JP2019006122A - Control of print head - Google Patents

Abstract

To provide a printing method that prevents a stitch line from occurring on a plurality of overlapping electrostatic inkjet print heads.SOLUTION: A plurality of overlapping print heads 300 comprise a row of discharge channels 301. Each of the discharge channels comprises an associated discharge electrode, and such a voltage that produces a concentrated part of a granular material created in a body of a printing fluid is added to this electrode. For making pixels to be printed by the overlapping discharge channels for each row of images, a value of a voltage pulse added to the overlapping printing heads is adjusted depending on positions of pixels in an overlapping area of print heads and depending on a size of a prescribed volume of a pixel.SELECTED DRAWING: Figure 4

Description

  The present invention relates to electrostatic ink jet printing technology, and more particularly to print heads and printers of the type as described in WO 93/11866 and related patent specifications.

  This type of electrostatic printer, by using an applied electric field, releases charged solid particles dispersed in a chemically inert insulating carrier fluid first to concentrate, and then the solid particles are discharged. discharge. As the applied electric field causes electrophoresis, concentration occurs and the charged particles move through the electric field toward the substrate until they meet the ink surface. Release occurs when the applied electric field creates an electrophoretic force large enough to overcome the surface tension. An electric field is created by creating a potential difference between the emission location and the substrate. This is accomplished by applying a voltage to the electrode at and / or around the emission location. A particular advantage of this type of printing technology compared to conventional drop-on-demand (DOD) printers is that they can print using gray scales that are not possible with conventional DOD printers.

  The position at which emission occurs is determined by the printhead geometry, the position and shape of the electrodes that create the electric field. Typically, a printhead consists of one or more protrusions from the printhead body, and these protrusions (also known as discharge uprights) have electrodes on their surfaces. The polarity of the bias applied to the electrode is the same as the polarity of the charged particles, so that the direction of the electrophoretic force is toward the substrate. Furthermore, the overall geometry of the printhead structure and the position of the electrodes are designed so that enrichment and then emission occur in highly localized areas around the tip of the protrusion.

  In order to operate reliably, the ink must flow continuously through the discharge location to replenish the discharged particles. In order to allow this flow, the ink must have a low viscosity, typically a few centipoise. The released material becomes even more viscous due to the concentration of the particles. As a result, this technique can be used to print on non-absorbent substrates because the material does not spread significantly when impacted.

  The art includes various printhead designs such as in WO 93/11866, WO 97/27058, WO 97/27056, WO 98/32609, WO 01/30576 and WO 03/101741. All of which are related to the so-called Tonejet® method described in WO 93/11866.

  FIG. 1 is a view of the tip region of an electrostatic printhead 1 of the type described in the prior art, showing several discharge uprights 2 each having a tip 21. Between each two emitting uprights, there is a wall 3 (also called a cheek) that defines the boundary of each emitting cell 5. In each cell, the ink flows in two paths 4, and one of the side surfaces of the discharge upright portion 2 and the ink meniscus in use are fixed between the top of the cheek and the top of the discharge upright portion. . In this geometry, the positive z-axis direction is defined as the direction from the substrate to the print head, the x-axis is the direction along the tip of the discharge upright, and the y-axis is these Is perpendicular to.

  FIG. 2 is a schematic diagram of the xz plane of one discharge cell 5 of the same print head 1, which is cut along the center of the tip of the upright portion 2 and viewed along the y-axis. . This figure shows the cheek 3 and the discharge upright portion 2, which define the position of the discharge position 6, the position of the ink path 4, the position of the discharge electrode 7, and the position of the ink meniscus 8. The solid arrow 9 indicates the discharge direction, which is also the direction toward the substrate. Each upright 2 and its associated electrode and ink path efficiently form a discharge channel. Typically, the pitch between the emission channels is 168 μm (this gives a print density of 150 dpi). In the example shown in FIG. 2, the ink normally flows in the direction away from the reader in this paper.

  FIG. 3 is a schematic view of the same print head 1 in the yz plane, showing a side view of the discharge upright along the x-axis. This figure shows the discharge upright 2, the position of the upright electrode 7 and the element known as the intermediate electrode (10). The intermediate electrode 10 has a structure having an electrode 101 on its inner surface (sometimes over the entire surface), and is biased to a potential different from that of the emission electrode 7 of the emission upright portion 2 in use. The intermediate electrodes 10 may be patterned such that each emitting upright 2 has an electrode facing the individually assignable emitting upright 2, or the entire surface of the intermediate electrode 10 has a constant bias. The metal may be uniformly treated so as to be held in The intermediate electrode 10 acts as an electrostatic shield by selecting the emission channel from an external electric field, and the electric field at the emission position 6 can be carefully controlled.

  The solid arrow 11 indicates the discharge direction, which also points in the direction of the substrate. In FIG. 3, ink normally flows from left to right.

During operation, the substrate is usually held in a grounded state (0 V), and the electrode V _IE is applied between the intermediate electrode 10 and the substrate. A further potential difference V _B is applied between the intermediate electrode 10 and the electrode 7 above the emission upright 2 and the cheek 3, so that the potential of these electrodes is V _IE + V _B. The amplitude of V _B is selected to generate an electric field at the emission location 6 that concentrates the particles but does not emit the particles. Emission occurs spontaneously when the particle's electrophoretic force is actually biased with a V _B higher than a certain threshold voltage V _S corresponding to the strength of the electric field that balances the surface tension of the ink. Therefore, in this case, V _B is always selected to be smaller than V _S. When V _B is applied, the ink meniscus moves forward to cover much of the discharge upright 2. To release the concentrated particles, the amplitude further voltage pulse V _P is applied to the release uprights 2, as a result, the potential difference between the emission uprights 2 and the intermediate electrode 10 is V B ₊ V _P. The emission will continue for the duration of the voltage pulse. Typical values for these biases are V _IE = 500 volts, V _B = 1000 V, and V _P = 300 volts.

  The electrodes actually added in use may be derived from the bit values of individual pixels of the printed bitmapped image. Using conventional design graphics software (eg Adobe Photoshop), bitmapped images are created or processed and stored in memory, from memory, many ways (parallel port, USB port, per purpose) Data can be output to the drive electronics of the printhead by the data movement hardware created, and voltage pulses applied to the discharge electrodes of the printhead are created.

  One advantage of this type of electrostatic printer is that grayscale printing can be performed by adjusting either the duration or amplitude of the voltage pulse. Voltage pulses are created such that the amplitude of individual pulses is derived from bitmap data, or the duration of pulses is derived from bitmap data, or a combination of both techniques. Also good.

  A printhead with many discharges is manufactured side by side with a number of cells 5 of the type shown in FIGS. 1 to 3 along the x-axis in order to prevent gaps in the print medium arising from the spaces between the individual printheads. It may be necessary to “overlap” the edges of adjacent printheads by staggering the printhead positions in the y-axis direction. The control computer converts the image data (bitmapped pixel values) stored in memory into a voltage waveform (typically a digital square pulse) that is individually applied to each emitter. Supply. By moving the print head in a controlled manner relative to the substrate, a large area image can be printed on the substrate in multiple “bands”. Use multiple passes of one or more printheads to build a wider image than the printhead and to "scan" or index the entire substrate with a single printhead by multiple passes It is also known to do.

  However, stitch lines often result from the use of overlapping printheads or from overlapping in multiple passes, and therefore alternate techniques (from adjacent printheads or from the same or different printheads). It is also known to use alternating one pixel or group of pixels from different paths) to disperse and hide the effects of the edges of the print strip obtained from the overlapping ends of the printhead. It is generally recognized that a stitching strategy is necessary to obtain good print quality at the connection between the printed strips. A known technique is by the use of a strategy of alternating two elements (ie, printing a given pixel by one printhead or another printhead). For example, alternating pixels along the x-axis are printed from adjacent overlapping printheads. Or from one strip to the next by gradually decreasing the number of adjacent pixels printed from one print head and increasing the number of adjacent pixels printed from another print head Blends can be used. This latter technique can be extended by dithering printing in the y-axis direction. Another known technique is to use saw-shaped leaves or sinusoidal “stitches” to disturb visible stitch lines.

  These techniques all differ in that they can print alternately between the nozzles of two overlapping printheads, the success of which is the accuracy and registration of the two printhead droplets. And is particularly sensitive to factors such as substrate swinging between printhead lines. This can be mitigated by stitch dispersion and deliberate movement, which breaks visible lines and eliminates errors beyond the width of the overlap of adjacent printed strips.

In accordance with the present invention, a two-dimensional bitmapped image having a number of pixels in a column for printing with a plurality of overlapping printheads or one or more printheads indexed to overlapping positions. A method of printing, wherein the printhead or each printhead has a row of discharge channels, each discharge channel having an associated discharge electrode, against which the printing fluid is in use. Sufficient voltage is applied to produce a concentrated portion of particulate material created in the body, and one of the many predetermined volumes ejected as print droplets from selected ejection channels of the overlapping printheads is Each predetermined vibration as determined by the bit value of each image pixel to produce a concentrated portion of charged particulate matter. And the voltage pulse duration is added to the electrode of the selected discharge channel,
For each image column, the value of the voltage pulse applied to the overlapping printheads to create the pixels printed by the overlapping emission channels depends on the position of the pixels in the overlapping area of the printhead, and A method is provided that is adjusted depending on the size of the predetermined volume of the pixel.

  This technique provides those skilled in the art with an alternative strategy of creating each printed pixel in the overlapping area of the printhead resulting from both printheads in the overlapping area. That is, the emissions from one print head and the emissions from overlapping print heads are combined to provide the required size and / or density of pixels. The relative contributions of the two printheads change so that the contribution from one printhead gradually disappears and the contribution from the other printheads gradually increases so that they overlap, along the overlapping area. . This reduces the sensitivity to dot position errors and substrate sway. This is because such an error is less likely to create a white space between dots.

  This gradual change technique overlaps so that the pulse length (or amplitude if not length) of the emitted voltage pulse is reduced and other print heads gradually increase as one print head gradually decreases. Including changing the volume of the droplets that give the pixels to be printed in the area, the sum of the prints from the two heads uniformly produces the optical density required for the entire overlap.

This technique cannot be used for other gray scale ink jet technologies, and its discharge requires a high level of variable droplet size control, so a fixed series of droplet sizes. Limited. In contrast, the Tonejet® method as described above has the feature that the discharge volume can be changed continuously and assignable by a pulse length control mechanism.
In the Tonejet® method, a continuous tone pulse value can be assigned at a given pixel level to create a desired dot diameter. Such correction is not possible with conventional drop-on-demand (DOD) printheads where the droplet solution is quantized by chamber size, nozzle size, and the like.

  Print through a single printhead, or print the required pixels from multiple (alternately arranged) printheads located close to each other, or the same printhead or different Similar challenges arise when printing pixels from multiple passes of the printhead, and the same solution can be used. The print head may be indexed multiple times.

  In order to provide the necessary “gradual change”, a gradually changing function is defined for each printhead or strip of the print to define a gradually changing profile over the overlapping area. To simplify computer calculations, it is common to limit the drop volume of a Tonejet® type printhead to many predetermined sizes. In the method of the present invention, it is advantageous to provide different drop volume functions with different drop volumes. This stems from the fact that the additional print density of the pixels printed by the two drops follows a non-linear function with respect to the drop volume.

The invention further provides an apparatus for printing a two-dimensional bitmapped image having many pixels in a column, the apparatus comprising one or more indexed to a plurality of overlapping printheads or overlapping positions. A print head, each or each print head having a row of discharge channels, each discharge channel having an associated discharge electrode, against which the body of the printing fluid is in use. Sufficient voltage is applied to produce a concentrated portion of particulate material produced therein, and one of the many predetermined volumes ejected as print droplets from a selected ejection channel of the overlapping printhead is charged to a predetermined volume. Each predetermined amplitude as determined by the bit value of each image pixel to produce a concentrated part of the granular material Voltage pulse of the preliminary duration is added to the electrode of the selected discharge channel,
For each image column, the value of the voltage pulse applied to the overlapping printheads to create the pixels printed by the overlapping emission channels depends on the position of the pixels in the overlapping area of the printhead, and A device is characterized in that it is adjusted depending on the size of the predetermined volume of the pixel.

  The plurality of overlapping print heads may be fixed at predetermined positions with respect to each other during use.

  The plurality of overlapping printheads are a first printhead that prints in a single pass through the print substrate and a same print that prints in a subsequent pass through the print substrate and overlaps with the position of the first printhead in place. A head or another print head may be included. The first printhead may be indexed to pass through the substrate at a distance equal to the width of the printhead channel row that is less than the desired overlap.

  The printhead may be one of many identical printheads arranged in modules parallel to each other and corrected by a portion of the distance between adjacent emission channels so that the printed image is Has a resolution greater than the distance between adjacent emission channels. The plurality of modules may overlap each other to allow a printing width that is greater than the width of the individual modules. Alternatively, the modules may be indexed to pass through the substrate at a distance equal to the width of the printhead channel row that is smaller than the desired overlap.

  In the case of a single printhead, the printhead may be indexed to a portion of the distance between adjacent emission channels so that the printed image has a greater resolution than the distance between adjacent emission channels. Have.

  Preferably, the value of the voltage pulse applied to the overlapping printhead is determined from a predetermined gradually changing function depending on the predetermined volume size of the pixels printed in the overlapping area of the printhead (300). May be.

  Before the pixel value is converted into a voltage pulse of each predetermined amplitude and duration and printed, the bit value of the pixel depends on the position of the pixel in the overlapping area of the printhead, and the predetermined value of the pixel It may be adjusted depending on the size of the volume.

  Alternatively, the bit value of the pixel of the image may be provided to the drive electronics of the printhead, which converts this value into a voltage pulse, before the voltage pulse value is applied to the printhead's emission electrode, May be determined depending on the position of the pixel in the overlapping region of the pixel and depending on the size of the predetermined volume of the pixel.

式中、ｆ_Ａは、プリントヘッド／帯状部分Ａの徐々に変化する関数であり、
ｆ_Ｂは、ｆ_Ａの鏡像である、プリントヘッド／帯状部分Ｂの徐々に変化する関数であり、
ｆ_ｍｉｎは、最小の印刷可能なレベルを与える、徐々に変化する関数の最小値であり、
ｘは、重なり合う領域全体で正規化された位置であり、０≦ｘ≦１であり、
αは、徐々に変化する関数の累乗である。 In a particular method, a gradually changing function of the following form can be used to define a gradually changing profile over the overlapping areas of the two printheads / bands of prints A and B:
(formula)

Where f _A is a gradually changing function of print head / band A,
f _B is a gradually changing function of the printhead / band B, which is a mirror image of f _A
f _min is the minimum of a gradually changing function that gives the minimum printable level;
x is a normalized position over the entire overlapping region, 0 ≦ x ≦ 1,
α is a power of a gradually changing function.

  In a color printer, a printhead of each color having different and gradually changing functions may be provided. Also, the overlapping positions between different color printheads may be different.

  The gradually changing function moves so that the gradually changing center point is effectively “dithered” around the overlap area, so that stitching of the print strip further reduces observable artifacts. Furthermore, it may be adjusted randomly or according to an appropriate waveform function.

A gradually changing function may be applied to one of many stages when processing image printing. For example,
In the controlling computer's raster image processing software, a modified aspect of each strip of the bitmap image may be given and then converted into print pulses by the drive head drive electronics in the normal manner .
The drive electrical section of the printhead, in this case programmed to create a modified pulse amplitude or duration in response to incoming pulse data according to the location of the overlapping area emitter. Also good.

  The gradually changing function may be applied to the pixel value data in the form of software math, or may be applied in the form of a look-up table stored in the memory of the controlling computer. Data is supplied to an electronic device or a pulse generating electronic device.

  Examples of the method and apparatus of the present invention are described below with reference to the accompanying drawings.

FIG. 1 is a CAD diagram showing details of discharge channels and ink supply paths of an electrostatic printer. FIG. 2 is a schematic view in the xz plane of an emission channel in an electrostatic printhead of the type shown in FIG. FIG. 3 is a schematic diagram in the yz plane of an emission channel in an electrostatic printhead of the type shown in FIG. FIG. 4 shows a plan view of a portion of an example of a multi-print head printer. FIG. 5 shows a plan view of a number of printhead modules mounted together. FIG. 6 shows an example of another multi-print head printer in which four modules are arranged. FIG. 7 is a block diagram of some printer elements of the example of FIGS. FIG. 8 is a flowchart illustrating a process for creating print data for individual printheads of the illustrated printer. FIG. 9 is a flow chart illustrating the process of applying each gradually changing function to print data for a printhead pair of the illustrated printer (for simplicity). FIG. 10 shows a series of pulse length curves corresponding to the last iteration of the calculated parameter. FIG. 11 shows a series of gradually changing functions plotted to show voltage pulse length multipliers for overlapping positions between adjacent printhead pairs. FIG. 12 is a block diagram showing how the amplitude of the emitted pulse can be adjusted and an associated waveform diagram showing the resulting adjusted pulse amplitude. FIG. 13 is a block diagram showing how the duration of the emitted pulse can be adjusted and an associated waveform diagram showing the resulting adjusted pulse duration. FIG. 14 is a diagram of an exemplary look-up table representing voltage pulse values that are adjusted according to a corresponding gradually changing function.

  The example shown with reference to FIGS. 4-11 can utilize a printhead and printing process as generally described with reference to FIGS.

  FIG. 4 shows a print bar or print module 300 that utilizes four printheads 300A-D, each having a plurality of printing positions (emissions) in a spatial arrangement giving 150 channels per inch (60 channels per centimeter). (Channel or channel) 301 (printing at 150 dpi), in use, to give a strip of the appropriate printed image, and in order to stitch the printing of each adjacent strip, Arrow 302), with each print head and its adjacent print heads such that many discharge channels 301 (10 in this case) overlap between print head pairs 300A / 300B, 300B / 300C and 300C / 300D. Have an overlap between.

  FIG. 5 utilizes four printheads 300A-D and channel spatial arrangement (150 dpi) of the same configuration as FIG. 4, but the printheads are substantially aligned with each other in the intended substrate movement direction. With a module 300 corrected in a direction transverse to the direction of movement of the printing substrate by the distance necessary to perform the necessary high-definition printing, in this case 600 dpi (correction is about 42 μm) A further example of a printer is shown. In this case, adjacent pixels of the printed image are printed from adjacent printheads and aligned to each other, but corrected to give the desired print band to achieve the required print density. A plurality of modules 300 placed in position produce the desired overall print width in a manner similar to the example of FIG. 4, and thus each module's modules are stitched together to stitch the strips of print together. Each print head has a similar overlap. Multiple modules 300 together provide the printer with enough width to print at 600 psi in a single pass through the substrate.

  In a variation (not shown), only one module, such as FIG. 5, can be used to produce the required number of strips to produce the required overall width of the print. The base material is indexed so as to pass a plurality of times in the direction crossing the moving direction. In this case, the overlap of adjacent indexed positions is given in the same way as the overlap between the modules of FIG. 5 to allow stitching between one strip and another strip.

  FIG. 6 shows a further embodiment having modules 300-1, 300-2, 300-3, 300-4 arranged to provide 600 psi printing from a printhead having a 150 dpi spatial arrangement. In this case, each module is substantially the same as the module of FIG. 4, but each successive module can be repositioned in the direction of movement of the print substrate of about 42 μm or corrected laterally. The In this case, each module as in FIG. 4 is arranged between four adjacent printheads 300A, 300B, etc., or a series of four alternating ones that are substantially aligned with one another in the direction 302 of substrate movement. Stitching may also be performed between printed strips printed by the print head.

  A further example of a printhead (not shown) utilizes a single printhead that is indexed to substantially one quarter of the printhead width during transit, (a) from a 150 dpi printhead to 600 psi Give print (shown), and (b) give an overall print width (number of indexing movements, and hence the number of passes determined by the desired overall print width), which is significantly larger than the width of the print head. . In this case, from each pass, 150 dpi printed strips are alternately arranged to produce a 600 dpi printed product. Overlap between 150 dpi strips occurs at the 1st, 5th, 9th, etc. pass / index, and the stitching of the strips corresponds to the 1st, 5th, 9th, etc. pass / split. Occurs between opposite sides of a feed (one) printhead. Similarly, the overlap and stitching of the 150 dpi strips will be the second, sixth, tenth, etc., third, seventh, eleventh, etc., fourth, eighth, twelfth, etc. Happens between.

  Each example uses a substrate position synchronization signal (eg, derived from a shaft encoder 216 (see FIG. 7) or a substrate position servo controller) to correct the printhead along the direction of print substrate movement. The droplets are reliably printed at the appropriate time. Such a process is well understood in the art and does not form part of the present invention. The use of shaft encoders can lead to potential problems arising from the relative speed change of the substrate relative to the printhead, a printer with multiple offset printheads, or a single printhead or printhead module (as such Overcoming the potential problems arising from printhead modification in the direction of movement of the printing substrate of the printer that passes multiple times).

  Before describing an example of the method of the present invention, there are two commonly available methods for controlling the volume of a printed (or ejected) droplet using the Tonejet® method. It would be useful to describe.

Figure 12 is usable to control the amplitude of the emission voltage pulse V _E for each discharge portion of the print head (uprights 2 and the tip 21), thereby the printed bitmap pixel value ₁ shows a block diagram of a circuit 30 that converts _Pn (having an 8-bit number, i.e. having a value between 0 and 255) into a low-amplitude voltage by a digital-to-analog converter circuit 31 whose output has a fixed duration is gated by the pulse V _G, defining the duration of the high voltage pulse V _P applied to the discharge portion of the printhead. The low voltage pulse is then amplified by the high voltage linear amplifier 32 to obtain a high voltage pulse V _P (typically amplitude 100-400V) depending on the bit value of the pixel, which is the bias voltage V _Overlapped with _B and V _IE to give the emission pulse V _E = V _IE + V _B + V _P.

Figure 13 is usable to control the duration of the emission voltage pulse V _E for each discharge portion of the printhead, thereby "print the output of the counter to the print starting pixel to be set to a high The transition of the “synchronous” signal PS loads the value P _{n of the} bitmap pixel to be printed into the counter 41, and the successive cycles of the clock input to the counter (at time T) decrement the counter until the counter reaches zero, A block diagram of an alternative circuit 40 for resetting the counter output to low is shown. Thus, the output of the counter is a logic level pulse V _PT whose duration is proportional to the pixel value (the product of the pixel value P _n and the clock period T), which is then the high voltage switching circuit 42. To switch from a low voltage (V _IE + V _B ) to a high voltage (V _IE + V _B + V _P ), so that the duration-controlled emission pulse V _E = V _IE + V _B + V _P Generate.

The P _n value of the printed bitmap pixel corresponds to a duty cycle (of the emission pulse) of 0% to 100%. Typically, when printing at a resolution of 600 psi and the relative movement between the printing substrate and the printhead is 1 ms ⁻¹ this value is 0 μm to 42 μm pulse with a 42 μm pulse repetition period. Equal to length.

  Of these alternative techniques, it is actually easier to adjust the duration of the pulse, but either technique may be appropriate in a given environment and both are used together May be.

  During operation, one embodiment of the invention uses, for example, any of a number of well-known image creation software packages (eg, Adobe Illustrator), as shown in FIGS. The color image 200 created by this is uploaded to the memory 21 of the computer 202. The initial image 200 is then converted into raster data within the computer 202 using image processing software 203 (see FIGS. 7 and 8), and then a corresponding color bitmap image 204 is created and stored in the memory 205. To do. The color profile 206 is then applied to the bitmap image and a calibration is performed to achieve the toner response of the printing process, and then each color component of the pixel is assigned one of a different “level” number (n). Each pixel is “screened” or filtered (207), and data (in this case, representing the CMYK n-level image 208) is stored in RAM 209, and the individual primary color elements are assigned to the respective pixels. Separate the data sets 212c, 212m, 212y and 212k (210).

  Given a known number of print strips or strips required to build, the grayscale data for each primary color is obtained for a data set, in this case a pair of overlapping strips. Divided into two data sets 302A, 302B, or print heads 300A / 300B (pixel count of the entire print substrate provided by one print head) representing pixel values for each stage of the individual print head width. (213). These data sets provide bitmaps corresponding to the emission channels 301 of the individual printheads 300A, 300B that are used to print the final image.

  FIG. 9 illustrates a “stitching” process of one color separation print strip made by adjacent print heads 300A and 300B, specifically for each appropriate gradually varying function for pixel values. Indicates the application of. The desired gradually changing function is stored in a corresponding lookup table 214 held in memory 215. Each level of each color pixel value typically has a separate and gradually changing function held in a lookup table 214. The individual gradually changing functions are then applied to the individual according to the color and level for creating the pulse length value (or pulse amplitude value or both) for creating the respective printhead pulse data sets 304A, 304B. 300A and 300B are applied to 303A / 303B for each pixel in the bitmap data set.

  Then, in step 305A / 305B, pulse data 304A, 304B is transferred to drive cards (pulse generating electronics) 306A, 306B according to the relative position of the print substrate and print head (as determined by shaft encoder 216). And using this data, if desired, determining the length of the drive pulse applied to the individual printhead emission channel 301 and applying a voltage pulse of a predetermined duration and / or amplitude to the pulse of each pixel. Create according to the data. This data is moved in a time-dependent manner relative to the correction of the ejection channel 301 of one printhead 300A from the correction of the ejection channel of the substrate position, the adjacent overlapping printhead 300B.

  The process of creating and applying a gradually changing function to print a cylindrical substrate using two overlapping heads extending across the width of the substrate, two 150 ”per overlapping inch printhead. An example is described in which four passes through the channel are used and the substrate is rotated four times to achieve full coverage at 600 dpi. The described gradual change technique can be applied directly to the overlapping portions of multiple or single printheads that are passed one or more times over the substrate.

  In the embodiment described, an overlap of 10 printhead channels (40 pixels) is used. However, the width of the overlapping region affects the visibility of the connection, and generally, the larger the overlap, the more error can be eliminated and the joint becomes invisible. This must be balanced with the desire to have the smallest overlap to maximize print width.

Prepare a series of test images with a single printhead to create the required gradual function and select the gradual function to experimentally determine the most effective And printed it. The images used were benchmark test images that included the full range of print levels. The image was screened using a standard four-level error diffusion method, and the dot size was 0%, 50%, 75% and 100% of the maximum dot size giving the maximum required printing optical optimum density. The initial function parameters were estimated and then repeated twice until the print quality appeared acceptable. The parameters were then calculated as follows:

  For information, the pulse length curve corresponding to the last iteration of the parameters is plotted in FIG.

式中、ｆ_Ａは、プリントヘッド／帯状部分Ａの徐々に変化する関数であり、
ｆ_Ｂは、ｆ_Ａの鏡像である、プリントヘッド／帯状部分Ｂの徐々に変化する関数であり、
ｆ_ｍｉｎは、最小の印刷可能なレベルを与える、徐々に変化する関数の最小値であり、
ｘは、重なり合う領域全体で正規化された位置であり、０≦ｘ≦１であり、
αは、徐々に変化する関数の累乗である。 As described above, this example uses a gradually varying function of the following form for each drop volume size level to overlap the two printheads / bands 300A of prints A and B: Define a gradually changing profile across the area,
(formula)

Where f _A is a gradually changing function of print head / band A,
f _B is a gradually changing function of the printhead / band B, which is a mirror image of f _A
f _min is the minimum of a gradually changing function that gives the minimum printable level;
x is a normalized position over the entire overlapping region, 0 ≦ x ≦ 1,
α is a power of a gradually changing function.

Examples of gradually changing functions are plotted in FIG. This function produces a linear change when α = 1, a convex curve when α <1, and a concave curve when α> 1. FIG. 11 shows the gradually changing function for α = 1, 0.5 and 2. Here, f _min is set to 0.2.

  A gradually changing function is applied to the image data by multiplying it with the image pixel value. After this is screened, i.e., the pixel value is calculated by other methods, it may be applied to the image data and applied to raster image processing in the controlling computer or printhead drive electronics. Since the gradually changing function depends on the gray level / drop volume size, the function to apply to a given pixel is selected according to the screened value of the pixel. For example, a 50% level pixel is multiplied by a gradually changing function for the 50% level. Thus, there is a non-zero drop size in the screened image, so there are gradually changing functions that are included as many curves (eg, 3-4 level images; 8 level images 7).

The pixel value obtained by multiplying an image pixel at level P _L by a gradually changing function at that level is derived from:

When considering a general gradually changing function on one side (B),
(formula)

For each pixel level L of the screened image, there is a gradually changing function f _L (x).
(formula)

Ｐ_ｍｉｎＬは、最小の望ましいピクセル値であり、ピクセルの元々の値Ｐ_Ｌが何であれ、ほぼ同じである。 The level L pixel at position x of the entire image is gradually changed by multiplying its level P _L by a gradually changing function at that level.
(formula)

P _minL is the smallest desired pixel value and is approximately the same whatever the original value P _L of the pixel.

であり、式中、Ｐ_Ａは、ヘッド／帯状部分Ａのピクセルの改変した値であり、
Ｐ_Ｂは、ヘッド／帯状部分Ｂのピクセルの改変した値であり、
Ｐ_ｍｉｎＬは、最小の望ましいピクセル値である。 Thus, the pixel value obtained by multiplying the level P _{L of the} image pixel by the gradually changing function at that level is
(formula)

Where P _A is a modified value of the head / band A pixel,
P _B is a modified value of the pixel of the head / band B,
P _minL is the smallest desired pixel value.

International Publication No. 93/11866 Pamphlet WO 97/27058 Pamphlet International Publication No. 97/27056 Pamphlet International Publication No. 98/32609 Pamphlet WO 01/30576 pamphlet International Publication No. 03/101741 Pamphlet International Publication No. 93/11866 Pamphlet

Claims (20)

Two-dimensional bitmapping with many pixels in a column for printing with multiple overlapping printheads, one printhead indexed to overlapping positions or multiple printheads indexed to overlapping positions A method for printing a printed image,
The printhead or each printhead has a row of discharge channels, each discharge channel having an associated discharge electrode, for which the particulates produced in use in the body of the printing fluid From a plurality of overlapping printheads, a single printhead indexed to the overlapping position, or a selected emission channel of the plurality of printheads indexed to the overlapping position. Each predetermined amplitude, as determined by the bit value of each image pixel, to produce a predetermined volume of charged particulate concentrate in one of many predetermined volumes ejected as printed droplets and A voltage pulse of duration is applied to the electrode of the selected emission channel,
For each row of images, a plurality of overlapping printheads, one printhead indexed to overlapping positions or a plurality of printheads indexed to overlapping positions to create pixels printed by overlapping emission channels Depending on the position of the pixel in the overlapping area of the printhead and the size of the predetermined volume of the pixel, the emission volume for each pixel can be varied. It is variably adjusted so that it can be adjusted to
The predetermined volume size of each pixel corresponds to a predetermined fading function depending on it,
Each overlapping printhead or one or more printheads indexed to the overlapping position may contribute the contribution to each non-blank pixel in the overlapping area of the printhead to the overlapping area or one or more of the one or more printheads. Based on a predetermined fading function appropriate for each predetermined volume size of each non-blank pixel to be printed at the position of each non-blank pixel in the overlapping area of the print heads in one discharge Print,
Method. A plurality of overlapping printheads are used that are fixed in place relative to each other in use,
The method of claim 1. The one or more print heads are printed in a first pass to the print substrate and printed in a subsequent pass to the print substrate and overlap the predetermined position with the position of the first print head. Including a printhead or another printhead,
The method of claim 1. The first printhead is indexed between passes on the substrate at a distance equal to the width of the printhead channel row and less than a distance equal to the desired overlap of the passes.
The method of claim 3. Each printhead is one of many identical printheads arranged in modules parallel to each other and corrected by a portion of the distance between adjacent emission channels so that the printed image is adjacent Having a resolution greater than the distance between the emitting channels to be
The method of claim 1. Including a plurality of said modules overlapping each other, allowing a printing width greater than the width of the individual modules;
The method of claim 5. The module is indexed between passes on the substrate at a distance equal to the width of the printhead channel row and less than a distance equal to the desired overlap of the passes.
The method of claim 5. The one or more printheads are indexed to a portion of the distance between adjacent emission channels so that the printed image has a resolution greater than the distance between adjacent emission channels;
The method of claim 3. Before the pixel values are converted into voltage pulses of respective predetermined amplitudes and durations and printed, the bit value of the pixels depends on the position of the pixels in the overlapping area of the one or more printheads, and Adjusted depending on the size of a given volume of pixels,
The method according to claim 1. A bit value of the pixel of the image is provided to the drive electrical section of the print head, which converts this value into a voltage pulse, and one or more before the voltage pulse value is applied to the emission electrode of one or more print heads. Depending on the position of the pixel in the overlapping area of the print head and depending on the predetermined volume size of the pixel,
The method according to claim 1. Each predetermined fading function is non-linear,
The method according to claim 1. An apparatus for printing a two-dimensional bitmapped image having many pixels in a row, the apparatus comprising a plurality of overlapping printheads (300), one printhead indexed to overlapping positions or overlapping A plurality of printheads indexed to a position, each printhead or each printhead having a row of emission channels (301), each emission channel having an associated emission electrode (7). The electrode is energized with a sufficient voltage to create a particulate concentrator created in the body of the printing fluid in use, and a plurality of overlapping printheads, one printhead indexed to overlapping positions Or from selected discharge channels of multiple printheads indexed to overlap Each predetermined amplitude and duration as determined by the bit value of each image pixel to produce a concentrated portion of a predetermined volume of charged particulate matter in one of many predetermined volumes emitted as droplets. A voltage pulse of time (VE) is applied to the electrode of the selected emission channel,
For each row of images, multiple overlapping printheads, one printhead indexed to the overlap location, or multiple indexed to the overlap location to create pixels printed by the overlapping emission channels (301) The value of the voltage pulse applied to each print head depends on the position of the pixel in the overlapping area of the print head, and on the predetermined volume size of the pixel, the emission volume for each pixel. Is variably adjusted so that it can be variably adjusted,
The predetermined volume size of each pixel corresponds to a predetermined fading function depending on it,
Each overlapping printhead or one or more printheads indexed to the overlapping position may contribute the contribution to each non-blank pixel in the overlapping area of the printhead to the overlapping area or one or more of the one or more printheads. Based on a predetermined fading function appropriate for each predetermined volume size of each non-blank pixel to be printed at the position of each non-blank pixel in the overlapping area of the print head in a single emission Print,
apparatus. Having a plurality of overlapping printheads fixed in position relative to each other in use;
The apparatus according to claim 12. A first printhead arranged to print in a first pass to the print substrate and the same printhead printed in a subsequent pass to the print substrate and overlapping in position with the first printhead Including another printhead,
The apparatus according to claim 12. The first printhead is indexed between passes on the substrate at a distance equal to the width of the printhead channel row and less than the desired overlap of the passes.
The apparatus according to claim 14. Each printhead is one of many identical printheads arranged in modules parallel to each other and corrected by a portion of the distance between adjacent emission channels so that the printed image is adjacent Having a resolution greater than the distance between the emitting channels to be
The apparatus according to claim 12. Including a plurality of said modules overlapping each other, allowing a printing width greater than the width of the individual modules;
The apparatus of claim 16. Modules are indexed between passes on the substrate at a distance equal to the width of the printhead channel row and less than the desired overlap of the passes.
The apparatus of claim 16. One or more printheads are arranged to be indexed to a portion of the distance between adjacent emission channels so that the printed image has a resolution greater than the distance between adjacent emission channels;
The apparatus according to claim 14.   An apparatus for performing the method according to any of claims 1-11.

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