Impact position deviation amount detection method, printing apparatus, and impact position deviation amount detection program

Abstract

To accurately detect the magnitude of an impact position deviation (impact position deviation amount), which is one type of nozzle discharge failure in an inkjet printing apparatus.SOLUTION: An impact position deviation amount detection method calculates a provisional impact position on a printing sheet where the ink discharged from a nozzle is expected to land (S311), calculates an actual impact position at which the ink discharged from the nozzle actually lands on the printing sheet (S312), obtains a difference between the actual impact position and the provisional impact position as a first difference amount (S313), obtains a moving average of the first difference amount (S314), obtains a difference between the moving average of the first difference amount and the first difference amount as a second difference amount (S315), obtains an average of the second difference amounts for a nozzle that belongs to a group different from a target nozzle and is pre-associated with the target nozzle as an average second difference amount corresponding to the target nozzle (S316), and obtains a difference between the second difference amount and the average second difference amount as the impact position deviation amount (S317).SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The present invention relates to a printing device having an ink ejection head (print head) equipped 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 "defective ejection nozzles"). [Background technology]

[0002] Inkjet printing devices are widely known, performing printing by ejecting ink onto a printing medium such as printing paper. Inkjet printing devices can experience problems such as drying of the ink due to evaporation of the solvent near the nozzle, the infiltration of air bubbles into the nozzle, and the adhesion of dust to the nozzle. This can lead to nozzle ejection failure. When ejection failure occurs, dots corresponding to the defective nozzle are missing from the printed image, i.e., missing dots occur. In this case, for example, operations are performed to restore the function of the defective nozzle (cleaning or flushing), or alternatively, ink droplets that should be ejected by the defective nozzle are ejected by another nozzle.

[0003] Nozzle ejection defects can be roughly classified into three types, which will be explained with reference to FIGS. 32 to 34. Note that FIGS. 32 to 34 show portions of a printed image obtained by printing a regular, stepped pattern (test pattern), with the black shaded areas indicating ink coverage. In the dotted line area labeled 91 in FIG. 32, no ink is applied to the area where ink should be applied. Hereinafter, this type of ejection defect will be referred to as "non-ejection." In the dotted line area labeled 92 in FIG. 33, the shape of the ink-applied area differs from the original shape. Hereinafter, this type of ejection defect will be referred to as "shape defect." Shape defects also include ejection defects that result in faint ink due to insufficient density and ejection defects in which the ink-applied area spreads in the paper width direction (main scanning direction) (a direction perpendicular to the transport direction of the print paper). In the dotted line area labeled 93 in FIG. 34, ink is applied to an area that is shifted in the paper width direction from the area where ink should be applied. Hereinafter, this type of ejection defect will be referred to as "landing position deviation."

[0004] In conventional inkjet printing devices, the above-mentioned ejection defects are detected by, for example, a numerical analysis method or a machine learning method based on an image (image data) obtained by capturing an image of a printed predetermined test pattern (typically the above-mentioned regular stepped pattern) using an imaging device. Note that ejection defects may also be detected by visually inspecting the printed image of the predetermined test pattern.

[0005] Incidentally, when detecting landing position deviation using a numerical analysis method, it is necessary to determine, based on a captured image, the distance between the position on the printing paper where ink is supposed to land (hereinafter referred to as the "landing reference position") and the position on the printing paper where the ink actually lands (hereinafter referred to as the "landing position deviation amount"). In this regard, Japanese Patent Application Laid-Open No. 2011-194734 discloses a method in which the landing reference position corresponding to each nozzle is determined by calculating a moving average based on the captured image, and whether or not the nozzle being evaluated is a defective ejection nozzle is determined based on the difference between the determined landing reference position and the actual ink landing position. In this regard, for example, assume that a captured image is obtained that includes five linear patterns 102a to 102e corresponding to five nozzles, as shown in FIG. In this case, if the position of linear pattern 102a is P1+e1, the position of linear pattern 102b is P2+e2, the position of linear pattern 102c is P3+e3, the position of linear pattern 102d is P4+e4, and the position of linear pattern 102e is P5+e5, then the landing reference position P3s corresponding to linear pattern 102c (the landing reference position corresponding to the nozzle that formed linear pattern 102c by ejecting ink) can be calculated using the following formula. P3s=(P1+e1+P2+e2+P4+e4+P5+e5) / 4 =(P1+P2+P4+P5) / 4+(e1+e2+e4+e5) / 4 Then, the difference between the reference landing position calculated by the above formula and the actual landing position of the ink is calculated, and based on this difference, it is determined whether the nozzle that formed the linear pattern 102c is causing a landing position deviation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-194734 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when using a moving average method, it is thought that the amount of deviation in landing position cannot be determined with sufficient accuracy. In other words, it is thought that deviation in landing position, which is one type of nozzle ejection defect, cannot be detected with sufficient accuracy. This is explained below.

[0008] When printing on print paper using an inkjet printing device, the print paper may expand or contract during transport. This expansion or contraction can occur in both the transport direction and the width direction of the print paper. If the print paper expands or contracts in the width direction, even if ink is ejected from multiple nozzles so that multiple linear patterns are printed at equal intervals in the width direction, the multiple linear patterns will not actually be printed at equal intervals in the width direction on the print paper. Because print paper has both areas that expand and areas that contract in the width direction, using a large number of data points to calculate the moving average increases the susceptibility to errors caused by the expansion or contraction of the print paper. Even if ink is ejected normally from the nozzles, a significant difference may occur between the reference landing position and the actual landing position of the ink. In other words, the amount of landing position deviation may not be calculated correctly. On the other hand, using a small number of data points to calculate the moving average increases the influence of data from defective nozzles on the moving average calculation results if the data used includes data from the defective nozzles. In this case, the amount of landing position deviation may also be calculated incorrectly. Furthermore, the amount of deviation in the landing position may not be accurately determined due to the influence of errors that occur when the imaging device captures the printed image of the test pattern. As described above, conventional methods cannot detect the amount of deviation in the landing position with sufficient accuracy.

[0009] Therefore, an object of the present invention is to provide an inkjet printing apparatus that can accurately detect the magnitude of landing position deviation (amount of landing position deviation), which is one type of nozzle ejection defect. [Means for solving the problem]

[0010] A first invention is a method for detecting an amount of deviation in an ink landing position in a printing device having a plurality of nozzles that eject ink onto a printing medium transported in a first direction, the method comprising: an inspection chart printing step of causing the printing device to print an inspection chart including M rows of inspection patterns that correspond one-to-one to the M groups obtained by grouping the plurality of nozzles, where M is an integer of 2 or greater; an inspection chart imaging step of imaging the inspection chart printed in the inspection chart printing step; a reference position calculation step of determining, as a reference position, a position where ink ejected from each of the plurality of nozzles is expected to land on the printing medium, with each of the plurality of nozzles being a target nozzle; an actual landing position calculation step of determining, based on the captured image obtained in the inspection chart imaging step, the position where the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation step of calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation step of calculating, as a moving average corresponding to the target nozzle, an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at positions within a predetermined distance in a second direction perpendicular to the first direction from a position where the target nozzle is to land ink; a second difference amount calculation step of calculating a difference between the difference between the actual landing position and the reference position and the moving average as a second difference amount; an average second difference amount calculation step of calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation step of calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; The present invention is characterized by comprising:

[0011] The second invention is the first invention, The second difference amount calculation step is characterized in that the second difference amount is determined by calculating the difference between the first difference amount determined in the first difference amount calculation step and the moving average determined in the moving average calculation step.

[0012] The third invention is the first invention, In the second difference amount calculation step, the sum of the reference position calculated in the reference position calculation step and the moving average calculated in the moving average calculation step is calculated as an ideal impact position, and the second difference amount is determined by calculating the difference between the actual impact position calculated in the actual impact position calculation step and the ideal impact position.

[0013] The fourth invention is the first invention, In the average second difference amount calculation step, the two or more nozzles that are pre-associated with the target nozzle include nozzles that belong to all groups different from the group to which the target nozzle belongs.

[0014] The fifth invention is the first invention, With regard to the average second difference amount calculation step, the two or more nozzles pre-associated with the target nozzle include a predetermined number of nozzles that belong to each of two or more groups different from the group to which the target nozzle belongs, and that should land ink at a position close to the position at which the target nozzle should land ink in the second direction.

[0015] The sixth invention is the first invention, In the reference position calculation step, a nozzle pitch, which is the distance between two adjacent nozzles in the second direction, is calculated based on the positions of two position marks included in the captured image and the number of nozzles that should land ink in an area corresponding to the area between the two position marks; The reference position for each nozzle is determined using the nozzle pitch.

[0016] The seventh invention is the first invention, The actual landing position calculation step includes: a captured image dividing step of dividing the captured image into K pieces in the first direction, where K is an integer equal to or greater than 2, so that each divided image corresponds to one nozzle in the first direction; an average value calculation step of calculating an average value of data of a plurality of pixels included in the first direction for each of the K divided images obtained in the captured image division step; an actual landing position specifying step of determining the actual landing position for each nozzle based on the average value calculated in the average value calculating step; The present invention is characterized by comprising:

[0017] The eighth invention is any one of the first to seventh inventions, Each of the M stages of the inspection patterns is characterized in that it is made up of a plurality of linear patterns that extend in the first direction and that should be arranged at equal intervals in the second direction.

[0018] A ninth aspect of the present invention is a printing device including a plurality of nozzles that eject ink onto a printing medium transported in a first direction, an imaging device that captures a print image, and a control unit that controls the ejection of ink from the plurality of nozzles and the imaging of the print image by the imaging device, The control unit an inspection chart printing process that controls ink ejection from the plurality of nozzles so as to print an inspection chart including M rows of inspection patterns that correspond one-to-one to M groups obtained by grouping the plurality of nozzles, where M is an integer equal to or greater than 2; an inspection chart imaging process for imaging the inspection chart printed by the inspection chart printing process with the imaging device; a reference position calculation process in which each of the plurality of nozzles is designated as a target nozzle, and a position where ink ejected from the target nozzle is expected to land on the printing medium is determined as a reference position; an actual landing position calculation process for determining, based on the captured image obtained by the inspection chart imaging process, the position at which the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation process for calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation process for calculating, as a moving average corresponding to the target nozzle, an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at positions within a predetermined distance in a second direction perpendicular to the first direction from a position where the target nozzle is to land ink; a second difference amount calculation process for calculating a second difference amount by calculating the difference between the actual landing position and the reference position and the moving average; an average second difference amount calculation process for calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation process for calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; The present invention is characterized by carrying out the following.

[0019] A tenth aspect of the present invention is a program for detecting an amount of deviation in an ink landing position in a printing device that includes a plurality of nozzles that eject ink onto a printing medium that is transported in a first direction and an imaging device that captures an image of a print medium, the program comprising: A computer included in the printing device an inspection chart printing step of controlling ink ejection from the plurality of nozzles so as to print an inspection chart including M rows of inspection patterns that correspond one-to-one to M groups obtained by grouping the plurality of nozzles, where M is an integer equal to or greater than 2; an inspection chart imaging step of imaging the inspection chart printed in the inspection chart printing step with the imaging device; a reference position calculation step of determining, as a reference position, a position where ink ejected from each of the plurality of nozzles is expected to land on the printing medium, with each of the plurality of nozzles being a target nozzle; an actual landing position calculation step of determining, based on the captured image obtained in the inspection chart imaging step, the position where the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation step of calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation step of calculating, as a moving average corresponding to the target nozzle, an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at positions within a predetermined distance in a second direction perpendicular to the first direction from a position where the target nozzle is to land ink; a second difference amount calculation step of calculating a difference between the difference between the actual landing position and the reference position and the moving average as a second difference amount; an average second difference amount calculation step of calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation step of calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; The present invention is characterized in that the following is executed. [Effects of the Invention]

[0020] According to the first aspect of the present invention, the difference between the "difference between the actual landing position and the reference position (first difference amount)" and the "moving average of the difference between the actual landing position and the reference position (first difference amount)" is calculated as the second difference amount, and then the average of the second difference amounts for nozzles belonging to a different group from the target nozzle is calculated as the average second difference amount corresponding to the target nozzle. The difference between the second difference amount and the average second difference amount is then calculated as the landing position deviation amount. Here, the second difference amount is affected by both the landing position deviation and the expansion / contraction of the printing medium. Furthermore, the average second difference amount is primarily affected by the expansion / contraction of the printing medium. Therefore, by using the difference between the second difference amount and the average second difference amount as the landing position deviation amount, the impact of the expansion / contraction of the printing medium on the landing position deviation amount calculated for each nozzle can be reduced compared to conventional methods, even if a large number of data points are used to calculate the moving average. As described above, it is possible to accurately detect the magnitude of landing position deviation (landing position deviation amount), which is one type of nozzle ejection defect, in a printing device equipped with multiple nozzles that eject ink. Furthermore, it is now possible to detect misalignment of ink droplets, which was not possible with conventional methods, thereby reducing the waste of printing media and ink caused by reprinting, thereby contributing to the achievement of the SDGs (Sustainable Development Goals).

[0021] According to the second invention, the same effects as those of the first invention can be obtained.

[0022] According to the third aspect of the invention, the same effects as those of the first aspect of the invention can be obtained.

[0023] According to the fourth aspect of the present invention, the influence of expansion and contraction of the printing medium on the amount of deviation in landing position determined for each nozzle can be effectively reduced.

[0024] According to the fifth aspect of the invention, it is possible to achieve the same effects as the first aspect of the invention while suppressing an increase in the calculation load.

[0025] According to the sixth aspect of the present invention, the reference position can be set relatively easily.

[0026] According to the seventh aspect of the present invention, it is possible to determine the actual landing position of the bullet with a relatively high degree of accuracy.

[0027] According to the eighth aspect of the present invention, it is also easy to visually check whether or not a deviation in landing position has occurred.

[0028] According to the ninth aspect of the invention, the same effects as those of the first aspect of the invention can be obtained.

[0029] According to the tenth aspect of the invention, the same effects as those of the first aspect of the invention can be obtained. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a diagram illustrating the overall configuration of a printing system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of the configuration of an inkjet printing apparatus according to the embodiment. [Figure 3] FIG. 2 is a plan view showing an example of the configuration of a recording unit in the embodiment. [Figure 4] 5A to 5C are diagrams for explaining the arrangement of nozzles in an ink ejection head in the embodiment. [Figure 5] FIG. 2 is a block diagram showing a hardware configuration of the print control device in the embodiment. [Figure 6] FIG. 2 is a block diagram showing a schematic functional configuration of a control unit realized by execution of a print control program in the print control device in the embodiment. [Figure 7] FIG. 2 is a diagram schematically illustrating an example of an inspection chart used in the embodiment. [Figure 8] 10A and 10B are diagrams for explaining grouping of nozzles in the embodiment. [Figure 9] 10 is a flowchart showing a general procedure for detecting a deviation in landing position in the embodiment. [Figure 10] 10 is a flowchart showing a procedure for calculating a landing position deviation amount in a comparative example. [Figure 11]10 is an example of a graph showing a first difference amount calculated based on a captured image of an inspection pattern of a certain row. [Figure 12] FIG. 10 is a diagram for explaining calculation of a moving average of a first difference amount. [Figure 13] 10 is an example of a graph showing a moving average of a first difference amount. [Figure 14] 10 is an example of a graph showing a second difference amount. [Figure 15] FIG. 10 is a diagram for explaining a case where data corresponding to each of 20 nozzles is used when calculating a moving average. [Figure 16] FIG. 10 is a diagram for explaining a case where data corresponding to each of four nozzles is used when calculating a moving average. [Figure 17] FIG. 3 is a block diagram showing a detailed configuration of a discharge defect detection unit in the embodiment. [Figure 18] 10 is a flowchart showing a procedure for calculating a landing position deviation amount in the embodiment. [Figure 19] 10A and 10B are diagrams for explaining calculation of a provisionally fixed bullet position in the embodiment. [Figure 20] 10 is a flowchart showing a procedure for determining an actual landing position in the embodiment. [Figure 21] FIG. 10 is a diagram for explaining division of a captured image in the embodiment. [Figure 22] 10A and 10B are diagrams for explaining trimming when dividing a captured image in the embodiment. [Figure 23] 10A and 10B are diagrams for explaining calculation of an average value of data of a plurality of pixels for each of the divided images in the embodiment. [Figure 24] FIG. 10 is a diagram for explaining that a second difference amount for each nozzle is obtained for each row of the test pattern in the embodiment. [Figure 25] FIG. 10 is a diagram for explaining calculation of an average second difference amount in the embodiment. [Figure 26]10 is an example of a graph showing an average second difference amount in the embodiment. [Figure 27] FIG. 10 is a diagram for explaining the effects of the embodiment. [Figure 28] FIG. 10 is a block diagram showing a detailed configuration of a discharge defect detection unit in a first modified example of the embodiment. [Figure 29] 10 is a flowchart showing a procedure for calculating a landing position deviation amount in a first modified example of the embodiment. [Figure 30] FIG. 10 is a diagram for explaining calculation of an average second difference amount in a second modification of the embodiment. [Figure 31] FIG. 10 is a diagram for explaining calculation of an average second difference amount in a second modification of the embodiment. [Figure 32] FIG. 10 is a diagram for explaining non-ejection. [Figure 33] FIG. 10 is a diagram for explaining a shape defect. [Figure 34] FIG. 10 is a diagram for explaining a deviation in landing position. [Figure 35] FIG. 10 is a diagram for explaining the technique disclosed in Japanese Patent Application Laid-Open No. 2011-194734. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0032] <1. Overall configuration of the printing system> FIG. 1 is a diagram illustrating the overall configuration of a printing system according to an embodiment of the present invention. This printing system comprises an inkjet printing device 10 and a print data generating device 30. The inkjet printing device 10 and the print data generating device 30 are connected to each other via a LAN 4. The print data generating device 30 generates print data by performing rasterization processing on input data such as a PDF file. This print data is not subjected to halftoning; halftoning is performed by a print control device 100 within the inkjet printing device 10, as described below. The print data generated by the print data generating device 30 is sent to the inkjet printing device 10 via the LAN 4. The inkjet printing device 10 comprises a printing machine main body 200 and a print control device 100 that controls the operation of the printing machine main body 200. The inkjet printing device 10 outputs a print image on printing paper as a printing medium based on the print data transmitted from the print data generating device 30, without using a printing plate. The present invention can also be applied when a printing medium other than printing paper (e.g., film) is used.

[0033] <2. Configuration of the printer body of the inkjet printing device> 2 is a schematic diagram showing an example of the configuration of the inkjet printing apparatus 10. As described above, the inkjet printing apparatus 10 is made up of the print control device 100 and the printing machine main body 200.

[0034] 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.

[0035] 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 imaging data (captured image) obtained by the inline scanner 40 capturing the print image is sent to the print control device 100. In the following, when the color of ink ejected from the head unit is not distinguished, the head unit will be denoted by the reference symbol 25.

[0036] FIG. 3 is a plan view showing an example of the configuration of the recording unit 205. As shown in FIG. 3, 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 (sub-scanning 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 number of nozzles (not shown in FIG. 3) 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.

[0037] FIG. 4 is a diagram illustrating the arrangement of nozzles in the ink ejection head 251. Typically, the ink ejection head 251 includes multiple rows of nozzle groups, each consisting of multiple nozzles arranged in the paper width direction. In the example shown in FIG. 4, the ink ejection head 251 includes four rows of nozzle groups. The portion marked with reference numeral 41 in FIG. 4 schematically shows the landing positions on the printing paper 5 of ink ejected from each nozzle. The multiple nozzles in the ink ejection head 251 are arranged so that the landing positions of ink ejected from the nozzles in the first row of nozzle group, the landing positions of ink ejected from the nozzles in the second row of nozzle group, the landing positions of ink ejected from the nozzles in the third row of nozzle group, and the landing positions of ink ejected from the nozzles in the fourth row of nozzle group are all different from one another. For example, the landing positions of ink ejected from the nozzles in the first row of nozzle group are between the landing positions of ink ejected from the nozzles in the third row of nozzle group and the landing positions of ink ejected from the nozzles in the fourth row of nozzle group. In the example shown in Figure 4, the landing position 42 of ink ejected from the nozzle marked with the symbol 252(p) is a position between the landing position 43 of ink ejected from the nozzle marked with the symbol 252(q) and the landing position 44 of ink ejected from the nozzle marked with the symbol 252(r).

[0038] The configurations shown in FIGS. 2 to 4 are merely examples, and the specific configurations of the printing mechanism 201, the recording unit 205, and the ink ejection head 251 are not particularly limited.

[0039] <3. Hardware configuration of print control device> FIG. 5 is a block diagram showing the hardware configuration of the print control device 100. As shown in FIG. 5, 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.

[0040] The auxiliary storage device 121 stores a print control program 13 (a program for controlling the execution of printing processing by the printing press main body 200). In this embodiment, the print control program 13 includes, as a subprogram, a landing position deviation detection program for detecting the magnitude of landing position deviation (amount of landing position deviation), which is one type of nozzle ejection failure. The CPU 111 reads the print control program 13 stored in the auxiliary storage device 121 into the memory 112 and executes it to realize 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, for example, a user 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.

[0041] In the example shown in FIG. 5, 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 150 (described later) (see FIG. 6), some of the components and the remaining components can be realized by different processors. Furthermore, a configuration including an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) can also be adopted.

[0042] <4. Outline of functional configuration of print control device> 6 is a block diagram showing a schematic functional configuration of the control unit 150 that is realized by executing the print control program 13 in the print control device 100. The control unit 150 includes a transport control unit 151, an ink discharge control unit 152, a drying control unit 153, an imaging control unit 154, a data storage unit 155, a discharge defect detection unit 156, a print data correction unit 157, and a halftone processing unit 158.

[0043] The conveyance control unit 151 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. 2). The drying control unit 153 controls the temperature (drying temperature) at which the drying mechanism 206 dries the printing paper 5 after printing. The imaging control unit 154 controls the timing at which the inline scanner 40 captures the image of the printed image.

[0044] The data storage unit 155 temporarily stores the rasterized print data 50 sent from the print data generating device 30. The data storage unit 155 also stores inspection chart data 51 representing an inspection chart for detecting nozzles with ejection problems. The inspection chart will be described in detail later.

[0045] The discharge failure detection unit 156 detects discharge-failed nozzles based on a captured image (captured image data) 60 obtained by capturing an image of the printed image of the inspection chart with the inline scanner 40. Discharge failure information 52 that identifies the discharge-failed nozzles is then output from the discharge failure detection unit 156. The discharge failure detection unit 156 will be described in detail later.

[0046] Based on the defective discharge information 52, the print data correction unit 157 corrects the rasterized print data 50 stored in the data storage unit 155 so as to compensate for the defective discharge of the nozzles. More specifically, based on the defective discharge information 52, the print data correction unit 157 corrects the print data 50 so as to compensate for the defective discharge of the nozzles determined to be in a defective discharge state by the defective discharge detection unit 156. More specifically, for example, the print data 50 is corrected so as to increase the amount of ink discharged from nozzles surrounding the nozzle determined to be in a defective discharge state. The corrected print data 53 is then output from the print data correction unit 157.

[0047] The halftone processing unit 158 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 (L size, M size, and S size) are prepared. In this embodiment, the halftone processing is performed on the inspection chart data 51 and the corrected print data 53 output from the print data correction unit 157. Note that the specific method of halftone processing is not particularly limited, and known methods such as error diffusion and dithering can be used.

[0048] The ink discharge control unit 152 controls the discharge of ink from each nozzle 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 158. For example, the ink discharge timing and the ink discharge amount are controlled.

[0049] <5. Inspection chart> FIG. 7 is a diagram schematically illustrating an example of an inspection chart 70 used in this embodiment. As shown in FIG. 7, the inspection chart 70 is configured with a regular, stepped pattern. Specifically, the inspection chart 70 includes 16 stages of inspection patterns 71(1) to 71(16), and each stage of the inspection pattern 71 is configured with a plurality of linear patterns 72 that extend in the transport direction of the printing paper 5 and should be arranged at equal intervals in the paper width direction. Each linear pattern 72 is formed by ejecting ink from one nozzle. The transport direction of the printing paper 5 corresponds to the first direction, and the paper width direction corresponds to the second direction.

[0050] In this embodiment, in order to print the test chart 70 including the 16-column test patterns 71(1) to 71(16) as described above, the nozzles included in each head unit 25 are grouped into 16 groups. The 16 groups correspond one-to-one to the 16-column test patterns 71(1) to 71(16), and the test pattern 71 for the column corresponding to each group is formed on the printing paper 5 by ejecting ink from the nozzles belonging to each group.

[0051] Here, let us assume that the ink landing positions in the paper width direction when no nozzle ejection defects occur are as shown in Fig. 8. In this case, if the number of nozzles included in the head unit 25 is P (for convenience, let us assume that P is an integer multiple of 16), Q is an arbitrary integer between 0 and ((P / 16)-1), and Z is an arbitrary integer between 1 and 16, then, for example, the nozzle that ejects ink to the landing position indicated by the symbol 7 (16 x Q + Z) in Fig. 8 is included in the group corresponding to the Zth test pattern 71(Z).

[0052] While the inspection chart 70 shown here is comprised solely of a regular stepped pattern, this is not intended to be limiting. For example, the inspection chart may also include a tint pattern of uniform overall density that is formed by ejecting ink from all nozzles in one head unit 25 in addition to the regular stepped pattern. While the inspection chart 70 shown here includes 16-stage inspection patterns 71(1) to 71(16), this is not intended to be limiting. It is possible to use an inspection chart 70 that includes M-stage inspection patterns 71 that correspond one-to-one to M groups obtained by grouping multiple nozzles, where M is an integer greater than or equal to 2.

[0053] 6. Outline of procedure for detecting deviation in impact position The outline of the procedure for detecting deviation in landing position will be described with reference to the flowchart shown in FIG. 9. First, the inspection chart 70 is printed (Step S10). More specifically, the halftone processing unit 158 performs halftone processing on the inspection chart data 51 stored in the data storage unit 155. The ink ejection control unit 152 controls the ejection of ink from each nozzle based on the halftone image data 54 obtained by the halftone processing, thereby printing the inspection chart 70 on the printing paper 5. After the inspection chart 70 is printed, the inline scanner 40 captures a printed image of the inspection chart 70 (the printed image obtained in Step S10) under the control of the imaging control unit 154 (Step S20). Then, the ejection failure detection unit 156 calculates the amount of deviation in landing position (the amount of deviation in landing position of ink ejected from each nozzle) for each nozzle included in each head unit 25 based on the captured image 60 obtained in Step S20 (Step S30). The process performed in Step S30 will be described in detail later. After calculating the amount of deviation in landing positions, the amount of deviation in landing positions is compared with a predetermined threshold value (step S40). If the amount of deviation in landing positions is greater than the threshold value, the nozzle in question is determined to be causing deviation in landing positions. On the other hand, if the amount of deviation in landing positions is equal to or less than the threshold value, the nozzle in question is determined to be not causing deviation in landing positions.

[0054] Although the focus here has been on detecting misalignment of landing positions, in actual operation, non-ejection and shape defects are also detected. Regarding this, the specific method for detecting non-ejection and shape defects is not particularly limited. For example, non-ejection and shape defects can be detected using a method that uses machine learning.

[0055] In this embodiment, the inspection chart printing step is realized by step S10, and the inspection chart imaging step is realized by step S20. Furthermore, the inspection chart printing process is realized by the processing of step S10, and the inspection chart imaging process is realized by the processing of step S20.

[0056] 7. Calculating the impact position deviation The calculation of the amount of deviation in landing position will be described in detail below. First, the procedure in a comparative example will be described, and then the configuration and procedure in this embodiment will be described.

[0057] 7.1 Calculation of landing position deviation in comparative example 10, the procedure for calculating the amount of deviation in landing position in the comparative example will be described. First, based on the captured image 60 of the inspection chart 70 and the design information of the inspection chart 70, the positions where ink ejected from each nozzle is expected to land on the printing paper 5 (hereinafter referred to as "temporary landing positions") are calculated (step S301). Next, based on the captured image 60 of the inspection chart 70, the positions where ink ejected from each nozzle actually lands on the printing paper 5 (hereinafter referred to as "actual landing positions") are calculated (step S302).

[0058] Then, for each nozzle, the distance between the actual landing position determined in step S302 and the temporary settling position determined in step S301 (the difference between the actual landing position and the temporary settling position) is calculated as a first difference amount (step S303). Here, it is assumed that if the actual landing position is shifted to the right of the temporary settling position in the transport direction of the printing paper 5, the first difference amount is a positive value, and if the actual landing position is shifted to the left of the temporary settling position in the transport direction of the printing paper 5, the first difference amount is a negative value. FIG. 11 is an example of a graph showing the first difference amount calculated based on a captured image 60 of the test pattern 71 for one tier. As mentioned above, when printing is performed on the printing paper 5, the printing paper 5 may expand or contract as it is being transported. Therefore, as can be seen from FIG. 11, even if there is no landing position shift due to nozzle ejection defects, the first difference amount varies depending on the nozzle position.

[0059] After calculating the first difference amount, a moving average of the first difference amount in the paper width direction is calculated (step S304). If any nozzle is referred to as a "nozzle of interest," the moving average corresponding to the nozzle of interest is calculated using the first difference amounts for n nozzles that should land ink at positions close to the landing position of ink ejected from the nozzle of interest, where n is a natural number. If n is 10, the moving average corresponding to the nozzle of interest is calculated by dividing the sum of the first difference amounts for the 10 nozzles that should land ink at positions close to the landing position of ink ejected from the nozzle of interest by 10. In this regard, assume that an image such as that shown in FIG. 12 has been obtained as a captured image 60 of a certain row of the test pattern 71. In this case, for example, the moving average corresponding to the nozzle that formed the linear pattern denoted by reference numeral 74 is calculated by dividing the sum of the first difference amounts for the five nozzles that formed the linear pattern in the portion denoted by reference numeral 741 and the five nozzles that formed the linear pattern in the portion denoted by reference numeral 742 by 10. Furthermore, for example, the moving average corresponding to the nozzles that formed the linear pattern marked with the symbol 75 is calculated by dividing the sum of the first difference amounts for the five nozzles that formed the linear pattern present in the portion marked with the symbol 751 and the five nozzles that formed the linear pattern present in the portion marked with the symbol 752 by 10.

[0060] Fig. 13 is a graph showing the moving average of the first difference amount when the graph showing the first difference amount is the graph shown in Fig. 11. As can be seen by comparing Fig. 11 and Fig. 13, the graph showing the moving average of the first difference amount shows smoother changes in value than the graph showing the first difference amount. In other words, the graph showing the moving average of the first difference amount shows the overall trend of the first difference amount in the paper width direction.

[0061] After calculating the moving average of the first difference amount, the difference between the first difference amount calculated in step S303 and the moving average calculated in step S304 is calculated as the second difference amount (step S305). More specifically, the second difference amount is calculated by subtracting the moving average calculated in step S304 from the first difference amount calculated in step S303. If the graph representing the first difference amount is the graph shown in FIG. 11 and the graph representing the moving average is the graph shown in FIG. 13, the graph representing the second difference amount will be as shown in FIG. 14. As can be seen by comparing FIG. 11 and FIG. 14, the second difference amount is generally closer to 0 than the first difference amount.

[0062] In this comparative example, the second difference amount calculated in step S305 is treated as the amount of deviation in the landing position, and the amount of deviation in the landing position is compared with a predetermined threshold value to determine whether or not a deviation in the landing position has occurred.

[0063] However, the comparative example, like the method described in JP 2011-194734 A, uses a moving average, making it impossible to detect landing position deviations with sufficient accuracy. For example, if data corresponding to each of 20 nozzles is used to calculate the moving average, the moving average of the first difference amounts for the nozzles corresponding to the linear pattern indicated by reference numeral 76 in FIG. 15 uses data corresponding to each nozzle that forms the linear pattern (excluding the linear pattern indicated by reference numeral 76) within the range indicated by reference numeral 77 in FIG. 15. Within the range indicated by reference numeral 77 in FIG. 15, the expansion / contraction state of the printing paper 5 can vary significantly depending on the position (i.e., the relationship between the actual landing position and the provisionally fixed landing position can vary significantly depending on the position). As a result, even if the moving average of the first difference amounts is subtracted from the first difference amount, the landing position deviation amount cannot be calculated with sufficient accuracy. Furthermore, for example, when calculating the moving average, if data corresponding to each of the four nozzles is used, the moving average of the first difference amount for the nozzle corresponding to the linear pattern denoted by reference numeral 78 in FIG. 16 is calculated using data corresponding to each nozzle that formed the linear patterns (excluding the linear pattern denoted by reference numeral 78) within the range denoted by reference numeral 79 in FIG. 16. Here, assume that the linear pattern denoted by reference numeral 791 in FIG. 16 was formed by a nozzle causing a landing position deviation. In this case, because the number of data items used to calculate the moving average is small, the data corresponding to the nozzle causing the landing position deviation will cause a relatively large error in the calculation result of the moving average. As a result, even if the moving average of the first difference amount is subtracted from the first difference amount, the landing position deviation amount will not be calculated with high accuracy.

[0064] 7.2 Calculation of landing position deviation in this embodiment Next, the calculation of the amount of deviation of landing positions in this embodiment will be described. Fig. 17 is a block diagram showing the detailed configuration of the discharge defect detection unit 156 in this embodiment. Fig. 18 is a flowchart showing the calculation procedure for the amount of deviation of landing positions in this embodiment.

[0065] 17, discharge defect detection unit 156 includes a temporary landing bullet position calculation unit 610, an actual landing bullet position calculation unit 620, a first difference amount calculation unit 630, a moving average calculation unit 640, a second difference amount calculation unit 650, an average second difference amount calculation unit 660, a landing position deviation amount calculation unit 670, and a comparison unit 680. Note that discharge defect detection unit 156 also includes components for detecting discharge defects and components for detecting shape defects, but these are omitted from FIG.

[0066] When calculating the amount of deviation in the landing position, the temporary fixed bullet position calculation unit 610 first calculates the temporary fixed bullet position 61 based on the captured image 60 of the inspection chart 70 and the design information of the inspection chart 70 (step S311). Specifically, the temporary fixed bullet position 61 is calculated, for example, as follows. When the inspection chart 70 is printed (step S10 in FIG. 9), position marks 88 and 89 for calculating the temporary fixed bullet position 61 are also printed, as shown in FIG. 19, for example. Then, based on the captured image of the printed image (the captured image obtained in step S20 in FIG. 9), the number of linear patterns present in the area corresponding to the gap between the two position marks 88 and 89 is counted. Based on the count value thus obtained (i.e., the number of nozzles that should land ink in the area corresponding to the gap between the two position marks 88 and 89) and the positions (coordinates) of the two position marks 88 and 89, the nozzle pitch (the distance between two adjacent nozzles in the paper width direction) is calculated. Then, based on the position (coordinates) of one position mark 88 and the nozzle pitch, a temporary fixed bullet position 61 is determined for each nozzle that ejects ink into the area corresponding to the gap between the two position marks 88, 89. In this embodiment, the temporary fixed bullet position 61 corresponds to the reference position.

[0067] Next, the actually landed bullet position calculation unit 620 calculates the actually landed bullet position 62 based on the captured image 60 of the inspection chart 70 (step S312). The calculation of the actually landed bullet position 62 will be further described with reference to the flowchart shown in FIG.

[0068] First, the captured image 60 is divided into K portions (split images) in the transport direction of the printing paper 5, where K is an integer greater than or equal to 2 (step S410). In step S410, the boundaries between columns are determined based on the design information of the inspection chart 70 or the pixel values of the captured image 60, and the captured image 60 is divided so that each split image corresponds to one column (in other words, so that each split image corresponds to one nozzle in the transport direction of the printing paper 5). For example, if the captured image 60 shown in part A of FIG. 21 is obtained, the captured image 60 is divided into four split images 601 to 604 as shown in part B of FIG. 21. Note that the boundaries between columns contain a lot of noise. For example, as shown in the portion labeled 81 in FIG. 22, gaps may occur due to adjustment of the ink ejection head 251. Therefore, it is preferable to remove the upper and lower end portions of the split images (i.e., the boundaries between columns) by trimming.

[0069] Next, for each of the K divided images obtained in step S410, the average value of the data (pixel values) of multiple pixels contained in the transport direction of the printing paper 5 is calculated (step S420). This corresponds to converting a captured image such as that shown in part A of Fig. 23 into one-dimensional data such as that shown in part B of Fig. 23. Note that it is preferable to normalize the average value data obtained in step S420, for example, by setting the paper white portion to 0 and the maximum density portion to 255.

[0070] Finally, based on the average values calculated in step S420 (preferably, the average values after normalization), actual landing positions 62 for each nozzle are determined (step S430). For this purpose, the peak positions are calculated as real numbers using techniques such as centroid calculation, equiangular linear fitting, spline interpolation, and Gaussian fitting based on the values of the pixels where the average value peaks (for example, the pixels designated by symbols PE1 to PE5 in part B of FIG. 23) and their neighboring pixels (for example, based on the values of a total of three pixels), and the peak positions are determined as actual landing positions 62.

[0071] Regarding the calculation of the actual impact bullet position 62, step S410 realizes the captured image division step, step S420 realizes the average value calculation step, and step S430 realizes the actual impact bullet position identification step.

[0072] After calculating the actual landing position 62, the first difference amount calculation unit 630 calculates the distance between the actual landing position 62 calculated in step S312 and the temporarily settled bullet position 61 calculated in step S311 (the difference between the actual landing position and the temporarily settled bullet position) as the first difference amount 63 (step S313). An example of a graph showing the first difference amount 63 calculated based on the captured image 60 of the inspection pattern 71 of one stage is as shown in FIG.

[0073] Next, the moving average calculation unit 640 calculates a moving average 64 of the first difference amount 63 in the paper width direction based on the first difference amount 63 calculated in step S313 (step S314). As described above, if an arbitrary nozzle is referred to as a "nozzle of interest," the moving average 64 corresponding to the nozzle of interest is calculated using the first difference amounts 63 for n nozzles, where n is a natural number, that should cause ink to land at a position close to the landing position of ink ejected from the nozzle of interest. More specifically, the moving average 64 corresponding to the nozzle of interest is calculated as the average of the first difference amounts 63 for two or more nozzles (n nozzles) that belong to the same group as the nozzle of interest and that should cause ink to land at a position within a predetermined distance in the paper width direction from the position where the nozzle of interest should land ink.

[0074] Thereafter, the second difference amount calculation unit 650 calculates the difference between the first difference amount 63 calculated in step S313 and the moving average 64 calculated in step S314 as the second difference amount 65 (step S315). Specifically, the second difference amount calculation unit 650 calculates the second difference amount 65 by subtracting the moving average 64 calculated in step S314 from the first difference amount 63 calculated in step S313. By calculating the second difference amount 65 for each nozzle for each row of the test pattern in step S315, 16 graphs are obtained, each representing the second difference amount 65 for each nozzle and corresponding to the 16 rows of test patterns 71(1) to 71(16), as shown schematically in FIG. 24. Note that the processing in steps S311 to S315 in this embodiment is the same as the processing in steps S301 to S305 in the comparative example.

[0075] After calculating the second difference amount 65, the average second difference amount calculation unit 660 calculates the average of the second difference amounts 65 at the position of each nozzle as the average second difference amount 66 (step S316). In step S316, each of the multiple nozzles included in the head unit 25 is designated as a target nozzle, and the average second difference amount 66 is calculated as follows. Here, the nozzle corresponding to the linear pattern designated by reference numeral 83 in FIG. 25 is designated as the target nozzle, and a method for calculating the average second difference amount 66 for the target nozzle will be described. As can be seen from FIG. 25, the target nozzle belongs to the group corresponding to the third-stage test pattern 71(3). In this case, when calculating the average second difference amount 66, data on the second difference amount 65 for nozzles that belong to a group other than the group corresponding to the third-stage test pattern 71(3) and that are to land ink at a position close to the position in the paper width direction where the target nozzle is to land ink is used. Specifically, data on the second difference amounts 65 for the 15 nozzles that should land ink within the range indicated by the arrow labeled 84 in FIG. 25, i.e., the 15 nozzles corresponding to the 15 linear patterns labeled 46(1) to 46(15) in FIG. 25, is used. For this purpose, these 15 nozzles are pre-assigned to the nozzle of interest. Ultimately, the average of the second difference amounts 65 for these 15 nozzles is used as the average second difference amount 66 for the nozzle of interest. As described above, in step S316 of this embodiment, the average of the second difference amounts 65 for the nozzles that belong to all groups different from the group to which the nozzle of interest belongs and that are pre-associated with the nozzle of interest is calculated as the average second difference amount 66 corresponding to the nozzle of interest. By sequentially setting multiple nozzles that belong to the group corresponding to the third-stage test pattern 71(3) as the nozzle of interest and calculating the average second difference amount 66, a graph such as that shown in FIG. 26 is obtained as a graph representing the average second difference amount 66.

[0076] The second difference amount 65 is affected not only by the impact position deviation, but also by the expansion and contraction of the printing paper 5 and errors that occur when the inline scanner 40 captures the printed image of the inspection chart 70 (however, the following focuses on the impact of the expansion and contraction of the printing paper 5). The average second difference amount 66 is obtained by averaging such second difference amounts 65. Typically, the number of nozzles that cause impact position deviation is significantly smaller than the number of nozzles included in the head unit 25. Therefore, the average second difference amount 66 is hardly affected by the impact position deviation. As described above, the average second difference amount 66 is mainly affected by the expansion and contraction of the printing paper 5.

[0077] After calculating the average second difference amount 66, the impact position deviation amount calculation unit 670 calculates, for each nozzle, the difference between the second difference amount 65 calculated in step S315 and the average second difference amount 66 calculated in step S316 as the impact position deviation amount 67 (step S317). More specifically, the impact position deviation amount 67 is calculated by subtracting the average second difference amount 66 calculated in step S316 from the second difference amount 65 calculated in step S315.

[0078] After the difference between the second difference amount 65 and the average second difference amount 66 is calculated as the landing position deviation amount 67 in the above manner, the comparison unit 680 compares the landing position deviation amount 67 with a predetermined threshold. As a result, if the landing position deviation amount is greater than the threshold, it is determined that the target nozzle is causing landing position deviation, and if the landing position deviation amount is equal to or less than the threshold, it is determined that the target nozzle is not causing landing position deviation. Then, in response to this determination, discharge defect information 52 is output from the discharge defect detection unit 156.

[0079] In this embodiment, step S311 implements a reference position calculation step, step S312 implements an actual impact position calculation step, step S313 implements a first difference amount calculation step, step S314 implements a moving average calculation step, step S315 implements a second difference amount calculation step, step S316 implements an average second difference amount calculation step, and step S317 implements an impact position deviation amount calculation step. Also, step S311 implements a reference position calculation process, step S312 implements an actual impact position calculation process, step S313 implements a first difference amount calculation process, step S314 implements a moving average calculation process, step S315 implements a second difference amount calculation process, step S316 implements an average second difference amount calculation process, and step S317 implements an impact position deviation amount calculation process.

[0080] <8. Effects> According to this embodiment, the difference between the "difference between the actual landing position 62 and the temporarily settled bullet position 61 (first difference amount 63)" and the "moving average 64 of the difference between the actual landing position 62 and the temporarily settled bullet position 61 (first difference amount 63)" is calculated as the second difference amount 65. Then, the average of the second difference amounts 65 for nozzles belonging to a different group from the nozzle of interest is calculated as the average second difference amount 66 corresponding to the nozzle of interest. The difference between the second difference amount 65 and the average second difference amount 66 is calculated as the landing position deviation amount. Here, the second difference amount 65 is affected by landing position deviation and by expansion and contraction of the printing paper 5. Furthermore, the average second difference amount 66 is mainly affected by expansion and contraction of the printing paper 5. Therefore, by using the difference between the second difference amount 65 and the average second difference amount 66 as the landing position deviation amount 67, the impact of expansion and contraction of the printing paper 5 on the landing position deviation amount 67 calculated for each nozzle can be reduced compared to conventional methods, even if a large number of data points are used to calculate the moving average. That is, the impact position deviation amount 67 can be determined with high precision.

[0081] The accuracy of determining the landing position deviation amount 67 will be explained using hypothetical numerical values. Assume that the deviation amount of the printing paper 5 at the position of the target nozzle is 20 μm, and the actual landing position deviation amount for the target nozzle is 10 μm. In this case, the first difference amount 63 is 30 μm. Assume that the moving average 64 of the first difference amount 63 is 23 μm. In this case, the second difference amount 65 is 7 μm (= 30 μm - 23 μm). Since the actual landing position deviation amount is 10 μm, the error of 3 μm (= 10 μm - 7 μm) results from the large number of data points used to calculate the moving average 64. If the nozzle that is pre-assigned to the target nozzle in order to determine the average second difference amount 66 is called the "corresponding nozzle," the deviation amount of the printing paper 5 at the position of the corresponding nozzle is considered to be approximately equal to the deviation amount of the printing paper 5 at the position of the target nozzle (20 μm). Furthermore, it is considered that the "moving average 64 of the first difference amount 63" for the corresponding nozzle is approximately equal to the "moving average 64 of the first difference amount 63" for the target nozzle (23 μm). Furthermore, as described above, the average second difference amount 66 is hardly affected by the impact position deviation. From the above, the average second difference amount 66 is approximately -3 μm (= 20 μm - 23 μm). As a result, the impact position deviation amount 67 is approximately 10 μm (= 7 μm - (-3 μm)). In this way, the impact position deviation amount 67 calculated by the method of this embodiment is approximately equal to the actual impact position deviation amount.

[0082] Next, let's assume that the amount of deviation of the printing paper 5 at the position of the nozzle of interest is 20 μm, and that the actual amount of deviation of the landing position for the nozzle of interest is 0 μm. In this case, the first difference amount 63 is 20 μm. Again, let's assume that the moving average 64 of the first difference amount 63 is 23 μm. In this case, the second difference amount 65 is -3 μm (= 20 μm - 23 μm). Because the actual amount of deviation of the landing position is 0 μm, the error of 3 μm (= 0 μm - (-3 μm)) is due to the large number of data points used to calculate the moving average 64. In this example, the average second difference amount 66 is approximately -3 μm (= 20 μm - 23 μm). As a result, the amount of deviation of the landing position 67 is approximately 0 μm (= -3 μm - (-3 μm)). In this way, the amount of deviation of the landing position 67 can be accurately determined even for nozzles that are not causing landing position deviation.

[0083] For a certain case in which data corresponding to 20 nozzles was used to calculate the moving average 64 of the first difference amount 63, a graph showing the second difference amount (the landing position deviation amount in the comparative example) 65 is shown in section A of FIG. 27, and a graph showing the landing position deviation amount 67 is shown in section B of FIG. 27. In this case, the standard deviation of the second difference amount 65 is 0.64 pixels (2.7 μm), while the standard deviation of the landing position deviation amount 67 is 0.47 pixels (2.0 μm). Note that the imaging resolution of the inline scanner 40 is 600 dpi. As described above, the number of nozzles causing landing position deviation is significantly smaller than the number of nozzles included in the head unit 25, so the standard deviations of the second difference amount 65 and the landing position deviation amount 67 should be close to zero. Considering this, it can be seen that the accuracy of calculation of the amount of deviation of landing positions is higher in this embodiment than in the comparative example, because the standard deviation of the amount of deviation of landing positions 67 in this embodiment is smaller than the standard deviation of the second difference amount (the amount of deviation of landing positions in the comparative example) 65. Since the amount of deviation of landing positions can be calculated with such high accuracy, it is possible to detect the deviation of landing positions with high accuracy.

[0084] As described above, this embodiment enables an inkjet printing device to accurately detect the magnitude of landing position deviation (amount of landing position deviation), which is one type of nozzle ejection defect. Furthermore, because it is now possible to detect landing position deviation that could not be detected using conventional methods, it is possible to reduce the waste of printing paper 5 and ink due to reprinting. In this way, it is possible to contribute to the achievement of the SDGs (Sustainable Development Goals).

[0085] <9. Variations> Modifications of the above embodiment will now be described.

[0086] <9.1 First Modification> In the above embodiment, the difference between the moving average 64 of the first difference amount 63 and the first difference amount 63 is calculated as the second difference amount 65. However, the present invention is not limited to this. The sum of the temporary fixed bullet position 61 and the moving average 64 of the first difference amount 63 may be calculated as the ideal impact position, and the difference between the actual impact position 62 and the ideal impact position may be calculated as the second difference amount 65.

[0087] Fig. 28 is a block diagram showing the detailed configuration of the discharge defect detection unit 156 in this modified example. Fig. 29 is a flowchart showing the procedure for calculating the amount of deviation in landing position in this modified example. Below, we will explain the points that are different from the above embodiment.

[0088] Steps S321 to S324 are the same as steps S311 to S314 in the above embodiment. After calculating the moving average 64 of the first difference amount 63 in step S324, the ideal landing position calculation unit 652 calculates the ideal position (ideal landing position) where the ink ejected from each nozzle should land (step S325). Specifically, the ideal landing position calculation unit 652 calculates the ideal landing position by adding the temporary landing position 61 calculated in step S321 and the moving average 64 calculated in step S324. Then, the second difference amount calculation unit 650 calculates the difference between the actual landing position 62 calculated in step S322 and the ideal landing position calculated in step S325 as the second difference amount 65 (step S326). Specifically, second difference amount calculation section 650 calculates second difference amount 65 by subtracting the ideal landing position calculated in step S325 from the actual landing position 62 calculated in step S322. Steps S327 to S328 are the same as steps S316 to S317 in the above embodiment.

[0089] According to this modification, the difference between the actual landing position 62 and the ideal landing position is calculated as the second difference amount 65. Here, the ideal landing position is the sum of the temporarily settled bullet position 61 and the moving average 64 of the first difference amount 63. Therefore, the difference between the actual landing position 62 and the sum of the temporarily settled bullet position 61 and the moving average 64 of the first difference amount 63 is the second difference amount 65. In other words, the second difference amount 65 is calculated by subtracting the moving average 64 of the first difference amount 63 from the difference between the actual landing position 62 and the temporarily settled bullet position 61. Since the difference between the actual landing position 62 and the temporarily settled bullet position 61 is the first difference amount 63, the second difference amount 65 is calculated by subtracting the moving average 64 of the first difference amount 63 from the first difference amount 63. As described above, the second difference amount 65 calculated in this modification is equal to the second difference amount 65 calculated in the above embodiment. Therefore, the landing position deviation amount 67 obtained in this modified example is equal to the landing position deviation amount 67 obtained in the above embodiment. Therefore, according to this modified example, as in the above embodiment, it is possible to accurately detect the magnitude of landing position deviation (landing position deviation amount), which is one type of nozzle ejection defect, in an inkjet printing device.

[0090] <9.2 Second Modification> In the above embodiment, when calculating the average second difference amount 66 for the nozzle of interest, data on the second difference amounts 65 for nozzles belonging to all groups other than the group to which the nozzle of interest belongs was used. However, the present invention is not limited to this. The average second difference amount 66 for the nozzle of interest may be calculated using data on the second difference amounts 65 for a predetermined number of nozzles belonging to some groups (two or more groups) other than the group to which the nozzle of interest belongs.

[0091] In this modified example, for example, the average second difference amount 66 for the nozzle of interest is calculated using data on the second difference amounts 65 for eight nozzles (nozzles belonging to each of eight groups) that are to land ink at positions near (near in the paper width direction) the position where the nozzle of interest is to land ink. In this case, the average second difference amount 66 for the nozzle corresponding to the linear pattern labeled 85 in FIG. 30 is calculated by calculating the average of the second difference amounts 65 for the eight nozzles that correspond to each of the eight linear patterns labeled 47(1) to 47(8) in FIG. 30. Furthermore, the average second difference amount 66 for the nozzle corresponding to the linear pattern labeled 86 in FIG. 31 is calculated by calculating the average of the second difference amounts 65 for the eight nozzles that correspond to each of the eight linear patterns labeled 48(1) to 48(8) in FIG. 31. To achieve this, each nozzle is previously associated with eight nozzles as described above.

[0092] As described above, in this modified example, in step S316 of Figure 18, the average of the second difference amounts 65 for nozzles that belong to each of some groups (two or more groups) different from the group to which the target nozzle belongs and that are pre-associated with the target nozzle is calculated as the average second difference amount 66 corresponding to the target nozzle.

[0093] According to this modification, it is possible to accurately detect the magnitude of landing position deviation (amount of landing position deviation), which is one type of nozzle ejection defect, while suppressing an increase in the calculation load for the inkjet printing device.

[0094] <10.Other> In the above embodiment (including the modified example), an inkjet printing device 10 that performs color printing is used. However, the present invention is not limited to this, and an inkjet printing device that performs monochrome printing may also be used.

[0095] Furthermore, in the above-described embodiment (including the modified examples), an inkjet printing apparatus 10 using aqueous ink was employed. However, the present invention is not limited to this, and an inkjet printing apparatus using 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 irradiating it with ultraviolet light is provided inside the printing mechanism 201 (see FIG. 2) instead of the drying mechanism 206.

[0096] It is also possible to carry out a step of correcting the landing position deviation of the nozzles where the landing position deviation has been confirmed, based on the amount of landing position deviation calculated in the above embodiment (including the modified example). [Explanation of symbols]

[0097] 10...Inkjet printing device 13...Print control program 40...Inline scanner 61...Temporary fixed bullet position 62...Actual impact position 63...First difference amount 64...(First difference amount) moving average 65…Second difference amount 66…Average second difference amount 67...Amount of deviation in impact position 70...Inspection chart 72...Linear pattern 100...printing control device 156...Discharge defect detection unit 157...Print data correction unit 200...printing machine body 201...Printing mechanism 205...Recording Department 251...Ink ejection head 610...Temporary fixed bullet position calculation unit 620...Actual impact position calculation unit 630...First difference calculation unit 640...Moving average calculation unit 650…Second difference calculation unit 652...Ideal impact position calculation unit 660…Average second difference calculation unit 670... Impact position deviation amount calculation unit 680...Comparison section

Claims

1. 1. A method for detecting an amount of deviation in an ink landing position in a printing device having a plurality of nozzles that eject ink onto a printing medium that is transported in a first direction, comprising: an inspection chart printing step of causing the printing device to print an inspection chart including M rows of inspection patterns that correspond one-to-one to the M groups obtained by grouping the plurality of nozzles, where M is an integer equal to or greater than 2; an inspection chart imaging step of imaging the inspection chart printed in the inspection chart printing step; a reference position calculation step of determining, as a reference position, a position where ink ejected from each of the plurality of nozzles is expected to land on the printing medium, with each of the plurality of nozzles being a target nozzle; an actual landing position calculation step of determining, based on the captured image obtained in the inspection chart imaging step, the position where the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation step of calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation step of calculating, as a moving average corresponding to the target nozzle, an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at a position within a predetermined distance in a second direction perpendicular to the first direction from a position where the target nozzle is to land ink; a second difference amount calculation step of calculating a difference between the difference between the actual landing position and the reference position and the moving average as a second difference amount; an average second difference amount calculation step of calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation step of calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; a method for detecting a deviation amount of a landing position,

2. 2. The method for detecting an amount of deviation of a landing position according to claim 1, wherein in the second difference amount calculation step, the second difference amount is calculated by calculating a difference between the first difference amount calculated in the first difference amount calculation step and the moving average calculated in the moving average calculation step.

3. 2. The method for detecting an amount of deviation of a landing position according to claim 1, wherein in the second difference amount calculation step, an ideal landing position is calculated as a sum of the reference position calculated in the reference position calculation step and the moving average calculated in the moving average calculation step, and the second difference amount is calculated by calculating a difference between the actual landing position calculated in the actual landing position calculation step and the ideal landing position.

4. 2. The method for detecting an amount of deviation of an impact position according to claim 1, wherein, in the average second difference amount calculation step, the two or more nozzles that are pre-associated with the target nozzle include nozzles that belong to all groups different from the group to which the target nozzle belongs.

5. 2. The method for detecting an amount of deviation in an impact position according to claim 1, wherein, in the average second difference amount calculation step, the two or more nozzles pre-associated with the target nozzle include a predetermined number of nozzles that belong to each of two or more groups that are different from the group to which the target nozzle belongs, and that should land ink at a position close to a position at which the target nozzle should land ink in the second direction.

6. In the reference position calculation step, a nozzle pitch, which is the distance between two adjacent nozzles in the second direction, is calculated based on the positions of two position marks included in the captured image and the number of nozzles that should land ink in an area corresponding to the area between the two position marks; 2. The method for detecting an amount of deviation of a landing position according to claim 1, wherein the reference position for each nozzle is determined using the nozzle pitch.

7. The actual landing position calculation step includes: a captured image dividing step of dividing the captured image into K pieces in the first direction, where K is an integer equal to or greater than 2, so that each divided image corresponds to one nozzle in the first direction; an average value calculation step of calculating an average value of data of a plurality of pixels included in the first direction for each of the K divided images obtained in the captured image division step; an actual landing position specifying step of determining the actual landing position for each nozzle based on the average value calculated in the average value calculating step; 2. The method for detecting a deviation amount of a landing position according to claim 1, further comprising:

8. 8. The method for detecting the amount of deviation of an impact position according to claim 1, wherein each of the M stages of the inspection patterns is composed of a plurality of linear patterns extending in the first direction and arranged at equal intervals in the second direction.

9. A printing device including a plurality of nozzles that eject ink onto a printing medium transported in a first direction, an imaging device that captures a print image, and a control unit that controls the ejection of ink from the plurality of nozzles and the imaging of the print image by the imaging device, The control unit an inspection chart printing process that controls ink ejection from the plurality of nozzles so as to print an inspection chart including M rows of inspection patterns that correspond one-to-one to M groups obtained by grouping the plurality of nozzles, where M is an integer equal to or greater than 2; an inspection chart imaging process for imaging the inspection chart printed by the inspection chart printing process with the imaging device; a reference position calculation process in which each of the plurality of nozzles is designated as a target nozzle, and a position where ink ejected from the target nozzle is expected to land on the printing medium is determined as a reference position; an actual landing position calculation process for determining, based on the captured image obtained by the inspection chart imaging process, the position at which the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation process for calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation process for calculating an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at a position within a predetermined distance in a second direction perpendicular to the first direction from a position where ink is to be landed by the target nozzle, as a moving average corresponding to the target nozzle; a second difference amount calculation process for calculating a difference between the actual landing position and the reference position and the moving average as a second difference amount; an average second difference amount calculation process for calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation process for calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; A printing device that executes the above.

10. 1. A computer program for detecting an amount of deviation in an ink landing position in a printing device including a plurality of nozzles that eject ink onto a printing medium transported in a first direction and an imaging device that captures an image of a print medium, the computer program comprising: A computer included in the printing device an inspection chart printing step of controlling ink ejection from the plurality of nozzles so as to print an inspection chart including M rows of inspection patterns that correspond one-to-one to M groups obtained by grouping the plurality of nozzles, where M is an integer equal to or greater than 2; an inspection chart imaging step of imaging the inspection chart printed in the inspection chart printing step with the imaging device; a reference position calculation step of determining, as a reference position, a position where ink ejected from each of the plurality of nozzles is expected to land on the printing medium, with each of the nozzles being a target nozzle; an actual landing position calculation step of determining, based on the captured image obtained in the inspection chart imaging step, the position where the ink ejected from the target nozzle actually lands on the printing medium as the actual landing position; a first difference amount calculation step of calculating a difference between the actual landing position and the reference position as a first difference amount; a moving average calculation step of calculating, as a moving average corresponding to the target nozzle, an average of the first difference amounts for two or more nozzles that belong to the same group as the target nozzle and that are to land ink at a position within a predetermined distance in a second direction perpendicular to the first direction from a position where the target nozzle is to land ink; a second difference amount calculation step of calculating a difference between the difference between the actual landing position and the reference position and the moving average as a second difference amount; an average second difference amount calculation step of calculating an average of the second difference amounts for two or more nozzles that belong to a different group from the target nozzle and are associated in advance with the target nozzle, as an average second difference amount corresponding to the target nozzle; a landing position deviation amount calculation step of calculating the difference between the second difference amount and the average second difference amount as the landing position deviation amount; 10. A program for detecting a deviation amount of a landing position, comprising:

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