JP5883313B2 - Image recording apparatus, correction coefficient acquisition method, and image recording method - Google Patents

Description

  The present invention relates to an image recording apparatus and an image recording method for recording an image by an ink jet method, and a correction coefficient for acquiring a correction coefficient used for correcting an ink ejection amount from the plurality of ejection ports in the image recording apparatus. It relates to the acquisition method.

  2. Description of the Related Art Conventionally, an image recording apparatus that records an image on a recording medium by an ink jet method by moving a discharge unit in which a plurality of nozzles that discharge minute ink droplets are arranged relative to the recording medium. It is used. In such an apparatus, the amount of ink discharged from a plurality of nozzles varies depending on the processing accuracy of the nozzles and the mounting accuracy of the discharge portions, and as a result, uneven density and uneven stripes occur on the recording medium. Sometimes.

  In the ink jet recording apparatus disclosed in Patent Document 1, a technology for suppressing density unevenness is obtained by printing a basic pattern for density unevenness measurement, imaging it with a CCD line sensor, and assigning a correction function to each nozzle based on the imaging result. It is disclosed.

  On the other hand, in Patent Document 2, in an electrophotographic color copying apparatus, using a plurality of achromatic patches having different gradation levels and a plurality of different chromatic patches, variations in the spectral sensitivity of the CCD of the scanner unit, and the like. Techniques for correcting are disclosed.

Japanese Patent No. 3160318 JP 2009-135704 A

  By the way, in the ink jet recording apparatus of Patent Document 1, due to variations in spectral sensitivity of a plurality of image sensors (CCD) in a CCD line sensor, light amount unevenness of a light source, aged deterioration, and the like, There is a risk that density unevenness is erroneously detected at a position where there is no density unevenness. As a result, the amount of ink discharged from each nozzle is excessively corrected, and determination of a correction function for each nozzle (ie, discharge correction for each nozzle) takes a long time.

  In the color copying apparatus of Patent Document 2, it is necessary to use a plurality of achromatic patches having different gradation levels and a plurality of different chromatic patches in order to correct variations in the spectral sensitivity of the CCD of the scanner unit. A great deal of time is required to correct the dispersion of spectral sensitivity.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to perform efficient and highly accurate discharge correction while suppressing excessive correction.

The invention according to claim 1 is an image recording apparatus that records an image by an ink jet method, and ejects a minute droplet of ink from a plurality of ejection openings arranged in an ejection opening arrangement direction toward a recording medium. By controlling the ejection unit, the movement mechanism that moves the recording medium relative to the ejection unit in a movement direction that intersects the ejection port arrangement direction, and the ejection unit and the movement mechanism, the recording is performed. A control unit that records an image on a medium; an imaging unit that includes a plurality of imaging elements arranged in an element arrangement direction that intersects the moving direction; and a plurality of ejection ports that are used to record an image on the recording medium. A storage unit that stores a correction coefficient used for correcting the ink ejection amount of the ink, and the control unit acquires a plurality of test images by imaging a test pattern having a predetermined target density a plurality of times by the imaging unit. To test An image acquisition unit, a density variation width acquisition unit that obtains a density variation range that is a difference between a maximum value and a minimum value of an output from an image sensor corresponding to each ejection port, based on the plurality of test images; A correction image acquisition unit that records a correction pattern on a correction medium so as to achieve the target density by the unit, captures the correction pattern by the imaging unit, and acquires a correction image; and A density error that is the difference between the output density that is output from the image sensor corresponding to each ejection port and the target density is obtained, and the density error is determined based on the density fluctuation range corresponding to the density error . A correction coefficient acquisition unit that determines a correction coefficient of the ejection port based on the density error when the value is equal to or greater than the value;

  A second aspect of the present invention is the image recording apparatus according to the first aspect, wherein the moving mechanism reciprocally moves the medium on which the test pattern is recorded relative to the imaging unit in the moving direction. The test image acquisition unit is movable, and the medium in which the test pattern is recorded is reciprocated relative to the imaging unit, and the imaging of the test pattern is repeatedly performed by the imaging unit.

  A third aspect of the present invention is the image recording apparatus according to the first or second aspect, wherein the test pattern includes a mark for alignment, and the test image acquisition unit corresponds to the imaging unit of the test pattern. A relative position in the element arrangement direction is acquired, and only an imaging result in which the relative position is within a predetermined range is included in the plurality of test images.

  A fourth aspect of the present invention is the image recording apparatus according to any one of the first to third aspects, wherein the recording medium passes through a position facing the ejection unit once to the recording medium. Recording of the image is completed.

  A fifth aspect of the present invention is the image recording apparatus according to any one of the first to fourth aspects, wherein the density fluctuation range acquisition unit includes a plurality of test images acquired in the past within a predetermined period from the present time. The density fluctuation range is obtained also using the difference between the maximum value and the minimum value of the output from the image sensor corresponding to each of the ejection ports obtained based on the above.

According to a sixth aspect of the present invention, there is provided a discharge unit that discharges micro droplets of ink from a plurality of discharge ports arranged in the discharge port arrangement direction toward the recording medium, and the recording medium intersects with the discharge port arrangement direction. A moving mechanism that moves relative to the discharge unit in a moving direction, and a control unit that records an image on the recording medium by controlling the discharge unit and the moving mechanism, and intersects the moving direction. In an image recording apparatus for recording an image by an ink jet method, comprising an imaging unit having a plurality of imaging elements arranged in an element arrangement direction, when recording an image on the recording medium, A correction coefficient acquisition method for acquiring a correction coefficient used for correcting an ink ejection amount, wherein a) a test pattern having a predetermined target density is captured a plurality of times by the imaging unit to acquire a plurality of test images. B) obtaining a density fluctuation range which is a difference between the maximum value and the minimum value of the output from the image sensor corresponding to each ejection port based on the plurality of test images; and c) by the ejection unit. Recording a correction pattern on a correction medium so as to achieve the target density, and capturing the correction pattern by the imaging unit to obtain a correction image; and d) each ejection port in the correction image. A density error that is a difference between the output density that is output from the corresponding image sensor and the target density is obtained, and the density error is equal to or greater than a value that is determined based on the density fluctuation range corresponding to the density error. A step of determining a correction coefficient for the ejection port based on the density error.

According to a seventh aspect of the present invention, there is provided a discharge unit that discharges micro droplets of ink from a plurality of discharge ports arranged in the discharge port arrangement direction toward the recording medium, and the recording medium intersects the discharge port arrangement direction. A moving mechanism that moves relative to the discharge unit in a moving direction, and a control unit that records an image on the recording medium by controlling the discharge unit and the moving mechanism, and intersects the moving direction. An image recording method in an image recording apparatus for recording an image by an inkjet method, comprising: an imaging unit having a plurality of imaging elements arranged in an element arrangement direction, and a) when recording an image on the recording medium wherein the step of determining a correction factor to be used for the discharge amount of the correction of the ink from the plurality of outlets, b) by controlling the said discharging portion and said moving mechanism while using the correction coefficient, the recording And a2) the step of acquiring a plurality of test images by a1) imaging a test pattern having a predetermined target density a plurality of times by the imaging unit; A step of obtaining a density fluctuation range which is a difference between the maximum value and the minimum value of the output from the image pickup device corresponding to each ejection port based on the test image, and a3) so that the target density is obtained by the ejection unit. Recording a correction pattern on a correction medium, capturing the correction pattern by the imaging unit to obtain a correction image, and a4) output from an image sensor corresponding to each ejection port in the correction image A density error that is a difference between the output density and the target density is obtained, and when the density error is not less than a value determined based on the density fluctuation range corresponding to the density error, the density error is Based on And a step of determining a correction coefficient of the discharge port.

  In the present invention, it is possible to perform the discharge correction efficiently and with high accuracy while suppressing excessive correction.

It is a figure which shows the structure of an image recording device. It is a bottom view which shows a discharge unit. It is a bottom view which shows an inkjet head. It is a bottom view which shows an imaging part. It is a block diagram which shows the function of a control unit. It is a figure which shows the flow of acquisition of a correction coefficient. It is a top view of a test medium. It is a figure which shows the density | concentration of a test image. It is a figure which shows a density fluctuation range. It is a figure which shows output density. It is a figure which shows the ratio of the dispersion | variation in a density | concentration. It is a figure which shows the mark for alignment.

  FIG. 1 is a diagram showing a configuration of an image recording apparatus 1 according to the first embodiment of the present invention. The image recording apparatus 1 is a sheet-type printing apparatus that sequentially records color images (that is, performs color printing) on a recording medium 9 that is a plurality of printing sheets by an inkjet method.

  As shown in FIG. 1, the image recording apparatus 1 moves a plurality of recording media 9 in a moving direction that is the (+ Y) direction in FIG. The discharge unit 3 that discharges micro droplets of ink, the supply unit 51 that supplies the recording medium 9 to the moving mechanism 2, the discharge unit 52 that receives the recording medium 9 after printing from the moving mechanism 2, and the recording medium 9 are imaged. An imaging unit 6 and a control unit 4 that controls these mechanisms are provided. The discharge unit 3 and the imaging unit 6 are arranged above the moving mechanism 2 (on the (+ Z) side) and are fixed to a frame (not shown).

  The moving mechanism 2 includes a plurality of stages 21, an annular guide 22, and a belt driving mechanism 23. Each of the plurality of stages 21 sucks and holds one sheet-like recording medium 9. The guide 22 internally includes a belt to which a plurality of stages 21 are connected, and guides the plurality of stages 21. The belt driving mechanism 23 moves the belt in the guide 22 counterclockwise in FIG. 1, thereby moving the stage 21 holding the recording medium 9 below the discharge unit 3 and the imaging unit 6 (that is, (−Z)). Side) in the (+ Y) direction.

  The belt drive mechanism 23 is controlled by a control unit 41 (see FIG. 5), which will be described later, of the control unit 4, thereby switching the belt movement direction to the opposite direction and moving the belt clockwise in FIG. 1. Thereby, the stage 21 holding the recording medium 9 moves in the (−Y) direction below the discharge unit 3 and the imaging unit 6. That is, the moving mechanism 2 can reciprocate the stage 21 relative to the ejection unit 3 and the imaging unit 6 in the transport direction.

  FIG. 2 is a bottom view showing the discharge unit 3. The discharge unit 3 includes a plurality of (four in this embodiment) ink jet heads 31 that eject inks of different colors, and these ink jet heads 31 have the same structure. The plurality of inkjet heads 31 are arranged in the Y direction (that is, the movement direction) and attached to the attachment portion 30 of the discharge unit 3.

  The most (−Y) side inkjet head 31 in FIG. 2 ejects K (black) color ink, and the (+ Y) side inkjet head 31 of the K inkjet head 31 is C (cyan) color ink. The (+ Y) side inkjet head 31 of the C inkjet head 31 ejects M (magenta) color ink, and the (+ Y) side inkjet head 31 ejects Y (yellow) color ink. Discharge. The discharge unit 3 may be provided with an ink jet head for other colors such as light cyan, light magenta, and white.

  FIG. 3 is a bottom view showing one inkjet head 31. Other inkjet heads 31 have the same structure as that shown in FIG. As shown in FIG. 3, the inkjet head 31 includes a plurality (six in this embodiment) of heads 32 each having a similar structure. The plurality of heads 32 are arranged in the X direction perpendicular to the Y direction so as to be alternately positioned on the (−Y) side and the (+ Y) side of the center rib 311. In other words, the plurality of heads 32 are arranged in the X direction in a so-called staggered pattern.

  Each head 32 includes a plurality of ejection ports 33 arranged in the X direction. The plurality of heads 32 are arranged such that all the discharge ports 33 are arranged at an equal pitch in the X direction. In the following description, the X direction is also referred to as “ejection port arrangement direction”. In other words, each inkjet head 31 includes a plurality of ejection ports 33 arranged in the ejection port arrangement direction perpendicular to the moving direction. Note that the discharge port arrangement direction is not necessarily perpendicular to the movement direction, and may be any direction that intersects the movement direction.

  In the image recording apparatus 1, each inkjet head 31 extends over the entire recording area on the recording medium 9 in the X direction perpendicular to the moving direction (in the present embodiment, over the entire X direction of the recording medium 9). ) Provided. Then, the ejection unit 3 and the moving mechanism 2 are controlled by the control unit 41 (see FIG. 5), and the recording medium 9 passes through the position of the ejection unit 3 facing the plurality of inkjet heads 31 only once ( That is, the recording medium 9 moves relative to the ejection unit 3 only once in the moving direction), whereby the image recording on the recording medium 9 is completed. In other words, the image recording apparatus 1 performs single pass printing on the recording medium 9.

  FIG. 4 is a bottom view showing the imaging unit 6. As shown in FIG. 4, the imaging unit 6 is a line sensor having a plurality of imaging elements 61 arranged in the X direction, and the imaging element 61 is a CCD (Charge Coupled Device) element. When the X direction in which the plurality of imaging elements 61 are arranged is referred to as an “element arrangement direction”, in this embodiment, the element arrangement direction coincides with the discharge port arrangement direction and is perpendicular to the movement direction. Note that the element arrangement direction is not necessarily perpendicular to the movement direction, and may be any direction that intersects the movement direction.

  As shown in FIG. 1, the imaging unit 6 is arranged on the (+ Y) side, which is downstream of the ejection unit 3 in the moving direction of the recording medium 9, and is on the recording medium 9 with respect to the X direction perpendicular to the moving direction. It is provided over the entire recording area (in the present embodiment, over the entire X direction of the recording medium 9). Then, when the recording medium 9 passes the position facing the imaging unit 6 only once (that is, when the recording medium 9 moves relative to the imaging unit 6 only once in the moving direction), recording is performed. Imaging of the medium 9 is completed. In the present embodiment, the positions in the X direction of the plurality of imaging elements 61 of the imaging unit 6 coincide with the positions in the X direction of the plurality of ejection ports 33 of each inkjet head 31. In other words, each image sensor 61 corresponds to one ejection port 33 of each inkjet head 31.

  FIG. 5 is a block diagram showing the function of the control unit 4, and FIG. 5 also shows a part of the configuration of the image recording apparatus 1 connected to the control unit 4. The control unit 4 includes the above-described control unit 41 and a storage unit 42 that stores various information. The control unit 41 includes a recording control unit 411, a test image acquisition unit 412, a density fluctuation range acquisition unit 413, a correction image acquisition unit 414, and a correction coefficient acquisition unit 415.

  As described above, the recording control unit 411 controls the moving mechanism 2 and the ejection unit 3 to record an image on the recording medium 9. The storage unit 42 stores a correction coefficient used for correcting the amount of ink discharged from the plurality of discharge ports 33 of the discharge unit 3. In the recording control unit 411, the ink ejection amount from the plurality of ejection ports 33 of the ejection unit 3 is corrected based on the plurality of correction coefficients stored in the storage unit 42, whereby density unevenness on the recording medium 9 is corrected. Occurrence of unevenness and streaks is prevented.

  Next, the flow of obtaining the correction coefficient in the image recording apparatus 1 will be described with reference to FIG. In the image recording apparatus 1, first, a medium 96 on which a test pattern 95 for correcting density unevenness shown in FIG. 7 is recorded (hereinafter referred to as “test medium 96”) is held by the stage 21 (see FIG. 1). The test pattern 95 has a plurality of (six in this embodiment) rectangular regions 951 arranged in the moving direction (Y direction) of the stage 21. The width in the X direction of each region 951 is equal to or larger than the width in the X direction of the plurality of imaging elements 61 of the imaging unit 6. In each area 951, an image having a uniform density is recorded. The density of each region 951 is 100%, 80%, 50%, 30%, 10%, and 5% in order from the (+ Y) side.

  The test medium 96 may be a printing paper similar to the recording medium 9 or another medium. The test pattern 95 may be recorded on the test medium 96 by the image recording apparatus 1 or may be recorded on the test medium 96 by another type of image recording apparatus. If the ink used for recording the test pattern 95 has a large dry-down, it is preferable to use the test medium 96 after a predetermined time has elapsed since the test pattern 95 was recorded.

  Subsequently, the moving mechanism 2 shown in FIG. 1 is driven, and the test medium 96 moves below the imaging unit 6. Then, when the moving mechanism 2 and the imaging unit 6 are controlled by the test image acquisition unit 412 illustrated in FIG. 5, the test medium 96 reciprocates relative to the imaging unit 6 below the imaging unit 6. Imaging of the test pattern 95 by the imaging unit 6 is repeatedly performed. In the present embodiment, the test pattern 95 is imaged four times by the imaging unit 6. The plurality of images of the test pattern 95 acquired by the imaging unit 6 are sent to the test image acquisition unit 412. In the test image acquisition unit 412, a plurality of images in a region 951 having a predetermined density (100% in the present embodiment, hereinafter referred to as “target density”) are obtained from a plurality of images of the test pattern 95. Obtained as a test image (step S11).

  FIG. 8 is a diagram showing the density of a plurality of test images. The horizontal axis in FIG. 8 indicates the positions in the X direction of the plurality of imaging elements 61 of the imaging unit 6, and the vertical axis indicates the test image density at each position in the X direction, that is, output values from the plurality of imaging elements 61. Indicates the value converted to concentration. In FIG. 8, the density of the four test images acquired by the four imaging operations in step S <b> 11 is indicated by four solid lines 81.

  Next, the density fluctuation range is a difference between the maximum value and the minimum value of the output from the image sensor 61 corresponding to each ejection port 33 of the inkjet head 31 based on the plurality of test images by the density fluctuation width acquisition unit 413. Is obtained (step S12). The density fluctuation range is actually obtained as a difference between the maximum value and the minimum value obtained by converting the output value from each image sensor 61 into the density. In FIG. 8, the magnitude of the density fluctuation range of one image sensor 61 is indicated by a line 82.

  FIG. 9 is a diagram illustrating the density fluctuation range of all the image sensors 61 of the imaging unit 6. The horizontal axis in FIG. 9 indicates the position in the X direction, and the vertical axis indicates the density fluctuation range. A solid line 83 in FIG. 9 indicates the density fluctuation range, and a broken line 84 indicates a fluctuation threshold that is a value determined for each image sensor 61 based on the density fluctuation range. In the present embodiment, the fluctuation threshold is 0.5 times the density fluctuation width. The variation threshold value may be changed as appropriate as long as it is determined based on the density variation range.

  When the density fluctuation range is acquired, the correction medium, which is the same printing paper as the recording medium 9, is held by the stage 21. Subsequently, when the moving mechanism 2 and the discharge unit 3 are controlled by the correction image acquisition unit 414 illustrated in FIG. 5, the correction pattern is set so that the correction medium passing under the discharge unit 3 has the target density. Is recorded. In the present embodiment, similarly to the test pattern 95, a plurality of rectangular regions having respective densities of 100%, 80%, 50%, 30%, 10%, and 5% are arranged in the Y direction. The pattern for use is recorded on the correction medium.

  The width in the X direction of the correction pattern is equal to the width in the X direction of the plurality of ejection ports 33 of the inkjet head 31 and the width in the X direction of the plurality of imaging elements 61 of the imaging unit 6. Then, when the moving mechanism 2 and the imaging unit 6 are controlled by the correction image acquisition unit 414, the correction pattern on the correction medium passing under the imaging unit 6 is imaged and the correction image is acquired. (Step S13). The correction medium may be another medium different from the recording medium 9.

  Next, the correction coefficient acquisition unit 415 outputs an output density (that is, a value obtained by converting the output value from each image sensor 61 into a density) that is an output from the image sensor 61 corresponding to each ejection port 33 in the correction image. Then, a density error which is an absolute value of a difference from the target density is obtained. Then, the density error of each ejection port 33 is compared with the variation threshold value (see FIG. 9) of the image sensor 61 corresponding to each ejection port 33, and the ejection port 33 whose density error is greater than or equal to the variation threshold value is extracted as a correction target. Is done.

  FIG. 10 is a diagram showing the output density. The horizontal axis in FIG. 10 indicates the position in the X direction, and the vertical axis indicates the density. A solid line 86 in FIG. 10 indicates the output density. The density error described above is an absolute value of the difference between the target density indicated by the solid line 86 and the broken line 87. Two two-dot chain lines 88 in FIG. 10 indicate a target density obtained by adding a fluctuation threshold value and a target density obtained by subtracting the fluctuation threshold value. The discharge port 33 extracted as a correction target is a discharge port included in a region 89 where the solid line 86 in FIG. 10 is equal to or higher than the upper one-dot chain line 88 or lower than the lower one-dot chain line 88. The correction coefficient acquisition unit 415 determines a correction coefficient for each ejection port 33 that is a correction target based on the density error of each ejection port 33 (step S14). For example, when the output density is smaller than the target density, the correction coefficient is obtained by adding a value obtained by dividing the density error by the target density to 1, and when the output density is larger than the target density, the density error is calculated as the target density. It is obtained by subtracting the value divided by 1 from 1.

  In the image recording apparatus 1, Steps S <b> 13 and S <b> 14 are repeated a predetermined number of times (three times in the present embodiment) (Step S <b> 15), and the finally determined correction coefficient is stored in the storage unit 42. (Step S16) and used in the next step S17. In other words, the correction coefficient stored in the storage unit 42 in step S16 is a final correction coefficient, and the correction coefficient determined in step S14 is a provisionally determined temporary correction coefficient.

  In the image recording apparatus 1, the above-described steps S <b> 11 to S <b> 16 are performed with the density (80%, 50%, 30%, 10%, 5%) of the other area 951 of the test pattern 95 as the target density, respectively. A correction coefficient at each density is determined. Note that the number of repetitions of steps S13 and S14 is not limited to three, and may be two or four or more. Alternatively, steps S13 and S14 may be performed only once. The steps S13 and S14 may be repeated until the correction pattern is recorded and imaged using the correction coefficient determined in step S14 until the density error of the correction image falls within a predetermined range. Good.

  In the image recording apparatus 1, the recording control unit 411 controls the ejection unit 3 and the moving mechanism 2 while using the correction coefficient determined in step S14, thereby recording an image on the recording medium 9 (step S1). S17). Specifically, in the original image data of the image recorded on the recording medium 9, the density of the pixel corresponding to each ejection port 33 to be corrected is changed using a correction coefficient (for example, the pixel of the original image data). Is multiplied by a correction coefficient) to generate corrected data. Then, halftone dot data is generated from the corrected data using the threshold matrix, and ejection data indicating the ejection amount of ink from each ejection port 33 is generated based on the halftone data, and the ink is generated based on the ejection data. Is discharged. That is, the ink ejection amount from each ejection port 33 to be corrected is corrected using the correction coefficient. The corrected ink discharge amount may be the amount of ink discharged from the discharge port 33 at a time, and ink is discharged from the discharge port 33 during the movement of the recording medium 9 by a predetermined distance. It may be the number of times (that is, the total ejection amount of ink during a predetermined distance).

  By the way, an image recording apparatus that captures a correction pattern recorded so as to obtain a target density, obtains a correction image, and determines correction coefficients for all the ejection openings based on the difference between the correction image and the target density. (Hereinafter referred to as “comparative image recording apparatus”), in the comparative image recording apparatus, the difference between the correction image and the target density due to variations in the spectral sensitivity of the plurality of image sensors in the imaging unit. However, there is a risk of being calculated to be larger than actual. As a result, the amount of ink ejected from each ejection port is excessively corrected, and a long time is required to determine the correction function for each ejection port.

  On the other hand, in the image recording apparatus 1 according to the present embodiment, a test pattern with a target density is captured a plurality of times to obtain a plurality of test images, and the density fluctuation range in the image sensor 61 corresponding to each ejection port 33 Desired. Subsequently, a correction pattern is recorded so as to obtain a target density, and the correction pattern is captured to obtain a correction image. Then, the discharge port 33 whose density error, which is the difference between the output density of the image for correction and the target density, is not less than the fluctuation threshold value based on the density fluctuation range is extracted as a correction target. A correction coefficient based on the density error is determined. Thereby, excessive correction due to variations in spectral sensitivity among the plurality of image sensors 61 can be suppressed, and efficient and highly accurate ejection correction can be performed.

  FIG. 11 is a diagram illustrating a result of comparison between the image recording apparatus 1 and the image recording apparatus of the comparative example regarding the variation in the density of the image recorded on the recording medium 9. The horizontal axis of FIG. 11 represents the image density, and the vertical axis represents the standard deviation of the density of the image recorded by the image recording apparatus of the comparative example divided by the standard deviation of the density of the image recorded by the image recording apparatus 1. Show things.

  As shown in FIG. 11, at the densities of 100%, 50%, 30%, 10% and 5%, the standard deviation of the density of the image recorded by the image recording apparatus 1 is recorded by the image recording apparatus of the comparative example. It can be seen that efficient and highly accurate ejection correction is performed, which is smaller than the standard deviation of the image density. As described above, the structure of the image recording apparatus 1 capable of performing efficient and highly accurate ejection correction is the single-pass printing in which the density unevenness of the image due to the ejection unevenness from the plurality of ejection openings is more conspicuous than the interless printing. It is particularly suitable for an image recording apparatus in which

  In the image recording apparatus 1, in step S11, the test medium 96 is reciprocated relative to the imaging unit 6, and the test pattern 95 is repeatedly imaged to obtain a plurality of test images. Thereby, a plurality of test images can be easily acquired. In addition, in comparison with the case where a plurality of test images are acquired by sequentially imaging a plurality of test media 96 on which test patterns 95 are recorded, the relative position in the X direction with respect to the imaging unit 6 of the test pattern 95 in a plurality of imaging operations is obtained. Variation is suppressed. As a result, in a plurality of times of imaging of the test pattern 95, the displacement of the position in the X direction on the test pattern 95 imaged by each imaging element 61 is suppressed, and more accurate ejection correction can be performed.

  In the image recording apparatus 1, in step S <b> 11, the test pattern 95 is recorded on each of the plurality of test media 96 by the ejection unit 3, and the plurality of test media 96 are sequentially imaged by the imaging unit 6, thereby A test image may be acquired. In this case, each test pattern 95 preferably includes an alignment mark. FIG. 12 is a diagram illustrating an example of the alignment mark 952. In FIG. 12, the alignment marks 952 are a plurality of straight lines that are parallel to the Y direction and protrude to the (+ Y) side and the (−Y) side of the test pattern 95.

  In step S11, a plurality of test media 96 are sequentially imaged to obtain a plurality of images, and based on the position of the alignment mark 952 in each image, the X of the test pattern 95 for the imaging unit 6 at the time of each image acquisition is obtained. The relative position with respect to the direction (that is, the element arrangement direction) is acquired by the test image acquisition unit 412. Only a result of imaging in which the relative position is within a predetermined range (for example, an image in which the deviation of the relative position from the target position is a predetermined allowable value or less) is used for the calculation of the density fluctuation range in step S12. Included in test images. Thereby, in the plurality of test images, a shift in the position in the X direction on the test pattern 95 captured by each image sensor 61 is suppressed, and more accurate ejection correction can be performed.

  As the alignment mark 952, for example, a straight line parallel to the Y direction having a different density may be provided in the region 951 of the test pattern 95. In this case, the density fluctuation range of the image sensor 61 corresponding to the alignment mark 952 is obtained using another test pattern 95 in which the position of the alignment mark 952 in the X direction is changed. In addition, each region 951 of the test pattern 95 is divided into a plurality of unit regions arranged in the X direction, and the position of the adjacent unit region in the Y direction is shifted, so that the boundary between the adjacent unit regions is an alignment mark. 952 may be used.

  By the way, the above-described correction coefficient is determined at a predetermined frequency (for example, once every two or three days). In the image recording apparatus 1, the density fluctuation range (hereinafter referred to as “past density fluctuation range”) acquired at the time of determination of correction coefficients performed in the past within a predetermined period (for example, 30 days or 6 months) from the present. ) Is stored in the storage unit 42, and in step S12 described above, the density fluctuation range may be obtained using these past density fluctuation ranges. When determining past correction coefficients, a plurality of test images are acquired in the same manner as described above, and the past density fluctuation range is an imaging corresponding to each discharge port 33 obtained based on the plurality of test images. This is the difference between the maximum value and the minimum value of the output from the element 61.

  When using the past density fluctuation range, in step S12, the density fluctuation range acquisition unit 413 calculates the maximum value and the minimum value of the output from each imaging element 61 obtained based on the plurality of test images acquired this time. The difference is obtained as the temporary density fluctuation range. Then, the temporary density fluctuation range and an average value of a plurality of past density fluctuation ranges stored in advance in the storage unit 42 are obtained as the density fluctuation range.

  In this way, by obtaining the density fluctuation range in consideration of the past density fluctuation range, excessive correction due to sudden variation in output from the image sensor 61 is suppressed, and more efficient and highly accurate ejection correction is performed. be able to. The determination of the density fluctuation range using the past density fluctuation range may be performed by various methods other than those described above. For example, the density fluctuation range may be a weighted average of the temporary density fluctuation range and the past density fluctuation range considering a weight that gradually decreases from the present to the past.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various change is possible.

  For example, in step S <b> 11, the number of times the test pattern 95 is captured is not limited to four, and it is only necessary that the test pattern 95 is captured a plurality of times by the imaging unit 6 to obtain a plurality of test images. In step S13, the correction pattern may be captured a plurality of times, and a correction image may be acquired using a plurality of imaging results. Specifically, for example, an average value of a plurality of imaging results is used as the correction image. In step S15, the dot data may be corrected by using the correction coefficient by the recording control unit 411, or the ejection data may be corrected.

  In the image recording apparatus 1, each imaging element 61 of the imaging unit 6 may overlap two or more ejection ports 33 in the Y direction. In this case, the output density corresponding to each ejection port 33 includes an image sensor group corresponding to each ejection port 33, that is, one or two imaging devices 61 overlapping each ejection port 33 in the Y direction, and in the X direction. You may obtain | require by interpolating the output from the continuous several image pick-up element 61. FIG. Further, the image pickup device 61 of the image pickup unit 6 may be a complementary metal oxide semiconductor (CMOS) device.

  In the above embodiment, when a plurality of test images are acquired by sequentially capturing a plurality of test patterns 95, the alignment mark 952 is provided on the test pattern 95. However, the alignment mark 952 is moved. It may also be provided when a plurality of test images are acquired by reciprocating one test pattern 95 below the imaging unit 6 by the mechanism 2. Also in this case, in step S11, based on the position of the alignment mark 952 in each image, the relative position in the X direction (that is, the element arrangement direction) of the test pattern 95 with respect to the imaging unit 6 at the time of each image acquisition is Acquired by the test image acquisition unit 412. Only the imaging results whose relative positions are within a predetermined range are included in the plurality of test images used for calculating the density fluctuation range in step S12. Thereby, in the plurality of test images, a shift in the position in the X direction on the test pattern 95 captured by each image sensor 61 is suppressed, and more accurate ejection correction can be performed.

  In the image recording apparatus 1, if the recording medium 9 moves relative to the ejection unit 3 in the Y direction, for example, the ejection unit 3 is moved by the moving mechanism 2 above the stopped printing medium 9. You may move in the Y direction. The structure of the image recording apparatus 1 may be applied to, for example, an image recording apparatus that performs interlaced printing, or may be applied to an image recording apparatus that records an image on a long roll paper.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Image recording apparatus 2 Moving mechanism 3 Ejection unit 6 Imaging part 9 Recording medium 31 Inkjet head 33 Ejection port 41 Control part 42 Storage part 61 Imaging element 95 Test pattern 96 Test medium 411 Recording control part 412 Test image acquisition part 413 Density fluctuation range Acquisition unit 414 Correction image acquisition unit 415 Correction coefficient acquisition unit 952 Registration mark S11 to S17 Steps

Claims (7)

An image recording apparatus for recording an image by an inkjet method,
A discharge unit that discharges micro droplets of ink from a plurality of discharge ports arranged in the discharge port array direction toward the recording medium;
A movement mechanism that moves the recording medium relative to the ejection unit in a movement direction that intersects the ejection port arrangement direction;
A control unit for recording an image on the recording medium by controlling the ejection unit and the moving mechanism;
An imaging unit having a plurality of imaging elements arranged in an element arrangement direction intersecting the moving direction;
A storage unit that stores a correction coefficient used to correct the ejection amount of ink from the plurality of ejection ports when an image is recorded on the recording medium ;
With
The control unit is
A test image acquisition unit for acquiring a plurality of test images by imaging a test pattern of a predetermined target density a plurality of times by the imaging unit;
Based on the plurality of test images, a density fluctuation width obtaining unit that obtains a density fluctuation width that is a difference between the maximum value and the minimum value of the output from the image sensor corresponding to each ejection port;
A correction image acquisition unit that records a correction pattern on a correction medium so as to achieve the target density by the ejection unit, images the correction pattern by the imaging unit, and acquires a correction image;
A density error that is a difference between the output density that is output from the image sensor corresponding to each ejection port in the correction image and the target density is obtained, and the density error corresponds to the density fluctuation range corresponding to the density error. A correction coefficient acquisition unit that determines a correction coefficient of the discharge port based on the density error when the value is equal to or greater than a value determined based on
An image recording apparatus comprising: The image recording apparatus according to claim 1,
The moving mechanism is capable of reciprocating relative to the imaging unit in the moving direction with respect to the medium on which the test pattern is recorded;
The image recording apparatus, wherein the test image acquisition unit reciprocally moves the medium on which the test pattern is recorded relative to the imaging unit, and repeatedly captures the test pattern by the imaging unit. . The image recording apparatus according to claim 1, wherein:
The test pattern includes an alignment mark,
The test image acquisition unit acquires a relative position of the test pattern with respect to the imaging unit with respect to the element arrangement direction, and only the imaging results with the relative position within a predetermined range are included in the plurality of test images. An image recording apparatus. The image recording apparatus according to any one of claims 1 to 3,
The image recording apparatus according to claim 1, wherein the recording of the image on the recording medium is completed when the recording medium passes once through a position facing the ejection unit. The image recording apparatus according to any one of claims 1 to 4,
The difference between the maximum value and the minimum value of the output from the image sensor corresponding to each of the ejection ports, which is obtained by the density fluctuation range acquisition unit based on a plurality of test images acquired in the past within a predetermined period from the present time The image recording apparatus is characterized in that the density fluctuation range is obtained also using the image recording apparatus. A discharge unit that discharges micro droplets of ink from a plurality of discharge ports arranged in the discharge port arrangement direction toward the recording medium, and the recording medium with respect to the discharge unit in a moving direction that intersects the discharge port arrangement direction A moving mechanism that moves relative to each other, a control unit that records an image on the recording medium by controlling the discharge unit and the moving mechanism, and a plurality of elements arranged in an element arrangement direction that intersects the moving direction. In an image recording apparatus that records an image by an ink jet method and includes an imaging unit having an image sensor, the image recording apparatus is used for correcting the ejection amount of ink from the plurality of ejection ports when recording an image on the recording medium. A correction coefficient acquisition method for acquiring a correction coefficient,
a) capturing a plurality of test images by imaging a test pattern having a predetermined target density a plurality of times by the imaging unit;
b) obtaining a density fluctuation range that is a difference between the maximum value and the minimum value of the output from the image sensor corresponding to each ejection port based on the plurality of test images;
c) recording a correction pattern on a correction medium so as to achieve the target density by the ejection unit, capturing the correction pattern by the imaging unit, and obtaining a correction image;
d) A density error that is a difference between an output density that is an output from the image sensor corresponding to each ejection port in the correction image and the target density is obtained, and the density fluctuation corresponds to the density error. A step of determining a correction coefficient for the discharge port based on the density error when the value is equal to or greater than a value determined based on a width;
A correction coefficient acquisition method comprising: A discharge unit that discharges micro droplets of ink from a plurality of discharge ports arranged in the discharge port arrangement direction toward the recording medium, and the recording medium with respect to the discharge unit in a moving direction that intersects the discharge port arrangement direction A moving mechanism that moves relative to each other, a control unit that records an image on the recording medium by controlling the discharge unit and the moving mechanism, and a plurality of elements arranged in an element arrangement direction that intersects the moving direction. An image recording method in an image recording apparatus for recording an image by an inkjet method, comprising an imaging unit having an imaging element,
a) determining a correction coefficient used for correcting the ejection amount of ink from the plurality of ejection ports when recording an image on the recording medium ;
b) recording an image on the recording medium by controlling the ejection unit and the moving mechanism using the correction coefficient;
With
Step a)
a1) A step of acquiring a plurality of test images by imaging a test pattern having a predetermined target density a plurality of times by the imaging unit;
a2) obtaining a density fluctuation range which is a difference between the maximum value and the minimum value of the output from the image sensor corresponding to each ejection port based on the plurality of test images;
a3) recording a correction pattern on a correction medium so as to achieve the target density by the ejection unit, capturing the correction pattern by the imaging unit, and obtaining a correction image;
a4) A density error that is a difference between an output density that is an output from an image sensor corresponding to each ejection port in the correction image and the target density is obtained, and the density error corresponds to the density error. A step of determining a correction coefficient for the discharge port based on the density error when the value is equal to or greater than a value determined based on a width;
An image recording method comprising:

Images