Defective nozzle detection method and printing apparatus

Abstract

To provide a printer capable of detecting a defective nozzle with higher accuracy than before.SOLUTION: Theoretical and actual values of an interval between two linear patterns included in a test chart are calculated (S40, S50). For each linear pattern, errors (first errors) between theoretical values and intervals from a linear pattern on the left side, errors (second errors) between theoretical values and intervals from a linear pattern on the right side, and averages (average errors) of the first errors and the second errors are calculated (S60). The actual position of the linear pattern at which the minimum average difference is obtained is set as a reference position (S70). The ideal position of each linear pattern is calculated based on the reference position (S80). Differences between the ideal positions and the positions in the captured image are calculated for the respective linear patterns (S90), and it is determined whether or not the nozzles corresponding to the respective linear patterns are defective nozzles based on the differences (S100).SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a printing device having an ink ejection head (print head) with a large number of nozzles that eject ink, and more particularly to a technology for detecting nozzles in such a printing device that are in a defective ejection state (hereinafter referred to as "faulty nozzles"). [Background technology]

[0002] Inkjet printing devices are widely known, which print by ejecting ink onto a print medium such as printing paper or film using heat or pressure. Inkjet printing devices are provided with a head unit consisting of multiple ink ejection heads, each for a different ink color, extending in a direction perpendicular to the direction of transport of the print medium (hereinafter referred to as the "paper width direction"). Each ink ejection head includes multiple nozzles that eject ink. The gradation of a printed image is expressed by controlling the on / off state of ink ejection from each of the multiple nozzles, or by controlling the drop size of the ink ejected from each of the multiple nozzles in multiple stages.

[0003] In inkjet printing devices such as those described above, if the ejection interval (a time interval, not a spatial interval) becomes long, during printing, problems such as the ink drying out due to evaporation of the solvent near the nozzle, the intrusion of air bubbles into the nozzle, and the adhesion of dust to the nozzle may occur. In other words, nozzle ejection problems may occur. When ejection problems occur, defects in the printed image such as white streaks and missing dots may occur. In such cases, for example, operations are performed to restore the function of the defective nozzle (cleaning or flushing), or alternative droplet ejection is performed by having another nozzle eject the ink droplets that should be ejected by the defective nozzle.

[0004] In order to prevent defects from being included in the printed image shipped as an actual product, defective nozzles are detected based on a captured image (captured data) obtained by capturing the printed image of the test chart with an imaging device (such as an inline scanner). FIG. 31 is a diagram schematically illustrating an example of a portion of such a test chart 90. The test chart 90 is composed of a regular, stepped pattern made up of multiple linear patterns 9 extending in the transport direction of the printing paper. Each linear pattern 9 is formed by ejecting ink from one nozzle multiple times in succession. In the example shown in FIG. 31, the test chart 90 is divided into five blocks 91(1) to 91(5), each containing eight linear patterns 9. The eight linear patterns 9 contained in each block 91 are arranged at equal intervals in the paper width direction.

[0005] A conventional method for detecting defective nozzles will be described below, assuming that the test chart 90 shown in Fig. 31 is used. Note that while the range shown in Fig. 31 is the inspection range, an actual inspection range will contain a much larger number of linear patterns 9. Furthermore, hereinafter, the coordinate in the paper width direction will be referred to as the X coordinate, and the coordinate in the print paper transport direction will be referred to as the Y coordinate.

[0006] Once a captured image of the printed image of the test chart 90 is obtained, the length of the inspection range in the paper width direction and the number of linear patterns 9 per block (in other words, the number of nozzles per block) are calculated based on the captured image. This further calculates the theoretical value of the spacing between two adjacent linear patterns 9 in the paper width direction. The position (position in the captured image) of the leftmost linear pattern 9 in each block 91 (the linear pattern 9 included in the dotted line portion marked with reference numeral 92 in FIG. 31 ) is used as a reference position, and the coordinate value (X coordinate value) of the reference position is added by an integer multiple (1 to 7 times) of the theoretical value to calculate the ideal positions where the second to eighth linear patterns 9 from the left of each block 91 should be formed. If the length of the inspection range in the paper width direction is 40 (the unit of length is omitted here), the number of linear patterns 9 per block is 8, and therefore the theoretical value of the spacing between two adjacent linear patterns 9 in the paper width direction is 5. In this case, if the X coordinate value of the linear pattern 9 at the left end of block 91(2) is 2, then the X coordinate of the ideal position of the fifth linear pattern 9 from the left in block 91(2) is calculated to be 22. After the ideal position of each linear pattern 9 is determined in the above manner, the ideal position of each linear pattern 9 is compared with the actual position in the captured image to determine whether the nozzle corresponding to each linear pattern 9 is a faulty nozzle. In this regard, for example, if the linear pattern 9 corresponding to a certain nozzle is not within a predetermined range from the ideal position, then the nozzle is determined to be experiencing non-ejection, i.e., not ejecting any ink, and if the actual position of the linear pattern 9 corresponding to a certain nozzle is away from the ideal position by more than a predetermined distance, then the nozzle is determined to be experiencing deviation in the landing position.

[0007] In relation to the present invention, Japanese Patent Application Laid-Open Publication No. 2011-201051 discloses a method for accurately identifying a reference position for determining the position of each line (linear pattern) constituting a test pattern (test chart) even when the resolution of the scanned image (captured image) is low. According to this method, reference position detection bars, which are solid images, are provided at the top and bottom of the test pattern, and projection graphs of optical density in the X and Y directions are created for the corner areas (four corners) of the test pattern. Then, by detecting edges where density changes in each projection graph, the X and Y coordinate values ​​of the corners of the test pattern are determined, and these are used as reference positions. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-201051 Summary of the Invention [Problem to be solved by the invention]

[0009] However, with conventional methods for detecting faulty nozzles, if the nozzle corresponding to the linear pattern 9 at the end of each block 91 (in the above example, the left end) is faulty, the ideal position of each linear pattern 9 cannot be accurately determined. For example, if the nozzle corresponding to the end linear pattern 9 is experiencing ejection failure, as shown by the dotted line portion labeled 95 in FIG. 32, or if the nozzle corresponding to the end linear pattern 9 is experiencing a landing position shift, as shown by the dotted line portion labeled 96 in FIG. 33, the ideal position of each linear pattern 9 cannot be accurately determined. Furthermore, with the method disclosed in Japanese Patent Application Laid-Open No. 2011-201051, if the nozzle corresponding to the end of the reference position detection bar is faulty, the projection graph cannot be accurately created, and the X-coordinate value of the corner of the test pattern cannot be accurately detected. Therefore, the position (ideal position) of each line cannot be accurately determined. For these reasons, conventional methods have been unable to detect faulty nozzles with sufficient accuracy.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a printing device that is capable of detecting defective nozzles with higher accuracy than conventional methods. [Means for solving the problem]

[0011] A first invention is a method for detecting defective nozzles in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, the method comprising: a test chart printing step of printing a test chart, which is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and is divided into a plurality of blocks in the second direction while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the first direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation step of calculating, based on the captured image, an actual value of an interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the first direction is a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting step of setting, as a reference position, an actual position of a linear pattern among the (N-2) linear patterns for which the smallest average error is obtained in the error calculation step, for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating a difference in the first direction between the ideal position and an actual position based on the captured image for each linear pattern; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; The present invention is characterized by comprising:

[0012] The second invention is the first invention, When two linear patterns adjacent to the linear pattern corresponding to the reference position in the first direction are defined as a first adjacent linear pattern and a second adjacent linear pattern, the ideal position calculation step is characterized in that the ideal position is calculated based on the actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern.

[0013] The third invention is the second invention, In the ideal position calculation step, the average of the actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern is calculated as an average actual distance, and the ideal position is calculated by regarding the distance between the two linear patterns constituting each linear pattern pair as the average actual distance.

[0014] The fourth invention is the first invention, In the ideal position calculation step, for each of the plurality of blocks, the average of the actual values ​​of linear pattern pairs among the (N-1) linear pattern pairs, for which the difference between the actual value calculated in the actual value calculation step and the theoretical value calculated in the theoretical value calculation step is less than or equal to a predetermined threshold, is calculated as an average actual distance, and the ideal position is calculated by regarding the distance between the two linear patterns constituting each linear pattern pair as the average actual distance.

[0015] The fifth invention is the first invention, the test chart includes a first mark representing a first predetermined position in the first direction and a second mark representing a second predetermined position in the first direction; the defective nozzle detection method includes an image extraction step of extracting an image of a range between the first mark and the second mark in the first direction from the captured image, The theoretical value calculation step is characterized in that the theoretical value is calculated based on the distance between the first mark and the second mark, the number of linear patterns to be included in the image extracted in the image extraction step, and the number of blocks.

[0016] The sixth invention is any one of the first to fifth inventions, The plurality of blocks are K blocks (K is an integer of 3 or more), The test chart is characterized in that, where P is an integer between 2 and K, the N linear patterns included in the Pth block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)th block.

[0017] A seventh aspect of the present invention is a method for detecting defective nozzles in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, the method comprising: a test chart printing step of printing a test chart, which is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and is divided into a plurality of blocks in the second direction while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the first direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation step of calculating, based on the captured image, an actual value of an interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the first direction is a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting step of setting a reference position for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating a difference in the first direction between the ideal position and an actual position based on the captured image for each linear pattern; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that N linear patterns included in a P-th block are formed at positions shifted a certain distance in the first direction from N linear patterns included in a (P-1)-th block, where P is an integer between 2 and K, and For the first block, the Kth block, and the block for which the minimum average error obtained in the error calculation step is equal to or less than a predetermined threshold, the reference position setting step sets the actual position of the linear pattern for which the minimum average error is obtained in the error calculation step among the (N-2) linear patterns as the reference position; For the Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, where Q is an integer between 2 and (K-1) and J is an integer between 2 and (N-1), inclusive, the reference position setting step is characterized in that, if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q-1)th block in the error calculation step is less than the predetermined threshold and the average error obtained in the error calculation step for the Jth linear pattern included in the (Q+1)th block in the error calculation step is less than the predetermined threshold, the reference position is set based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block.

[0018] The eighth invention is the seventh invention. For the Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, the reference position setting step is characterized in that the center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block is set as the reference position.

[0019] A ninth aspect of the present invention is a method for detecting defective nozzles in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, the method comprising: a test chart printing step of printing a test chart divided into a plurality of blocks in the first direction, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the second direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation step of calculating, based on the captured image, an actual value of the interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the second direction is defined as a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting step of setting, as a reference position, an actual position of a linear pattern among the (N-2) linear patterns for which the smallest average error is obtained in the error calculation step, for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating a difference in the second direction between the ideal position and an actual position based on the captured image for each linear pattern; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; The present invention is characterized by comprising:

[0020] A tenth aspect of the present invention is the ninth aspect of the present invention, When two linear patterns adjacent to the linear pattern corresponding to the reference position in the second direction are defined as a first adjacent linear pattern and a second adjacent linear pattern, the ideal position calculation step is characterized in that the ideal position is calculated based on the actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern.

[0021] An eleventh aspect of the present invention is the tenth aspect of the present invention, In the ideal position calculation step, the average of the actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern is calculated as an average actual distance, and the ideal position is calculated by regarding the distance between the two linear patterns constituting each linear pattern pair as the average actual distance.

[0022] A twelfth aspect of the present invention is the ninth aspect of the present invention, In the ideal position calculation step, for each of the plurality of blocks, the average of the actual values ​​of linear pattern pairs among the (N-1) linear pattern pairs, for which the difference between the actual value calculated in the actual value calculation step and the theoretical value calculated in the theoretical value calculation step is less than or equal to a predetermined threshold, is calculated as an average actual distance, and the ideal position is calculated by regarding the distance between the two linear patterns constituting each linear pattern pair as the average actual distance.

[0023] A thirteenth aspect of the present invention is a method for detecting defective nozzles in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, the method comprising: a test chart printing step of printing a test chart divided into a plurality of blocks in the first direction, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the second direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation step of calculating, based on the captured image, an actual value of the interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the second direction is defined as a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting step of setting a reference position for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating a difference in the second direction between the ideal position and an actual position based on the captured image for each linear pattern; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that N linear patterns included in a P-th block are formed at positions shifted a certain distance in the first direction from N linear patterns included in a (P-1)-th block, where P is an integer between 2 and K, and For the first block, the Kth block, and the block for which the minimum average error obtained in the error calculation step is equal to or less than a predetermined threshold, the reference position setting step sets the actual position of the linear pattern for which the minimum average error is obtained in the error calculation step among the (N-2) linear patterns as the reference position; For the Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, where Q is an integer between 2 and (K-1) and J is an integer between 2 and (N-1), inclusive, the reference position setting step is characterized in that, if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q-1)th block in the error calculation step is less than the predetermined threshold and the average error obtained in the error calculation step for the Jth linear pattern included in the (Q+1)th block in the error calculation step is less than the predetermined threshold, the reference position is set based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block.

[0024] A fourteenth aspect of the present invention is the thirteenth aspect of the present invention, For the Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, the reference position setting step is characterized in that the center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block is set as the reference position.

[0025] A fifteenth aspect of the present invention is a printing device, a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device, the image capturing device capturing a printed image of the test chart, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer equal to or greater than 4) each of the plurality of blocks being formed so that the interval between two adjacent linear patterns in the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation unit that calculates, based on the captured image, an actual value of an interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in the first direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting unit that sets, as a reference position, an actual position of a linear pattern that has obtained the smallest average error among the (N-2) linear patterns by the error calculation unit for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; The present invention is characterized by comprising:

[0026] A sixteenth aspect of the present invention is a printing device, comprising: a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device, the image capturing device capturing a printed image of the test chart, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer equal to or greater than 4) each of the plurality of blocks being formed so that the interval between two adjacent linear patterns in the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation unit that calculates, based on the captured image, an actual value of an interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in the first direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting unit that sets a reference position for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that N linear patterns included in a P-th block are formed at positions shifted a certain distance in the first direction from N linear patterns included in a (P-1)-th block, where P is an integer between 2 and K, and For the first block, the Kth block, and the block for which the minimum average error obtained by the error calculation unit is equal to or less than a predetermined threshold, the reference position setting unit sets the actual position of the linear pattern for which the minimum average error is obtained by the error calculation unit among the (N-2) linear patterns as the reference position; For the Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, where Q is an integer between 2 and (K-1) and J is an integer between 2 and (N-1), the reference position setting unit sets the reference position based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block if the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q-1)th block is less than the predetermined threshold and the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q+1)th block is less than the predetermined threshold.

[0027] A seventeenth aspect of the present invention is the sixteenth aspect of the present invention, For the Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, the reference position setting unit sets the center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block as the reference position.

[0028] An eighteenth invention is a printing device, a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a test chart that is divided into a plurality of blocks in the first direction and that is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, and that detects faulty nozzles from among the plurality of nozzles based on an image obtained by the imaging device capturing a printed image of the test chart, the test chart including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in a second direction orthogonal to the first direction is constant, and Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation unit that calculates, based on the captured image, an actual value of the interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in position in the second direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting unit that sets, as a reference position, an actual position of a linear pattern that has obtained the smallest average error among the (N-2) linear patterns by the error calculation unit for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; The present invention is characterized by comprising:

[0029] A nineteenth aspect of the present invention is a printing device, a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a test chart that is divided into a plurality of blocks in the first direction and that is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, and that detects faulty nozzles from among the plurality of nozzles based on an image obtained by the imaging device capturing a printed image of the test chart, the test chart including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in a second direction orthogonal to the first direction is constant, and Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation unit that calculates, based on the captured image, an actual value of the interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in position in the second direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other as a second linear pattern pair; a reference position setting unit that sets a reference position for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that N linear patterns included in a P-th block are formed at positions shifted a certain distance in the first direction from N linear patterns included in a (P-1)-th block, where P is an integer between 2 and K, and For the first block, the Kth block, and the block for which the minimum average error obtained by the error calculation unit is equal to or less than a predetermined threshold, the reference position setting unit sets the actual position of the linear pattern for which the minimum average error is obtained by the error calculation unit among the (N-2) linear patterns as the reference position; For the Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, where Q is an integer between 2 and (K-1) and J is an integer between 2 and (N-1), the reference position setting unit sets the reference position based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block if the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q-1)th block is less than the predetermined threshold and the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q+1)th block is less than the predetermined threshold.

[0030] The 20th invention is the 19th invention, For the Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, the reference position setting unit sets the center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block as the reference position. [Effects of the Invention]

[0031] According to the first aspect of the present invention, a captured image of a printed image of a test chart divided into multiple blocks in a direction perpendicular to the direction in which the multiple nozzles are arranged is used to calculate an average error representing how close the spacing between two adjacent linear patterns in the direction in which the multiple nozzles are arranged is to a theoretical value for each linear pattern included in each of the multiple blocks (excluding the linear patterns at both ends). The actual position of the linear pattern with the smallest average error is then set as the reference position, and the ideal position of each linear pattern is calculated based on the reference position. Unlike conventional methods, this allows the accurate determination of the reference position for each block, even if the nozzle corresponding to the linear pattern at the end of each block is defective, thereby accurately determining the ideal position of each linear pattern. As a result, the difference between the actual position of each linear pattern and the ideal position (the difference in the direction in which the multiple nozzles are arranged) is accurately calculated, making it possible to accurately determine whether the nozzle corresponding to each linear pattern is defective. As described above, a printing device can detect defective nozzles with greater accuracy than conventional methods. This will, for example, reduce the waste of printing media and ink caused by reprinting, thereby contributing to the achievement of the SDGs (Sustainable Development Goals).

[0032] According to the second invention, the actual values ​​of the distance between the linear pattern corresponding to the reference position and each of the two linear patterns adjacent to it (adjacent in the direction in which the multiple nozzles are arranged) are close to the theoretical values, and therefore, by calculating the ideal position based on such actual values, the ideal position of each linear pattern can be determined more accurately.

[0033] According to the third aspect of the invention, the same effects as those of the second aspect of the invention can be obtained.

[0034] According to the fourth aspect of the present invention, the average actual distance between the two linear patterns constituting a linear pattern pair is calculated using only images of normally printed linear patterns. Since the ideal position is calculated assuming that the distance between the two linear patterns constituting each linear pattern pair is the average actual distance, the ideal position of each linear pattern can be determined with higher accuracy.

[0035] According to the fifth aspect of the present invention, when processing to detect faulty nozzles, an image of the range between the two identified positions is extracted, which allows the number of nozzles corresponding to the range to be processed to be accurately identified, thereby improving the accuracy of detecting faulty nozzles.

[0036] According to the sixth aspect of the present invention, the multiple linear patterns included in the test chart are arranged regularly, so that defective nozzles can be detected more accurately by visually checking the captured image of the test chart.

[0037] According to the seventh aspect of the present invention, for each linear pattern (excluding the linear patterns at both ends) included in each of a plurality of blocks in a captured image of a printed image of a test chart, an average error is calculated to indicate how close the spacing between two adjacent linear patterns is to a theoretical value, and for a block in which the minimum average error is greater than a predetermined threshold, a reference position is set based on the positions of the linear patterns in the two adjacent blocks. As a result, the ideal position of each linear pattern can be correctly determined even for blocks in which there is no linear pattern pair (two adjacent linear patterns) with a spacing close to the theoretical value.

[0038] According to the eighth aspect of the invention, the same effects as those of the seventh aspect of the invention can be obtained.

[0039] According to the ninth aspect of the present invention, based on a captured image of a printed image of a test chart divided into multiple blocks in the direction in which the multiple nozzles are arranged, an average error is calculated for each linear pattern (excluding the linear patterns at both ends) included in each of the multiple blocks, representing how close the distance between two adjacent linear patterns in a direction perpendicular to the direction in which the multiple nozzles are arranged is to a theoretical value. The actual position of the linear pattern for which the smallest average error is obtained is then set as a reference position, and the ideal position of each linear pattern is calculated based on the reference position. Unlike conventional methods, this allows the reference position for each block to be accurately determined, even if a nozzle corresponding to a linear pattern at the end of each block is defective, thereby accurately determining the ideal position of each linear pattern. As a result, the difference between the actual position of each linear pattern and the ideal position (the difference in the direction perpendicular to the direction in which the multiple nozzles are arranged) can be accurately calculated, making it possible to accurately determine whether the nozzle corresponding to each linear pattern is defective. As described above, a printing device can detect defective nozzles with greater accuracy than conventional methods. This will, for example, reduce the waste of printing media and ink caused by reprinting, thereby contributing to the achievement of the SDGs (Sustainable Development Goals).

[0040] According to the tenth aspect of the present invention, the actual values ​​of the distance between the linear pattern corresponding to the reference position and each of two adjacent linear patterns positioned in a direction perpendicular to the direction in which the multiple nozzles are arranged are close to the theoretical values, and therefore, by calculating the ideal position based on such actual values, the ideal position of each linear pattern can be determined more accurately.

[0041] According to the eleventh aspect of the invention, the same effects as those of the tenth aspect of the invention can be obtained.

[0042] According to the twelfth aspect of the invention, the same effects as those of the fourth aspect of the invention can be obtained.

[0043] According to the thirteenth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained.

[0044] According to the fourteenth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained.

[0045] According to the fifteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0046] According to the sixteenth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained.

[0047] According to the seventeenth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained.

[0048] According to the eighteenth aspect of the present invention, the same effects as those of the ninth aspect of the present invention can be obtained.

[0049] According to the nineteenth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained.

[0050] According to the twentieth aspect of the present invention, the same effects as those of the seventh aspect of the present invention can be obtained. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a schematic diagram illustrating an example of the configuration of an inkjet printing apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing an example of the configuration of a recording section in the first embodiment. [Figure 3] FIG. 3 is a diagram for explaining an example of nozzle arrangement in the first embodiment. [Figure 4] FIG. 2 is a block diagram showing a hardware configuration of a print control device in the first embodiment. [Figure 5] FIG. 2 is a block diagram showing a schematic functional configuration of a control unit that is realized by a print control program being executed by a print control device in the first embodiment. [Figure 6] FIG. 2 is a diagram schematically showing the overall configuration of a test chart in the first embodiment. [Figure 7]FIG. 2 is a diagram schematically showing a part of a test chart in the first embodiment. [Figure 8] FIG. 2 is a diagram schematically showing a part of the entire test chart that corresponds to an inspection range for one processing in the first embodiment. [Figure 9] FIG. 4 is a diagram for explaining an outline of how a faulty nozzle is detected in the first embodiment. [Figure 10] FIG. 4 is a diagram for explaining an outline of how a faulty nozzle is detected in the first embodiment. [Figure 11] FIG. 2 is a block diagram showing a detailed configuration of a faulty nozzle detection unit in the first embodiment. [Figure 12] 6 is a flowchart showing a detailed procedure for processing to detect a faulty nozzle in the first embodiment. [Figure 13] FIG. 10 is a diagram for explaining that each process is performed based on the position of the center of gravity of a linear pattern in the first embodiment. [Figure 14] FIG. 10 is a diagram for explaining that each process is performed based on the position of the center of gravity of a linear pattern in the first embodiment. [Figure 15] FIG. 2 is a diagram for explaining a linear pattern pair in the first embodiment. [Figure 16] FIG. 10 is a diagram for explaining calculation of an average error in the first embodiment. [Figure 17] FIG. 2 is a diagram for explaining setting of a reference position in the first embodiment. [Figure 18] FIG. 10 is a diagram for explaining calculation of an ideal position in the first embodiment. [Figure 19] FIG. 10 is a diagram for explaining calculation of an average actual interval in the first modified example of the first embodiment. [Figure 20] FIG. 10 is a diagram for explaining calculation of an ideal position in the first modified example of the first embodiment. [Figure 21]FIG. 10 is a diagram for explaining setting of a reference position in a second modified example of the first embodiment. [Figure 22] FIG. 10 is a diagram for explaining an outline of a second embodiment of the present invention. [Figure 23] FIG. 10 is a diagram for explaining blocks in the second embodiment. [Figure 24] FIG. 11 is a diagram for explaining a theoretical value of the interval between two linear patterns in the second embodiment. [Figure 25] FIG. 11 is a diagram for explaining a linear pattern pair in the second embodiment. [Figure 26] FIG. 11 is a diagram for explaining setting of a reference position in the second embodiment. [Figure 27] FIG. 11 is a diagram for explaining calculation of an ideal position in the second embodiment. [Figure 28] FIG. 10 is a diagram for explaining calculation of an average actual interval in the first modified example of the second embodiment. [Figure 29] FIG. 10 is a diagram for explaining calculation of an ideal position in the first modified example of the second embodiment. [Figure 30] FIG. 10 is a diagram for explaining setting of a reference position in a second modified example of the second embodiment. [Figure 31] FIG. 10 is a diagram schematically illustrating an example of a part of a test chart in a conventional example. [Figure 32] 10A and 10B are diagrams for explaining why the ideal position of each linear pattern cannot be correctly determined in a conventional example. [Figure 33] 10A and 10B are diagrams for explaining why the ideal position of each linear pattern cannot be correctly determined in a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0052] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0053] <1. First embodiment> <1.1 Overall configuration of inkjet printing device> FIG. 1 is a schematic diagram showing an example of the configuration of an inkjet printing apparatus 10 according to a first embodiment of the present invention. This inkjet printing apparatus 10 is composed of a printing press main body 200 and a print control device 100 that controls the operation of the printing press main body 200. This inkjet printing apparatus 10 outputs a print image onto printing paper 5 as a printing medium, without using printing plates, based on print data, which is data that has been rasterized and is sent via a network such as a LAN. Note that the present invention can also be applied when a printing medium other than printing paper (for example, film) is used.

[0054] The printing machine main body 200 includes a paper feed section 202 that supplies printing paper (in this example, rolled printing paper) 5 to the printing mechanism 201, the printing mechanism 201 that prints on the printing paper 5, and a paper winding section 208 that winds up the printing paper 5 into a roll after printing.

[0055] The printing mechanism 201 includes a first drive roller 203 for transporting the printing paper 5 inside, a plurality of support rollers 204 for transporting the printing paper 5 inside the printing mechanism 201, a recording unit 205 for recording a print image on the printing paper 5, a drying mechanism 206 for drying the printing paper 5 on which the print image has been recorded, and a second drive roller 207 for outputting the printing paper 5 from inside the printing mechanism 201. The recording unit 205 is composed of a K head unit 25K that ejects K (black) ink, a C head unit 25C that ejects C (cyan) ink, an M head unit 25M that ejects M (magenta) ink, and a Y head unit 25Y that ejects Y (yellow) ink. The printing mechanism 201 also includes an inline scanner 40 as an imaging device that captures the print image recorded on the printing paper 5 by the recording unit 205. The captured image (captured data) obtained by capturing the print image with the inline scanner 40 is sent to the print control device 100, and the captured image is used in the print control device 100 to perform a process of detecting defective nozzles. Note that, in the following, when there is no need to distinguish between the colors of ink ejected from the head units, the head units will be denoted by the reference symbol 25.

[0056] <1.2 Recording unit configuration> FIG. 2 is a plan view showing an example of the configuration of the recording unit 205. As shown in FIG. 2, the recording unit 205 is composed of a K-color head unit 25K, a C-color head unit 25C, an M-color head unit 25M, and a Y-color head unit 25Y, which are arranged in a row in the transport direction of the printing paper 5. Each head unit 25 is composed of a plurality of ink ejection heads (print heads) 251 arranged in a staggered pattern. Each ink ejection head 251 includes a large number of nozzles (not shown in FIG. 2) that eject ink. Each nozzle of the ink ejection head 251 included in the K-color head unit 25K ejects K-color ink, each nozzle of the ink ejection head 251 included in the C-color head unit 25C ejects C-color ink, each nozzle of the ink ejection head 251 included in the M-color head unit 25M ejects M-color ink, and each nozzle of the ink ejection head 251 included in the Y-color head unit 25Y ejects Y-color ink.

[0057] FIG. 3 is a diagram illustrating the arrangement of nozzles 252 in an ink ejection head 251. Typically, the ink ejection head 251 includes multiple rows of nozzle groups, each consisting of a plurality of nozzles 252 arranged in the paper width direction. In the example shown in FIG. 3, the ink ejection head 251 includes four rows of nozzle groups. The paper width direction corresponds to the first direction, and the transport direction of the printing paper 5 corresponds to the second direction. In FIG. 3, the portion labeled with reference numeral 41 schematically shows the landing positions (landing positions in the paper width direction) of ink ejected from each nozzle 252 on the printing paper 5. The multiple nozzles 252 in the ink ejection head 251 are arranged so that the landing positions of ink ejected from the nozzles 252 included in the first row of nozzle groups, the landing positions of ink ejected from the nozzles 252 included in the second row of nozzle groups, the landing positions of ink ejected from the nozzles 252 included in the third row of nozzle groups, and the landing positions of ink ejected from the nozzles 252 included in the fourth row of nozzle groups are all different from one another. For example, the landing position of ink ejected from each nozzle 252 included in the first nozzle group is a position between the landing position of ink ejected from the nozzles 252 included in the third nozzle group and the landing position of ink ejected from the nozzles 252 included in the fourth nozzle group. In the example shown in Fig. 3, the landing position 42 of ink ejected from the nozzles labeled 252(p) is a position between the landing position 43 of ink ejected from the nozzles labeled 252(q) and the landing position 44 of ink ejected from the nozzles labeled 252(r). Note that the arrangement shown in Fig. 3 is just one example, and the specific arrangement of the multiple nozzles 252 is not particularly limited as long as the multiple nozzles 252 are arranged in the paper width direction.

[0058] In this embodiment, a test chart or the like is printed by ejecting ink from a fixed ink ejection head 251 while the printing paper 5 is moving. That is, in this embodiment, a one-pass inkjet printing device 10 is used. However, the present invention can also be applied to a shuttle inkjet printing device. In a shuttle inkjet printing device, the ink ejection head moves from one end of a printing medium such as printing paper to the other end while ejecting ink (i.e., after moving in the main scanning direction), and then moves a predetermined distance in the sub-scanning direction (a direction perpendicular to the main scanning direction). Then, the ink ejection head moves from the other end of the printing medium to the one end while ejecting ink. Then, the ink ejection head again moves a predetermined distance in the sub-scanning direction. In this way, in a shuttle inkjet printing device, the ink ejection head moves in the sub-scanning direction to form a print image on the entire printing medium from top to bottom. From the above, the present invention can be applied if an inkjet printing device is used that prints by relatively moving the positional relationship between the ink ejection head and the printing medium in a direction perpendicular to the direction in which multiple nozzles are arranged (paper width direction).

[0059] <1.3 Hardware configuration of print control device> FIG. 4 is a block diagram showing the hardware configuration of the print control device 100. As shown in FIG. 4, the print control device 100 includes a main body 110, an auxiliary storage device 121, an optical disk drive 122, a display unit 123, a keyboard 124, and a mouse 125. The main body 110 includes a CPU 111, a memory 112, a first disk interface unit 113, a second disk interface unit 114, a display control unit 115, an input interface unit 116, and a communication interface unit 117. The CPU 111, the memory 112, the first disk interface unit 113, the second disk interface unit 114, the display control unit 115, the input interface unit 116, and the communication interface unit 117 are connected to one another via a system bus. The auxiliary storage device 121 is connected to the first disk interface unit 113. The optical disk drive 122 is connected to the second disk interface unit 114. The display control unit 115 is connected to a display unit (display device) 123. A keyboard 124 and a mouse 125 are connected to the input interface unit 116. The printing machine main body 200 is connected to the communication interface unit 117 via a communication cable. The communication interface unit 117 is also connected to the LAN 4. The auxiliary storage device 121 is a magnetic disk device or the like. An optical disk 19, which is a computer-readable recording medium such as a CD-ROM or DVD-ROM, is inserted into the optical disk drive 122. The display unit 123 is a liquid crystal display or the like. The display unit 123 is used to display information desired by the operator. The keyboard 124 and mouse 125 are used by the operator to input instructions to this printing control device 100.

[0060] The auxiliary storage device 121 stores a print control program 13 (a program for controlling the execution of printing processing by the printing machine main body 200). In this embodiment, the print control program 13 includes a subprogram for detecting defective nozzles. The CPU 111 reads the print control program 13 stored in the auxiliary storage device 121 into the memory 112 and executes it, thereby realizing various functions of the print control device 100. The memory 112 includes RAM (Random Access Memory) and ROM (Read Only Memory). The memory 112 functions as a work area for the CPU 111 to execute the print control program 13 stored in the auxiliary storage device 121. The print control program 13 is provided by being stored on the computer-readable recording medium (non-transitory recording medium). That is, a user, for example, purchases an optical disc 19 as a recording medium for the print control program 13, inserts it into the optical disc drive 122, reads the print control program 13 from the optical disc 19, and installs it in the auxiliary storage device 121.

[0061] In the example shown in FIG. 4, the print control device 100 is provided with only one CPU 111 as a processor, but this is not limited to this. A configuration using multiple processors, such as a configuration using multiple CPUs, can also be adopted. As the processor, in addition to the CPU 111, an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), etc. can also be adopted. A combination of multiple types of processors can also be used. For example, with regard to the internal components of the control unit 130 (described later, see FIG. 5), some of the components and the remaining components can be implemented by different processors. Furthermore, a configuration including an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) can also be adopted.

[0062] <1.4 Functional configuration> 5 is a block diagram showing a schematic functional configuration of the control unit 130 that is realized by executing the print control program 13 on the print control device 100. The control unit 130 includes a transport control unit 131, an ink discharge control unit 132, a drying control unit 133, an imaging control unit 134, a data storage unit 135, a defective nozzle detection unit 136, a print data correction unit 137, and a halftone processing unit 138.

[0063] The conveyance control unit 131 controls the speed (conveyance speed) at which the conveyance mechanism 29 conveys the printing paper 5. The conveyance mechanism 29 is realized by a paper delivery unit 202, a first drive roller 203, a plurality of support rollers 204, a second drive roller 207, and a paper winding unit 208 (see FIG. 1). The drying control unit 133 controls the temperature (drying temperature) at which the drying mechanism 206 dries the printing paper 5 after printing. The imaging control unit 134 controls the timing at which the inline scanner 40 captures the image of the printed image.

[0064] The data storage unit 135 temporarily stores print data 50 sent via the network. The data storage unit 135 also stores test chart data 51 representing a test chart used in the process of detecting defective nozzles. The test chart will be described in detail later.

[0065] The defective nozzle detection unit 136 detects defective nozzles based on a captured image (captured image data) 60 obtained by capturing an image of the printed image of the test chart with the inline scanner 40. Then, defective nozzle information 52 that identifies the defective nozzles is output from the defective nozzle detection unit 136. The defective nozzle detection unit 136 will be described in detail later.

[0066] Based on the defective nozzle information 52, the print data correction unit 137 corrects the print data 50 stored in the data storage unit 135 to compensate for the nozzle ejection defects. For example, the print data 50 is corrected so that the amount of ink ejected from the nozzles surrounding the nozzle determined to be defective increases. The corrected print data 53 is then output from the print data correction unit 137.

[0067] The halftone processing unit 138 performs halftone processing on the data to be printed, thereby generating halftone image data 54 that includes information indicating the ink dot size corresponding to each pixel. For example, three ink dot sizes (large, medium, and small) are prepared. In this embodiment, halftone processing is performed on the test chart data 51 and the corrected print data 53 output from the print data correction unit 137. Note that the specific method of halftone processing is not particularly limited, and known methods such as error diffusion and dithering can be used.

[0068] The ink discharge control unit 132 controls the discharge of ink from each nozzle 252 included in the four head units 25K, 25C, 25M, and 25Y that make up the recording unit 205, based on the halftone image data 54 generated by the halftone processing unit 138. For example, the ink discharge timing and the ink discharge amount are controlled.

[0069] <1.5 Test Chart> Next, the test chart used in the process of detecting defective nozzles will be described. Fig. 6 is a diagram schematically illustrating the overall configuration of the test chart 30. The test chart 30 includes a K chart 30(K) formed by ejecting ink from the nozzles 252 included in the K head unit 25K, a C chart 30(C) formed by ejecting ink from the nozzles 252 included in the C head unit 25C, an M chart 30(M) formed by ejecting ink from the nozzles 252 included in the M head unit 25M, and a Y chart 30(Y) formed by ejecting ink from the nozzles 252 included in the Y head unit 25Y. The K chart 30(K), the C chart 30(C), the M chart 30(M), and the Y chart 30(Y) are arranged side by side in the transport direction of the printing paper 5.

[0070] FIG. 7 is a schematic diagram showing a portion of a test chart 30. This test chart 30 is composed of a regular, stepped pattern consisting of numerous linear patterns 3 extending in the transport direction of the printing paper 5. Each linear pattern 3 is formed by ejecting ink from one nozzle 252 multiple times (e.g., 52 times) in succession. This test chart 30 also includes multiple nozzle number identification marks 32. By defining the range between two adjacent nozzle number identification marks 32 as the inspection range for one process when detecting defective nozzles, the number of nozzles 252 corresponding to the inspection range can be accurately identified, thereby improving the accuracy of defective nozzle detection. In the example shown in FIG. 7, the test chart 30 is divided into 16 blocks 31(1) to 31(16), and multiple linear patterns 3 are arranged at equal intervals in the paper width direction in each block 31. For ease of explanation, the linear patterns may be designated by a number other than 3. Each of the multiple nozzle number identification marks 32 is formed using multiple (e.g., 16) nozzles 252 adjacent to each other in the paper width direction. Since it is extremely rare for multiple (e.g., 16) nozzles 252 adjacent to each other in the paper width direction to malfunction at the same time, the nozzle number identification marks 32 are reliably formed.

[0071] For ease of explanation, unless otherwise specified, it is assumed below that the portion of the entire test chart 30 corresponding to the inspection range 6 (the range between two nozzle number identification marks 32) for one processing cycle is as shown in FIG. 8. The test chart 30 shown in FIG. 8 is divided into five blocks 31(1) to 31(5), each including five linear patterns 3. The length of the inspection range 6 in the paper width direction is 25 (again, the unit of length is omitted). Note that the horizontal dotted line labeled 71 in FIG. 8 and the vertical dotted line labeled 72 in FIG. 8 are dotted lines shown for explanatory purposes, and these dotted lines are not actually printed together with the linear patterns 3 (the same applies to FIGS. 22 and 23).

[0072] Here, we will generalize the test chart 30 in the portion corresponding to the inspection range 6. The test chart 30 is composed of a plurality of linear patterns 3 to be formed by ejecting ink from a plurality of nozzles 252, where K is an integer of 3 or greater, and is divided into K blocks in the transport direction of the printing paper 5. Where N is an integer of 4 or greater, each of the K blocks includes N linear patterns 3 to be formed so that the spacing between two adjacent linear patterns 3 in the paper width direction is constant. Where P is an integer of 2 or greater and K or less, the test chart 30 is configured so that the N linear patterns 3 included in the Pth block are each formed at a position shifted a certain distance in the paper width direction from the N linear patterns 3 included in the (P-1)th block.

[0073] <1.6 How to detect defective nozzles> A method for detecting faulty nozzles will be described below. In this embodiment, faulty nozzles are detected based on the position (X coordinate value) of the linear pattern 3 in the captured image 60 in the paper width direction. In a second embodiment, which will be described later, faulty nozzles are detected based on the position (Y coordinate value) of the linear pattern 3 in the captured image 60 in the transport direction of the printing paper 5.

[0074] <1.6.1 Overview> In this embodiment, the distance between two linear patterns 3 adjacent in the paper width direction is determined based on the captured image 60 of the printed image of the test chart 30. For each linear pattern 3 other than the linear patterns 3 located at both ends in each block 31, the distance between the linear pattern 3 to the left (hereinafter referred to as the "first distance value") and the distance between the linear pattern 3 to the right (hereinafter referred to as the "second distance value") are obtained. Then, when the average of the "difference between the first distance value and the theoretical value (the theoretical value of the distance between two linear patterns 3)" and the "difference between the second distance value and the theoretical value" is defined as the "average error," the position (position in the captured image 60) of the linear pattern 3 at which the smallest average error is obtained in each block 31 is set as the reference position. The average of the first and second spacing values ​​for the linear patterns 3 corresponding to the reference position set in this way is found as the "average actual spacing," and the ideal position of each linear pattern 3 is found by adding or subtracting an integer multiple of the average actual spacing to or from the coordinate value (X coordinate value) of that reference position. By comparing the ideal position found in this way with the actual position in the captured image 60, it is determined whether or not the nozzle corresponding to each linear pattern 3 is a faulty nozzle.

[0075] Assuming that the captured image 60 of the printed image of the test chart 30 is as shown in FIG. 9, focus on block 31(2) in FIG. 9. The dotted line portion labeled 731 indicates the spacing between the two linear patterns 3 in block 31(2). The length of the inspection area 6 in the paper width direction is 25, and the number of linear patterns 3 per block is 5, so the theoretical spacing between the two linear patterns 3 is 5. Therefore, in this case, the linear pattern 3 with the smallest average error among the linear patterns 3 included in block 31(2) is the linear pattern labeled 732. Therefore, the position of this linear pattern 732 is set as the reference position. Since the average actual spacing is 5, as shown in FIG. 10, the ideal positions of the linear patterns 3 other than linear pattern 732 (see the dotted line portions labeled 741 to 744) can be determined by adding or subtracting an integer multiple of 5 to or from the X coordinate of the reference position (see the dotted line portion labeled 733).

[0076] <1.6.2 Details of detecting defective nozzles> Fig. 11 is a block diagram showing the detailed configuration of the defective nozzle detection unit 136. As shown in Fig. 11, the defective nozzle detection unit 136 includes a theoretical value calculation unit 361, an actual value calculation unit 362, an error calculation unit 363, a reference position setting unit 364, an ideal position calculation unit 365, a difference calculation unit 366, and a defect determination unit 367.

[0077] 12 is a flowchart showing the detailed steps of the process for detecting defective nozzles. First, a test chart 30 is printed (step S10). Specifically, halftone processing is performed on the test chart data 51 stored in the data storage unit 135 to generate halftone image data 54, and the ink discharge control unit 132 controls the amount of ink discharged from each nozzle 252 based on the halftone image data 54, thereby forming a printed image of the test chart 30 on the printing paper 5 (see FIG. 5).

[0078] After printing the test chart 30, the printed image of the test chart 30 is imaged by the in-line scanner 40 (step S20). The imaged image (image data) 60 thus obtained is provided to the control unit .

[0079] The captured image 60 obtained by the inline scanner 40 capturing the printed image of the test chart 30 is multi-tone image data, but the processes from step S40 onward are performed on binary image data. Therefore, a process of binarizing the multi-tone image data is performed (not shown in the flowchart). Furthermore, the linear patterns 3 in the captured image 60 are not necessarily straight lines as shown in FIG. 13 . The linear patterns 3 in the captured image 60 may be, for example, images as shown in FIG. 14 . Therefore, in the processes from step S40 onward, calculations related to position are performed based on the center of gravity position of each linear pattern 3 in the paper width direction in the captured image 60. However, as long as the position can be clearly identified, calculations related to position may be performed based on a position other than the center of gravity position. For example, calculations related to position may be performed based on the coordinates of the left end (or right end) of the detected linear pattern 3 in the paper width direction.

[0080] After the binarized captured image 60 is obtained, an image of the inspection range 6 is extracted (step S30). In this regard, as described above, the test chart 30 includes a plurality of nozzle number identification marks 32. In step S30, an image of the range between two nozzle number identification marks 32 is extracted from the captured image 60 as the image of the inspection range 6. Since the image of the inspection range 6 is extracted in this way in step S30, the processing from step S40 onwards is performed for each inspection range 6. Note that, hereinafter, the image extracted in step S30 will also be referred to as the "captured image 60."

[0081] Thereafter, the theoretical value calculation unit 361 calculates a theoretical value 61 of the distance between two adjacent linear patterns 3 in the paper width direction (step S40). Specifically, in step S40, the theoretical value 61 is calculated based on the distance between the center of gravity in the paper width direction of the nozzle number identification mark 32 (hereinafter referred to as the "first mark") corresponding to the left end of the inspection range 6 and the center of gravity in the paper width direction of the nozzle number identification mark 32 (hereinafter referred to as the "second mark") corresponding to the right end of the inspection range 6, the number of linear patterns 3 to be included in the image (captured image 60) extracted in step S30, and the number of blocks 31. The center of gravity of the first mark corresponds to a first predetermined position, and the center of gravity of the second mark corresponds to a second predetermined position. In the example of the test chart 30 shown in FIG. 8, the number of linear patterns 3 to be included in the image (captured image 60) extracted in step S30 is 25, and the number of blocks 31 is 5. Therefore, the number of linear patterns 3 to be included in each block 31 is 5. Furthermore, the distance between the first mark and the second mark is 25. Therefore, by dividing 25 by 5, the theoretical value 61 is calculated as 5.

[0082] Next, the actual value calculation unit 362 calculates the actual value (value in the captured image 60) 62 of the distance between two linear patterns 3 for all combinations of two linear patterns 3 adjacent in the paper width direction based on the captured image 60 (step S50). In this regard, if two linear patterns 3 adjacent in the paper width direction are defined as a "linear pattern pair," each block 31 includes four linear pattern pairs. For example, if the five linear patterns 3 included in block 31(3) are labeled with symbols 75(1) to 75(5) as shown in FIG. 15, block 31(3) includes a linear pattern pair PA1 consisting of linear pattern 75(1) and linear pattern 75(2), a linear pattern pair PA2 consisting of linear pattern 75(2) and linear pattern 75(3), a linear pattern pair PA3 consisting of linear pattern 75(3) and linear pattern 75(4), and a linear pattern pair PA4 consisting of linear pattern 75(4) and linear pattern 75(5). In this way, four linear pattern pairs are formed by the five linear patterns 3. In step S50, an actual value 62 of the distance between two linear patterns 3 that form such a linear pattern pair is calculated. As described above, in step S50, a combination of two linear patterns 3 adjacent in the paper width direction is considered to be a linear pattern pair, and for each of the (N-1) (four in the example shown in Figure 8) linear pattern pairs composed of N (five in the example shown in Figure 8) linear patterns 3 contained in each of the multiple blocks 31, the actual value 62 of the spacing between the two linear patterns 3 constituting the linear pattern pair is calculated based on the captured image 60.

[0083] Next, the error calculation unit 363 calculates the average error 63 described above for each linear pattern 3 except for the linear patterns 3 located at both ends of each block 31 (step S60). In this regard, the linear patterns 3 other than the linear patterns 3 located at both ends of each block 31 form linear pattern pairs with the linear pattern 3 adjacent to them on the left, and also form linear pattern pairs with the linear pattern 3 adjacent to them on the right. Here, one of the two linear pattern pairs thus formed is defined as a "first linear pattern pair," and the other as a "second linear pattern pair." In step S60, for each linear pattern 3 except for the linear patterns 3 located at both ends of each block 31, the difference between the theoretical value 61 calculated in step S40 and the actual value (corresponding to the above-mentioned first interval value) 62 calculated in step S50 for the first linear pattern pair is calculated as a first error, and the difference between the theoretical value 61 calculated in step S40 and the actual value (corresponding to the above-mentioned second interval value) 62 calculated in step S50 for the second linear pattern pair is calculated as a second error. Then, the average of the first error and the second error is calculated as an average error 63. As described above, in step S60, for each of the (N-2) (3 in the example shown in Figure 8) linear patterns 3 out of the N (5 in the example shown in Figure 8) linear patterns 3 included in each of the multiple blocks 31, excluding the linear patterns 3 at both ends, a first error which is the difference between the theoretical value 61 and the actual value 62 for the first linear pattern pair, a second error which is the difference between the theoretical value 61 and the actual value 62 for the second linear pattern pair, and an average error 63 which is the average of the first error and the second error are calculated.

[0084] Calculation of the average error 63 will be further described with reference to Fig. 16. In Fig. 16, the linear pattern of interest is denoted by reference symbol 76, the linear pattern that constitutes the first linear pattern pair with the linear pattern 76 is denoted by reference symbol 76L, and the linear pattern that constitutes the second linear pattern pair with the linear pattern 76 is denoted by reference symbol 76R. If the theoretical value 61 calculated in step S40 is the distance value indicated by the arrow denoted by reference symbol L0, a difference (first error E1) between an actual value L1 (the distance between the linear pattern 76 and the linear pattern 76L) for the first linear pattern pair and the theoretical value L0, and a difference (second error E2) between an actual value L2 (the distance between the linear pattern 76 and the linear pattern 76R) for the second linear pattern pair and the theoretical value L0 are calculated, and further, the average of the first error E1 and the second error E2 is calculated as the average error 63.

[0085] After calculating the average error 63, the reference position setting unit 364 sets the actual position of the linear pattern 3 for which the smallest average error 63 was obtained as the reference position 64 for each block 31 (step S70). Specifically, in step S70, for each of the multiple blocks 31, the actual position (position in the captured image 60) of the linear pattern 3 for which the smallest average error 63 was obtained in step S60 among the (N-2) linear patterns 3 (three in the example shown in FIG. 8) is set as the reference position 64. For example, assume that a certain block 31 includes eight linear patterns 77(1) to 77(8) as shown in FIG. 17. The dotted line portion labeled 770 indicates the actual value 62 of the spacing between two linear patterns 3 adjacent in the paper width direction. In this example, in step S60, the average error 63 is calculated for each of the six linear patterns 77(2) to 77(7). If the theoretical value 61 calculated in step S40 is 5, then among the linear patterns 77(2) to 77(7), the linear pattern 77(6) has the smallest average error 63. Therefore, the actual position of the linear pattern 77(6) is set as the reference position 64.

[0086] After setting the reference position 64, the ideal position calculation unit 365 calculates an ideal position 65, which is a position where each linear pattern 3 should be formed, based on the reference position 64 (step S80). More specifically, when two linear patterns adjacent in the paper width direction to the linear pattern 3 corresponding to the reference position 64 are defined as a first adjacent linear pattern and a second adjacent linear pattern, in step S80, the average of the actual value 62 of the interval between the linear pattern 3 corresponding to the reference position 64 and the first adjacent linear pattern (corresponding to the first interval value described above) and the actual value 62 of the interval between the linear pattern 3 corresponding to the reference position 64 and the second adjacent linear pattern (corresponding to the second interval value described above) is calculated as the average actual interval, and the ideal position 65 is calculated by regarding the interval between the two linear patterns 3 constituting each linear pattern pair as the average actual interval. 17, linear pattern 77(6) is the linear pattern corresponding to reference position 64, linear pattern 77(5) is the first adjacent linear pattern, and linear pattern 77(7) is the second adjacent linear pattern. The actual value 62 of the distance between linear pattern 77(6) corresponding to reference position 64 and first adjacent linear pattern 77(5) is 4.9, and the actual value 62 of the distance between linear pattern 77(6) corresponding to reference position 64 and second adjacent linear pattern 77(7) is 5.2. Therefore, the average actual distance is 5.05. In this case, as shown in FIG. 18, by adding or subtracting an integer multiple of 5.05, which is the average actual interval, to or from the X coordinate value of the reference position 64 (the actual position of the linear pattern 77(6)), the ideal positions 65 of each of the linear patterns 77(1) to 77(5) and 77(7) to 77(8) other than the linear pattern 77(6) corresponding to the reference position 64 are calculated.

[0087] Next, the difference calculation unit 366 calculates the difference 66 in the paper width direction between the ideal position 65 calculated in step S80 and the actual position based on the captured image 60 for each linear pattern 3 (step S90). Finally, the defect determination unit 367 determines whether the nozzle corresponding to each linear pattern 3 is a defective nozzle based on the difference 66 calculated in step S90 (step S100). This completes the process of detecting defective nozzles.

[0088] In this embodiment, step S10 realizes the test chart printing step, step S20 realizes the imaging step, step S30 realizes the image extraction step, step S40 realizes the theoretical value calculation step, step S50 realizes the actual value calculation step, step S60 realizes the error calculation step, step S70 realizes the reference position setting step, step S80 realizes the ideal position calculation step, step S90 realizes the difference calculation step, and step S100 realizes the defect determination step.

[0089] <1.7 Effects> According to this embodiment, based on a captured image 60 of a printed image of a test chart 30 divided into five blocks 31(1) to 31(5) in the transport direction of the printing paper 5 (a direction perpendicular to the direction in which the multiple nozzles 252 are arranged), an average error 63 is calculated for each linear pattern 3 (excluding the linear patterns 3 at both ends) included in each of the five blocks 31(1) to 31(5), representing how close the spacing between two adjacent linear patterns 3 in the paper width direction is to a theoretical value 61. The actual position of the linear pattern 3 for which the smallest average error 63 is obtained is set as a reference position 64, and an ideal position 65 of each linear pattern 3 is calculated based on the reference position 64. As a result, unlike conventional methods, the reference position 64 in each block 31 can be accurately determined, and the ideal position 65 of each linear pattern 3 can be accurately determined, even if the nozzle 252 corresponding to the linear pattern 3 at the end of each block 31 is a defective nozzle. As a result, the difference 66 between the actual position of each linear pattern 3 and the ideal position 65 (the difference in the paper width direction) can be calculated with high accuracy, making it possible to accurately determine whether or not the nozzle corresponding to each linear pattern 3 is a defective nozzle. As described above, according to this embodiment, it is possible to detect defective nozzles with higher accuracy than conventional inkjet printing devices 10. This reduces the wasteful consumption of printing paper 5 and ink due to reprinting, for example, and can contribute to the achievement of the SDGs (Sustainable Development Goals).

[0090] <1.8 Variations> <1.8.1 First modified example> In the first embodiment, the ideal position 65 of each linear pattern 3 is calculated by regarding the distance between the two linear patterns 3 constituting each linear pattern pair as the average of the distance between the linear pattern 3 corresponding to the reference position 64 and the first adjacent linear pattern and the distance between the linear pattern 3 corresponding to the reference position 64 and the second adjacent linear pattern. In contrast, in this modified example, in step S80 of Fig. 12 , the average of the actual values ​​62 of the linear pattern pairs for which the difference between the actual value 62 calculated in step S50 and the theoretical value 61 calculated in step S40 is equal to or less than a predetermined threshold is calculated as the average actual distance, and the ideal position 65 of each linear pattern 3 is calculated by regarding the distance between the two linear patterns 3 constituting each linear pattern pair as the average actual distance.

[0091] For example, assume that block 31(3) contains five linear patterns 78(1) to 78(5) as shown in FIG. 19. The dotted line portion labeled 780 indicates the actual value 62 of the spacing between two adjacent linear patterns in the paper width direction. The position of linear pattern 78(2) is the reference position 64. Here, assume that the threshold value for comparing the difference between actual value 62 and theoretical value 61 is set to 0.5. In this case, for the linear pattern pair consisting of linear pattern 78(4) and linear pattern 78(5), the difference is greater than the threshold value, and for the other linear pattern pairs, the difference is equal to or less than the threshold value. Therefore, in this example, the average actual spacing is 4.9, which is the average of the actual value 62 of 5.0 for the linear pattern pair consisting of linear pattern 78(1) and linear pattern 78(2), the actual value 62 of 4.9 for the linear pattern pair consisting of linear pattern 78(2) and linear pattern 78(3), and the actual value 62 of 4.8 for the linear pattern pair consisting of linear pattern 78(3) and linear pattern 78(4). Then, as shown in Figure 20, by adding or subtracting an integer multiple of 4.9, which is the average actual spacing, to or from the X coordinate value of reference position 64 (the actual position of linear pattern 78(2)), the ideal position 65 of each of linear patterns 78(1), 78(3) to 78(5) other than linear pattern 78(2) corresponding to reference position 64 is calculated.

[0092] According to this modification, the average actual distance is calculated as the average of the actual distances 62 between the two linear patterns 3 constituting a linear pattern pair using only images of normally printed linear patterns 3. Since the ideal position 65 is calculated assuming that the distance between the two linear patterns 3 constituting each linear pattern pair is the average actual distance, the ideal position 65 of each linear pattern 3 can be determined with high accuracy.

[0093] <1.8.2 Second modified example> In the first embodiment, the actual position of the linear pattern 3 for which the smallest average error 63 was obtained was set as the reference position 64 for each block 31. In this case, if the smallest average error 63 is a large value, an inappropriate position would be set as the reference position 64. Therefore, in this modified example, for a block 31 for which the smallest average error 63 is larger than a predetermined threshold, the reference position 64 is set based on the positions of the linear pattern 3 in two blocks 31 adjacent to each other in the transport direction of the printing paper 5. This will be explained in detail below.

[0094] Assume that an image such as that shown in FIG. 21 is extracted as the image of inspection range 6 in step S30 of FIG. 12. In the example shown in FIG. 21, for block 31(2), the average error 63 is relatively large for all three linear patterns 3 except for the linear patterns 3 at both ends. Focusing on block 31(1), the distance between linear pattern 791 and linear pattern 792 is close to the theoretical value 61 of the distance between two linear patterns, and the distance between linear pattern 792 and linear pattern 793 is also close to the theoretical value 61 of the distance between two linear patterns. Focusing on block 31(3), the distance between linear pattern 794 and linear pattern 795 is close to the theoretical value 61 of the distance between two linear patterns, and the distance between linear pattern 795 and linear pattern 796 is also close to the theoretical value 61 of the distance between two linear patterns. In such a case, the center of gravity of the six linear patterns 791-796 (the position indicated by the dotted line with reference numeral 79a in FIG. 21) is considered to be the ideal position of linear pattern 79b. Furthermore, by setting this ideal position as the reference position 64 for block 31(2), it is considered that the ideal position 65 of each linear pattern 3 within that block 31(2) can be determined with high accuracy. Therefore, in this example, the center of gravity of the six linear patterns 791-796 is set as the reference position 64 for block 31(2).

[0095] More specifically, in this modified example, when the number of blocks 31 is K, Q is an integer between 2 and (K-1) inclusive, and J is an integer between 2 and (N-1) inclusive (where N is the number of linear patterns 3 included in each block 31), and for the Qth block for which the minimum average error 63 obtained in step S60 of FIG. 12 is greater than a predetermined threshold, in step S70 of FIG. 12, the average error 63 obtained in step S60 for the Jth linear pattern 3 included in the (Q-1)th block is equal to or less than the predetermined threshold, and the average error 63 obtained in step S60 for the Jth linear pattern 3 included in the (Q+1)th block is equal to or less than the predetermined threshold. If the average error 63 obtained in step S60 is equal to or less than the predetermined threshold, the center of gravity position calculated from the actual position of the (J-1)th linear pattern 3 included in the (Q-1)th block, the actual position of the Jth linear pattern 3 included in the (Q-1)th block, the actual position of the (J+1)th linear pattern 3 included in the (Q-1)th block, the actual position of the (J-1)th linear pattern 3 included in the (Q+1)th block, the actual position of the Jth linear pattern 3 included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern 3 included in the (Q+1)th block is set as the reference position 64. Note that for the first block, the Kth block, and any block for which the minimum average error 63 obtained in step S60 is equal to or less than the predetermined threshold, the actual position of the linear pattern 3 among the (N-2) linear patterns 3 for which the minimum average error 63 was obtained in step S60 is set as the reference position 64 in step S70.

[0096] According to this modification, even in a block 31 in which a linear pattern pair having an interval close to the theoretical value 61 does not exist, the ideal position 65 of each linear pattern 3 can be correctly determined.

[0097] 2. Second embodiment <2.1 Overview> In the first embodiment described above, it was assumed that nozzles causing deviations in the landing position in the paper width direction were detected. However, as shown by the dotted line portion labeled 80 in Figure 22, for example, deviations in the landing position in the transport direction of the printing paper 5 can also occur. Therefore, a second embodiment of the present invention will be described in which defective nozzles are detected based on the position (Y coordinate value) of the linear pattern 3 in the captured image 60 in the transport direction of the printing paper 5.

[0098] The overall configuration of the inkjet printing device 10 (see FIG. 1), the configuration of the recording unit 205 (see FIG. 2), the arrangement of the nozzles 252 in the ink ejection head 251 (see FIG. 3), the hardware configuration of the print control device 100 (see FIG. 4), the general functional configuration of the control unit 130 (see FIG. 5), and the configuration of the faulty nozzle detection unit 136 (see FIG. 11) are the same as those in the first embodiment. However, the detailed operation of each component in the faulty nozzle detection unit 136 differs from that in the first embodiment.

[0099] The test chart 30 used is similar to that of the first embodiment. However, in this embodiment, the test chart 30 is divided into a plurality of blocks so that multiple linear patterns 3 to be formed at positions with the same Y coordinate value are included in different blocks, and multiple linear patterns 3 to be formed at positions with close X coordinate values ​​are included in the same block. More specifically, as shown in Fig. 23, one block is formed for every five linear patterns 3 that form one integrated staircase pattern. In the example shown in Fig. 23, the test chart 30 includes 25 linear patterns 3, and therefore the test chart 30 is divided into five blocks 33(1) to 33(5).

[0100] The test chart 30 in the portion corresponding to the inspection range 6 in this embodiment will be generalized. The test chart 30 is composed of a plurality of linear patterns 3 to be formed by ejecting ink from a plurality of nozzles 252, where K is an integer of 3 or greater, and is divided into K blocks in the paper width direction. Where N is an integer of 4 or greater, each of the K blocks includes N linear patterns 3 to be formed so that the interval (interval between center of gravity positions) between two adjacent linear patterns 3 in the transport direction of the printing paper 5 is constant. Where P is an integer between 2 and K, the test chart 30 is configured so that the N linear patterns 3 included in the Pth block are each formed at a position offset a certain distance in the paper width direction from the N linear patterns 3 included in the (P-1)th block.

[0101] <2.2 How to detect defective nozzles> The detailed procedure for the process of detecting defective nozzles will be described with reference to the flowchart shown in Fig. 12. The processes in steps S10 to S30 are the same as those in the first embodiment.

[0102] After the image of the inspection range 6 is extracted in step S30, the theoretical value calculation unit 361 calculates a theoretical value 61 of the distance between two linear patterns 3 adjacent to each other in the transport direction of the printing paper 5 (step S40). In step S40, the theoretical value 61 is calculated based on the distance from the top to the bottom of the inspection range 6, the number of linear patterns 3 to be included in the image (captured image 60) extracted in step S30, and the number of blocks 33. In this embodiment, the Y coordinate values ​​of the top and bottom of the inspection range 6 are fixed values. Here, it is assumed that the distance from the top to the bottom of the inspection range 6 is 15 (see FIG. 24). Furthermore, the number of linear patterns 3 to be included in each block 33 is 5 (see FIG. 23). Therefore, by dividing 15 by 5, the theoretical value 61 is calculated as 3. The distance between two linear patterns 3 is the distance from the Y coordinate value of the center of gravity position of one of the two linear patterns 3 to the Y coordinate value of the center of gravity position of the other of the two linear patterns 3, as shown in Figure 24.

[0103] Next, based on the captured image 60, the actual value calculation unit 362 calculates the actual value (value in the captured image 60) 62 of the distance between two linear patterns 3 for all combinations of two linear patterns 3 that are adjacent in position in the transport direction of the printing paper 5 (step S50). In this regard, if two linear patterns 3 that are adjacent in position in the transport direction of the printing paper 5 are defined as a "linear pattern pair," each block 33 includes four linear pattern pairs. For example, if the five linear patterns 3 included in block 33(3) are labeled with symbols 81(1) to 81(5) as shown in FIG. 25, block 33(3) includes a linear pattern pair PA11 consisting of linear pattern 81(1) and linear pattern 81(2), a linear pattern pair PA12 consisting of linear pattern 81(2) and linear pattern 81(3), a linear pattern pair PA13 consisting of linear pattern 81(3) and linear pattern 81(4), and a linear pattern pair PA14 consisting of linear pattern 81(4) and linear pattern 81(5). In this way, four linear pattern pairs are formed by the five linear patterns 3. In step S50, an actual value 62 of the distance between two linear patterns 3 that form such a linear pattern pair is calculated. As described above, in step S50, a combination of two linear patterns 3 that are adjacent in position in the transport direction of the printing paper 5 is considered to be a linear pattern pair, and for each of the (N-1) (four in the example shown in Figure 23) linear pattern pairs composed of N (five in the example shown in Figure 23) linear patterns 3 contained in each of the multiple blocks 33, the actual value 62 of the distance between the two linear patterns 3 that make up the linear pattern pair is calculated based on the captured image 60.

[0104] Next, the error calculation unit 363 calculates the average error 63 for each linear pattern 3 except for the linear patterns 3 located at both ends (top and bottom) of each block 33 (step S60). In this regard, the linear patterns 3 other than the linear patterns 3 located at both ends of each block 33 form linear pattern pairs with the adjacent linear pattern 3 on the downstream side in the transport direction of the printing paper 5, and also form linear pattern pairs with the adjacent linear pattern 3 on the upstream side in the transport direction of the printing paper 5. Here, one of the two linear pattern pairs thus formed is defined as the "first linear pattern pair" and the other as the "second linear pattern pair." In step S60, for each linear pattern 3 except for the linear patterns 3 located at both ends of each block 33, the difference between the theoretical value 61 calculated in step S40 and the actual value 62 calculated in step S50 for the first linear pattern pair is calculated as a first error, and the difference between the theoretical value 61 calculated in step S40 and the actual value 62 calculated in step S50 for the second linear pattern pair is calculated as a second error. Then, the average of the first error and the second error is calculated as an average error 63. As described above, in step S60, for each of the (N-2) (3 in the example shown in Figure 23) linear patterns 3 out of the N (5 in the example shown in Figure 23) linear patterns 3 included in each of the multiple blocks 33, excluding the linear patterns 3 at both ends, a first error which is the difference between the theoretical value 61 and the actual value 62 for the first linear pattern pair, a second error which is the difference between the theoretical value 61 and the actual value 62 for the second linear pattern pair, and an average error 63 which is the average of the first error and the second error are calculated.

[0105] After calculating the average error 63, the reference position setting unit 364 sets the actual position of the linear pattern 3 for which the smallest average error 63 was obtained as the reference position 64 for each block 33 (step S70). More specifically, in step S70, for each of the multiple blocks 33, the actual position (position in the captured image 60) of the linear pattern 3 for which the smallest average error 63 was obtained in step S60 among the (N-2) linear patterns 3 (three in the example shown in FIG. 23) is set as the reference position 64. For example, assume that a certain block 33 includes eight linear patterns 82(1) to 82(8) as shown in FIG. 26. The dotted line portion labeled 820 indicates the actual value 62 of the interval between two adjacent linear patterns 3 in the transport direction of the printing paper 5. In this example, in step S60, the average error 63 is calculated for each of the six linear patterns 82(2) to 82(7). If the theoretical value 61 calculated in step S40 is 3, then among the linear patterns 82(2) to 82(7), the linear pattern 82(6) has the smallest average error 63. Therefore, the actual position of the linear pattern 82(6) is set as the reference position 64.

[0106] After setting the reference position 64, the ideal position calculation unit 365 calculates an ideal position 65, which is a position where each linear pattern 3 is to be formed, based on the reference position 64 (step S80). More specifically, when two linear patterns adjacent to the linear pattern 3 corresponding to the reference position 64 in the transport direction of the printing paper 5 are defined as a first adjacent linear pattern and a second adjacent linear pattern, in step S80, the average of the actual value 62 of the distance between the linear pattern 3 corresponding to the reference position 64 and the first adjacent linear pattern and the actual value 62 of the distance between the linear pattern 3 corresponding to the reference position 64 and the second adjacent linear pattern is calculated as the average actual distance, and the ideal position 65 is calculated by regarding the distance between the two linear patterns 3 constituting each linear pattern pair as the average actual distance. In this regard, in the example shown in FIG. 26 , the linear pattern 82(6) is the linear pattern corresponding to the reference position 64, the linear pattern 82(5) is the first adjacent linear pattern, and the linear pattern 82(7) is the second adjacent linear pattern. The actual value 62 of the interval between the linear pattern 82(6) corresponding to the reference position 64 and the first adjacent linear pattern 82(5) is 2.9, and the actual value 62 of the interval between the linear pattern 82(6) corresponding to the reference position 64 and the second adjacent linear pattern 82(7) is 3.2. Therefore, the average actual interval is 3.05. In this case, as shown in FIG. 27 , the ideal positions 65 of each of the linear patterns 82(1) to 82(5) and 82(7) to 82(8) other than the linear pattern 82(6) corresponding to the reference position 64 are calculated by adding or subtracting an integer multiple of 3.05, which is the average actual interval, to or from the Y coordinate value of the reference position 64 (the actual position of the linear pattern 82(6)).

[0107] Next, the difference calculation unit 366 calculates the difference 66 in the conveyance direction of the printing paper 5 between the ideal position 65 calculated in step S80 and the actual position based on the captured image 60 for each linear pattern 3 (step S90). Finally, the defect determination unit 367 determines whether the nozzle corresponding to each linear pattern 3 is a defective nozzle based on the difference 66 calculated in step S90 (step S100). This completes the process of detecting defective nozzles.

[0108] <2.3 Effects> According to this embodiment, based on a captured image 60 of a printed image of a test chart 30 divided into five blocks 33(1) to 33(5) in the paper width direction (the direction in which the multiple nozzles 252 are arranged), an average error 63 is calculated for each linear pattern 3 included in each of the five blocks 33(1) to 33(5) (excluding the linear patterns 3 at both ends), representing how close the spacing between two adjacent linear patterns 3 in the transport direction of the printing paper 5 is to a theoretical value 61. The actual position of the linear pattern 3 with the smallest average error 63 is then set as a reference position 64, and an ideal position 65 of each linear pattern 3 is calculated based on the reference position 64. As a result, unlike conventional methods, the reference position 64 in each block 33 can be accurately determined, and the ideal position 65 of each linear pattern 3 can be accurately determined, even if the nozzle 252 corresponding to the linear pattern 3 at the end of each block 33 is a defective nozzle. As a result, the difference 66 between the actual position of each linear pattern 3 and the ideal position 65 (the difference in the transport direction of the printing paper 5) can be calculated with high accuracy, making it possible to accurately determine whether or not the nozzle corresponding to each linear pattern 3 is a defective nozzle. As described above, according to this embodiment, as with the first embodiment, it is possible to detect defective nozzles with higher accuracy than conventionally possible for the inkjet printing device 10. This reduces the wasteful consumption of printing paper 5 and ink due to reprinting, for example, and can contribute to the achievement of the SDGs (Sustainable Development Goals).

[0109] <2.4 Modifications> This embodiment can also employ the same modifications (first and second modifications) as those of the first embodiment, and specific examples thereof will be described below.

[0110] <2.4.1 First modified example> Here, we will assume that block 33(3) contains five linear patterns 83(1) to 83(5) as shown in Figure 28. The dotted line portion labeled 830 indicates the actual value 62 of the distance between two adjacent linear patterns in the transport direction of print paper 5. The position of linear pattern 83(2) is the reference position 64. Here, we will assume that the threshold value for comparing the difference between actual value 62 and theoretical value 61 is set to 0.5. In this case, for the linear pattern pair consisting of linear pattern 83(4) and linear pattern 83(5), the difference is greater than the threshold value, and for the other linear pattern pairs, the difference is equal to or less than the threshold value. Therefore, in this example, the average actual spacing is 2.9, which is the average of 3.0, which is the actual value 62 for the linear pattern pair consisting of linear pattern 83(1) and linear pattern 83(2), 2.9, which is the actual value 62 for the linear pattern pair consisting of linear pattern 83(2) and linear pattern 83(3), and 2.8, which is the actual value 62 for the linear pattern pair consisting of linear pattern 83(3) and linear pattern 83(4). Then, as shown in Fig. 29 , by adding or subtracting an integer multiple of 2.9, which is the average actual spacing, to or from the Y coordinate value of reference position 64 (the actual position of linear pattern 83(2)), the ideal positions 65 of each of linear patterns 83(1), 83(3) to 83(5) other than linear pattern 83(2) corresponding to reference position 64 are calculated.

[0111] <2.4.2 Second modified example> Assume that an image such as that shown in FIG. 30 is extracted as the image of inspection range 6 in step S30 of FIG. 12. In the example shown in FIG. 30, for block 33(2), the average error 63 is relatively large for all three linear patterns 3 except for the linear patterns 3 at both ends (top and bottom). Focusing on block 33(1), the distance between linear pattern 841 and linear pattern 842 is close to the theoretical value 61 of the distance between two linear patterns, and the distance between linear pattern 842 and linear pattern 843 is also close to the theoretical value 61 of the distance between two linear patterns. Focusing on block 33(3), the distance between linear pattern 844 and linear pattern 845 is close to the theoretical value 61 of the distance between two linear patterns, and the distance between linear pattern 845 and linear pattern 846 is also close to the theoretical value 61 of the distance between two linear patterns. In this modified example, in the same manner as in the second modified example of the first embodiment, the positions of the centers of gravity of the six linear patterns 841 to 846 are set to the reference position 64 for the block 33(2).

[0112] <3.Other> The present invention is not limited to the above-described embodiments (including modifications) and can be implemented in various modifications without departing from the spirit of the present invention. For example, the above-described embodiments (including modifications) employ an inkjet printing apparatus 10 that performs color printing. However, the present invention is not limited to this, and an inkjet printing apparatus that performs monochrome printing may also be employed. Furthermore, the above-described embodiments (including modifications) employ an inkjet printing apparatus 10 that uses aqueous ink. However, the present invention is not limited to this, and an inkjet printing apparatus that uses UV ink (ultraviolet-curable ink), such as an inkjet printing apparatus for label printing, may also be employed. In this case, an ultraviolet irradiation mechanism that cures the UV ink on the printing paper 5 by ultraviolet irradiation is provided inside the printing mechanism 201 (see FIG. 1 ) instead of the drying mechanism 206. [Explanation of symbols]

[0113] 3...Linear pattern 10...Inkjet printing device 30...Test chart 40...Inline scanner 130...Control unit 136...Faulty nozzle detection unit 200...printing machine body 205...Recording Department 251...ink ejection head 361...Theoretical value calculation section 362...Actual value calculation unit 363...Error calculation section 364...Reference position setting section 365…Ideal position calculation unit 366...Difference calculation part 367…Defective judgment section

Claims

1. 1. A method for detecting a defective nozzle in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, comprising: a test chart printing step of printing a test chart, which is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and is divided into a plurality of blocks in the second direction while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the first direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation step of calculating, based on the captured image, an actual value of an interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the first direction is a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting step of setting, as a reference position, an actual position of a linear pattern among the (N-2) linear patterns for which the smallest average error is obtained in the error calculation step, for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; A defective nozzle detection method comprising:

2. 2. The defective nozzle detection method described in claim 1, characterized in that, when two linear patterns adjacent to the linear pattern corresponding to the reference position in the first direction are defined as a first adjacent linear pattern and a second adjacent linear pattern, in the ideal position calculation step, the ideal position is calculated based on an actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and an actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern.

3. 3. The defective nozzle detection method according to claim 2, characterized in that in the ideal position calculation step, the average of the actual value of the spacing between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the spacing between the linear pattern corresponding to the reference position and the second adjacent linear pattern is calculated as an average actual spacing, and the ideal position is calculated by regarding the spacing between the two linear patterns that make up each linear pattern pair as the average actual spacing.

4. The defective nozzle detection method of claim 1, characterized in that in the ideal position calculation step, for each of the plurality of blocks, the average of actual values ​​for linear pattern pairs among the (N-1) linear pattern pairs for which the difference between the actual value calculated in the actual value calculation step and the theoretical value calculated in the theoretical value calculation step is less than a predetermined threshold is calculated as an average actual spacing, and the ideal position is calculated by regarding the spacing between the two linear patterns that make up each linear pattern pair as the average actual spacing.

5. the test chart includes a first mark representing a first predetermined position in the first direction and a second mark representing a second predetermined position in the first direction; the defective nozzle detection method includes an image extraction step of extracting an image of a range between the first mark and the second mark in the first direction from the captured image, 2. The faulty nozzle detection method according to claim 1, wherein in the theoretical value calculation step, the theoretical value is calculated based on the distance between the first mark and the second mark, the number of linear patterns that should be included in the image extracted in the image extraction step, and the number of blocks.

6. The plurality of blocks are K blocks (K is an integer of 3 or more), A defective nozzle detection method described in any one of claims 1 to 5, characterized in that the test chart is configured so that, where P is an integer between 2 and K, the N linear patterns included in the Pth block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)th block.

7. 1. A method for detecting a defective nozzle in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, comprising: a test chart printing step of printing a test chart, which is made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and is divided into a plurality of blocks in the second direction while relatively moving a positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the first direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation step of calculating, based on the captured image, an actual value of an interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the first direction is a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting step of setting a reference position for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that, where P is an integer between 2 and K, the N linear patterns included in the P-th block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)-th block, respectively; For the first block, the Kth block, and the block for which the minimum average error obtained in the error calculation step is equal to or less than a predetermined threshold, the reference position setting step sets the actual position of the linear pattern for which the minimum average error is obtained in the error calculation step among the (N-2) linear patterns as the reference position; a faulty nozzle detection method, wherein Q is an integer between 2 and (K-1) inclusive, and J is an integer between 2 and (N-1) inclusive, and for a Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, in the reference position setting step, if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q-1)th block in the error calculation step is less than the predetermined threshold, and if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q+1)th block in the error calculation step is less than the predetermined threshold, the reference position is set based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block.

8. 8. The defective nozzle detection method of claim 7, wherein for a Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, in the reference position setting step, a center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block is set as the reference position.

9. 1. A method for detecting a defective nozzle in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, comprising: a test chart printing step of printing a test chart divided into a plurality of blocks in the first direction, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, while relatively moving the positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the second direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation step of calculating, based on the captured image, an actual value of the interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the second direction is defined as a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting step of setting, as a reference position, an actual position of a linear pattern among the (N-2) linear patterns for which the smallest average error is obtained in the error calculation step, for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; A defective nozzle detection method comprising:

10. 10. The defective nozzle detection method of claim 9, wherein when two linear patterns adjacent to the linear pattern corresponding to the reference position in the second direction are defined as a first adjacent linear pattern and a second adjacent linear pattern, in the ideal position calculation step, the ideal position is calculated based on the actual value of the distance between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the distance between the linear pattern corresponding to the reference position and the second adjacent linear pattern.

11. 11. The defective nozzle detection method of claim 10, wherein in the ideal position calculation step, the average of the actual value of the spacing between the linear pattern corresponding to the reference position and the first adjacent linear pattern and the actual value of the spacing between the linear pattern corresponding to the reference position and the second adjacent linear pattern is calculated as an average actual spacing, and the ideal position is calculated by regarding the spacing between the two linear patterns that make up each linear pattern pair as the average actual spacing.

12. The defective nozzle detection method of claim 9, characterized in that in the ideal position calculation step, for each of the plurality of blocks, the average of actual values ​​for linear pattern pairs among the (N-1) linear pattern pairs for which the difference between the actual value calculated in the actual value calculation step and the theoretical value calculated in the theoretical value calculation step is less than a predetermined threshold is calculated as an average actual spacing, and the ideal position is calculated by regarding the spacing between the two linear patterns that make up each linear pattern pair as the average actual spacing.

13. 1. A method for detecting a defective nozzle in a printing device that has a print head including a plurality of nozzles arranged in a first direction and prints onto a printing medium by ejecting ink from the plurality of nozzles, comprising: a test chart printing step of printing a test chart divided into a plurality of blocks in the first direction, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles, while relatively moving the positional relationship between the print head and the printing medium in a second direction perpendicular to the first direction, the test chart including N linear patterns (N is an integer of 4 or more) each to be formed so that the interval between two adjacent linear patterns in the second direction is constant; an imaging step of acquiring a captured image by imaging the print image obtained in the test chart printing step; a theoretical value calculation step of calculating a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation step of calculating, based on the captured image, an actual value of the interval between two linear patterns constituting a linear pattern pair, for each of (N-1) linear pattern pairs constituted by the N linear patterns included in each of the plurality of blocks, where a combination of two linear patterns adjacent to each other in the second direction is defined as a linear pattern pair; an error calculation step of calculating, for each of (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error which is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error which is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error which is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting step of setting a reference position for each of the plurality of blocks; an ideal position calculation step of calculating an ideal position where each linear pattern is to be formed based on the reference position; a difference calculation step of calculating, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination step of determining whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that, where P is an integer between 2 and K, the N linear patterns included in the P-th block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)-th block, respectively; For the first block, the Kth block, and the block for which the minimum average error obtained in the error calculation step is equal to or less than a predetermined threshold, the reference position setting step sets the actual position of the linear pattern for which the minimum average error is obtained in the error calculation step among the (N-2) linear patterns as the reference position; a faulty nozzle detection method, wherein Q is an integer between 2 and (K-1) inclusive, and J is an integer between 2 and (N-1) inclusive, and for a Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, in the reference position setting step, if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q-1)th block in the error calculation step is less than the predetermined threshold, and if the average error obtained in the error calculation step for the Jth linear pattern included in the (Q+1)th block in the error calculation step is less than the predetermined threshold, the reference position is set based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block.

14. 14. The faulty nozzle detection method according to claim 13, wherein, for a Qth block for which the minimum average error obtained in the error calculation step is greater than the predetermined threshold, in the reference position setting step, a center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block is set as the reference position.

15. a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device when the imaging device captures a printed image of the test chart, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in a second direction orthogonal to the first direction, the plurality of blocks including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation unit that calculates, based on the captured image, an actual value of an interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in the first direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting unit that sets, as a reference position, an actual position of a linear pattern that has obtained the smallest average error among the (N-2) linear patterns for each of the plurality of blocks by the error calculation unit; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; A printing device comprising:

16. a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device when the imaging device captures a printed image of the test chart, the test chart being made up of a plurality of linear patterns to be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in a second direction orthogonal to the first direction, the plurality of blocks including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns adjacent to each other in the first direction; an actual value calculation unit that calculates, based on the captured image, an actual value of an interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in the first direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting unit that sets a reference position for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the first direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that, where P is an integer between 2 and K, the N linear patterns included in the P-th block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)-th block, respectively; For the first block, the Kth block, and the block for which the minimum average error obtained by the error calculation unit is equal to or less than a predetermined threshold, the reference position setting unit sets the actual position of the linear pattern for which the minimum average error is obtained by the error calculation unit among the (N-2) linear patterns as the reference position; a printing device characterized in that, for a Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, where Q is an integer greater than or equal to 2 and (K-1) and J is an integer greater than or equal to 2 and (N-1), the reference position setting unit sets the reference position based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block if the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q-1)th block is less than or equal to the predetermined threshold and the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q+1)th block is less than or equal to the predetermined threshold.

17. 17. The printing device of claim 16, wherein for a Qth block for which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, the reference position setting unit sets, as the reference position, a center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block.

18. a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device when the imaging device captures a printed image of the test chart, the test chart being made up of a plurality of linear patterns that should be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in the first direction, the plurality of blocks including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in a second direction orthogonal to the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation unit that calculates, based on the captured image, an actual value of the interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in position in the second direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting unit that sets, as a reference position, an actual position of a linear pattern that has obtained the smallest average error among the (N-2) linear patterns for each of the plurality of blocks by the error calculation unit; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; A printing device comprising:

19. a print head including a plurality of nozzles arranged in a first direction, the plurality of nozzles ejecting ink onto a print medium to form a print image on the print medium; an imaging device that captures the print image; a faulty nozzle detection unit that detects faulty nozzles from among the plurality of nozzles based on an image captured by the imaging device when the imaging device captures a printed image of the test chart, the test chart being made up of a plurality of linear patterns that should be formed by ejecting ink from the plurality of nozzles and divided into a plurality of blocks in the first direction, the plurality of blocks including N linear patterns (N is an integer equal to or greater than 4) that should be formed so that the interval between two adjacent linear patterns in a second direction orthogonal to the first direction is constant; Equipped with The defective nozzle detection unit a theoretical value calculation unit that calculates a theoretical value of the interval between two linear patterns that are adjacent in position in the second direction; an actual value calculation unit that calculates, based on the captured image, an actual value of the interval between two linear patterns that constitute a linear pattern pair for each of (N-1) linear pattern pairs that are constituted by the N linear patterns included in each of the plurality of blocks, where the combination of two linear patterns that are adjacent in position in the second direction is a linear pattern pair; an error calculation unit that calculates, for each of the (N-2) linear patterns excluding the linear patterns at both ends of the N linear patterns included in each of the plurality of blocks, a first error that is a difference between the theoretical value and an actual value for the first linear pattern pair, a second error that is a difference between the theoretical value and an actual value for the second linear pattern pair, and an average error that is an average of the first error and the second error, when one of two linear pattern pairs including each linear pattern excluding the linear patterns at both ends of the N linear patterns is defined as a first linear pattern pair and the other linear pattern pair is defined as a second linear pattern pair; a reference position setting unit that sets a reference position for each of the plurality of blocks; an ideal position calculation unit that calculates an ideal position where each linear pattern should be formed based on the reference position; a difference calculation unit that calculates, for each linear pattern, a difference in the second direction between the ideal position and an actual position based on the captured image; a defect determination unit that determines whether or not a nozzle corresponding to each linear pattern is a defective nozzle based on the difference; Including, The plurality of blocks are K blocks (K is an integer of 3 or more), the test chart is configured such that, where P is an integer between 2 and K, the N linear patterns included in the P-th block are formed at positions shifted a certain distance in the first direction from the N linear patterns included in the (P-1)-th block, respectively; For the first block, the Kth block, and the block for which the minimum average error obtained by the error calculation unit is equal to or less than a predetermined threshold, the reference position setting unit sets the actual position of the linear pattern for which the minimum average error is obtained by the error calculation unit among the (N-2) linear patterns as the reference position; a printing device characterized in that, for a Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, where Q is an integer greater than or equal to 2 and (K-1) and J is an integer greater than or equal to 2 and (N-1), the reference position setting unit sets the reference position based on the actual position of the linear pattern included in the (Q-1)th block and the actual position of the linear pattern included in the (Q+1)th block if the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q-1)th block is less than or equal to the predetermined threshold and the average error obtained by the error calculation unit for the Jth linear pattern included in the (Q+1)th block is less than or equal to the predetermined threshold.

20. 20. The printing device of claim 19, characterized in that for the Qth block in which the minimum average error obtained by the error calculation unit is greater than the predetermined threshold, the reference position setting unit sets the reference position to a center of gravity position calculated from the actual position of the (J-1)th linear pattern included in the (Q-1)th block, the actual position of the Jth linear pattern included in the (Q-1)th block, the actual position of the (J+1)th linear pattern included in the (Q-1)th block, the actual position of the (J-1)th linear pattern included in the (Q+1)th block, the actual position of the Jth linear pattern included in the (Q+1)th block, and the actual position of the (J+1)th linear pattern included in the (Q+1)th block.

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