JP2007253464A - Image forming device adjusting discharge timing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which forms high definition images which rarely undergo a variation in a hue and a color drift by controlling discharge timing in accordance with images such as characters, line drawings, photographs and forms high definition images which rarely undergo a variation in a hue and a color drift without changing the images to be formed by internal processing of the device. <P>SOLUTION: The image forming device has a data analyzer 11 which analyzes density information relating to image data and the number of discharges per prescribed area, a control board 7 which receives image data from a computer 4 and generates reference ink discharge timing, sets the amount of drift on the basis of the result of the analysis when the data analyzer 11 analyzes the image data, a lookup table 8 which stores the amount of drift set by the control board 7, a head driving circuit 12 which receives ink discharge timing generated by the control board 7 by adding the drift to the reference ink discharge timing and image data, and a plurality of recording heads 3 which discharge inks on the basis of the ink discharge timing by the control of the head driving circuit 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that adjusts ejection timing.

  In recent years, an image forming apparatus that forms an image on a recording medium causes the recording unit to convey the recording medium below each recording head. At that time, for example, color inks such as Black (K), Cyan (C), Magenta (M), and Yellow (Y) are ejected from a plurality of recording heads onto a recording medium to form an image.

  FIGS. 26A and 26B are schematic top views of the periphery of a recording head arranged in such an image forming apparatus.

  Each color recording head 3 is short. The recording heads 3 are line head mechanisms that are arranged side by side so as to alternate in the recording medium width direction (direction orthogonal to the recording medium conveyance direction) and to overlap (connect) a part of the recording width. .

  In the case of the line head mechanism, for example, the ink ejected from the recording head 3M1 and the recording head 3Y1 is mainly landed at the position where the ink ejected from the recording head 3C1 lands, and an image is formed. Similarly, the ink ejected from the recording head 3M6 and the recording head 3Y6 is mainly landed at the position where the ink ejected from the recording head 3C6 lands, and an image is formed. In this way, six strip-shaped recording areas are formed in the recording medium conveyance direction.

The ink jet recording apparatus disclosed in Patent Document 1 includes a piezoelectric ceramic substrate, a nozzle plate, a nozzle, an ink flow path, a side wall, a cover plate, an ink supply unit, and an ink introduction port. This ink jet recording apparatus performs color image recording by discharging ink of at least two different colors onto a recording medium from nozzles of respective recording heads.
JP 2004-066494 A

  However, in the above-described line head mechanism, displacement (arrangement displacement) in the width direction of the recording medium may occur at each connecting portion of the short recording head 3. When the misalignment occurs in the joint portion, the landing position of each color ink is shifted in the recording medium width direction in each band-shaped recording area. In such a case, if there is an inclination in the conveyance direction of the recording medium 1, color misregistration occurs clearly as shown in FIG.

  Even when there is no inclination in the conveyance direction of the recording medium 1, color misregistration occurs. Even when the same image is formed on the six strip-shaped recording portions in such a state, the hues of the strips are different.

The reason why the hues differ in this way will be described in detail with reference to FIG.
FIG. 27 shows an arrangement relationship of each color recording head No. 1 (3C1, 3M1, 3Y1), No. 2 (3C2, 3M2, 3Y2), No. 3 (3C3, 3M3, 3Y3) and the ink in this arrangement relationship. It is a schematic top view showing a landed recording medium.

  The band recorded by the combination of the recording head 3C1, the recording head 3M1, and the recording head 3Y1 in the left part will be described. The nozzles of the recording head 3C1 and the nozzles of the recording head 3Y1 are arranged on the same straight line with respect to the recording medium conveyance direction. Therefore, the C ink and Y ink land on almost the same recording area. The nozzles of the recording head 3M1 are shifted in the recording medium width direction with respect to the nozzles of the recording head 3C1 and the recording head 3Y1. Therefore, the M ink is landed with a deviation from the landing positions of the C ink and the Y ink. This landing position is a position shifted by 0.5 dots in the recording medium width direction from the recording area where the C ink and Y ink have landed. In this case, the overlapping portion of the C ink and the Y ink has a color that approximates Green (Gn). This is referred to as Case1.

  Next, a band recorded by a combination of the recording head 3C2, the recording head 3M2, and the recording head 3Y2 in the center will be described. The nozzles of the recording head 3M2 and the nozzles of the recording head 3Y2 are arranged on the same straight line with respect to the recording medium conveyance direction. Therefore, the M ink and the Y ink land on almost the same recording area. The nozzles of the recording head 3C2 are shifted in the recording medium width direction with respect to the nozzles of the recording head 3M2 and the recording head 3Y2. Therefore, the C ink landed with a deviation from the landing positions of the M ink and the Y ink. This landing position is a position shifted by 0.5 dots in the recording medium width direction from the recording area where the M ink and Y ink have landed. In this case, the overlapping portion of M ink and Y ink has a color that approximates Red (R). This is referred to as Case2.

  Finally, a band recorded by the combination of the recording head 3C3, the recording head 3M3, and the recording head 3Y3 in the right part will be described. The nozzle of the recording head 3C3, the nozzle of the recording head 3M3, and the nozzle of the recording head 3Y3 are arranged on the same straight line with respect to the recording medium conveyance direction. Therefore, the three colors land at almost the same position. Since all colors overlap, it is a color with a gray (Gy). This is Case 3.

FIG. 28 is a distribution diagram in which hues generated by landing of each color are measured and plotted on the a ^* b ^* plane of the L ^* a ^* b ^* space. Since the L ^* value does not change greatly due to landing deviation, the coordinates of the a ^* b ^* plane can be viewed. Case1, Case2, and Case3 are the combination of impacts. Case3 is the central part of the distribution, Case1 is a color that approximates Gn, so it is a part closer to Green, and Case2 is a color that approximates R Plotted in the portion from Red.

  Thus, since Case 1 and Case 2 are in the positions farthest from each other, a maximum color difference occurs, and the operator visually recognizes this color difference (difference between Case 1 and Case 2).

  Characters and line drawings formed in a single color do not reach a level at which the operator can visually recognize the color difference even if there is a slight inclination in the conveyance direction of the recording medium and a slight displacement of the recording head. However, as described above, characters and line drawings formed of a plurality of colors are visually recognized by the operator as color misregistration due to an inclination in the conveyance direction of the recording medium and a misalignment of the connecting portions between the recording heads. Also, a region where a color image is formed on a certain wide surface such as a photograph is visually recognized as a difference in hue.

  Further, the offset image forming apparatus rotates the dot grid of ink ejected for each color at a constant angle (screen angle) so that the landing position does not shift as described above, and the dot grid points for each color overlap. I try not to be. However, in order to form image data having a screen angle, it is necessary to use a high-resolution ink jet head or increase the resolution of an image formed on a recording medium by scanning the ink jet head a plurality of times. As a result, the apparatus becomes expensive, or much time is required for image formation.

  Therefore, the present invention forms a high-quality image with little change in hue and color shift by controlling the ejection timing according to images such as characters, line drawings, and photographs without increasing the resolution of the image, and the image to be formed It is an object of the present invention to provide an image forming apparatus that forms an image with little change in hue and color misregistration with respect to any image by processing inside the apparatus without changing the image quality.

  In order to solve the above problems, a short recording head having a plurality of ink ejection portions that eject ink onto a recording medium, a recording head array in which a plurality of recording heads are arranged in a direction orthogonal to the recording medium conveyance direction, and the recording head A recording head unit in which columns are provided at equal intervals along the recording medium conveyance direction for each of a plurality of ink colors, a control unit that generates a reference ink ejection timing of ink ejected from each ink ejection unit, and a recording medium And a head driving unit that drives the recording head to eject the ink based on the ink ejection timing with respect to the image data. The control unit includes a reference ink ejection unit for each ink ejection unit. Provided is an image forming apparatus characterized in that an arbitrary delay amount is set for each timing, and an ink discharge timing is generated by adding the delay amount.

  The present invention forms an image with little hue and color shift change by controlling the discharge timing according to an image such as a character, line drawing, or photograph without increasing the resolution of the image, and changes the image to be formed. Accordingly, it is possible to provide an image forming apparatus that forms an image with little change in hue and color shift with high quality by processing inside the apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In the following description of each embodiment, in the drawings, the conveyance direction of the recording medium is the X-axis direction or the sub-scanning direction, and the direction orthogonal to the conveyance direction is the Y-axis direction, the main scanning direction, or the width direction of the recording medium. . A direction orthogonal to the X-axis and Y-axis directions is taken as a Z-axis direction or a vertical direction.

  The reference ink ejection timing is the ejection of ink to land the ink droplet on the normal landing point (center value) of the recording medium when ink is ejected from the nozzle provided in the recording head and landed on the recording medium. The delay amount (deviation amount) refers to the ratio of deviation from the center value, the ink ejection timing refers to the ejection timing obtained by adding a delay amount to the reference ink ejection timing, and the maximum deviation amount , Refers to the maximum amount of delay.

  First, the first embodiment will be described. In this embodiment, the nozzles provided in the recording head can set the shift amount independently of each other, thereby generating the ink discharge timing for each nozzle.

Since the schematic configuration of the image forming apparatus in the present embodiment is substantially the same as that of FIG. 26 described above, the same components will be described with the same reference numerals.
As shown in FIG. 26, the image forming apparatus includes a transport unit 2 that transports the recording medium 1 below the recording head 3, and Black (K), Cyan (C), for example, on the recording medium 1 transported by the transport unit 2. , Magenta (M), Yellow (Y) or the like is ejected, and a recording head 3 that forms an image and a maintenance station 13 that performs maintenance of the recording head 3 are provided.

  The recording head 3 is arranged in the order of K, C, M, and Y from upstream to downstream in the recording medium conveyance direction. In each color recording head 3, six short recording heads are alternately arranged along the Y-axis direction. At that time, in the six short recording heads (recording head 3K1, recording head 3K2, recording head 3K3, recording head 3K4, recording head 3K5, recording head 3K6) that discharge K ink, a part of one short recording head Is overlapped with the other short recording head. Therefore, the recording head can eject ink over the entire width of the recording medium 1.

  Further, by individually adjusting the ink ejection timing of the short recording head, it is possible to eject ink in the same manner as the line head type recording head. The same applies to the other recording heads 3.

  A maintenance station 13 for recovering the ejection of the recording head 3 is arranged corresponding to each recording head 3 downstream of the recording head 3 in the transport direction.

  A transport belt (not shown) is disposed below the recording head 3. The transport belt receives the recording medium 1 transported by the transport unit 2 and transports the recording medium 1 so as to face the recording head 3.

Next, the control system in the present embodiment will be described with reference to FIG. A portion surrounded by a broken line in FIG. 1 corresponds to the printer engine 15.
The computer 4 and the printer engine 15 are connected to each other via the control board 7 so that they can communicate with each other. The computer 4 transmits image data to the RIP 5 and the control board 7. The RIP 5 performs raster conversion on the received image data in accordance with the resolution and the number of gradations of the image forming apparatus.

  The printer engine 15 includes an operation panel 6 that is operated when an operator selects an image forming mode, which will be described later, and image data output after raster conversion by the RIP 5 into K, C, M, and Y colors. Data to be stored, a buffer 10 for sequentially cutting out and storing the stored image data, density information relating to the image data stored in the buffer 10, and data for analyzing the number of discharges per predetermined area Control that receives image data from the analyzer 11 and the computer 4 to generate a reference ink discharge timing for each nozzle, which will be described later, and sets a deviation amount based on the analysis result when the data analyzer 11 analyzes the image data. The board 7, the look-up table 8 for storing the deviation amount set by the control board 7, and the control board 7 An ink discharge timing is generated by adding a deviation amount to the timing. The head drive circuit 12 receives the ink discharge timing and the image data via the data analyzer 11, and the ink discharge is controlled by the head drive circuit 12. There are provided a plurality of recording heads 3 that eject ink based on timing.

The deviation amount added to the reference ink ejection timing is randomly set according to the image mode from the maximum deviation amount stored in the control board 7 when the operator selects the image mode. Further, the data analyzer 11 analyzes the image data and calculates the pixel occupation rate and the ink acceptance rate. Analysis The image density is determined by the calculation result. The control board 7 sets the maximum deviation amount large when the image density is higher than the first density threshold, and sets the maximum deviation amount small when the image density is low. Further, when the analysis result is higher than the second density threshold value higher than the first density threshold value, the maximum delay amount is set small. (Details will be described later)
Further, the operator can select an image forming mode and a data processing method similarly to the operation panel 6 via application software on the computer.

  In addition, “text mode”, “photo mode”, and “automatic mode” are set as image modes that can be selected from the operation panel 6 or the computer 4.

  In the “character mode”, for example, in order to form a single-color character or line, the smoothness of dots is more important than the uniformity of hue. In the “photo mode”, the uniformity of hue is more important than the smoothness of dots in order to form an image such as a photograph formed with halftone. The “automatic mode” emphasizes the balance between the smoothness of dots and the uniformity of hue. Thus, the operator can select whether or not to eliminate the hue change by selecting each mode.

  Next, the size of the dot diameter of the ink ejected from the nozzles during image formation will be described with reference to FIG.

  The recording head 3 is provided with a plurality of nozzles in the Y-axis direction, for example, at a 300 dpi pitch. The ink ejected from each nozzle can be recorded in 8 gradations on a dpi lattice (hereinafter referred to as a pixel) to be recorded on the recording medium 1. The nozzle can perform gradation recording by setting the ejected drop to a minimum unit of 6 pl and ejecting ink with a plurality of drops directed to one pixel. If the maximum value of the drop is 7, the gradation is 8 including the case where no discharge is performed. FIG. 2 schematically shows the dot diameter when the eight gradation dots are ejected onto the recording medium 1.

  Next, a calculation method in which the data analyzer 11 analyzes the image data and calculates the pixel occupation rate and the ink acceptance rate will be described with reference to FIG.

The data analyzer 11 analyzes the data area (P pixel × Q pixel which is an analysis area) stored in the buffer 10. One square shown in the figure represents one pixel. A square in which no number is written in the analysis area indicates that ink is not ejected from the recording head 3. The squares on which numbers are written indicate that ink is ejected from the recording head 3. The numbers described in the squares indicate the number of gradations (the number of gradation drops that is the size of the dot diameter) shown in FIG.
The pixel occupancy calculated by the data analyzer 11 refers to the ratio of ejection pixels (number of dots) in the analysis region (P pixels × Q pixels).
Pixel occupancy = number of dots / (P × Q)
Ask for.

If it is within the black frame shown in the figure,
Pixel occupation ratio = 4 / (11 × 2) = 0.18.

  When this pixel occupancy is higher than the first ink ejection number threshold, the maximum deviation amount is set large, and when the pixel occupancy is lower than the first ink ejection number threshold, the maximum deviation amount is set small. When the second ink discharge number threshold value is higher than the first ink discharge number threshold value, the maximum delay amount is set small.

As shown in FIG. 2, the size of the dot diameter driven into one pixel can be changed from 1 drop to 7 drop in this embodiment, and the amount of ink driven into one pixel also changes by this change.
The ink acceptance rate calculated by the data analyzer 11 refers to the ratio of the sum of the number of drops in this area to the maximum number of drops that can be driven into this analysis area (7 in the present embodiment).
Ink acceptance rate = Σ (number of drops) / (P × Q) / 7
Ask for.

  Thus, the data analyzer 11 calculates the ink acceptance rate and the pixel occupation rate from the analysis region (P pixel × Q pixel) in the analysis of the image data. The obtained analysis result is output to the control board 7.

  Next, referring to FIG. 4A and FIG. 4B, the table 1 stores the deviation amount set by the control board 7 based on the analysis result output from the data analyzer 11 and the table 1 stores the reference ink ejection timing. An example of the ink landing position when ink is ejected at the ejection timing to which the deviation amount is added will be described.

When the recording head 3 has N nozzles, if the pixel frequency is 5 kHz, the interval between one line corresponds to 200 (μs). The time actually used for ejection in this interval is about 50 (μs).
FIG. 4A shows Table 1 in which the shift amount is stored. The reference ink ejection timing in the present embodiment is a timing at which ink is ejected at a pixel frequency of 200 (μs), and is generated when the control board 7 receives the image data output from the computer 4 as described above. . The shift amount is added to the reference ink ejection timing by changing the pixel frequency.

  In Table 1, the maximum deviation amount is set to 50% based on the analysis result. Table 1 stores a shift amount from the first line to the last line for each of a plurality of nozzles 1 to N. If there is no deviation amount (ink is ejected at the reference ink ejection timing), the deviation amount is set to 0%.

  In FIG. 4B, ink is ejected at the ink ejection timing generated by adding the reference ink ejection timing to the shift amount stored in Table 1, and the landing position of the ink landed on the recording medium at that time Is shown.

  The landing position of the ink ejected at the ink ejection timing when there is no deviation is the intersection of the broken lines shown in FIG.

  Further, the landing position of the ink ejected at the ink ejection timing when the deviation amount is added (the numerical value is not 0%) is deviated in the X-axis direction from the intersecting portion of the broken line shown in FIG. .

  For example, the shift amount of the third nozzle on the second line shown in FIG. 4A is set to 0%. Therefore, this deviation amount is added to the reference ink discharge timing to generate the ink discharge timing. When ink is ejected based on this ejection timing, as shown in FIG. 4B, the ink is ejected on the intersection of broken lines, and the landing position does not deviate.

  Further, for example, the shift amount of the Nth nozzle on the first line shown in FIG. 4A is set to 40%. Therefore, this deviation amount is added to the reference ink discharge timing to generate the ink discharge timing. When ink is ejected based on this ejection timing, as shown in FIG. 4B, the landing position is shifted by an amount corresponding to 40% of the dot pitch in the second line direction with respect to the intersection of the broken lines. become.

  Note that the control board 7 can set the maximum deviation amount according to the type of recording medium used and each recording head array. Further, an average value of the set deviation amounts may be calculated and stored in the lookup table 8.

  Next, the relationship among the data analyzer 11, the head drive circuit 12, and the recording head 3 will be described with reference to FIG.

  The recording head 3 is provided with a thermistor (not shown), and temperature information of the recording head 3 detected by the thermistor is transmitted to the head driving circuit 12 between the recording head 3 and the head driving circuit 12. The head drive circuit 12 controls the voltage for driving the recording head 3 based on this temperature information.

  Further, the image data output from the data analyzer 11 and the ink discharge timing generated by adding the deviation amount to the reference ink discharge timing and analyzed by the data analyzer 11 as described above are output to the head drive circuit 12. Is done. Further, the head drive circuit 12 outputs the voltage, the above-described image data, and the ejection timing to the recording head 3. The recording head 3 that has received the output discharges ink.

  FIG. 6 shows an example of the landing position of the ink on the recording medium when the ink is ejected at the ejection timing described above.

  FIG. 6 shows the case where the arrangement of the short recording heads 3 is misaligned in the Y-axis direction, the inclination of the recording medium 1 in the conveyance direction, and the meandering of the recording medium to be conveyed as in the conventional example of FIG. Therefore, it is assumed that the color overlap of each color is shifted.

  FIG. 6A shows a case where ink is ejected at the reference ink ejection timing and the ink landing position is not shifted in the recording medium direction.

  In the rightmost band shown in FIG. 6A, C, M, and Y inks land on the same recording area. Therefore, the image formed on the recording medium 1 approximates Gy. In the central band, the M ink and the Y ink are shifted in the Y-axis direction by 0.5 dots with respect to the C ink. Therefore, the image formed on the recording medium 1 by the overlap of the C ink and the M ink approximates R. In the leftmost band, only the M ink is shifted in the 0.5-dot pixel Y-axis direction with respect to the C ink and the Y ink. The image formed on the recording medium 1 by the overlap of the C ink and the Y ink approximates Gn.

  Next, in FIGS. 6B and 6C, when the overlap of each color is shifted under the same conditions as in FIG. 6A, the ink is discharged at the ink discharge timing obtained by adding the shift amount to the reference ink discharge timing. When the ink is ejected and landed on the recording medium, the ink landing position is shifted in the recording medium direction.

  For example, when a deviation amount of 15% at maximum is added to the reference ink ejection timing and ejection is performed at the ink ejection timing, the landing position is slightly shifted in the recording medium direction as shown in FIG.

  For example, when an amount of deviation of 30% at maximum is added to the reference ink discharge timing and the ink is discharged at the ink discharge timing, the landing position is greatly shifted in the recording medium direction as shown in FIG.

  By increasing the maximum amount of deviation as in the leftmost band shown in FIG. 6C, uniform and dense overlap of dots of each color as in the rightmost band shown in FIG. As a result, all of the dots are landed on the plain part evenly, and the ground color of the recording medium is exposed at random as in the leftmost band shown in FIG. 6C.

  In other words, when ink is ejected at an ink ejection timing to which a shift amount is added, the landing position is shifted, and the tendency to approximate Gn, R, and Gy is reduced.

  As a result, the color difference that was noticeable between the adjacent short heads as shown in FIG. 28 is reduced.

  When referring to the shift amount from the lookup table 8, the maximum shift amount is set to 50% in FIG. 4A, but the maximum shift amount is set to 15% in FIG. 6B and the maximum shift in FIG. 6C. The deviation amount is set to 30%. In the present embodiment, the shift amount can be set randomly for each pixel in the region within the range of the maximum shift amount that can be arbitrarily set.

  When setting the maximum deviation amount, the dot diameter is uniform in FIG. 4B, but actually, the dot diameter differs depending on the gradation control as shown in FIG. Therefore, when the dot diameter is small (1 dpd shown in FIG. 2) and when the dot diameter is large (7 dpd shown in FIG. 2), the image density per unit area or the amount of ejected ink is different when forming an image. In addition to the size of the dot diameter, the image density and the ink amount differ depending on the number of dots ejected per unit area.

  The above points will be described with reference to FIGS. FIG. 7 is a diagram showing the relationship between the image density and the hue change (color difference ΔE) caused by the skew of the recording medium. FIG. 8 is a conceptual diagram when obtaining the maximum deviation amount from the size of the dot diameter and the number of dots. The ink is ejected per unit area (analysis region) on the vertical axis with the size of the dot diameter as the amount of ink received. The horizontal axis shows the ratio of the number of dots to be plotted as the pixel occupancy rate.

  The image density shown in FIG. 7 is determined by obtaining the pixel occupancy and ink acceptance amount shown in FIG. As shown in FIG. 7, the hue change (color difference ΔE) is small when the image density is low and high, and the hue change (color difference ΔE) due to color misregistration is large when the image density is intermediate (halftone). It will be. When this image density is higher than the first density threshold (right side shown in FIG. 7), the control board 7 sets the maximum delay amount to a large value and lower than the first density threshold (shown in FIG. 7). On the left), the control board 7 sets the maximum delay amount small. When the second density threshold is higher than the first density threshold, the control board 7 sets the maximum delay amount to be small.

The phenomenon in which the hue change occurs differs depending on the overlapping ratio of each color dot.
For example, when the dot diameter is small, such as 1 dpd shown in FIG. 2, the amount of ink received by the recording medium is small. When the ink acceptance amount is small and the pixel occupancy is small, the probability that the image data that has been subjected to color error diffusion will be landed on the same pixel (same part) is low, and the background color of the recording medium is wide. Yes (exposed). Therefore, even if the landing position is shifted, the hue hardly changes. Therefore, the deviation amount added to the reference ink discharge timing is set to 0%, and ink is discharged at the reference ink discharge timing. As a result, the ink lands as shown by the nozzle 3 in the line 2 shown in FIG. The same applies when the pixel occupation ratio is small and the ink acceptance amount is large, and when the pixel occupation ratio is large and the ink acceptance amount is small.
In addition, when the pixel occupancy is high, the dot diameter is large, and the ink acceptance amount is large as in 7 dpd shown in FIG. Therefore, even if the landing position is deviated, the color overlap hardly changes and the hue change is small. Therefore, in the same manner as described above, the amount of deviation added to the reference ink discharge timing is set to 0% to discharge ink.

  In such a combination region where the hue change is small, the deviation amount is set to 0%, and ink can be ejected at the reference ink ejection timing, so that a fine (high quality) image can be formed.

  For example, an image in which monochromatic characters and lines are formed on the ground has a low pixel occupancy rate and a small ink acceptance amount. Therefore, the image density is low and the shift amount is set to 0%, so that the reference ink discharge timing is set. By discharging the ink, smooth characters and lines can be formed.

  Similarly, a photo or a solid image portion has a high pixel density and a high ink density, and thus has a high image density. Therefore, it is possible to form a fine (high quality) image by setting the deviation amount to 0% and ejecting ink at the reference ink ejection timing.

  However, for example, when the ground color is exposed by nearly 50% because both the pixel occupation ratio and the ink acceptance amount are appropriate, the hue change (color difference ΔE) becomes the largest as shown in FIG. In other words, the ground color exposure rate is determined by two factors: the pixel occupation rate and the ink acceptance amount. This exposure rate affects the hue change (color difference ΔE) when color misregistration occurs. For this reason, in the combined region of the pixel occupancy rate and the ink acceptance amount where the hue change is greatest (especially when both the pixel occupancy rate and the ink acceptance amount described above are appropriate), the hue change is reduced by largely shifting the landing position. can do. Therefore, it is necessary to add a large amount of deviation to the reference ink ejection timing as shown in FIG.

  Thus, by setting the deviation amount large, the landing position deviates from the intersection shown in FIG. 4B (for example, the nozzle 3 in the first line), and the exposure of the ground color of the recording medium 1 can be suppressed, and the hue changes. Can be reduced.

  For example, an image such as a photographic region formed with a halftone image density can be formed by shifting the landing position and reducing the hue change by setting a large shift amount.

  Note that when an image such as a character or a line is formed in one color, the image forming apparatus forms an image using dark color ink (Light Color) and light color ink (Light Color) of the same system. At that time, the image forming apparatus forms an image mainly by discharging light-colored ink to a portion with a low density and dark-color ink to a portion with a high density. The dark color ink and the light color ink are discharged from different recording heads (Light Color Head, Dark Color Head).

  Therefore, the relationship between the dark color ink and the light color ink will be described with reference to FIG. The curve showing the OD value shown in FIG. 9 shows the optical density obtained by using different heads for both the dark and light inks and changing the amount of each head to be shot in accordance with the gradation.

  When light-colored ink is ejected and the driving amount increases, the OD value (image density) also increases. When the OD value increases and reaches the middle as shown in FIG. 7, the hue change (color difference ΔE) becomes large. For this reason, the amount of dark color ink is gradually increased, and the amount of light color ink is decreased. As a result, the OD value increases, and the hue change (color difference ΔE) can be reduced as shown in FIG. In this way, when an image is formed by ejecting dark color ink and light color ink for one color, in order to reduce the hue change (color difference ΔE), the ejection of the dark color ink and light color ink is shifted. It is preferable to form.

  Next, with reference to FIGS. 10 to 13, Table 2 to Table 6 in which the maximum shift amount of each image mode among the shift amounts stored in the lookup table 8 will be described.

  Table 2 shown in FIG. 10 stores the maximum shift amount when an image is formed using only dark-colored four-color ink and the operator selects the automatic mode.

  Since no hue is applied to K, no maximum shift amount is input. Thereby, since the landing position of the K ink does not shift, the image can be recorded smoothly.

  Table 3 shown in FIG. 11 stores the maximum shift amount when an image is formed using only dark four-color ink and the operator selects the photo mode.

  Since no hue is applied to K, no maximum shift amount is input. Thereby, since the landing position of the K ink does not shift, the image can be recorded smoothly.

  For C, M, and Y, as shown in FIG. 8, the amount of deviation is set according to the combination of the pixel occupation ratio and the ink acceptance amount. Since Y has low sensitivity to human eyes, the maximum deviation amount of Y is set equal to or larger than the maximum deviation amounts of C and M. In this way, the image is formed so that the landing positions of the C ink and the M ink are largely shifted and the visible image roughness is hardly affected.

  Table 4 shown in FIG. 12 stores the maximum amount of deviation when an image is formed using only dark-colored four-color ink and the operator selects the character mode.

  In this case, since the pixel occupation ratio is low and the ink acceptance amount is small as described above, the maximum shift amount of all four colors is set to zero. Thereby, smooth characters and lines can be formed.

  In Table 5 shown in FIG. 13 (a) and Table 6 shown in FIG. 13 (b), images are formed by using four colors (8 colors in total) of dark and light colors, and the operator takes a photograph. Stores the maximum shift amount of each color when the mode is selected. Table 5 is a look-up table that stores the maximum shift amount of the dark-colored four-color ink, and Table 6 stores the maximum shift amount of the light-colored four-color ink.

As shown in FIG. 9, since the dark color system is used only in a portion where the pixel occupation ratio is high and the ink acceptance amount is large, a shift amount is mainly set in that portion. Since K is used only for local parts such as characters and inking, the maximum shift amount is set to zero. As described above, Y ink has low sensitivity to human eyes. Therefore, the maximum deviation amount of Y ink is set equal to or larger than the maximum deviation amount of C and M inks.
As shown in FIG. 9, in the light color system, K does not affect the hue, so the maximum shift amount is set to zero. Further, since C, M, and Y have low sensitivity to eyes, the maximum deviation amount of C, M, and Y shown in Table 6 is set to be the same or larger than the maximum deviation amount shown in Table 5. is doing. Further, the maximum deviation amount of Y ink is set to be the same or larger than the maximum deviation amount of C and M inks.

Next, the flow of image formation in this embodiment will be described with reference to FIG.
The control board 7 determines whether or not the operator has selected the automatic mode as the image forming mode via the computer 4 or the operation panel 6 (Step 1).

  Next, when the image forming mode is the automatic mode (Step 1: Yes), Table 2 is specified in the lookup table to be referred to (Step 2). Then, image formation starts (Step 3).

  When the image forming mode is not the automatic mode (Step 1: No), the control board 7 determines whether the operator has selected the photo mode as the image forming mode via the computer 4 or the operation panel 6 (Step 4).

  When the image forming mode is the photo mode (Step 4: Yes), Table 3 or Table 5 and Table 6 are specified in the lookup table to be referred to (Step 5). Then, image formation starts (Step 3).

  When the image forming mode is not the photo mode (Step 4: No), the control board 7 determines whether the operator has selected the character mode as the image forming mode via the computer 4 or the operation panel 6 (Step 6).

  When the image forming mode is the character mode (Step 6: Yes), Table 4 is specified in the lookup table to be referred to (Step 7). Then, image formation starts (Step 3).

  When the image forming mode is not the character mode (Step 6: No), the process returns to Step 1.

  When image formation starts, the image data raster-converted by the RIP 5 is accumulated in the memory 9 for each color (Step 8), and the accumulated image data is sequentially cut out and stored in the buffer 10 (Step 9).

  Then, the data analyzer 11 analyzes the stored image data and calculates the pixel occupation rate and the ink acceptance rate. Based on this calculation result, the control board 7 sets a deviation amount, adds the deviation amount to the reference ink ejection timing, and generates an ejection timing.

  When the control board 7 adds the shift amount, the control board 7 refers to any one of Tables 2 to 6 specified in Step 2, Step 5, and Step 7 from the lookup table 8 in accordance with the selected image mode. A deviation amount is randomly set and added within the range of the maximum deviation amount stored in the referenced table (Step 10). Then, the control board 7 outputs the ink ejection timing to the data analyzer 11.

  Next, the data analyzer 11 outputs ink ejection timing and image data to the head drive circuit 12 (Step 11).

Then, it is determined whether or not to end the data transfer (Step 12).
When the process is to be ended (Step 12: Yes), ink is ejected from each nozzle to complete image formation (Step 14).
If not finished (Step 12: No), the image data stored in the buffer 10 is cleared (Step 14), and the process returns to Step 9.

  As described above, in this embodiment, when adding a deviation amount to the reference ink ejection timing, the deviation amount is determined based on the image information of the image, the pixel occupation rate obtained by analyzing the image information, and the calculation result of the ink reception amount. It is set within the range of deviation. Therefore, in the present embodiment, the landing position can be shifted in accordance with the image. This makes it possible to achieve both uniform hue and smooth line according to line drawings, characters, photographs, etc., and form a high-quality image. The deviation amount may be set within the range of the average deviation amount described above.

  Further, in the present embodiment, even in a recording head capable of forming an image by changing the gradation, by analyzing the combination of the pixel occupation ratio and the ink acceptance amount, a deviation amount is set according to the image, and the ink landing position is determined. It is possible to shift. Therefore, in the same manner as described above, it is possible to achieve both uniformity of color and smoothness of lines according to line drawings, characters, photographs, etc., and high quality images can be formed.

  Further, when the operator selects an image mode such as a character, line drawing, or photograph from the computer 4 or the operation panel 6, the maximum shift amount stored in the table set according to each mode is referred to. By setting the amount of deviation at random within this maximum amount of deviation, the character portion is displayed in a line ( The ejection timing is generated so that the dots are smooth, and by ejecting ink based on this timing, a high-quality image can be formed.

  In addition, by referring to a table that stores the amount of deviation according to the color of the head, the color with high eye sensitivity can reduce the amount of deviation, and the color with low sensitivity can be increased, and according to line drawings, characters, photographs, etc. It is possible to achieve both uniformity of color and smoothness of the line, and a high quality image can be formed.

  Next, a second embodiment according to the present invention will be described.

  Constituent parts similar to those of the first embodiment described above are given the same reference numerals, and detailed descriptions thereof are omitted.

  The recording head in this embodiment will be described with reference to FIG. FIG. 15A is a schematic cross-sectional view of the recording head. FIG. 15B is a plan view of the nozzle plate.

  In the first embodiment described above, in the recording head 3 having N nozzles, the shift amount can be set for each nozzle and the ink ejection timing can be generated for each nozzle. A deviation amount is set for each group having ink and ink ejection timing is generated.

  As shown in FIG. 15A, the recording head 3 is provided with a plurality of channels 32 in parallel from the common ink chamber 31 toward the nozzle plate 33. The channel 32 is, for example, a piezo. When the side wall of the channel 32 is displaced so as to enlarge or reduce the volume in the channel 32, a wave is generated thereby, and ink is ejected from the nozzle 34 by this wave.

  In the case of such a recording head 3, the side wall of one channel 32 is common to the side wall of the other adjacent channel 32 (although a space is provided for easy viewing in the drawing). Therefore, a control unit (not shown) cannot eject ink from all the channels 32 simultaneously or individually as in the first embodiment described above.

  For this reason, as shown in FIG. 15B, the recording head 3 is provided with groups (A phase, B phase, C phase) on the nozzle plate 34 that can eject ink from the nozzles 34 at intervals of three. . These A-phase, B-phase, and C-phase nozzles 34 cause ink to be ejected with a time difference. In addition, the nozzles 34 in each phase are sequentially shifted by approximately 1/3 (μm) of the pixel grid interval in the X-axis direction so as to correspond to the time difference between the A phase, the B phase, and the C phase.

  Next, time charts for the A phase, the B phase, and the C phase will be described with reference to FIGS.

  FIG. 16A shows a time chart for driving the A phase, the B phase, and the C phase. FIG. 16B shows a time chart in which a surplus time α (μs) is provided between the phases. FIG. 16C shows a time chart in which the total remaining time 3α (μs) is randomly provided between the phases. FIG. 17 shows a set interval of the total remainder time 3α (μs).

  Ink is ejected from the A-phase nozzle 34 in the first line. When ink ejection from the A-phase is completed, ink ejection begins from the B-phase nozzle 34, and when ink ejection from the B-phase nozzle 34 is terminated, the C-phase ink is discharged. Ink ejection starts from the nozzle 34, and when ink ejection from the nozzle 34 from the C phase ends, ink ejection starts from the A phase nozzle 34 in the second line.

  When the pixel frequency is 4.8 (kHz), the time interval from the ink ejection from the A-phase nozzle 34 in the first line to the ink ejection from the A-phase nozzle 34 in the second line is shown in FIG. Thus, the time interval is 3T = 210 (μs).

  Of these, the time during which ink is actually ejected from the A-phase nozzle 34 is T = 70 (μs). Further, in order to earn a deviation amount, it is necessary to delay the pixel frequency and provide a delay time (remainder time α (μs)) in the ejection time of each phase. Therefore, if a surplus time α (μs) is provided after ejection of each phase, the time interval becomes 3 (T + α) (μs) as shown in FIG. FIG. 16C shows a time chart when the total remaining time 3α (μs) is randomly provided, for example, between the A phase and the B phase on the first line and between the B phase and the C phase on the second line. It shows.

  When adding an amount of deviation to the reference ink ejection timing as in the first embodiment described above, ejecting ink at the ink ejection timing, and shifting the ink landing position to form an image, in this embodiment, The excess time α (μs) corresponds to the amount of deviation.

  More specifically, the ink ejection timing is generated by setting the total remainder time 3α (μs) collectively or randomly and setting between the phases.

  That is, the total remaining time 3α (μs) is divided into four sections T1 to T4 shown in FIG. 17, that is, before the A phase (T1), between the A phase and the B phase (T2), and between the B phase and the C phase (T3). ), After the C phase (T4), or by dividing and setting at random, the ink ejection timing is generated, and the ink landing position is shifted to form an image.

Usually, the pixel grid interval D of 300 (dpi) is approximately 85 (μm), and the time T required for driving is 70 (μs). Table 7 shown in FIG. 18 includes a maximum shift amount ΔD (μm) from the pixel grid, a total remaining time 3α (μs) necessary to generate the maximum shift amount ΔD, a pixel frequency (kHz) in this case, The relationship between the deviation amount (%) is shown.
Next, the relationship between the method of setting the total remainder time 3α (μs) and the deviation amount based on the total remainder time 3α (μs) will be described with reference to FIGS.

  Table 8 shown in FIG. 19A shows an example in which the total remainder time 3α (μs) is divided into two and set to any two of the four sections, or collectively to any one of the four sections. .

Specifically, when the total remaining time 3α (μs) is 60 (μs), Table 8 is divided every 30 (μs) and randomly distributed to any two of T1 to T4 described above, or 60 (μs). As an example, the amount of deviation (%) in the A phase, B phase, and C phase for each line is randomly changed when it is randomly allocated to any one of T1 to T4. Yes.
The deviation (%) shown in Table 8 is added to the reference ink ejection timing, and ink is ejected at the ink ejection timing. The ink landing position at that time is shown in FIG.

  The horizontal axis shown in FIG. 19B indicates the nozzle numbers 1 to 8, and the vertical axis indicates the lines 1 to 9. When the deviation amount is 0%, the center position of the ink shown in FIG. 19B is arranged at the intersection of the horizontal axis and the vertical axis. When the amount of deviation is set, if it is 0% or more, it is displaced upward with respect to the horizontal axis, and if it is 0% or less, it is shifted downward in the horizontal axis. The nozzle numbers 1, 4, and 7 on the horizontal axis correspond to the A phase, 2, 5, and 8 correspond to the B phase, and 3, 6 correspond to the C phase.

  Table 9 shown in FIG. 20A shows an example in which the total remaining time 3α (μs) is collectively set to one of the four sections.

Specifically, when the total remaining time 3α is 60 (μs) as in the above-described Table 8, Table 9 is a group of 60 (μs), randomly distributed to any one of T1 to T4, and 1 when distributed. An example is shown in which the deviation amounts (%) in the A phase, the B phase, and the C phase for each line change randomly.
The amount of deviation is the same as Table 8, but the rate at which 60 (μs) enters T1 is increasing. The deviation (%) shown in Table 9 is added to the reference ink ejection timing, and ink is ejected at the ink ejection timing. The ink landing position at that time is shown in FIG.

  The horizontal and vertical axes shown in FIG. 20B are the same as those in FIG. Compared with FIG. 19B, the deviation amount of the landing position shown in FIG.

  Table 10 shown in FIG. 21A shows an example in which the total remaining time 3α (μs) is set larger than that of Table 9, and the total remaining time 3α (μs) is collectively set to one of the four sections. Yes.

Specifically, Table 10 sets the total remaining time 3α to 115 (μs), and randomly distributes 115 (μs) to any one of T1 to T4. When the distribution is performed, the A phase, the B phase, and the C An example is shown in which the amount of deviation (%) in the phase changes randomly.
The deviation (%) shown in Table 10 is added to the reference ink ejection timing, and ink is ejected at the ink ejection timing. The ink landing position at that time is shown in FIG.

  The horizontal and vertical axes shown in FIG. 21B are the same as those in FIG. Compared with FIG. 19B, the variation in the landing position is larger than that in FIG.

  In this way, by slowing down the pixel frequency (kHz), the total remaining time 3α (μs) is randomly set before and after each phase as shown in FIGS. 19 (a), 20 (a), and 21 (a). Set all together. Accordingly, it is possible to form an image by shifting the landing position as shown in FIGS. 19B, 20B, and 21B.

  Further, as shown in FIG. 16B, the remaining time α (μs) is set uniformly after each phase. As a result, no shift amount is added, and an image can be formed without shifting the landing position.

  Next, a table storing the number of divisions of the total remaining time 3α (μs) in each recording mode will be described.

  For example, when the total remaining time 3α is 115 (μs), if the number of divisions is 1, 115 (μs) is randomly set to T1 to T4, and the landing positions are greatly shifted. When the number of divisions is 3, 115/3 = 35 (μs) is set evenly at three locations T2 to T4, and the landing position does not deviate. The effect of changing the number of divisions depending on the ink color is the same as that of the recording head in the first embodiment.

  Table 11 shown in FIG. 22 stores the number of divisions when the total remaining time 3a (μs) is set to 60 (μs) in the four-color automatic mode.

Table 12 shown in FIG. 23 stores the number of divisions when the total remaining time 3a is set to 115 (μs) in the four-color photo mode.
Table 13 shown in FIG. 24 stores the number of divisions when the total remaining time 3a (μs) is set to 30 (μs) in the four-color character mode.
The number of divisions stored in each table is arranged based on the concept described with reference to FIG.

  Next, the flow of image formation in this embodiment will be described with reference to FIG.

  The control board 7 determines whether or not the operator has selected the automatic mode as the image forming mode via the computer 4 or the operation panel 6 (Step 21).

  Next, when the image forming mode is the automatic mode (Step 21: Yes), Table 11 in which the total remaining time 3α (μs) is set to 60 (μs) is specified (Step 22). Then, image formation starts (Step 23).

  When the image forming mode is not the automatic mode (Step 21: No), the control board 7 determines whether or not the operator has selected the photo mode as the image forming mode via the computer 4 or the operation panel 6 (Step 24).

  When the image forming mode is the photographic mode (Step 24: Yes), Table 12 in which the total remaining time 3α (μs) is set to 115 (μs) is specified (Step 25). Then, image formation starts (Step 23).

  When the image forming mode is not the photo mode (Step 24: No), the control board 7 determines whether or not the operator has selected the character mode as the image forming mode via the computer 4 or the operation panel 6 (Step 26).

  When the image forming mode is the character mode (Step 26: Yes), Table 13 in which the total remaining time 3α (μs) is set to 30 (μs) is specified (Step 27). Then, image formation starts (Step 23).

  When the image forming mode is not the character mode (Step 2: No), the process returns to Step 1.

  When the image formation starts, the printer engine 15 stores the image data raster-converted by the RIP 5 in the memory 9 for each color (Step 28), and sequentially stores the stored image data in the buffer 10 (Step 29). ).

  Then, the data analyzer 11 analyzes the stored image data and calculates the pixel occupation rate and the ink acceptance rate. Based on the calculation result, the control board 7 sets the total remaining time 3α (μs) and generates the discharge timing.

  When the control board 7 sets the total remaining time 3α (μs), the control board 7 selects any one of Tables 11 to 13 specified in Step 21, Step 24, and Step 26 from the lookup table 8 according to the selected image mode. Refer to The division number stored in the referenced table is referred to, the division number is randomly set to T1 to T4, and the total remaining time 3α (μs) is divided (Step 30). Then, the control board 7 outputs the ink ejection timing to the data analyzer 11.

  Next, the data analyzer 11 outputs the ejection timing and the image data to the head drive circuit 12 (Step 31).

  Then, it is determined whether or not to end the data transfer (Step 32).

  If the process is to be ended (Step 32: Yes), the image formation is ended (Step 33).

  If not finished (Step 32: No), the image data stored in the buffer 10 is cleared (Step 34), and the process returns to Step 29.

  In the present embodiment, as described above, for example, for the recording head 3 that ejects K ink, as shown in FIG. 16B, the remaining time α (μs) is evenly inserted after each phase. The amount of deviation can be set to a small value, and the deviation of the landing position can be reduced.

  Alternatively, for a recording head that discharges Y ink with low eye sensitivity or a light-colored color, the ratio of dividing the total remainder time 3α (μs) is reduced or collectively set to T1 to T4 at random. The deviation of the landing position can be increased.

  Therefore, a high quality image can be formed by setting the total remaining time 3α (μs) large in the photo mode and setting the total remaining time 3α (μs) small in the character mode.

  Further, even in the same photo mode, the pixel occupancy rate and the ink acceptance amount are calculated by the data analyzer 11, and the maximum deviation amount of the ejection timing is selected from the lookup table 8. By controlling the number of divisions of the total remainder time 3α (μs) and the distribution to T1 to T4 so as to correspond to the maximum deviation amount, the pixel grid is controlled (FIGS. 19B, 20B, and 21). The landing deviation (at the intersection of the horizontal axis and the vertical axis shown in (b)) can be controlled, and an effect equivalent to that of a head capable of controlling the discharge timing for each nozzle can be obtained.

  As described above, this embodiment uses a piezo, has a plurality of nozzles, and controls the total remaining time 3α (μs) even in a head that sequentially ejects ink for each of a plurality of groups. The position can be controlled, and ink can be ejected at ejection timings suitable for line drawings, characters, photographs, etc., and a high-quality image can be formed.

  In the present embodiment, the number of divisions of the total remaining time 3α (μs) and the total remaining time 3α (μs) are put together in T1 to T4, or are equally placed before and after each phase, or divided into a plurality of random numbers. The distribution method, such as whether to distribute to T1 to T4, is controlled. As a result, the landing position can be controlled, ink can be ejected at ejection timings suitable for line drawings, characters, photographs, etc., and a high-quality image can be formed.

  In the analysis region P × Q of the data analyzer 11, the number of pixels P is set equal to the number of nozzles N of the recording head 3. In addition, when the number Q of pixels is set to 1 and a long horizontal line is recorded, for example, the pixel occupancy is close to 100% and the ink acceptance rate is increased, which makes it difficult to distinguish between characters and photographs. turn into. Therefore, the number of pixels Q is desirably an integer greater than 1, and the number of pixels Q is preferably set to about 2 to 5.

  In addition, in order to set the number of divisions for the total remainder time 3α (μs) for each data line, the analysis regions are overlapped and scanned by shifting each line, and the total remainder time 3α (μs) is averaged. It is preferable to determine the number of divisions.

  In each of the above-described embodiments, the image data captured from the computer 4 is temporarily stored in the memory 9 and cut into the buffer 10, and the image information is analyzed by the data analyzer 11. However, the present embodiment is not limited to this. For example, the storage unit having the memory 9 and the buffer 10 in common can capture the image data, and the storage unit can analyze the image information.

  Further, in each of the above-described embodiments, it has been described that the data analyzer 11 refers to the lookup table 8 via the control board 7. The present embodiment is not limited to this, and the same effect can be obtained by providing a plurality of lookup tables inside the data analyzer 11.

  Further, in each of the above-described embodiments, it has been described that the data analyzer 11 outputs the protrusion timing to the head drive circuit 12. Further, the above-described embodiments are not limited to this, and the data analyzer 11 may be configured as a part of the head drive circuit 12.

2 is a block diagram of a control system of the image forming apparatus according to the first embodiment of the present invention. FIG. FIG. 6 is a diagram showing the size of the dot diameter of ink ejected from a nozzle when gradation control is performed to form an image. It is a figure shown about the area | region which a data analyzer analyzes. FIG. 4A shows Table 1 storing the deviation amount for each nozzle, and FIG. 4B shows the ink ejection timing generated by adding the deviation amount stored in Table 1 to the reference ink ejection timing. FIG. 4 is a diagram illustrating a landing position of ink ejected and landed on a recording medium at that time. FIG. 4 is a diagram illustrating a relationship among a data analyzer, a head driving circuit, and a recording head. FIG. 6A shows the landing positions of the inks that are ejected at the reference ink ejection timing and are not shifted in the recording medium direction. FIG. 6B shows a landing position that is slightly shifted in the recording medium direction by adding a deviation amount of 15% at the maximum to the reference ink discharge timing and discharging at the ink discharge timing. FIG. 6C shows a landing position that is largely displaced in the recording medium direction by adding a deviation amount of, for example, a maximum of 30% to the reference ink ejection timing and ejecting at the ink ejection timing. FIG. 6 is a diagram illustrating a relationship between an image density and a hue change (color difference ΔE) caused by a skew of a recording medium. FIG. 5 is a conceptual diagram for obtaining the maximum deviation amount from the size of the dot diameter and the number of dots. The number of dots ejected per unit area (analysis area) on the vertical axis with the dot diameter size as the ink acceptance amount. The ratio is shown as the pixel occupancy on the horizontal axis. It shows about the relationship between dark color ink and light color ink. Table 2 shows the maximum amount of deviation when an image is formed using only dark-colored four-color inks and the operator selects the automatic mode. Table 3 shows the maximum amount of deviation when an image is formed using only dark-colored four-color ink and the operator selects the photo mode. Table 4 is a table 4 in which an image is formed using only dark-colored four-color inks and the maximum shift amount when the operator selects the character mode is stored. FIG. 13A shows Table 5 in which an image is formed using dark-colored four-color ink and the maximum shift amount when the operator selects the photo mode is stored. FIG. 13B shows Table 6 in which an image is formed using light-colored four-color ink and the maximum shift amount when the operator selects the photo mode is stored. 3 is a flowchart illustrating a flow of image formation in the first embodiment. FIG. 15A is a schematic cross-sectional view of the recording head. FIG. 15B is a plan view of the nozzle plate. FIG. 16A shows a time chart for driving the A phase, the B phase, and the C phase. FIG. 16B shows a time chart in which a surplus time α (μs) is provided between the phases. FIG. 16C shows a time chart in which the total remaining time 3α (μs) is randomly provided between the phases. It shows the set interval of the total remainder time 3α (μs). The relationship between the maximum shift amount ΔD (μm) from the pixel grid, 3α (μs) required to generate the maximum shift amount ΔD, and the pixel frequency (kHz) and shift amount (%) in this case is shown. Table 7 is shown. FIG. 19A shows Table 8 showing an example in which the total remainder time 3α (μs) is divided into two and set to any two of the four sections or collectively to any one of the four sections. FIG. 19B shows the landing position of the ink when the deviation amount (%) shown in Table 8 is added to the reference ink discharge timing and ink is discharged at the ink discharge timing. FIG. 20A shows Table 9 showing an example in which the total remaining time 3α (μs) is set to one of the four sections together, and FIG. 20B shows the shift amount shown in Table 9. (%) Is added to the reference ink discharge timing, ink is discharged at the ink discharge timing, and the ink landing position at that time is shown. FIG. 21A shows an example in which Table 10 shows an example in which the total remaining time 3α (μs) is set to be larger than that of Table 9, and the total remaining time 3α (μs) is set to any one of the four sections. FIG. 21B shows the landing position of the ink when the deviation amount (%) shown in Table 10 is added to the reference ink discharge timing and ink is discharged at the ink discharge timing. In the case of the four-color automatic mode, Table 11 storing the number of divisions when the total remaining time 3a (μs) is set to 60 (μs) is shown. In the case of the four-color photo mode, Table 12 storing the number of divisions when the total remaining time 3a is set to 115 (μs) is shown. In the case of the four-color character mode, Table 13 storing the number of divisions when the total remaining time 3a (μs) is set to 30 (μs) is shown. 10 is a flowchart illustrating a flow of image formation in the second embodiment. 1 is a schematic top view of the periphery of a recording head 3 disposed in an image forming apparatus. FIG. 3 is a schematic top view showing an arrangement relationship of each color recording head and a recording medium on which ink is landed in the arrangement relationship. It is the distribution map which measured the hue which arises by the landing of each color, and plotted on the a ^* b ^* plane of L ^* a ^* b ^* space.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Recording medium, 2 ... Conveyance part, 3 ... Recording head, 4 ... Computer, 5 ... RIP, 6 ... Operation panel, 7 ... Control board, 8 ... Look-up table, 9 ... Memory, 10 ... Buffer, 11 ... Data Analyzer: 12 ... Head drive circuit, 13 ... Maintenance station, 15 ... Printer engine, 31 ... Common ink chamber, 32 ... Channel, 33 ... Nozzle plate, 34 ... Nozzle.

Claims (19)

A short recording head having a plurality of ink discharge portions for discharging ink onto a recording medium;
A recording head array in which a plurality of the recording heads are arranged in a direction orthogonal to the recording medium conveyance direction;
A recording head unit in which the recording head row is provided at equal intervals along the recording medium conveyance direction for each of a plurality of ink colors;
A control unit that generates a reference ink discharge timing of ink when discharging from each of the ink discharge units;
A head drive unit that drives the recording head to eject the ink;
In an image forming apparatus comprising:
The control unit sets an arbitrary delay amount for each ink discharge unit and for each reference ink discharge timing, generates an ink discharge timing to which the delay amount is added, and generates the ink discharge timing based on the ink discharge timing. An image forming apparatus, wherein the head driving unit is controlled to discharge the liquid. The controller is
Set the maximum value of the delay amount for each recording head row,
The image forming apparatus according to claim 1, wherein the delay amount for each of the ink ejection units is set within the range of the maximum delay amount.   The image forming apparatus according to claim 2, wherein the control unit sets the maximum delay amount according to an image forming mode set by a user.   The image forming apparatus according to claim 2, wherein the control unit sets the maximum delay amount according to a type of the recording medium.   The image forming apparatus according to claim 2, wherein the control unit sets the maximum delay amount for each of the recording head arrays that eject the different inks.   The control unit sets the maximum delay amount set for the recording head row that discharges the ink having a low ink-specific density characteristic to the recording head row that discharges the ink having a high ink-specific density characteristic. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is larger than the maximum delay amount.   The image forming apparatus according to claim 6, wherein the ink having a low density characteristic specific to the ink is yellow, and the ink having a high density characteristic specific to the ink is black.   The ink having a low density characteristic specific to the ink is a light ink in the same color ink, and the ink having a high density characteristic specific to the ink is a dark ink in the same color ink. Image forming apparatus. The controller is
An average value of the delay amount is set for each recording head row,
The image forming apparatus according to claim 1, wherein the delay amount for each of the ink ejection units is set within the range of the average delay amount. Further comprising a data analysis unit for analyzing the image data,
The image forming apparatus according to claim 2, wherein the control unit sets the delay amount and generates the ink ejection timing based on an analysis result of the data analysis unit.   The image forming apparatus according to claim 10, wherein the data analysis unit analyzes density information of the image data.   When the density information is higher than the first density threshold, the control unit increases the maximum delay amount, and when the density information is lower than the first density threshold, the control unit decreases the maximum delay amount. The image forming apparatus according to claim 11.   12. The image forming apparatus according to claim 11, wherein when the density information is higher than a second density threshold that is higher than the first density threshold, the control unit reduces the maximum delay amount.   The image forming apparatus according to claim 10, wherein the data analysis unit analyzes the number of ejections per predetermined area.   When the ejection number is higher than the first ejection number threshold, the control unit increases the maximum delay amount, and when the ejection number is lower than the first ejection number threshold, the control unit 15. The image forming apparatus according to claim 14, wherein the maximum delay amount is reduced.   16. The image according to claim 15, wherein when the ejection number is higher than a second ink ejection number threshold value that is higher than the first ink ejection number threshold value, the control unit reduces the maximum delay amount. Forming equipment.   11. The image forming apparatus according to claim 10, wherein the data analysis unit analyzes both density information and the number of ejections per predetermined area. A short recording head having a plurality of ink discharge portions for discharging ink onto a recording medium;
A recording head array in which a plurality of the recording heads are arranged in a direction orthogonal to the recording medium conveyance direction;
A recording head unit in which the recording head row is provided at equal intervals along the recording medium conveyance direction for each of a plurality of ink colors;
A control unit that generates a reference ink discharge timing of ink when discharging from each of the ink discharge units;
A head drive unit that drives the recording head to eject the ink;
In an image forming apparatus comprising:
The ink discharge unit is divided into a plurality of groups that can be controlled simultaneously,
The controller is
A total delay time β with respect to a total ink discharge time NT required to make a round of ink discharge from the plurality of ink discharge units divided into the N groups;
A reference ink ejection time NT + β comprising the sum of the total ink ejection time NT and the total delay time β;
And set each
Within the reference ink ejection time NT + β, a total delay time β is alternatively assigned before and after the N ink ejection times T, and the ink ejection timings of the respective groups are generated. An image forming apparatus that controls the head driving unit so as to discharge the ink based on the image forming apparatus. A short recording head having a plurality of ink discharge portions for discharging ink onto a recording medium;
A recording head array in which a plurality of the recording heads are arranged in a direction orthogonal to the recording medium conveyance direction;
A recording head unit in which the recording head row is provided at equal intervals along the recording medium conveyance direction for each of a plurality of ink colors;
A control unit that generates a reference ink discharge timing of ink when discharging from each of the ink discharge units;
A head drive unit that drives the recording head to eject the ink;
In an image forming apparatus comprising:
The short recording head is divided into a plurality of groups in which the plurality of nozzles can simultaneously control ejection,
The controller is
A total delay time β with respect to a total ink discharge time NT required to make a round of ink discharge from the plurality of ink discharge units divided into the N groups;
A reference ink ejection time NT + β comprising the sum of the total ink ejection time NT and the total delay time β;
A plurality of delay times β ′ obtained by dividing the total delay time β into random amounts, and
And set each
Within the reference ink discharge time NT + β, the plurality of delay times β ′ are respectively assigned to a plurality of arbitrary timings before and after the N ink discharge times T, and the ink discharge timings of the respective groups are generated. An image forming apparatus, wherein the head driving unit is controlled to discharge the ink based on an ink discharge timing.

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