JP5417052B2 - Inkjet printing device - Google Patents

Description

  The present invention relates to an inkjet printing apparatus that performs printing on a print medium by ejecting ink with an inkjet head.

  In a line-type ink jet printing apparatus having a plurality of ink jet heads for ejecting ink, there may be a difference in print density between the ink jet heads due to the characteristics of each ink jet head.

  Therefore, in general, maintenance personnel who maintain the inkjet printing apparatus need to adjust the inkjet heads so that there is no difference in print density between the inkjet heads.

  Patent Document 1 proposes an ink jet recording apparatus that adjusts the voltage difference for ejecting ink droplets from nozzles for each ink jet and adjusts the density of the entire plurality of ink jet heads.

JP 2006-137040 A

  However, in the ink jet recording apparatus described in Patent Document 1, the maintenance staff adjusts the voltage difference for ejecting ink droplets from the nozzles for each ink jet by checking the printing paper printed with a single solid color. Depending on the ink color, it may be difficult to adjust the value of the ejection voltage.

  For example, when checking printing paper printed with an ink color with low visibility such as yellow (Y), it is difficult to determine the difference in printing density, and it is difficult to appropriately adjust the voltage difference. This makes it difficult to adjust the ink jet head so that there is no difference in print density between ink jet heads.

  The present invention has been made in view of the above problems, and an inkjet printing apparatus capable of easily adjusting the density of each inkjet head even in an inkjet head having a low visibility color. The purpose is to provide.

In order to achieve the above object, a first feature of an ink jet printing apparatus according to the present invention is that an ink reservoir chamber for storing ink is provided, and an ink jet head for discharging the ink from a nozzle communicating with the ink reservoir chamber is provided. an inkjet unit respectively for each ink color of the ink in the conveying direction and a direction that is substantially perpendicular of the printing sheet transported a plurality arranged, the first color ink to color before Symbol printing paper to the ink jet head After printing an image on the printing paper by discharging, the discharged ink of the first color is applied to the same surface of the printed printing paper rotated substantially perpendicular to the transport direction. by superimposing and printing an image by ejecting a second color ink other than the ink of the first color and the ejection to the ink-jet head printing And control means, and an image reading means for reading an image of the printed the printed sheet, the image based on the image read by the reading means, low visibility of the first color and of the second color Discharge correction means for calculating a density correction coefficient for correcting an ink discharge amount by the ink jet head so as to eliminate a print density difference between the ink jet heads in an ink color, and the first color and the first color One of the two colors is a color with low visibility, and the other is a color other than a color with low visibility.

  According to the ink jet printing apparatus according to the present invention, even in an ink jet head having a low visibility, adjustment can be easily performed so that the density of each ink jet head is uniform.

1 is a diagram illustrating a schematic configuration of an inkjet printing apparatus according to an embodiment of the present invention. It is a top view of the inkjet head unit with which the printing part of the inkjet printing apparatus which concerns on embodiment of this invention is provided. (A) is sectional drawing of the inkjet head with which the inkjet printing apparatus 1 which concerns on embodiment of this invention is provided, (b) is the lower surface of the inkjet head with which the inkjet printing apparatus 1 which concerns on embodiment of this invention is provided. FIG. It is a functional block diagram which shows the functional structure of the inkjet printing apparatus which concerns on embodiment of this invention. It is the flowchart which showed the process sequence of the density adjustment process by the inkjet printing apparatus which concerns on embodiment of this invention. It is the figure which showed an example of the screen displayed on the display / input panel of the operation panel of the inkjet printing apparatus which concerns on embodiment of this invention. It is a figure showing an example of paper P printed by cyan (C) and yellow (Y) by the ink jet printer concerning an embodiment of the invention. It is the figure which showed an example of the message displayed on the display / input panel of the operation panel with which the inkjet printing apparatus which concerns on embodiment of this invention is provided. FIG. 5 is a diagram illustrating an example of a sheet when the same direction printing mode is selected in the inkjet printing apparatus according to the embodiment of the present invention. FIG. 5 is a diagram illustrating an example of a sheet when a 90 ° rotation mode is selected in the inkjet printing apparatus according to the embodiment of the present invention. It is the flowchart which showed the process sequence of the printing process by the inkjet printing apparatus which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Overall configuration of inkjet printing apparatus>
FIG. 1 is a diagram showing a schematic configuration of an ink jet printing apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an ink jet printing apparatus 1 according to the present embodiment includes an image reading unit 2, a paper feeding unit 3, a printing unit 4, a paper discharging unit 5, an operation panel unit 6, and a control unit. 7.

  The image reading unit 2 is provided on the upper part of the ink jet printing apparatus 1 and photoelectrically reads an image of a document that is an object to be copied by an apparatus such as a scanner, and R, G, and B of each pixel constituting the image. The component digital image signal is output. The digital image signal output from the image reading unit 2 is input to the control unit 7 and subjected to predetermined image processing. Based on the processed digital image signal, the printing unit 4 prints an image on a sheet. .

  The paper feed unit 3 includes a paper feed base 8 on which the paper P, which is a printing medium, is stacked, a paper feed roller 9 that picks up and conveys the paper P one by one from the paper feed base 8, and a paper feed roller 9 And a registration roller pair 10 that corrects the skew feeding of the paper P conveyed from the printer and supplies it to the printing unit 4 at a predetermined timing. The registration roller pair 10 is intermittently rotated by a drive source (not shown).

  The printing unit 4, based on the digital image signal output from the control unit 7, ejects ink, which is a color material for image formation, and attaches it to the paper P to print an image; A conveyance unit 12 that conveys the paper P fed out from the paper supply unit 3 to the inkjet head unit 11, a double-side conveyance unit 13 that conveys the paper P that has been printed on one side in double-sided printing in the direction of arrow B, and single-sided in double-sided printing A double-sided stack tray 14 on which the printed paper P is once discharged.

  The inkjet head unit 11 has a plurality of line-type inkjet heads 110 to 117 in which a plurality of nozzles are arranged in a direction orthogonal to the transport direction of the paper P.

  The ink jet heads 110 to 117 are arranged above the transport unit 12 at predetermined intervals, and in order from the paper feeding side, black (K), cyan (C), magenta (M), and yellow (Y) inks are printed on paper. It discharges to P. At the time of printing, various colors are formed by ejecting these inks superimposed on the same pixel. The ink jet heads 110 to 117 are supplied with ink from an ink cartridge having an ink tank via an ink supply path (both not shown).

  The transport unit 12 includes an annular transport belt 15 that rotates, a drive roller 16 that drives the transport belt 15 to rotate, and a transport belt roller 17 that is a follower roller of the drive roller 16. The transport belt 15 is an endless belt having a large number of holes, adsorbs the paper P by negative pressure generated by sucking air from the holes by a suction fan (not shown), and transports the paper P in the direction of arrow A. To do.

  The paper discharge unit 5 stores the paper P on which an image is printed by the inkjet head unit 11.

  The operation panel unit 6 includes an operation key, a display / input panel, and the like. Various operations such as printing start are performed when the user presses the operation key or touches the display / input panel. The requested operation signal is generated, and the generated operation signal is supplied to the control unit 7.

  The control unit 7 performs central control of the inkjet printing apparatus 1.

  FIG. 2 is a plan view of the inkjet head unit 11 provided in the printing unit 4.

  The inkjet head unit 11 includes inkjet heads of black (K), cyan (C), magenta (M), and yellow (Y). Specifically, the inkjet head unit 11 includes inkjet heads 110a to 110c and inkjet heads 111a to 111c that store black (K) ink, and inkjet heads 112a to 112c and inkjet heads that store cyan (C) ink. 113a to 113c, inkjet heads 114a to 114c and inkjet heads 115a to 115c storing magenta (M) ink, and inkjet heads 116a to 116c and inkjet heads 117a to 117c storing yellow (Y) ink. .

  The inkjet heads 110a to 110c and the inkjet heads 111a to 111c are arranged in two rows in the main scanning direction so that black (K) ink can be ejected without gaps in the main scanning direction of the paper P being conveyed. ing.

  Similarly, in the inkjet heads of cyan (C), magenta (M), and yellow (Y) colors, cyan (C), magenta (M), and magenta (M), respectively, without gaps in the main scanning direction of the conveyed paper P. In order to be able to eject yellow (Y) ink, each is arranged in two rows in the main scanning direction.

  The ink jet heads 110a to 110c are provided with an ink reservoir chamber for storing black (K) ink, and a piezo element is disposed as a piezoelectric element in the ink reservoir chamber. Then, when an ejection voltage is applied to the piezo element, ink is ejected from a nozzle communicating with the ink reservoir chamber.

  3A is a cross-sectional view of the inkjet head 110a included in the inkjet printing apparatus 1 according to the embodiment of the present invention, and FIG. 3B is a cross-sectional view of the inkjet printing apparatus 1 according to the embodiment of the present invention. It is a bottom view of the inkjet head 110a provided.

  As shown in FIGS. 3A and 3B, in the inkjet head 110a, a plurality of nozzles 110n are formed on the nozzle plate 110np, for example, at a density of 300 nozzles per inch (300 dpi) along the main scanning direction. In addition, corresponding to each nozzle 110n, each ink reservoir chamber 110ir for temporarily storing the black (K) ink IK is formed with both sides surrounded by partition walls 110k.

  A plurality of piezo elements 110p are fixed to each nozzle 110n on a diaphragm 110s opposed to the nozzle plate 110np with each ink reservoir 110ir interposed therebetween.

  Therefore, for example, when an ejection voltage is applied to the piezo element 110p arranged second from the left in the drawing, the diaphragm 110s is displaced toward the nozzle 110n corresponding to the piezo element 110p, so that the ink corresponding to the piezo element 110p and the nozzle 110n. Ink IK is ejected from the nozzles 110n due to volume changes in the reservoir 110ir.

  Similarly, black (K), cyan (C), magenta (M), and yellow (Y) inkjet heads 112 to 117 included in the inkjet head unit 11 have the same configuration as the inkjet head 110a.

  As described above, the inkjet printing apparatus 1 according to the embodiment of the present invention includes six inkjets in the main scanning direction for each color of black (K), cyan (C), magenta (M), and yellow (Y). Thus, ink is ejected without a gap in the main scanning direction, and printing is performed on the paper P conveyed in the sub-scanning direction (conveying direction). Therefore, due to the characteristics of the respective inkjet heads 110 to 117, the ejection amounts ejected by the inkjet heads 110 to 117 based on images of the same color and the same density become non-uniform, that is, the inkjet head 110 printed on the paper P. A print density difference between ˜117 may occur.

  Therefore, in the inkjet printing apparatus 1 according to the embodiment of the present invention, the ejection voltage of the inkjet head is adjusted so that there is no difference in print density between inkjet heads.

<Functional Configuration of Inkjet Printing Apparatus 1>
FIG. 4 is a functional configuration diagram showing a functional configuration of the inkjet printing apparatus 1 according to the embodiment of the present invention.

  As shown in FIG. 4, the inkjet printing apparatus 1 includes an image reading unit 2, a paper feeding unit 3, a printing unit 4, a paper discharge unit 5, an operation panel unit 6, and a control unit 7. Among these configurations, the image reading unit 2, the paper feeding unit 3, the printing unit 4, and the paper discharge unit 5 have been described above, and a description thereof will be omitted.

  The operation panel unit 6 is provided on the upper part of the inkjet printing apparatus 1 and inputs a display / input panel 61, a start key for starting a printing operation, a stop key for stopping a printing operation, and the number of prints. Various operation keys such as a numeric keypad (not shown) for supplying the operation signal to the control unit 7 based on a user operation.

  The display / input panel 61 of the operation panel unit 6 includes a pressure-sensitive or electrostatic transparent touch panel disposed on the front surface and a liquid crystal display panel (none of which is shown) disposed on the back surface of the touch panel. doing. The user can perform various setting input operations by directly touching the surface of the touch panel with a finger or the like while viewing the display screen of the liquid crystal display panel.

  The display / input panel 61 designates printing conditions such as a printing mode (normal printing mode or test pattern printing mode), which will be described later, and a sub mode (same direction printing mode or 90 ° rotation mode) according to a user operation. Display a screen for

  Further, the display / input panel 61 displays a screen for selecting an ink color for adjusting the print density between the inkjet heads in accordance with a user operation.

  The control unit 7 includes a RAM 71, a ROM 72, and a control unit 75.

  The RAM 71 is composed of a volatile semiconductor or the like, and stores data or the like necessary for the control unit 75 to execute various processes. Further, the RAM 71 eliminates the difference in printing density between the inkjet heads of the same color, that is, the ejection amount of ink ejected for each inkjet head based on the image of the same color and the same density is made uniform. A density correction coefficient for each ink jet head calculated by an ejection correction unit 75a described later is stored.

  The ROM 72 is composed of a nonvolatile semiconductor or the like and stores various control programs executed by the control unit 75.

  The ROM 72 stores the luminance of each color of black (K), cyan (C), magenta (M), and yellow (Y) as a luminance table. Further, the ROM 72 stores a reference luminance corresponding to a combination of cyan (C) and yellow (Y) and a reference luminance corresponding to a combination of magenta (M) and yellow (Y) as a luminance reference table. Here, the reference luminance is such that the print density difference between the inkjet heads is eliminated, that is, the ejection amount of ink ejected for each inkjet head based on images of the same color and the same density is made uniform. This is a preset print density that is a reference when the test pattern printing mode is selected.

  The control unit 75 includes an ejection correction unit 75a and a print control unit 75b in terms of its functions.

  The discharge correction unit 75a is a density correction for correcting the discharge voltage applied to the inkjet head based on the image read by the image reading unit 2 so as to eliminate the print density difference between the inkjet heads in the same ink color. Calculate the coefficient.

  When the test pattern printing mode is selected, the printing control unit 75b prints an image on the paper P by causing the ink jet head to eject ink with low visibility and other one color, respectively. 4 is printed.

  In addition, when the normal printing mode is selected, the print control unit 75b determines the ink discharge amount based on the image read by the image reading unit 2 and the density correction coefficient for each inkjet head stored in the RAM 71. The image is printed, and the image is printed on the paper P by causing the ink jet head to eject ink with the calculated ink ejection amount.

<Operation of Inkjet Printing Apparatus 1>
Next, the operation of the ink jet printing apparatus 1 according to the embodiment of the present invention will be described.

  The inkjet printing apparatus 1 according to the embodiment of the present invention mainly performs density adjustment processing and printing processing. Therefore, each process will be described in detail below.

≪Density adjustment process≫
Details of the density adjustment processing in the inkjet printing apparatus 1 according to the embodiment of the present invention will be described.

  FIG. 5 is a flowchart showing a processing procedure of density adjustment processing by the inkjet printing apparatus 1 according to the embodiment of the present invention.

  As shown in FIG. 5, the control unit 75 determines whether or not the test pattern printing mode / sub mode is set (step S101). Specifically, the control unit 75 determines whether or not an operation signal for setting the test pattern print mode and an operation signal for setting the sub mode are supplied from the display / input panel 61 of the operation panel unit 6 by a user operation. Determine. Here, the test pattern printing mode refers to a printing mode for adjusting the ejection voltage of the inkjet head.

  FIG. 6 is a diagram showing an example of a screen displayed on the display / input panel 61 of the operation panel 6 of the inkjet printing apparatus 1 according to the embodiment of the present invention.

  As shown in FIG. 6, the display / input panel 61 displays a normal print mode 202 and a test pattern print mode 203 as settable print modes. When the test pattern printing mode 203 is set, a unidirectional printing mode 204 and a 90 ° rotation printing mode 205 are further displayed as settable sub-modes.

  The user performs an operation of selecting one of the normal printing mode 202 and the test pattern printing mode 203. When the user performs an operation of selecting the test pattern printing mode 203, an operation of selecting one of the same direction printing mode 204 and the 90 ° rotation printing mode 205 is further performed.

  Thereafter, when the user depresses the setting button 206, the operation panel 6 generates an operation signal corresponding to the user's operation, and supplies the generated operation signal to the control unit 75.

  The control unit 75 causes the RAM 71 to store the set print mode (normal print mode or test pattern print mode) and sub mode (same direction print mode or 90 ° rotation print mode) based on the supplied operation signal. .

  If it is determined in step S101 that the test pattern printing mode is selected (in the case of YES), the control unit 75 selects the head among black (K), cyan (C), magenta (M), and yellow (Y). It is determined which is selected as the density adjustment color for adjusting the interval (step S103). Specifically, the control unit 75 adjusts the density between the heads of black (K), cyan (C), magenta (M), and yellow (Y) from the operation panel unit 6 by a user operation. It is determined whether or not an operation signal indicating the ink color selected as the color has been supplied.

  If it is determined in step S103 that the density adjustment color has been selected (in the case of YES), the user sets a non-printed white or near-colored paper P in the image reading unit 2, and then the control unit In step S105, it is determined whether reading is requested. Specifically, the control unit 75 determines whether or not an operation signal requesting to start reading is supplied from the operation panel unit 6 by a user operation.

  If it is determined in step S105 that the start of reading has been requested, the image reading unit 2 reads the image of the set paper P (step S107). Specifically, the image reading unit 2 generates digital image signals of R component, G component, and B component of the loaded paper P, and supplies the generated digital image signal to the control unit 75.

  Next, the control unit 75 converts the digital image signals of the R component, G component, and B component supplied from the image reading unit 2 into luminance signals (step S109).

  Then, based on the luminance signal converted in step S109 and the luminance table stored in the ROM 72, the control unit 75 determines the luminance of the color of the paper P (paper color) and the density adjustment color selected in step S103. It is determined whether or not the difference from the luminance exceeds a predetermined threshold value (step S111). Specifically, the control unit 75 extracts the luminance of the density adjustment color selected in step S103 from the luminance table stored in the ROM 72, and calculates the difference from the luminance converted in step S109. Then, the control unit 75 determines whether or not the calculated difference exceeds a predetermined threshold value. Here, if the difference between the brightness of the paper color and the brightness of the density adjustment color exceeds a predetermined threshold, the density adjustment color has high visibility with respect to the paper color, and the brightness and density adjustment of the paper color. If the difference from the luminance of the color is equal to or less than a predetermined threshold, it is determined that the density adjustment color has low visibility with respect to the paper color.

  If it is determined in step S111 that the difference between the brightness of the paper color and the brightness of the density adjustment color has exceeded a predetermined threshold (in the case of YES), the print control unit 75b uses the density adjustment color ink. Printing is performed (step S113). Specifically, the sheet feeding unit 3 picks up the sheets P stacked on the sheet feeding table 8 one by one and conveys them to the printing unit 4 by the conveying unit 12. Printing is performed by ejecting ink onto the paper P. The paper discharge unit 5 discharges the paper P printed with the density-adjusted color ink.

  On the other hand, if it is determined in step S111 that the difference between the brightness of the paper color and the brightness of the density adjustment color is equal to or less than a predetermined threshold value (in the case of NO), the control unit 75 has selected the superimposed color. It is determined whether or not (step S115). Specifically, the control unit 75 uses the operation panel 6 by the user's operation to select any one of black (K), cyan (C), magenta (M), and yellow (Y) as a superimposed color. It is determined whether an operation signal to be selected is supplied.

  If it is determined in step 115 that the superimposed color has been selected (YES), the control unit 75 determines whether or not a print start is requested (step S117). Specifically, the control unit 75 determines whether or not an operation signal for requesting to start printing is supplied from the operation panel unit 6 by a user operation.

  In step S117, when it is determined that the print start is requested (in the case of YES), the control unit 75 determines which of the same direction print mode and the 90 ° rotation print mode is the sub mode stored in the RAM 71. Determination is made (step S119).

  If it is determined in step S119 that the same direction printing mode is set, the density adjustment color ink and the superimposed color ink selected in step S115 are superimposed and printed (step S121). Specifically, the sheet feeding unit 3 picks up the sheets P stacked on the sheet feeding table 8 one by one and conveys them to the printing unit 4 by the conveying unit 12. Printing is performed by ejecting ink and superimposed color ink onto the paper P, respectively. Then, the paper discharge unit 5 discharges the paper P printed with the density adjustment color and the superimposed color ink.

  FIG. 7 is a diagram illustrating an example of the paper P printed with the density adjustment color and the superimposed color by the inkjet printing apparatus 1 according to the embodiment of the present invention. Here, yellow (Y) is selected as the density adjustment color, cyan (C) is selected as the superimposed color, and the paper color of the paper P is white.

  As shown in FIG. 7, the print density of the print images 201, 202, 204, and 206 printed by the yellow (Y) inkjet heads 117a, 116a, 116b, and 116c, and the yellow (Y) inkjet heads 117b and 117c. The print density of the printed images 203 and 205 is different. In such a case, yellow (Y) has low visibility with respect to the paper color of the paper P, and as described later, it is difficult for the image reading unit 2 to detect this difference in print density. .

  Therefore, images 211 and 112 printed on paper P printed in yellow (Y) are superimposed by cyan (C) inkjet heads 113a, 112a, 113b, 112b, 113c, and 112c, which are superimposed colors. 212, 213, 214, 215, 216.

  Thus, cyan (C) with high visibility with respect to the paper color of the paper P is superimposed on the print image printed with yellow (Y) with low visibility with respect to the paper color of the paper P. As a result, the density difference of the printing density of yellow (Y) becomes remarkable. Thereby, as will be described later, the image reading unit 2 can detect a difference in print density of yellow (Y).

  On the other hand, if it is determined in step S119 that the 90 ° rotation printing mode is set, ink of density adjustment color (here, yellow (Y) is selected as the density adjustment color) is used. And printing (step S123). Specifically, the sheet feeding unit 3 picks up the sheets P stacked on the sheet feeding table 8 one by one and conveys them to the printing unit 4 by the conveying unit 12, and the printing unit 4 displays yellow (Y). Printing is performed by ejecting the ink on the paper P. The paper discharge unit 5 discharges the paper P printed with yellow (Y) ink.

  Next, the operation panel 6 displays a message on the display / input panel 61 for instructing the discharged paper P to be rotated 90 ° with respect to the transport direction and set in the paper feeding unit 3 (step S125). .

  FIG. 8 shows an example of a message displayed on the display / input panel 61.

  As shown in FIG. 8, for example, the operation panel 6 displays a message such as “Please rotate and set the paper by 90 °” on the display / input panel 61.

  Then, after the user rotates the discharged paper P by 90 ° with respect to the transport direction and stacks the paper P on the paper feed tray 8, the control unit 75 determines whether or not a print start is requested. (Step S127).

  When it is determined in step S127 that the start of printing has been requested (in the case of YES), the superimposed color ink selected in step S115 (here, cyan (C) ink is selected as the superimposed color). Is used for printing (step S129).

  FIG. 9 is a diagram showing an example of the paper P when the same direction printing mode is selected in the inkjet printing apparatus 1 according to the embodiment of the present invention, and FIG. 10 is a diagram in which the 90 ° rotation mode is selected. FIG. 6 is a diagram showing an example of a sheet P in a case where

  In step S121, when printing is performed with the yellow (Y) ink and the cyan (C) ink superimposed, there is a print density difference between the cyan (C) ink jet heads or the yellow (Y) ink jet. It may be difficult to detect whether there is a print density difference between the heads.

  Specifically, as shown in FIG. 9, the print density of the print images 201, 202, 204, and 206 printed by the yellow (Y) inkjet heads 117a, 116a, 116b, and 116c, and the yellow (Y) inkjet The print density of the print images 203 and 205 printed by the heads 117b and 117c is different, and the print images 241, 244 and 245 printed by the cyan (C) ink jet heads 113a, 112b, 113c and 112c. When the print density of H.246 is different from the print density of the print images 242 and 243 printed by the cyan (C) inkjet heads 112a and 113b, cyan (C) and yellow (Y) are printed on the paper P. If the transport direction is the same, the cyan (C) ink Whether there is a print density difference between Ttoheddo, or print density difference between the ink jet head for yellow (Y) to detect whether there from becoming difficult.

  For example, a print image 232 printed by superimposing cyan (C) on a print image printed in yellow (Y) has a print density difference between cyan (C) inkjet heads, or yellow (Y) It is difficult to detect whether there is a print density difference between the inkjet heads.

  On the other hand, as shown in FIG. 10, in step S123, printing is performed with yellow (Y) ink, and the paper P is rotated 90 ° with respect to the transport direction and then printed with cyan (C) ink. In this case, the print density of the printed images 201, 202, 204, and 206 printed by the yellow (Y) inkjet heads 117a, 116a, 116b, and 116c, and the yellow (Y) inkjet heads 117b and 117c are printed. The print density of the print images 203 and 205 is different, and the print density of the print images 244 and 245 printed by the cyan (C) ink jet heads 112b and 113c and the print density of the cyan (C) ink jet head 113b are printed. Suppose the print density of the printed image 243 is different

  Even in such a case, the image reading unit 2 is printed by the yellow (Y) inkjet heads 117a, 116a, 117b, 116b, 117c, and 116c, and is printed by the cyan (C) inkjet head 113c. , 252, 253, 254, 255, and 256, the print density difference between the yellow (Y) inkjet heads can be detected regardless of the print density difference between the cyan (C) inkjet heads.

  Next, after the user sets the paper P printed with cyan (C) ink in the image reading unit 2, the control unit 75 determines whether or not a reading start is requested (step S131). Specifically, the control unit 75 determines whether or not an operation signal requesting to start reading is supplied from the operation panel unit 6 by a user operation.

  When it is determined in step S131 that the reading start is requested, the image reading unit 2 reads the image of the set paper P (step S133). Specifically, the image reading unit 2 generates digital image signals of R component, G component, and B component of the loaded paper P, and supplies the generated digital image signal to the control unit 75.

  Next, the control unit 75 converts the digital image signals of the R component, G component, and B component supplied from the image reading unit 2 into luminance signals (step S135).

  Then, the discharge correction unit 75a of the control unit 75 calculates a density correction coefficient based on the luminance signal converted in step S135 (step S137). Specifically, first, the ejection correction unit 75a averages the luminance signal for each inkjet head. Then, the discharge correction unit 75a extracts the reference brightness of cyan (C) and yellow (Y) from the brightness reference table stored in the ROM 72, and averages the brightness of each inkjet head with respect to the extracted reference brightness. The ratio is calculated, and the calculated value is used as the density correction coefficient.

  Next, the control unit 75 stores the density correction coefficient for each ink jet calculated in step S137 in the RAM 71 (step S139).

  As described above, according to the inkjet printing apparatus 1 according to the embodiment of the present invention, the test pattern printing mode is selected, and the density between the inkjet heads is adjusted with respect to the inkjet head having a color with low visibility relative to the paper color. In this case, for example, printing is performed using an ink color ink with low visibility such as yellow (Y) when the paper color is white and the other one color ink, and the printed paper P The density correction coefficient for correcting the ejection voltage applied to the inkjet head is determined so as to eliminate the print density difference of the same ink color between the inkjet heads based on the image read from Easily eliminate print density differences between inkjet heads even in inkjet heads with low visibility. It is possible to adjust the urchin inkjet head.

  Further, according to the inkjet printing apparatus 1 according to the embodiment of the present invention, when the same direction printing mode is selected, the yellow (Y) ink (without rotating the paper P by 90 ° with respect to the transport direction) Since ink of ink having low visibility with respect to paper color and cyan (C) ink (ink that does not correspond to ink with low visibility with respect to paper color) are overlaid and printed, cyan (C) When the print density difference between the inkjet heads is stored, the user can adjust the inkjet head more quickly while saving the trouble of rotating the paper P.

  Furthermore, according to the inkjet printing apparatus 1 according to the embodiment of the present invention, when the 90 ° rotation mode is selected, the transport direction when printing cyan (C) and yellow (Y) on the paper P is 90. Therefore, even when there is a print density difference between cyan (C) inkjet heads, it is possible to easily detect a print density difference for each yellow (Y) inkjet head and eliminate this print density difference. The ink jet head can be adjusted.

  In the above-described embodiment, the case where the paper P is white or a color that is normally used has been described. However, the present invention is not limited to this, and the printing density difference between the inkjet heads is corrected using colored paper or the like. It is also possible to do.

≪Print processing≫
Details of the printing process in the inkjet printing apparatus 1 according to the embodiment of the present invention will be described.

  FIG. 11 is a flowchart showing the processing procedure of the printing process by the inkjet printing apparatus 1 according to the embodiment of the present invention.

  As shown in FIG. 11, the control unit 75 determines whether or not the normal printing mode is selected (step S201). Specifically, the control unit 75 determines whether or not an operation signal for setting the normal print mode is supplied from the operation panel unit 6 by a user operation. Here, the normal print mode refers to a print mode in which printing is performed based on an image read by the image reading unit 2.

  If it is determined in step S201 that the normal printing mode has been selected (YES), the control unit 75 determines whether or not the start of printing has been requested (step S202).

  If it is determined in step S202 that the start of printing has been requested (in the case of YES), the image reading unit 2 reads an image of the document (step S203). Specifically, the image reading unit 2 photoelectrically reads an image of a document as a copy by a built-in scanner and outputs digital image signals of R component, G component, and B component of each pixel constituting the image. The generated digital image signal is supplied to the control unit 75.

  Next, the print control unit 75b of the control unit 75 reads the density correction coefficient for each inkjet head stored in the RAM 71 (step S204).

  Then, the print control unit 75b of the control unit 75 calculates the ink discharge amount based on the image read by the image reading unit 2 in step S203 and the density correction coefficient for each inkjet head read in step S204. Then, an image is printed on the paper P by causing the ink jet head to eject ink with the calculated ink ejection amount (step S205).

  As described above, according to the inkjet printing apparatus 1 according to the embodiment of the present invention, when the test pattern printing mode is selected and the density between the inkjet heads is adjusted for the inkjet head having a low visibility color, the visual recognition is performed. Based on the image read from the printed paper P, the same ink color print density difference between the inkjet heads is eliminated. Thus, when the density correction coefficient for correcting the ejection voltage applied to the inkjet head is determined and the normal printing mode is selected, the ejection voltage is determined based on the determined density correction coefficient and printing is performed. Even in an inkjet head with low visibility, there is no difference in print density between inkjet heads. You can print, it is possible to improve the quality of printing. In particular, when printing is performed on the entire surface of the paper P using a color with low visibility, there is no difference in print density between the inkjet heads, and a good printed matter can be obtained.

  In the inkjet printing apparatus 1 according to the embodiment of the present invention, when ink is ejected from the nozzles communicating with the ink reservoir chamber, the ejection voltage is applied to each piezoelectric element (piezoelectric element) provided corresponding to each nozzle. Although a piezo method is employed in which the vibration plate is applied to displace the ink in the ink reservoir chamber from the nozzles, the present invention is not limited to this. For example, a film boiling state occurs when the ink is heated by an electrostatic method in which an ejection voltage is applied to the electrostatic gap to displace the diaphragm to eject ink from the nozzles from the nozzles, or by a minute heater in the ink reservoir. A film boiling ink jet method in which ink is ejected from a nozzle by a pressure change caused by bubbles generated by the bubbles may be applied.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printing apparatus 2 ... Image reading part 3 ... Paper feed part 4 ... Printing part 5 ... Paper discharge part 6 ... Operation panel part 7 ... Control unit 11 ... Inkjet head unit 12 ... Conveyance part 61 ... Display / input panel 75 ... Control part 75a ... Discharge correction part 75b ... Print control part 110a-110c, 111a-111c, 112a-112c, 113a-113c, 114a-114c, 115a-115c, 116a-116c, 117a-117c ... Inkjet head 110ir ... Ink reservoir Chamber 110k ... Partition 110n ... Nozzle 110p ... Piezo element (piezoelectric element)
110s ... Diaphragm

Claims (1)

An ink reservoir chamber for storing ink is provided, and an ink jet head that discharges the ink from a nozzle communicating with the ink reservoir chamber is set for each ink color of the ink in a direction substantially perpendicular to the transport direction of the transported printing paper. A plurality of inkjet units,
After printing an image on the printing paper by ejecting a first ink color to the color of the previous SL printing paper to the ink jet head, the printed which is rotated substantially at right angles to the transport direction against the same surface of the printing paper, the discharge was superimposed on the ink of the first color, by discharging a second color ink other than the first color ink the ejection to the ink-jet head Print control means for printing an image;
Image reading means for reading an image of the printed printing paper;
Based on the image read by the image reading means, the ink by the ink jet head so as to eliminate the print density difference between the ink jet heads in the ink color having low visibility among the first color and the second color. and a discharge correcting means for calculating a density correction coefficient for correcting the ejection amount,
One of the first color and the second color is a color with low visibility, and the other is a color other than a color with low visibility .

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