JP2016140985A - Inkjet recording device and ink discharge failure detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording device and an ink discharge failure detection method which can efficiently detect and cope with an ink discharge failure at an appropriate frequency and according to appropriate criteria.SOLUTION: The inkjet recording device, which discharges ink through openings respectively of a plurality of nozzles to form an image on a recording medium, comprises: an image forming control part that discharges ink from the openings of the plurality of nozzles to output a predetermined test image relating to detection of an ink discharge failure; a reading part that reads out the test image; and an analysing part that performs detection of a failure of ink discharge through the openings on the basis of the read-out test image. The analysing part changes criteria level relating to the detection of the discharge failure responding to a normal image to be formed.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an ink jet recording apparatus and an ink ejection defect detection method.

  There is an ink jet recording apparatus that forms an image on a recording medium by ejecting ink from openings of a plurality of nozzles arranged on the recording medium. In this ink jet recording apparatus, the amount of ink discharged from the nozzle opening decreases from the initial value due to nozzle clogging or the like, and the ink is not completely discharged or the direction of discharge changes. Ink ejection failure may occur.

  In an ink jet recording apparatus, such an ink ejection defect leads to a decrease in the quality of a formed image. Therefore, conventionally, in an ink jet recording apparatus, an inspection of the ejection state of ink from the nozzle opening is periodically performed. As an inspection of the ink ejection state, there is a method of capturing a test image formed on a recording medium and analyzing the captured data. In this method, conventionally, ink ejection failure from each nozzle opening is determined by ejecting ink separately from each nozzle opening and examining the presence / absence and density of the ink ejection.

  Further, in the ink jet recording apparatus, the quality of the formed image due to the ink ejection failure is adjusted by adjusting the ink ejection amount from the nozzle opening adjacent to the defective nozzle causing the ink ejection failure based on the inspection result. There are complementary techniques that compensate for the decrease, and techniques that remove the cause of clogging of dried ink and the like by cleaning the ink ejection surface.

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

  Therefore, Patent Document 1 discloses a technique for changing the inspection frequency of an ink ejection defect according to the reliability determined according to an output target image or the like. Japanese Patent Application Laid-Open No. 2005-228561 discloses a technique that allows a user to change a level corresponding to density unevenness caused by factors including ink ejection failure.

  In Patent Document 3, the user can set whether or not to perform an operation for detecting an ink ejection failure and a recovery operation for an ejection failure nozzle automatically. A technique for causing a user to display whether or not to execute a detection operation or a recovery operation is disclosed. In Patent Document 4, the number of detected defective nozzles, the status such as the arrangement and color type are digitized based on visibility and the like, and if this numeric value is less than or equal to a value preset by the user, image formation is performed. There is disclosed a technique for continuing image formation as it is without stopping the operation or performing a recovery operation.

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

  However, ink discharge failures progress gradually, and the level of problematic ink discharge failures can change sequentially depending on the image formation method and content, so there is a need not to reduce the inspection frequency associated with images. There is. Also, if ejection failure from each nozzle is determined based on a uniform standard and complement setting is performed by other nozzles, the number of defective nozzles including minor ejection failures will increase, and the image quality after supplement setting will be reduced. There arises a problem that it becomes difficult to set the supplement. Therefore, there is a problem that it is not possible to efficiently inspect for ink ejection defects on the basis of an appropriate frequency and an appropriate response.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus and an ink discharge failure detection method capable of efficiently detecting a discharge failure of ink on the basis of enabling appropriate frequency and appropriate response.

In order to achieve the above object, the invention according to claim 1
An inkjet recording apparatus that forms an image on a recording medium by discharging ink from openings of a plurality of nozzles,
An image formation control unit that discharges ink from the openings of the plurality of nozzles and outputs a predetermined test image relating to detection of ink discharge failure;
A reading unit for reading the test image;
An analysis unit for detecting ejection failure from the opening based on the read test image;
With
The analysis unit is characterized in that a determination reference level relating to detection of the ejection failure is changed according to a normal image to be formed.

The invention described in claim 2 is the ink jet recording apparatus according to claim 1,
The test image is an image having a predetermined density,
The analysis unit is characterized in that, based on the density unevenness of the test image, a determination is made regarding the presence or absence of the ejection failure.

The invention described in claim 3 is the ink jet recording apparatus according to claim 2,
The test image is a halftone image.

Invention of Claim 4 is an inkjet recording device as described in any one of Claims 1-3,
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.

Invention of Claim 5 is an inkjet recording device as described in any one of Claims 1-4,
The analysis unit is characterized in that the determination reference level is changed in accordance with image quality required for the normal image.

Invention of Claim 6 is an inkjet recording device as described in any one of Claims 1-5,
The analysis unit is characterized in that the determination reference level is changed in accordance with the type of the normal image.

The invention according to claim 7 is the ink jet recording apparatus according to claim 6,
The normal image type includes text and image.

Invention of Claim 8 is an inkjet recording device as described in any one of Claims 1-7,
The analysis unit is characterized in that the determination reference level is changed according to a density distribution related to the normal image.

The invention according to claim 9 is the inkjet recording apparatus according to claim 2 or 3,
When the image forming control unit determines that there is the ejection failure based on the test image by the analysis unit, the image formation control unit outputs a defective nozzle specifying image for specifying a defective nozzle related to the ejection failure,
The analysis unit is characterized in that the defective nozzle is specified by analyzing the defective nozzle specifying image read by the reading unit.

The invention according to claim 10 is the ink jet recording apparatus according to claim 9,
The analysis unit is characterized in that the specific reference level of the defective nozzle is changed according to the change of the determination reference level.

The invention according to claim 11 is the ink jet recording apparatus according to claim 9 or 10,
When the defective nozzle is not specified in the outputted defective nozzle specifying image, the analysis unit changes the determination reference level in a severe direction to determine the presence or absence of the discharge defect in the test image. It is said.

The invention according to claim 12 is the ink jet recording apparatus according to any one of claims 9 to 11,
The image formation control unit adjusts at least one of an ink discharge amount and a discharge frequency of a nozzle within a predetermined proximity range related to the ink discharge range of the specified defective nozzle, and The test image is output while complementing the influence.

The invention according to claim 13
A method for detecting defective ink ejection from the plurality of nozzles in an inkjet recording apparatus that forms an image on a recording medium by ejecting ink from openings of the plurality of nozzles,
An image formation control step for outputting a predetermined test image relating to detection of ink ejection failure by ejecting ink from the openings of the plurality of nozzles;
A reading step of reading the test image;
An analysis step for detecting a discharge failure from the opening based on the read test image;
Including
In the analysis step, a determination reference level related to detection of the ejection failure is changed according to a normal image to be formed.

  According to the present invention, in the ink jet recording apparatus and the ink discharge failure detection method, there is an effect that the ink discharge failure can be efficiently detected based on a standard that enables appropriate frequency and appropriate response.

1 is a diagram illustrating an overall configuration of an inkjet recording apparatus according to an embodiment of the present invention. It is a block diagram explaining the internal structure of an inkjet recording device. It is a bottom view which shows the opposing surface with the recording medium of an inkjet head. 5 is a flowchart illustrating a control procedure of image forming processing. It is a figure which shows the example of the formation image in which the test image which concerns on discharge failure 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 specific 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 a correction setting process. It is a figure which shows the example of the reference level set in an inkjet recording device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an overall configuration of an inkjet recording apparatus 100 according to the present embodiment. FIG. 2 is a block diagram illustrating the internal configuration of the inkjet recording apparatus 100.

  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 moves the transport belt 112 around. The recording medium P arranged on the conveyance belt 112 moves in a predetermined conveyance direction by the rotation operation of the conveyance motor 111. Or the structure by which the conveyance part 11 moves the recording medium P arrange | positioned on the surface of the said conveyance drum to a rotation direction by rotating a cylindrical conveyance drum may be sufficient.

  The inkjet head 12 includes a plurality of nozzles whose 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 discharge unit 122 is operated by the drive voltage output from the drive circuit 121 based on the control signal from the control unit 14, so that the timing is controlled and the ink is discharged from the openings of the plurality of nozzles. The An image is formed by landing on the recording medium P on which the ejected ink is conveyed. The inkjet head 12 is not particularly limited, but is a line head here, and nozzles are provided so that ink can be ejected over the width in which the image of the recording medium P can be formed in the width direction perpendicular to the transport direction. It is arranged. The plurality of nozzles are provided so that, for example, four color inks of Y (yellow), M (magenta), C (cyan), and K (black) can be independently ejected.

FIG. 3 is a bottom view showing a surface (bottom surface) facing 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 portions in the width direction are the positions in the width direction of the nozzles provided at the end portions in the width direction of the other head modules 120. Are arranged to overlap. With such an arrangement, the ink can be ejected seamlessly in the width direction as a whole. The nozzles that eject ink of each color are, for example, arranged at 1200 dpi (dots per inch) in the width direction, that is, the interval (pitch) in the width direction of adjacent nozzles is about 21 μm. Here, the size (diameter) of dots (landing range) formed when ink droplets ejected from one nozzle land on the recording medium P is about 60 μm. That is, the landing ranges on the recording medium P of ink ejected from adjacent nozzles overlap each other.

The image reading unit 13 includes an image sensor 131 that is arranged on the downstream side of the inkjet head 12 in the conveyance direction of the recording medium P and captures (reads) an image formed by the inkjet head 12.
The image sensor 131 is, for example, a line sensor that obtains a one-dimensional image by arranging a plurality of CCD (Charge Coupled Device) or CMOS sensors, which are imaging elements using photoelectric conversion, in the width direction of the recording medium P. 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 arrangement) of each image sensor 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 normal transport speed of the recording medium P in the ink jet recording apparatus 100. That is, the image sensor 131 does not acquire an image with a resolution corresponding to the nozzle arrangement.

  As shown in FIG. 2, the control unit 14 includes a memory 141, a CPU (Central Processing Unit) 142, a ROM (Read Only Memory) 143, a RAM (Random Access Memory) 144, etc., which are connected to a bus 145. Thus, signals can be exchanged between the units of the inkjet recording apparatus 100. The control unit 14 is connected to an external computer or storage device such as an external print server or personal computer (PC) via the communication unit 16 and transmits / receives a print job, image data to be formed, and the like.

  The memory 141 temporarily stores image data to be imaged input from an external computer or storage device. In addition, the data stored in the memory 141 is a table that stores position data of nozzles (defective nozzles) identified as having an ink ejection defect among the plurality of nozzles of the inkjet head 12 and their complementary settings. A defective nozzle storage unit 141a is included. The complementary setting relating to the defective nozzle is separately determined and stored according to the determination reference level of the defective ink ejection as described later. The memory is composed of a combination of a RAM and a non-volatile memory, and those that are held regardless of the power supply state of the inkjet recording apparatus 100 such as the defective nozzle storage unit 141a are stored in the non-volatile memory.

  The CPU 142 performs overall control of the overall operation of the inkjet recording apparatus 100 and performs various arithmetic processes. The CPU 142 outputs control signals to the transport unit 11, the inkjet head 12, and the image reading unit 13 according to the program read from the ROM 143, and performs various processes related to image formation. Here, the CPU 142 may be provided with a single processor to perform the control operation intensively, or specially for various control processes such as transport control of the recording medium P by the transport unit 11 and drive control of the inkjet head 12. It may be provided with individualized processors.

  The ROM 143 stores a control program related to image formation and initial setting data. During 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 corresponding to the contents of nozzle inspection and adjustment.

  The RAM 144 provides a working memory space to the CPU 142 and stores temporary data. In addition, 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 nozzles related to defective ink ejection.

  The operation display unit 15 includes a display panel that performs display according to a control signal from the CPU 142, and an operation key that receives an input operation from the outside. The display panel is not particularly limited, but is a liquid crystal display (LCD), for example. Further, instead of the operation keys or together with the operation keys, a structure in which display and input operation reception are used together may be provided by providing a touch panel stacked on the LCD display screen.

Next, an image forming operation in the inkjet recording apparatus 100 of the present embodiment will be described.
In the ink jet recording apparatus 100 of the present embodiment, one of a plurality of image quality levels is selected during image formation to form an image. At this time, a defective nozzle is set and a complementary setting is made for the defective nozzle in accordance with the image quality level.

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

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

  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) the test image, and obtain image data of the read test image (step S4).

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

Next, the operation content of the nozzle ink ejection defect inspection in the inkjet recording apparatus 100 of the present embodiment will be described.
In the ink discharge defect inspection of the present embodiment, first, a discharge defect detection operation for detecting the presence or absence of ink discharge defects is performed in parallel with normal image formation, and if an ink discharge defect is detected, if necessary, A defective nozzle specifying operation for specifying a nozzle causing an ink ejection defect is performed.

  FIG. 5 is a diagram illustrating 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 leading edge and the trailing edge of an area set as a range for forming an image to be formed (normal image F) related to a print job (a formation area in which a normal image can be formed) In general, a blank area (outside the normal image forming area) is provided. Then, in any of these blank areas, here, in the last blank area, missing change charts C21 to C24, which are test images for performing an inspection related to the presence or absence of ink ejection failure, are formed for each color ink of CMYK. The Since these missing change charts C21 to C24 only need to be able to distinguish between light and shade, they are each formed in a strip shape in the width direction corresponding to the width in which the nozzles for ejecting ink of each color in the inkjet head 12 are arranged.

FIG. 5B shows an enlarged part of the test image in FIG.
For the test images of the missing change charts C21 to C24, halftone images of a predetermined density (gradation) are used for each color ink. The halftone gradation is set to a value at which a change in density is likely to occur largely due to a missing nozzle, for example, 30%. The halftone image can be generated by applying various known methods such as a dither method and an error diffusion method.

The presence or absence of ink ejection related to the halftone image is determined based on the integrated density value in the transport direction of the halftone image. By doing in this way, the information of the halftone pattern expressing the gradation by the area and the density information can be grasped as almost the same information. These missing change chart data are read from the test image data 143a of the ROM 143, and ink is sequentially ejected from each nozzle to a position specified by the halftone pattern to form a halftone image. In addition, ideally, the halftone pattern preferably has been subjected to well-known nozzle missing correction, shading correction, and the like related to an ejection failure nozzle that has already been detected. As a result, the image sensor 131 described later can determine whether there is a nozzle that has newly caused an ink ejection failure without considering nozzle missing information or liquid volume variation information.
That is, in the ink jet recording apparatus 100, even when the gradation values of the image data to be printed are the same, the appropriate amount of liquid ejected from each nozzle varies. Variation in 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, which is correction for making the density uniform for each nozzle, is performed. Specifically, the ink discharge amount from the nozzles is adjusted according to the variation for each nozzle.

  In the ink jet recording apparatus 100, a representative value of density in each reading region (reading range) that can be discriminated by the image sensor 131 is obtained from the halftone image, instead of the dots formed by the ejected individual ink droplets. Then, the density between these reading areas is detected, and it is determined whether or not there is a nozzle causing ink ejection failure in each reading area. At this time, in the detection of 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 the halftone image using the missing change charts C21 to C24 of the present embodiment, the gradation value obtained by integrating and averaging the pixel values of the test image photographed by the image sensor 131 in each reading area, and the background Using a median filter as a value, a value obtained in a wider range than the reading area is compared. In this median filter, a median (median value) of gradation values obtained in a predetermined number of reading areas in the width direction with the reading area to be analyzed as the center is acquired. In the analysis of the present embodiment, when the gradation value of each pixel column is smaller than the background value by a predetermined reference value or more, it is determined that the nozzle defect is generated in the area including the pixel. The term “nozzle missing” here includes not only a state where ink is not ejected at all, but also a state where the ink ejection amount is greatly reduced and a state where the ink ejection direction is changed.

  The number of reading areas (number of taps) for obtaining a median as a background value is determined as appropriate. As the number of taps increases, the accuracy of the median increases, and it becomes possible to detect missing nozzles more reliably, while the calculation time increases. Therefore, the number of taps is set so as to improve the accuracy within a possible range according to the conveyance speed of the recording medium P, the transfer speed of the read data, the calculation speed and load of the CPU 142, 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. The median filter generally detects a large local change such as missing one nozzle with high accuracy, but uses other filters such as a moving average value or a spatial frequency filter (such as a low-pass filter). Even detection is possible.

  In the inkjet recording apparatus 100, a reference value (determination reference level) for determining whether or not a nozzle is missing can be changed in a predetermined plurality of steps. Here, the reference value is changed in accordance with the image quality required for the normal image F. The required image quality is not particularly limited, but is acquired based on image formation properties set in advance by the user. For example, when the required image quality level is “Premium”, “High-definition”, etc., the judgment standard level is set strict (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 to be loose (the reference value is large).

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

  FIG. 6 is a flowchart showing the control procedure of the correction setting process that is 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 making a setting for complementing the ink discharge amount that should be discharged by the specified defective nozzle by the discharge from other nozzles, and a normal image F is formed on each recording medium P. Each time it is called in the image forming process and 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). . If the halftone image has not been detected as defective, that is, the ink ejection failure has not been detected in the correction setting process up to the previous time, or the complementary setting for the detected ink ejection defective portion has already been performed. 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). The control unit 14 sets a determination reference level for defect detection according to the determined image quality (step S13).

  The control unit 14 analyzes the halftone image acquired this time and detects an ink ejection failure (step S14). The control unit 14 determines whether or not an ink ejection failure has been detected based on the set determination reference level (reference value) (step S15). If it is determined that no ink ejection failure has been 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 a command to output a missing position specifying chart (defective nozzle specifying image) (step S16). Then, the control unit 14 ends the correction setting process.

  On the other hand, in the determination process in step S11, it is determined that the halftone image is not defectively detected, that is, it is determined that the ink ejection defect is detected in the previous correction setting process and the complementary setting has not yet been made. In this case (“NO” in step S11), the control unit 14 reads image data captured by the image sensor 131 of the missing position specifying chart on which image formation has been performed based on the command output in the process of step S16 (step S22). ).

FIG. 7 is a diagram illustrating an example of a formed image of the missing position specifying chart L.
This missing position specifying chart L is a test image in which ink is ejected in a ladder shape or a lattice shape so that the landing positions on the recording medium P of the ink ejected for each nozzle are separated from each other. Part a) is shown. Here, each line extending in the transport direction indicates an ink landing position from a different nozzle. Depending on the density and formation position of each of these lines, the density deviation more than the reference value due to non-ejection of ink and the decrease in ejection amount (weak emission) and / or the deviation more than the reference value of the landing position due to bending in the ink ejection direction. A position where such a dot defect occurs is specified.

  The missing position specifying chart L is included in the test image data 143a and preset and stored. Further, the missing position specifying chart L formed at this time may not be for all the nozzles but only for the area where the defect is detected. Reference values relating to determination of density deviation and landing position deviation are collectively referred to as a specific reference level hereinafter.

  The control unit 14 sets a specific reference level for defective nozzles according to the determination reference level for defect detection set in the process of step S13 (step S23). The control unit 14 also tightens the specific reference level when the determination reference level is severe, and also loosens the specific reference level when the determination reference level is loose. The control unit 14 analyzes the captured image data of the read missing position specifying chart L, and specifies the dot missing position based on the set specific reference level (step S24). Further, the control unit 14 identifies a defective nozzle (nozzle missing position) causing an ink ejection failure from the dot missing position.

  For example, as shown in FIG. 7B, when the reference value (half the width w) of the landing position is set for the normal discharge positions i1 to i4 indicated by the broken lines, the solid lines are indicated by the solid lines. Assuming that the ink has landed at 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 are determined to be normal discharge. . On the other hand, the shift amounts d2 and d4 of the landing positions r2 and r4 from the normal discharge positions i2 and i4 are equal to or larger than the reference value, and the dot dropout occurs in the normal discharge positions i2 and i4. It is determined that the corresponding nozzle is a defective nozzle.

  In addition, the identification of the defective nozzle may be determined by combining the results identified by a plurality of missing position specifying charts without being determined only by one missing position specifying chart L. For example, all the defective nozzles identified at least once in the past 10 missing position specifying charts may be determined as defective nozzles.

  The control unit 14 determines whether or not the dot missing position (defective nozzle) has been successfully identified (step S25). If it is determined that the dot missing position has not been successfully identified (“NO” in step S25), the control unit 14 increases the defect detection determination reference level set in step S13 from the next time (strictly). Set) (step S27). This prevents the missing position specifying chart L from being repeatedly output without specifying the defective nozzle that causes the defect detection even though the defect detection is performed in the halftone image every 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 has been successfully identified (“YES” in step S25), the control unit 14 performs correction settings relating to the complement of ink ejection according to the identified dot missing position (step S25). S26). The control unit 14 performs this complementation by changing the ink discharge amount of a nozzle (for example, both adjacent nozzles) 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 for defect detection. If it is expected that the defect detection criterion level cannot be cleared only by changing the ink discharge amount, the control unit 14 stops the image forming operation and causes the operation display unit 15 to perform a cleaning operation or replacement of the inkjet head. Prompt display. 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 a defective ink discharge from the nozzle opening is detected, the control unit 14 detects the defective ink discharge for the recording medium P in which the detection has been performed in the determination process of step S15. It is determined whether or not a normal image is formed in an area including the ink and the ink color, and if no image formation is performed in the area and the ink color, it is determined that no defect is detected. The correction setting process may be terminated without shifting to the process of S16.

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

[Modification]
FIG. 9 is a modified example 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. The description is omitted.

  When branching to “YES” in the determination processing in step S11, the control unit 14 (CPU 142) determines the type of the normal image F formed together with the halftone image (step 12a). In addition, the control unit 14 acquires the density distribution of the normal image F (step S12b). The control unit 14 sets a determination reference level (reference value) related to detection of defective ink ejection based on the determination result and the acquired data in the processes of steps S12a and S12b (step S13).

  As described above, in this modification, the determination reference level (reference value) relating 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, when the normal image F is composed only of text, the determination reference level is set to be slightly lowered (increase the reference value), and when the normal image F is an image, the determination reference level is severely increased ( The reference value can be reduced). Further, the determination reference level can be changed according to the density (density distribution) of the image included in the normal image F. The level of the density is determined according to an index value based on any one or a combination of the maximum value, the average value, the median value, and the like of the density in the image.

FIG. 10 is a diagram illustrating an example of the determination reference level set in the ink jet recording apparatus 100 of the present embodiment.
The determination reference level (reference value) can 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 acquired in advance and a reference value profile corresponding to the position in the width direction can be set. In high density parts and image parts, unevenness and streaks due to missing nozzles tend to be noticeable, so the judgment standard level is set to be strictly increased (small standard value). In low density parts and text-only parts, the judgment standard level is set. Set loosely (larger reference value).

  Such a setting can be appropriately switched for each page of the output image. Further, for example, when different images are added to each page with respect to a common image as in variable printing, the reference value profile may be changed in units of pages according to the added image. Further, 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 reference level.

  Such a change in the determination reference level (reference value) according to the position in the width direction can also be applied to the process of step S27 in the correction setting process described above. In other words, when a defective nozzle is not specified despite the fact that a defect has been detected, it is possible to make a setting for raising the determination reference level in the area where the defect has been detected.

As described above, the present embodiment is an ink jet recording apparatus 100 that forms an image on a recording medium by ejecting ink from openings of a plurality of nozzles, and the control unit 14 includes openings of a plurality of nozzles. The image reading unit 13 is provided to output the missing change charts C21 to C24, which are test images relating to the inspection of the ink ejection failure, and read the test image, and the control unit 14 reads the test image. Based on the above, the presence or absence of defective ink ejection from the nozzle opening is determined. At this time, the control unit 14 as the analysis unit changes the determination reference level related to the presence or absence of ejection failure according to the normal image to be formed.
In other words, it is possible to detect an ink ejection defect that causes a decrease in image quality for current image formation on the basis of an appropriate frequency and an appropriate response without reducing the inspection frequency itself of the ink ejection defect. Thereby, an appropriate image can be formed more efficiently and promptly.

  Further, the missing change charts C21 to C24 having a predetermined density are first output as test images, and the presence / absence of ejection failure is first determined based on density unevenness, so that a test image having a large image size for always identifying a defective nozzle is output. Therefore, an increase in the area of the recording medium necessary for outputting the test image can be suppressed.

  In addition, since the test image is a halftone image having a predetermined density, it is possible to easily detect the occurrence of a new nozzle defect based on the determination of light and shade.

  Further, since the control unit 14 as the image formation control unit forms a test image outside the formation area where the normal image can be formed on the recording medium P, the recording medium P is not wastefully consumed. In addition, it is possible to reliably generate the nozzle defect in the normal image formed on the recording medium P and obtain an appropriate image.

Further, the control unit 14 as the analysis unit changes the determination reference level according to the image quality required for the normal image. Therefore, the determination reference is easily determined according to the property setting of the print job, and appropriate image formation and Defect detection can be performed.
In addition, since it may occur that an image can be formed using a defective nozzle at a level that is difficult to use for a high-quality image, it has been performed more than necessary depending on the usage mode of the inkjet recording apparatus 100. It is possible to suppress an increase in labor and cost related to maintenance such as replacement of the ink jet head and cleaning of the ink discharge surface.

  Further, the control unit 14 as the analysis unit changes the determination reference level according to the type of the normal image, so that an image having an image quality with no problem can be flexibly acquired according to the output image, and most uniformly. Compared to the case where inspections are performed according to strict standards, it is possible to suppress an increase in maintenance labor and expenses.

  The normal image type includes text and image. By dividing the judgment standard level between text parts that do not cause reading problems even if there are some streaks and density irregularities, and image parts where these streaks and density irregularities tend to affect the image quality, it is efficient and accurate as a whole. Image formation with image quality can be performed.

  Further, since the control unit 14 as the analysis unit changes the determination reference level according to the density distribution related to the normal image, it is possible to obtain uniform image quality without waste according to the interval between images or the position in the width direction of the image. .

  Further, when it is determined that the test image has an ink ejection failure, the control unit 14 as the image formation control unit outputs a missing position specifying chart L for specifying a defective nozzle related to the ink ejection failure, Since the control unit 14 as the analysis unit analyzes the missing position specifying chart L read by the image reading unit 13 and specifies defective nozzles, the number of nozzles and the nozzle density of the inkjet head increase and the entire missing position specifying chart L is obtained. Even if the area required for the output is increased, the output frequency of the missing position specifying chart L can be reduced without reducing the detection frequency of the ink ejection failure. In addition, in order to specify a defective nozzle, it is only necessary to output a missing position specifying chart corresponding to an area where it is determined that there is an ink ejection failure in the test image. Can also be reduced. Thereby, consumption of the recording medium P and ink can be reduced more efficiently than before.

  Further, the control unit 14 as the analysis unit changes the specific reference level of the defective nozzle according to the change of the determination reference level. Therefore, it is possible to prevent repeated output of the missing position specifying chart L due to failure to identify defective nozzles even though ink ejection failure is detected, or to maintain the image quality when ink ejection failure is detected. It is possible to prevent the occurrence of such a situation that many defective nozzles are identified as described above, and to accurately maintain the image quality while suppressing unnecessary labor and cost increase.

  In addition, when a defective nozzle is not specified in the outputted missing position specifying chart L, the control unit 14 as an analysis unit determines whether or not there is a discharge failure in the test image by changing the determination reference level in a strict direction. Thus, it is possible to prevent the situation where the missing position specifying chart L is repeatedly output from continuing. In addition, this makes it possible to match the determination reference level related to the subsequent missing change chart and the specified reference level related to the missing position specifying chart L in a well-balanced manner.

  In addition, the control unit 14 as an image formation control unit adjusts at least one of the ink discharge amount and the discharge frequency of the nozzles within a predetermined proximity range related to the ink discharge range of the specified defective nozzle. The test image is output while compensating for the influence of the defective nozzle. Therefore, when the normal setting is performed and the normal image F is formed based on the complementary setting, the test image corresponding to the complementary setting is formed so that the output normal image F is more Newly generated defective nozzles can be detected at the judgment reference level accurately reflected.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above embodiment, the case where the complementary setting is performed for the defective nozzle has been described. However, even when the operation for cleaning the ink ejection surface of the inkjet head 12 is selected according to the number or arrangement of the defective nozzles. good.

  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 missing can be detected by a change in shading. Alternatively, the defective nozzle is identified by forming a missing position specifying chart L as a test image from the beginning without partially or constantly detecting the missing nozzle depending on the number of nozzles, the size of the margin in the recording medium P, and the like. Even in this 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 according to the normal image to be formed independently of the determination reference level of the missing change chart. That is, when the normal image is a text image or an image with low density and the nozzle missing is not conspicuous, the specific reference level is loosely lowered (the reference value of the density change amount from the reference density and the landing from the reference position). If the normal image is a high-density image or an image image where the missing nozzles are conspicuous, increase the specific reference level strictly (the density from the reference density). The reference value of the change 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. However, the test image may be formed in the normal image formation area in accordance with the normal image F to be formed. In particular, when an inspection image related to another inspection is output as the normal image F, the test image may be simultaneously formed in the formation region. 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 forming width. However, when the normal image F is formed only in a part in the width direction, the test image is formed only in the part. May be formed.

  In the above embodiment, text and image images are taken as examples of image types. However, line drawings such as graphs and figures, paint data, and photo data may be distinguished from each other.

  Further, the required image quality, the image type, and the density distribution may be used in combination for setting the determination reference level and the specific reference level. Each weighting can be set as appropriate. In this case, a part of the settings, for example, the setting and weighting of the determination reference level and the specific reference level according to the required image quality may be performed by the user through 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 the failure nozzle identification according to the failure detection fails, the specific reference level can be lowered instead of or in addition to raising the determination reference level.

  Further, in the above embodiment, the test image with the complementary setting for the already specified defective nozzle is output and the defect detection is performed, but the test image without any complementary setting is output, and the previous test image New defect detection may be performed based on the difference from the imaging data.

In the above-described 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 can be applied to detection of ink ejection defects even in a scan system. I can do it.
In addition, specific details such as the configuration, processing contents, and procedures shown in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 11 Conveyance part 111 Conveyance motor 112 Conveyance belt 12 Inkjet head 120 Head module 121 Drive circuit 122 Ink discharge part 13 Image reading part 131 Image sensor 14 Control part 141 Memory 141a Defective nozzle storage part 142 CPU
143 ROM
143a Test image data 144 RAM
145 Bus 15 Operation display unit 16 Communication unit 100 Inkjet recording devices C21 to C24 Missing change chart F Normal image F21 to F24 Normal image L Missing position specifying chart P Recording medium

Claims (13)

An inkjet recording apparatus that forms an image on a recording medium by discharging ink from openings of a plurality of nozzles,
An image formation control unit that discharges ink from the openings of the plurality of nozzles and outputs a predetermined test image relating to detection of ink discharge failure;
A reading unit for reading the test image;
An analysis unit for detecting ejection failure from the opening based on the read test image;
With
The ink jet recording apparatus, wherein the analysis unit changes a determination reference level related to detection of the ejection failure according to a normal image to be formed. The test image is an image having a predetermined density,
The inkjet recording apparatus according to claim 1, wherein the analysis unit makes a determination regarding the presence or absence of the ejection failure based on density unevenness of the test image.   The inkjet recording apparatus according to claim 2, wherein the test image is a halftone image.   4. The image forming control unit according to claim 1, wherein the image forming control unit causes the test image to be formed outside a forming region in which the normal image can be formed on the recording medium. 5. Inkjet recording device.   5. The inkjet recording apparatus according to claim 1, wherein the analysis unit changes the determination reference level according to an image quality required for the normal image.   The inkjet recording apparatus according to claim 1, wherein the analysis unit changes the determination reference level according to a type of the normal image.   The inkjet recording apparatus according to claim 6, wherein the normal image type includes text and an image.   The inkjet recording apparatus according to claim 1, wherein the analysis unit changes the determination reference level according to a density distribution related to the normal image. When the image forming control unit determines that there is the ejection failure based on the test image by the analysis unit, the image formation control unit outputs a defective nozzle specifying image for specifying a defective nozzle related to the ejection failure,
The inkjet recording apparatus according to claim 2, wherein the analysis unit analyzes the defective nozzle specifying image read by the reading unit and specifies the defective nozzle.   The inkjet recording apparatus according to claim 9, wherein the analysis unit changes a specific reference level of the defective nozzle according to a change in the determination reference level. When the defective nozzle is not specified in the outputted defective nozzle specifying image, the analysis unit changes the determination reference level in a severe direction to determine the presence or absence of the discharge defect in the test image. An ink jet recording apparatus according to claim 9 or 10.   The image formation control unit adjusts at least one of an ink discharge amount and a discharge frequency of a nozzle within a predetermined proximity range related to the ink discharge range of the specified defective nozzle, and The inkjet recording apparatus according to claim 9, wherein the test image is output while complementing the influence. A method for detecting defective ink ejection from the plurality of nozzles in an inkjet recording apparatus that forms an image on a recording medium by ejecting ink from openings of the plurality of nozzles,
An image formation control step for outputting a predetermined test image relating to detection of ink ejection failure by ejecting ink from the openings of the plurality of nozzles;
A reading step of reading the test image;
An analysis step for detecting a discharge failure from the opening based on the read test image;
Including
In the analysis step, a determination reference level related to detection of the ejection failure is changed according to a normal image to be formed.

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