JP6417650B2 - Ink jet recording apparatus and ink discharge defect detection method - Google Patents

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 a plurality of arranged nozzles onto the recording medium. In this ink jet recording apparatus, defective ink ejection from the nozzles leads to a decrease in the quality of the formed image. Therefore, conventionally, the discharge state from the nozzles is regularly inspected. In addition, in the ink jet recording apparatus, there is a technique that compensates for a decrease in the quality of a formed image due to defective ink discharge from the nozzles by adjusting the ink discharge amount from adjacent nozzles based on the inspection result.

  As an inspection related to defective ink ejection from a nozzle, there is a method of capturing a test image formed on a recording medium and analyzing the captured data. In this type of ink ejection defect inspection, conventionally, a method of individually inspecting dots or lines of droplets ejected from each nozzle and landed on a recording medium is used. However, due to high-speed image formation and high accuracy of the formed image, it is difficult to perform imaging at an accuracy corresponding to each landing range at low cost, or the landing ranges of adjacent droplets overlap. Therefore, there is a problem that separation is difficult.

  Therefore, Patent Document 1 discloses a technique for forming test images in a lattice shape or a ladder shape by shifting the timing of ink ejection from adjacent nozzles, and analyzing each captured image data. In Patent Document 2, when the landing range of the ink droplets ejected from the nozzles and the imaging range do not match, an expected value is calculated by weighting the landing area from the nozzle corresponding to each imaging range. A technique for identifying a nozzle that has caused an ink ejection defect based on a difference between the expected value and an actually measured value based on imaging data is disclosed.

JP 2002-79663 A Japanese Patent Laid-Open No. 2006-199048

  However, if a conventional test image is formed and used to detect the presence or absence of ink ejection failure, the size of the image formed on the recording medium becomes large, and the calculation and data transmission work becomes extra. End up. Therefore, in consideration of the frequency with which ink ejection defects actually occur, in many cases, there is a problem in that the recording medium is wasted and the processing becomes complicated each time. In addition, when a test image is formed outside the normal image formation range of the recording medium, that is, in a blank area, it is necessary to divide the test image into a plurality of recording media, and until the test is completed. There is a problem that it takes time.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus and a method for detecting an ink ejection defect that can easily and promptly check for the presence or absence of ink ejection from a nozzle without wasting a recording medium.

In order to achieve the above object, the present invention described in claim 1
An ink jet recording apparatus that forms an image on a recording medium by ejecting ink from a plurality of nozzles,
An image formation controller that discharges ink from the plurality of nozzles and outputs a single halftone image having a predetermined density as a test image;
A reading unit for reading the test image;
An analysis unit that determines only the presence or absence of ejection failure from the nozzle based on the density of the read test image,
The dot occupancy rate of dots constituting the test image Ri value der of 60% or less than 20%
The analysis unit is configured to determine whether or not there is a nozzle causing an ink ejection failure for each reading region corresponding to a plurality of nozzles that can be determined by the reading unit from the halftone image . .
According to a second aspect of the present invention, in the inkjet recording apparatus according to the first aspect, the reading unit reads the test image with a resolution lower than a resolution corresponding to a nozzle arrangement of the plurality of nozzles.

The invention described in claim 3 is 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 outside a normal image formation region on the recording medium.

According to a fourth aspect of the present invention, in the ink jet recording apparatus according to the third aspect ,
A transport unit that transports the recording medium in a predetermined transport direction;
The normal image is another inspection image related to an inspection application different from the test image,
The inspection image is formed in the same number as the plurality of blocks for each of the plurality of blocks divided in the direction orthogonal to the conveyance direction,
The analysis unit is characterized by determining the presence or absence of ejection failure from the nozzle for each block based on the test image.

The invention according to claim 5 is the ink jet recording apparatus according to claim 3 or 4 ,
The image formation control unit outputs the normal image and the test image using ink used for forming the normal image on the same surface of the recording medium.

Invention of Claim 6 is an inkjet recording device as described in any one of Claims 1-5 ,
A transport unit that transports the recording medium in a predetermined transport direction;
The length of the test image in the transport direction is 50% or more and less than 100% of the unit length of the halftone image.

The invention according to claim 7 is the ink jet recording apparatus according to any one of claims 1 to 6 ,
When the analysis unit determines that the test image has an ink ejection failure, the image formation control unit outputs a defective nozzle identification image for identifying a defective nozzle related to the ink 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 8 is the ink jet recording apparatus according to claim 7 ,
A defective nozzle storage unit that stores the defective nozzle specified by the analysis unit;
The analysis unit is characterized in that a new defective nozzle is identified by comparing the defective nozzle detected and stored from the previous defective nozzle identification image with the defective nozzle detected this time.

The invention according to claim 9 is the ink jet recording apparatus according to claim 7 or 8 ,
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 the influence is interpolated.

The invention of claim 10, wherein, in the ink jet recording apparatus according to any one of claims 7-9,
In the case where a new ink discharge failure is detected from the test image by the analysis unit, the image formation control unit is configured so that any of the nozzles in the range where the discharge failure is detected forms a normal image. It is characterized in that it is determined whether or not it has been used, and if it is determined that it has not been used, the next normal image is formed without forming the defective nozzle specifying image.

The invention according to claim 11 is the ink jet recording apparatus according to any one of claims 1 to 9 ,
The image formation control unit outputs the test image using only ink used in a normal image formed on the recording medium.

The invention according to claim 12 is the inkjet recording apparatus according to any one of claims 1 to 11 , wherein
A transport unit that transports the recording medium in a predetermined transport direction;
The plurality of nozzles are arranged partially overlapping with respect to the length of the recording medium in the direction orthogonal to the transport direction,
The image formation control unit forms the test image by adjusting the ink discharge amount from the plurality of nozzles so that the ink discharge amount is substantially equal at each position in a direction orthogonal to the conveyance direction of the recording medium. It is characterized by that.

The invention according to claim 13 is the ink jet recording apparatus according to any one of claims 1 to 12 ,
The image formation control unit outputs the test image in which shading characteristics of the plurality of nozzles are corrected.

The invention according to claim 14
A method for detecting defective ink ejection of the plurality of nozzles in an ink jet recording apparatus that forms an image on a recording medium by ejecting ink from each of the plurality of nozzles,
An image forming control step of discharging ink from the plurality of nozzles and outputting a single halftone image of a predetermined density as a test image;
A reading step of reading the test image by a reading unit ;
An analysis step for determining only the presence or absence of ejection failure from the nozzle based on the density of the read test image;
Including
The dot occupancy of the dots constituting the test image is a value of 20% or more and 60% or less,
The analyzing step is characterized in that, from the halftone image, it is determined whether or not there is a nozzle causing an ejection failure for each reading region corresponding to a plurality of nozzles that can be determined by the reading unit.

  According to the present invention, the ink jet recording apparatus has an effect that it is possible to easily and quickly inspect for ink ejection defects from the nozzles without wasting a recording medium.

1 is a diagram illustrating an overall configuration of an ink jet 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. 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 figure which shows the contrast between the drawing area | region with a nozzle defect, and the drawing area without a nozzle defect | deletion at the time of forming the halftone image which generated 1 nozzle defect | deletion in each density | concentration. It is a graph which shows the influence of the length of the missing change chart with respect to the detection of 1 nozzle missing. It is a flowchart which shows the control procedure of a correction setting process. It is a figure which shows the other example of the formation image in which the test image which concerns on discharge failure detection operation is included. It is a flowchart which shows the control procedure of a gradation correction process.

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 faces the conveyance surface of the recording medium P and is disposed on the downstream side of the inkjet head 12 in the conveyance direction.
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. Also, corresponding to the inkjet head 12 capable of color (CMYK) output, a formed image can be acquired 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, data 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 or image data to be printed.

  The memory 141 temporarily stores image data to be printed input from an external computer or storage device. The memory 141 includes a defective nozzle storage unit 141a in which position data of nozzles (defective nozzles) identified as defective ejection by inspection among the plurality of nozzles of the inkjet head 12 and interpolation settings thereof are stored in a table.

  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 controlled centrally by one processor, or may be an individual processor specialized 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.

  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. Also, 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 nozzles related to ink ejection failure.

  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 touch sensor that is stacked on the LCD panel may be used as a touch panel so that display and operation reception can be used together.

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 according to the present embodiment, first, a discharge defect detection operation for detecting the presence or absence of an ink discharge defect is performed, and if an ink discharge defect is detected, a nozzle that causes an ink discharge defect as necessary. The defective nozzle specifying operation for specifying the is performed.

  FIG. 4 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. 4A, a blank area is provided at the leading and trailing ends of an area (normal image formation area) set as a range for forming an image formation target image (normal image) related to a print job. (Outside the normal image forming area) is provided. Then, in any of these blank areas, here, in the leading 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 These missing change charts C21 to C24 are each formed in a band 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. 4B 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 defined as, for example, a dot occupancy ratio in an area of 256 dots (unit length) × 256 dots set as a unit area for expressing each color of 256 gradations. That is, the dot occupancy rate of 30% means that 19660 pixels are occupied among the pixels (65536 pixels) constituting 256 × 256 dots. As the type of halftone, various halftone images such as a dither method and an error diffusion method can be applied.
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. Moreover, ideally, the halftone pattern is preferably subjected to known nozzle missing correction, shading correction, or the like. As a result, the image sensor 131 described later can determine whether there is a nozzle that has caused an ejection failure without taking into account information on missing nozzles, information on variations in liquid amount, and the like.
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 this case, it is possible to perform the image formation of the missing change charts C21 to C24 in a state where the ink ejection interpolation is performed on the nozzle in which the ejection failure has already occurred.
On the other hand, it is possible to perform image formation of the missing change charts C21 to C24 without performing ink ejection interpolation. In this case, the current density abnormality detection position may be compared with the previous density abnormality detection position, and the defective nozzle identification operation may be performed only for a new abnormality occurrence location and a location where the abnormality mode has changed.

As the density of the halftone image and the length of each halftone image in the conveyance direction, those suitable for the above detection method are selected.
FIG. 5 shows a halftone image formed at each density of 16 gradations selected from among the density of 256 gradations, and a halftone image in which one nozzle is missing for each density of the 16 gradations. It is a figure which shows the contrast (gradation difference) with the case where it forms. Here, the horizontal axis indicates the normalized ink adhesion amount (dot occupancy), that is, the ratio of the nozzles that ejected ink among all the nozzles. In the present embodiment, the value “1” on the horizontal axis indicates that the dot occupancy is 100%, and corresponds to an ink amount of 8.6 ml · m ⁻² .

  In practice, the dot occupancy and density in a halftone image are not simply proportional. Compared with the case where the dot occupancy is low (low gradation) or high (high gradation), when the dot occupancy is an intermediate value, a change in density when nozzle missing occurs greatly appears. Here, when the dot occupancy is about 20% to 60%, and more preferably about 30%, the contrast between the nozzle missing portion and the normal portion is large, and the scanner used in this embodiment has a large contrast. It can be seen that the difference is about 13 to 15 gradations in 256 gradations. That is, when there is a recording medium surface on which ink has not landed or when there are many overlapping portions of the ink landing range, a difference in contrast is unlikely to occur. Therefore, a halftone image with a dot occupancy of 30% is used here. With a dot occupancy of about 20% to 60%, a halftone image close to the high gradation side having a density of 120 to 200 gradations is formed. This correspondence greatly depends on the dot diameter of the ejected ink. For example, when the dot diameter is larger than that of the present embodiment, the area where the dots overlap is larger in the high density portion than in the present embodiment. In such a case, the range of the dot occupancy where the contrast is highest shifts to the side where the dot occupancy is lower than the range shown in FIG.

  On the other hand, in the processing related to nozzle missing detection in the image reading unit 13, the size of the halftone image in each reading area is proportional to the length of the recording medium P in the transport direction, and is representative of the halftone density in each reading area. The variation in value decreases as the length increases.

FIG. 6 is a chart showing the influence of the length of the missing change chart on the detection of missing one nozzle.
As described above, in this embodiment, a dither matrix composed of 256 × 256 dots is used, and the length per side is about 5.4 mm. This length corresponds to 64 pixels in the image sensor 131 that acquires an image at 300 dpi in the transport direction.
As shown in FIG. 6, in this halftone image, if there are 140 dots (140/256 with respect to the unit length of the halftone pattern), that is, a length of 35 pixels or more, sufficient contrast can be obtained. (○). On the other hand, in the case of 120 dots (120/256 with respect to the unit length of the halftone pattern), that is, a halftone image having a length of 30 pixels, a result in which the contrast is slightly lowered (Δ) is obtained. Accordingly, it is desirable that the halftone image be formed with a length corresponding to a half period (about 2.7 mm) of the unit region length (unit length of the halftone image). On the other hand, even if the length of the halftone image is extended, the contrast is not further increased.
However, this is not limited to the dither method, and can also be applied to the error diffusion method. This is because this halftone period is ultimately affected by the spatial frequency of the halftone pattern at a given dot occupancy. Even in this case, it is desirable to calculate the optimum length in the transport direction from the relationship between the length in the transport direction and the contrast.

Here, when the dot occupancy in the halftone image is different from 30%, the length necessary for obtaining a sufficient contrast is also different, and therefore, it is set appropriately. Specifically, when the dot occupancy is lower than 30%, the necessary length is increased. However, if the dot occupancy is too low, the required length becomes too large compared to the size of the margin area. Therefore, the dot occupancy is within an appropriate range in consideration of this point, for example, the required length. Is set in a range not exceeding the unit area length.
The gradation difference (contrast) between the one-nozzle missing area and the normal ink ejection area is determined by the dot occupancy as shown in FIG. However, depending on the size of the formed halftone image, the pattern of the halftone, and the density of the halftone, the dot occupancy (number of ejections) from each nozzle is often not exactly equal. . When a dither method or an error diffusion method is used to form a halftone image, a difference in the number of dots may occur for each nozzle depending on the length in the transport direction (halftone period). This influence becomes relatively small as the number of ink ejections from each nozzle increases, that is, as the halftone image becomes longer (in inverse proportion), and can be ignored. In the result of FIG. 5, 140 dots with respect to a dot occupancy of 30%, that is, about 47 times of ink ejection from each nozzle, even if the number of ink ejections increases or decreases, the required contrast is It shows that there is no effect. Further, when the length in the transport direction is further extended, the effect of improving the contrast related to the number of ink ejections is reduced. On the other hand, since the image forming area is widened and an extra recording medium is consumed, the halftone image The length of is preferably kept at an appropriate value rather than longer than necessary.

  In the analysis of the halftone image using the missing change chart of the present embodiment, each pixel value of the test image captured by the image sensor 131 is integrated and averaged in each reading area, and a median is used as the background value. A value acquired in a wider range than the reading area is compared using a filter. 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 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.

  FIG. 7 is a flowchart showing a control procedure of correction setting processing executed by the control unit 14 of the present embodiment.

  This correction setting process is a process for performing an ink ejection defect inspection and a setting for interpolating an ink ejection amount that should be ejected by the specified defective nozzle. An image is formed on each recording medium P, for example, at a predetermined interval. It is automatically executed every time it is done.

  When the correction setting process is started, first, the control unit 14 (CPU) determines whether or not the defect detection of the halftone image related to the missing change chart has not been made (step S11). The halftone image is not defectively detected, that is, the ink ejection failure has not been detected in the previous correction setting process or the detected ink ejection defective part has already been set for interpolation. If it is determined (“YES” in step S11), the control unit 14 analyzes the halftone image acquired this time and detects ink ejection failure (step S12).

  The control unit 14 determines whether or not an ink ejection failure has been detected (step S13). If it is determined that a discharge failure has not been detected (“NO” in step S13), the processing by the control unit 14 ends. If it is determined that a discharge failure has been detected (“YES” in step S13), the control unit 14 issues a command to output a missing position specifying chart (step S14). Then, the control unit 14 ends the correction setting process.

  On the other hand, if it is determined in the determination process in step S11 that the halftone image is not defective (“NO” in step S11), the control unit 14 performs ink ejection in the halftone image. It is determined whether or not such a defect is detected (step S21). If it is determined that the defect detection related to the ink ejection is not performed in the halftone image (“NO” in step S21), it is in another abnormal state, and the processing of the control unit 14 is abnormal. Move to the corresponding process.

  If it is determined that a defect relating to ink ejection has been detected in the halftone image, that is, it has been determined in the previous interpolation setting process that an ink ejection defect has been detected and interpolation settings have not yet been made (step When “YES” in S21), 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 Step S14 (Step S22). This missing position specifying chart (defective nozzle specifying image) is a well-known test image in which ink is ejected in a ladder shape or a lattice shape for each nozzle, and is used for specifying a dot missing position as in the conventional case. The missing position specifying chart is set and stored in advance in the test image data 143a.

  The control unit 14 analyzes the captured image data of the read missing position specifying chart, and specifies the dot missing position related to the ink ejection failure (step S23). In addition, the control unit 14 identifies a defective nozzle causing an ink ejection defect from the dot missing position. The control unit 14 performs setting for interpolating the ink adhesion amount at the specified dot missing position (step S24). The control unit 14 performs this interpolation by changing the ink discharge amount of the nozzle adjacent to the defective nozzle. Alternatively, if the abnormality in the ink adhesion amount cannot be resolved only by changing the ink ejection amount, the control unit 14 stops the image forming operation and prompts the operation display unit 15 to prompt the user to perform the cleaning operation or the replacement of the inkjet head. Can also be performed. Then, the control unit 14 ends the correction setting process.

  When a defective ink discharge from the nozzle is detected, the control unit 14 determines, in the determination process in step S13, the region including the nozzle in which the defective ink discharge is detected and the ink color for the detected recording medium P. In step S14, it is determined whether or not normal image formation has been performed. If image formation has not been performed, it may be determined that there is no problem and the process does not proceed to step S14.

  FIG. 8 is a diagram illustrating another example of a formed image including a test image according to the ejection failure detection operation of the present embodiment.

  The test image of this missing change chart is formed on another test image (inspection image), here, for example, on the same recording medium P as the test chart related to the gradation correction processing. In this test image, the same test charts C31 to C36 are formed in parallel in the width direction in six columns, and the missing change charts C21 to C24 are formed in the blank area above the width direction.

  In this embodiment, the imaging data of each block R31 to R36 corresponding to the range in the width direction of the test charts C31 to C36 in the missing change chart is analyzed, and an ink ejection defect is generated in each of the blocks R31 to R36. It is determined whether or not a defective nozzle is included. Then, among the blocks R31 to R36, the test charts C31 to C36 corresponding to any of the blocks in which the defective nozzles are not included in any of the missing change charts C21 to C24 related to the four color inks and a normal image is formed. By selecting and using, gradation correction processing is performed.

  FIG. 9 is a flowchart showing a control procedure of the gradation correction process executed by the control unit 14.

  In this gradation correction process, the processes in step S14 and steps S22 to S24 related to the missing position specifying chart are the same as the processes in the correction setting process, and detailed description thereof will be omitted.

  When the gradation correction process is started, first, the control unit 14 determines whether there is a block in which no defective image is detected among the blocks R31 to R36 in the halftone image related to the missing change chart, that is, In at least one of the blocks R31 to R36 in the gradation correction process up to the previous time, it is determined whether or not an ink ejection failure has been detected or whether the detected ink ejection failure has already been set for interpolation (step S31). When it is determined that there is a block in which no defective image is detected among the blocks R31 to R36 (“YES” in step S31), the control unit 14 adds the blocks R31 to R36 to the halftone image acquired this time. Is set (step S32). Next, the control unit 14 detects an image defect related to an ink ejection defect for each of the set blocks R31 to R36 (step S33).

  The control unit 14 determines whether or not image defects are detected in all the blocks R31 to R36 (step S34). If it is determined that an image defect has been detected in all the blocks R31 to R36 (“YES” in step S34), the process of the control unit 14 proceeds to step S14.

  If it is determined that no image defect is detected in all the blocks R31 to R36 (“NO” in step S34), the control unit 14 performs a test corresponding to the block in which no image defect is detected. One of the charts, that is, the gradation correction chart, is selected by a predetermined method, and gradation correction is performed using the selected test chart (step S36). The test chart selection method can be determined as appropriate. For example, the control unit 14 can select a test chart corresponding to the leftmost block (the block R31 side) where no image defect related to ink ejection is detected. When the gradation correction ends, the control unit 14 ends the gradation correction process.

If it is determined in the determination process in step S31 that there is no block in which no defective image is detected among the blocks R31 to R36 (“NO” in step S31), the control unit 14 determines that all the blocks R31 to R31 are not detected. In R36, it is determined whether or not ink ejection failure is detected (step S41).
If it is determined that ink ejection failure is not detected in all the blocks R31 to R36 (“NO” in step S41), this is a state relating to other abnormality, and the control unit 14 Perform processing corresponding to the abnormality.

  If it is determined that the ejection failure is detected in all the blocks R31 to R36 (“YES” in step S41), the process of the control unit 14 proceeds to step S22. In this case, the control unit 14 can perform control so that the gradation correction process is started again after the gradation correction process is completed once by performing the nozzle missing interpolation setting in the processes of steps S22 to S24. .

  As described above, the ink jet recording apparatus 100 according to the present embodiment includes the image reading unit 13 and the control unit 14. The control unit 14 ejects ink from a plurality of nozzles, outputs a halftone image of a predetermined density as a missing change chart, and ejects from the nozzles based on the shade of the missing change chart read by the image reading unit 13. Determine if there is a defect. Therefore, it is possible to easily and promptly check whether there is a discharge failure from the nozzle without outputting the defective nozzle identification chart every time. Thereby, it is possible to save the ink discharge amount for inspection and the area of the recording medium P necessary for forming a test image. Normally, only the presence / absence of ejection failure from the nozzles is detected, so that complicated processing is not required, and therefore the discrimination processing can be performed quickly and easily without increasing the load on the CPU 142.

  Further, since the control unit 14 forms the missing change chart outside the normal image forming area on the recording medium P, that is, in the blank area, it is not necessary to consume the recording medium P unnecessarily for the missing change chart. . Further, the user can easily know the presence or absence of ink ejection defects in association with all the recording media P.

  In addition, as a normal image, a plurality of other test charts for inspection use different from the missing change chart are formed for each of a plurality of blocks divided in the width direction orthogonal to the transport direction by the transport unit 11, and the control unit 14. Thus, an inspection can be performed using a test chart formed in any of the blocks determined as having no nozzle ejection failure. Therefore, it is possible to easily perform a reliable inspection that is not affected by the ink ejection failure without wasting the recording medium P.

  Further, since the normal image and the missing change chart by the ink used for forming the normal image are output on the same surface of the recording medium P, the defective nozzle is generated without affecting the normal image. Sometimes, it is possible to quickly know the recording medium P in which a problem has occurred, and to easily discard only the recording medium P or to perform image formation again after setting interpolation.

  Further, by setting the dot occupancy ratio related to the image formation of the nozzle missing chart to 20% or more and 60% or less, the density is changed with good contrast according to the change in the ink discharge amount due to the nozzle missing, and detection is performed with higher accuracy. I can do it.

  In addition, the halftone image related to the nozzle missing chart is 50% or more and less than 100% of the unit length, thereby efficiently detecting the presence or absence of a defective nozzle while suppressing the paper width used in a range where the contrast is not lowered. I can do it.

  Further, when it is determined by the analysis of the nozzle missing chart that there is an ink ejection defect, a missing position specifying chart is output separately, and the defective nozzle is specified based on the image read by the image reading unit 13. That is, since the missing position specifying chart is output only when there is a defective nozzle that is actually specified by the missing position specifying chart, normally, only the presence or absence of an ink ejection defect is confirmed without consuming the recording medium P wastefully. I can do it.

  In addition, a defective nozzle storage unit 141a for storing the specified defective nozzle is provided, and the newly detected defective nozzle is compared with the defective nozzle detected and stored from the previous defective nozzle specifying image. Identify the resulting defective nozzle. Therefore, for the nozzles that can be handled by the interpolation process, after the interpolation setting is performed once, it is not necessary to deal with it, and at the same time, the interpolation setting related to the newly generated defective nozzle is changed to the already detected defective nozzle or interpolation. This can be done easily while considering the influence of the setting.

  In addition, the influence of the defective nozzle is interpolated by adjusting at least one of the ink discharge amount and the discharge frequency of the nozzles in the predetermined proximity range where the ink landing ranges of the specified defective nozzle overlap. However, since the missing change chart is output, it is possible to inspect whether or not there is an influence of the defective nozzle in accordance with the actual ink ejection control.

  Also, when a new ink discharge failure is detected from the missing change chart, it is determined whether or not at least one of the nozzles within the range where the discharge failure is detected has been used for normal image formation. If it is determined that it is not used, the next normal image is formed without forming the missing position specifying chart. Therefore, even when a new ink ejection failure is detected, if the ejection failure is in a range that does not affect the quality of the detected image, normal image formation is interrupted. Therefore, the processing relating to image formation can be promptly advanced without giving an unnecessary waiting time to the user.

  In addition, since the missing change chart is output using only the ink used in the normal image formed on the recording medium P, the waste ink generated by performing the inspection not used for image formation every time is used. Consumption and waste of inspection time can be reduced.

  In addition, the nozzle holes respectively formed on the bottom surfaces of the plurality of head modules 120 are arranged so that the nozzles at both ends of the adjacent head modules 120 overlap in a staggered arrangement, and an equal amount of ink is ejected from all the nozzles. In this configuration, the ink density at that position in the width direction is increased. Accordingly, even in the case of image formation of a missing change chart, the ink discharge amount from each nozzle is controlled in advance so that the ink density at the overlapping position is equal to the ink density at the portion where the other nozzle positions do not overlap. deep. Accordingly, it is possible to easily detect an ink ejection failure while following the ink ejection related to the actual image formation, and it is possible to mount and arrange the plurality of head modules 120 on the inkjet head 12 without difficulty.

  In addition, since a test image in which shading characteristics related to a plurality of nozzles are corrected is output and ink discharge failure is detected, ink discharge failure from the nozzles can be easily performed without considering variations in the ink discharge amount of each nozzle. Detection can be performed.

  When detecting an ink ejection failure of a plurality of nozzles in the inkjet recording apparatus 100, as described above, a halftone image is formed, and the presence or absence of nozzle ejection failure is determined based on the density of the captured halftone image. Therefore, it is possible to easily know the presence or absence of defective nozzle ejection for each recording medium P on which an image has been formed without using a defective nozzle specifying image that is a precise and space-consuming inspection image.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above embodiment, the missing change chart is formed in the leading blank area of the recording medium P. However, the present invention is not limited to this, and it may be formed in the trailing blank area.
Further, when image formation is performed on both surfaces of the recording medium P, the inspection may be performed collectively by forming them at one place, for example, at the end of the back surface. Also, in the case where the direction of image formation on both sides is reversed and a missing change chart is formed on both sides, the leading edge of each recording medium is formed so that missing change charts are formed at substantially the same position on the front and back sides. Alternatively, the missing change chart may be output to the margin area and the trailing margin area.

  In the above embodiment, the line head inkjet head 12 has been described as an example. However, the present invention can also be applied to an inkjet recording apparatus having a serial head inkjet head.

  In the above embodiment, CMYK four color inks are provided, and the missing change chart is formed for each of these four color inks. However, the present invention is not limited to this. The number of ink colors may be different. Further, it is not always necessary to form a missing change chart for four color inks. For example, only missing ink charts for colors of ink used in a normal image formed on a recording medium on which the missing change chart is formed. It is good also as forming.

  In addition, when an image formed with CMYK inks is picked up with RGB wavelengths by the image sensor 131, the spectral characteristics of Y and C are different. Therefore, a common non-change chart is formed and individually at each wavelength. It is good also as imaging.

  In the above-described embodiment, the case where a missing change chart is formed on the recording medium P on which a normal image is formed or another test chart is formed has been described. In other cases, for example, a dedicated test is performed. Even when a missing change chart is formed on a sheet, if you want to use a test sheet that can be reused by changing the size of the test sheet or erasing the missing change chart, It is possible to easily and reliably detect nozzle ejection defects while reducing the required amount.

In the above embodiment, the missing position specifying chart is output when an image defect related to the ejection failure nozzle is detected or when the ink is used in a reading area where the image defect is detected after that. In other cases, for example, the missing position specifying chart is output even before the print job is interrupted and the standby state is entered without using the ink in the reading area where the image defect is detected. Is possible. On the other hand, when output together with other test charts, not only when image defects are detected in all reading areas, but also when image defects are detected in some reading areas, After the correction process related to the test chart is completed, a missing position specifying chart may be output to perform settings related to nozzle missing interpolation.
In addition, specific details such as the configuration, structure, control procedure, and numerical values shown in the above embodiments 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 device C21-C24 Missing change chart C31-C36 Test chart P Recording medium R31-R36 Block

Claims (14)

An ink jet recording apparatus that forms an image on a recording medium by ejecting ink from a plurality of nozzles,
An image formation controller that discharges ink from the plurality of nozzles and outputs a single halftone image having a predetermined density as a test image;
A reading unit for reading the test image;
An analysis unit that determines only the presence or absence of ejection failure from the nozzle based on the density of the read test image,
The dot occupancy of the dots constituting the test image is a value of 20% or more and 60% or less,
The analysis unit is configured to determine whether or not there is a nozzle causing ink ejection failure for each reading region corresponding to a plurality of nozzles that can be determined by the reading unit, from the halftone image. Inkjet recording device.   The inkjet recording apparatus according to claim 1, wherein the reading unit reads the test image at a resolution lower than a resolution corresponding to a nozzle arrangement of the plurality of nozzles.   The ink jet recording apparatus according to claim 1, wherein the image formation control unit forms the test image outside a normal image formation region on the recording medium. A transport unit that transports the recording medium in a predetermined transport direction;
The normal image is another inspection image related to an inspection application different from the test image,
The inspection image is formed in the same number as the plurality of blocks for each of the plurality of blocks divided in the direction orthogonal to the conveyance direction,
The inkjet recording apparatus according to claim 3, wherein the analysis unit determines whether or not there is a discharge failure from the nozzle for each of the blocks based on the test image.   5. The image forming control unit according to claim 3, wherein the normal image and the test image using the ink used for forming the normal image are output on the same surface of the recording medium. Inkjet recording device. A transport unit that transports the recording medium in a predetermined transport direction;
6. The inkjet recording according to claim 1, wherein a length of the test image in the transport direction is 50% or more and less than 100% of a unit length of the halftone image. apparatus. When the analysis unit determines that the test image has an ink ejection failure, the image formation control unit outputs a defective nozzle identification image for identifying a defective nozzle related to the ink ejection failure,
The ink jet recording apparatus according to claim 1, wherein the analysis unit analyzes the defective nozzle specifying image read by the reading unit and specifies the defective nozzle. A defective nozzle storage unit that stores the defective nozzle specified by the analysis unit;
The said analysis part compares the said defective nozzle detected and memorize | stored from the said defective nozzle specific image last time, and the defective nozzle detected this time, and identifies a new defective nozzle. The ink jet recording apparatus described.   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 9. The ink jet recording apparatus according to claim 7, wherein the test image is output while interpolating the influence.   In the case where a new ink discharge failure is detected from the test image by the analysis unit, the image formation control unit is configured so that any of the nozzles in the range where the discharge failure is detected forms a normal image. It is determined whether or not it has been used, and if it is determined that it has not been used, the next normal image is formed without forming the defective nozzle specific image. The ink jet recording apparatus according to any one of 9.   The said image formation control part outputs the said test image only using the ink used with the normal image formed on the said recording medium, The any one of Claims 1-9 characterized by the above-mentioned. Inkjet recording apparatus. A transport unit that transports the recording medium in a predetermined transport direction;
The plurality of nozzles are arranged partially overlapping with respect to the length of the recording medium in the direction orthogonal to the transport direction,
The image formation control unit forms the test image by adjusting the ink discharge amount from the plurality of nozzles so that the ink discharge amount is substantially equal at each position in a direction orthogonal to the conveyance direction of the recording medium. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is used.   The inkjet recording apparatus according to claim 1, wherein the image formation control unit outputs the test image in which shading characteristics of the plurality of nozzles are corrected. A method for detecting defective ink ejection of the plurality of nozzles in an ink jet recording apparatus that forms an image on a recording medium by ejecting ink from each of the plurality of nozzles,
An image forming control step of discharging ink from the plurality of nozzles and outputting a single halftone image of a predetermined density as a test image;
A reading step of reading the test image by a reading unit ;
An analysis step for determining only the presence or absence of ejection failure from the nozzle based on the density of the read test image;
Including
The dot occupancy of the dots constituting the test image is a value of 20% or more and 60% or less,
The analyzing step determines from the halftone image whether or not there is a nozzle causing an ejection failure for each reading region corresponding to a plurality of nozzles that can be discriminated by the reading unit. Defect detection method.