JP2018047584A - Inkjet recording device and image quality adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording device that can perceive timing for adjustment for recording an image at a proper gradation in response to change of ink discharge operation, and an image quality adjusting method.SOLUTION: An inkjet recording device (1) comprises: a recording portion that records an image to be recorded, on a recording medium by discharging ink to the medium; a control portion (40) that performs a control process related to recording operation of the image to be recorded by the recording portion, acquires a correspondence relation between a brightness value to be read out from a surface of the recording medium and a prescribed color measurement value, and detects a change related to operation of the recording portion on the basis of a read-out result of the brightness value; and an output correcting portion (26) that corrects image data on the image to be recorded so that the color measurement value to be obtained, according to the correspondence relation, from the read-out result of the brightness value of the image to be recorded is identical to a value indicating a hue corresponding to a density gradation firstly set for the image to be recorded.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an ink jet recording apparatus and an image quality adjustment method.

  2. Description of the Related Art Conventionally, there is an image forming apparatus that forms an image by coloring each position on the surface of a recording medium with an appropriate density using a color material such as ink or toner. In the image forming apparatus, an appropriate color material consumption amount and a driving amount further corresponding to the color material consumption amount are determined for the density gradation value indicated by the image data, and the coloring operation is performed.

  In the image recording apparatus, in order to appropriately maintain the relationship between the density gradation value and the color material consumption amount, a test image having a plurality of density gradations is formed on the recording medium, and the density gradation of the formed test image is formed. There is a technology that actually reads, compares, and adjusts. However, conventionally, there is a problem that it takes time and labor to measure an accurate density gradation with a color system color value corresponding to human vision.

  On the other hand, in Patent Document 1, a correspondence table of colorimetric values and luminance values (luminance of reflected light from an illuminated test image) of a plurality of density gradation test images (patch pattern images) is generated. A technique has been disclosed in which a luminance reading value obtained by a sensor capable of high-speed reading is converted into a colorimetric value by the correspondence table to obtain an accurate colorimetric value quickly. Further, in Patent Document 1, an accurate density gradation is obtained by correcting the correspondence relationship between the colorimetric value and the read value in accordance with a change in the read characteristic due to deterioration of the sensor or contamination of the light incident window. A technique for stably obtaining the above is disclosed.

Japanese Patent Laid-Open No. 2005-43617

  However, when an image is formed by ejecting ink onto a recording medium in an ink jet recording apparatus, the ink ejection speed, the shape of the ejected ink droplet, the amount of ink, and the like may change depending on the conditions over time. Along with this, since the landing area per ink droplet landing on the recording medium changes, there is a problem that the correspondence between the colorimetric value and the luminance value also changes. On the other hand, there is a problem that adjusting this correspondence frequently requires an excessive amount of labor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus and an image quality adjusting method capable of easily knowing the adjustment timing for recording an image with an appropriate gradation in accordance with a change in ink ejection operation. .

In order to achieve the above object, the invention according to claim 1
A recording unit for recording an image to be recorded by discharging ink onto a recording medium;
A control processing unit for performing a control process related to a recording operation of a recording target image by the recording unit;
A relationship acquisition unit for acquiring a correspondence relationship between a luminance value read from the surface of the recording medium and a predetermined colorimetric value;
The colorimetric value obtained according to the correspondence relationship from the reading result of the luminance value of the recording target image on the surface of the recording medium is a value indicating the color corresponding to the density gradation initially determined for the recording target image. A correction unit for correcting the image data of the recording target image;
A change detection unit that detects a change related to the operation of the recording unit based on a reading result of the luminance value;
An ink jet recording apparatus comprising:

The invention described in claim 2 is the ink jet recording apparatus according to claim 1,
The control processing unit causes the recording unit to record a recording target image including an inspection image portion having a predetermined density gradation,
The change detection unit corresponds to a case where the coverage of the recording medium by the ejected ink in the inspection image portion has changed by a predetermined level or more from the timing at which the correspondence relationship was most recently acquired as a change related to the operation of the recording unit. A change in luminance value of the inspection image portion to be detected is detected.

The invention described in claim 3 is the ink jet recording apparatus according to claim 1 or 2,
When the change detection unit detects a change related to the operation of the recording unit that is equal to or greater than a predetermined reference, the control processing unit records a test image including a plurality of density gradation test image portions by the recording unit. The relationship acquisition unit acquires update data of the correspondence relationship based on the test image, and updates the correspondence relationship with the update data.

According to a fourth aspect of the present invention, in the ink jet recording apparatus according to the third aspect,
The recording unit records the recording target image by ejecting a plurality of colors of ink;
The test image includes the plurality of density gradation inspection image portions for each of the plurality of colors of ink.

Invention of Claim 5 is an inkjet recording device as described in any one of Claims 2-4,
When the normal processing target image is recorded on the recording medium, the control processing unit causes the recording unit to record a recording target image including at least a part of the inspection image portion in a margin portion of the output target image. ,
The change detecting unit detects a change related to the operation of the recording unit that is equal to or greater than a predetermined reference based on a reading result of a luminance value of the recorded inspection image portion.

The invention according to claim 6 is the ink jet recording apparatus according to claim 5,
The control processing unit changes at least a part of the inspection image portion to be recorded in the margin portion every time the output target image is recorded.

The invention according to claim 7 is the ink jet recording apparatus according to any one of claims 1 to 6,
The relationship acquisition unit acquires a plurality of the correspondence relationships for each predetermined type of recording medium.

The invention according to claim 8 is the ink jet recording apparatus according to claim 7,
The types of the recording medium include coated paper with coating and plain paper without coating.

The invention according to claim 9 is the ink jet recording apparatus according to claim 7 or 8,
The type of the recording medium can be additionally set.

The invention according to claim 10 is the ink jet recording apparatus according to any one of claims 1 to 9,
The recording unit records an image by discharging at least cyan, magenta, and yellow inks,
The correspondence relationship associates a green luminance value or red luminance value read from a C color image with cyan ink with a colorimetric value of the C color image, and a green luminance value read from an M color image with magenta ink. The colorimetric values of the M color image are associated with each other, and the blue luminance value read from the Y color image with yellow ink is associated with the colorimetric value of the Y color image.

The invention according to claim 11 is the ink jet recording apparatus according to any one of claims 1 to 10,
The recording unit records an image by ejecting each color ink of cyan, magenta, yellow, and black,
The correspondence relationship is such that the luminance value read from the inspection image portion of each ink of cyan, magenta, and black is associated with the Y value of the XYZ color system or the L * value of the L * a * b * color system, yellow It is characterized in that the luminance value read from the inspection image portion by ink is associated with the Z value of the XYZ color system or the b * value of the L * a * b * color system.

The invention according to claim 12 is the ink jet recording apparatus according to any one of claims 1 to 11,
A reading unit that reads the luminance value on the surface of the recording medium is provided.

The invention according to claim 13 is the ink jet recording apparatus according to any one of claims 1 to 12,
With a display,
When the change detecting unit detects a change related to the operation of the recording unit that exceeds a predetermined reference, the change detecting unit causes the display unit to perform a predetermined display indicating the detection of the change.

The invention according to claim 14 is the ink jet recording apparatus according to claim 13,
It has an operation reception unit that receives user operations,
The change detection unit receives an operation for selecting whether or not to update the correspondence relationship by the operation reception unit after the predetermined display is performed by the display unit.

The invention according to claim 15 is:
An image quality adjustment method for an inkjet recording apparatus including a recording unit that records an image to be recorded by discharging ink onto a recording medium,
A relationship acquisition step of acquiring a correspondence relationship between a luminance value read from the surface of the recording medium and a predetermined colorimetric value;
The colorimetric value obtained according to the correspondence relationship from the reading result of the luminance value of the recording target image on the surface of the recording medium is a value indicating the color corresponding to the density gradation initially determined for the recording target image. A correction step of correcting the image data of the recording target image,
A change detecting step for detecting a change related to the operation of the recording unit based on a reading result of the luminance value;
It is characterized by including.

  According to the present invention, there is an effect that it is possible to easily know the timing of adjustment for recording an image with an appropriate gradation according to a change in the ink ejection operation.

1 is an overall schematic diagram illustrating an ink jet recording apparatus according to an embodiment of the present invention. It is a figure which shows the nozzle surface of a recording part. It is a block diagram which shows the function structure of an inkjet recording device. It is a figure which shows the example of the correspondence of a luminance value and a colorimetric value. It is a figure which shows the example of the patch image which shows several density gradation about each ink color. It is a flowchart which shows the control procedure of a correspondence table setting process. It is a figure which shows the example of a density nonuniformity detection image. It is a flowchart which shows the control procedure of a density nonuniformity correction process. It is a figure which shows the example of the output image which concerns on the luminance value change detection in a normal image. It is a figure which shows the example of the output image which concerns on the luminance value change detection in a normal image. It is a flowchart which shows the control procedure of a fluctuation | variation detection process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall schematic diagram of an ink jet recording apparatus 1 according to the present embodiment.

  The inkjet recording apparatus 1 includes a transport unit 10, an image forming unit 20, an image reading unit 30 (reading unit), a control unit 40 (control processing unit, relationship acquisition unit, change detection unit) and the like.

  The conveyance unit 10 includes a driving roller 11 and a conveyance belt 12. The rotation of the driving roller 11 causes the outer peripheral surface of the conveyance belt 12 to move relative to the image forming unit 20 in a predetermined conveyance direction using the conveyance surface. The recording medium P placed on the transport surface is moved in the transport direction.

  The image forming unit 20 performs a recording operation of forming an image by ejecting ink from nozzles and landing on the upper surface of the recording medium P. Here, the image forming unit 20 includes four head units 21Y, 21M, 21C, and 21K (hereinafter collectively referred to as a head unit 21; a recording unit), each of which is supplied from an ink storage unit (not shown). , Magenta, cyan and black inks (plural colors) are ejected. Each of these head units 21 is provided with nozzles over the recordable width of the maximum size recording medium P that can be transported by the transport unit 10 in the width direction perpendicular to the transport direction, so that ink can be ejected. It has become.

FIG. 2 is a bottom view showing a surface facing the transport surface of the head unit 21K.
Since the head units 21C, 21M, and 21Y have the same configuration as the head unit 21K, description thereof will be omitted.

  The head unit 21K is provided with eight recording heads 211 in which a plurality of nozzle openings are arranged at predetermined intervals in the width direction on the bottom surface, and these are arranged in a staggered pattern so that the width A line head is configured in which nozzle openings are arranged at uniform intervals over the maximum width (recordable width) that can be recorded on the recording medium P in the direction. That is, the head unit 21K is fixed during image formation, and forms an image by a one-pass method by sequentially ejecting ink to different positions in the transport direction according to the transport of the recording medium P.

  The recording heads 211 are arranged so that the arrangement ranges of the nozzle openings in the adjacent recording heads 211 in the width direction partially overlap each other. The relative positional relationship of these recording heads 211 is inspected and held, and the overlapping portion is adjusted so that ink is ejected by the nozzles of any recording head 211 based on the information on the relative positional relationship. This makes it possible to form a uniform image.

  The image reading unit 30 is provided on the downstream side in the transport direction of the recording medium P with respect to the image forming unit 20, and captures an image formed on the recording surface of the recording medium P by the image forming unit 20. Output as data. The image reading unit 30 includes a line sensor 32 (see FIG. 3; imaging sensor) in which imaging elements are arranged over the width that can be recorded by the head unit 21 in the width direction. While the conveyance unit 10 moves the recording medium P relative to the image reading unit 30 in the conveyance direction, the line sensor 32 sequentially acquires one-dimensional image data in the imaging target range in the width direction, thereby recording. A two-dimensional image on the medium P can be obtained. As the line sensor 32, for example, a CCD sensor (Charge Coupled Device), a CMOS sensor (Complementary Metal Oxide Semiconductor), or the like is used. Normally, the arrangement interval in the width direction of the image sensor is wider than the arrangement interval in the width direction of the nozzle openings in the recording head 211. That is, the imaging resolution of the line sensor 32 is lower than the recording resolution of the image forming unit 20.

  The control unit 40 performs overall control of the operation of each unit of the inkjet recording apparatus 1.

  FIG. 3 is a block diagram showing a functional configuration of the inkjet recording apparatus 1 of the present embodiment.

  In addition to the control unit 40, the conveyance unit 10, the image forming unit 20, and the image reading unit 30, the inkjet recording apparatus 1 includes a communication unit 50, a storage unit 60, an operation display unit 70, and a bus 80. Etc.

  The control unit 40 performs a control operation that comprehensively controls the overall operation of the inkjet recording apparatus 1. The control unit 40 also performs adjustments related to ink ejection based on the test image formed by the image forming unit 20 and read by the image reading unit 30, and performs overall image quality and ink ejection from each nozzle opening. Various control processes such as inspection and handling related to are performed.

  The control unit 40 includes a CPU 41 (Central Processing Unit), a ROM 42 (Read Only Memory), a RAM 43 (Random Access Memory), and the like. The CPU 41 performs arithmetic processing and executes various processes related to operation control. The ROM 42 stores a control program related to operation control. As the ROM 42, a mask ROM, a readable / writable nonvolatile memory such as a flash memory, or a combination thereof is used.

  The RAM 43 provides a working memory space to the CPU 41 and stores temporary data and various settings. As the RAM 43, various volatile memories such as SRAM and DRAM are used.

  The transport unit 10 includes a transport motor 14 and an encoder 15. The transport motor 14 rotates at a predetermined speed based on a control signal from the control unit 40 and rotates the driving roller 11 to rotate the transport belt 12 in the transport direction. The encoder 15 measures the conveyance speed. As the encoder 15, a rotary encoder that measures the rotational speed of the driving roller 11 or the transport motor 14 as well as the one that directly measures the moving speed of the transport belt 12 can be used. The conveyance speed is fed back to the control unit 40 and used for adjusting the set speed, or used for calculating the moving distance from a predetermined timing, and used for adjusting the ink discharge position on the recording medium P. Or

  The image forming unit 20 includes an image processing unit 25, an output correction unit 26 (correction unit), a head drive unit 27, and the like. The head drive unit 27 outputs a drive signal for operating the ink discharge mechanism in the recording head 211 of each head unit 21, and discharges ink from the opening of the operation target nozzle at an appropriate timing. These drive signals are output in parallel to each head unit 21 (recording head 211). The drive signal is output in synchronization with the encoder 15 that measures the conveyance speed (position) of the recording medium P by the conveyance unit 10. As an ink discharge mechanism, for example, a voltage is applied to a piezoelectric element provided along an ink flow path communicating with a nozzle to deform the piezoelectric element, and pressure is applied to the ink in the ink flow path with a predetermined pressure pattern. In addition, a piezo type that ejects ink, or heat is generated by flowing current through a heating wire, and the ink in the ink flow path is heated and partly vaporized, causing a volume change and ejecting by applying pressure to the ink. A thermal type is used.

  In the inkjet recording apparatus 1, when forming a grayscale image, the image forming unit 20 performs grayscale expression by performing halftone processing and using the ink coverage on the surface of the recording medium. That is, the image processing unit 25 generates the density gradation image by converting the density gradation in the image data of the image to be recorded into the liquid amount per droplet or the number of droplets per unit area, and the head driving unit 27 Ink is ejected from each nozzle opening according to the density gradation image. As the halftone processing, a method based on a predetermined dither matrix, an error diffusion method, or the like is used.

  Based on the output correction table 62, the output correction unit 26 corrects the output image data (density gradation image) from each nozzle in order to record an image with uniform color according to the density gradation of the recorded image.

  The image reading unit 30 includes an imaging drive unit 31 and a line sensor 32. The imaging drive unit 31 operates each imaging device of the line sensor 32 to detect the amount of incident light detected by the imaging device, that is, the brightness value of reflected light in the reading range of the surface of the recording medium P by each imaging device. Is generated and output to the control unit 40 (RAM 43) or the storage unit 60. The imaging data may be directly output to the RAM 43 or the storage unit 60 by DMA (Direct Memory Access) without being controlled by the CPU 41. Further, a predetermined calibration operation may be performed at the time of conversion from incident light amount data to imaging data. The line sensor 32 is arranged with wavelength filters and / or image sensors that can detect the luminance of each wavelength band of RGB. Further, the image reading unit 30 may include an illumination unit that irradiates the surface of the recording medium P with a predetermined amount of light.

  The communication unit 50 acquires image formation data and a print job from an external computer terminal or a print server according to a predetermined communication protocol, and outputs a status signal related to image formation.

  The storage unit 60 stores image formation data acquired through the communication unit 50 and processing data thereof. The storage unit 60 may store various execution programs related to image formation, and the CPU 41 reads out and loads the execution program into the RAM 43 when the execution program is executed. As the storage unit 60, for example, an HDD (Hard Disk Drive) or flash memory and a RAM (DRAM) are used together, image data is temporarily stored in the RAM, and setting data is stored in the flash memory or the like.

The setting data stored in the nonvolatile memory includes a luminance value colorimetric value conversion table 61, an output correction table 62, and the like.
The luminance value colorimetric value conversion table 61 is a table for converting luminance values read by the line sensor 32 of the image reading unit 30 into colorimetric values obtained by a predetermined external colorimeter. The table data is set for each type of recording medium P and each ink color, and can be updated. The gradation of the luminance value (colorimetric value) defined by the table data is appropriately determined to be 2 or more, and the gradation can be determined by linear interpolation or the like.

The output correction table 62 is a table for correcting the output image data in order to form an image with gradation according to the output image data by the head driving unit 27 of the inkjet recording apparatus 1 of the present embodiment. In the inkjet recording apparatus 1, an image is recorded with the same density gradation in accordance with a deviation of an actual applied voltage of the head driving unit 27 and a variation in characteristics of a load (piezoelectric element) driven by the head driving unit 27. Even if it tries, the density gradation of the recorded image will vary. Therefore, here, in order to obtain the density gradation given by the output image data, the output at the density gradation is output with the density gradation corrected by the output correction table 62. In the output correction table 62, a correction amount is determined and stored for each of a predetermined number of nozzles in each head unit 21 (recording head 211), and is used complementarily according to the nozzle position.
Prior to correction with output image data, the voltage applied by the head drive unit 27 that can be controlled in units of coarse nozzle areas as compared with the processing using the output correction table 62, the pulse width of the pulse voltage applied to the piezoelectric element, etc. It may be possible to perform a pre-stage homogenization process that changes.

  The operation display unit 70 displays a user input operation acceptance screen and status information as the display unit 71, and accepts a user input operation as the operation acceptance unit 72 and outputs an operation signal to the control unit 40. The operation display unit 70 is provided with, for example, a touch sensor and a liquid crystal screen overlapped with each other, and includes these drivers. Alternatively, a display screen according to another display method such as an organic EL display may be used for display, or an LED lamp for status display may be used in combination. In addition, a push button switch, a rotation switch, or the like may be provided for accepting the operation instead of or in addition to the touch panel.

  The bus 80 is a path for transmitting and receiving signals between the control unit 40 and other components.

  Next, change detection and adjustment of the ink ejection operation in the inkjet recording apparatus 1 of the present embodiment will be described.

  In the ink jet recording apparatus 1 of the present embodiment, is an image formed with an appropriate density by the image forming unit 20 based on the luminance value of a halftone image of a predetermined density captured by the line sensor 32 of the image reading unit 30? Whether or not there is a deviation from the appropriate density is corrected. At this time, the magnitude of the luminance value acquired by the sensor is not necessarily proportional to the density gradation of the color that humans perceive visually. Therefore, in the inkjet recording apparatus 1, a luminance value colorimetric value conversion table 61 for converting luminance values into color density gradations is stored in the storage unit 60 in advance, so that colorimetric values, that is, density gradations change. It is determined whether or not an image is formed with an appropriate density gradation according to the corresponding value.

FIG. 4 is a diagram illustrating an example of a correspondence relationship between luminance values and colorimetric values.
FIG. 4A shows a luminance value obtained by measuring reflected light obtained by illuminating an image of K color (black) ink at a predetermined illuminance in the G color wavelength band of the sensor of the image reading unit 30, and L * a *. It is a figure which shows the example of the relationship with the value of the L * component of the colorimetric value in a b * color system.

In the ink jet recording apparatus, the density of each color of CMYK changes according to the coverage of ink that lands on the recording medium. For example, the darkness of the K color can be defined by the L * component of the value measured by printing a halftone image with the K color ink, that is, the brightness. However, the luminance value read by the sensor, here, the luminance value in the G color wavelength band and the size of the L * component are not proportional and are on a predetermined curve. Must be retained.
Similarly, the brightness value of each ink of cyan, magenta, and black is associated with the L * value of the L * a * b * color system or the Y value of the XYZ color system, and the brightness value of the yellow ink Is associated with the b * value in the L * a * b * color system or the Z value in the XYZ color system, and the corresponding relationship is maintained.

On the other hand, the two curves shown in FIG. 4B show the relationship between the liquid amount per unit area and the L * component of the colorimetric value when the droplet amount of the K ink dots is varied. ing. When the dot droplet amount is different, that is, when the covering area is different, the relationship between the liquid amount per unit area and the lightness (L * value) slightly changes. That is, in the ink jet recording apparatus 1, even when an image having the same density gradation is output in accordance with a calibration operation such as unevenness correction, if the image forming conditions such as the ink discharge amount change, the coverage per dot changes. However, the relationship between the liquid volume and the color value changes. In addition, the relationship between the liquid amount and the luminance value also changes. As a result, a color value that is the same as the luminance value (that is, a colorimetric value obtained by a colorimeter) may not be obtained. In this way, when the correspondence between the luminance value and the colorimetric value changes in response to the change in the coverage ratio exceeding a predetermined level according to the change in the operation of the recording unit, the held correspondence is updated. Need to do.
Corresponding to the difference in ink spreading and penetration characteristics on the recording medium P, the coverage with respect to the ink ejection amount (droplet amount) is the type of recording medium P (including the difference in surface quality), for example, There is also a great difference between coated paper and non-coated plain paper. Accordingly, it is necessary to maintain a corresponding relationship for each type of the recording medium P. In the inkjet recording apparatus 1, since the types of the recording medium P can be set widely, in addition to a predetermined typical type of the recording medium P, a new one is added according to a user's input operation to the operation receiving unit 72 or the like. Additional types can be set.

  FIG. 5 is a diagram showing an example of a halftone image (patch image) showing a plurality of density gradations for each ink color. Here, a patch image (inspection image portion having a predetermined density gradation) indicating 16 density gradations in the transport direction is sequentially formed for each of the four colors of ink (YMCK).

  The image of each density gradation portion of each ink is read by the line sensor 32 to obtain a luminance value, and the image of each density gradation portion is measured by an external colorimeter and associated with each other. Thus, a correspondence relationship between the luminance value and the colorimetric value at a plurality of density gradations can be obtained for each ink.

  FIG. 6 is a flowchart showing a control procedure by the control unit 40 of the correspondence table setting process executed in the inkjet recording apparatus 1 of the present embodiment.

This correspondence table setting process is activated when the inkjet recording apparatus 1 is activated for the first time, when the recording head 211 or the head unit 21 is replaced, or when a command is detected based on a user input operation or the like. Is done.
When the correspondence table setting process is started, the control unit 40 (CPU 41) acquires the type of the recording medium P that is an image recording target (step S101). The control unit 40 causes the image forming unit 20 to form the above-described patch image on the recording medium P as a test image (step S102). In addition, the control unit 40 causes the formed patch image to be captured by the sensor of the image reading unit 30 (step S103).

  The control unit 40 acquires a luminance value for each density gradation of each ink color based on the imaging data (step S104). Here, the control unit 40 acquires the luminance value of the B color band wavelength data for the Y color ink, and acquires the luminance value of the G color band wavelength data for each of the M, C, and K color inks. .

  The control unit 40 acquires data of colorimetric values measured for each density gradation of each ink color from the outside via the communication unit 50 (step S105). The control unit 40 associates the luminance value with the colorimetric value for each density gradation of each ink color (acquires update data of the correspondence relationship) (step S106; relationship acquisition step). The control unit 40 stores the obtained correspondence data in the storage unit 60 as the luminance value colorimetric value conversion table 61 for the acquired recording medium (step S107). Then, the control unit 40 ends the correspondence table setting process.

  If the luminance value colorimetric value conversion table 61 is already held and each luminance value acquired in the process of step S104 does not deviate by more than a predetermined upper limit width, the process does not proceed to step S105 and subsequent steps. The process can be terminated as it is. That is, the trouble of acquiring the colorimetric values is saved, and the luminance value colorimetric value conversion table 61 is not updated.

FIG. 7 is a diagram illustrating an example of the density unevenness detection image.
This density unevenness detection image is obtained by forming a halftone image in which ink is ejected from the nozzle openings of the head unit 21 shown in FIG. 2 at a uniform frequency. This halftone image is formed with a plurality of density gradations, here, 12 gradations in the transport direction. When the halftone image of each gradation is read by the image reading unit 30 and the luminance value is converted into a colorimetric value, the variation in the width direction of the colorimetric value is not within a predetermined range. Is configured to correct the ink discharge amount from the nozzle opening in the corresponding range so as to fall within the predetermined range (so as to have a value indicating the color according to the initially determined density gradation) When the image is recorded, the output correction unit 26 reflects the setting on the image data (corrects the image data) to eliminate density unevenness.

FIG. 8 is a flowchart showing a control procedure by the control unit 40 of density unevenness correction processing which is a correction step of the image quality adjustment method executed in the inkjet recording apparatus 1 of the present embodiment.
This density unevenness correction process is subsequently executed when the luminance value colorimetric value conversion table 61 is updated by the above-described correspondence table setting process. Further, this density unevenness correction processing is periodically called and executed at a predetermined frequency, for example, at the start of the first image recording operation once a day or at the first timing when the type of the recording medium is changed. .

  When the density unevenness correction process is started, the control unit 40 causes the image forming unit 20 to record a density unevenness detection image on the recording medium P (step S121). Further, the control unit 40 causes the image reading unit 30 to capture the density unevenness detection image recorded on the recording medium P (step S122).

  The control unit 40 acquires the luminance value distribution in the width direction for each halftone image of each density gradation from the imaging data (step S123). The control unit 40 refers to the luminance value colorimetric value conversion table 61 and converts each luminance value into a colorimetric value (step S124). Based on the distribution of the colorimetric values, the control unit 40 creates a correction table relating to the correction amount of the image data for obtaining a uniform colorimetric value in the width direction for the same density gradation, and as the output correction table 62 It memorize | stores in the memory | storage part 60 (step S125). Then, the control unit 40 ends the density unevenness correction process.

FIG. 9 and FIG. 10 are diagrams illustrating examples of output images related to luminance value change detection in a normal image.
In the inkjet recording apparatus 1, when a normal recording target image (output target image) is output, a patch image for detecting a change in luminance value can be formed in the margin portion. The patch image is at least a part of the image (inspection target image) shown in FIG. 5, and the part is, for example, for each output of the recording target image, as shown in FIGS. It is changed in order. Further, the density gradation value of each patch image may be changed every cycle.

  A part of the patch image is read by the image reading unit 30, and the obtained luminance value is changed from the luminance value originally assumed from the ink color and density gradation value by a predetermined upper limit range, that is, the head. It is used to detect whether a change related to the operation of the unit 21 has occurred.

  FIG. 11 is a flowchart showing a control procedure by the control unit 40 of the variation detection process executed in the inkjet recording apparatus 1 of the present embodiment.

This variation detection process is periodically executed in a situation where a margin can be formed while being replaced with a test image related to another inspection as necessary when a normal recording target image is output.
When the variation detection processing is started, the control unit 40 (CPU 41) adds a halftone image of a predetermined density gradation of each color as a test image to the margin of the normal recording target image by the image processing unit 25. Output image data is generated (step S141).

  The control unit 40 causes the image forming unit 20 to form an output image on the recording medium P based on the generated output image data (step S142). The control unit 40 causes the image reading unit 30 to capture at least a test image portion of the output image (step S143). The control unit 40 acquires the luminance value of each halftone image from the imaging data (step S144), and converts it into a calorimetric value with reference to the luminance value calorimetric value conversion table 61 (step S145).

The control unit 40 calculates a deviation from the density gradation in the original data of the halftone image for the colorimetric values of the obtained halftone image of each ink color (step S146). The control unit 40 determines whether or not the deviation is within a predetermined reference range (step S147). When it is determined that it is within the reference range (“YES” in step S147), the control unit 40 ends the variation detection process.
The processes in steps S144 to S147 constitute a change detection step.

  If it is determined that the deviation is not within the reference range (“NO” in step S147), the control unit 40 executes the correspondence table setting process prior to the next density unevenness correction process. As such, setting (flag setting) is performed (step S148). Then, the control unit 40 ends the variation detection process.

  Note that the control unit 40 may immediately stop the recording operation of the recording target image in the process of step S148, and may further notify the user that the correspondence relationship between the luminance value and the colorimetric value should be updated. good. For example, the control unit 40 sends a control signal to the display unit 71 to display that the correspondence relationship between the luminance value and the colorimetric value should be updated, and to stop the normal recording operation of the recording target image. Then, the control unit 40 determines whether or not an input operation requesting execution of the correspondence table setting process (an operation requesting an update in an operation for selecting whether to update) is detected, and is determined to be detected. In this case, the correspondence table setting process shown in FIG. 6 may be activated to shift the process. In this case, even if there is no execution request by a user input operation or the like, the processing may be automatically shifted at a timing when a normal image recording operation being executed is divided.

As described above, the inkjet recording apparatus 1 according to the present embodiment includes the image forming unit 20 (head unit 21) that records the recording target image by ejecting ink onto the recording medium P, and the control unit 40. The unit 40 performs control processing related to the recording operation of the image to be recorded by the image forming unit 20 (head unit 21) as a control processing unit, and is read from the surface of the recording medium P by the image reading unit 30 as a relationship acquisition unit. The correspondence relationship between the luminance value and the predetermined colorimetric value is acquired, and the change detection unit detects a change related to the operation of the image forming unit 20 (head unit 21) based on the reading result of the luminance value. In addition, the output correction unit 26 of the image forming unit 20 initially determines the colorimetric value obtained according to the correspondence from the result of reading the luminance value of the recording target image on the surface of the recording medium for the recording target image. It operates as a correction unit that corrects the image data of the recording target image so as to have a value indicating the color corresponding to the density gradation.
In this way, a change in the operation of the head unit 21 is detected using luminance value data that can be read at a high speed by the image reading unit 30 to determine when to update the luminance value colorimetric value conversion table 61. Therefore, it is possible to easily know the adjustment timing for recording an image with an appropriate gradation according to a change in the ink ejection operation.

  Further, the control unit 40 causes the head unit 21 to record a recording target image including an inspection image portion (patch image) having a predetermined density gradation as a control processing unit, and relates to the operation of the head unit 21 as a change detection unit. As a change, the luminance value of the inspection image portion corresponding to a case where the coverage of the recording medium P by the ejected ink in the inspection image portion has changed by a predetermined level or more from the timing at which the luminance value colorimetric value conversion table 61 was most recently acquired. Detect changes. Thus, by detecting the change in the luminance value according to the change in the coverage, it is possible to easily know the appropriate update timing quantitatively.

Further, when a change related to the operation of the head unit 21 exceeding a predetermined reference is detected as a change detection unit, the control unit 40 serves as a control processing unit a patch image including a plurality of density gradation inspection image portions. The data is recorded by the head unit 21, and the update data of the luminance value colorimetric value conversion table 61 based on the patch image is acquired as a relationship acquisition unit, and the luminance value colorimetric value conversion table 61 is updated with the update data.
In this way, when a change that leads to a change in the correspondence between the luminance value and the colorimetric value is detected, it is possible to prevent the user from forgetting to update the data by quickly moving to an update data acquisition operation. The luminance value calorimetric value conversion table 61 can be reliably maintained in an appropriate state at an appropriate timing.

  The head unit 21 discharges a plurality of colors of ink to record a recording target image, and the test image (patch image) includes a plurality of density gradation test image portions for each of the plurality of colors of ink. As described above, since the correspondence between the luminance value and the colorimetric value is different for each ink color, an appropriate correspondence can be maintained by performing a change detection operation that leads to a change in the correspondence for each ink color. .

Further, when the normal output target image is recorded on the recording medium P as the control processing unit, the control unit 40 includes at least a part of the inspection image portion (patch image) in the margin portion of the output target image. The recording target image is recorded by the head unit 21, and the change detection unit detects a change related to the operation of the head unit 21 exceeding a predetermined reference based on the reading result of the luminance value of the recorded inspection image portion.
In this way, the detection-dedicated patch image is not periodically output to the recording medium P, but is output part by part in the margin, thereby reducing the waste of the recording medium P and discharging ink of each color. It is possible to detect the change of the head unit 21 according to the above as needed, and to know whether the luminance value colorimetric value conversion table 61 shows an appropriate relationship.

  Moreover, the control part 40 changes at least one part of the test | inspection image part recorded on a blank part as a control process part for every recording of an output object image. That is, when patch images for all density gradations of all ink colors cannot be output in the margin, the recording medium P is wasted within the replacement cycle by switching these in order. It is possible to detect a change related to the operation of the head unit 21 promptly without any change.

  In addition, the control unit 40 acquires a plurality of luminance value colorimetric value conversion tables 61 for each type of recording medium determined in advance as a relationship acquisition unit. In the ink jet recording apparatus 1, ink can be ejected to a wide variety of recording media, and the degree of penetration and spread of the landed ink varies greatly depending on the type of the recording medium P, so the coverage is also large. Different. Therefore, by holding a plurality of luminance value colorimetric value conversion tables 61 in advance according to the types of these recording media, when the recording medium P on which image recording is performed is switched, an appropriate luminance is simply obtained. A homogeneous image with an appropriate density can be recorded on the recording medium P simply by selecting the colorimetric value conversion table 61.

  The type of the recording medium P includes coated paper with coating and plain paper with no coating. As the recording medium P on which an image is recorded by the ink jet recording apparatus 1, these two types are representative, and the coverage is greatly different for an equal amount of ink ejection. By holding the colorimetric value conversion table 61 in advance and updating it as necessary, an appropriate and uniform image can be recorded on each recording medium P with a small number of classifications.

  Further, since the type of the recording medium P can be additionally set, the brightness value colorimetric value conversion table 61 corresponding to the type is stored when image recording on a special type of recording medium is newly performed. Additional storage is possible, and appropriate image recording on a new type of recording medium P can be easily performed without having to rewrite the luminance value calorimetric value conversion table related to the other type of recording medium P that has been held in the past. It becomes. Therefore, user convenience can be improved.

  The head unit 21 discharges at least each ink of cyan, magenta, and yellow to record an image, and the luminance value colorimetric value conversion table 61 stores a green luminance value or a green luminance value read from a C color image with cyan ink. The red luminance value and the colorimetric value of the C color image are associated with each other, the green luminance value read from the M color image with magenta ink and the colorimetric value of the M color image are associated with each other, and the Y color image with the yellow ink The blue luminance value read from the image is associated with the colorimetric value of the Y color image. As described above, the correspondence between the read luminance value of each color ink landed on the recording medium P and the colorimetric value only needs to be held for the minimum necessary luminance value, so that detection and processing can be facilitated. In addition, the size of the luminance value colorimetric value conversion table 61 need not be increased more than necessary.

The head unit 21 discharges cyan, magenta, yellow, and black inks to record an image, and the luminance value calorimetric value conversion table 61 includes an inspection image portion using cyan, magenta, and black inks. Is associated with the Y value of the XYZ color system or the L * value of the L * a * b * color system, and the luminance value read from the inspection image portion with yellow ink is the Z value of the XYZ color system. Or, it is associated with the b * value of the L * a * b * color system.
Similarly, the colorimetric values associated with the luminance values of the inks that have landed on the recording medium P need only be determined and held within the range necessary for considering the correspondence, so that the processing can be easily stopped. The size of the luminance value calorimetric value conversion table 61 can be maintained at an appropriate size.

  In addition, the inkjet recording apparatus 1 includes an image reading unit 30 that reads the luminance value on the surface of the recording medium. Therefore, a change related to the operation of the recording unit based on the luminance value can be detected immediately and easily inside the inkjet recording apparatus 1. In particular, since such a change can be detected easily and quickly in the middle of recording an image at high speed, it becomes possible to record a uniform image stably.

In addition, the inkjet recording apparatus 1 includes a display unit 71, and when the control unit 40 detects a change related to the operation of the head unit 21 that is equal to or greater than a predetermined reference as a change detection unit, the change is displayed on the display unit 71. A predetermined display indicating detection is performed.
In this way, it is possible to make the user of the ink jet recording apparatus 1 and the monitor of the operation status easily and promptly know by displaying the state that the luminance value colorimetric value conversion table 61 needs to be updated. And forgetting to perform the process can be prevented, and the recording operation in the ink jet recording apparatus 1 can be made to quickly follow the correspondence between the appropriate luminance value and the colorimetric value.

In addition, the control unit 40 includes an operation reception unit 72 that receives a user operation. The control unit 40 causes the display unit 71 to perform a predetermined display as a change detection unit, and then the luminance value colorimetric value conversion table 61 is displayed by the operation reception unit 72. An operation for selecting whether or not to update is accepted.
Therefore, for example, in the middle of an image recording operation, when the image recording operation is interrupted and it is not desired to immediately perform the patch image recording operation related to the update of the luminance value calorimetric value conversion table 61, a series of images The update is suspended until the recording operation is completed, and the convenience of the user can be improved.

Further, the image quality adjustment method according to the present embodiment acquires the correspondence between the luminance value of the surface of the recording medium P read by the image reading unit 30 and a predetermined colorimetric value, that is, the luminance value colorimetric value conversion table 61. In the relationship acquisition step, the colorimetric value obtained in accordance with the luminance value colorimetric value conversion table 61 from the reading result of the luminance value of the recording target image on the surface of the recording medium P becomes the density gradation initially determined for the recording target image. A correction step of correcting the image data of the recording target image so as to obtain a value indicating the corresponding color, and a change detection step of detecting a change related to the operation of the head unit 21 based on the reading result of the luminance value.
As described above, in the ink jet recording apparatus 1, the coverage of the ink on the recording medium P can be changed due to various factors. Therefore, the correspondence relationship between the luminance value and the colorimetric value also changes according to the change in the coverage. Therefore, by performing the process of detecting such a change based on the reading result of the luminance value, whether or not the luminance value colorimetric value conversion table 61 needs to be updated can be easily and quickly updated. It is possible to make the supervisor know. Therefore, the user, the administrator, the maintenance person, etc. of the inkjet recording apparatus 1 do not need to update the luminance value colorimetric value conversion table 61 more than necessary, and reliably perform the luminance value colorimetry when necessary. The value conversion table 61 can be updated.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above-described embodiment, the colorimetric value is acquired using an external colorimeter, the colorimetric value data is acquired via the communication unit 50, and is read by the image reading unit 30. However, the inkjet recording apparatus 1 may include a colorimeter, measure both the colorimetric value and the luminance value, and the control unit 40 may acquire and associate all of them.

  In the above embodiment, the image reading unit 30 includes the line sensor 32 and uses the luminance value read by the line sensor 32. However, the luminance value may be acquired by a two-dimensional sensor other than the line sensor. These sensors may be fixed sensors provided over the maximum recording width of the recording medium P, or may be scan-type sensors that can move in the width direction.

  In the above embodiment, a part of the patch image provided together with the normal image is provided at the upstream and downstream ends in the transport direction with respect to the normal image. Or may be formed only on either side of the width direction. Further, it is not always necessary to record a part of the patch image together with all the normal images.

  Further, when outputting a normal image with insufficient margin for forming a part of the patch image, a process of outputting the entire patch image to the recording medium P may be inserted every time a predetermined number of normal images are output.

  In the above-described embodiment, the description has been made by taking coated paper and plain paper as examples of the recording medium. However, the recording medium is not limited to the paper medium, and may include various films, thin films, substrates, and the like. Further, a different luminance value calorimetric value conversion table 61 can be determined depending on the presence or absence of preprocessing for these recording media.

  In the above-described embodiment, the configuration capable of ejecting CMYK four color inks has been described as an example. However, the number of ink colors is not limited thereto. For example, these intermediate color inks may be further ejected. For these inks, an appropriate detection wavelength band of luminance values, a corresponding colorimetric value component, and the like are determined.

  In the above embodiment, the display operation on the display unit 71 notifies the user that the luminance value calorimetric value conversion table 61 needs to be updated. In addition to or instead of this, audio output is performed. For example, notification may be performed, or an e-mail may be transmitted to the administrator.

  In the above-described embodiment, the image reading unit 30 is provided, and all the reading of the image and the detection of the change related to the operation of the image forming unit 20 (head unit 21) are performed inside the inkjet recording apparatus 1. A similar process may be performed by connecting an additional reading sensor and causing the control unit 40 to input a reading result via the communication unit 50. However, in order to prevent the influence due to the difference in the reading luminance value between the sensors, the same reading sensor is normally preferably used continuously, and when the reading sensor is changed, the luminance value calorimetric value conversion table 61 is also used. Updated.

Moreover, in the said embodiment, although demonstrated taking the example of the inkjet recording device 1 which has a line head, it is not restricted to this. The present invention can be applied to all inkjet recording apparatuses having a recording head in which a plurality of nozzle openings are arranged and each ejects ink.
In addition, specific details such as the configuration, processing contents, and procedures shown in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 10 Conveyance part 11 Drive roller 12 Conveyance belt 14 Conveyance motor 15 Encoder 20 Image formation part 21, 21C, 21M, 21Y, 21K Head unit 211 Recording head 25 Image processing part 26 Output correction part 27 Head drive part 30 Image Reading unit 31 Imaging drive unit 32 Line sensor 40 Control unit 41 CPU
42 ROM
43 RAM
50 communication unit 60 storage unit 61 luminance value colorimetric value conversion table 62 output correction table 70 operation display unit 71 display unit 72 operation reception unit 80 bus P recording medium

Claims (15)

A recording unit for recording an image to be recorded by discharging ink onto a recording medium;
A control processing unit for performing a control process related to a recording operation of a recording target image by the recording unit;
A relationship acquisition unit for acquiring a correspondence relationship between a luminance value read from the surface of the recording medium and a predetermined colorimetric value;
The colorimetric value obtained according to the correspondence relationship from the reading result of the luminance value of the recording target image on the surface of the recording medium is a value indicating the color corresponding to the density gradation initially determined for the recording target image. A correction unit for correcting the image data of the recording target image;
A change detection unit that detects a change related to the operation of the recording unit based on a reading result of the luminance value;
An ink jet recording apparatus comprising: The control processing unit causes the recording unit to record a recording target image including an inspection image portion having a predetermined density gradation,
The change detection unit corresponds to a case where the coverage of the recording medium by the ejected ink in the inspection image portion has changed by a predetermined level or more from the timing at which the correspondence relationship was most recently acquired as a change related to the operation of the recording unit. The inkjet recording apparatus according to claim 1, wherein a change in luminance value of the inspection image portion to be detected is detected. When the change detection unit detects a change related to the operation of the recording unit that is equal to or greater than a predetermined reference, the control processing unit records a test image including a plurality of density gradation test image portions by the recording unit. The inkjet recording apparatus according to claim 1, wherein the relationship acquisition unit acquires update data of the correspondence relationship based on the test image and updates the correspondence relationship with the update data. The recording unit records the recording target image by ejecting a plurality of colors of ink;
The inkjet recording apparatus according to claim 3, wherein the test image includes an inspection image portion having a plurality of density gradations for each of the plurality of colors of ink. When the normal processing target image is recorded on the recording medium, the control processing unit causes the recording unit to record a recording target image including at least a part of the inspection image portion in a margin portion of the output target image. ,
The change detection unit detects a change related to the operation of the recording unit that is equal to or greater than a predetermined reference based on a reading result of a luminance value of the recorded inspection image portion. An ink jet recording apparatus according to claim 1.   6. The ink jet recording apparatus according to claim 5, wherein the control processing unit changes at least a part of the inspection image portion to be recorded in the blank portion every time the output target image is recorded.   The inkjet recording apparatus according to claim 1, wherein the relationship acquisition unit acquires a plurality of the correspondence relationships for each type of recording medium determined in advance.   8. The ink jet recording apparatus according to claim 7, wherein the types of the recording medium include coated paper with coating and plain paper without coating.   9. The ink jet recording apparatus according to claim 7, wherein the type of the recording medium can be additionally set. The recording unit records an image by discharging at least cyan, magenta, and yellow inks,
The correspondence relationship associates a green luminance value or red luminance value read from a C color image with cyan ink with a colorimetric value of the C color image, and a green luminance value read from an M color image with magenta ink. The colorimetric value of the M color image is associated with each other, and the blue luminance value read from the Y color image with yellow ink is associated with the colorimetric value of the Y color image. The ink jet recording apparatus according to one item. The recording unit records an image by ejecting each color ink of cyan, magenta, yellow, and black,
The correspondence relationship is such that the luminance value read from the inspection image portion of each ink of cyan, magenta, and black is associated with the Y value of the XYZ color system or the L * value of the L * a * b * color system, yellow The luminance value read from the inspection image portion by ink is associated with the Z value of the XYZ color system or the b * value of the L * a * b * color system. The ink jet recording apparatus described.   The inkjet recording apparatus according to claim 1, further comprising a reading unit that reads a luminance value of the surface of the recording medium. With a display,
The said change detection part makes the said display part perform the predetermined | prescribed display which shows the detection of the said change, when the change which concerns on the operation | movement of the said recording part more than a predetermined reference | standard is detected. The inkjet recording apparatus according to any one of 12. It has an operation reception unit that receives user operations,
The change detection unit receives an operation for selecting whether or not to update the correspondence relationship by the operation reception unit after the predetermined display is performed by the display unit. Inkjet recording apparatus. An image quality adjustment method for an inkjet recording apparatus including a recording unit that records an image to be recorded by discharging ink onto a recording medium,
A relationship acquisition step of acquiring a correspondence relationship between a luminance value read from the surface of the recording medium and a predetermined colorimetric value;
The colorimetric value obtained according to the correspondence relationship from the reading result of the luminance value of the recording target image on the surface of the recording medium is a value indicating the color corresponding to the density gradation initially determined for the recording target image. A correction step of correcting the image data of the recording target image,
A change detecting step for detecting a change related to the operation of the recording unit based on a reading result of the luminance value;
An image quality adjustment method comprising: