JP6897992B2 - Adjustment method in inkjet printing equipment and inkjet printing equipment - Google Patents

Description

An inkjet printing device having a function of improving the print image quality when printing on a predetermined substrate by a predetermined printing method using a predetermined device equipped with a predetermined ink in a printing device using an inkjet head. And a method for improving print image quality in an inkjet printing apparatus.

As is well known, inkjet technology is used as an on-demand non-contact printing technology in a wide range of applications such as printing on paper media, decorating building materials and automobile parts, and applying functional materials to electrical parts. It has begun to be used in so-called industrial applications where inkjet printing equipment is used for the production of products.

There are two main printing methods for inkjet. One is the so-called single-pass method that requires high speed, and when printing, there are errors in the amount of ink ejected and the direction of ejection due to individual differences in the characteristics of each nozzle in the inkjet head, and individual differences in the characteristics of each inkjet head itself. The color density of the original image data to be printed differs from the color density of the actual printed matter, which is caused by an error in the amount of ink ejected or the direction of ejection due to the ink jet, and streaks at the joints between a plurality of adjacent inkjet heads. Conventionally, there has been a problem that it is difficult to ensure print quality due to an ink density error. The other is the so-called multi-pass method that requires high print quality, and details will be explained below, but there has been a problem that the printing speed is slow and it is not suitable for industrial use, and even if it is the multi-pass method. There is a problem that a certain degree of ink density error occurs.

Individual inkjet heads used in industrial inkjet printing equipment generally have a large number of nozzles inside each of them, and usually, by having 1000 or more nozzles, the range in which printing can be performed at one time is increased. We are trying to improve the sex.

For example, one inkjet head model has 1024 ink ejection nozzles in one inkjet head, which are arranged in a row. By ejecting ink from the nozzle at a predetermined position while the head or the printed matter moves, an arbitrary image can be drawn on a two-dimensional plane.

As described above, in the inkjet printing apparatus, where ink density error occurs due to a plurality of factors, regarding the error caused by the ink ejection amount, ejection direction, ejection speed, etc. of each nozzle in each inkjet head. Has proposed this countermeasure in Patent Document 1 as a prior art related to this countermeasure. As an overview, in order to correct errors in the ink ejection amount, ejection direction, ejection speed, etc. of each nozzle in one inkjet head, a test pattern is printed, and the test pattern is read by an image pickup device. Ink density correction data is calculated based on the read image data, and the image data to be printed is converted based on the correction data. The prior art is mainly used in small household inkjet printing equipment.

Japanese Patent Application Laid-Open No. 5-220977

However, in the inkjet printing apparatus for industrial use, which has been developed in recent years, it is necessary to increase the speed for high productivity and to increase the size accordingly, and it is common to use a plurality of heads for each color. .. In this way, with the increase in size and scale of the inkjet printing device, in addition to the error in the ink ejection amount and the ejection direction for each nozzle in each inkjet head, mutual inkjet heads when a plurality of inkjet heads are connected are connected. Ink density non-uniformity such as so-called streaks at the joints between multiple inkjet heads becomes more conspicuous due to errors in the ink ejection amount and ejection direction between the ink jets and the increase in the number of connected inkjet heads. There is a problem that the image quality of the image drawn is deteriorated more remarkably due to the ink density error caused by a plurality of factors.

In addition, in inkjet printing equipment for industrial use, not only water-based inks for printing on paper, but also solvent-based inks, UV inks, and functional inks such as insulators, conductors, and adhesives are ejected with so-called thermal heads. Instead, a piezoelectric inkjet head equipped with a piezoelectric element such as a piezo element is generally used. Due to structural reasons and the manufacturing method of the piezoelectric inkjet head, the error in ink density due to the error in the ink ejection amount and ejection direction between individual inkjet heads is more remarkable than that in the thermal head, and this error. In response to this, there is an example in which the error in ink density is corrected by adjusting the voltage applied to the piezoelectric element. However, when high image quality is required, the ink density may not be sufficiently corrected only by adjusting the applied voltage. The problem is that the ink density error occurs in the part showing high color density, the part showing medium color density, and the part showing low color density in the color density of the printed image, respectively. Where the degree of error is different Since the adjustment of the applied voltage to the inkjet head can be performed only by a fixed value, it is possible to correct a certain color density part by the applied voltage, but the other color density parts are different at the same time. It is caused by the inability to apply the applied voltage.

Further, in the case of using an inkjet printing device as a production facility in an industrial application, it is expected that an inkjet printing device will be added according to an increase in the production amount of the production object, but individual differences occur in the manufacture of the inkjet head. Therefore, even if the same type of inkjet printing device has the same design, there is a problem that an error occurs in the color and ink density of the printed matter for each individual inkjet printing device actually produced. This is particularly noticeable in industrial inkjet printing equipment, which is becoming larger in size. Then, such a problem is a method disclosed in Patent Document 1 which is premised on correcting an ink density error of a printed matter in a small inkjet printing apparatus and is premised on correcting an ink density error of one inkjet head, and others. According to the conventional invention, it is not possible to collectively solve the ink density error that occurs in the large-sized industrial inkjet printing apparatus. The problem is that in multi-pass printing, as described below, when printing the lines of the pixels that make up the image, one line or adjacent lines are printed using different nozzles, so the nozzles. It is possible to alleviate the ink density error that occurs mainly due to individual differences, but it is particularly noticeable in single-pass inkjet printing equipment that pursues high-speed printing because processing such as multi-pass printing cannot be performed. Will occur in.

Further, as a printing method of an inkjet printing apparatus, there is a multi-pass method in which the same portion is divided into a plurality of times and printed in order to pursue high image quality, although the productivity is lowered. In this regard, even with the multi-pass method, the so-called number of passes, which is the number of times the same part is printed in order to improve the productivity of printed matter with the aim of speeding up printing, is defined as the number of passes. A method to reduce it as much as possible can be considered. However, even with this method, there is a problem that it is difficult to achieve both image quality and productivity because the image quality is eventually deteriorated by reducing the number of passes. Since the relationship between the nozzle and the image data becomes complicated in the multipath method, such a problem cannot be solved by directly applying the invention disclosed in Patent Document 1.

The present invention has been proposed to solve the above problems, and not only the error of the ink ejection amount and the ejection direction of each nozzle in each inkjet head, but also the mutual error when a plurality of inkjet heads are connected. Multiple ink jet heads such as so-called streaks and other non-uniformity of ink density at the joints between multiple inkjet heads due to errors in the amount and direction of ink ejection between the inkjet heads and the increase in the number of connected inkjet heads. The present invention proposes a print image quality improving method in an inkjet printing apparatus and an inkjet printing apparatus having a function of collectively eliminating all the ink density errors caused by the above factors and improving the printed image quality more than the conventional method.

The following methods are proposed to solve the above problems.

That is, according to the present invention, in an inkjet printing apparatus that prints by relatively moving an inkjet head having a plurality of nozzles and an object to be printed, an error in ink density, which is the density of ink to be ejected from the inkjet head. In the method of correcting the above, a step of adjusting the usage conditions of the inkjet head to individually adjust the ink density, and printing a color density pattern and a test pattern having four or more alignment marks arranged on the outer periphery of the color density pattern are printed. A modification including a step of imaging a test pattern to create a test pattern image, a step of reading the coordinates of the alignment mark on the test pattern image, and a step of calculating a deformation parameter of the color density pattern. A test pattern deformation processing step including a parameter calculation step and a step of deforming the color density pattern on the test pattern image based on the deformation parameter, and correction data based on the measurement data of the deformed test pattern image. It has a correction data calculation step to be calculated and a step of correcting an ink density error in the entire image printed on the printed matter by converting the entire image to be printed based on the correction data.
In the deformation parameter calculation step, parameters for using the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image for correction are calculated.
The test pattern deformation processing step is characterized in that the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image are corrected by the deformation parameters.

Further, in the present invention, a group of inkjet heads configured to have a width corresponding to the printing width by mounting two or more ink jet heads is mounted for one type or more of ink, and the printed material is once printed. In an inkjet printing apparatus that is a single-pass system in which printing is completed only by passing through the nozzle surface side of the head group, the density of ink to be ejected from each of the inkjet heads is adjusted by adjusting the usage conditions of the inkjet heads. A means for adjusting the ink density, a means for printing a color density pattern and a test pattern having four or more alignment marks arranged on the outer periphery of the color density pattern, and a means for imaging the test pattern to create a test pattern image. A deformation parameter calculating means including a test pattern imaging means for printing, a means for reading the coordinates of the alignment mark on the test pattern image, and a means for calculating the deformation parameter of the color density pattern, and a deformation parameter calculating means on the test pattern image based on the deformation parameter. A test pattern deformation processing means including a means for deforming the color density pattern, a correction data calculation means for calculating correction data based on the measurement data of the deformed test pattern image, and printing based on the correction data should be performed. It has a means for correcting an ink density error in the entire image printed on a printed matter by converting the entire image.
The deformation parameter calculating means calculates a parameter that uses the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image for correction.
The test pattern deformation processing means is characterized in that the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image are corrected by the deformation parameters.

In addition, the present invention
The printed matter and the inkjet head are moved in a direction parallel to the direction in which the nozzles of the inkjet head are lined up relative to the basic unit, which is the width to be printed by one movement scanning of the inkjet head, and the inkjet head and the printed matter are moved. A multi-pass printing device equipped with one or more of the inkjet heads, which completes printing by ejecting ink while moving and scanning the ink a plurality of times in a direction perpendicular to the direction in which the nozzles are lined up. In the above, a means for adjusting the ink density, which is the density of the ink to be ejected from each of the inkjet heads, by adjusting the usage conditions of the inkjet head, and a color density having a width of two or more basic units. A means for printing a pattern and a test pattern having four or more alignment marks arranged on the outer periphery of the color density pattern, a test pattern imaging means for imaging the test pattern and creating a test pattern image, and a test pattern image. A test including a deformation parameter calculation means including a means for reading the coordinates of the alignment mark and calculating a deformation parameter of the color density pattern, and a means for deforming the color density pattern on the test pattern image based on the deformation parameter. It is printed on the printed matter by converting the pattern deformation processing means, the correction data calculation means that calculates the correction data based on the measurement data of the deformed test pattern image, and the entire image to be printed based on the correction data. It has a means to correct the ink density error in the entire image.
The deformation parameter calculating means calculates a parameter that uses the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image for correction.
The test pattern deformation processing means is characterized in that the coordinates on the plane orthogonal coordinate system of the pixels constituting the color density pattern on the test pattern image are corrected by the deformation parameters.

According to the present invention, in a large-sized industrial inkjet printing apparatus, an ink density error of a nozzle in an inkjet head that cannot be sufficiently corrected by a conventional method, an ink density error between individual inkjet heads constituting an inkjet head group, and an adjacent ink jet head group. Inkjet density error at the joint part of the inkjet head, ink density error caused by individual differences between the manufactured individual inkjet printing devices, and ink density error at the adjacent part between the basic units described later in multi-pass printing. , All of them can be efficiently and highly corrected at once, and high-quality printing can be realized in the single-pass method. Even in the multi-pass method printing, as described later, printing with a smaller number of passes and printing with a larger number of passes can be achieved. High-quality printing equal to or better than that can be achieved.

It is a figure explaining the general printing method in single-pass type printing. It is a figure explaining the ink density error correction which occurs between a plurality of inkjet heads carried out by a prior art. It is a figure which shows the measurement example of the density | concentration data which read and measured the test pattern. It is a figure explaining the relationship between the ink density correction and the target density value which should be targeted at the time of correction. It is a figure which shows the example of the test pattern in the printing of a single pass method. It is a figure which shows the measurement example of the ink density data in single-pass type printing. It is a figure explaining the overlap process of an inkjet head. It is a flowchart of the work procedure of this invention in a single pass system. This is an example of ink density error measurement when the input color density is 9 steps in total. It is a graph which cut out and plotted the ink density error data in n nozzles and the nozzles around them. It is explanatory drawing of the logic which calculates the correction data. It is a flowchart of the work of converting the image data based on the correction data created in the single pass method. It is a figure which shows the example which converted the ink density error of n nozzles based on the correction data. It is explanatory drawing of an example of the degrading process. It is a figure explaining the general printing method of the multi-pass type printing. It is a figure which shows the example of the test pattern in the multipath printing. It is a figure which shows the example of the inkjet head which has 1000 nozzles, and the correspondence relationship between the nozzle used for printing and the printed pixel. It is a flowchart of the work procedure of this invention in a multipath system. It is a flowchart of the work of converting image data based on the correction data created in the multipath method. It is a figure which shows the structural example of the inkjet printing apparatus which used this invention. It is a conceptual diagram which shows that the captured image is deformed based on the calculated parameter. It is a figure which shows the example of the wide test pattern which cannot fit in a scanner.

Hereinafter, the first embodiment will be described in detail with reference to the drawings.

FIG. 1 shows an example of a general print configuration in the single pass method. The inkjet head 1a, the inkjet head 1b, the inkjet head 1c, and the inkjet head 1d are arranged in a horizontal row in the nozzle row direction of the inkjet head to form an inkjet head group, so that printing is wider than the width of one inkjet head. Cover the area. The print area on the object to be printed 2 is divided into a region 3 to a region 6, and the print region to which each inkjet head constituting the inkjet head group should be in charge of printing, the region 3 is the head 1a, the region 4 is the head 1b, and the region. 5 is in charge of the head 1c, and the region 6 is in charge of the head 1d. When the printed matter 2 passes directly under the nozzle surface of the inkjet head 1a from the inkjet head 1a, the inkjet head 1a to the nozzle of the inkjet head 1d By ejecting the ink, an image is printed on the object to be printed when the object to be printed has passed. In FIG. 1, the inkjet heads 1a to 1d are arranged in a staggered pattern, but as long as they are arranged so as to cover the printed area, an arrangement method other than the staggered arrangement may be used, and the inkjet head group is formed. The number of inkjet heads can be added or decreased depending on the width of the printed matter. In addition, in FIG. 1, the individual adjacent inkjet heads are arranged so as to overlap each other in a partially overlapping manner, and this point will be described in detail below, but depending on the specifications of the inkjet head to be used, they may overlap. An arrangement method that does not wrap can also be assumed.

FIG. 2 shows an example of correction by a conventional method for an ink density error of a printed matter, which occurs between a plurality of inkjet heads and the color density of the original image data to be printed is different from the color density of the actual printed matter. FIG. 2A is a graph of the ink density error before correction, and FIG. 2B is a graph of the ink density error after correction. Similar to FIG. 1, the printed area on the printed matter 2 is divided into an area 3 to an area 6, the area 3 is the inkjet head 1a, the area 4 is the inkjet head 1b, the area 5 is the inkjet head 1c, and the area 6 is the inkjet head 1d. Shows an example in charge of printing. Although the present invention can be used even when a thermal inkjet head is used, the inkjet head in the example shown here assumes a so-called piezo inkjet head that uses a piezoelectric element and ejects ink by a piezoelectric effect. .. As described above, even if the inkjet heads are of the same model, there are individual differences mainly due to the use of the piezo element, and as shown in FIG. 2A, the ink density errors from the inkjet heads 1a to the inkjet heads 1d are large. When an image is printed without correction, the ink density differs greatly depending on the print area, which adversely affects the image quality. Here, FIG. 2B shows an example in which the drive voltage of the piezo element, which is the usage condition of each inkjet head, is adjusted to correct the ink density error between the plurality of inkjet heads. Comparing FIG. 2 (a) and FIG. 2 (b), although a certain degree of correction can be made, there is a limit to the range of the applied voltage that can be adjusted, and as described above, the adjustment of the applied voltage is a fixed value. There is also a problem that different ink density errors that occur in different color density bands cannot be corrected at once. In addition, changing the drive voltage changes the ejection speed of the ejected ink droplets, which causes changes in the landing position on the base material, which affects the image quality of the printed image. Problems may occur.

FIG. 3 is a measurement example of ink density data obtained by printing a test pattern in the configuration shown in FIG. 1 and reading and measuring the test pattern. In this example, the dark color density data example is the measurement data 7 and the light color density data. An example is the measurement data 8, and the measurement data 7 and the areas 3 to 6 of the measurement data 8 correspond to the print area of the object to be printed in FIG. In the example of FIG. 3, the ink density error in the inkjet head 1a is the largest, is a little in the inkjet head 1b, and is almost nonexistent in the inkjet head 1c and the inkjet head 1d. This is an example in which the average density in the inkjet head is higher than the others by the inkjet head 1c.

Further, in this example, the ink density of the joint portion between the inkjet heads 1a and 1b in FIG. 3 is high, and so-called black streaks appearing in a band shape on the printed image of the portion having the high ink density is generated, and the inkjet head. The ink density of the adjacent joints between 1b and 1c and 1c and 1d is low, and so-called white streaks appear as bands on the printed image.
Normally, the measurement data 7 and the measurement data 8 usually show the same tendency as long as the measurement data of the parts having different color densities are printed using the same inkjet head, but the amount to be corrected. Is often different. Therefore, a test pattern for each different concentration, which will be described separately, will be used.

FIG. 4 is a graph showing a measured value of color density and a target density value for explaining the relationship between the ink density correction and the target density value to be targeted at the time of correction. The horizontal axis shows the position in the print width direction, and the vertical axis shows the color density. The measurement data 10 shows the measured value of the color density of the test pattern. It can be seen that the color density value is high at a certain position and the color density value is low at a certain position. This is corrected and correction data is created so that the color density becomes uniform. First, it is necessary to determine the standard value of the color density that should be the target. In the example shown in FIG. 4, the target concentration value (target concentration) 9 shown by the solid line was taken as the average value of the total concentration. In this case, the correction data 11 describes the measured value in detail below, but the numerical value is calculated by a predetermined method. However, to explain the outline, the portion where the color density value is high is lowered. The correction data is generated in the above, the correction data is generated so that the portion having a low density value becomes high, and the portion having the same density as the target density is not corrected.

Here, the target concentration value (target concentration) can be set to a designated value such as 9a and 9b. As a case where this method should be executed, it is assumed that a plurality of printing devices of the same model for printing using the same printed matter and the same ink are installed in a production factory. In this case, it is necessary to print an image having the same color density value and tint regardless of which of the installed printing devices is used for printing. For example, in a printed matter such as a building material in which a plurality of printed matter are used side by side on one side, all the color density values need to be uniform, and if there is even a slight error in the color density value in the printed matter, the printed matter becomes a commercial product. It becomes a situation where the quality cannot be maintained. Therefore, in order to avoid such a situation, it is necessary to correct the ink density so that all the installed printing devices have the same color density value. For example, when there are printing devices from Units 1 to 5 to be installed, assuming that the measured value of the newly installed Unit 2 is the measurement data 10, the color density measured by printing the test pattern on the Unit 2 alone. The correction value calculated from the average of the values is set as the correction data 11, and the corrected density value of the Unit 1 itself that has already been installed is set as the target density value (target density) 9a. When the color density value of Unit 1 is used as a reference value, the target density value of Unit 2 is set to the target density value (target density) 9a. If the corrected concentration value of Unit 1 is the target concentration value (target concentration) 9b, the target concentration value of Unit 2 may be set to the target concentration value (target concentration) 9b in order to match this. Then, by simultaneously performing a process of adjusting the correction value calculated from the average value of the total density of the Unit 2 unit to a predetermined target density, the ink density error and the inkjet head group generated in each inkjet head itself can be determined. Not only the ink density error between each of the constituent inkjet heads and the density error in the adjacent portion of the inkjet heads constituting the inkjet head group, but also the ink density error caused by individual differences between the devices can be corrected at once.

FIG. 5 shows an example of a test pattern in single-pass printing. The test pattern image has at least a color density pattern and an alignment mark for measuring the ink density. The alignment mark 12a, the alignment mark 12b, the alignment mark 12c, and the alignment mark 12d have functions for detecting the print position of the test pattern, the imaging resolution, the inclination of the image, and the like, respectively. As described above, it is arranged on the outer peripheral portion of the color density pattern. .. The shape of the alignment mark may be a shape that is easy to use for computer processing, even if it is not circular. Since the imaging conditions and specific data processing are not directly related to the present invention, detailed description thereof will be omitted, but the imaging resolution of the test pattern needs to be equal to or higher than the resolution to be corrected and the spatial frequency. Further, the dynamic range of the image pickup apparatus needs to be non-saturated in the bright direction even in the non-printed portion and not saturated in the dark direction even in the maximum density portion.

Further, in the example of FIG. 5, the color density pattern has 16 levels of color density including the non-printed portion. It is not necessarily limited to 16 patterns, and it is not necessary to arrange them in the order of color density stages, but the purpose of having a plurality of color density patterns is wide because the occurrence of ink density error that occurs during printing differs depending on the color density. This is because it is necessary to perform ink density correction so that the color density changes linearly for each color density region, and the ink density errors that occur in multiple color densities are measured and correction data is generated. By doing so, more accurate correction becomes possible, and by setting a target density value for each of a plurality of color densities, even higher accuracy correction becomes possible.

FIG. 6 shows the test pattern of FIG. 5 as measured values 13 and 14 as individual measured values in the regions of two color densities in the measurement example. Here, the measured values at the print width end portion 15a and the print width end portion 15b both show a tendency for the color density value to decrease uniformly, but this is caused by the optical blur phenomenon of the image pickup apparatus. As a result of the blurring phenomenon, the color density value at the edge of the print width cannot be measured accurately. This is unavoidable no matter how expensive the imaging device is. The same phenomenon occurs even when the test pattern used in the multipath type inkjet printing apparatus shown in FIG. 16 described later is imaged. In this case, it is possible to avoid the optical problem of the image pickup apparatus by applying the averaging process in the vicinity of the end portion to the end portion of the test pattern of FIG. Further, when the test pattern in the case of the multipath method shown in FIG. 16 is imaged to calculate the ink density error, a process different from this is performed, and the details of this point will be described later.

FIG. 21 is a conceptual diagram showing that the captured image is deformed based on the calculated parameters. When a commercially available inexpensive image pickup device (scanner) is used, the position coordinates of the pixels on the captured test pattern image and the position coordinates of the pixels on the actual test pattern image before printing are used due to the accuracy of the scanner. Explains how to perform practical level imaging because a significant error occurs during measurement.

First, an example of how and how much error occurs in the captured image of the scanner by imaging a glass mask, which is a high-precision measure, using a commercially available scanner shown on the left side of FIG. 21 is shown below.
I read a 140 mm x 350 mm rectangular glass mask, but the upper left origin 201. Assuming that the coordinates of are matched with (0,0), the upper right vertex 202. The coordinates of (140-0.639 mm, 0) are the lower right apex 203. The coordinates of (140 + 0.166 mm, 350 + 0.139 mm) are the lower left apex 204. There is an error in the coordinates of each vertex, such as the coordinates of (0 + 0.974 mm, 350 + 0.182 mm). For example, in the case of a 600 dpi head, the nozzle spacing is about 42 μm , so if 5 nozzles are displaced, 42 μm × = 210 μm . From the viewpoint of density measurement for each nozzle of the present invention, a deviation of 210 μm in the measurement position means that the nozzle position is deviated by 5 nozzles, and assuming a head of 1000 nozzles, let's correct the # 503 nozzle. This means that the 508th nozzle was corrected.

In order to solve the above problems, it is possible to take a method of correcting the position error of each pixel constituting the test pattern image captured by the imaging device (scanner) as follows.
(1) As shown in the examples of FIGS. 5, 16 and 22, four or more alignment marks are printed on the outer peripheral portion of the color density pattern constituting the test pattern. In the example of FIG. 5, the alignment mark 12a, the alignment mark 12b, the alignment mark 12c, and the alignment mark 12d correspond to this.
(2) The XY coordinates on the plane orthogonal coordinate system of the alignment mark are read, and the deformation parameters for deforming the image so as to match the theoretical values are calculated and calculated.
(3) At least the color density pattern portion of the test pattern image captured based on the calculated deformation parameters is two-dimensionally deformed.
(4) The nozzle is cut out (specified) and the density is measured based on the deformed image.

First, the above "(1) printing four or more alignment marks on the outer peripheral portion of the color density pattern constituting the test pattern" will be described. In the example of FIG. 5, four or more marks indicated by the alignment mark 12a, the alignment mark 12b, the alignment mark 12c, and the alignment mark 12d are printed on the outer peripheral portion of the color density pattern. It is preferable that the alignment marks are arranged at least at the four corners of the color density pattern as in the examples of FIGS. 5, 16 and 22. The number of alignment marks is not limited to four, and the larger the number, the more accurately the position error of the test pattern image can be corrected.

Next, "(2) the XY coordinates of the alignment mark on the plane orthogonal coordinate system are read, and the deformation parameters for deforming the image so as to match the theoretical values are calculated and calculated."
In the example of FIG. 5, the alignment mark can be identified by the thickness of the black solid, white solid, and black circle line at the center. Then, by labeling the central portion of each alignment mark, the center coordinates of the alignment mark can be obtained, and the coordinates of the alignment mark can be read.
Here, the theoretical coordinates of the alignment mark on the plane orthogonal coordinate system are set to (X1, Y1), (X2, Y2), (X3, Y3), and (X4, Y4), and the read coordinates by the image pickup device (scanner) are set. , (X1, y1), (x2, y2), (x3, y3), (x4, y4).
Here, the following relational expression is established, and the deformation parameters a11, a12, a13, a14, b11, b12, b13, and b14 are calculated by this relational expression.
X1 = a11 × x1 + a12 × y1 + a13 × x1 × y1 + a14
X2 = a11 x x2 + a12 x y2 + a13 x x2 x y2 + a14
X3 = a11 x x3 + a12 x y3 + a13 x x3 x y3 + a14
X4 = a11 x x4 + a12 x y4 + a13 x x4 x y4 + a14
Y1 = b11 x x1 + b12 x y1 + b13 x x1 x y1 + b14
Y2 = b11 x x2 + b12 x y2 + b13 x x2 x y2 + b14
Y3 = b11 x x3 + b12 x y3 + b13 x x3 x y3 + b14
Y4 = b11 x x4 + b12 x y4 + b13 x x4 x y4 + b14

Next, at least the color density pattern portion of the test pattern image captured based on the calculated deformation parameters will be two-dimensionally deformed.
The entire captured image is converted using the parameters a11, a12, a13, a14, b11, b12, b13, and b14 obtained above. If the coordinates on the plane orthogonal coordinate system of the pixel with the color density pattern in the image of the test pattern imaged before the deformation are (xi, yi) and the coordinates after the deformation are (Xi, Yi), then Xi = a11 × xi + a12 × yi + a13 × xi × yi ＋ a14
Yi = b11 x xi + b12 x yi + b13 x xi x yi + b14
It becomes.
Explaining with the example of FIG. 21, the reference coordinates after deformation are 205. However, after transformation, the upper right apex is 206. , The lower right vertex after deformation is 207. , The lower left vertex after deformation is 208. Based on this, the position error of the captured test pattern image can be corrected two-dimensionally by transforming the entire test pattern image at once.

In addition, when the above-mentioned glass mask was used to print a test pattern of 600 dpi, and a predetermined position on the glass mask was verified as a point of interest by imaging at 600 dpi, the nozzle position error was 1-2 nozzles. It was within (42-84 μm). An error of this degree can be evaluated as an error within a practical range.

An example of an imaging method for a wide test pattern as shown in FIG. 22 will be described.
Generally, commercially available scanners are A3 size or A3 size at most. Even in the longitudinal direction, only about 400 mm can be imaged at one time. On the other hand, an inkjet printing machine may have a printing width of 1 m or more. For example, when the print width is 1.2 m, the alignment marks arranged in the print width direction in a size of 40 cm that can be imaged by a scanner are divided into three parts so as to include both the alignment marks of the divided portions.
After that, the test pattern images divided and captured on the software may be combined at 0-40 cm, 40-80 cm, and 80-120 cm, respectively. By adding a plurality of alignment marks in the test pattern, in the example of FIG. 22, the left image, the center image, and the right image are read into the scanner three times, and the coordinates of the alignment marks shared by each image are calculated. By combining internally, it becomes possible to measure the ink density error even in an inkjet printing device that requires a wide test pattern.

FIG. 7 is an explanatory diagram relating to the overlap processing of the inkjet heads. In FIG. 7, two adjacent inkjet heads overlap each other by four nozzles. X shown in FIG. 7 indicates a pixel in charge of printing by the inkjet head on the left side, and □ shown in FIG. 7 indicates a pixel in charge of printing by the inkjet head on the right side. When printing the width of four overlapping nozzles, the right inkjet head and the left inkjet head are in charge of printing alternately, so that the ink density error in the overlapping portion can be reduced. By performing the density correction means described above after reducing the overall density difference in this process, it is possible to improve the image quality with higher accuracy.

On the premise of the above, an embodiment of the present invention in single-pass printing will be described as Example 1, which is one of the best embodiments of the present invention.

Hereinafter, the first embodiment will be described in detail with reference to FIGS. 8 to 13. First, FIG. 8 shows a procedure for creating ink density error correction data in the single-pass method, and FIG. 12 shows a work procedure flow for converting image data based on the correction data created for the image data to be printed.

First, the creation of ink density error correction data will be described with reference to FIG. First, in the usage condition adjusting step 31, the ink density error is corrected for each of the plurality of inkjet heads constituting the inkjet head group by adjusting the applied voltage, which is a conventional method. The usage condition adjusting step 31 corresponds to the process described with reference to FIG. Next, in the overlap processing step 32, the inkjet head group is formed, and the overlap processing of the connecting portion of the inkjet heads that are adjacent to each other and overlap each other is performed. The specific content of the overlap processing corresponds to the processing described in FIG. 7. By the processing up to step 2, the ink density error between the inkjet heads constituting the inkjet group and the ink density error at the joint portion are improved to some extent, but the image quality required for the product is insufficient. It becomes.

Next, in the test pattern preparation step 33, the test pattern image to be printed described in FIG. 5 is prepared, and the print gamma correction is performed on the test pattern image in the print gamma correction step 34. The printer gamma correction, which will be described in detail later, refers to a means for correcting a change in the color density of an actual printed matter so that it becomes linear for each density with respect to the image data to be printed.

After that, in the test pattern printing step 35, a test pattern corresponding to the entire printable width formed by the inkjet head group is printed. The test pattern to be printed is shown in FIG. 5 in this embodiment. As described above, the width of the test pattern to be printed includes the ink density error of the nozzles in one inkjet head, the ink density error between the individual inkjet heads constituting the inkjet head group, and the joint portion of the adjacent inkjet heads. From the viewpoint of collectively correcting all of the ink density error of the above ink jet density error and the ink density error caused by individual differences between the manufactured individual inkjet printing devices, it is desirable that the total printable width is sufficient.

Then, in the test pattern imaging step 36, the printed test pattern is imaged. The means for imaging may be a scanner or other imaging means, but it is necessary to image the entire test pattern with a required accuracy such as a predetermined resolution. Further, at this time, by applying the averaging process for setting the color density near the edge to the print width edge of the captured test pattern image shown in FIG. 6, the above-mentioned optical problem of the image pickup apparatus can be avoided. It can contribute to the creation of more accurate correction data.

Finally, in the correction data calculation step 37, the color density of the image of the captured test pattern is measured, the ink density error is calculated, and then the ink density error correction data is created using the calculated numerical value.

Here, a specific ink density error correction data calculation method will be described with reference to FIGS. 9 to 11.

FIG. 9 is a measurement example of ink density data different from that of FIG. 3, and is a measurement example of ink density when the color density steps input for printing are 9 steps in total. The range of the color density of the input data is one of 256 steps from 0 to 255, and it is assumed that the larger the number, the higher the color density. In FIG. 9, the input data 255 has the highest color density, and the color density becomes lower as it becomes smaller as 224, 192, 160, 128, 96, 64, 32, 0. Since 0 is not printed, it is the density of the base material, and the ink density is 0. The horizontal axis represents the position of the image in the print width direction as in the above example, in other words, the position of the nozzle. The position of the n nozzle is shown on the horizontal axis of FIG. The vertical axis represents the concentration, and in the figure, the concentration at the time of the input data 255 is shown at the highest concentration, and is described below according to the input data. In this example, it is assumed that the image is composed of 8 bits, but it is also assumed that the image is composed of different numbers of bits such as 16 bits. FIG. 9 shows the concentrations of each concentration, in this case, the concentrations of all nozzles and all regions in nine stages. This is the overall picture of the measurement data. In FIG. 9, the measurement data is the ink density in the color density band of the nine input data, but in the case of 8 bits, 256 points of data are required, and these data are estimated and created by a method such as linear interpolation. Things are also possible.

FIG. 10 shows a graph obtained by cutting out and plotting ink density error data in the n nozzles of FIG. 9 and the nozzles around the nozzles. In FIG. 10, ink density error data of three nozzles of n nozzles and adjacent n + 1 nozzles and n + 2 nozzles are plotted. The position may be grasped by the nozzle number or the position number of the image. FIG. 10 shows the state of the ink density at the position printed by the n nozzles in the print area. In the example of FIG. 10, the concentration of the n + 2 nozzles is low, and the n nozzles are the thickest. For example, when printing a 500 mm width with a resolution of 600 dpi, a head width of 500 / 25.5 × 600 = 11811 nozzles is required, and 11811 ink density error data for one nozzle shown in the graph of FIG. 10 are measured. Will be done. However, from the viewpoint of increasing the processing speed, it is possible to make one graph with two or more nozzles, and from the viewpoint of improving the resolution, it is possible to make one graph with two nozzles or more. In the case of 2 nozzles and 1 graph, the number of graphs is 5905, and in the case of 1 nozzle and 2 graphs, the number is 23622.

FIG. 11 illustrates the logic for calculating the correction data. The data of n nozzles and the target density value (target density) data which is the target density of correction are shown. According to FIG. 11, when converting the measurement data of the n nozzles into the target density value, it can be seen that the ink density output from the n nozzles at the time of the input data Di is P1 and the target density value is P2. Therefore, in order to output the ink density of P2 using the n nozzle, it is necessary to set the input data to Do. Therefore, by creating a table that converts Di to Dо, it is possible to output the ink density of P2 from the n nozzles.

By executing the above steps, not only the ink density error that occurs in the individual inkjet heads that make up the inkjet head group, but also the ink density error between the individual inkjet heads that make up the inkjet head group, and the adjacent inkjet heads. Ink density error correction data that can collectively correct all of the ink density error at the joints and the ink density error caused by individual differences between the manufactured individual inkjet printing devices can be obtained by executing one procedure. Can be calculated.

Next, based on FIG. 12, the image data conversion operation will be described based on the correction data created for the image data to be printed.

First, in step 38, image data to be printed is prepared, and the image data is converted into a CMYK image of an RGB image and color profile conversion by step 39, and then print gamma conversion is performed as image data in step 40. Execute for.

Here, an example of image data processing performed between steps 38 and 40 will be described in detail.

In this example, the image data to be printed is RGB multi-valued data before the start of processing, and each color is usually composed of 8 bits. This is just an example, and other gradations such as 16 bits and 12 bits are assumed, and different data formats such as palettes are also assumed. The image data is converted into multi-valued data (usually 8 bits) of ink color CMYK via a color profile. Since different printing devices have different inks and other functions, there is a problem that the colors are different even if the same image data is printed. Therefore, in general, a standard profile called an ICC profile is used. As a result, color reproducibility that does not depend on the printing device can be realized.

The printer gamma conversion is a means for correcting the change in the color density of the actual printed matter so as to be linear with respect to the image data to be printed, and the actual situation is often a table conversion. In addition, since the ink density error correction according to the present invention is often performed by making full use of a plurality of table conversions, it is assumed that the printer gamma conversion table and the ink density error correction table are combined and performed in one table. it can. By performing in one table, the amount of information to be processed can be minimized, and data processing can be speeded up.

After the above steps 40 are completed, in the image conversion (ink density error correction) step 41, the entire printed image is converted using the ink density error correction data created in the correction data calculation step 37. Here, an example of converting an image based on the calculated ink density error correction data will be described in detail. FIG. 13 shows an example in which an image is converted in 256 steps of input data with respect to the ink density error of n nozzles. When the ink density error correction data of all the density bands from 0 to 255 calculated based on the calculation method shown in FIG. 11 is plotted, an example as shown in FIG. 13 is obtained. Therefore, if the color density of the image to be printed is converted from the corrected output data plotted in FIG. 13 and printed, the n nozzles can perform printing with the same ink density as the target density value. By performing this step for all nozzles or all position data, it is possible to correct the ink density error in all regions and all color density regions. If the density error correction of the image conversion (ink density error correction) step 41 is executed before the steps 38 to 40 in FIG. 12 are executed, the corrected density is eventually deviated by the conversion process from the steps 38 to 40. Therefore, it is desirable that the image conversion (ink density error correction) step 41 is executed after the steps up to step 40 are completed.

Finally, the degrading process is executed on the printed image corrected as the degrading process step 42 in FIG. Here, the degrading process will be described in detail. FIG. 14 is an explanatory diagram of an example of degradation processing. Generally, image data has 8 bits and 256 density gradations, but the gradation that can be realized with an inkjet head is not ejected in the case of a model that can eject three sizes of droplets, for example, small droplets, medium droplets, and large droplets. Since it has only four gradations including the case, it is necessary to reduce the image data of 256 gradations of density gradation to four gradations. The horizontal axis of FIG. 14 indicates input data and has 256 gradations from 0 to 255. The vertical axis is the printing rate of each droplet, 100% indicates a state in which all dots are printed in a predetermined area, and 50% means that dots are printed in 50% of the predetermined area. Indicates the state of printing. In FIG. 14, while the input data is 0-a, only the small droplets change to a print rate of 0% -100%. While the input data is ab, the printing rate of small droplets changes to 100% -0%, and the printing rate of medium droplets changes to 0% -100%. While the input data is b-255, the printing rate of medium droplets changes to 100% -0%, and the printing rate of large droplets changes to 0% -100%. That is, it can be said that 100% of the printing rate of small droplets corresponds to the input data a, 100% of the printing rate of medium droplets corresponds to the input data b, and 100% of the printing rate of large droplets corresponds to the input data 255. Of course, this relationship depends on the characteristics of the base material and ink, and if 100% of the large droplets are used, the ink density to be printed may be too high. In this case, adjust so that 100% of the large droplets are not used. In some cases.

By performing all the above steps and printing the corrected print image data with an inkjet printing device, the ink density error of the nozzles of the individual inkjet heads that make up the inkjet head group and the individual that makes up the inkjet head group. Inkjet density error between inkjet heads, ink density error at the joint of adjacent inkjet heads, and ink density error caused by individual differences between individual inkjet printing devices manufactured can all be highly corrected at once. As a result, high-quality printing can be realized.

The second embodiment will be described in detail below with reference to the drawings.

FIG. 15 shows a general printing configuration example in normal multi-pass printing. As described above, the multi-pass method is a method of printing the same part by dividing it into a plurality of times. In FIG. 15, the first scan 16 indicates the first drawing scan, ink is ejected and drawn while moving and scanning in the X direction indicated by the arrow, and this operation is repeated with the second scan 17 and the third scan 18. Is done. This example is a method called 3 passes in which the same portion is divided into 3 parts and printed, and shows a method in which a part of the printed image is completed by three times of overlay printing from the first scan 16 to the third scan 18. In the first scan 16, the first drawing is performed using the lower third portion of the inkjet head shown in FIG. A single scan usually prints about one-third of the final density, which is the ink density of the final printed image.

The second scan 17 indicates the second drawing scan and prints using the lower two-thirds of the head. Similar to the case of the first scan 16, the portion printed twice is about two-thirds of the final density, and the lower half is about one-third of the final density.

The third scan 18 shows the third drawing scan and prints using the entire inkjet head. The portion printed three times overprints becomes the final image that has achieved the final density, and the printing of that portion is completed. After that, multi-pass printing is to repeat drawing scans such as 4th scan 19 and 5th scan 20 to form an entire image. Here, the relationship between the printed matter and the head is relative, and the head may move in the X direction of the arrow and the printed matter may move in the Y direction.

In FIG. 15, an image having a length of one-third that of the inkjet head is printed in one scan, but the basic unit in the multi-pass printing according to the present invention is printing in one scan. Indicates the length of the image to be printed. In this example, the length of one-third of the inkjet head is the basic unit, but of course, if the number of printing divisions is increased, the basic unit becomes relatively short, and if the number of divisions is decreased, the basic unit becomes relatively long. Further, the basic unit is not necessarily limited to a fraction of the length in the nozzle row direction of the inkjet head.

FIG. 16 shows an example of a test pattern corresponding to FIG. The print width is more than twice the basic unit of printing. FIG. 16A is an example in which the print width is twice the basic unit, and FIG. 16B is an example in which the print width is five times the basic unit. In FIG. 15, it is assumed that the head moves in the X direction and the printed matter moves in the Y direction. A whitish or blackish streak may appear between the Nth scan and the n + 1th scan. This cause may be a physical phenomenon due to the accuracy of the movement amount of the printed matter or the error of how the ink spreads on the base material due to the physical influence of the ink and the base material at the boundary of the basic unit. It is described by the term banding in the inkjet printer industry. In the present invention, banding is also an ink density error to be solved. In this regard, in FIG. 16A, banding may occur by inserting two basic units of printing and printing the test pattern so that the boundary between scans is included in the test pattern. The area is secured. In FIG. 16B, five basic printing units are inserted to further increase the amount of information. Increasing the basic unit amount enables more detailed ink density error measurement by increasing the amount of information, but there is a problem that the amount of information increases and the processing load increases.

Regarding the processing of the blurring phenomenon at the print width end of the captured test pattern image described in the above description of FIG. 6 when the ink density error is calculated by imaging the multipath test pattern of FIG. explain. In the case of the multi-pass method, the existence of an ink density error at the joint portion of the basic unit to be printed is directly linked to the occurrence of the above-mentioned banding, and therefore a more accurate calculation of the ink density error is required. Part processing is especially important. Therefore, in this case, the numerical value of the ink density error calculated from both ends of the adjacent portion of the basic unit printed on the imaged test pattern is applied to the print width end portion. That is, to explain with the example of FIG. 16A, each basic unit is printed in each basic unit as long as the nozzles used by using the same inkjet head in all passes are divided and printed by the same division method. The occurrence of ink density error within a unit is theoretically the same or similar. Therefore, in the example of FIG. 16 (a), the numerical value of the upper end of the lower basic unit in contact with the portion adjacent to the basic unit of FIG. 16 (a) at the portion where the blur phenomenon occurs at the uppermost print width end of FIG. 16 (a). To apply. Further, the numerical value at the lower end of the upper basic unit in contact with the portion adjacent to the basic unit in FIG. 16A is applied to the blurring phenomenon occurrence portion at the lowermost print width end portion in FIG. 16A. This process theoretically makes it possible to perform more accurate processing of the print width edge.

Further, here, the imaging conditions in the case of imaging the test pattern of FIG. 16 will be described in detail. In multipath printing, the resolution of the image printed on the printed matter is not uniform. In addition, due to the banding problem peculiar to multi-pass printing and the need to match the nozzle used below with the printed image, the resolution of the captured test pattern is determined by the printed test pattern. It is necessary to match the resolution with the resolution of the captured test pattern image. Therefore, when imaging a test pattern, it is necessary to set a condition for matching the resolution with the resolution of the printed test pattern.

It will be described with reference to FIG. 17 that the positional relationship between the inkjet nozzle and the printed image is fixed in multi-pass printing. Inkjet head 1 in FIG. 17 shows an inkjet head having 1000 nozzles, in which nozzles for ejecting numbered inks are shown. Assuming that the inkjet head is used to perform 4-pass multi-pass printing, the printing of each pass starts from nozzle numbers 1 to 250, nozzles 201b, starting from nozzle 201a in the figure for the inkjet head nozzle. It is divided into four sections: nozzle numbers 251 to 500, nozzle numbers 501 to 750 starting from nozzle 201c, and nozzle numbers 751 to 1000 starting from nozzle 201d, and each section is shared and executed. ..

17 (a) and 17 (b) are diagrams showing the correspondence between the nozzle used for printing and the printed pixel, and the image data is shown with the upper left reference, and the number of the nozzle 201 and the number of the pixel 204 are used. , The correspondence between the printed pixels and the nozzles used for printing is shown. In FIG. 17, although the same 4-pass printing is performed, two types of 4-pass printing examples shown in FIGS. 17 (a) and 17 (b) are shown. FIG. 17A shows four passes that quadruple the resolution in the nozzle row direction, and one pixel line is printed by one nozzle. FIG. 17B shows that the resolution in the nozzle direction is doubled. A line of one pixel is printed with two nozzles. Since the details of these effects are not directly related to the present invention, the description thereof will be omitted.

In the example of FIG. 17A, the first line, which is the left writing position, is the first nozzle, the second line is the 251st nozzle, the third line is the 501st nozzle, and the fourth line is the 751st nozzle. It is printed, and the numbers of the pixels that make up the image correspond to the nozzle numbers. In the example of FIG. 17B, the first line, which is the left writing position, is the first nozzle and the 501st nozzle, the second line is the 251st nozzle and the 751st nozzle, and the third line is the second nozzle and the 502. The numbers of the pixels that make up the image correspond to the nozzle numbers, such as the number nozzle.

In this way, the positional relationship between the image and the nozzle number can be made constant. In other words, this method makes it possible to make the relationship between the ink density error caused by the nozzle, the connecting portion of the adjacent inkjet heads, and the like and the positional relationship of the pixels constituting the image constant.

In the case of single-pass printing, as described above, when the printed object passes directly under the nozzle surface of the inkjet head, ink is ejected from the nozzle and an image is printed on the printed object. Since it is a drawing method and the resolution depends on the nozzle of the inkjet head, in the example of 1 of the inkjet head in FIG. 17, the line of the first pixel is printed by the first nozzle and the second. The line of the pixel is printed by the second nozzle, and as a result, the positional relationship between the inkjet nozzle and the printed image is automatically made constant.

On the premise of the above, as Example 2 which is one of the best examples of the present invention, an embodiment of the present invention in multipath printing will be described.

FIG. 18 is a work procedure flow of the present invention in the multipath method, and will be described based on this. FIG. 18 shows a procedure for creating ink density error correction data, and FIG. 19 shows a work procedure flow for converting image data based on the correction data created for the image data to be printed. Since the procedure is basically the same as that of the single-pass method already described in the first embodiment, the common parts will be omitted as appropriate.

First, the creation of ink density error correction data will be described with reference to FIG. First, in the usage condition adjusting step 51, the applied voltage, which is a conventional method, is adjusted to correct the ink density error for each of the individual inkjet heads constituting the inkjet head group, and then the overlap processing step. At 52, the overlap processing of the connecting portion of the inkjet head is performed. The overlap processing step 52 is necessary only when the inkjet heads overlap as described in FIG. 7 above.

Next, in the test pattern preparation step 53, the test pattern image described with reference to FIG. 16 is prepared, and the print gamma correction is performed on the test pattern image in the print gamma correction step 54.
After that, in the test pattern printing step 55, a test pattern corresponding to the entire printable width formed by the inkjet head group is printed. Further, as described in FIG. 16, the width of the test pattern to be printed is preferably a width of two or more basic units.

Then, in the test pattern imaging step 56, the printed test pattern is imaged. At this time, it is important to calculate a more accurate ink density error by applying the above-mentioned processing for the blur phenomenon to the print width end portion of the captured test pattern image described as described above.

Finally, in the correction data calculation step 57, the color density of the image of the captured test pattern is measured, the ink density error is calculated, and then the ink density error correction data is created using the calculated numerical value. The specific correction data calculation method is basically the same as the ink density error correction data calculation in the case of single-pass printing, but the test pattern is also imaged collectively for the part where banding occurs. Since it is calculated above, it is characteristic that the correction data of the banding part can also be calculated at once.

By executing the above procedure, not only the ink density error that occurs in each inkjet head itself, but also the banding that occurs at the boundary of the basic unit, and when multiple inkjet heads are used, the individual inkjet heads that make up the inkjet head group. Ink density error that can collectively correct all of the ink density error between the ink jet heads, the ink density error at the joint of the adjacent inkjet heads, and the ink density error caused by the individual differences between the individual inkjet printing devices manufactured. The correction data can be calculated by executing one procedure.

Next, based on FIG. 19, the image data conversion operation will be described based on the correction data created for the image data to be printed.

In step 58, image data to be printed is prepared, and the image data is converted from an RGB image to a CMYK image and color profile conversion by step 59, and then print gamma conversion is performed on the image data in step 60. And execute.

After the above steps 60 are completed, in the image conversion (ink density error correction) step 61, the entire printed image is converted using the ink density error correction data created in the correction data calculation step 57. If the density error correction of the image conversion (ink density error correction) step 61 is executed before the steps 58 to 60 are executed, the corrected density will be out of order due to the conversion process from the steps 58 to 60. Therefore, it is the same as in the first embodiment that the image conversion (ink density error correction) step 61 is preferably executed after the steps up to step 60 are completed. Finally, the degrading process is executed on the printed image corrected as the degrading process step 62.

By performing all the above steps and printing the corrected print image data with an inkjet printing device, not only the ink density error that occurs in each inkjet head itself, but also the banding that occurs at the boundary of the basic unit and a plurality of When the inkjet heads of the above are used, it arises from the ink density error between the individual inkjet heads constituting the inkjet head group, the ink density error at the joint portion of the adjacent inkjet heads, and the individual difference between the manufactured individual inkjet printing devices. All of the ink density errors can be corrected at once, and as a result, high-quality printing can be realized.

Note that FIG. 20 is a configuration example of the inkjet printing apparatus of the present invention. The inkjet printing apparatus in the configuration example includes a printing unit 101, a printing unit 103, and a winding unit 105 of the printed matter. An inkjet head is mounted on the printing unit 103, and this configuration example may be a single-pass system or a multi-pass system. The test pattern printed by the printing unit 103 is read by a scanner used as the image pickup apparatus 109 and processed by a computer. The image pickup apparatus 109 can be incorporated in an inkjet printing apparatus to automatically print a test pattern, image a test pattern, calculate correction data, correct print data, and the like.

The effects of the present invention described above can be summarized as follows.

After correcting the ink density error such as adjusting the applied voltage for each inkjet head, the printed image is converted based on the correction data calculated based on the printed and read test pattern, so that the entire mounted inkjet head group can be displayed. On the other hand, the ink density can be corrected, and in the industrial inkjet printing apparatus, high-quality printing with a high degree of perfection, which cannot be realized by the conventional correction method, can be realized.

After correction by the overlap processing described later for the connecting part between adjacent inkjet heads, print image correction is performed based on the correction data calculated based on the read test pattern, so that the degree of perfection in the inkjet printing device for industrial use is achieved. High image quality was achieved.

In an inkjet printing device using the single-pass method, a test pattern is printed using the entire printing width of the inkjet head group for each type of ink, and image conversion is performed based on the correction data calculated using the printed test pattern. It is possible to correct all the ink density differences for each inkjet head nozzle, the ink density differences between the inkjet heads that make up the inkjet head group, and the ink density differences at the joints between the individual adjacent inkjet heads all at once. It became possible.

By setting a reference value to be used as a reference in ink density correction and having a means for switching the target value to be corrected for ink density to a reference value, it has become possible to correct the density difference between devices.

In an inkjet printing device using a multi-pass method, the relationship between the printed image data and the nozzle is made constant, and the width is based on a test pattern with a width of 2 units or more, which is the width to be printed by one moving scan of the inkjet head. By generating correction data, correction is possible even in the multi-pass method, and it is possible to print high-quality images even with a smaller number of passes, so it is possible to achieve both high image quality and high-speed printing. Became.

1 Inkjet head 2 Printed matter 9 Target density value (target density)
10 Measurement data 11 Correction data 12 Alignment mark 15 Printing width end 31 Usage condition adjustment process 32 Overlap processing process 35 Test pattern printing process 36 Test pattern imaging process 37 Correction data calculation process 41 Image conversion (ink density error correction) process 42 Degradation processing process 201 Nozzle 204 pixels

Claims (9)

By moving the inkjet head in which a plurality of nozzles for ejecting ink according to the image data are arranged and the printed matter relatively in the first direction intersecting the arrangement direction of the plurality of nozzles, the printed matter is printed. In the adjustment method in an inkjet printing device that prints,
The ejection condition setting process for setting the ink ejection conditions of the plurality of nozzles , and the ejection condition setting process.
According to the ink ejection conditions set in the ejection condition setting step, the printed matter corresponds to the color density pattern composed of a plurality of pixels corresponding to the plurality of nozzles and the color density pattern , and the first. the terms second direction, at different positions relative to each other, the test pattern printing step of printing a test pattern Ru comprising a plurality of alignment marks arranged in the outer peripheral region of the color density pattern perpendicular to the direction and the first direction When,
And an imaging step of image shooting the color density pattern and the plurality of alignment marks of the test pattern wherein printed on the substrate in the test pattern printing process,
The plurality of nozzles and the plurality of alignment marks captured in the imaging step were imaged according to the position information related to the first direction and the position information related to the second direction of the plurality of alignment marks captured in the imaging step. The correspondence relationship of the color density pattern with the plurality of pixels is corrected, and the conversion data for converting the image data corresponding to the plurality of nozzles is corrected for the plurality of nozzles. A conversion data acquisition step of acquiring using the density data of the plurality of pixels of the color density pattern, and
An adjustment method comprising a conversion step of converting the image data based on the conversion data corresponding to the plurality of nozzles acquired in the conversion data acquisition step. In the conversion data acquisition step, the density data of the pixels at the second direction end , which could not be accurately measured among the density data of the plurality of pixels of the color density pattern, is added to the density data near the second direction end. The adjustment method according to claim 1, further comprising a step of applying pixel density data. The imaging step includes a step of dividing the test pattern into a plurality of images in the second direction and imaging, and a step of combining the plurality of divided test pattern images captured by the conversion data acquisition step between adjacent portions. The adjustment method according to claim 1 or 2, wherein the adjustment method includes. By moving the inkjet head in which a plurality of nozzles for ejecting ink according to image data are arranged and the printed matter relatively in a first direction intersecting the arrangement directions of the plurality of nozzles, the printed matter is printed. In an inkjet printing device that prints
Discharge condition setting means for setting ink ejection conditions for the plurality of nozzles , and
According to the ink ejection conditions set in the ejection condition setting means, the printed matter corresponds to the color density pattern composed of a plurality of pixels corresponding to the plurality of nozzles and the color density pattern , and the first. respect of direction and a second direction perpendicular to the first direction, at different positions relative to each other, the test pattern printing means for printing a plurality of test patterns Ru provided with alignment marks arranged in the outer peripheral region of the color density pattern When,
And an imaging means for image shooting the color density pattern and the plurality of alignment marks of the test pattern wherein printed on the substrate in the test pattern printing means,
The plurality of alignment marks captured by the imaging means were imaged by the plurality of nozzles and the imaging means according to the position information related to the first direction and the position information related to the second direction. The correspondence relationship of the color density pattern with the plurality of pixels is corrected, and the conversion data for converting the image data corresponding to the plurality of nozzles is corrected for the plurality of nozzles. A conversion data acquisition means acquired by using the density data of the plurality of pixels of the color density pattern, and
An inkjet printing apparatus comprising: a conversion means for converting the image data based on the conversion data corresponding to the plurality of nozzles acquired by the conversion data acquisition means. The inkjet printing apparatus is a single-pass method in which printing is performed by the object to be printed once relatively passing through the nozzle surface side of the inkjet head in which the plurality of nozzles are arranged in the first direction. The inkjet printing apparatus according to claim 4, wherein the inkjet printing apparatus is provided. An operation in which the inkjet printing apparatus prints a basic unit having a predetermined width in the second direction by relatively moving and scanning the inkjet head and the printed matter in the first direction. The claim is a multi-pass system in which printing is performed by repeating the operation of moving the inkjet head and the printed matter in the second direction relative to the basic unit. Item 4. The inkjet printing apparatus according to Item 4. The converted data reception means, of the density in the second direction ends near the exact density data of the pixel of the could not be measured the second axial end of the data of the plurality of pixels of the color density pattern The inkjet printing apparatus according to any one of claims 4 to 6, further comprising means for applying pixel density data. The conversion data acquisition means is printed on the imaged test pattern on the density data of the pixels at the second direction end, which could not be accurately measured among the density data of the plurality of pixels of the color density pattern. The inkjet printing apparatus according to claim 6 , further comprising means for applying density data of pixels at both ends of adjacent portions of the basic unit to the corresponding second directional end. The imaging means includes means for dividing the test pattern into a plurality of images in the second direction and imaging the test pattern, and includes means for combining the plurality of test pattern images captured by the conversion data acquisition means between adjacent portions for dividing the image. The inkjet printing apparatus according to any one of claims 4 to 8 , wherein the inkjet printing apparatus is characterized in that.

Images