JP2014004736A - Image recording apparatus, defective discharge detection method, test chart generation method, and test chart data generation program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine defective discharge with high accuracy and at high speed depending on an image.SOLUTION: An image recording apparatus includes movement means for relatively moving a liquid discharge head including a plurality of nozzles for discharging liquid and a recording medium, control means for performing recording on the recording medium by discharging the liquid from the plurality of nozzles while relatively moving the liquid discharge head and the recording medium, test chart data generation means for generating test chart data based on image data, test chart recording means for recording a test chart on the recording medium by the control means based on the test chart data, read data acquisition means for acquiring read data of the recorded test chart, and defect detection means for detecting the discharge-defective nozzle by analyzing the read data of the test chart.

Description

  The present invention relates to an image recording apparatus, an ejection failure detection method, a test chart creation method, and a test chart data generation program, and more particularly to a technique for detecting a defective nozzle in a liquid ejection head in which a plurality of nozzles that eject liquid are arranged.

  Many techniques have been proposed for detecting defective nozzles such as ink not being ejected in an inkjet head in which a plurality of nozzles that eject ink are arranged.

  For example, Patent Document 1 discloses an image formed on a medium by ejecting a fluid while the nozzle is moved relative to the medium in the relative movement direction based on the image data. Reading with a sensor so that the reading resolution is lower than that, generating reference data having the same resolution as the reading resolution in the relative movement direction based on the image data, and the data in the relative movement direction in the data read by the sensor A plurality of read data pixels on the same column and a plurality of reference data pixels corresponding to the plurality of read data pixels in the reference data, respectively, and detecting ejection failure of the nozzles. A defect detection method is disclosed.

  According to this technique, since the ejection failure of the nozzle is determined based on detection results on a plurality of reading lines, erroneous detection can be prevented. Further, according to such a discharge failure detection method, it is possible to reduce the amount of processing data in discharge failure detection while maintaining the accuracy of discharge failure detection.

JP 2010-240885 A

  However, the technique described in Patent Document 1 has the following problems.

(1) Accuracy of ejection failure detection The failure nozzle is determined by comparing the pixels of the reference image data and the read image data. In the case of a printer using CMYK ink, which color (what It is necessary to detect whether a problem has occurred in the color nozzle). For example, when there is a difference between the reference image data and the reference image data in gray color, it can be seen that there is a difference between the reference image data and the read image data, but a complicated color determination process for determining which color is generated is necessary. .

  Depending on the pattern of the output image, there may be a case where the position error and the image defect cannot be distinguished. For example, when there is a fine striped pattern perpendicular to the nozzle arrangement direction in the output image, if the alignment in the nozzle arrangement direction is not accurate, streaky irregularities (defective nozzles) and misalignment will occur when the difference is taken. It is difficult to tell the difference from the resulting pattern.

(2) Data processing amount When performing wide-width and high-speed printing in a single-pass inkjet recording apparatus, even if the reading resolution in the paper feed direction is set low, ejection failure detection processing is performed on the actual image over the entire image area. It is difficult.

  For example, if the recording resolution of the output device is 720 dpi vertical × 1440 dpi horizontal, if an image of A2 size (594 vertical × 420 mm horizontal) is captured as it is with 8 bits each for RGB, the image data size is about 1 GB. It becomes. Even if the reading resolution in the paper feed direction is lowered, the amount of data is still large. In order to perform processing using this data, a high-speed and large-capacity image processing apparatus is required.

  The present invention has been made in view of such circumstances, and an image recording apparatus, an ejection failure detection method, a test chart creation method, and test chart data capable of accurately and quickly determining ejection failure according to an image. An object is to provide a generation program.

  In order to achieve the above object, one aspect of an image recording apparatus includes a liquid discharge head including a plurality of nozzles that discharge liquid, a moving unit that relatively moves the liquid discharge head and the recording medium, and a liquid discharge Control means for performing recording on a recording medium by discharging liquid from a plurality of nozzles while relatively moving the head and the recording medium, a data acquisition means for acquiring image data to be recorded on the recording medium, and an image Test chart data generating means for generating test chart data based on the data, test chart recording means for recording the test chart on the recording medium by the control means based on the test chart data, and read data of the recorded test chart Read image acquisition means for acquiring the error, and failure detection means for analyzing the read data of the test chart and detecting nozzles with defective discharge With.

  According to this aspect, the test chart data is generated based on the image data recorded on the recording medium, the test chart is recorded on the recording medium based on the generated test chart data, and the recorded test chart Since the reading data is acquired and the reading data of the test chart is analyzed to detect the defective nozzle, it is possible to detect the defective nozzle with high accuracy according to the pattern of the output image. Further, since the data processing amount is small, a defective nozzle can be detected at high speed.

  The test chart data generation means includes a frequency calculation means for calculating the density frequency for each pixel row parallel to the direction of relative movement, and a plurality of nozzles based on the calculated density frequency for each pixel row. It is preferable that a patch density determination unit for determining the patch density of the test chart data is generated, and test chart data is generated from the determined patch density. Accordingly, appropriate test chart data can be generated, and defective nozzle detection corresponding to the pattern of the output image can be performed.

  It is preferable that the patch density determination unit calculates the density that maximizes the frequency for each pixel column, and determines the calculated density as the patch density of the nozzle corresponding to the pixel column among the plurality of nozzles. Thereby, the patch density of a plurality of nozzles can be determined appropriately.

  The patch density determination means calculates a maximum density among the densities whose frequency exceeds a predetermined value for each pixel column, and determines the calculated density as a patch density of a nozzle corresponding to the pixel column among a plurality of nozzles. Also good. Since unevenness is more conspicuous at a high density, defective nozzles can be detected with high accuracy by determining the patch density of a plurality of nozzles in this way.

  The test chart data generating means preferably includes a smoothing processing means for reducing high frequency components for the patch density of a plurality of nozzles. In this way, defective nozzles can be detected with high accuracy by reducing high-frequency gradation fluctuations.

  You may provide the resolution conversion means which makes the resolution of the direction orthogonal to the direction of the relative movement of the acquired image data lower than the recording resolution of a some nozzle. By generating test chart data with a low resolution, it is possible to reduce high-frequency gradation fluctuations, so that defective nozzles can be detected with high accuracy.

  The data acquisition means acquires first image data to be output processed and second image data having a lower resolution in a direction orthogonal to the direction of relative movement than at least the first image data, and a test The chart data generation means may generate test chart data based on the second image data. Thereby, high-frequency gradation fluctuations can be reduced, so that defective nozzles can be detected with high accuracy.

  It is preferable that the defect detection unit includes an integration average unit that averages the read data in the direction of relative movement and converts the read data into one-dimensional data. Thereby, a defective nozzle can be detected with high accuracy.

  The defect detection means preferably includes visual characteristic filter means for converting the read data into a signal that takes human visual characteristics into consideration. Thereby, a defective nozzle can be detected with high accuracy.

  The defect detection unit may include a comparison unit that compares the read data with a threshold value to detect a defective nozzle. Thereby, a defective nozzle can be detected with high accuracy.

  The threshold is preferably set for each gradation of the patch density. Thereby, a defective nozzle can be detected with high accuracy. Further, in the case where a plurality of liquid discharge heads that discharge liquids of different colors are provided, the threshold is preferably set for each color. Thereby, a defective nozzle can be detected with high accuracy.

  You may provide the notification means to notify a user that the nozzle of the discharge defect was detected. Further, there may be provided recovery means for performing a recovery operation for a defective nozzle when a defective nozzle is detected.

  It is preferable that the test chart data generation unit adds mark data for associating the positional relationship between the plurality of nozzles of the liquid ejection head and the read pixels when the recorded test chart is read to the test chart data. Thereby, the position of the defective nozzle can be specified.

  The test chart generation unit may include a merge processing unit that merges the test chart data and the image data. In this case, the merge processing means preferably merges the test chart data on the downstream side in the direction of relative movement in the image data. Thereby, a defective nozzle can be detected with high accuracy.

  A plurality of liquid ejection heads that eject liquids of different colors are provided, the image data is image data of a plurality of colors recorded by the plurality of liquid ejection heads, and the test chart data generation means includes a plurality of tests for each color. The chart data is generated, and the merge processing unit may merge one test chart data among the plurality of test chart data into the image data. As a result, the amount of read image data can be reduced, and high-speed processing is possible.

  In order to achieve the above-mentioned object, one aspect of a test chart creation method is that an image is formed on a recording medium by ejecting liquid from a plurality of nozzles of the liquid ejection head while relatively moving the liquid ejection head and the recording medium. A method for creating a test chart for detecting defective ejection nozzles of an image recording apparatus for recording, a data acquisition step for acquiring image data to be recorded on a recording medium, and test chart data based on the acquired image data A test chart data generation step for generating a test chart and a test chart recording for recording a test chart on a recording medium by ejecting liquid from a plurality of nozzles based on the test chart data while relatively moving the liquid ejection head and the recording medium Process.

  This test chart creation method corresponds to a method for producing an object (test chart). According to this aspect, it is possible to create a test chart for accurately detecting defective nozzles of the liquid ejection head according to the pattern of the output image.

  In order to achieve the above object, one aspect of the test chart data generation program is an image on a recording medium by ejecting liquid from a plurality of nozzles while relatively moving a liquid ejection head having a plurality of nozzles and the recording medium. A test chart data generation program for causing a computer to realize a function of generating test chart data for detecting defective ejection nozzles of an image recording apparatus for recording image data, and acquiring data for acquiring image data to be recorded on a recording medium The computer implements a function and a test chart data generation function for generating test chart data based on the acquired image data.

  According to this aspect, it is possible to generate test chart data for accurately detecting defective nozzles of the liquid ejection head in accordance with the pattern of the output image.

  In order to achieve the above object, one aspect of the ejection failure detection method is to record on a recording medium by ejecting liquid from the plurality of nozzles while relatively moving a liquid ejection head having a plurality of nozzles and the recording medium. A data acquisition process for acquiring image data to be performed, a test chart data generation process for generating test chart data based on the acquired image data, and a plurality of tests based on the test chart data while relatively moving the liquid ejection head and the recording medium A test chart recording step for recording a test chart on a recording medium by discharging a liquid from the nozzle, a read image acquisition step for reading the recorded test chart and acquiring read data of the test chart, and a test chart A defect detection step of analyzing the read data and detecting a nozzle with defective discharge.

  According to this aspect, it is possible to accurately detect defective nozzles of the liquid ejection head in accordance with the pattern of the output image.

  According to the present invention, by outputting a test chart generated according to an output image, and reading this test chart to detect defective nozzles, it is possible to accurately detect defective nozzles according to the pattern of the output image. . Further, since the data processing amount is small, a defective nozzle can be detected at high speed.

Block diagram showing configuration of image recording apparatus Block diagram showing the internal configuration of the test chart creation unit Flow chart showing test chart creation process The figure which shows the histogram of the density in image data and image position I The figure which shows an example of the frequency distribution in a certain image position The figure which shows density distribution of the test chart image data of M version The figure which shows an example of the image data by which the test chart image data was merged Block diagram showing the internal configuration of the defective nozzle detector Flow chart showing detection process for defective nozzles Diagram showing examples of human visual characteristics The figure which shows an example of the data before and after the visual characteristic correction | amendment of a read image The figure which shows an example of test chart image data and mark data The figure which shows the histogram of the density in image data and image position I Diagram showing density distribution of test chart image data The figure which shows an example of the image data by which the test chart image data was merged The figure which shows the other example of the image data by which the test chart image data was merged A diagram showing a configuration example of an inkjet recording apparatus Plane perspective view showing a structural example of the head and a partial enlarged view Plane perspective view showing another structural example of the head Sectional view showing the three-dimensional configuration of the ink chamber unit Block diagram showing system configuration of inkjet recording apparatus

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

<Overall configuration of image recording apparatus>
FIG. 1 is a block diagram showing the configuration of the image recording apparatus according to this embodiment. The image recording apparatus 10 includes an input interface 12, a CMS unit 13, a test chart creation unit 14, a gamma conversion unit 16, a halftone processing unit 18, a head unit 20, a conveyance unit 22, an image reading unit 24, and a defective nozzle detection unit 26. And a machine control unit 28 and the like.

  The image recording apparatus 10 uses the cyan (C), magenta (M), yellow (Y), and black (K) color inks for the image data input from the input interface 12 (an example of a data acquisition unit). This is an ink jet printer that records on the P recording surface.

  The CMS unit 13 performs a color matching process for matching the color of the input image data with the target, and at the same time, a process of separating the output image into four CMYK colors (3-4 conversion (RGB-CMYK)). And 4-4 conversion (CMYK-CMYK)). As a result, CMYK monochrome gradation is obtained.

  The test chart creation unit 14 analyzes the CMYK image data generated by the CMS unit 13 and creates a test chart image. Details of this processing will be described later.

  The gamma conversion unit 16 performs calibration processing for each color on the CMYK image data, and adjusts output characteristics (gamma conversion).

  The halftone processing unit 18 performs halftone processing on the color data of each color subjected to gamma conversion using an error diffusion method or a dither matrix method, and generates dot data of each color.

  The head unit 20 includes inkjet heads 20C, 20M, 20Y, and 20K (an example of a liquid discharge head) that discharge CMYK color inks (an example of a liquid). The transport unit 22 (an example of a moving unit) transports the placed paper P in a predetermined direction (transport direction) with respect to the head unit 20.

  The inkjet heads 20C, 20M, 20Y, and 20K for each color complete the drawing of the entire drawing area of the paper P in the paper width direction (direction perpendicular to the transport direction) at a time (with one paper feed) at a predetermined recording resolution. It has a nozzle row (corresponding to a plurality of nozzles).

  With this nozzle row, the head unit 20 draws an image with a predetermined resolution in one transport (single pass) of the paper P by the transport unit 22.

  The image reading unit 24 is a scanner including a linear sensor type imaging device in which a large number of photoelectric conversion elements (photosensitive pixel units) are arranged in a line. The image reading unit 24 reads an image drawn on the paper P with a predetermined resolution and converts it into read image data.

  The defective nozzle detection unit 26 detects defective discharge nozzles of the respective color inkjet heads 20 </ b> C, 20 </ b> M, 20 </ b> Y, and 20 </ b> K of the head unit 20 based on the read image data acquired by the image reading unit 24. Here, the defective ejection nozzle refers to a non-ejection nozzle that cannot eject ink or a bending nozzle whose ejection direction is deviated by a predetermined amount or more from a predetermined direction.

  A machine control unit 28 (an example of a control unit) controls each unit of the image recording apparatus 10. In addition, based on the detected information on the defective nozzles, the user is notified that a defective nozzle has been detected, and performs processing such as wiping and forced ejection to recover the defective nozzle.

<First Embodiment>
[Test chart creation process]
FIG. 2 is a block diagram showing an internal configuration of the test chart creation unit 14. As shown in the figure, the test chart creation unit 14 includes a frequency calculation unit 51, a patch density calculation unit 52, a smoothing processing unit 53, a merge processing unit 54, and the like. The operation of each part will be described later.

  Next, test chart creation processing will be described with reference to the flowchart shown in FIG. The test chart creation unit 14 creates a histogram for each column corresponding to the nozzles based on the CMYK image data, and sets the most frequent color (most frequent density) as the patch color (patch density) of the column. create.

  Here, a case where the image data 11 shown in FIG. 4A is input to the image recording apparatus 10 as output image data will be described. This image data 11 indicates a so-called “Hinomaru”, and the circular area 11a in the central portion is red, and the other area 11b is white. Therefore, the ratio of each color ink in each area when the image data 11 is recorded is (C, M, Y, K) = (0, 100, 100, 0) for the area 11a and (C, M, Y, for the area 11b). K) = (0,0,0,0).

  Here, it is assumed that the resolution of the image data 11 and the recording resolution of the head unit 20 are the same. If they do not match, the image data 11 may be scaled by a resolution conversion means (not shown) to match the recording resolution of the head unit 20.

  Image data 11 (an example of a data acquisition process) input to the image recording apparatus 10 is decomposed into CMYK image data by the CMS unit 13 (step S1).

  The frequency calculation unit 51 (an example of the frequency calculation unit) of the test chart creation unit 14 performs (for each CMYK color image data (Cyan version, Magenta version, Yellow version, blacK version) for each image position i corresponding to each nozzle. The frequency h (d) of each density d [dot%] with respect to the image data Image (i, y) is calculated (for each row parallel to the paper transport direction) (step S2, an example of a frequency calculation step).

  FIG. 4B is a diagram showing histograms of the density d of the Yellow version (Y version) and the Magenta version (M version) at the image position I of the image data 11 shown in FIG. 4A. In this example, the frequency of the density d at the image position I is 40% for 0% and 60% for 100% for both the Y and M plates.

  FIG. 4C is a diagram showing histograms of the density d of the Black version (B version) and the Cyan version (C version) at the image position I. In this example, the density d of the image position I is 100% at 0% for both the B and C plates.

  Next, the patch density calculation unit 52 (an example of the patch density determination unit) calculates the patch density P (i) at each image position i for each color image data of CMYK (step S3). Here, based on the histogram of density d at each image position i, the density having the maximum frequency is defined as the patch density P (i) at that position.

  In the case of the image data 11, the patch density P (i) of the Y and M plates is the same, P (i) = 100% at some positions i including the region 11a, and P (i) at other positions i. i) = 0%. Further, the patch density P (i) of the B and C plates is P (i) = 0% at all positions i.

  When there is a defective ejection nozzle, white streaks appear in the recorded image. This white streak is characterized by unevenness being more noticeable at a higher density than at a lower density. Therefore, when there are two or more frequency distributions, a method of selecting the frequency with the highest concentration among frequencies exceeding a certain ratio can be used. For example, if the frequency distribution shown in FIG. 5 is obtained, 75 [%] having the highest density among the frequencies exceeding the frequency H may be selected as the patch density P (i) at that position. it can. The value of the frequency H may be appropriately determined in view of the required quality.

  In this embodiment, an example in which one of the most frequently used concentrations is selected to generate test chart data will be described. However, two frequently used concentrations or N concentrations are selected to generate test chart data. It can also be easily extended.

  Next, the test chart creation unit 14 (an example of a test chart data generation unit) has a distribution of P (i) in the nozzle arrangement direction based on the patch density P (i) of each color and is uniform in the paper feed direction. Test chart image data (unevenness detection pattern) is created (step S4, an example of a test chart image data generation step).

  In addition, since the ejection failure nozzle detection is determined based on a difference from the surrounding image, it is necessary to reduce high-frequency gradation fluctuations. Therefore, the test chart image data is subjected to low-frequency filter processing on the distribution of P (i) in the smoothing processing unit 53 (an example of the smoothing processing means), so that it is convenient at the time of subsequent ejection failure nozzle detection. It is preferable to perform a smoothing process for reducing high frequency components in the nozzle arrangement direction.

  As the filter process, for example, as a simplest example, a high-frequency component can be removed by using a process based on the moving average method shown in the following formula 1.

  Here, 2n + 1 indicates the size of the filter, and may be set appropriately to an appropriate value that can remove high-frequency components.

  In addition, various known smoothing techniques can be used as long as the process reduces high frequency components.

  FIG. 6 is a diagram showing the density distribution of the M-size test chart image data. The patch density P (i) with respect to the nozzle position i calculated in step S3 is represented by a solid line, and the patch density P (i) is subjected to smoothing processing. The obtained density distribution is indicated by a broken line. In the density distribution after the smoothing process, high-frequency components are reduced to such an extent that the presence or absence of unevenness can be confirmed by human eyes. For example, the differential coefficient of the smoothing process is set so that the edge portion due to the presence of the sun circle changes smoothly over several mm or more.

  In the above description, it has been described that the resolution of the image data and the recording resolution of the head unit 20 are the same. However, apart from the image data (image data to be output), an image having a lower resolution than that. Data can be combined and input as an input image. Here, as the low-resolution image data, for example, a thumbnail image used for display (a thinned image of image data after CMYK conversion, for example, an image of about 72 dpi) can be used. The low resolution image data only needs to have a low resolution in the nozzle arrangement direction.

  Based on the low-resolution image data, frequency calculation and patch density determination are performed, patch density P (i ′) of each color is generated at low resolution, and enlargement processing is performed to obtain recording resolution data P (i). Generate. By performing the calculation at a low resolution, a patch can be generated at a high speed, and a smoothing process for further reducing high-frequency fluctuation components becomes unnecessary.

  If low resolution image data cannot be input in advance, the input image data may be generated by reducing the resolution using a resolution conversion means (not shown).

  The test chart image data created in this way is merged on the downstream side (rear end) or the upstream side (front end) of the output image in the merge processing unit 54 (an example of the merge processing means) to generate one image. (Step S5).

  FIG. 7 shows the C version test chart image data 11C, the M version test chart image data 11M, the Y version test chart image data 11Y, and the K version test chart image data 11K on the downstream side of the output image data 11. It is a figure which shows an example of image data 11 'which merged. In this example, since the inkjet heads 20C and 20K are not used in the output image, the portions of the test chart image data 11C and 11K are blank. Further, the test chart image data 11M and 11Y are data to be ejected at the same density (100%) only in a range where the area 11a is larger than the area 11b.

  In general, since an inkjet head often has gradually deteriorated ejection accuracy during drawing, it is preferable to detect an ejection failure nozzle after drawing an output image. Therefore, the test chart image data is preferably arranged on the downstream side (rear end) of the paper P with respect to the output image data. In addition, the arrangement order of the test chart images of each color is not particularly limited.

  Also, unnecessary color test charts need not be output. Therefore, in the example shown in FIG. 7, only the test chart image data 11M and 11Y may be merged with the output image data 11.

  The length of the test chart image data 11C, 11M, 11Y, and 11K for each color in the paper conveyance direction may be determined as appropriate based on the paper conveyance speed, the reading speed of the image reading unit 24, and the like. In addition, the generation processing of the test chart image data 11C, 11M, 11Y, and 11K for each color may be performed in parallel for four colors or serially.

  The image data 11 ′ is subjected to gamma conversion and halftone conversion (step S6), and is drawn as one image on the paper P transported by the transport unit 22 in the head unit 20 (an example of a test chart recording unit) ( Step S7, an example of a test chart recording process).

[Detection processing for defective nozzles]
FIG. 8 is a block diagram illustrating an internal configuration of the defective nozzle detection unit 26. As shown in the figure, the defective nozzle detection unit 26 (an example of a defect detection unit) includes an integration average unit 61, a visual characteristic filter unit 62, a comparison unit 63, a nozzle position specifying unit 64, and the like. The operation of each part will be described later.

  Next, the ejection failure nozzle detection process will be described with reference to the flowchart shown in FIG. The image recording apparatus 10 reads the test chart image drawn on the paper P in the above step S7, and detects a defective ejection nozzle.

  The image reading unit 24 (an example of a read image acquisition unit) reads a test chart image portion of the image output on the paper P, and generates read image data (step S11). In the present embodiment, the read image data is acquired by the image reading unit 24 provided in the image recording apparatus 10, but the test chart image portion is read by a scanner provided outside the image recording apparatus 10, and the read data May be configured to be acquired by the image recording apparatus 10.

  This read image data is converted into an optimum signal by the color plate. In general, a scanner captures a signal by decomposing it into RGB, but a signal generated by weighted averaging of these RGB signals, for example, a luminance value (Y value) or L * is selected here. Since yellow has low visibility, RGB B signals may be directly selected from the above signals.

  The integration averaging unit 61 (an example of integration averaging means) of the defective nozzle detection unit 26 performs integration averaging on the read image data Image_scan (X, Y) in the sheet conveyance direction to reduce noise, and generates one-dimensional data Image_Sum (X ) (Step S12).

Next, the visual characteristic filter unit 62 (an example of visual characteristic filter means) performs visual characteristic correction (VTF correction) in consideration of human visual spatial frequency characteristics (VTF; Visual Transfer Function) (step S13). In general printing applications, it is considered that there is no problem if the difference or defect in the printed image is not seen by humans (if it cannot be perceived as a defect). Therefore, the visual characteristic filter unit 62 matches the reading characteristic of the image reading unit 24 and applies a kind of low-pass filter (VTF) according to the human visual characteristic F _VTF to obtain Image_Sum_mod1 (X).

  FIG. 10 is a diagram illustrating an example of human visual characteristics, in which the horizontal axis represents the spatial frequency (cycle / millimeter) and the vertical axis represents the response. The vertical axis represents the relative value normalized by setting the maximum value of response sensitivity to “1”. Human vision has a maximum sensitivity (referred to as “1”) near a spatial frequency of 0.8 cycles / millimeter (c / mm), for example. When the spatial frequency is 2 cycles / millimeter (c / mm), the response is about 0.4. Hereinafter, the response sharply decreases as the spatial frequency increases, and becomes a substantially zero value at the spatial frequency of 6 to 8 cycles / millimeter. And have.

  For such a model of human visual frequency characteristics, the document "Design of minimumvisual modulation halftone patterns" by the author J. Sullivan, L. Ray, and R. Miller, IEEE Trans. Syst. Man Cybern., Vol121, No.1. 33-38 (1991). By converting image data by applying a low-pass filter corresponding to human visual characteristics, even if high-frequency unevenness that is invisible to humans is generated, it is not determined as an ejection failure.

  FIG. 11 is a diagram illustrating an example of data before and after correcting visual characteristics of a read image. In FIG. 11, the horizontal axis is the read pixel position of the image reading unit 24, the vertical axis is a value in luminance units (max−luminance value) where the min value is white and the max value is black, and the broken line is Image_Sum (X), The solid line indicates Image_Sum_mod1 (X).

  The comparison unit 63 (an example of comparison means) compares this Image_Sum_mod1 (X) with a preset threshold value α, determines that a portion that is lower than the threshold value α is a portion where white stripes can be perceived, and discharge failure nozzles (Step S14, an example of a defect detection step).

  Note that the value of the threshold value α can be set for each gradation and for each color. Further, it can be arbitrarily determined according to the user's judgment criteria.

  In performing such processing, it is considered sufficient that the reading resolution of the image reading unit 24 is twice the cutoff frequency of the visual characteristic. Therefore, the resolution may be lower than the recording resolution, and the ejection failure nozzle can be detected with a small amount of image data without increasing the reading resolution in the nozzle arrangement direction of the image reading unit 24 more than necessary.

  Information on the detected defective ejection nozzle is notified to the machine control unit 28 from the defective nozzle detection unit 26 (corresponding to a notification unit). The machine control unit 28 notifies the user that a defective nozzle has been detected, or causes the defective nozzle to be recovered, and performs a recovery operation for the defective nozzle such as wipe or forced discharge (corresponding to a recovery means) ( Step S15).

  In addition, in order to easily specify the position of the defective ejection nozzle, a mark that can specify the nozzle position (nozzle number) may be drawn together with the test chart image.

  The position of the paper P shifts (including skew) due to a shift in the transportability of the paper P, and the difference in the amount of ink applied to the recording surface of the paper P (the difference in water content) depending on the density of the image at the time of drawing The sheet may expand and the image may expand or contract. In such a case, the positional relationship between the reading pixels of the image reading unit 24 and the nozzles of the ink jet heads 20C, 20M, 20Y, and 20K for each color is shifted. It is also conceivable that the positional relationship shifts due to distortion of the optical system itself of the image reading unit 24.

  In order to correct such positional deviation, correction of image expansion / contraction, or distortion of the optical system, a mark serving as a mark is drawn with a predetermined nozzle together with the test chart image, and this mark is read by the image reading unit 24. Read with. By analyzing the read image in the nozzle position specifying unit 64, it is possible to take correspondence between the read pixel of the image reading unit 24 that has read the mark and the nozzle number on which the mark is drawn.

  Here, the operation of the nozzle position specifying unit 64 will be described.

  FIG. 12A is a diagram illustrating an example of test chart image data 11M and mark data 30M drawn by each nozzle of the inkjet head 20M. The mark data 30M draws a linear pattern substantially parallel to the paper conveyance direction at a predetermined interval in the nozzle arrangement direction, and associates the nozzle position of the inkjet head 20M with the read pixel position of the image reading unit 24. It becomes the standard when doing. In this example, the mark data 30M is arranged on the downstream side of the test chart image data 11M, but may be arranged on the upstream side.

  The illustrated example is an example in which the linear pattern is drawn using one pixel of the recording resolution, but the pattern is drawn with an arbitrary number of pixels of 2, 3,..., N. Can be used. Also, by not drawing only the corresponding position, it is possible to use mark data in which a white line is drawn while the background is black.

  The nozzle number for recording the mark data 30M is, for example, 0, 1000, 2000,..., And a known nozzle interval in the nozzle arrangement direction (nozzle row direction) in the substantial nozzle row of the inkjet head 20M. It is preset so that Note that the interval is not necessarily a constant interval.

  In the arrangement of the mark data 30M recorded at this time, if each mark is distinguished by giving a mark number k from one end on the paper P (for example, the left end in FIG. 12A), k is An integer), the nozzle number Index_nozzle (k) for writing the k-th mark is represented by a set of sequences of multiples of 1000, for example, 0, 1000, 2000, 3000...

  That is, Index_nozzle (k) = {0, 1000, 2000, 3000,...} Is preset as a nozzle number for writing a mark.

  Next, the read pixel number obtained by reading the k-th mark in the read pixel row of the image reading unit 24 is defined as Index_CCD (k, 1). Here, the upper margin of the M-size test chart image is n = 1. Index_CCD (k, n) cuts out the mark position from the read image Img_scan (i, n) read by the image reading unit 24, calculates the edge position from the cut out image, and the mark position is the number of pixels of the read image. It can be obtained by calculating.

  Assuming that the image data converted into the output nozzle resolution is Img_mod2 (x, n), the pixel value of each nozzle number x is obtained as follows.

First, “k ₁ ” satisfying Index_nozzle (k ₁ −1) ≦ x <Index_nozzle (k ₁ ) is obtained.

  As the magnification, linear interpolation of the mark position can be used.

The ratio p of the internal fraction is expressed by the following formula (Formula 2),
(Expression 2) p = {x-Index_Nozzle (k ₁ -1)} / {Index_Nozzle (k ₁ ) -Index_Nozzle (k ₁ -1)}
The reference data after nozzle resolution conversion is
(Formula 3) Img_mod2 (x, n) = Img_scan (Index_CCD (p, 1), n)
It becomes. Here, Index_CCD (p, n) can be obtained by interpolation from integer values before and after p when p is handled as a real number instead of an integer.

Further, the following formula (Formula 4),
(Expression 4) Index_CCD (k, n) = {n × Index_CCD (p, 1)} + {(1-n) × Index_CCD (p, N)}
Can be used to set the nth column mark read pixel number Index_CCD (k, n) in the middle of the nozzle arrangement direction.

In Index_nozzle (k), by preparing k as many as the number of nozzles, it is possible to accurately correspond each nozzle directly to the pixel position of the read image. In this case, as in the mark data 31M shown in FIG. 12B, the marks of the respective nozzles can be drawn on the test chart by shifting them one step at a time. Also, the mark data _32M H shown in FIG. 12 (c), as 32M _L, it may be disposed separately on the downstream side and the upstream side of the test chart image data 11M. The length of the mark in the paper conveyance direction may be determined as appropriate according to the reading resolution of the image reading unit 24 in the paper conveyance direction.

  As described above, by specifying the nozzle at the place where the image defect has occurred in the nozzle position specifying unit 64, an image in which the defect is not conspicuous can be drawn by the defective discharge nozzle correction mechanism (not shown). The ejection failure nozzle correction mechanism corrects the ejection failure nozzle using, for example, surrounding pixels of the ejection failure nozzle.

  As described above, in the present embodiment, the presence or absence of a defective ejection nozzle is determined using a test chart that considers output image data, so that there is little false detection and high-accuracy detection according to the output image is possible. It becomes. For example, even if a nozzle that is not used has a discharge failure, it is not detected in this embodiment. Therefore, unnecessary notification operation and recovery work can be omitted.

  In addition, since the test chart image data has a pattern with a substantially uniform density, it is easy to determine high-frequency unevenness due to defective ejection nozzles. In addition, the amount of read image data is small, and high-speed processing can be performed at low cost.

  Furthermore, the resolution of the image reading unit is determined by visual characteristics, and is lower than the image recording resolution. Therefore, the number of read image data is reduced, and high-speed processing is possible at low cost.

<Second Embodiment>
Next, the case where the image data 41 shown in FIG. 13A is input to the image recording apparatus 10 as output image data will be described with reference to the flowchart of FIG.

  The image data 41 input to the image recording apparatus 10 is decomposed into CMYK image data in the CMS unit 13 (step S1).

  The test chart creation unit 14 uses the CMYK color image data (Cyan version, Magenta version, Yellow version, blacK version) for each density d [dot%] with respect to the image data Image (i, y) at the image position i in the nozzle arrangement direction. ] Frequency h (d) is calculated (step S2).

  FIGS. 13B to 13E are diagrams showing histograms of the density d of the C, M, Y, and K plates at the image position I of the image data 41 shown in FIG. 13A. .

  Next, for each color image data of CMYK, a patch density P (i) at each image position i is calculated (step S3). Here, based on the histogram of the density d at each image position i, the highest density among the frequencies exceeding the frequency H is defined as the patch density P (i) at that position.

  Therefore, in the example shown in FIGS. 13B to 13E, the patch density P (I) of the C plate is 25%, the patch density P (I) of the M plate is 100%, and the patch density P (Y of the Y plate is I) is 75%, and the patch density P (I) of the K plate is 75%.

  Next, based on the patch density P (i) of each color, test chart image data having a distribution of P (i) in the nozzle arrangement direction and uniform in the paper feed direction is created (step S4). Similarly to the first embodiment, low frequency filter processing is performed on the distribution of P (i), and smoothing processing is performed to reduce high frequency components in the nozzle arrangement direction.

  FIGS. 14A to 14D are diagrams showing density distributions of test chart image data after smoothing processing for the C, M, Y, and K plates, respectively.

  The test chart image data created in this way is merged with the downstream side or the upstream side of the output image to generate one image (step S5).

  FIG. 15 shows the C-side test chart image data 41C, the M-side test chart image data 41M, the Y-side test chart image data 41Y, and the K-side test chart image data 41K on the downstream side of the output image data 41. It is a figure which shows an example of image data 41 'which merged.

  The image data 11 'is subjected to gamma conversion and halftone conversion (step S6), and is drawn on the paper P as one image from the head unit (step S7).

  By performing the reading process on the test chart image drawn on the paper P in the same manner as in the first embodiment, it is possible to detect defective ejection nozzles.

  Here, the test chart image for four colors is merged with the output image data to output a test chart for four colors for one image output, but one color for one image output. A test chart image may be output.

  FIGS. 16A to 16D show image data 42C obtained by merging the C version test chart image data 41C on the downstream side of the output image data 41, and the M version test chart on the downstream side of the output image data 41. Image data 42M obtained by merging the image data 41M, image data 42Y obtained by merging the Y version test chart image data 41Y on the downstream side of the output image data 41, and K version test chart image data on the downstream side of the output image data 41 It is a figure which shows an example of the image data 42K which merged 41K.

  By outputting the image data 42C, 42M, 42Y, and 42K in order and detecting defective ejection nozzles, the area occupied by the test chart image can be reduced. In addition, each of the inkjet heads 20C, 20M, 20Y, and 20K for each color is detected once for each of the four image outputs, so the number of data for performing the defective ejection nozzle detection process is reduced, and processing is performed at high speed. It can be performed.

  Note that a test chart image for two colors or three colors may be output for one image output.

<Image recording device>
<Configuration example of inkjet recording apparatus>
Next, a configuration example of an inkjet recording apparatus will be described as a further specific example of the image recording apparatus 10 described in FIG.

  FIG. 17 is a diagram illustrating a configuration example of the ink jet recording apparatus according to the embodiment of the present invention. The ink jet recording apparatus 100 includes ink jet heads 172M, 172K, 172C, and a recording medium 124 (corresponding to “medium”, hereinafter sometimes referred to as “paper” for convenience) held on the drawing drum 170 of the drawing unit 116. 172Y is a printing machine that forms a desired color image by ejecting a plurality of colors of ink from 172Y. A treatment liquid (here, a coagulation treatment liquid) is applied onto the recording medium 124 before ink ejection, This is an on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method in which an ink liquid is reacted to form an image on a recording medium 124 is applied.

  As shown in the figure, the ink jet recording apparatus 100 mainly includes a paper feeding unit 112, a treatment liquid application unit 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a paper discharge unit 122.

(Paper Feeder)
The paper supply unit 112 is a mechanism that supplies the recording medium 124 to the processing liquid application unit 114. A recording medium 124 that is a sheet is stacked on the paper feeding unit 112. The recording media 124 are fed one by one from the sheet feeding tray 150 of the sheet feeding unit 112 to the processing liquid applying unit 114. Here, a sheet (cut paper) is used as the recording medium 124, but a configuration in which continuous paper (roll paper) is cut to a required size and fed is also possible.

(Processing liquid application part)
The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  The processing liquid application unit 114 includes a paper feed cylinder 152, a processing liquid drum 154, and a processing liquid coating device 156. The processing liquid drum 154 includes a claw-shaped holding means (gripper) 155 on the outer peripheral surface thereof, and the recording medium 124 is sandwiched between the claw of the holding means 155 and the peripheral surface of the processing liquid drum 154. The tip can be held. The treatment liquid drum 154 may be provided with a suction hole on the outer peripheral surface thereof and connected to a suction unit that performs suction from the suction hole. As a result, the recording medium 124 can be held in close contact with the peripheral surface of the treatment liquid drum 154.

  A processing liquid coating device 156 is provided outside the processing liquid drum 154 so as to face the peripheral surface thereof. The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller partially immersed in the processing liquid in the processing liquid container, and the recording medium 124 on the anix roller and the processing liquid drum 154. And a rubber roller that transfers the measured processing liquid to the recording medium 124. According to the processing liquid coating apparatus 156, the processing liquid can be applied to the recording medium 124 while being measured. In the present embodiment, the configuration in which the application method using the roller is exemplified, but the present invention is not limited to this. For example, various methods such as a spray method and an ink jet method can be applied.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

(Drawing part)
The drawing unit 116 includes a drawing drum 170, a paper holding roller 174, and ink jet heads 172M, 172K, 172C, and 172Y. Similar to the treatment liquid drum 154, the drawing drum 170 includes a claw-shaped holding means (gripper) 171 on the outer peripheral surface thereof.

  The inkjet heads 172M, 172K, 172C, and 172Y are full-line inkjet recording heads (inkjet heads) each having a length corresponding to the maximum width of the image forming area on the recording medium 124. Is formed with a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  The liquid droplets (liquid) of the corresponding color ink are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held in close contact with the drawing drum 170, thereby applying the treatment liquid. The ink comes into contact with the processing liquid previously applied to the recording surface in the section 114, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. Thereby, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  That is, the recording medium 124 is transported at a constant speed by the drawing drum 170, and the operation of relatively moving the recording medium 124 and each of the inkjet heads 172M, 172K, 172C, 172Y in this transport direction is performed only once ( In other words, an image can be recorded in the image forming area of the recording medium 124 in one sub-scan. Single-pass image formation with such a full-line (page wide) head is a multi-pass with a serial (shuttle) type head that reciprocates in the direction (main scanning direction) orthogonal to the recording medium conveyance direction (sub-scanning direction). High-speed printing is possible as compared with the case where the method is applied, and print productivity can be improved.

  Note that the configuration is not limited to the CMYK standard color (four colors), and light ink, dark ink, and special color ink may be added as necessary. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

(Drying part)
The drying unit 118 is a mechanism for drying moisture contained in the solvent separated by the color material aggregating action, and includes a drying drum 176 and a solvent drying device 178. Similar to the processing liquid drum 154, the drying drum 176 includes a claw-shaped holding unit (gripper) 177 on the outer peripheral surface thereof, and the holding unit 177 can hold the leading end of the recording medium 124.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176, and includes a plurality of halogen heaters 180 and hot air ejection nozzles 182 disposed between the halogen heaters 180. Various drying conditions can be realized by appropriately adjusting the temperature and air volume of the hot air blown toward the recording medium 124 from each hot air ejection nozzle 182 and the temperature of each halogen heater 180.

  The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

(Fixing part)
The fixing unit 120 includes a fixing drum 184, a halogen heater 186, a fixing roller 188, and an inline sensor 190. Like the processing liquid drum 154, the fixing drum 184 includes a claw-shaped holding unit (gripper) 185 on the outer peripheral surface, and the leading end of the recording medium 124 can be held by the holding unit 185.

  With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  The fixing roller 188 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 124. The The recording medium 124 is sandwiched between the fixing roller 188 and the fixing drum 184 and nipped with a predetermined nip pressure, and a fixing process is performed. The fixing roller 188 is configured by a heating roller incorporating a halogen lamp or the like, and is controlled to a predetermined temperature.

  The in-line sensor 190 reads an image (including a density correction test pattern, a non-ejection nozzle detection test pattern, a nozzle position association mark, and the like) formed on the recording medium 124, and determines the image density and the image density. A means for detecting defects and the like, and a CCD line sensor, a CCK camera, or the like is applied. The inline sensor 190 corresponds to the image reading unit 24 described with reference to FIG.

  Instead of ink containing a high boiling point solvent and polymer fine particles (thermoplastic resin particles), an ink containing a monomer component that can be polymerized and cured by ultraviolet (UV) exposure may be used. In this case, the inkjet recording apparatus 100 is provided with means for irradiating actinic rays, such as a UV lamp or an ultraviolet LD (laser diode) array, instead of the fixing roller 188 for heat fixing.

(Output section)
Subsequent to the fixing unit 120, a paper discharge unit 122 is provided. The paper discharge unit 122 includes a discharge tray 192. Between the discharge tray 192 and the fixing drum 184 of the fixing unit 120, a transfer drum 194, a conveyance belt 196, and a stretching roller 198 are in contact with each other. Is provided. The recording medium 124 is sent to the conveyor belt 196 by the transfer drum 194 and discharged to the discharge tray 192. Although the details of the paper transport mechanism by the transport belt 196 are not shown, the recording medium 124 after printing is held at the front end of the paper by a gripper (not shown) gripped between the endless transport belt 196, and the transport belt 196. Is carried above the discharge tray 192.

  Although not shown in FIG. 19, the ink jet recording apparatus 100 of this example includes an ink storage / loading unit for supplying ink to each ink jet head 172M, 172K, 172C, 172Y, processing liquid, in addition to the above configuration. A means for supplying a processing liquid to the applying unit 114 and a head maintenance unit for cleaning each ink jet head 172M, 172K, 172C, 172Y (nozzle surface wiping, purging, nozzle suction, etc.) Are provided with a position detection sensor for detecting the position of the recording medium 124 and a temperature sensor for detecting the temperature of each part of the apparatus.

<Head structure>
Next, the structure of the head will be described. Since the structures of the heads 172M, 172K, 172C, and 172Y are common, the heads are represented by the reference numeral 250 in the following.

  18A is a plan perspective view showing an example of the structure of the head 250, and FIG. 18B is an enlarged view of a part thereof. 19 is a perspective plan view showing another structural example of the head 250, and FIG. 20 is a three-dimensional configuration of one-channel droplet discharge elements (ink chamber units corresponding to one nozzle 251) serving as recording element units. FIG. 19 is a cross-sectional view (a cross-sectional view taken along line AA in FIG. 18).

  As shown in FIG. 18A, the head 250 of this example includes a plurality of ink chamber units (droplet discharge elements) each including a nozzle 251 that is an ink discharge port, a pressure chamber 252 corresponding to each nozzle 251, and the like. 253 in a two-dimensional arrangement in a matrix, so that the substantial nozzle interval (projection) projected along the longitudinal direction of the head (direction orthogonal to the paper feed direction) (projection) Nozzle pitch) is increased.

  Nozzle rows having a length corresponding to the entire width Wm of the drawing area of the recording medium 124 are configured in a direction (arrow M direction; main scanning direction) substantially orthogonal to the feeding direction (arrow S direction; sub-scanning direction) of the recording medium 124. The form to do is not limited to this example. For example, instead of the configuration of FIG. 18A, as shown in FIG. 19A, short head modules 250 ′ in which a plurality of nozzles 251 are two-dimensionally arranged are arranged in a staggered manner and connected. Thus, there are a mode in which a line head having a nozzle row having a length corresponding to the full width of the recording medium 124 and a mode in which the head modules 250 ″ are connected in a row as shown in FIG. 19B.

  The pressure chamber 252 provided corresponding to each nozzle 251 has a substantially square planar shape (see FIGS. 18A and 18B), and the nozzle 251 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 254 is provided on the other side. Note that the shape of the pressure chamber 252 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 20, the head 250 has a structure in which a nozzle plate 251A in which nozzles 251 are formed and a flow path plate 252P in which flow paths such as a pressure chamber 252 and a common flow path 255 are formed are laminated and joined. . The nozzle plate 251A constitutes a nozzle surface (ink ejection surface) 250A of the head 250, and a plurality of nozzles 251 communicating with the pressure chambers 252 are two-dimensionally formed.

  The flow path plate 252P forms a side wall of the pressure chamber 252 and a flow path that forms a supply port 254 as a narrowed portion (most narrowed portion) of an individual supply path that guides ink from the common flow path 255 to the pressure chamber 252. It is a forming member. For convenience of explanation, the flow path plate 252P has a structure in which one or a plurality of substrates are stacked, although it is illustrated in a simplified manner in FIG.

  The nozzle plate 251A and the flow path plate 252P can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common flow channel 255 communicates with an ink tank (not shown) as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 252 via the common flow channel 255.

  A piezoelectric actuator 258 having an individual electrode 257 is joined to a diaphragm 256 constituting a part of the pressure chamber 252 (the top surface in FIG. 20). The diaphragm 256 of this example is made of silicon (Si) with a nickel (Ni) conductive layer functioning as a common electrode 259 corresponding to the lower electrode of the piezoelectric actuator 258, and is arranged corresponding to each pressure chamber 252. It also serves as a common electrode for the actuator 258. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (conductive material), such as stainless steel (SUS).

  By applying a driving voltage to the individual electrode 257, the piezoelectric actuator 258 is deformed and the volume of the pressure chamber 252 is changed, and ink is ejected from the nozzle 251 due to the pressure change accompanying this. When the piezoelectric actuator 258 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 252 from the common flow channel 255 through the supply port 254.

  As shown in FIG. 18B, the ink chamber units 253 having such a structure are arranged in a fixed manner along a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. By arranging a large number of patterns in a lattice pattern, the high-density nozzle head of this example is realized. In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 251 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  In the implementation of the present invention, the arrangement form of the nozzles 251 in the head 250 is not limited to the illustrated example, and various nozzle arrangement structures can be applied. For example, instead of the matrix array described in FIG. 20, a linear array of lines, a V-shaped nozzle array, and a zigzag (W-shaped) nozzle array having a V-shaped array as a repeating unit. Etc. are also possible.

  The means for generating the discharge pressure (discharge energy) for discharging the droplets from each nozzle in the inkjet head is not limited to the piezoelectric actuator (piezoelectric element), but the thermal method (the pressure of film boiling due to the heating of the heater) Various pressure generating elements (energy generating elements) such as heaters (heating elements) and other actuators based on other systems can be applied. Corresponding energy generating elements are provided in the flow path structure according to the ejection method of the head.

<Description of control system>
FIG. 21 is a block diagram showing a system configuration of the inkjet recording apparatus 100. 21, the inkjet recording apparatus 100 includes a communication interface 270, a system controller 272, an image memory 274, a ROM 275, a motor driver 276, a heater driver 278, a print control unit 280, an image buffer memory 282, a head driver 284, and the like. I have.

  The communication interface 270 is an interface unit (image input unit) that receives image data sent from the host computer 286. As the communication interface 270, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  The image data sent from the host computer 286 is taken into the inkjet recording apparatus 100 via the communication interface 270 and temporarily stored in the image memory 274. The image memory 274 is a storage unit that stores an image input via the communication interface 270, and data is read and written through the system controller 272. The image memory 274 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 272 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 100 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 272 controls the communication interface 270, the image memory 274, the motor driver 276, the heater driver 278, and the like, and performs communication control with the host computer 286, read / write control of the image memory 274 and ROM 275, and the like. At the same time, a control signal for controlling the motor 288 and the heater 289 of the transport system is generated.

  Further, the system controller 272 performs landing error measurement calculation that performs calculation processing for generating non-ejection nozzle position, landing position error data, density distribution data (density data), and the like from the read data read from the inline sensor 190. 272A, and a density correction coefficient calculator 272B that calculates a density correction coefficient from the measured landing position error information and density information. The system controller 272 includes the defective nozzle detection unit 26 shown in FIG. Each of these functional blocks can be realized by ASIC, software, or an appropriate combination.

  The density correction coefficient data obtained by the density correction coefficient calculation unit 272B is stored in the density correction coefficient storage unit 290.

  In the ROM 275, the program executed by the CPU of the system controller 272 and various data necessary for the control (data for ejecting a density correction parameter measurement chart and a test chart for detecting a non-ejection nozzle position, Including non-ejection nozzle information) is stored. The ROM 275 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. Further, by utilizing the storage area of the ROM 275, a configuration in which the ROM 275 is also used as the density correction coefficient storage unit 290 is possible.

  The image memory 274 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 276 is a driver (drive circuit) that drives the conveyance motor 288 in accordance with an instruction from the system controller 272. The heater driver 278 is a driver that drives the heater 289 such as the drying unit 118 in accordance with an instruction from the system controller 272.

  The print control unit 280 performs processes such as various processes and corrections for generating a droplet ejection control signal from image data (multi-value input image data) in the image memory 274 according to the control of the system controller 272. In addition to functioning as signal processing means, it also functions as drive control means for controlling the ejection drive of the head 250 by supplying the generated ink ejection data to the head driver 284.

  That is, the print control unit 280 includes a density data generation unit 280A, a correction processing unit 280B, an ink ejection data generation unit 280C, and a drive waveform generation unit 280D. The print control unit 280 includes the test chart creation unit 14 shown in FIG. Each of these functional blocks can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit 280A is a signal processing unit that generates initial density data for each ink color from input image data, and performs density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion. Process.

  The correction processing unit 280B is a processing unit that performs density correction calculation using the density correction coefficient stored in the density correction coefficient storage unit 290, and performs unevenness correction processing.

  The ink ejection data generation unit 280C is a signal processing unit including a halftoning processing unit that converts the corrected image data (density data) generated by the correction processing unit 280B into binary or multivalued dot data. Value (multi-value) conversion processing is performed.

  The ink discharge data generated by the ink discharge data generation unit 280C is given to the head driver 284, and the ink discharge operation of the head 250 is controlled.

  The drive waveform generator 280D is means for generating a drive signal waveform for driving the piezoelectric actuator 258 (see FIG. 20) corresponding to each nozzle 251 of the head 250, and the signal generated by the drive waveform generator 280D. (Drive waveform) is supplied to the head driver 284. Note that the signal output from the drive waveform generation unit 280D may be digital waveform data or an analog voltage signal.

  The drive waveform generation unit 280D selectively generates a drive signal for a recording waveform and a drive signal for an abnormal nozzle detection waveform. Various waveform data are stored in the ROM 275 in advance, and waveform data to be used is selectively output as necessary. The ink jet recording apparatus 100 shown in this example applies a common drive power waveform signal to each piezoelectric actuator 258 of the head 250 and connects to the individual electrode of each piezoelectric actuator 258 according to the ejection timing of each piezoelectric actuator 258. A driving method is adopted in which ink is ejected from the nozzles 251 corresponding to the piezoelectric actuators 258 by switching on and off of the switch elements (not shown).

  The print control unit 280 includes an image buffer memory 282, and image data, parameters, and other data are temporarily stored in the image buffer memory 282 when image data is processed in the print control unit 280. In FIG. 21, the image buffer memory 282 is shown in a form associated with the print control unit 280, but can also be used as the image memory 274. Also possible is an aspect in which the print control unit 280 and the system controller 272 are integrated to form a single processor.

  Data of an image to be printed is input from the outside via the communication interface 270 and stored in the image memory 274. At this stage, for example, RGB multivalued image data is stored in the image memory 274.

  In the inkjet recording apparatus 100, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image data (for example, RGB data) stored in the image memory 274 is sent to the print controller 280 via the system controller 272, and the density data generator 280A and correction processor 280B of the print controller 280 are sent. The ink data is converted into dot data for each ink color through the ink ejection data generation unit 280C.

  The dot data is generally generated by performing color conversion processing and halftone processing on image data. The color conversion processing is processing for converting image data expressed in sRGB or the like (for example, RGB 8-bit image data) into color data for each color of ink used in the ink jet printer (in this example, KCMY color data). is there.

  The halftone process is a process of converting the color data of each color generated by the color conversion process into dot data of each color (KCMY dot data in this example) by a process such as an error diffusion method or a threshold matrix method. .

  That is, the print control unit 280 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 280 is stored in the image buffer memory 282. The dot data for each color is converted into CMYK droplet ejection data for ejecting ink from the nozzles of the head 250, and the ink ejection data to be printed is determined.

  The head driver 284 includes an amplifier circuit, and drives the piezoelectric actuator 258 corresponding to each nozzle 251 of the head 250 in accordance with the print contents based on the ink ejection data and the drive waveform signal given from the print controller 280. A drive signal is output. The head driver 284 may include a feedback control system for keeping the head driving conditions constant.

  In this way, the drive signal output from the head driver 284 is applied to the head 250, whereby ink is ejected from the corresponding nozzle 251. An image is formed on the recording medium 124 by controlling ink ejection from the head 250 in synchronization with the conveyance speed of the recording medium 124.

  As described above, based on the ink discharge data and the drive signal waveform generated through the required signal processing in the print controller 280, the control of the discharge amount and discharge timing of the ink droplets from each nozzle via the head driver 284. Is done. Thereby, a desired dot size and dot arrangement are realized.

  As described with reference to FIG. 17, the inline sensor 190 includes a linear sensor type imaging device in which a large number of photoelectric conversion elements (photosensitive pixel portions) are arranged in a line, reads an image printed on the recording medium 124, Necessary signal processing or the like is performed to detect the printing status (whether ejection is performed, droplet ejection variation, optical density, etc.), and the detection result is provided to the print controller 280 and the system controller 272.

  For the inline sensor 190, for example, an imaging device capable of color separation is used, such as a 3CCD color line sensor in which CCD line sensors for RGB colors are arranged. By using such a color imaging device, information of each color that can be printed by the inkjet recording apparatus 100 can be read.

  The in-line sensor 190 has a photoelectric conversion element array (read pixel array) that can read an image corresponding to the width on the recording medium in a width direction orthogonal to the conveying direction of the recording medium 124 at a time (by one transport). It is installed in the recording medium conveyance path. While the recording medium printed by the head 250 is conveyed in one direction, the inline sensor 190 reads an image on the paper and converts it into an image signal. In this way, electronic image data (read data) of the read image read by the inline sensor 190 is generated.

  The reading resolution of the inline sensor 190 is preferably as high as possible in the width direction of the recording medium 124. Ideally, it is desirable that the reading resolution is twice or more the recording resolution in the width direction of the head 250. For example, when the recording resolution of the head 250 is 600 dpi, it is desirable that the reading resolution in the width direction of the in-line sensor 190 is 1200 dpi or more, which is twice that. However, it is not always necessary to use such a high-resolution scanner when implementing the present invention.

  On the other hand, the reading resolution in the conveyance direction of the inline sensor 190 may be lower than the recording resolution of the head 250 in accordance with the resolution that the inline sensor 190 can process data. For example, the reading resolution in the conveyance direction of the inline sensor 190 can be a low resolution of 1/10 or less than the reading resolution in the width direction. Specifically, in the case of a 600 dpi head 250, the scanning resolution of the inline sensor 190 in the transport direction can be set to 100 dpi, and can be 1/12 of the scanning resolution in the width direction (for example, 1200 dpi).

  The print controller 280 performs various corrections to the head 250 based on information obtained from the in-line sensor 190 as necessary, and performs cleaning operations (nozzle recovery operations) such as preliminary ejection, suction, and wiping as necessary. Control.

  The maintenance mechanism 294 in the drawing includes members necessary for head maintenance, such as an ink receiver, a suction cap, a suction pump, and a wiper blade.

  The operation unit 296 as a user interface includes an input device 297 and a display unit (display) 298 for an operator (user) to make various inputs. The input device 297 can employ various forms such as a keyboard, a mouse, a touch panel, and buttons. By operating the input device 297, the operator can input printing conditions, select an image quality mode, input / edit attached information, search information, and the like. Various information such as input contents and search results are This can be confirmed through display on the display unit 298. The display unit 298 also functions as means for displaying a warning such as an error message.

  An aspect in which all or part of the processing functions of the landing error measurement calculation unit 272A, the density correction coefficient calculation unit 272B, the density data generation unit 280A, and the correction processing unit 280B described in FIG. Is possible. A configuration in which the host computer 286 bears all or part of the functions of the system controller 272 is also possible. The machine control unit 28 described with reference to FIG. 1 may be incorporated in the host computer 286 or in the inkjet recording apparatus 100.

<Other variations>
In the above embodiment, an ink jet recording apparatus of a method (direct recording method) in which an ink droplet is directly formed on the recording medium 124 has been described. However, the scope of application of the present invention is not limited to this, and once, The present invention is also applied to an intermediate transfer type image forming apparatus that forms an image (primary image) on an intermediate transfer member and transfers the image onto a recording sheet in a transfer unit to form a final image. be able to.

<Means for moving the head and paper relative to each other>
In the above-described embodiment, the configuration in which the recording medium is transported to the stopped head is exemplified. However, in the implementation of the present invention, a configuration in which the head is moved with respect to the stopped recording medium (the drawing medium) is also possible. is there.

<About recording media>
“Recording medium” is a generic term for a medium on which dots are recorded by droplets ejected from a liquid ejection head, and is a variety of terms such as a printing medium, a recording medium, an image forming medium, an image receiving medium, and an ejection medium. Includes what is called. In the practice of the present invention, the material, shape, etc. of the recording medium are not particularly limited, and a print on which a resin sheet such as continuous paper, cut paper, seal paper, OHP sheet, film, cloth, nonwoven fabric, wiring pattern, or the like is formed. It can be applied to various media regardless of the substrate, rubber sheet, and other materials and shapes.

<Device application example>
In the above embodiment, application to an inkjet recording apparatus for graphic printing has been described as an example, but the scope of application of the present invention is not limited to this example. For example, a wiring drawing apparatus for drawing a wiring pattern of an electronic circuit, a manufacturing apparatus for various devices, a resist printing apparatus that uses a resin liquid as a functional liquid for ejection, a color filter manufacturing apparatus, and a material deposition material. The present invention can be widely applied to an inkjet apparatus that draws various shapes and patterns using a liquid functional material, such as a fine structure forming apparatus that forms a structure.

  The technical scope of the present invention is not limited to the scope described in the above embodiment. The configurations and the like in the respective embodiments can be appropriately combined among the respective embodiments without departing from the spirit of the present invention. Further, a program to be executed by a computer for implementing each embodiment is also included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 10 ... Image recording device, 11, 11 ', 41, 41', 42C, 42M, 42Y, 42K ... Image data, 11a ... Circular area, 11b ... Other area, 11C, 11M, 11Y, 11K, 41C, 41M , 41Y, 41K ... test chart image data, 12 ... input I / F, 14 ... test chart creation unit, 20 ... head unit, 22 ... transport unit, 24 ... image reading unit, 26 ... defective nozzle detection unit, 28 ... machine Control unit, 30M ... mark data, 51 ... frequency calculation unit, 52 ... patch density calculation unit, 53 ... smoothing processing unit, 54 ... merge processing unit, 61 ... integral averaging unit, 62 ... visual characteristic filter unit, 63 ... comparison unit 64: Nozzle position specifying part, P: Paper

Claims (20)

A liquid discharge head having a plurality of nozzles for discharging liquid;
Moving means for relatively moving the liquid ejection head and the recording medium;
Control means for performing recording on the recording medium by ejecting liquid from the plurality of nozzles while relatively moving the liquid ejection head and the recording medium;
Data acquisition means for acquiring image data to be recorded on the recording medium;
Test chart data generating means for generating test chart data based on the image data;
Test chart recording means for recording a test chart on the recording medium by the control means based on the test chart data;
Read image acquisition means for acquiring read data of the recorded test chart;
A failure detection means for analyzing the read data of the test chart and detecting a nozzle having a discharge failure;
An image recording apparatus comprising: The test chart data generation means includes
For the image data, a frequency calculating means for calculating the frequency of density for each pixel column parallel to the direction of relative movement
Patch density determining means for determining patch densities of the plurality of nozzles based on the calculated density frequency for each pixel row;
With
The image recording apparatus according to claim 1, wherein test chart data is generated from the determined patch density.   The patch density determination unit calculates a density having a maximum frequency for each pixel column, and determines the calculated density as a patch density of a nozzle corresponding to the pixel column among the plurality of nozzles. The image recording apparatus described in 1.   The patch density determining means calculates a maximum density among the densities whose frequency exceeds a predetermined value for each pixel column, and uses the calculated density for a nozzle patch corresponding to the pixel column among the plurality of nozzles. The image recording apparatus according to claim 2, wherein the density is determined.   5. The image recording apparatus according to claim 3, wherein the test chart data generation unit includes a smoothing processing unit that reduces high-frequency components for patch densities of the plurality of nozzles.   6. The image according to claim 2, further comprising a resolution conversion unit configured to lower a resolution in a direction orthogonal to a direction of the relative movement of the acquired image data to be lower than a recording resolution of the plurality of nozzles. Recording device. The data acquisition means acquires first image data to be output processed, and second image data having a lower resolution in a direction orthogonal to the direction of relative movement than at least the first image data,
The image recording apparatus according to claim 1, wherein the test chart data generating unit generates test chart data based on the second image data.   The image recording apparatus according to any one of claims 1 to 7, wherein the defect detection unit includes an integration average unit that integrates and averages the read data in the direction of relative movement and converts the read data into one-dimensional data.   9. The image recording apparatus according to claim 1, wherein the defect detection unit includes a visual characteristic filter unit that converts the read data into a signal in consideration of human visual characteristics.   10. The image recording apparatus according to claim 1, wherein the defect detection unit includes a comparison unit that compares the read data with a threshold value to detect a defective nozzle. 10.   The image recording apparatus according to claim 10, wherein the threshold is set for each gradation of the patch density.   The image recording apparatus according to claim 1, further comprising notification means for notifying a user that a nozzle with defective ejection has been detected.   13. The image recording apparatus according to claim 1, further comprising a recovery unit configured to perform recovery work for a defective nozzle when a defective nozzle is detected.   2. The test chart data generation unit adds mark data to the test chart data for associating a positional relationship between a plurality of nozzles of the liquid ejection head and a read pixel when the recorded test chart is read. 14. The image recording apparatus according to any one of items 1 to 13.   The image recording apparatus according to claim 1, wherein the test chart generation unit includes a merge processing unit that merges the test chart data and the image data.   The image recording apparatus according to claim 15, wherein the merge processing unit merges the test chart data downstream of the image data in the relative movement direction. It has a plurality of liquid discharge heads that discharge liquids of different colors,
The image data is image data of a plurality of colors recorded by the plurality of liquid ejection heads,
The test chart data generation means generates a plurality of test chart data for each color,
The image recording apparatus according to claim 15 or 16, wherein the merge processing unit merges one test chart data among the plurality of test chart data into the image data. Test for detecting defective nozzles of an image recording apparatus that records an image on the recording medium by discharging liquid from a plurality of nozzles of the liquid discharging head while relatively moving the liquid discharging head and the recording medium A chart creation method,
A data acquisition step of acquiring image data to be recorded on the recording medium;
A test chart data generation step for generating test chart data based on the image data;
A test chart recording step of recording a test chart on the recording medium by ejecting liquid from the plurality of nozzles based on the test chart data while relatively moving the liquid ejection head and the recording medium;
To create a test chart with Detecting a defective nozzle of an image recording apparatus that records an image on the recording medium by ejecting liquid from the plurality of nozzles while relatively moving a liquid ejection head having a plurality of nozzles and a recording medium A test chart data generation program for causing a computer to generate a function for generating test chart data,
A data acquisition function for acquiring image data to be recorded on the recording medium;
A test chart data generation function for generating test chart data based on the image data;
A test chart data generation program for realizing a computer. A data acquisition step of acquiring image data to be recorded on the recording medium by discharging liquid from the plurality of nozzles while relatively moving a liquid discharging head having a plurality of nozzles and the recording medium;
A test chart data generation step for generating test chart data based on the image data;
A test chart recording step for recording a test chart on the recording medium by ejecting liquid from the plurality of nozzles based on the test chart data while relatively moving the liquid ejection head and the recording medium;
A read image acquisition step of reading the recorded test chart and acquiring read data of the test chart;
A failure detection step of analyzing the read data of the test chart and detecting a nozzle having a discharge failure;
An ejection failure detection method comprising: