JP2010023459A - Nozzle defect examination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a nozzle is determined to be defective even though it is normal by blurring manner of ink in the case of executing the inspection by recording a test pattern consisting of a minute dot group onto non-coat paper in the nozzle defect inspection in an inkjet printer. <P>SOLUTION: Abnormal nozzles are found out from void lines generated in a solid recording area 31a in the test pattern, ink nondischarging or ink flying bending is determined from the presence or absence of dots by the dot group area 31b when there are the abnormal nozzles. In the nozzle defect inspection method, the abnormal nozzles are detected by preventing the erroneous determination by the blurring of ink even though the recording medium for recording the test pattern is the non-coat paper by the above defect determination. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nozzle defect inspection method for detecting a nozzle defect in a recording head mounted on an image recording apparatus and performing image recording by discharging ink.

  In general, an image recording apparatus known as an ink jet printer is equipped with a recording head in which a large number of nozzles for discharging minute ink droplets are arranged. Since these nozzles eject ink from a small-diameter ejection port, the nozzles are completely clogged by foreign matter such as lump of ink or paper dust adhering to the nozzle surface, or part of the nozzles are blocked. Discharged flight flight bending occurs. For this reason, when a nozzle failure is detected, cleaning by a maintenance process is performed. This nozzle failure is often found by white stripes or the like from an image actually recorded on a recording medium.

  In order to find a nozzle defect, for example, Patent Document 1 discloses a technique using a test pattern. In Patent Document 1, an image composed of a dot pattern (test pattern) is recorded on a recording medium, and the image is read by a scanner to determine whether or not the dot interval is a normal dot interval. In this determination, if the interval between adjacent dots is deviated from the regular dot interval, it is determined that a flight curve has occurred. On the other hand, if the read dot diameter is smaller than the regular dot diameter or there is no dot itself, it is determined that the nozzle is clogged. It is disclosed that a maintenance process corresponding to the defect form is performed for these nozzle defects.

In Patent Document 2, a dot pattern (test pattern) is recorded on a sheet, captured as an electronic image, subjected to image processing, and the interval and area between adjacent dots are measured, thereby discharging from each nozzle. A technique for determining a defect is disclosed. Further, Patent Document 3 discloses a method of reading a dot density with a light receiving element and identifying a nozzle (recording pixel) corresponding to a dot whose density does not reach a predetermined value as an abnormal nozzle.
JP 2006-281116 A JP 2005-014216 A JP 2002-079963 A

  As a recording medium for recording a test pattern as described in Patent Documents 1 to 3, a so-called coated paper having an ink jet recording layer such as glossy paper is used, and a sufficient effect can be obtained by finding a slight difference. Can be demonstrated.

  However, the user uses uncoated paper such as plain paper or recycled paper as a recording medium used for normal image recording from the viewpoint of cost and usability. Uncoated paper tends to spread the landed ink, and the degree of bleeding also varies.

  When a test pattern consisting of fine dot groups separated from each other at a predetermined interval is recorded on uncoated paper, the size of the dot diameter varies even though the nozzles of the recording head are normal, Depending on how the ink melts, there may be a positional deviation of the formed dots, a deformation of the shape, or a density difference of the dots.

  If the determination is made using such a test pattern, there is a possibility that an erroneous determination is made that there is an ink flight curve or ink non-ejection, although it is normal. As a result, the maintenance and adjustment of the recording head are performed wastefully.

In other words, in the technologies disclosed in Patent Documents 1 to 3, when a separate coated paper is not prepared, whether or not there is a problem with the paper itself or a problem with the nozzle in the quality determination is correct. It is difficult to judge. Accordingly, it is impossible to effectively detect the flying curve of the ink and the non-ejection of the ink.
Accordingly, an object of the present invention is to provide a nozzle defect inspection method using a test pattern that can correctly determine the ejection state of the nozzles of a recording head regardless of the type of the recording medium.

  In order to achieve the above object, according to an embodiment of the present invention, all the nozzles of a recording head that ejects ink are used, and a solid recording area for ejecting and recording ink from all the nozzles at the same time, and an adjacent nozzle are predetermined. A dot group area that is sequentially driven at intervals of time to eject and record ink, a recording step for recording a test pattern on a recording medium, and the test pattern recorded by the recording step is optically recorded The density of each nozzle dot line constituting the solid recording area is calculated over all the dot lines based on the image reading of the solid recording area read in the reading step and the solid recording area read in the reading step, Compare the calculated density for each dot line with a predetermined reference density, and eject ink from all nozzles of the ink ejection head. Based on the first inspection step for determining the presence or absence of an abnormal nozzle and the image information of the dot group area, the planned landing area of each dot corresponding to each nozzle of the recording head constituting the dot group area is set. Then, the density for each planned landing area is calculated over the total planned landing area, and the calculated density for each planned landing area is compared with a predetermined reference density, so that the non-ejection nozzles in the recording head Or the 2nd test | inspection step which judges the presence or absence of a flight curve nozzle is provided.

  According to the present invention, it is possible to provide a nozzle defect inspection method using a test pattern that can correctly determine the ejection state of the nozzles of the recording head regardless of the type of the recording medium.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration example of a nozzle defect inspection apparatus and an image recording apparatus according to the present embodiment. In each embodiment described below, a conveyance direction of a recording medium is defined as a sub-scanning direction (X direction), and a direction orthogonal to the conveyance direction is defined as a main scanning direction (Y direction). The vertical direction (or vertical direction) orthogonal to the X and Y directions is taken as the Z direction. Here, an example is a line head type ink jet printer in which the recording heads of each color are arranged in the sub-scanning direction and each color is longer than the medium width in the main scanning direction.

  FIG. 1 shows an inkjet printer (hereinafter referred to as a printer) 1 that is an image forming apparatus and an inspection device 2 that is mounted on the printer 1 and detects nozzle defects of a recording head 3 that ejects ink. The present embodiment is a configuration example in which the printer 1 and the inspection apparatus 2 are separate.

  The printer 1 stores a plurality of recording media 4 and sequentially supplies the recording media 4 one by one, a transport mechanism 6 that transports the recording media 4, and ejects ink as fine droplets onto the recording media 4. A recording head (droplet discharge head) 3 that forms an image, a recording medium cassette 7 that houses a plurality of recording media 4, and a printer control unit 8 that controls the entire apparatus including image recording.

  The inspection apparatus 2 images the transport mechanism 12 that transports the test recording medium 4a on which the test pattern is recorded, the recording medium detection sensor 13 provided on the carry-in side of the transport mechanism 12, and the test pattern of the test recording medium 4a. The imaging unit 14 includes an image processing and determination unit 15 that performs processing of a test pattern image signal captured by the imaging unit 14 and determines whether the nozzle is good or defective, and a display unit 16 that displays the image-processed test pattern image. Is done. Here, the image processing and determination unit 15 and the display unit 16 can be replaced by a personal computer, and are separate from the inspection apparatus body 10.

    The recording head 3 has a nozzle surface facing the recording medium 4. The nozzle surface is provided with a nozzle row in which 300 nozzles that eject ink are opened in a row. In the present embodiment, there are four recording heads 3C (cyan), 3K (black), 3M (magenta), 3Y (yellow) that eject at least four colors of ink from the upstream side in the transport direction. A single color image or a color image is recorded on the recording medium 4. In this embodiment, the line type recording head is described as an example. However, the present invention is not limited to this, and is a serial type recording head that repeatedly moves on the recording medium 1 in the main scanning direction. Can be applied similarly.

  In the present embodiment, two recording medium supply systems are provided, and both transfer the recording medium 4 to the transport mechanism 12. The recording medium supply unit 5 stores a plurality of recording media 4 in a tray (or cassette) attached to the outside of the apparatus, sequentially picks up one sheet at a time by the pickup roller 11, and supplies it to the transport mechanism 6. On the other hand, a recording medium cassette 7 provided inside the apparatus accommodates a plurality of recording media 4, is sequentially taken out one by one, and is supplied to the transport mechanism 6.

  The transport mechanism 6 includes, for example, at least two or more pulleys 17 and a transport belt 18 that is wound while tension is applied to these pulleys 17. A drive source such as a motor (not shown) is connected to at least one of the pulleys 17, and the conveyor belt 18 is rotated by rotating the pulley 17. The conveying belt 18 is provided with a large number of small holes (not shown) and is configured to face all the nozzle surfaces of the recording head 3 in parallel (or at the same interval). A fan 19 is provided inside the transport belt 18, and the recording medium 4 is transported while being sucked onto the transport belt 18 by the negative pressure of the fan 19, and passes through the front of the nozzle surface of the recording head 3. . The basic configuration of the transport mechanism 12 of the inspection apparatus 2 is the same as the transport mechanism 6 of the printer 1. In the present embodiment, the inspection apparatus 2 is configured as a separate body from the printer 1.

  The inspection device 2 includes an image processing and determination unit 15, a display unit 16, an inspection device body 10, a display unit 16, and an input unit 20. A recording medium detection sensor 13 and an imaging unit 14 are provided in the inspection apparatus main body 10.

In FIG. 2, the block configuration of the control system of the inspection apparatus 2 is shown and described.
The control system mainly includes an image processing and determination unit 15, a display unit 16, a recording medium detection sensor 13 and an imaging unit 14 in the inspection apparatus main body 10, a printer control unit 8 in the printer 1, and a display unit 16. And the input unit 20.

  The image processing and determination unit 15 includes an inspection device control unit 21, a test pattern storage unit 22, an image data storage unit 23, a density data conversion unit 24, a density data conversion unit 25, a filter unit 26, and a counting unit 27. The comparison operation unit 28 and the comparison operation unit 29 are included.

  The image processing and determination unit 15 processes the test pattern image signal imaged by the imaging unit 14 into image data, calculates the density of the target portion of the test pattern, or compares it with a reference provided in advance. The nozzle outside the reference is specified as an abnormal nozzle (nozzle with poor ink ejection).

Hereinafter, the configuration and operation of each component will be described in detail.
The inspection device control unit 21 includes a processing arithmetic circuit such as a CPU. The user operates the input unit 20 to instruct the inspection device control unit 21 to execute a nozzle defect inspection. The input unit 20 is configured by a keyboard, a touch panel, or the like, and inputs an instruction by a user operation.

Based on this instruction, the inspection apparatus control unit 21 selects one (or one set) from a plurality of test patterns stored in advance in the test pattern storage unit 22 and sends it to the printer control unit 8. As described above, the printer control unit 8 supplies and conveys the recording medium 4 and records a test pattern on the recording medium 4. The recording medium 4a on which the test pattern is recorded is carried into the inspection apparatus 2. Note that the recording medium 4a on which the test pattern is recorded and the recording medium 4 are the same medium (uncoated paper), and the reference numeral 4a is simply used for the purpose of description.

  When the recording medium detection sensor 13 detects the leading edge of the recording medium 4 a, it sends a detection signal to the inspection device control unit 21. The recording medium detection sensor 13 is a non-contact sensor such as an infrared sensor that detects light shielding by the recording medium 4. When the recording medium detection sensor 13 detects the recording medium 4, it sends a detection signal to the inspection apparatus control unit 21. In addition, the recording medium detection sensor 13 may be a mechanical switch having a contact piece with the recording medium 4 or the like.

  The imaging unit 14 includes a line sensor made up of an individual imaging element such as a CCD or CMOS, and a fixed focus imaging optical system, for example. The imaging unit 14 starts imaging (image reading) of the test pattern recorded on the recording medium 4a in response to a reading start instruction from the inspection device control unit 21, and reads the image until the imaging time set when the test pattern is selected. .

  The display unit 16 is a display device composed of a liquid crystal display or the like, and displays a captured test pattern and a determination result of good or bad.

  The test pattern storage unit 22 stores a plurality of test patterns in advance in association with the reading time. The selected test pattern is transmitted to the printer control unit 8 according to a command from the inspection apparatus control unit 21. The reading time is a time setting in consideration of the reading speed (recording medium conveyance speed) so that the area from the front end to the end of the test pattern can be completely imaged. The test pattern and reading time are set every time the nozzle inspection is performed.

The image data storage unit 23 temporarily stores a test pattern image (image data) captured by the imaging unit 14.
The density data conversion unit 24 converts the test pattern image read from the image data storage unit 23 as density data, and divides the density data of the solid recording area 31a of the test pattern image into density data for each nozzle line. The density data of each nozzle line is replaced with density characteristics (density data) of each nozzle forming the nozzle line.

The density data conversion unit 25 converts the test pattern image read from the image data storage unit 23 as density data, and divides the dot group area 31b of the test pattern image into density data for each nozzle area. The nozzle area is an area including dots and their surroundings set for each dot. Then, the highest (dark) value is calculated from the density data for each nozzle area including the dots. The filter unit 26 performs a filtering process on the density data replaced by the density data conversion unit 24 to facilitate detection of abnormal nozzles.
The comparison calculation unit 28 compares the density data subjected to the filter processing of each nozzle with a predetermined density threshold value that is arbitrarily set. Here, if the density data is a low (thin) density that does not reach the threshold value, the nozzle that provided the density data is determined to be an abnormal nozzle. On the other hand, if the density data is higher (darker) than the threshold, the nozzle is determined to be a normal nozzle. These determinations are made on the density data of all nozzles. In this determination, a comparison is made with respect to the threshold value. If the density is higher than the threshold value, the density difference between density data determined to be good is not a problem.

  When the comparison calculation unit 24 determines that there is an abnormal nozzle, the counting unit 27 determines the nozzle portion determined to be an abnormal nozzle from the density data for each nozzle area of the test pattern sent from the density data conversion unit 25. Check for dot data. If the highest density value of each nozzle area is larger than the set value, it is determined that “dot data is present”, and if it is smaller than the set value, “no dot data” is determined.

  Based on the presence or absence of the dot data confirmed by the counting unit 27, the comparison calculation unit 29 displays “no ink ejection” when there is no dot data for a nozzle determined to be an abnormal nozzle, and “ Ink flight bend ".

A recording operation in the image recording apparatus configured as described above will be described.
The recording medium 4 is taken out from the recording medium supply unit 5 and transferred to the transport mechanism 6. At the time of delivery, the orientation of the recording medium 4 is corrected to prevent it from being conveyed obliquely. In the transport mechanism 6, the recording medium 4 is transported while being sucked by the negative pressure of the fan 17, and passes through the front of the nozzle surface of the recording head 3. During this passage, ink of each color is ejected from each nozzle based on the image data transmitted from the printer control unit 8, and an image is recorded on the recording medium 4. Note that when a nozzle inspection is performed, a test pattern described later is recorded as an image.

Next, the inspection device 2 is configured as a separate body from the printer 1 and is connected so as to receive the recording medium 4a on which the test pattern is recorded from the discharge port of the printer at the time of inspection.

FIG. 3 shows the configuration of the test pattern used in this embodiment. FIG. 4 conceptually shows the relationship between the test pattern and the conveyance direction of the recording medium.
The test pattern 31 includes two areas, and forms a solid recording area 31a in which ink is ejected from all the nozzles of the recording head 3 on the leading end side (conveying direction) of the recording medium, and is subsequently separated from each other by a dot group area. 31b is formed.

  In the solid recording area 31a, recording is performed from all the nozzles of the recording head 3 with a width corresponding to the length of the nozzle row in the sub-scanning direction. The dot group area 31b is recorded so that the dots do not overlap, and a single row of dots is recorded by a plurality of nozzles spaced at regular intervals, and subsequently moved to the next nozzle one by one. Record a dot row in the next subsequent stage. In FIG. 3, all nozzles are divided into groups of four nozzles, and ink droplets are ejected from the first, fifth, ninth, twelfth,... To do. Next, ink is ejected from the 2, 6, 10, 13,. As described above, dividing a large number of nozzles into a plurality of groups and ejecting ink at different times is referred to as time-division ink ejection. This dot row recording is performed for all nozzles. As shown in FIG. 4, the recording medium 4 a recorded with such a test pattern first images (reads) the solid recording area 31 a by the imaging unit 14 and then images (reads) the dot group area 31 b. . The captured image signal of the test pattern is stored in the image data storage unit 23.

Next, the nozzle defect inspection by the nozzle inspection apparatus will be described with reference to the flowchart shown in FIG.
First, the inspection initial setting is performed before the nozzle defect inspection is performed. The inspection initial setting screen is displayed on the display unit 16 and the input unit 20 is operated. When it is determined that “abnormal nozzle is present” as a result of the nozzle defect inspection, the maintenance process, here the nozzle recovery by the cleaning operation is performed. It is selected whether or not to perform treatment (step S1). In this selection, if it is selected to perform the cleaning process (YES), the upper limit of the number of cleanings is set according to the type of nozzle failure (step S2). That is, the upper limit value of the number of times of cleaning is set when the nozzle failure is “ink non-ejection” and “ink flying curve”. This upper limit setting is a threshold value (number of times) for determining that the nozzle failure cannot be recovered only by the nozzle recovery treatment even if the cleaning operation is executed exceeding the set number of times. When this upper limit is reached, the cleaning operation is terminated.

  After confirming the inspection initial setting, the user issues a nozzle inspection instruction to the printer control unit 8 through the image processing and determination unit 15. In response to this inspection instruction, the test pattern data is read from the test pattern storage unit 22 and transmitted to the printer control unit 8 (step S3).

  The printer control unit 8 takes out the recording medium 4 from the recording medium supply unit 5 and conveys it by the conveyance mechanism 6, and records the above-described test pattern on the recording medium 4 (step S4).

  The test recording medium 4a on which the test pattern is recorded is transferred from the transport mechanism 6 to the transport mechanism 12 of the inspection apparatus 2 (step S5). At the time of delivery, it is desirable that the speed recorded by the recording head 3 of the printer, that is, the transport speed of the test recording medium 4a and the transport speed of the transport mechanism 12 of the inspection apparatus 2 are the same speed. The test recording medium 4a is transported by the transport mechanism 12, and the recording medium detection sensor 13 detects the leading end of the recording medium 4a and sends a detection signal (reading start signal) to the inspection apparatus control unit 21 (step S6). . The inspection device control unit 21 receives the detection signal, instructs the imaging unit 14 to start reading the test pattern (step S7), and also instructs the test pattern reading time (reading end time).

  The imaging unit 14 starts imaging (image reading) of the test pattern recorded on the recording medium 4a in response to a reading start instruction from the inspection apparatus control unit 21. First, the solid recording area 31a is imaged, and then the dot group area 31b is imaged (step S8). The captured test pattern image signal is input to the image data storage unit 23.

  The image processing and determination unit 15 performs a nozzle defect inspection by a subroutine described later on the captured image data (test pattern image) (step S9).

    Next, it is determined whether or not there is a nozzle defect in the inspection result of the nozzle defect inspection (step S10). If there is no nozzle failure in this determination (NO), the result is displayed on the display unit 16 (step S11), and the routine is terminated. Here, the fact that the nozzle is normal is displayed. On the other hand, if there is a nozzle failure (YES), it is determined whether or not the initial setting is set to perform the maintenance process (step S12). If it is determined that the execution of the cleaning process is not set (NO), the process proceeds to step S11 and the inspection result is displayed on the display unit 16. Here, it is displayed that there is a nozzle defect.

  Next, in step S12, when it is set to perform the cleaning process (YES), it is determined whether the inspection result of the nozzle failure is “ink non-ejection” or “ink flying curve”. (Step S13). If “no ink ejection” is determined in this determination, it is determined whether or not the number of cleanings performed so far exceeds the upper limit set number set in step S2 (step S14). Here, if the upper limit number of ink ejection failure is not reached (NO), a cleaning process is performed (step S15), the count is incremented by 1 (step S16), and the cleaning end is displayed (step S17). ). After the display, the process returns to step S3, the test pattern is recorded again on the recording medium, and the nozzle defect is inspected again.

  If the nozzle failure is “ink flying curve”, it is determined whether or not the number of cleanings performed so far exceeds the set number (step S18). If the set number of ink flight bends is not reached (NO), the cleaning process is performed (step S19), the number is incremented by one (step S20), and the end of cleaning is displayed. After the display, the process returns to step S3, and a nozzle defect inspection is performed again.

  If the cleaning process has reached the set number of times in both steps S14 and S18 (YES), it is determined that the nozzle defect cannot be recovered only by the nozzle recovery process by the cleaning process. In step S11, the nozzle defect is determined. Display that it was not possible to recover and exit.

Next, the first subroutine for nozzle defect inspection in step S9 in FIG. 5 will be described with reference to the flowchart shown in FIG.
First, a test pattern image is read out as image data from the image data storage unit 23 to the density data conversion unit 24 and converted into density data (step S31).

  Next, filter processing is performed on the converted density data (step S32). In this embodiment, a high-pass filter is used to eliminate the low frequency region so that an abnormal nozzle can be easily detected from the density data.

  Next, in order to examine the density characteristics for each nozzle, the density data of the solid recording area subjected to the filter process is divided for each nozzle line (dot line) (step S33). A nozzle line here refers to the dot row | line | column comprised by 1-300 each nozzle, and comprised by the line form along a subscanning direction.

Thereafter, in order to sequentially check the density of the nozzle line, the first nozzle line is designated (step S34), and the density data of the first nozzle line is compared with a predetermined threshold value a set arbitrarily. (Step S35). The threshold value a is set to a density at which it can be determined as white stripes (white spots), and can be set to a different value for each type of recording medium on which the test pattern is recorded.
In this comparison, when the density is higher (higher) than the threshold value a (YES), it is determined that the target nozzle that forms the nozzle line is normal. If it is determined to be normal, it is determined whether or not the comparison has been made for all the nozzle lines (step S36). If the inspected nozzle lines NL has not reached 300 of the total number of nozzle lines (NO), the next A nozzle line is designated (step S37), and similarly compared with the threshold value a.

  If the inspected nozzle line NL reaches 300 of the total number of nozzle lines in step S36 (YES), it is determined that the nozzle line is normal or not defective (step S38). On the other hand, if it is determined in step S35 that the density is lower (thin) than the density of the threshold value a (NO), the target nozzle corresponding to the nozzle line is determined to be abnormal, and the dot group area is divided into a plurality of nozzle areas. (Step S39). In the determination of the density of the nozzle line, if it is determined that there is at least one nozzle line having a density lower than the threshold value a, the nozzle defect immediately after the subsequent uninspected nozzle line NL is not inspected. It is determined that there is, and the process proceeds to step S39 and subsequent steps.

  Here, FIG. 7 shows the concept of the nozzle area 32 in each dot of the dot group area 31b of the test pattern.

  The nozzle area 32 is an area defined on the memory in which the image data of the test pattern is stored. For each dot, the nozzle area 32 is an area of a predetermined size including the dot and the periphery thereof, and the size thereof is an adjacent dot. It is set so as not to include. The position of the nozzle area 32 is not set with reference to the recorded dots, but is defined by assuming the landing positions of the dots that can be recorded.

  Next, the maximum density value is calculated for each nozzle area 32 (step S40). This is because the highest (dark) area, that is, the maximum density value is calculated in the area, for example, spread due to bleeding of uncoated paper, and the formed dot position (center position) may deviate from the target position. Even if the dot shape is not the target shape, it can be determined whether or not ink is ejected from the nozzle. When there is a dot, the highest density in the portion where the dot is recorded is extracted. If there is no dot data due to ink ejection failure, the highest value in the area is extracted.

  In order to sequentially check the density data of these nozzle areas 32, the first nozzle area NA is designated from the plurality of nozzle areas 32 (step S41), and the dot count number D is initialized to 0 (step S42). ).

  For the designated first nozzle area 32, the maximum density value is compared with a preset threshold value b (step S43). The preset threshold value b is a density reference value obtained when dots are recorded on the recording medium. In this comparison, if the calculated maximum density value is larger than the threshold value b (YES), it is determined that a recorded dot exists, and counts up as the number D of dots constituting the dot group area 31b (step S44). ). Then, it is determined whether or not the nozzle area NA has reached 300 as the total number of nozzle areas (step S45). If the nozzle area NA has not yet reached (nozzle area to be inspected remains) (NO), the next nozzle The area 32 is designated (step S46), the process returns to step S43, and the threshold value b is compared with the maximum density value of the next nozzle area. On the other hand, if the calculated maximum density value is smaller than the threshold value a (NO), it is determined that there is no dot in the nozzle area 32, and the process proceeds to step S45 without counting up the number of dots D.

  That is, by calculating the maximum density value in each nozzle area 32, for example, the landing position is shifted from the target position due to bleeding of uncoated paper, or the landing shape (area) is not the target shape (area). Even if a dot is recorded on the recording medium and the dot image data exists in the nozzle area 32, the dot density value should be the highest in the nozzle area. Exceeds the threshold b. As a result, it can be determined that there is a dot. On the contrary, when there is no dot image data in the nozzle area 32 due to ink non-ejection, the extracted maximum density value is very low and falls below the threshold value b, so it can be determined that there is no dot. .

  In step S45, if the inspected nozzle area number NA reaches the total number of nozzle areas (YES), it is determined whether or not the counted dot number D matches the number of nozzles used in recording the test pattern image. (Step S47). In this determination, if there is a difference between the number of driven nozzles and the count result of the number of dots D (NO), “no ink ejection” (step S48), and if there is no difference (YES), It is determined that the flight bends (step S49), the process returns, and the process returns to step S10 in FIG.

  As described above, according to the nozzle defect inspection by the first subroutine, if it is determined that there is an abnormal nozzle by determining the nozzle line NL in the solid recording area 31a of the test pattern (determination based on the threshold value), the dot group area 31b. Depending on the presence / absence of a dot, it can be determined that the presence of a dot is “ink flying curve” and the absence of a dot is “ink ejection failure”. Thereby, even if the recording medium for recording the test pattern is uncoated paper, it is possible to detect an abnormal nozzle, and it is possible to select and implement a suitable maintenance process or repair.

  Here, with reference to FIG. 8 and FIG. 9, detection of “ink non-ejection” and “ink flying curve” of the recording head for the test pattern in the present embodiment will be described. FIG. 8 shows an example in which dots are not recorded due to non-ejection of ink, and FIG. 9 shows an example in which dots are recorded with a deviation from a desired position due to ink flight bending.

  In the recording head 3, when there is an abnormal nozzle that causes non-ejection in the nozzle row, as shown in FIG. 8, white spots are generated in the solid recording area 31 a (the ink droplets have not landed). Line 41 is produced. Further, when there is a nozzle (abnormal nozzle) that causes ink flying bend in the recording head 3, as shown in FIG. 9, a white having a width narrower than the blank line 41 in the solid recording area 31a. A missing line 44 is generated.

  Such white-out lines 41 and 44 are caused by the presence of abnormal nozzles, so that ink does not adhere to the solid recording area, and a streaky white (color of the base of the recording medium) line is generated, or abnormal nozzles record. The ink density of the part in charge of is low (thin).

  Next, in the dot group area 31b, when an ink non-ejection defect occurs due to an abnormality in the nozzle, ink (ink droplets) is not ejected from the abnormal nozzle, so the dot 42 indicated by the broken line in FIG. Not formed. In addition, when a defect in the ink flight curve occurs, as shown by the dot 43 in FIG. 9, the ejection direction deviates from the target direction and the landing position is deviated, but the ink has landed. Therefore, there are dots at positions that are not originally intended.

  By using uncoated paper for recording the test pattern, ink bleeding is large, or the degree of ink bleeding varies depending on the ink landing position. As a result, even if the dot shape does not become the target shape or the position where the maximum density occurs due to bleeding occurs, as described above, if only the presence or absence of dots can be determined, ink ejection or ink flight It is possible to accurately determine whether it is bent.

  As described above, according to the present embodiment, even if ordinary paper (uncoated paper) that is normally used is used as a recording medium for recording a test pattern, ejection failure or flight at each nozzle of the recording head. Can accurately determine the bend. Accordingly, it is possible to prevent the maintenance process from being performed due to an erroneous determination.

  In addition, it is possible to shift to nozzle defect inspection without using an expensive coated paper with little ink bleeding as a recording medium for recording a test pattern. There is no need to insert or replace (or uncoated paper).

Next, FIG. 10 is a diagram showing a first modification of the test pattern used in the first embodiment described above.
The test pattern according to the first modification is an example in which the set of the solid recording area 31a and the dot group area 31b is arranged in a plurality of stages in the sub-scanning direction.

  As described above, by arranging the test patterns in a plurality of stages, for example, as in the printer 1 shown in FIG. 1, the recording heads that eject inks of different colors are arranged in a plurality of stages along the sub-scanning direction. Even in the arrangement, by shifting the recording position, it is possible to perform a nozzle defect inspection in a recording head of all ink colors with a test pattern recorded on one recording medium.

Next, FIGS. 11A and 11B are diagrams showing a second modification of the test pattern used in the first embodiment described above. Here, FIG. 11A shows an example of arrangement of test patterns, and FIG. 11B shows an example of arrangement of recording heads to which this test pattern is applied.
In the test pattern shown in FIG. 11A, a set of a solid recording area 31a-1 and a dot group area 31b-1 is arranged in two rows along the main scanning direction and alternately arranged back and forth in the sub scanning direction. Yes. Of these sets of areas, the sets adjacent to each other in the front-rear direction are arranged so that the ends overlap each other. This test pattern is suitable for a recording head as shown in FIG.

  FIG. 11B shows a configuration in which short recording heads 3C-1 to 3C-n having nozzle rows shorter than the width of the recording medium are used in place of the one line head. The plurality of short recording heads 3C-1 to 3C-n are alternately arranged along the main scanning direction and arranged in the front-rear direction when viewed from the transport direction. This is a so-called staggered arrangement. Further, both ends of the short recording head 3C adjacent in the front and rear are arranged so as to have overlapping portions of several nozzles. By having overlapping portions at both ends of the recording head 3C as described above, an image can be recorded without a gap even if the recording head is not a single long recording head.

  By using the test pattern according to the second modification, the defect inspection for each nozzle is executed with the test pattern separated for each recording head on the recording heads which are alternately arranged and have overlapping portions in the recording area. it can.

  Further, by combining the first modification and the second modification, all the ink colors in the recording head for a plurality of ink colors and each nozzle of all the recording heads for each recording head (nozzle row) are combined. On the other hand, the inspection can be performed with the test pattern recorded on one recording medium.

  Next, a test pattern for a multi-tone recording head will be described as a third modification. With reference to FIG. 12, the setting of the ink density when the solid recording area 31a of the test pattern is formed on the test recording medium will be described.

  In the above-described embodiment, the density of the solid recording area 31a is read, and if the density corresponding to each nozzle line is lower (thin) than the set threshold value a, it is determined that the nozzle is defective. In other words, when either one of the ink ejection failure or the ink flight curve occurs, it is detected as “nozzle failure”. Here, as a factor that causes the density of the nozzle line to be lower than the threshold value a, a white line is generated. That is, in order to detect a nozzle failure, a white line due to the nozzle failure must appear in the solid recording area 31a. However, depending on the density of the solid recording area 31a, ink bleeding on uncoated paper may be severe, and even if a nozzle defect occurs, white lines may not appear or may appear only slightly.

  FIG. 12 shows the relationship in the case of performing solid recording with each density and all nozzles in the multi-tone recording head. In the case of a binary recording head, the ink density is constant, and the ejected ink is blurred on uncoated paper. Even if there is a slight ink flight curve, the white lines that originally appear in the solid recording portion are blurred. This makes it difficult to detect a white line. In addition, when area gradation is performed, ink ejection from some nozzles on the way is intentionally stopped and dots are thinned out, so it is difficult to determine the ink flight curve for all nozzles.

  On the other hand, in the multi-tone recording head, while all the nozzles are driven, the density is changed by changing the ink discharge amount and changing the dot diameter. Therefore, all the dots are recorded without thinning out the dots. For this reason, not only when ink ejection failure occurs but also when slight ink flight bend occurs, the density at which the white line 51 by solid recording can be detected at any density in the musical tone. That is, in a solid recording area having a density where bleeding does not occur so much, a slight white line 51 can be detected, and a nozzle in charge of the white line 51 can be detected as an abnormal nozzle by this detection. .

  As described above, the test pattern (solid recording portion) in which the gradation value changes stepwise is recorded on the recording medium 4a. A test pattern having a gradation value having the least influence of bleeding is selected from the gradation values. The gradation value does not have to change continuously during recording, and even if the gradation line has a width that can be distinguished for each gradation value, it is recorded intermittently (like a barcode). Good. Since this test pattern is used for inspection and the nozzle failure inspection is performed by the above-described inspection sequence, it is possible to detect the nozzle failure accurately even with uncoated paper, as with coated paper.

Next, a second embodiment will be described.
With reference to the flowcharts shown in FIGS. 13A and 13B, the nozzle defect inspection in the second embodiment will be described. The nozzle defect inspection apparatus and the image recording apparatus of the present embodiment are the same as the configuration example of the first embodiment shown in FIGS. 1 and 2 and thus will not be described. The inspection method will be described here.
The present embodiment is an inspection method in which a test pattern is recorded over a plurality of or a plurality of recording media, and these are repeatedly inspected to increase the inspection accuracy of nozzle defect inspection.

  First, as an initial setting for inspection, an inspection initial setting screen is displayed and the input unit 20 is operated to set the number of test pattern recordings (or the number of recording media to be recorded) (step S51). The following steps S52 to S59 correspond to the above-described steps S1 to S8, and will be described briefly here.

  Next, when it is determined that the result of the nozzle defect inspection is “abnormal nozzle present”, it is selected whether or not to perform nozzle recovery treatment by cleaning processing (step 52). When the cleaning process is performed (YES), the upper limit of the number of executions is set according to “ink non-ejection” and “ink flight curve” (step S53). When this upper limit is reached, the cleaning process is terminated. After the setting, an instruction for nozzle inspection is issued to the printer control unit 8, and test pattern data is transmitted from the test pattern storage unit 22 to the printer control unit 8 (step S54).

  After receiving the data, the printer control unit 8 takes out the recording medium 4 and records the test pattern described above on the recording medium 4 (step S55). The recorded test recording medium 4a is transferred from the transport mechanism 6 to the transport mechanism 12 of the inspection apparatus 2 (step S56).

  The recording medium detection sensor 13 detects the leading end of the test recording medium 4a being conveyed, and sends the detection signal to the inspection apparatus control unit 21 (step S57). The inspection device control unit 21 receives the detection signal, instructs the imaging unit 14 to start reading the test pattern (step S58), and also instructs the test pattern reading time (reading end time).

The imaging unit 14 starts imaging (image reading) of the test pattern recorded on the recording medium 4a in response to a reading start instruction from the inspection apparatus control unit 21. First, the solid recording area 31a is imaged, and then the dot group area 31b is imaged and read (step S59). The captured test pattern image signal is input to the image data storage unit 23.
The image processing and determination unit 15 performs nozzle defect inspection by the subroutine described with reference to FIG. 6 described above on the captured image data (test pattern image) (step S60).

  Next, in the nozzle defect inspection, it is determined whether or not there is a nozzle defect (step S61). If it is determined that there is no nozzle defect (NO), whether or not the number of recording sheets set in step S51 has been reached. That is, it is determined whether or not the inspection of the required number of test patterns has been completed (step S62). If it is determined that the required number has been reached (YES), a result indicating no defect is displayed on the display unit 16 (step S63), and the inspection is terminated. On the other hand, if the inspection of the required number of test patterns has not been completed (NO), the process returns to step S55, and the test pattern is recorded again to perform the nozzle defect inspection. If it is determined in step S61 described above that there is a nozzle defect (NO), a signal for stopping image recording of the test pattern is transmitted from the inspection apparatus control unit 21 to the printer control unit 8 to test the test pattern. Is stopped (step S64).

  Next, in step S72, it is determined whether or not cleaning is set (step S65). If it is not set (NO), the process proceeds to step S63, and there is a nozzle defect on the display unit 16. Display. On the other hand, if the cleaning execution is set (YES), it is determined whether the result of the nozzle defect inspection performed in step S60 is ink ejection failure or flight bending (step S66).

  If it is determined in step S66 that the abnormal nozzle is not ejecting ink, the number of times the cleaning process has been performed for the ink non-ejection performed so far is confirmed, and it is determined whether or not the number set in step S53 has been reached. (Step S67). If the number of executions of the cleaning process has reached the set number of times (YES), the process proceeds to step S63, and the inspection result of the nozzle failure and the result of the cleaning process are displayed on the display unit 16 and the process is terminated. On the other hand, if the number of times the cleaning process has been performed is equal to or less than the set number (NO), the cleaning process is performed (step S68), and the number of times the cleaning process has been set for the non-ejection is counted up (step S69). The result of the cleaning process performed on the display unit 16 is displayed (step S70). The result of this cleaning process is not a result of whether or not ink ejection has been improved by the cleaning process, but a result display of whether or not the cleaning process designated in advance has been completed. In order to check again whether or not the ink ejection failure has been improved, the setting of the number of recorded test patterns is cleared (step S74), the process returns to step S54, the test pattern is read, and the image record is recorded on the recording medium. In this case, the nozzle defect inspection is continued again. Therefore, if the ink non-ejection has been improved by the above-described cleaning process, it is determined that there is no abnormal nozzle in the next nozzle inspection.

  Similarly, if it is determined in step S66 that the abnormal nozzle is bent in flight, the number of cleaning processes performed for the flying curve performed so far is confirmed, and it is determined whether or not the number of times set in step S53 has been reached. (Step S71). If the number of executions of the cleaning process has reached the set number of times (YES), the process proceeds to step S63, and the inspection result of the nozzle failure and the result of the cleaning process are displayed on the display unit 16 and the process is terminated. On the other hand, if the number of executions of the cleaning process is less than or equal to the set number (NO), the cleaning process is performed (step S72), and the number of executions of the cleaning process set in the flight bend is counted up (step S73). After proceeding to Steps S70 and S74 and displaying the result of the cleaning process, the test pattern recording number setting is cleared again to check whether or not the flight curve is improved (Step S94). Returning to step S54, the nozzle defect inspection is performed again.

  As described above, according to the present embodiment, the test pattern is recorded up to the number set in parallel while performing the nozzle defect inspection. Therefore, when it is determined that there is a nozzle defect and the recording up to the set number has not been completed, the recording of the test pattern is continued. On the other hand, if it is determined that there is no nozzle defect and the recording up to the set number of sheets has not been completed, the recording of the test pattern onto the recording medium is terminated, so that the recording of an extra test pattern is prevented. be able to.

  Further, according to the present embodiment, the image information of the solid recording area 31a and the dot group area 31b of the test pattern is read at once, but the image of the solid recording area 31a is first acquired and processed. Only when the result is an inspection result with an abnormal nozzle later, a step of acquiring an image of the dot recording area may be performed. Thereby, when there is no abnormality in the nozzle defect inspection in the solid recording area, it is possible to shorten the image reading time of the dot group portion.

  Furthermore, the number of times the cleaning process is set when inspecting nozzle defects is not limited to the number of times performed uniformly for all recording heads to be inspected. For example, in an image recording apparatus equipped with a plurality of recording heads. Alternatively, the number of cleaning processes or the presence / absence of the cleaning process may be set individually. As a result, the set number of cleaning processes is performed only on the recording head having the abnormal nozzle.

  In the present embodiment, the image recording apparatus and the inspection apparatus are separately provided so as to be received from the recording medium discharge side (downstream in the transport direction) of the transport mechanism of the image recording apparatus. However, the present invention is not limited to this. Alternatively, it may be provided on the downstream side of the transport system in the inspection apparatus (in the main body frame). An imaging camera and image processing means may be arranged inside a droplet discharge device such as an ink jet printer, and nozzle discharge defects may be automatically inspected inside the droplet discharge device.

  According to the present embodiment, nozzle ejection abnormalities (ink non-ejection / ink flying bend) are reliably detected even with low-cost uncoated paper without using expensive coated paper with low ink solubility. be able to. Further, there is no misjudgment that determines that a normal nozzle is defective, and there is no waste of performing head maintenance processing for unnecessary head recovery.

The embodiment described above includes the following present invention.
(1) a step of ejecting ink from a nozzle of a recording head that ejects ink in the form of droplets to record a test pattern on a sheet; a step of optically reading the recorded test pattern; and the read test pattern Inspecting nozzle abnormalities in the recording head based on the nozzle defect inspection method,
The test pattern includes a solid recording area and a dot group area in which dots are separated from each other. The solid recording area is read in the reading step, the dot group area is read, and the solid recording area is read in the inspection step. For all the nozzle lines constituting the nozzle line, the density for each nozzle line is calculated, the nozzle line density is compared with the predetermined density over all the nozzle lines, and the presence or absence of the nozzle is judged. Determining whether the abnormality of the nozzle is an ink ejection failure or a flight curve of the ink ejected from the nozzle by checking the presence or absence of a dot in the dot group area corresponding to the nozzle judged to be abnormal. Nozzle defect inspection method.

(2) A recording step of ejecting ink from the nozzles of the recording head to record a test pattern on the paper, a reading step of optically reading the recorded test pattern, and a nozzle of the recording head based on the read test pattern An inspection step for inspecting abnormality, and a nozzle defect inspection method comprising:
The test pattern is composed of a solid recording area and a dot group area spaced apart from each other. The solid recording area is read in the reading step, the dot group area is read, and a solid recording area is configured in the inspection step. For all nozzle lines, the density for each nozzle line is calculated, the density of the nozzle line is compared with a predetermined density over all nozzle lines, and the presence or absence of nozzle abnormality is determined. By counting the number of dots in the group area and comparing the counted number of dots with the number of nozzles driven to form the dots in the dot group area, ink was not ejected from the nozzle or ejected from the nozzle. A method for inspecting defective nozzles, comprising determining whether the ink is bent or not.

(3) By confirming the presence or absence of dots in the dot group area on the test pattern corresponding to the nozzle determined to be abnormal, it is possible to determine whether ink is ejected from the nozzle or the flight of the ink ejected from the nozzle is bent. In the nozzle defect inspection method characterized by determining,
When there is no dot in the dot group area corresponding to the abnormal nozzle determined from the inspection result, it is determined that ink is not ejected, and there is a dot in the dot group area corresponding to the nozzle determined to be the abnormal nozzle Is a nozzle defect inspection method according to (1), in which it is determined that the flying curve of ink at the nozzle.

(4) In a nozzle defect inspection method for comparing the number of dots in the dot group area on the counted test pattern with the number of nozzles driven to form dots,
If the number of dot group areas on the test pattern is smaller than the number of nozzles driven to form dots, it is determined that the nozzles do not eject ink, and the number of dot group areas on the test pattern forms dots. The nozzle defect inspection method according to (2), wherein when the number of nozzles driven for the same reason is determined, it is determined that the flying ink of the nozzles is bent.

(5) A nozzle defect inspection device for detecting a nozzle defect of a recording head,
Nozzle defect of a recording head including a camera for optically imaging a test pattern, an image processing unit, an inspection unit for performing an inspection, an output unit for an inspection result, and a maintenance processing unit for performing a predetermined recording head recovery procedure based on the result Inspection device.

(6) An image recording apparatus comprising the recording head nozzle defect inspection method and inspection apparatus according to any one of (1) to (5).
(7) An inspection method for defective nozzles, in which a plurality of test patterns are recorded in order to increase the inspection accuracy, and a plurality of test patterns are inspected for defective nozzles. The nozzle inspection method according to any one of (1) to (6), in which, when a nozzle failure is found, the recording of the test pattern is stopped before all the expected number of recordings is recorded.

FIG. 1 is a schematic diagram illustrating a configuration example of a nozzle defect inspection apparatus and an image recording apparatus according to the present embodiment. FIG. 2 is a diagram illustrating a block configuration of a control system of the inspection apparatus. FIG. 3 is a diagram showing the configuration of the test pattern used in this embodiment. FIG. 4 is a diagram conceptually illustrating the relationship between the test pattern and the recording medium conveyance direction. FIG. 5 is a flowchart for explaining nozzle defect inspection by the nozzle inspection apparatus. FIG. 6 is a flowchart for explaining a first subroutine for nozzle defect inspection in step S9 of FIG. FIG. 7 is a diagram showing the concept of the nozzle area in each dot of the dot group area of the test pattern. FIG. 8 is a diagram illustrating an example in which ink non-ejection dots are generated in the dot group area. FIG. 9 is a diagram showing an example in which the ink flight curve occurs in the dot group area. FIG. 10 is a diagram showing a first modification of the test pattern used in the first embodiment described above. FIGS. 11A and 11B are diagrams showing a second modification of the test pattern used in the first embodiment described above. FIG. 12 shows the relationship in the case of performing solid recording with each density and all nozzles in the multi-tone recording head. FIG. 13A is a flowchart for explaining nozzle defect inspection according to the second embodiment. FIG. 13B is a flowchart for explaining the nozzle defect inspection in the second embodiment following FIG. 13A.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printer (image recording device), 2 ... Inspection apparatus, 3 ... Recording head, 4 ... Recording medium, 4a ... Test recording medium, 5 ... Recording medium supply part, 6, 12 ... Conveyance mechanism, 7 ... Recording medium cassette, DESCRIPTION OF SYMBOLS 8 ... Printer control part, 11 ... Pick-up roller, 13 ... Recording medium detection sensor, 14 ... Imaging part, 15 ... Image processing and judgment part, 10 ... Inspection apparatus main body, 16 ... Display part, 17 ... Pulley, 18 ... Conveyance belt , 19 ... fan, 20 ... input unit, 21 ... inspection device control unit, 22 ... test pattern storage unit, 23 ... image data storage unit, 24, 25 ... density data conversion unit, 26 ... filter unit, 27 ... counting unit, 28, 29: Comparison operation unit.

Claims (9)

Using all the nozzles of the recording head that ejects ink, the solid recording area where ink is ejected from all nozzles at the same time and the adjacent nozzles are sequentially driven at predetermined time intervals to eject ink and record A dot group area, and a recording step for recording a test pattern configured on a recording medium;
A step of optically reading the test pattern recorded by the recording step;
Based on the image information of the solid recording area read in the reading step, the density for each dot line of the nozzles constituting the solid recording area is calculated over all the dot lines, and the calculated density for each dot line. Comparing with a predetermined reference density, and determining whether or not there is an abnormal nozzle in which ink ejection is abnormal among all nozzles of the ink ejection head;
Based on the image information of the dot group area, a spot landing area for each dot corresponding to each nozzle of the recording head constituting the dot group area is set, and the density for each spot landing area is set to all the spot landing areas. A second inspection step for determining whether or not there is a non-ejection nozzle or a flying bent nozzle in the recording head by comparing the calculated density for each planned landing area with a predetermined reference density; ,
A nozzle defect inspection method characterized by comprising:   2. The nozzle defect inspection method according to claim 1, wherein the second step is executed when it is determined in the first inspection step that the abnormal nozzle is present. 3.   The second inspection step determines that there is an ink non-ejection nozzle when the calculated density of the planned landing area is less than the reference density, and when the calculated density of the planned landing area is equal to or higher than the reference density. The nozzle defect inspection method according to claim 2, wherein it is determined that there is a flying curve nozzle.   In the second inspection step, the number of dots having a density equal to or higher than a reference density is counted, and the counted number of dots is compared with a predetermined reference number, whereby an ink non-ejection nozzle or an ink flying bent nozzle in the recording head is used. The nozzle defect inspection method according to claim 2, wherein the presence or absence of the nozzle is determined.   In the second inspection step, when the counted number of dots is smaller than the reference number, it is determined that there is a non-ejection nozzle, and when the counted number of dots is greater than the reference number, it is determined that there is a flying bent nozzle. The nozzle defect inspection method according to claim 4, wherein:   The nozzle defect inspection method according to claim 2, wherein the recording step records a plurality of sets of test patterns along a dot line direction.   3. The test pattern according to claim 2, wherein, in the recording step, when the image is recorded by a plurality of recording heads, the test pattern is recorded at a position spaced apart on a recording medium for each recording head. Nozzle defect inspection method.   In the recording step, before the test pattern is recorded, a solid recording pattern in which only one nozzle is not driven is recorded on a recording medium for each of a plurality of gradations so that only one dot line is a white stripe. The nozzle defect according to claim 2, wherein the test pattern is recorded using a gradation of a solid recording pattern in which a white line of one dot line is visually recognized from among a plurality of solid recording patterns. Inspection method. The reading step includes
A first reading step for reading a solid recording area;
A second reading step of reading a dot group area, and the first inspection step is executed after the first step is completed,
The second reading step is executed only when it is determined in the first inspection step that there is an ejection abnormal nozzle,
The nozzle defect inspection method according to claim 1, wherein the second inspection step is performed after the second reading step is completed.

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