JP7259351B2 - Liquid ejection device and ejection failure detection method - Google Patents

Description

The present invention relates to a liquid ejection apparatus and an ejection failure detection method.

Patent Document 1 discloses a technique for inspecting a recorded image using a one-dimensional line sensor. Further, Patent Document 1 discloses that a two-dimensional surface sensor may be used in place of the one-dimensional line sensor.

However, Patent Document 1 does not disclose how the two-dimensional surface sensor is used to inspect the image, and there is a fear that the image cannot be inspected accurately and efficiently.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to enable an ejection failure nozzle to be identified accurately and efficiently.

In order to solve the above-described problems and achieve the object, the present invention provides a liquid ejection head having at least one or more nozzle rows in which a plurality of nozzles for ejecting liquid are arranged in a predetermined direction, and a predetermined number of the nozzle rows. a pattern in which units each including a row of a plurality of lines extending in a direction perpendicular to the row direction of the nozzles are arranged in a zigzag pattern by ejecting liquid from each of the plurality of nozzles divided into individual nozzles; a pattern forming unit that forms a mark that can be detected by a two-dimensional image sensor in at least three of the four corners; a two-dimensional image sensor that has an imaging range larger than that of the unit and images the pattern; and optics of the pattern. an imaging lens that forms an image on the light-receiving surface of the two-dimensional image sensor; and ejection failure detection that detects ejection failure nozzles existing in the plurality of nozzles from an image of the pattern captured by the two-dimensional image sensor. wherein the number of rows of the plurality of lines included in the unit of the pattern is at least twice the number of the nozzle rows, and the defective ejection detection unit detects images captured by the two-dimensional image sensor. Effective for specifying the position of the nozzle in the detection data based on the detection data and a predetermined threshold value by adopting the data with the highest contrast from the RGB data for each unit as the detection data. Based on the detection data updated by a nozzle position detection unit that determines the detection range, updates the detection data so as to replace data outside the effective detection range with predetermined data, and specifies the nozzle position. and determining a threshold value for judging the ejection failure nozzle, and detecting the ejection failure nozzle from the threshold value and the data on the position of the nozzle.

According to the present invention, it is possible to accurately and efficiently identify defective nozzles.

FIG. 1 is a perspective view showing an example of an inkjet recording apparatus according to a first embodiment; FIG. FIG. 2 is a plan view showing an example of the carriage and main scanning mechanism. FIG. 3 is a plan view showing the configuration of the recording head. FIG. 4 is a diagram schematically showing the nozzle surface of the recording head. FIG. 5 is a cross-sectional view showing a configuration example of an imaging unit. FIG. 6 is a block diagram showing electrical connections in the control system of the inkjet recording apparatus. FIG. 7 is a functional block diagram showing functions exhibited by the main control unit and functions exhibited by the two-dimensional sensor CPU. FIG. 8 is a diagram showing the configuration of a test pattern. FIG. 9 is an enlarged view of a test pattern unit. FIG. 10 is a diagram showing the positional relationship between test patterns and nozzles. FIG. 11 is a diagram showing the relationship between the imaging unit and nozzle positions. FIG. 12 is a diagram showing the reading order of each unit in the test pattern. FIG. 13 is a diagram showing a method of detecting nozzle positions. FIG. 14 is a diagram showing a plot example of values read by the two-dimensional image sensor. FIG. 15 is a diagram showing an example of detection data. FIG. 16 is a diagram showing an example in which the detection data is replaced with peak values for each nozzle position. FIG. 17 is a diagram showing a plot example when an ejection failure nozzle occurs. FIG. 18 is a diagram showing ejection failure nozzles when the detection data shown in FIG. 17 are replaced with peak values for each nozzle position. FIG. 19 is a diagram schematically showing the steps up to the registration of the position of the ejection failure nozzle. FIG. 20 is a flow chart showing the flow of detection processing for a defective ejection nozzle. FIG. 21 is a plan view showing an arrangement example of print heads according to a modification. FIG. 22 is a diagram showing the configuration of a test pattern according to the modification. 23 is a cross-sectional view illustrating a configuration example of an imaging unit according to a second embodiment; FIG. FIG. 24 is a diagram exemplifying RGB value data for each pixel position when an ultraviolet light source is used. FIG. 25 is a diagram showing a comparative example of measurement results when different light sources are used. FIG. 26 is a diagram showing the configuration of a test pattern. FIG. 27 is a diagram showing a comparative example of measurement results for white printing when different light sources are used. FIG. 28 is a diagram showing trend removal processing during pattern recognition according to the third embodiment. FIG. 29 is a diagram showing data that has been subjected to detrending processing and smoothing processing. FIG. 30 is a diagram showing data from which noise has been removed and the target range has been redefined.

Exemplary embodiments of a liquid ejection device and an ejection failure detection method will be described in detail below with reference to the accompanying drawings. In the following, a case in which an inkjet recording apparatus is applied as a liquid ejecting apparatus that ejects liquid will be described as an example, but the present invention is not limited to this.

(First embodiment)
[Description of Hardware Configuration of Inkjet Recording Apparatus]
Here, FIG. 1 is a perspective view showing an example of the inkjet printing apparatus 100 according to the first embodiment, and FIG. 2 is a plan view showing an example of the carriage 105 and main scanning mechanism 110. As shown in FIG. As shown in FIG. 1, the inkjet recording apparatus 100 includes a recording apparatus main body 101 and a support base 102. As shown in FIG. The inkjet recording apparatus 100 includes guide rods 103 and guide rails 104 on both side plates (not shown) inside a recording apparatus main body 101 . The guide rod 103 and the guide rail 104 hold the carriage 105 slidably in the arrow A direction. The inkjet recording apparatus 100 also includes an ink cartridge 107 .

As shown in FIG. 2, the carriage 105 is mounted with a recording head 106 having a liquid ejection head for ejecting ink droplets of each color supplied from an ink cartridge 107 . The print head 106 and carriage 105 constitute a liquid ejection unit. The recording head 106 includes recording heads 106k, 106c, 106m, and 106y corresponding to various inks of KCMY. The recording heads 106k, 106c, 106m, and 106y have a plurality of nozzles (see FIG. 3), and form images by selectively discharging ink droplets from the nozzles. The print heads 106 (print heads 106 k, 106 c, 106 m, and 106 y) are integrally provided with sub-tanks (not shown) that store ink supplied from the ink cartridges 107 .

Here, FIG. 3 is a plan view showing the configuration of the recording head 106. As shown in FIG. The printhead 106 (printheads 106k, 106c, 106m, and 106y) shown in FIG. 3 has four nozzle rows (rows A, B, C, and D in FIG. 3). The nozzle row has, for example, 320 nozzles per row, and one print head 106 has a total of 1280 nozzles in four rows.

Here, FIG. 4 is a diagram schematically showing the nozzle surface of the recording head 106. As shown in FIG. As shown in FIG. 4, each nozzle row of the print head 106 has nozzles arranged at intervals of 150 dpi. Further, each nozzle array of the print head 106 is arranged to be shifted in the sub-scanning direction B by 600 dpi. That is, each nozzle row of the print head 106 is arranged without overlapping droplets in one scan of the carriage 105 in the main scanning direction A. The image is 600 dpi.

Such nozzles of the print head 106 may cause ejection failure during use. Therefore, the inkjet printing apparatus 100 detects which nozzles of the printing head 106 are defective ejection nozzles, thereby making it possible to compensate for images formed by the defective ejection nozzles with other heads.

A main scanning mechanism 110 that moves and scans the carriage 105 includes a main scanning motor 111 arranged on one side in the main scanning direction A, a drive pulley 112 that is driven to rotate by the main scanning motor 111, and the other side in the main scanning direction A. and a belt member 114 that is looped between the drive pulley 112 and the driven pulley 113 . The driven pulley 113 is tensioned outward (in a direction away from the driving pulley 112) by a tension spring (not shown).

The belt member 114 pulls the carriage 105 in the main scanning direction A because a portion of the belt member 114 is fixed and held by a belt fixing portion provided on the back side of the carriage 105 . In the recording area of the main scanning area of the carriage 105 , the paper M, which is a sheet-like object to be conveyed whose end is inserted into the paper feed port 119 , is conveyed in a direction perpendicular to the main scanning direction A of the carriage 105 (sub-scanning direction). It is intermittently conveyed in the scanning direction/paper conveying direction) B. In the present embodiment, roll paper (paper M) is used as a sheet-like object to be conveyed.

Further, as shown in FIG. 1, the inkjet recording apparatus 100 includes a maintenance mechanism 115 that performs maintenance of the recording head 106 mounted on the carriage 105 .

Furthermore, as shown in FIG. 2, the inkjet recording apparatus 100 has a main scanning encoder sensor 117 arranged inside the carriage 105 . The inkjet recording apparatus 100 moves the carriage 105 while detecting the position in the main scanning direction A by continuously reading the encoder sheet 118 stretched over both side plates with the main scanning encoder sensor 117 .

In addition, as shown in FIG. 2, the inkjet recording apparatus 100 has an imaging section 120 on the carriage 105 . Here, FIG. 5 is a sectional view showing a configuration example of the imaging unit 120. As shown in FIG. As shown in FIG. 5, the imaging unit 120 is used for imaging a test pattern P formed on a sheet of paper M. As shown in FIG. The imaging unit 120 includes a two-dimensional image sensor 121, an imaging lens 122, a white LED (Light Emitting Diode) light source 124 that emits visible light, and a substrate 125 on which the two-dimensional image sensor 121 and the LED light source 124 are arranged. And prepare. The LED light source 124 irradiates the test pattern P formed on the paper M with light. The two-dimensional image sensor 121 is a CCD (Charge Coupled Device) sensor, a CMOS (Complementary metal-oxide-semiconductor) sensor, or the like. The imaging lens 122 forms an optical image of the test pattern P formed on the paper M on the light receiving surface of the two-dimensional image sensor 121 . The LED light source 124 is arranged on the substrate 125 so as to be symmetrical with respect to the two-dimensional image sensor 121 . With such a configuration, the imaging unit 120 converts light incident through the imaging lens 122 into an electrical signal by the two-dimensional image sensor 121 and outputs the electrical signal as a captured image of the test pattern P. FIG.

Next, a control system of the inkjet recording apparatus 100 will be described.

FIG. 6 is a block diagram showing electrical connections of the control system of the inkjet recording apparatus 100. As shown in FIG. As shown in FIG. 6, the inkjet recording apparatus 100 includes a control section 300 that controls each section. The control unit 300 includes a main control unit 301 , an FPGA (Field-Programmable Gate Array) 302 and a motor driver 303 .

A main control unit 301 includes a CPU (Central Processing Unit) that controls the entire inkjet printing apparatus 100, a ROM (Read Only Memory), a RAM (Random Access Memory), an I/F (InterFace), a timer, and the like. Including microcomputer.

The ROM of the main control unit 301 stores various programs executed by the CPU and various data. The RAM of the main control unit 301 temporarily stores data and programs when the CPU executes various programs. The CPU of the main control unit 301 reads the program stored in the ROM into the RAM and executes it, thereby comprehensively controlling each unit of the inkjet recording apparatus 100 . At this time, the CPU controls various operations in the inkjet printing apparatus 100 in cooperation with the FPGA 302 while communicating with the FPGA 302 . For example, the main control unit 301 has functions such as CPU control, memory control, ink discharge control, sensor control, and motor control.

A program executed by the inkjet recording apparatus 100 of the present embodiment is a file in an installable format or an executable format, and can be stored on a CD-ROM, flexible disk (FD), CD-R, DVD (Digital Versatile Disk), or the like. It may be configured to be recorded on a computer-readable recording medium and provided.

Furthermore, the program executed by the inkjet recording apparatus 100 of the present embodiment may be stored on a computer connected to a network such as the Internet, and provided by being downloaded via the network. Also, the program executed by the inkjet recording apparatus 100 of the present embodiment may be configured to be provided or distributed via a network such as the Internet.

A main control unit 301 drives and controls the recording head 106 . The main control unit 301 drives a main scanning motor 111 and a sub-scanning motor 310 that drives a conveying roller 311 for conveying the sheet M through a motor driver 303 .

The main control unit 301 connects a sub-scanning encoder sensor 312 for detecting the sub-scanning direction B of the sheet M in addition to the main-scanning encoder sensor 117 of the carriage 105 . The main control unit 301 receives encoder values from the main scanning encoder sensor 117 and the sub-scanning encoder sensor 312 respectively.

In addition, the main control section 301 connects the imaging section 120 . The main control unit 301 instructs the imaging unit 120 to perform imaging. The two-dimensional sensor CPU 123 provided in the imaging unit 120 performs imaging with the two-dimensional image sensor 121 according to instructions from the main control unit 301, and executes various processes based on the imaging data. The two-dimensional sensor CPU 123 transmits motion information obtained by various processes to the main control unit 301 .

[Description of Functional Configuration of Inkjet Recording Apparatus]
Next, the functions that the CPU of the main control unit 301 of the inkjet recording apparatus 100 exhibits by executing the program stored in the ROM and the functions that the two-dimensional sensor CPU 123 exhibits by executing the program will be described. Here, description of conventionally known functions will be omitted, and the characteristic functions exhibited by the inkjet recording apparatus 100 of the present embodiment will be described in detail.

FIG. 7 is a functional block diagram showing functions exhibited by the main control unit 301 and functions exhibited by the two-dimensional sensor CPU 123. As shown in FIG.

As shown in FIG. 7, the main control unit 301 functions as a pattern forming unit 401, a cleaning processing unit 402, a two-dimensional sensor instruction unit 403, and an ejection failure nozzle registration unit 404 by executing programs stored in the ROM. do.

Further, as shown in FIG. 7, the two-dimensional sensor CPU 123 functions as a nozzle position detection unit 501 and an ejection failure detection unit 502 by executing programs.

The pattern forming unit 401 drives and controls the recording head 106 and the main scanning mechanism 110 to form a test pattern P on the paper M. FIG.

Here, FIG. 8 is a diagram showing the structure of the test pattern P, and FIG. 9 is an enlarged diagram showing a unit of the test pattern P. As shown in FIG. As shown in FIG. 8, the pattern forming unit 401 forms a test pattern P by dividing all nozzles of one print head 106 into ten unit regions. More specifically, the pattern forming unit 401 has 128 nozzles (32 nozzles×4 rows) as one unit. Unit 1 is for the bottom 32 nozzles of the recording head 106 shown in FIG. 3, and unit 10 is for the top 32 nozzles of the recording head 106 shown in FIG.

As shown in FIG. 9, the pattern forming unit 401 forms lines by ejecting 40 dots of ink in the main scanning direction A from one nozzle in one unit. The reason why a line is formed instead of 1 dot is to make it easier for the two-dimensional image sensor 121 to detect an image formed by a nozzle having an ejection failure.

As shown in FIGS. 8 and 9, the pattern forming unit 401 forms a line with even-numbered nozzles in one unit to generate four columns for each color on the left side, and uses odd-numbered nozzles to form lines (lines). Form a line to generate 4 columns for each color on the right. That is, each unit of the test pattern P is formed with the number of rows twice the number of nozzle rows. The pattern forming unit 401 also forms a test pattern P in which the units of the test pattern P are alternately arranged in a zigzag pattern.

In the present embodiment, each unit of the test pattern P is formed with the number of rows twice the number of nozzle rows, but the present invention is not limited to this. may be formed by the number of columns.

Here, FIG. 10 is a diagram showing the positional relationship between the test pattern P and the nozzles. The positional relationship between the test pattern P and the nozzles shown in FIG. 10 represents the relationship between the nozzle numbers and the lines in the unit 1 (partially shown in FIG. 4) shown in FIG.

By doing so, in each unit of the test pattern P, space is taken in the sub-scanning direction B to prevent upper and lower nozzles and dots from overlapping each other. Further, since the test pattern P can be formed by one scan of the carriage 105 in the main scanning direction A, the pattern printing time can be shortened and the test pattern P can be formed small. can be read to a minimum.

In addition, as shown in FIGS. 8 and 9, the pattern forming unit 401 considers the stopping accuracy of the carriage 105, and sets at least three of the four corners of the unit of the test pattern P to a standard that can be detected by the two-dimensional image sensor 121. As shown in FIGS. A black frame, which is a line (mark) X, may be formed in each unit. The reference line X is a pattern smaller than the imaging range of the two-dimensional image sensor 121 . By forming such a reference line X, each unit can be reliably placed within the imaging range of the two-dimensional image sensor 121 .

Note that the reference line X does not have to be frame-shaped as long as there are reference lines or points that can identify at least three of the four corners. In that case, calculation is performed by a method of specifying the reference position coordinates of both ends from the data of the four corners. Also, the reference line X is formed with a size having a margin considering the reading position error in the two-dimensional image sensor 121 .

Note that, depending on the combination of ink colors in the print head 106, black (K) may not be available, or if the ink color of the print head 106 alone cannot form the black frame that is the reference line X, the pattern forming unit 401 , after the reference line X is drawn, a pattern for each nozzle position may be formed in the next scan.

Further, as shown in FIG. 8, the pattern forming section 401 displaces the ten units in the main scanning direction A by one unit. As a result, the test pattern P for 10 units of one printhead 106 can be formed only by moving the carriage 105 in the main scanning direction A without performing a paper feeding operation for at least one printhead 106 . By doing so, an image can be formed without transporting the paper M in the sub-scanning direction B, so that the image position deviation factor due to the transport error can be eliminated.

The two-dimensional sensor instructing section 403 instructs to move the two-dimensional image sensor 121 onto a predetermined unit of the test pattern P. FIG.

The nozzle position detection unit 501 moves the two-dimensional image sensor 121 onto a predetermined unit of the test pattern P according to the instruction from the two-dimensional sensor instruction unit 403 . The nozzle position detection unit 501 then corrects the magnification based on the imaging data captured by the two-dimensional image sensor 121 and detects the nozzle position.

Here, FIG. 11 is a diagram showing the relationship between the imaging unit 120 and nozzle positions. As shown in FIG. 11, the imaging unit 120 is installed so that the imaging lens 122 (two-dimensional image sensor 121) is positioned side by side at the position corresponding to the most downstream unit 1 in the sub-scanning direction B of the recording head 106. It is Also, the imaging range of the imaging unit 120 at one time is assumed to be substantially the same range as each unit in the test pattern P. FIG.

FIG. 12 is a diagram showing the reading order of each unit in the test pattern P. As shown in FIG. As shown in FIG. 12, the nozzle position detection unit 501 controls the carriage 105 in accordance with an instruction from the two-dimensional sensor instruction unit 403 to move the recording head 106 and the imaging unit 120 to the unit 1 in the test pattern P, which is the initial reading position. to move. As a result, the test pattern P can be read only by conveying the paper M in the sub-scanning direction B without returning the paper M after the printing of the test pattern P is finished. Since no return operation is performed, there is no time loss, and the return operation can avoid the influence of reading position deviation due to a decrease in conveying accuracy (the influence of paper slippage, etc.).

Here, FIG. 13 is a diagram showing a nozzle position detection method. In the example shown in FIG. 13, the reference line X is formed by reference lines A, B, C, and D. In the example shown in FIG. By providing such a reference line X, when the absolute distance (the number of pixels) between the reference lines AB and CD changes according to the distance between the paper M and the two-dimensional image sensor 121, the recording head 106 Solves the problem that the nozzle position cannot be specified correctly. More specifically, the nozzle position detection unit 501 divides the image data between the reference lines CD into 8 equal parts, and specifies the nozzle row (reading position) not by the absolute distance but by the relative distance, thereby changing the magnification. Even in such a case, the position is detected correctly by correcting the magnification. Also, the nozzle position detection unit 501 similarly divides the image data between the reference lines AB into 16 equal parts, and specifies the nozzle positions not by the absolute distance but by the relative distance.

Here, FIG. 14 is a diagram showing a plot example of values read by the two-dimensional image sensor 121. In FIG. The plot example shown in FIG. 14 is RGB value data for each pixel position read by the two-dimensional image sensor 121 by the method shown in FIG. The plot example shown in FIG. 14 is RGB value data for each pixel position obtained by reading cyan, yellow, magenta, and black from the left of the drawing. The horizontal axis shown in FIG. 14 is the pixel position, and the vertical axis shown in FIG. 14 is plotted on one graph after normalizing the three values of RGB from 0 to 1. FIG. In addition, the second yellow data from the left in the figure has no contrast and cannot be detected except for the complementary color B, so select the value with the largest contrast (the value of B in the second data) .

Here, FIG. 15 is a diagram showing an example of detection data. As shown in FIG. 15, the nozzle position detector 501 selects one data with the highest contrast (largest amplitude) from the RGB data in FIG. 14, for example, and adopts it as detection data. The reason why the data with the highest contrast is selected is that the data with the highest amplitude is less likely to be erroneously detected. As shown in FIG. 15, the nozzle position detector 501 vertically inverts the selected data and holds the maximum value (peak value) as the value of each nozzle position. In this case, data averaged at equally divided intervals (pixel range) may be used. FIG. 16 is a diagram showing an example in which the detection data is replaced with peak values for each nozzle position.

The nozzle position detection unit 501 can specify the nozzle position by equally dividing the both ends into 16 with the positions of the reference line A and the reference line B. FIG. At this time, even if the distances to the reference lines A and B are not strictly divided into 16 equal parts, if the distances to the reference lines A and B are determined by the ratio, the nozzle position detection unit 501 detects the relative distance and the distance between the equally spaced nozzles by the ratio. , the nozzle position can be calculated.

The ejection failure detection unit 502 detects whether each row of one unit has an ejection failure nozzle from the data at the nozzle positions detected by the nozzle position detection unit 501 , and transmits the data to the main control unit 301 .

Here, FIG. 17 is a diagram showing a plot example when an ejection failure nozzle occurs, and FIG. 18 is a diagram showing an ejection failure nozzle when the detection data shown in FIG. 17 is replaced with a peak value for each nozzle position. be. The example shown in FIG. 17 shows a transition from the normal state (a) to the state (b) in which the third nozzle has an ejection failure. The example shown in FIG. 18 represents that the RGB values at the third nozzle position are lower than the threshold. The ejection failure detection unit 502 transmits to the main control unit 301 the nozzle position information in which the RGB values are lower than the threshold value for each row of one unit as an ejection failure location.

The defective ejection nozzle registration unit 404 identifies the defective ejection nozzle based on the data sent from the two-dimensional sensor CPU 123 for each unit, and registers the position (number) of the defective ejection nozzle. Note that the defective ejection nozzle registration unit 404 identifies the nozzles of each print head 106 when there are a plurality of print heads 106 .

Here, FIG. 19 is a diagram schematically showing the steps up to the registration of the position of the ejection failure nozzle. As shown in FIG. 19 , upon receiving the nozzle position information of the ejection failure causing the pattern omission detected from the captured image captured by the two-dimensional image sensor 121 , the ejection failure nozzle registration unit 404 registers the A defective nozzle is registered in correspondence with the nozzle number.

The cleaning processing unit 402 controls the maintenance mechanism 115 to perform cleaning processing when there is an ejection failure.

Next, the flow of detection processing for ejection failure nozzles will be described.

FIG. 20 is a flow chart showing the flow of detection processing for a defective ejection nozzle executed by the main control unit 301 and the two-dimensional sensor CPU 123 .

First, the pattern forming unit 401 drives and controls the recording head 106 and the main scanning mechanism 110 to print a test pattern P on the paper M (step S1). Here, first, only the black frame that is the reference line X is printed, and then the units 1 to 10 within the black frame are printed in one scan to complete the test pattern P. FIG.

Next, the two-dimensional sensor instructing section 403 instructs to move the two-dimensional image sensor 121 onto a predetermined unit serving as the reading position of the test pattern P (step S2).

The nozzle position detection unit 501 moves the two-dimensional image sensor 121 onto a predetermined unit serving as the reading position of the test pattern P according to the instruction from the two-dimensional sensor instruction unit 403 (step S11).

Next, the nozzle position detection unit 501 corrects the magnification and detects the nozzle positions based on the imaging data obtained by imaging one unit of the test pattern P with the two-dimensional image sensor 121 (step S12).

Subsequently, the ejection failure detection unit 502 detects ejection failure nozzles within one unit from the data at the nozzle positions detected by the nozzle position detection unit 501 (step S13).

Then, the ejection failure detection unit 502 transmits the nozzle position information of the detected ejection failure nozzles in one unit to the main control unit 301 (step S14).

The ejection failure nozzle registration unit 404 identifies the ejection failure nozzle based on the received nozzle position information of the ejection failure nozzle (step S3).

Then, the defective ejection nozzle registration unit 404 registers the position (number) of the defective ejection nozzle (step S4). By using information about the nozzle positions (numbers) of the ejection failure nozzles registered in this way, it is possible to perform an ejection interpolation operation in which an image formed by the ejection failure nozzles is compensated for by other printheads.

If the two-dimensional sensor instruction unit 403 has not completed the detection process of the ejection failure nozzles for all the units forming the test pattern P (No in step S5), the process returns to step S2, and the two-dimensional image sensor 121 is set to the test pattern. Instruct to move to the unit next to P.

On the other hand, if the two-dimensional sensor instruction unit 403 has completed the ejection failure nozzle detection process for all the units forming the test pattern P (Yes in step S5), the ejection failure nozzle detection process is completed.

As described above, according to the present embodiment, a plurality of line arrays included in the unit of the test pattern P are configured with the number of arrays that is at least twice the number of nozzle arrays of one print head 106, thereby performing a test. While the size of the pattern P is reduced, the test pattern P can be formed in one scan without overlapping the dots of adjacent nozzles. Since all the test patterns P can be drawn without conveying the paper M, it is possible to reduce the influence of conveyance errors and efficiently detect defective ejection nozzles.

In addition, the two-dimensional image sensor 121 is arranged side by side at a position corresponding to the unit positioned most downstream in the sub-scanning direction B of the recording head 106, so that the paper M can be returned after printing of the test pattern P is completed. The reading operation of the test pattern P can be performed only by conveying the paper M in the sub-scanning direction B.

(Modification)
Next, a modified example will be described.

In the present embodiment, the detection process for ejection failure nozzles in one printhead 106 has been described, but the present invention is not limited to this, and can also be applied when a plurality of printheads 106 are used side by side.

Here, FIG. 21 is a plan view showing an arrangement example of the recording head 106 according to the modification. In the example shown in FIG. 21, three printheads 106 are arranged in a zigzag pattern. The three printheads 106 are arranged such that the nozzle rows overlap by 10 nozzles from the upstream side to the downstream side in the sub-scanning direction B of the paper M. As shown in FIG.

Further, as shown in FIG. 21, the imaging unit 120 is aligned with the imaging lens 122 ( It is installed so that the two-dimensional image sensor 121) is positioned.

FIG. 22 is a diagram showing the configuration of a test pattern P according to a modification. As shown in FIG. 22, the pattern forming unit 401 forms a test pattern P (see FIG. 8) in which all the nozzles of the print head 106 are divided into 10 unit regions for the three print heads 106. do. That is, the pattern forming section 401 forms the test pattern P for one carriage (30 units=3 heads×10 units) on the paper M. FIG. In addition, the pattern forming unit 401 arranges the three test patterns P corresponding to the three printheads 106 so as to shift each test pattern P in the main scanning direction A. FIG.

As a result, the test patterns P corresponding to 10 units can be formed by the three printheads 106 only by moving the carriage 105 in the main scanning direction A without performing the paper feeding operation for at least the three printheads 106 . . By doing so, an image can be formed without transporting the paper M in the sub-scanning direction B, so that the image position deviation factor due to the transport error can be eliminated.

Although it is possible to form three test patterns P corresponding to the three printheads 106 vertically in the sub-scanning direction B, by shifting them in the main scanning direction A according to the head arrangement, the ejection time can be shortened. It is possible to shorten the scanning distance.

In this case as well, the nozzle position detection unit 501 controls the carriage 105 in accordance with instructions from the two-dimensional sensor instruction unit 403 to detect the first read position, as in the detection process of defective ejection nozzles in one print head 106 . The recording head 106 and the imaging unit 120 are moved to the unit 1 in the test pattern P corresponding to the recording head 106 positioned most downstream in the sub-scanning direction B to capture an image.

(Second embodiment)
Next, a second embodiment will be described.

The second embodiment differs from the first embodiment in that an LED light source that emits ultraviolet light is added as a light source for imaging by the two-dimensional image sensor 121 . Hereinafter, in the description of the second embodiment, the description of the same portions as those of the first embodiment will be omitted, and the portions different from those of the first embodiment will be described.

FIG. 23 is a cross-sectional view showing a configuration example of the imaging unit 120 according to the second embodiment. The imaging unit 120 of the present embodiment is provided with an LED light source 126 that emits ultraviolet light, in addition to a white LED light source 124 that emits visible light, as light sources for imaging by the two-dimensional image sensor 121 . An LED light source 126 that emits ultraviolet light is arranged on the substrate 125 so as to be symmetrical with respect to the two-dimensional image sensor 121 . Also, the white LED light source 124 that emits visible light and the LED light source 126 that emits ultraviolet light are arranged in a row, and may be positioned inside or outside the two-dimensional image sensor 121 .

Here, FIG. 24 is a diagram exemplifying RGB value data for each pixel position when an ultraviolet light source is used. The data shown in FIG. 24 is RGB value data for each pixel position read by the two-dimensional image sensor 121 by the method shown in FIG. .

FIG. 24A shows an example of cyan read data, (b) yellow read data, (c) magenta read data, and (d) black read data. In FIG. 24, the pixel position is plotted on the horizontal axis, and the three values of RGB normalized from 0 to 255 are plotted on the vertical axis.

As shown in the reading results of FIGS. 24(a) to 24(d), which are read by the two-dimensional image sensor 121 by irradiating ultraviolet light from the LED light source 126, the values of R and B are saturated at the maximum value, and the G can only be read. However, the nozzle position detection unit 501 only needs to produce a contrast with any value of RGB. Therefore, even when the LED light source 126 is used, the nozzle position detection unit 501 can detect the test pattern P because the contrast is obtained by the value of G.

Here, FIG. 25 is a diagram showing a comparative example of measurement results when different light sources are used. FIGS. 25A and 25B compare the reading results of yellow under different light sources. In FIG. 25(a), the left side shows the reading result with the white LED light source 124 emitting visible light, and the right side shows the reading result with the LED light source 126 emitting ultraviolet light.

FIG. 25(b) is an enlarged view of the contrasted portion of FIG. 25(a). As shown in FIG. 25(b), in the case of reading yellow, the reading result from the LED light source 124 emitting visible light shown on the left shows the contrast of B, which is a complementary color, but the value is small. On the other hand, in the reading result with the LED light source 126 emitting ultraviolet light shown on the right, the numerical value of the G contrast is doubled compared to the reading result with visible light, making reading easier.

Next, the test pattern P' in this embodiment will be described.

FIG. 26 is a diagram showing the configuration of the test pattern P'. As shown in FIG. 26, the test pattern P' has the same basic configuration as the test pattern P shown in FIG. However, as a difference from the test pattern P shown in FIG. 8, when the light source of the imaging unit 120 is the LED light source 126 of ultraviolet light, visible light such as white and fluorescent colors other than cyan, yellow, magenta, and black Hard-to-read colors can be used. A test pattern P' shown in FIG. 26 is a pattern composed of four columns of yellow, cyan, magenta, and white.

FIG. 27 is a diagram showing a comparative example of measurement results for white printing when different light sources are used. The data shown in FIG. 27 is RGB value data for each pixel position when printing with white ink is read by the two-dimensional image sensor 121 by the method shown in FIG. FIG. 27(a) shows the result of reading with the LED light source 124 that emits visible light, and FIG. 27(b) shows the result of reading with the LED light source 126 that emits ultraviolet light. In FIG. 27, the pixel position is plotted on the horizontal axis, and the three values of RGB normalized from 0 to 255 are plotted on the vertical axis.

For example, when white ink is printed on white paper M, as shown in FIG. Cannot be detected. On the other hand, as shown in FIG. 27(b), with the LED light source 126 of ultraviolet light, contrast appears in the value of G and can be detected.

FIG. 27C shows the result of correcting the acquired RGB values on the light receiving side. By correcting on the light-receiving side in this manner, contrast can be obtained even with values other than G.

Although it is difficult to imagine printing with white ink on blank paper M, it is assumed that depending on needs, fluorescent color or lighter colored ink will be used. In addition, by using the LED light source 126 of ultraviolet light as a light source, the light source is faint in color and cannot be read with visible light, and white can be read even in colors that are difficult to read, so this detection method is effective. .

As described above, according to the present embodiment, when the test pattern is read by the two-dimensional image sensor 121, by using the LED light source 126 that emits ultraviolet light, even colors that are difficult to read with visible light can be read. easier.

(Third Embodiment)
Next, a third embodiment will be described.

The third embodiment differs from the first embodiment in that noise and uneven illumination are removed. Hereinafter, in the description of the third embodiment, the description of the same portions as those of the first embodiment will be omitted, and the portions different from those of the first embodiment will be described.

FIG. 28 is a diagram showing trend removal processing during pattern recognition according to the third embodiment.

The data shown in FIG. 28 indicates that the image picked up by the image pickup unit 120 has illuminance unevenness, so there is a possibility that the pattern may be missed if an attempt is made to detect a peak with a constant threshold value. If the dotted line is used as the threshold, the pattern on the left end in FIG. 28 will be missed.

Therefore, as shown in FIG. 28, the nozzle position detection unit 501 of the present embodiment performs the first processing for the masked target range of the outer frame reference line of the test pattern P in order to cope with the illuminance unevenness. Detrending the data to reveal variations in the data.

A trend is derived by obtaining a linear regression line. However, a regression curve may be used to derive the trend. The trend can be removed by using the following formula.
Detrended Data (X) = Data (X) - Regression Line (X)

At this time, as second processing, the nozzle position detection unit 501 performs smoothing processing on the data in advance so as not to amplify the noise, thereby removing the noise. Here, FIG. 29 is a diagram showing data obtained by subjecting the data to detrending processing and smoothing processing. As shown in FIG. 29, noise caused by uneven illumination is removed by executing the smoothing process.

Any algorithm may be used for the smoothing process as long as it is a low-pass filter. The processing timing may be analog processing or digital processing. In this embodiment, a moving average filter is used at the stage of digital processing.

By the way, in the data shown in FIG. 29, unremoved noise indicated by solid-line circles in FIG. Impossible things happen.

Therefore, the nozzle position detection unit 501 executes, as third processing, processing for removing unnecessary noise in order to detect light ink. More specifically, noise (indicated by a solid circle in FIG. 29) between the reference line and the test pattern P, which is the nozzle position specifying pattern, is removed.

Here, FIG. 30 is a diagram showing data in which noise is removed and the target range is redefined. As shown in FIG. 30, the method of setting only the test pattern P, which is the nozzle position specifying pattern, as the detection effective range uses the intersection of the threshold value (thick dotted line) and the target data.

As indicated by the one-dot chain line and the two-dot chain line in FIG. 30, the data outside the outermost intersection point is replaced so as not to become noise. At this time, if the value at the intersection of the threshold value (thick dotted line) and the target data is input as a constant value for the replacement data, the light ink at the beginning has a small peak and remains difficult to detect. Therefore, the replacement data is replaced with a one-dot chain line or "1" (two-dot chain line) that is inclined so as to easily cross the threshold value (thick dotted line), thereby optimizing the detection effective range determination threshold value.

As described above, according to the present embodiment, when the test pattern is read by the two-dimensional image sensor 121, by removing noise and illumination unevenness, it becomes difficult to miss the pattern at the beginning, and light and dark ink can be used. The pattern can be detected with high accuracy even if there is

In the present application, a "liquid ejection head" is a functional component that ejects and ejects liquid from nozzles.

The liquid to be ejected is not particularly limited as long as it has a viscosity and surface tension that can be ejected from the head. is preferred. More specifically, solvents such as water and organic solvents, colorants such as dyes and pigments, functional-imparting materials such as polymerizable compounds, resins, and surfactants, biocompatible materials such as DNA, amino acids, proteins, and calcium. , edible materials such as natural pigments, solutions, suspensions, emulsions, etc. These are, for example, inkjet inks, surface treatment liquids, components of electronic elements and light emitting elements, and formation of electronic circuit resist patterns It can be used for applications such as liquids for liquids and material liquids for three-dimensional modeling.

Piezoelectric actuators (laminated piezoelectric element and thin film piezoelectric element), thermal actuators that use electrothermal conversion elements such as heating resistors, and electrostatic actuators that consist of a diaphragm and a counter electrode are used as energy sources for liquid ejection. includes those that

A "liquid ejection unit" is a combination of functional parts and mechanisms integrated with a liquid ejection head, and is a collection of parts related to ejection of liquid. For example, the "liquid ejection unit" includes a combination of at least one of a supply/circulation mechanism, a carriage, a maintenance/recovery mechanism, and a main scanning movement mechanism with a liquid ejection head.

Here, integration means, for example, that the liquid ejection head and functional parts or mechanisms are fixed to each other by fastening, adhesion, or engagement, or that one is held movably with respect to the other. include. Also, the liquid ejection head, the functional parts, and the mechanism may be configured to be detachable from each other.

For example, there is a liquid ejection unit in which a liquid ejection head and a supply/circulation mechanism are integrated. Also, there is a type in which the liquid ejection head and the supply/circulation mechanism are integrated by being connected to each other by a tube or the like. Here, a unit including a filter can be added between the supply/circulation mechanism of these liquid ejection units and the liquid ejection head.

Further, there is a liquid ejection unit in which a liquid ejection head and a carriage are integrated.

Further, as a liquid ejection unit, there is one in which the liquid ejection head is movably held by a guide member constituting a part of the scanning movement mechanism, and the liquid ejection head and the scanning movement mechanism are integrated.

There is also a liquid ejection unit in which the liquid ejection head, the carriage, and the maintenance and recovery mechanism are integrated by fixing a cap member, which is a part of the maintenance and recovery mechanism, to a carriage to which the liquid ejection head is attached. .

Further, as a liquid ejection unit, there is one in which a tube is connected to a liquid ejection head to which a supply/circulation mechanism or a channel component is attached, and the liquid ejection head and the supply mechanism are integrated. The liquid in the liquid storage source is supplied to the liquid discharge head through this tube.

It is assumed that the main scanning movement mechanism also includes a single guide member. Also, the supply mechanism includes a single tube and a single loading unit.

In the present application, a "liquid ejection apparatus" is an apparatus that includes a liquid ejection head or a liquid ejection unit, drives the liquid ejection head, and ejects liquid. Liquid ejecting apparatuses include not only apparatuses capable of ejecting liquid onto an object to which liquid can adhere, but also apparatuses ejecting liquid into air or liquid.

The "liquid ejecting apparatus" can include means for feeding, transporting, and ejecting an object to which liquid can adhere, as well as a pre-processing device, a post-processing device, and the like.

For example, as a “liquid ejection device”, an image forming device that ejects ink to form an image on paper, a powder that forms a layer to form a three-dimensional object (three-dimensional object) There is a three-dimensional modeling apparatus (three-dimensional modeling apparatus) that ejects a modeling liquid onto a body layer.

Further, the "liquid ejecting apparatus" is not limited to one that visualizes significant images such as characters and graphics by ejected liquid. For example, it includes those that form patterns that have no meaning per se, and those that form three-dimensional images.

The above-mentioned "substance to which a liquid can adhere" means a substance to which a liquid can adhere at least temporarily, such as a substance to which a liquid adheres and adheres, a substance which adheres and permeates, and the like. Specific examples include media such as recording media such as paper, recording paper, recording paper, film, and cloth, electronic components such as electronic substrates and piezoelectric elements, powder layers (powder layers), organ models, and test cells. Yes, and unless otherwise specified, includes anything that has liquid on it.

The material of the above-mentioned "thing to which a liquid can adhere" may be paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc., as long as the liquid can adhere even temporarily.

Further, the ``liquid ejection device'' includes a device in which a liquid ejection head and an object to which liquid can be adhered move relative to each other, but is not limited to this. Specific examples include a serial type apparatus in which the liquid ejection head is moved and a line type apparatus in which the liquid ejection head is not moved.

In addition, as a "liquid ejection device", there are other processing liquid coating devices that eject processing liquid onto the paper surface in order to apply the processing liquid to the surface of the paper for the purpose of modifying the surface of the paper. There is an injection granulator that granulates fine particles of a raw material by injecting a composition liquid dispersed therein through a nozzle.

Further, the terms used in the present application, such as image formation, recording, printing, printing, printing, modeling, etc., are synonymous.

In the above-described embodiment, an example in which the liquid ejection apparatus according to the present invention is applied to an image forming apparatus having a printer configuration has been described, but the present invention is not limited to this. It can also be applied to a forming device.

REFERENCE SIGNS LIST 100 liquid ejection device 106 liquid ejection head 121 two-dimensional image sensor 401 pattern forming unit 404 ejection failure nozzle registration unit 501 nozzle position detection unit 502 ejection failure detection unit

JP 2017-047613 A

Claims (9)

a liquid ejection head including at least one or more nozzle rows in which a plurality of nozzles for ejecting liquid are arranged in a predetermined direction;
a pattern in which units each including a row of a plurality of lines extending in a direction orthogonal to the row direction of the nozzles are arranged in a zigzag pattern by liquid ejection from each of the plurality of nozzles obtained by dividing the nozzle row by a predetermined number ; a pattern forming unit that forms a mark detectable by a two-dimensional image sensor in at least three of the four corners of the unit of the pattern ;
a two-dimensional image sensor having an imaging range larger than that of the unit and imaging the pattern;
an imaging lens that forms an optical image of the pattern on the light receiving surface of the two-dimensional image sensor;
an ejection failure detection unit that detects an ejection failure nozzle existing in the plurality of nozzles from an image of the pattern captured by the two-dimensional image sensor;
with
the number of rows of the plurality of lines included in the unit of the pattern is at least twice the number of the nozzle rows;
The ejection failure detection unit includes:
Among the RGB data for each unit captured by the two-dimensional image sensor, data having the highest contrast is adopted as detection data, and the nozzles in the detection data are selected based on the detection data and a predetermined threshold value. a nozzle position detection unit that determines an effective detection range for identifying the position of the nozzle, updates the detection data so as to replace data outside the effective detection range with predetermined data, and identifies the position of the nozzle; Determining a threshold value for determining the ejection failure nozzle based on the updated detection data, and detecting the ejection failure nozzle from the threshold value and data on the nozzle position;
A liquid ejection device characterized by: The two-dimensional image sensor is arranged side by side at a position corresponding to the unit positioned most downstream in the sub-scanning direction of the liquid ejection head.
2. The liquid ejecting apparatus according to claim 1, wherein: The pattern forming unit forms a frame formed by four lines surrounding the unit as the mark.
3. The liquid ejecting apparatus according to claim 1 , wherein: The mark is formed in a size with a margin considering a reading position error in the two-dimensional image sensor.
3. The liquid ejecting apparatus according to claim 1 , wherein: The nozzle position detection unit corrects the magnification using the mark for each unit captured by the two-dimensional image sensor.
5. The liquid ejecting apparatus according to any one of claims 1 to 4, characterized in that: a faulty ejection nozzle registration unit that registers the position of the faulty ejection nozzle;
6. The liquid ejecting apparatus according to any one of claims 1 to 5 , characterized in that: Further comprising a light source for irradiating the pattern with ultraviolet light when imaging by the two-dimensional image sensor,
7. The liquid ejecting apparatus according to any one of claims 1 to 6 , characterized in that: The nozzle position detection unit removes noise and illuminance unevenness contained in the RGB data for each unit captured by the two-dimensional image sensor.
8. The liquid ejecting apparatus according to any one of claims 1 to 7, characterized in that: An ejection failure detection method for detecting an ejection failure nozzle in a liquid ejection head having at least one or more nozzle rows in which a plurality of nozzles for ejecting liquid are arranged in a predetermined direction, comprising:
a pattern in which units each including a row of a plurality of lines extending in a direction orthogonal to the row direction of the nozzles are arranged in a zigzag pattern by liquid ejection from each of the plurality of nozzles obtained by dividing the nozzle row by a predetermined number ; a pattern forming step of forming marks detectable by a two-dimensional image sensor in at least three of the four corners of the unit of the pattern ;
forming an optical image of the pattern on a light receiving surface of a two-dimensional image sensor with an imaging lens;
an ejection failure detection step of detecting an ejection failure nozzle existing among the plurality of nozzles from an image of the pattern captured by the two-dimensional image sensor that captures the pattern, the imaging range of which is larger than that of the unit;
including
the number of rows of the plurality of lines included in the unit of the pattern is at least twice the number of the nozzle rows;
The ejection failure detection step includes:
Among the RGB data for each unit captured by the two-dimensional image sensor, data having the highest contrast is adopted as detection data, and the nozzles in the detection data are selected based on the detection data and a predetermined threshold value. a nozzle position detection step of determining an effective detection range for identifying the position of the nozzle, updating the detection data so as to replace data outside the effective detection range with predetermined data, and identifying the position of the nozzle; Determining a threshold value for determining the ejection failure nozzle based on the updated detection data, and detecting the ejection failure nozzle from the threshold value and data on the nozzle position;
An ejection failure detection method characterized by:

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