideally suited for high-speed printing (e.g., nominally 5x print speed) in monochrome at all print resolutions. For example, as discussed above and referring to FIG. 4, when printing monochrome at 1200 dpi and 5x print speed, a 2.5 DP error occurs between the main nozzle area and the drop nozzle area. This error produces noticeable artifacts on the printed page.

[0062] Independent firing of drop nozzle areas Typically, an inkjet printhead receives its dot data and fires its nozzles column by column to eject droplets. A given nozzle device in a column fires when both the column enable signal and the column enable signal are set to 1 upon receiving a fire signal. In one firing cycle of the print chip, all nozzle columns receive a fire signal within the firing cycle time, resulting in firing of all enabled nozzle devices on the print chip. For a given number of nozzle columns, the firing cycle time is limited by the maximum firing frequency of each nozzle device—a physical limitation imposed by the maximum refill rate of each nozzle device.

[0063] Within each firing cycle, each nozzle column has an assigned column cycle time, which is the firing cycle time divided by the number of nozzle columns. In the case of dot-on-dot printing (e.g., CMYKK printing), the firing cycle must be measured in terms of one row time - i.e., the time it takes the media to advance one row or one vertical dot pitch (nominally 1600 dpi for the Memjet® print chip). The Memjet® print chip has five ink planes and ten nozzle columns (one pair of even and odd nozzle columns per ink plane). Each nozzle column has 1 / 10 of the row time. th is assigned to fire its nozzles at a default print speed (nominal 12 inches per second). When printing in monochrome at 5x print speed (nominal 60 inches per second), the media must advance 5 rows (or 5 vertical dot pitches) during one firing cycle. In other words, only two rows of nozzles can print in the time it takes the media to advance one dot pitch at a nominal 1600 dpi. This causes drop placement errors in certain print modes, such as 400 dpi and 1200 dpi printing at 5x print speed.

[0064] To address this issue when printing monochrome at five times the print speed, print chips according to the present invention are configured to fire nozzles in the drop nozzle region independently of the nozzles in the main nozzle region. Decoupling the firing of the nozzle row in the drop nozzle region from the firing of the corresponding nozzle row in the main nozzle region allows drops fired from the drop nozzle region to be perfectly aligned with drops fired from the main nozzle region, regardless of print speed and print resolution.

[0065] Previously, print chips known in the prior art fired nozzles by columns, such that all enabled nozzles in the same column fired within the allotted column time. (In practice, due to power constraints, all enabled nozzles in the same column do not fire simultaneously within the allotted column time. As described in U.S. Pat. No. 7,780,256, the contents of which are incorporated herein by reference, enabled nozzles are fired in span groups separated by a predetermined "span," and firing is ordered according to a predetermined "shift" within each span group.)

[0066] Therefore, independent firing of nozzles from the "same" nozzle row presents challenges from both an implementation and chip design perspective. Simply put, a print chip can be treated as having 20 nozzle rows—10 in the main nozzle region and 10 in the drop row region. Dot data and firing signals can then be sent to the print chip sequentially in 20 separate data pulses. However, this type of implementation is problematic because the data pulses contain unequal amounts of data. Those data pulses corresponding to the main nozzle region contain much more data than those corresponding to the drop nozzle region. And even within the drop nozzle region and the main nozzle region, each nozzle row has a different number of nozzles, requiring different amounts of data. However, data transfer should ideally be as smooth as possible, with the same data assigned to each data pulse.

[0067] 5 and 6, a print chip 20 according to one embodiment of the present invention is designed to receive dot data and fire signals column by column for each of the ten nozzle columns—i.e., each data pulse for each nozzle column includes dot data for the main nozzle region and the drop nozzle region, such that the data pulses contain the same amount of data (e.g., 640 bits corresponding to the 640 nozzles in each nozzle column). However, the second dot data associated with the drop nozzle region 11 is routed separately from the first dot data associated with the main nozzle region 13 by the chip's command unit 22. The command unit 22 sends the first dot data associated with the main nozzle region 13 directly to the corresponding first data latch 24, while the second dot data associated with the drop nozzle region 11 is routed to a dedicated buffer 26. The buffer 26 has a data capacity corresponding to the number of nozzles in the drop nozzle region 11.

[0068] Only after a predetermined delay obtained from a dedicated delay register in the command unit 22 is the second dot data stored in the buffer 26 transferred to the second data latch 28 corresponding to the drop nozzle region 11. The value of the predetermined delay stored in the delay register is configurable based on the print job and can be set by an upstream print controller (not shown) at the start of each print job based on the print speed and print resolution. In this way, dot data for the same line of printing can be transferred to the print chip 20 simultaneously with one data pulse, while the ejection of droplets at the drop nozzle region 11 is delayed relative to the ejection of droplets at the main nozzle region 13. Because the delay is determined by the print speed and print resolution, unlike the print chip 1 described in U.S. Pat. No. 7,290,852, the nozzle row 3 of the drop nozzle region 11 may be fired at a different time than the nozzle row of the main nozzle region 13 and not necessarily simultaneously with any other nozzle row of the main nozzle region.

[0069] The order in which the nozzle columns 3 are fired is determined based on optimum dot placement and minimum error for a given printing resolution and printing speed. The column firing order is determined by a print controller in communication with the print chip 20.

[0070] 6, the print chip 20 has a physical layout and architecture configured to efficiently use the available space on the chip. The first and second data latches 24, 28 corresponding to the main nozzle region 13 and the drop nozzle region 11 are positioned on opposite sides of their respective nozzle arrays. Data and power are received via a row of bond pads 30 positioned along one longitudinal side of the print chip 20 opposite the first data latch 24.

[0071] The second data latch 28, which receives the second dot data via the buffer 26, is positioned along the trailing row of the drop nozzle region 11—i.e., along the long side of the trapezoidal drop nozzle region. The first data latch 24, which receives the first dot data directly from the command unit 22, is positioned along the leading row of the main nozzle region 13. By positioning the second data latch 28 opposite the first data latch 24, the conductive traces can extend from the second data latch 28 across the print chip 20 toward the nozzle devices, rather than fanning outward from a single point. This arrangement therefore avoids highly concentrated current in one area of ​​the chip.

[0072] Figures 7A and 7B are simulated test prints showing the effect of independent firing of drop nozzle regions when printing at 400 dpi at a nominal 5x print speed. In Figure 7A, using the method described in U.S. Patent No. 7,290,852, the merged region between two adjacent print tips is visible as a hump due to imperfect dot placement in the drop nozzle region. However, as shown in Figure 7B, with independent firing of the drop nozzle regions, the merged region is not visible in the same print mode.

[0073] Sub-row firing Ideally, all nozzles in the main column portion of a given nozzle row should fire simultaneously; the same is true for nozzles in the drop column portion. Simultaneous firing of nozzles ensures that all drops corresponding to the same image row land simultaneously on the passing medium. In practice, however, as explained in U.S. Pat. No. 7,780,256, inherent power constraints on print chips make it impossible to fire all enabled nozzles simultaneously.

[0074] Thus, nozzles are logically grouped into consecutive span groups, with the number of nozzles in each span group defining a "span." Only one nozzle from each span group can fire at a time, and once that nozzle is fired, the next nozzle from each span group is then selected for firing. For example, if the span is 20, a print chip with 640 nozzles in each nozzle column would contain 32 consecutive span groups (each containing 20 nozzles), with every 20th nozzle being capable of firing simultaneously. Thus, in this example, each nozzle column would have 20 firing cycles within its allotted column time.

[0075] The distance from the earlier fired nozzle to the later fired nozzle in the same span group is defined as the "shift." Thus, a shift of 1 means that adjacent nozzles in each span group are fired. U.S. Patent No. 7,780,256 describes criteria for setting the span and shift for optimal ink refill and for minimizing aerodynamic interference of fluid crosstalk between ejected drops.

[0076] From the above, it is clear that the print media is constantly moving during single-pass printing, and therefore the effects of span and shift inevitably produce printing artifacts. For example, if the shift is 1, each line of print is effectively printed as a sawtooth. When printing at normal speed, the effects of span and shift are barely noticeable because the media is effectively stationary on the timescale of each row firing cycle, even though it is continuously moving. However, when printing at very high speeds, the media movement within one row firing cycle increases, and printing artifacts resulting from span and shift become more noticeable. For example, when printing at 10x speed using two aligned monochrome printheads, the media moves 2 DP within one row firing cycle. Therefore, the "height" of each sawtooth is 2 DP, which may be unacceptable for some printing applications.

[0077] In sub-column firing, nozzles from each ink plane share the printing of drops for each image row. Thus, if a monochrome Memjet® print chip has five ink planes (corresponding to 10 even / odd nozzle columns), columns 0, 2, 4, 6, and 8 can each fire 20% of the even drops, while columns 1, 3, 5, 7, and 9 can each fire 20% of the odd drops for a given image row. In contrast to traditional column-by-column firing, in which all enabled nozzles in the same nozzle column fire within one column time, in sub-column firing, all aligned nozzle columns on the print chip (e.g., all even nozzle columns or all odd nozzle columns) fire their enabled nozzles within one column time based on latched dot data. The column time is less than or equal to the time allotted to firing all nozzles in the print chip divided by the number of nozzle columns.

[0078] Advantageously, sub-column firing facilitates mapping of data for a given print row to whichever nozzle column is optimally positioned for horizontal alignment of the printed row of dots. Thus, instead of an error of 2 DP over one column firing cycle in the above example, by properly mapping the dot data across the five available nozzle columns in each column firing cycle, the error can be reduced to less than 1 DP. In effect, sub-column firing allows for a five-fold reduction in the height of the sawtooth artifact described above.

[0079] To enable sub-row firing, the number of nozzles in each span, N, must be an integer multiple of the number of ink planes, M. For example, if a Memjet print chip has five ink planes, the spans must be 5, 10, 15, 20, etc. As a result, the default number of nozzles per individual span used for firing, P, is N divided by M.

[0080] In one preferred sub-column firing scheme, the span is 5, the shift is 1, and different ink planes are printed sequentially from nozzles shifted along each span (e.g., column 0 is printed with the 0th nozzle from each span in the first 20% of the column time, column 2 is printed with the 1st nozzle from each span in the second 20% of the column time, column 4 is printed with the 2nd nozzle from each span in the third 20% of the column time, column 6 is printed with the 3rd nozzle from each span in the fourth 20% of the column time, and column 8 is printed with the 4th nozzle from each span in the last 20% of the column time). Advantageously, sub-column firing, when combined with appropriate mapping of row data to each nozzle column, reduces the effects of span and shift artifacts at very high printing speeds. An additional benefit is that because the shifted nozzles are not in the same nozzle column, problems associated with fluid crosstalk or ink refills do not occur when the shift value is 1.

[0081] It will, of course, be understood that the invention has been described by way of example only and modifications of detail may be made within the scope of the invention as defined in the appended claims.

Claims

1. 1. A method of printing an image from a print tip having a plurality of horizontal nozzle rows extending parallel to a longitudinal axis of the print tip, each nozzle row having a main row portion and a corresponding drop row portion vertically offset from and not overlapping the main row portion, the method comprising: determining a print speed and a print resolution of the image to be printed, the print speed and the print resolution being variable for different print jobs; determining a delay for the drop train portion based on the offset, the printing speed, and the printing resolution; storing the delay in a register of the print chip, the value of the delay stored in the register being configurable based on the print job; assigning dot data for an image row to each nozzle row based on the printing speed and the printing resolution, wherein each main row portion and its corresponding drop row portion are assigned dot data for the same image row; transmitting the dot data to the print chip, the dot data including first dot data for each main row portion and second dot data for each drop row portion; firing the main row portion of each nozzle row in a predetermined row-by-row order based on the printing speed and the printing resolution; firing the drop column portions of each nozzle column in the predetermined column-by-column order; each drop train portion is fired independently of its corresponding main train portion and delayed relative to its corresponding main train portion by the delay stored in the register, such that the delay aligns drops fired from each drop train portion with drops fired from its corresponding main train portion; The delay stored in the register is updated for different print jobs; the drop column portion of each nozzle column is horizontally positioned relative to its corresponding main column portion to maintain a constant horizontal dot pitch along the nozzle column; The method wherein the print chip is a monochrome print chip in which all nozzle rows are supplied with the same ink.

2. The first dot data is directly routed to a first data latch corresponding to the main column portion, and the second dot data is buffered in a dedicated buffer of the print chip; 2. The method of claim 1, wherein the buffered second dot data is transferred to a second data latch corresponding to the drop column portion based on the delay.

3. 3. The method of claim 2, wherein said first data latches are positioned in-line along one side of said main column portion, and said second data latches are positioned in-line along an opposite side of said drop column portion.

4. The method described in claim 1, wherein each drop column portion has a different length from the others.

5. The method of claim 4 , wherein the drop train portions are arranged together in a trapezoidal or triangular shape.

6. 2. The method of claim 1, wherein the dot data is sent to the print chip by row, and the same amount of dot data is sent for each nozzle row.

7. A print chip configured to carry out the method of any one of claims 1 to 6, said print chip comprising: an elongated silicon substrate defining leading and trailing longitudinal sides of the print chip; one or more circuit layers positioned on the silicon substrate; a MEMS layer positioned on said circuit layer, said MEMS layer comprising a plurality of parallel nozzle rows extending parallel to a longitudinal axis of said print chip, each nozzle row comprising a plurality of inkjet nozzle devices arranged in a main row portion and a drop row portion offset from said main row portion and not overlapping said main row portion; the circuit layer comprises a command unit for receiving a row of dot data for the print chip; a buffer for delaying nozzle firing of the drop column portion; a first row of data latches adjacent to and extending parallel to the leading main column portion on the leading side of the print chip; and a second row of data latches adjacent to and extending parallel to the trailing drop column portion on the opposite trailing side of the print chip; the command unit is configured to route first dot data directly to the first column of the data latches and route second dot data to the second column of the data latches via the buffer; In use, the leading side of the print tip is upstream relative to a media feed direction and the trailing side of the print tip is downstream relative to the media feed direction; the drop column portion of each nozzle column is horizontally positioned relative to its corresponding main column portion to maintain a constant horizontal dot pitch along the nozzle column; The print chip is a monochrome print chip in which the same ink is supplied to all nozzle rows.

8. a first set of conductive traces extending from a first column of the data latches toward the main column portion; and 8. The print chip of claim 7, wherein a second set of conductive traces extends from the second column of data latches toward the drop column portion in an opposite direction from the first set of conductive traces.

9. 9. The print chip of claim 8, wherein the drop column portions are arranged together in a trapezoidal shape, the trapezoid having a leading nozzle column and a parallel trailing nozzle column, the trailing nozzle column being relatively longer than the leading nozzle column.

10. The print chip of claim 9 , wherein the first and second sets of conductive traces are parallel to one another.

11. The print chip of claim 7 , wherein the command unit is positioned adjacent a trailing nozzle of the main row portion.

12. The print chip of claim 7 , wherein the command unit comprises a configurable register for storing a value for the delay period.

13. 8. The print chip of claim 7, further comprising an array of electrical pads positioned along the trailing side of the print chip, the command unit configured to receive the array of dot data via the electrical pads.

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