JP6536049B2 - Ink jet recording apparatus and method for detecting ink discharge failure - Google Patents

Description

  The present invention relates to an ink jet recording apparatus and a method of detecting an ink ejection failure.

  2. Description of the Related Art There is an inkjet recording apparatus which forms an image on a recording medium by discharging ink from the openings of nozzles arranged in plural numbers on the recording medium. In this ink jet recording apparatus, the ink discharge amount from the nozzle opening decreases from the initial value due to clogging of the nozzle or the like, and furthermore, the ink is not completely discharged, or the discharge direction is changed. Ink discharge failure may occur.

  In the ink jet recording apparatus, such an ink ejection failure leads to a reduction in the quality of the formed image. Therefore, conventionally, in the ink jet recording apparatus, the inspection of the discharge state of the ink from the nozzle opening is regularly performed. In the inspection of the ink ejection state, there is a method of imaging a test image formed on a recording medium and analyzing the imaging data. In this method, conventionally, an ink is separately discharged from each nozzle opening, and the discharge presence or absence and density of the ink are checked to determine the ink discharge failure from each nozzle opening.

  Further, in the ink jet recording apparatus, the quality of the formed image due to the ink discharge failure is adjusted by adjusting the ink discharge amount from the nozzle opening adjacent to the defective nozzle causing the ink discharge failure based on such inspection results. There is a complementary technology to compensate for the decrease, and a technology to remove the cause of clogging such as dried ink by cleaning the ink discharge surface.

  However, the required level of image quality varies depending on the content of the image to be formed, the application, and the like. Therefore, there is a problem that the frequency of repair and cleaning often increases more than necessary if processing for dealing with density unevenness and the like is performed on a uniform and strict standard every time.

  Therefore, Patent Document 1 discloses a technique of changing the inspection frequency of the ink ejection failure according to the reliability determined in accordance with the output target image or the like. Patent Document 2 discloses a technology that allows changing the level of response to uneven density caused by factors including ink discharge failure by user setting.

  Further, in Patent Document 3, it is possible for the user to set whether or not the detection operation of the ink discharge failure and the recovery operation of the discharge failure nozzle are automatically performed, and in the case where the setting is not performed automatically, periodically. A technique is disclosed that causes a display to inquire the user whether to execute the detection operation or the recovery operation. In Patent Document 4, the number of defective discharge nozzles detected and the situation such as arrangement and color type are quantified based on visibility and the like, and when the numerical value is equal to or less than a value preset by the user, image formation is performed. There is disclosed a technique for continuing the image formation as it is without stopping the operation or performing the recovery operation.

JP, 2009-248547, A JP, 2009-241536, A JP, 2009-172934, A JP, 2006-142807, A

  However, since the ink discharge failure gradually progresses, and the level of the ink discharge failure which is a problem may also change sequentially depending on the method and contents of the image formation, there is a demand that the inspection frequency concerning the image is not desired to be reduced. There is. In addition, when the ejection failure from each nozzle is determined based on a uniform standard and the complementation setting is performed by another nozzle, the number of defective nozzles including a slight ejection defect increases and the image quality after the complementation setting is degraded, and further There is a problem that the complement setting becomes difficult. Therefore, there is a problem that the inspection of the ink discharge failure can not be performed efficiently on the basis of enabling appropriate frequency and appropriate response.

  An object of the present invention is to provide an ink jet printing apparatus and an ink ejection failure detection method capable of efficiently detecting an ink ejection failure on the basis of enabling appropriate frequency and appropriate response.

In order to achieve the above object, the invention according to claim 1 is
An ink jet recording apparatus that ejects ink from the openings of a plurality of nozzles to form an image on a recording medium.
An image formation control unit that ejects ink from the openings of the plurality of nozzles and outputs a predetermined test image related to detection of ink ejection failure;
A reading unit that reads the test image;
An analysis unit that detects a discharge failure from the opening based on the read test image;
A storage unit that stores position data of a defective nozzle related to the ejection failure;
Equipped with
The analysis unit changes a determination reference level relating to the detection of the ejection failure according to a normal image to be formed.
The storage unit stores position data of defective nozzles obtained for each of the plurality of determination reference levels ,
The test image is an image of a predetermined density,
The analysis unit determines the presence or absence of the discharge failure based on the density unevenness of the test image,
The image formation control unit, when it is determined by the analysis unit that there is the discharge failure based on the test image, causes a defective nozzle identification image for specifying a defective nozzle related to the discharge failure to be output.
The analysis unit analyzes the defective nozzle identification image read by the reading unit to identify the defective nozzle, and when the defective nozzle is not identified in the output defective nozzle identification image, the determination criterion It is characterized in that the level is changed in a strict direction to determine the presence or absence of the ejection failure in the test image .

The invention according to claim 2 is the inkjet recording apparatus according to claim 1
The test image is characterized by being a halftone image.

The invention according to claim 3 relates to the ink jet recording apparatus according to claim 1 or 2 .
The image formation control unit is characterized in that the test image is formed on the recording medium outside the formation area where the normal image can be formed.

The invention according to claim 4 is the ink jet recording apparatus according to any one of claims 1 to 3 .
The analysis unit may change the determination reference level in accordance with the image quality required for the normal image.

The invention according to claim 5 is the inkjet recording apparatus according to any one of claims 1 to 4 .
The analysis unit may change the determination reference level in accordance with a type of the normal image.

The invention according to claim 6 relates to the ink jet recording apparatus according to claim 5 .
The type of the normal image includes text and an image.

The invention according to claim 7 is the inkjet recording apparatus according to any one of claims 1 to 6 .
The analysis unit is characterized in that the determination reference level is changed according to a density distribution of the normal image.

According to an eighth aspect of the present invention, in the inkjet recording apparatus according to any one of the first to seventh aspects,
The analysis unit may change a specific reference level of the defective nozzle according to a change of the determination reference level.

The invention according to claim 9 relates to the ink jet recording apparatus according to any one of claims 1 to 8 .
The image formation control unit adjusts at least one of the ejection amount and the ejection frequency of the ink by the nozzles within a predetermined proximity range related to the ink ejection range of the identified defective nozzle, to thereby select the defective nozzle. It is characterized in that the test image is output while complementing the influence.

The invention according to claim 10 is
A method of detecting an ink discharge failure from the plurality of nozzles in an ink jet recording apparatus in which an image is formed by discharging ink from the openings of the plurality of nozzles.
An image formation control step of discharging ink from the openings of the plurality of nozzles and outputting a predetermined test image related to detection of ink discharge failure;
A reading step of reading the test image;
An analysis step of detecting a discharge failure from the opening based on the read test image;
A storage step of storing position data of the defective nozzle relating to the ejection failure;
Including
In the analysis step, the determination reference level relating to the detection of the ejection failure is changed according to the normal image to be formed;
In the storing step, position data of the defective nozzle obtained for each of the plurality of determination reference levels is stored ,
The test image is an image of a predetermined density,
In the analysis step, determination as to the presence or absence of the discharge failure is performed based on density unevenness of the test image,
In the image formation control step, when it is determined in the analysis step that there is the discharge failure based on the test image, a defective nozzle identification image for specifying a defective nozzle related to the discharge failure is output.
In the analysis step, the defective nozzle identification image read in the reading step is analyzed to identify the defective nozzle, and when the defective nozzle is not identified in the output defective nozzle identification image, the determination criterion It is characterized in that the level is changed in a strict direction to determine the presence or absence of the ejection failure in the test image .

  According to the present invention, in the ink jet recording apparatus and the method for detecting an ink ejection defect, the ink ejection defect can be efficiently detected on the basis of enabling appropriate frequency and appropriate response.

FIG. 1 is a view showing the overall configuration of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an internal configuration of the inkjet recording apparatus. FIG. 5 is a bottom view showing the surface of the inkjet head facing the recording medium. 5 is a flowchart showing a control procedure of image formation processing. It is a figure which shows the example of the formation image in which the test image which concerns on discharge defect detection operation is contained. It is a flowchart which shows the control procedure of a correction setting process. It is a figure which shows the example of the formation image of a missing position identification chart. It is a figure which shows the example of the positional relationship of a normal image and a missing change chart. It is a modification of the flowchart which shows the control procedure of correction setting processing. FIG. 6 is a diagram showing an example of reference levels set in the inkjet recording apparatus.

Hereinafter, embodiments of the present invention will be described based on the drawings.
FIG. 1 is a view showing the overall configuration of an inkjet recording apparatus 100 according to the present embodiment. FIG. 2 is a block diagram for explaining the internal configuration of the inkjet recording apparatus 100. As shown in FIG.

  The inkjet recording apparatus 100 includes a transport unit 11, an inkjet head 12, an image reading unit 13 (reading unit), a control unit 14 (image formation control unit, analysis unit), an operation display unit 15, and the like.

  The transport unit 11 includes a transport belt 112 and a transport motor 111 that circumferentially moves the transport belt 112. The recording medium P disposed on the conveyance belt 112 is moved in a predetermined conveyance direction by the rotation operation of the conveyance motor 111. Alternatively, the transport unit 11 may be configured to move the recording medium P disposed on the surface of the transport drum in the rotational direction by rotating the cylindrical transport drum.

  The ink jet head 12 has a plurality of nozzles in which openings are arranged facing the conveyance surface of the recording medium P, a drive circuit 121, and an ink ejection unit 122. In the inkjet head 12, the ink discharger 122 operates by the drive voltage output from the drive circuit 121 based on the control signal from the controller 14, whereby the ink is discharged with the timing controlled from the openings of the plurality of nozzles. Ru. An image is formed by landing on the recording medium P on which the ejected ink is conveyed. The ink jet head 12 is not particularly limited, but here, it is a line head, and in the width direction perpendicular to the transport direction, the nozzles can eject ink across the width of the recording medium P where image formation is possible. It is arranged. Further, the plurality of nozzles are provided so as to be capable of independently discharging, for example, four color inks of Y (yellow), M (magenta), C (cyan), and K (black).

FIG. 3 is a bottom view showing the surface (bottom surface) opposite to the recording medium P in the inkjet head 12.
In the inkjet head 12, a plurality of head modules 120 are arranged in a staggered arrangement in the width direction. A plurality of nozzles are arranged in each of the head modules 120, and the nozzles provided at the end in the width direction are the positions of the nozzles provided at the ends in the width direction of the other head modules 120 and the positions in the width direction. Are arranged to overlap. With such an arrangement, the ink can be discharged without a break in the width direction as a whole. The nozzles that eject the ink of each color are arranged, for example, at 1200 dpi (dot per inch) in the width direction, that is, the interval (pitch) in the width direction of the adjacent nozzles is about 21 μm. Here, the size (diameter) of a dot (landing range) formed by landing of ink droplets ejected from one nozzle on the recording medium P is about 60 μm. That is, the landing ranges on the recording medium P of the ink ejected from the adjacent nozzles overlap each other.

The image reading unit 13 includes an image sensor 131 which is disposed on the downstream side of the ink jet head 12 in the transport direction of the recording medium P and picks up (reads) an image formed by the ink jet head 12.
The image sensor 131 is, for example, a line sensor in which a plurality of CCDs (Charge Coupled Device) or CMOS sensors, which are imaging devices using photoelectric conversion, are arranged in the width direction of the recording medium P to acquire one-dimensional images. is there. In addition, corresponding to the inkjet head 12 capable of color (CMYK) output, the formed image can be read for each of a plurality of wavelength components, for example, three wavelengths of R (red), G (green) and B (blue). ing.
The reading resolution (pixel array) by each imaging element of the image sensor 131 is, for example, 600 dpi in the width direction. Further, the image sensor 131 can output read data at 300 dpi in the transport direction to the control unit 14 with respect to the transport speed of the normal recording medium P in the inkjet recording apparatus 100. That is, the image sensor 131 does not acquire an image at a resolution corresponding to the array of nozzles.

  As shown in FIG. 2, the control unit 14 includes a memory 141, a central processing unit (CPU) 142, a read only memory (ROM) 143, a random access memory (RAM) 144, etc. Thus, signals can be exchanged among the units of the inkjet recording apparatus 100. Further, the control unit 14 is connected to an external computer such as an external print server or a personal computer (PC) or a storage device via the communication unit 16 to transmit and receive print jobs and image data to be subjected to image formation.

  The memory 141 temporarily stores image data of an image formation target input from an external computer or storage device. Further, in the data stored in the memory 141, the position data of the nozzles (defective nozzles) identified as having an ink ejection defect among the plurality of nozzles of the ink jet head 12 and their complementary settings are stored in a table The defective nozzle storage unit 141a is included. The complementary settings relating to the defective nozzle are separately determined and stored according to the determination reference level of the ink discharge failure as described later. The memory is configured by a combination of a RAM and a non-volatile memory, and the defective nozzle storage unit 141a is stored in the non-volatile memory as to what is held regardless of the power state of the inkjet recording apparatus 100.

  The CPU 142 generally controls the entire operation of the inkjet recording apparatus 100 and performs various arithmetic processing. The CPU 142 outputs control signals to the conveyance unit 11, the inkjet head 12, and the image reading unit 13 in accordance with the program read from the ROM 143, and performs various processes related to image formation. Here, the CPU 142 may be provided with one processor to perform the control operation intensively, or various control processes such as conveyance control of the recording medium P by the conveyance unit 11 and drive control of the inkjet head 12 may be performed. It may be equipped with a separate processor.

  The ROM 143 stores a control program related to image formation and initial setting data. During the operation of the inkjet recording apparatus 100, the CPU 142 reads out a control program and executes it on the RAM 144 or refers to initial setting data. The initial setting data includes test image data 143a according to the contents of the nozzle inspection and the adjustment.

  The RAM 144 provides the CPU 142 with a working memory space, and stores temporary data. The data of the inspection image captured by the image sensor 131 is temporarily stored in the RAM 144 and used for inspection corresponding to the captured test chart, for example, detection of a nozzle related to an ink ejection failure.

  The operation display unit 15 includes a display panel for performing display in accordance with a control signal from the CPU 142, and an operation key for receiving an input operation from the outside. The display panel is not particularly limited, and is, for example, a liquid crystal display (LCD). In addition, by providing a touch panel stacked and arranged on the display screen of the LCD in place of the operation key or together with the operation key, the display and the reception of the input operation may be used in combination.

Next, an image forming operation in the inkjet recording apparatus 100 of the present embodiment will be described.
In the inkjet recording apparatus 100 of the present embodiment, one of a plurality of image quality levels is selected to form an image when forming an image. At this time, according to the image quality level, the setting of the defective nozzle and the complementary setting for the defective nozzle are performed.

FIG. 4 is a flowchart showing a control procedure by the control unit 14 of the image forming process executed by the inkjet recording apparatus 100 of the present embodiment.
This image forming process is started by acquiring a print job relating to image formation.

  When the image forming process is started, the control unit 14 acquires property information such as the required image quality and the number of formed images from the print job (step S1). The control unit 14 acquires the complementary setting corresponding to the acquired required image quality from the defective nozzle storage unit 141a (step S2). At this time, the control unit 14 performs various kinds of processing, such as shading correction, on the image to be formed (normal image) as needed.

  The control unit 14 forms a normal image and a test image together on the recording medium P (step S3). The control unit 14 sends a control signal to the image reading unit 13, causes the image sensor 131 to read (capture) a test image, and acquires image data of the read test image (step S4).

  The control unit 14 calls and executes a correction setting process to be described later (step S5). The control unit 14 determines whether the formation of the acquired number of image formation is completed (step S6), and when it is determined that the formation is not completed ("NO" in step S6), the control unit The process of 14 returns to step S3. If it is determined that the process has ended ("YES" in step S6), the control unit 14 ends the image forming process.

Next, the operation contents of the ink discharge failure inspection of the nozzles in the inkjet recording apparatus 100 of the present embodiment will be described.
In the ink discharge failure inspection of the present embodiment, first, the discharge failure detection operation of detecting the presence or absence of the ink discharge failure is performed in parallel with the normal image formation, and when the ink discharge failure is detected, as necessary. A defective nozzle identification operation is performed to identify a nozzle causing an ink ejection failure.

  FIG. 5 is a view showing an example of a formed image including a test image according to the ejection failure detection operation of the present embodiment.

  As shown in FIG. 5A, the front end and the end of an area (a formation area in which a normal image can be formed) set as a range for forming an image to be formed (a normal image F) related to a print job In general, a blank area (usually outside the image formation area) is provided. Then, among any of these blank areas, here, missing change charts C21 to C24, which are test images for performing an inspection relating to the presence or absence of an ink ejection defect for each of the CMYK color inks, are formed in the last blank area. Ru. These missing change charts C21 to C24 are formed in a band shape in the width direction corresponding to the width of the nozzles for discharging the ink of each color in the ink jet head 12 as long as it is possible to discriminate the density.

FIG. 5B is an enlarged view of a part of the test image in FIG.
For the test images of the missing change charts C21 to C24, halftone images of predetermined densities (tones) of ink of each color are used. The gradation of this halftone is set to a value, for example, 30%, which is likely to cause a large change in density due to a missing nozzle. Halftone images can be generated by applying various known techniques such as dithering and error diffusion.

The presence or absence of the ejection of the ink related to the halftone image is determined based on the integrated value of the density in the conveyance direction of the halftone image. By doing this, it is possible to grasp the information of the halftone pattern representing the gradation by area and the density information as substantially equivalent information. The data of these missing change charts are read out from the test image data 143a of the ROM 143, and the ink is sequentially ejected from the respective nozzles at the position designated by the halftone pattern to form a halftone image. In addition, as this halftone pattern, ideally, it is preferable that a known nozzle missing correction, shading correction, and the like related to the ejection failure nozzle that has already been detected be applied. As a result, the image sensor 131 described later can determine whether there is a nozzle that is newly causing an ink discharge failure, without considering information on nozzle loss, information on variation in liquid amount, and the like.
That is, in the inkjet recording apparatus 100, even if the gradation value of the image data to be printed is the same, the amount of liquid ejected from each nozzle varies. The variation of the discharge amount for each nozzle causes variation in the density of the formed image. In order to eliminate this variation in density, shading correction is performed on each nozzle, which is a correction that makes the density uniform. Specifically, the amount of ink ejected from the nozzles is adjusted according to the variation among the nozzles.

  In the inkjet recording apparatus 100, representative values of the density in each reading area (reading area) which can be discriminated by the image sensor 131 are determined from the halftone image, not the dots of the ejected individual ink droplets. Then, the density between the reading areas is detected, and it is determined whether or not there is a nozzle causing an ink discharge failure in each reading area. At this time, in the detection of the ink ejection failure, the difference between the density of each reading area in the current image and the density of each reading area in the image related to the previous ejection failure detection operation may be taken.

  In the analysis of a halftone image using the missing change charts C21 to C24 of the present embodiment, the gradation values and the background obtained by integrating and averaging each pixel value of the test image captured by the image sensor 131 in each reading region A median filter is used as a value to compare with a value acquired in a wider range than the reading area. In this median filter, a median (median value) of gradation values obtained in a predetermined number of reading areas in the width direction centering on the reading area to be analyzed is acquired. Then, in the analysis of the present embodiment, when the tone value of each pixel row is smaller than the background value by a predetermined reference value or more, it is determined that the nozzle is missing in the region including the pixel. The term “nozzles” as used herein includes not only the state in which the ink is not discharged at all, but also the state in which the ink discharge amount is greatly reduced and the state in which the ink discharge direction is changed.

  The number of reading areas (the number of taps) for obtaining the median as the background value is appropriately determined. As the number of taps increases, the accuracy of the median increases, and while the nozzle chipping can be detected more reliably, the calculation time increases. Therefore, the number of taps is set so that the accuracy is improved in the possible range according to the transport speed of the recording medium P, the transfer speed of read data, the calculation speed of the CPU 142, the load, and the like. Here, for example, 20 is set as the number of taps.

  Note that the noise removal filter for obtaining the background value is not limited to the median filter. Median filters are generally accurate for detecting large local changes such as one-nozzle loss, but use other filters, such as moving averages or spatial frequency filters (such as low-pass filters). Even detection is possible.

  In the inkjet recording apparatus 100, the reference value (judgment reference level) for judging whether or not the nozzle is missing can be changed in a plurality of predetermined steps. Here, the change of the reference value is performed according to the image quality required for the normal image F. Although the required image quality is not particularly limited, it is acquired based on the image formation property preset by the user. For example, when the required image quality level is "fine", "high definition", etc., the determination reference level is set strictly (the standard value is small), the image formation property is "fast image output", and the required image quality level is In the case of "low definition" or the like, the determination reference level is set loose (the reference value is large).

  When the reference value is changed as described above, there may be nozzles that are determined to be defective nozzles or not determined depending on the magnitude of the reference value. Therefore, as described above, the defective nozzle storage unit 141a stores position data and complementary setting data of the defective nozzle for each color and each step of the reference value. When the reference value is switched to a different step, the image formation of the normal image F and the missing change charts C21 to C24 is performed based on the complementation setting corresponding to the reference value.

  FIG. 6 is a flowchart showing a control procedure of the correction setting process called and executed in the image forming process by the control unit 14 of the present embodiment.

  This correction setting process is a process for performing setting for complementing the ink ejection amount that should be ejected by the specified defective nozzle by ejection from another nozzle, and a normal image F is formed on each recording medium P Every time it is called in the image forming process, it is automatically executed each time.

  When the correction setting process is started, first, the control unit 14 (CPU) determines whether or not the defect detection of the halftone image according to the missing change charts C21 to C24 is not performed (step S11). . A defect in the halftone image is not detected, that is, the ink discharge defect is not detected in the correction setting process up to the previous time, or the complement setting is already performed on the ink discharge defect portion detected. If it is determined ("YES" in step S11), the control unit 14 determines the image quality required for the normal image F output together with the current missing change charts C21 to C24 (step S12). Control unit 14 sets a determination reference level of defect detection according to the determined image quality (step S13).

  The control unit 14 analyzes the halftone image acquired this time to detect an ink ejection failure (step S14). The control unit 14 determines whether an ink discharge failure is detected based on the set determination reference level (reference value) (step S15). If it is determined that the ink discharge failure is not detected ("NO" in step S15), the control unit 14 ends the correction setting process. If it is determined that an ink ejection failure has been detected ("YES" in step S15), the control unit 14 issues an instruction to output a missing position identification chart (defective nozzle identification image) (step S16). Then, the control unit 14 ends the correction setting process.

  On the other hand, in the determination process of step S11, it is not a state where defect detection of the halftone image is not performed, that is, it is determined that the ink discharge defect is detected in the correction setting process up to the previous time and the complementation setting is not performed yet. In the case ("NO" in step S11), the control unit 14 reads imaging data by the image sensor 131 of the missing position identification chart on which the image formation has been performed based on the command output in the process of step S16 (step S22). ).

FIG. 7 is a view showing an example of a formed image of the missing position specification chart L. As shown in FIG.
The missing position specifying chart L is a test image in which the ink is discharged in a ladder shape, a grid shape, or the like so that the landing position on the recording medium P of the ink discharged for each nozzle is separated. a) shows a part of it. Here, lines extending in the transport direction indicate ink landing positions from different nozzles. Depending on the density and formation position of each line, density deviation more than the reference value due to non-ejection of ink or reduction of ejection amount (weak emission) and / or deviation more than the reference value of landing position due to bending of the ink ejection direction The position where the dot missing has occurred is identified.

  The missing position specifying chart L is included in the test image data 143a and set and stored in advance. In addition, the missing position specifying chart L formed at this time may not be for all the nozzles, but may be only for the area in which the defect detection is performed. The reference values relating to the determination of the density deviation and the impact position deviation are hereinafter collectively referred to as a specific reference level.

  The control unit 14 sets the specific reference level of the defective nozzle according to the determination reference level of the defect detection set in the process of step S13 (step S23). The control unit 14 also makes the specific reference level stricter when the judgment reference level is severe, and loosens the specific reference level when the judgment reference level is loose. The control unit 14 analyzes the imaging data of the read missing position specifying chart L, and specifies the dot missing position based on the set specific reference level (step S24). In addition, the control unit 14 identifies a defective nozzle (a position of a missing nozzle) in which an ink discharge failure has occurred from the missing dot position.

  For example, as shown in FIG. 7B, when the reference value (half of the width w) of the landing position is set with respect to the normal discharge positions i1 to i4 shown by the broken lines, they are respectively shown by solid lines. Assuming that the ink lands on the landing positions r1 to r4, the deviation amounts d1 and d3 of the actual landing positions r1 and r3 from the normal discharge positions i1 and i3 are equal to or less than the reference value, and it is determined that the discharge is normal. . On the other hand, the deviation amounts d2 and d4 of the landing positions r2 and r4 from the normal ejection positions i2 and i4 are equal to or greater than the reference value, and dot omissions occur at the normal ejection positions i2 and i4, and these ejection positions i2 and i4 It is determined that the corresponding nozzles are defective nozzles.

  The identification of the defective nozzle may be determined by combining the results identified by a plurality of missing position identification charts, instead of determining only by the single missing position identification chart L. For example, all defective nozzles identified even once in the past ten missing position identification charts may be regarded as defective nozzles.

  The control unit 14 determines whether or not identification of the dot missing position (defective nozzle) has succeeded (step S25). If it is determined that identification of the dot missing position has not succeeded (“NO” in step S25), the control unit 14 increases the determination reference level of defect detection set in step S13 from the next time onward (strictly To do) (step S27). This prevents the defective position specification chart L from being repeatedly output without specifying a defective nozzle which is a cause of the defect detection although the defect detection is performed in the halftone image each time. Then, the control unit 14 ends the correction setting process and returns the process to the image forming process.

  If it is determined that the dot missing position identification has succeeded ("YES" in step S25), the control unit 14 performs correction setting relating to the complement of the ink discharge according to the identified dot missing position (step S26). The control unit 14 performs this complementation by changing the ink discharge amount of the nozzles (for example, the nozzles on both sides) close to the defective nozzle. The control unit 14 stores the complementary setting in the defective nozzle storage unit 141a as a setting corresponding to the determination reference level of the defect detection. When it is expected that the determination reference level of the defect detection can not be cleared only by the change setting of the ink ejection amount, the control unit 14 stops the image forming operation and causes the operation display unit 15 to perform the cleaning operation and the replacement of the inkjet head. Make a prompt message. Then, the control unit 14 ends the correction setting process and returns the process to the image forming process.

  In the correction setting process, when the ink discharge failure from the nozzle opening is detected, the control unit 14 detects the ink discharge failure for the recording medium P for which the detection is performed in the determination process of step S15. It is determined whether or not the normal image formation is performed by the area including the ink and the ink color, and if the image formation is not performed by the area and the ink color, it is determined that the defect is not detected. The correction setting process may be ended without shifting to the process of S16.

FIG. 8 is a diagram showing an example of the positional relationship between a normal image and a missing change chart.
While the missing change charts C21 to C24 for each color of CMYK are formed over the image formable width of the recording medium P, here, the drawing widths of the normal images F21 to F24 drawn for each color of CMYK are recorded respectively It occupies a part of the image formable width of the medium P. Therefore, for example, when the missing change in the missing change chart C21 is detected within the drawing width of the normal image F21, the determination process of step S15 branches to the process of step S16, and the drawing width of the normal image F21 deviates If a missing change is detected at the specified position, the correction setting process is terminated as it is, and the process returns to the image forming process.

[Modification]
FIG. 9 is a modification of the flowchart of the correction setting process shown in FIG.
This correction setting process is the same except that the process of step S12 of the correction setting process in the ink jet recording apparatus 100 of the above-described embodiment is replaced with steps S12a and S12b, and the same process contents have the same reference numerals. The explanation is omitted.

  If "YES" is determined in the determination process of step S11, the control unit 14 (CPU 142) determines the type of the normal image F formed together with the halftone image (step 12a). Further, the control unit 14 acquires the density distribution of the normal image F (step S12 b). The control unit 14 sets a determination reference level (reference value) related to the detection of the ink discharge failure based on the determination result and the acquired data in the process of steps S12a and S12b (step S13).

  As described above, in this modification, the determination reference level (reference value) related to the determination of the ink ejection failure is set based on the content such as the type of the normal image F. For example, if the normal image F consists only of text, the judgment reference level is lowered slightly (the reference value is set large), and if the normal image F is an image, the judgment reference level is strictly raised ( The reference value can be set small. Further, the determination reference level can be changed according to the level of the density of the image (density distribution) included in the normal image F. The height of the density is determined in accordance with the maximum value of the density in the image, an average value, a median, etc., or an index value based on a combination or the like.

FIG. 10 is a view showing an example of the determination reference level set in the inkjet recording apparatus 100 of the present embodiment.
The judgment reference level (reference value) can also be changed according to the position in the width direction in the page. In this case, for example, for a normal image F to be output, a density distribution can be obtained in advance, and a reference value profile corresponding to the position in the width direction can be set. In areas with high density or image areas, unevenness or streaks due to missing nozzles are likely to be noticeable, so the judgment reference level is set strictly higher (the reference value is smaller), and in areas with low density or text only, the judgment reference level It is set loosely (the reference value is large).

  Such setting can be performed by appropriately switching in page units of the output image. Further, for example, even when different images are added to common images as in variable printing, the reference value profile may be changed page by page according to the added images. In addition, after completion of variable printing, complementary data set at various reference levels can be organized and used as defective nozzle detection and complementary setting at each position and each reference level.

  The change of the determination reference level (reference value) according to the position in the width direction is also applicable to the process of step S27 in the correction setting process described above. That is, in the case where no defective nozzle is specified despite the fact that a defect is detected, setting can be made to raise the determination reference level in the region where the defect is detected.

As described above, the present embodiment is the inkjet recording apparatus 100 that ejects ink from the openings of the plurality of nozzles to form an image on the recording medium, and the control unit 14 includes the openings of the plurality of nozzles. The image reading unit 13 is provided with an image reading unit 13 that ejects the ink from the recording medium and outputs the missing change charts C21 to C24 that are test images related to the inspection of the ejection failure of the ink, and reads the test image. Based on the above, it is determined whether there is an ink discharge failure from the opening of the nozzle. At this time, the control unit 14 as the analysis unit changes the determination reference level relating to the presence or absence of the ejection failure according to the normal image to be formed.
That is, it is possible to detect an ink discharge failure that causes a reduction in image quality for the current image formation on the basis of enabling an appropriate frequency and an appropriate response without reducing the inspection frequency itself of the ink discharge failure. Thereby, an appropriate image can be formed more efficiently and quickly.

  In addition, since a lack of change chart C21 to C24 of a predetermined density is first output as a test image, and the presence or absence of ejection failure is first determined by uneven density, a large test image with a large image size for specifying defective nozzles is always output. It is not necessary to do this, and it is possible to suppress an increase in the area of the recording medium required to output a test image.

  In addition, since the test image is a halftone image of a predetermined density, it is possible to easily detect the occurrence of a new missing nozzle based on the judgment of density.

  In addition, since the control unit 14 as the image formation control unit forms the test image on the recording medium P outside the formation area where the normal image can be formed, the wasteful consumption of the recording medium P is not generated. In addition, it is possible to reliably perform the generation of the nozzle deficiency in the normal image formed on the recording medium P and to acquire an appropriate image.

In addition, since the control unit 14 as the analysis unit changes the determination reference level according to the image quality required for the normal image, the determination reference is easily determined according to the property setting of the print job and the like. Defect detection can be performed.
In addition, since a high quality image may sometimes be used to form an image using a defective nozzle which has become difficult to use, it has been performed more than necessary depending on the usage of the inkjet recording apparatus 100. It is possible to suppress an increase in time and cost for maintenance such as replacement of the ink jet head and cleaning of the ink discharge surface.

  In addition, since the control unit 14 as the analysis unit changes the determination reference level according to the type of the normal image, an image having no problem in image quality is flexibly acquired according to the output image, and Compared with the case where the inspection is performed under strict standards, it is possible to suppress the increase in maintenance time and cost.

  Further, the type of the normal image includes text and an image. Even if there are some streaks or density unevenness, the judgment reference level is divided into text parts that do not cause reading problems and image parts where these streaks or density unevenness easily affect the image quality, so that the entire system can be efficiently and accurately specified. Image formation of image quality can be performed.

  In addition, since the control unit 14 as the analysis unit changes the determination reference level according to the density distribution of the normal image, uniform image quality can be obtained without waste according to the inter-image or the position in the width direction of the image. .

  Further, when it is determined that the test image has an ink discharge failure, the control unit 14 as an image formation control unit causes the missing position identification chart L for specifying a defective nozzle related to the ink discharge failure to be output. The control unit 14 as an analysis unit analyzes the missing position identification chart L read by the image reading unit 13 to identify a defective nozzle, so the number of nozzles of the inkjet head and the nozzle density increase and the entire missing position identification chart L Even if the area required for the output of the above increases, the output frequency of the missing position specification chart L can be reduced without lowering the detection frequency of the ink discharge failure. Also, in order to identify a defective nozzle, it is only necessary to output a missing position identification chart corresponding to the area determined to have an ink ejection defect in the test image, so the output area itself of the missing position identification chart Can also be made smaller. As a result, the consumption of the recording medium P and the ink can be reduced more efficiently than before.

  Further, the control unit 14 as an analysis unit changes the specific reference level of the defective nozzle according to the change of the determination reference level. Therefore, the number necessary for maintaining the image quality when preventing the repetitive output of the missing position specification chart L due to the fact that the defective nozzle can not be identified even though the ink ejection failure is detected or the ink ejection failure is detected. It is possible to prevent the occurrence of a situation in which many defective nozzles are identified or the like, and to accurately maintain the image quality while suppressing unnecessary time and effort and cost increase.

  In addition, when the defective nozzle is not identified in the output defect position chart L, the control unit 14 as the analysis unit changes the determination reference level in a severe direction to determine the presence or absence of the ejection defect in the test image. Thus, it is possible to prevent the situation in which the missing position specifying chart L is repeatedly output is continued. Further, this makes it possible to make the determination reference level related to the subsequent missing change chart correspond to the specific reference level related to the missing position specification chart L in a well-balanced manner.

  Further, the control unit 14 as an image formation control unit adjusts at least one of the discharge amount and the discharge frequency of the ink by the nozzles within the predetermined proximity range related to the ink discharge range of the specified defective nozzle. The test image is output while complementing the influence of this defective nozzle. Therefore, when the complement setting is performed and the image formation of the normal image F is performed based on the complement setting, the test image according to the complement setting is formed to make the outputted normal image F more It is possible to detect a newly generated defective nozzle at a judgment reference level accurately reflected.

The present invention is not limited to the above embodiment, and various modifications are possible.
For example, in the above embodiment, the case where the complementary nozzle setting is performed on the defective nozzle has been described, but even if the operation of cleaning the ink ejection surface of the inkjet head 12 is selected according to the number and arrangement of the defective nozzles. good.

  Further, in the above embodiment, a halftone image is used as a test image. However, the present invention is not limited to this as long as nozzle loss can be detected due to a change in density. Alternatively, a defective nozzle is identified by forming a missing position identification chart L as a test image from the beginning without partially or always detecting a missing nozzle depending on the number of nozzles, the size of the margin in the recording medium P, etc. In any case, the present invention can be applied. When the missing change chart is not used, the specific reference level in the missing position specifying chart L is set independently in accordance with the normal image to be formed regardless of the determination reference level of the missing change chart. That is, when the normal image is a text image or an image with a low density, etc. and the nozzle missing is inconspicuous, the specific reference level is gently lowered (the reference value of the density change amount from the reference density and If the normal image is changed to a direction that increases the reference value of misregistration and the nozzle lacks such as high density images and image images, the specific reference level is strictly raised (density from the standard density) The reference value of the variation amount and the reference value of the deviation of the landing position from the reference position are reduced).

  In the above embodiment, the test image is always formed in the blank area, but may be formed in the normal image formation area according to the normal image F to be formed. In particular, when an inspection image relating to another inspection is output as the normal image F, a test image may be simultaneously formed in the formation area. Alternatively, the normal image and the missing position specifying chart L may be alternately formed on the recording medium P every other sheet.

  In the above embodiment, the test image is formed in the width direction to the full image formable width. However, when the normal image F is formed in only a part in the width direction, the test image is formed only in the part. May be formed.

  Further, in the above embodiment, text and an image have been described as examples of image types, but line drawings such as graphs and figures, paint data, picture data and the like may be distinguished.

  Further, the required image quality may be used in combination with the type of image and the density distribution for setting the determination reference level and the specific reference level. Each weighting may be set appropriately. Further, in this case, the user may perform some settings, for example, setting or weighting of a determination reference level or a specific reference level according to the required image quality by an input operation to the operation display unit 15.

  In the above embodiment, the specific reference level is set in conjunction with the determination reference level, but may be set separately. In addition, when identification of a defective nozzle according to the detection of a failure fails, it is also possible to reduce the specific reference level instead of or in addition to raising the determination reference level.

  Further, in the above embodiment, although the defect detection is performed by outputting the test image in which the complementation setting for the already identified defect nozzle is performed and the defect detection is performed, the test image in which the complementation setting is not performed is output. A new defect detection may be performed based on the difference with the imaging data.

In the above embodiment, an inkjet recording apparatus having a line head has been described as an example. However, the present invention is not limited to this, and the present invention may be applied to detection of an ink discharge failure even if it is of a scan type. It can.
In addition, specific details such as the configuration, processing contents, and procedures described in the above embodiment can be appropriately changed without departing from the scope of the present invention.

11 transport unit 111 transport motor 112 transport belt 12 inkjet head 120 head module 121 drive circuit 122 ink ejection unit 13 image reading unit 131 image sensor 14 control unit 141 memory 141 a defective nozzle storage unit 142 CPU
143 ROM
143a test image data 144 RAM
145 bus 15 operation display unit 16 communication unit 100 inkjet recording apparatus C21 to C24 missing change chart F normal image F21 to F24 normal image L missing position specifying chart P recording medium

Claims (10)

An ink jet recording apparatus that ejects ink from the openings of a plurality of nozzles to form an image on a recording medium.
An image formation control unit that ejects ink from the openings of the plurality of nozzles and outputs a predetermined test image related to detection of ink ejection failure;
A reading unit that reads the test image;
An analysis unit that detects a discharge failure from the opening based on the read test image;
A storage unit that stores position data of a defective nozzle related to the ejection failure;
Equipped with
The analysis unit changes a determination reference level relating to the detection of the ejection failure according to a normal image to be formed.
The storage unit stores position data of the defective nozzle obtained for each of the plurality of determination reference levels ,
The test image is an image of a predetermined density,
The analysis unit determines the presence or absence of the discharge failure based on the density unevenness of the test image,
The image formation control unit, when it is determined by the analysis unit that there is the discharge failure based on the test image, causes a defective nozzle identification image for specifying a defective nozzle related to the discharge failure to be output.
The analysis unit analyzes the defective nozzle identification image read by the reading unit to identify the defective nozzle, and when the defective nozzle is not identified in the output defective nozzle identification image, the determination criterion An ink jet recording apparatus characterized by changing the level in a strict direction to determine the presence or absence of the ejection failure in the test image . The test image is an ink jet recording apparatus according to claim 1, characterized in that the halftone image. The image formation control unit, an ink jet recording apparatus according to claim 1 or 2, wherein the forming the test image on said outer forming region normal image is formed can be set on the recording medium. The inkjet recording apparatus according to any one of claims 1 to 3 , wherein the analysis unit changes the determination reference level according to the image quality required for the normal image. The inkjet recording apparatus according to any one of claims 1 to 4 , wherein the analysis unit changes the determination reference level according to a type of the normal image. 6. The inkjet recording apparatus according to claim 5, wherein the type of the normal image includes text and an image. The inkjet recording apparatus according to any one of claims 1 to 6 , wherein the analysis unit changes the determination reference level according to a density distribution of the normal image. The inkjet recording apparatus according to any one of claims 1 to 7, wherein the analysis unit changes a specific reference level of the defective nozzle according to a change of the determination reference level. The image formation control unit adjusts at least one of the ejection amount and the ejection frequency of the ink by the nozzles within a predetermined proximity range related to the ink ejection range of the identified defective nozzle, to thereby select the defective nozzle. The ink jet recording apparatus according to any one of claims 1 to 8 , wherein the test image is output while complementing the influence. A method of detecting an ink discharge failure from the plurality of nozzles in an ink jet recording apparatus in which an image is formed by discharging ink from the openings of the plurality of nozzles.
An image formation control step of discharging ink from the openings of the plurality of nozzles and outputting a predetermined test image related to detection of ink discharge failure;
A reading step of reading the test image;
An analysis step of detecting a discharge failure from the opening based on the read test image;
A storage step of storing position data of the defective nozzle relating to the ejection failure;
Including
In the analysis step, the determination reference level relating to the detection of the ejection failure is changed according to the normal image to be formed;
In the storing step, position data of the defective nozzle obtained for each of the plurality of determination reference levels is stored ,
The test image is an image of a predetermined density,
In the analysis step, determination as to the presence or absence of the discharge failure is performed based on density unevenness of the test image,
In the image formation control step, when it is determined in the analysis step that there is the discharge failure based on the test image, a defective nozzle identification image for specifying a defective nozzle related to the discharge failure is output.
In the analysis step, the defective nozzle identification image read in the reading step is analyzed to identify the defective nozzle, and when the defective nozzle is not identified in the output defective nozzle identification image, the determination criterion A method of detecting an ink ejection failure, comprising determining the presence or absence of the ejection failure in the test image by changing the level in a strict direction .

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