JP2020069784A - Ink density error correction method for ink jet printer - Google Patents

Abstract

To solve the problem that an ink jet printer for industrial use needs to be faster and thereby made large-sized, but has a more remarkable decrease in picture quality of a drawn image caused owing to a plurality of factors caused as a result of an increase in size or scale.SOLUTION: After ink density errors by individual ink jet heads are corrected by adjusting use conditions of the ink jet heads, a print image is converted based upon correction data calculated based upon a test pattern which is printed and read so as to solve a plurality of factors of a decrease in picture quality together at a time. Consequently, an ink density error of printed matter, i.e. a difference between color density of original image data to be printed and color density of the actual printed matter can be corrected at high level, so that an ink jet printer for industrial use can perform high-picture-quality printing high in level of completion.SELECTED DRAWING: Figure 8

Description

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

As is well known, inkjet technology is used as a non-contact printing technology on demand, and is used in a wide range of applications such as printing on paper media, decorating building construction materials and automobile parts, and coating functional materials on electrical parts. It has begun to be used in so-called industrial applications where inkjet printing devices are used to produce products.

There are two major printing methods for inkjet. One is a so-called single-pass method that requires high-speed performance. When printing, an error in ink ejection amount or ejection direction due to individual differences in the characteristics of each nozzle in the inkjet head, individual differences in the characteristics of each inkjet head itself. A printed matter in which the color density of the original image data to be printed and the color density of the actual printed matter are different due to the error in the ink ejection amount and the ejection direction due to There has been a problem that it is difficult to secure print quality due to an ink density error. The other is a so-called multi-pass method that requires high print quality, and details will be described below. However, there has been a problem that the printing speed is slow and it is not suitable for industrial applications. There is a problem that a certain degree of ink density error occurs.

Each inkjet head used in an inkjet printing apparatus for industrial use generally has a large number of nozzles inside, and normally has 1000 or more nozzles, thereby increasing the range of printing at one time and producing the same. We are devising ways to improve sex.

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

As described above, in the ink jet printing apparatus, where the ink density error occurs due to a plurality of factors, the error caused by the ink ejection amount of each nozzle in each ink jet head, the ejection directionality, the ejection speed, etc. Patent Document 1 proposes this measure as a prior art related to this measure. As an outline, in order to correct errors such as the amount of ink ejected from each nozzle in one inkjet head, the ejection directionality, and the ejection speed, a test pattern is printed, and the test pattern is read by an imaging 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-sized household inkjet printing apparatuses.

JP-A-5-220977

However, in an inkjet printing apparatus for industrial use, which has been developed in recent years, it is generally necessary to use a plurality of heads for each color because it is necessary to increase the speed for high productivity and the size increase accordingly. .. As described above, with the increase in the size and scale of the inkjet printing apparatus, in addition to the error in the ink discharge amount and the discharge direction of each nozzle in each inkjet head, the mutual inkjet heads when a plurality of inkjet heads are connected are connected. Ink discharge amount and discharge direction error between them, and by increasing the number of inkjet heads connected, the non-uniformity of ink density such as so-called streaks in the joint portion between a plurality of inkjet heads becomes more prominent. The problem is that the image quality of an image drawn is more significantly deteriorated due to an ink density error caused by a plurality of factors.

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

Further, in the case of using the inkjet printing apparatus as a production facility for industrial use, it is expected that the inkjet printing apparatus will be added in accordance with the increase in the production amount of the production object. As a result, there is a problem in that the hue and the ink density of the printed matter may differ for each actually manufactured inkjet printing apparatus even if they are the same type of inkjet printing apparatus with the same design. In particular, in the inkjet printing apparatus for industrial use, which is becoming larger in size, it is particularly remarkable. Then, such a problem is premised on correcting the error of the ink density of the printed matter in a small inkjet printing apparatus, and the method disclosed in Patent Document 1 premised on the error density error correction of one inkjet head, and others. According to the conventional invention, it is impossible to collectively solve the ink density error that occurs in the large-sized inkjet printing apparatus for industrial use. Further, such a problem is that in the multi-pass printing, as described below, when printing lines of pixels forming an image, different nozzles are used to print one line or adjacent lines. It is possible to reduce the ink density error caused mainly by the individual difference of the above, to a certain extent, but it is particularly remarkable in the single-pass inkjet printing apparatus that pursues high-speed printing because processing such as multi-pass printing cannot be performed. Will occur.

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

The present invention has been proposed to solve the above problems, and not only the error in the ink ejection amount and ejection direction of each nozzle in each inkjet head, but also in the case where a plurality of inkjet heads are connected to each other. Due to the error in the ink ejection amount and ejection direction between inkjet heads, and the increase in the number of connected inkjet heads, the unevenness in the ink density such as so-called streaks in the joints between the inkjet heads may cause The present invention proposes an inkjet printing apparatus and a method for improving the printing image quality in the inkjet printing apparatus, which has a function of collectively eliminating all the ink density errors caused by the above factors and improving the printing image quality more than the conventional method.

In order to solve the above problems, the following methods are proposed.

That is, the present invention is, in an inkjet printing apparatus that performs printing by relatively moving an inkjet head having a plurality of nozzles and a printing object, an error in the ink density that is the density of the ink to be ejected by the inkjet head. In the method of correcting the above, a step of adjusting the use conditions of the inkjet head to individually adjust the ink density, and printing a test pattern having a color density pattern and four or more alignment marks arranged around the color density pattern And a step of imaging the test pattern to create a test pattern image, and a step of reading the coordinates of the alignment mark on the test pattern image and calculating a deformation parameter of the color density pattern. Based on the parameter calculation process and the deformation parameter A test pattern modification processing step including a step of modifying the color density pattern on the test pattern image, a correction data calculation step of calculating correction data based on measurement data of the modified test pattern image, and the correction data A step of correcting the ink density error in the entire image printed on the substrate by converting the entire image to be printed based on
The deformation parameter calculation step calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
The test pattern modification processing step is characterized in that the coordinates of the pixels forming the color density pattern on the test pattern image on the plane orthogonal coordinate system are corrected by the modification parameter.

According to the present invention, an inkjet head group configured to have a width corresponding to a printing width by mounting two or more inkjet heads is mounted for at least one type of ink, and the printing material is printed once on the inkjet head. In an inkjet printing apparatus that is a single-pass method in which printing is completed only by passing through the nozzle surface side of the head group, the ink concentration to be ejected from each inkjet head is adjusted by adjusting the usage conditions of the inkjet head. For adjusting the ink density, a means for printing a test pattern having a color density pattern and alignment marks arranged at four or more points on the outer periphery of the color density pattern, and an image of the test pattern to create a test pattern image The test pattern imaging means and the alignment pattern on the test pattern image. A test pattern modification process including a modification parameter calculation unit including a unit that reads the coordinates of the color density pattern and calculates a modification parameter of the color density pattern, and a unit that modifies the color density pattern on the test pattern image based on the modification parameter. Means, correction data calculating means for calculating correction data based on the measured data of the deformed test pattern image, and the entire image to be printed on the printing object by converting the entire image to be printed based on the correction data Has a means for correcting the ink density error in
The deformation parameter calculation means calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
The test pattern modification processing means is characterized by correcting the coordinates on the plane orthogonal coordinate system of the pixels forming the color density pattern on the test pattern image by the modification parameter.

Further, the present invention is
The printing material and the inkjet head are relatively moved in a direction parallel to the direction in which the nozzles of the inkjet head are aligned by a basic unit which is a width to be printed by one moving scan of the inkjet head, and the inkjet head and the printing object. The inkjet printing apparatus is a multi-pass system in which one or more inkjet heads are mounted, and the printing is completed by ejecting the ink while relatively moving and scanning the nozzles a plurality of times in the direction perpendicular to the direction in which the nozzles are arranged. 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 use conditions of the inkjet head, and a color density having a width of two or more of the basic units. Alignment mark with four or more points arranged around the pattern and the color density pattern Means for printing a test pattern, a test pattern imaging means for imaging the test pattern to create a test pattern image, and reading the coordinates of the alignment mark on the test pattern image and setting the deformation parameter of the color density pattern. Deformation parameter calculation means including calculation means, test pattern transformation processing means including means for transforming the color density pattern on the test pattern image based on the transformation parameters, and measurement of the transformed test pattern image A correction data calculation unit that calculates correction data based on the data; and a unit that corrects an ink density error in the entire image printed on the printing target by converting the entire image to be printed based on the correction data,
The deformation parameter calculation means calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
The test pattern modification processing means is characterized by correcting the coordinates on the plane orthogonal coordinate system of the pixels forming the color density pattern on the test pattern image by the modification parameter.

According to the present invention, in a large-sized inkjet printing apparatus for industrial use, ink density error of nozzles in an inkjet head that cannot be sufficiently corrected by a conventional method, ink density error between individual inkjet heads forming an inkjet head group, Ink density error in the connecting part of inkjet heads, ink density error caused by individual differences between manufactured individual inkjet printing devices, and in multi-pass printing, ink density error in the adjacent part between basic units described later is also included. , All of them can be efficiently and highly adjusted in a batch, and high-quality printing can be realized in the single-pass method. Even in the multi-pass method, printing with a smaller number of passes and printing with a larger number of passes as described later. It is possible to realize high-quality printing equivalent to or better than.

FIG. 6 is a diagram illustrating a general printing method in single-pass printing. FIG. 6 is a diagram illustrating ink density error correction that occurs between a plurality of inkjet heads according to a conventional technique. It is a figure which shows the measurement example of the density data which read and measured the test pattern. FIG. 6 is a diagram illustrating a relationship between ink density correction and a target density value that should be a target during correction. It is a figure which shows the example of a test pattern in printing of a single pass system. FIG. 6 is a diagram showing an example of measurement of ink density data in single-pass 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 there are a total of nine levels of input color density. 6 is a graph obtained by cutting out and plotting ink density error data for n nozzles and their surrounding nozzles. It is explanatory drawing of the logic which calculates correction data. 7 is a flowchart of a work for converting 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 a gradation reduction process. FIG. 6 is a diagram illustrating a general printing method of multi-pass printing. It is a figure which shows the example of a test pattern in the printing of a multipass system. It is a figure which shows the example of the inkjet head which has 1000 nozzles, and the correspondence of the nozzle used for printing and the pixel printed. It is a flowchart of the work procedure of this invention in a multipass system. It is a flowchart of the operation | work which converts image data based on the correction data produced in the multipass system. It is a figure which shows the structural example of the inkjet printing device which used this invention. It is a conceptual diagram which shows that a captured image is deformed based on the calculated parameter. It is a figure which shows the example of a wide test pattern which does not fit into 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 respectively arranged in a horizontal row in the nozzle row direction of the inkjet head to form an inkjet head group, thereby printing wider than one inkjet head. Cover the area. The print area on the substrate 2 is divided into areas 3 to 6, and the print areas to be printed by the individual inkjet heads forming the inkjet head group are as follows: area 3 is head 1a, area 4 is head 1b, and area 4 is head 1b. 5 has a configuration in which the head 1c is in charge of the area 1 and the region 6 is in charge of the head 1d. By ejecting the ink, an image is printed on the printing material when the printing material passes through. In FIG. 1, the inkjet heads 1a to 1d are arranged in a zigzag manner, but any arrangement method other than the zigzag arrangement may be used as long as they are arranged so as to cover the print area, and an inkjet head group is formed. The number of inkjet heads can be added or reduced depending on the width of the printing material. In FIG. 1, adjacent ink jet heads are arranged so as to partially overlap each other, so-called overlapping. This point will be described in detail below. However, depending on the specifications of the ink jet heads to be used, the ink jet heads may be overlapped. Arrangement methods that do not wrap are also conceivable.

FIG. 2 shows an example of correction by an existing method for an ink density error of a printed matter that occurs between a plurality of ink jet heads and the color density of the original image data to be printed is different from the actual printed matter. 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 printing area on the printing material 2 is divided into areas 3 to 6, area 3 is an inkjet head 1a, area 4 is an inkjet head 1b, area 5 is an inkjet head 1c, and area 6 is an inkjet head 1d. Shows the example in charge of printing. Note that the present invention can be used even when a thermal inkjet head is used, but the inkjet head in the example shown here is a so-called piezo inkjet head that uses a piezoelectric element to eject 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 piezo elements, and as shown in FIG. 2A, the ink density errors of the inkjet heads 1a to 1d are large. However, when an image is printed without correction, the image density is adversely affected because the ink densities greatly differ for each print area. Here, FIG. 2B shows an example in which the driving voltage of the piezo element, which is the usage condition, is adjusted for each inkjet head to correct the ink density error between the inkjet heads. Comparing FIG. 2 (a) and FIG. 2 (b), although a certain degree of correction can be made, the range of the applied voltage that can be adjusted is limited, and as described above, the adjustment of the applied voltage is a fixed value. There is also a problem that it is not possible to collectively correct ink density errors that differ in the degree of occurrence in different color density bands. Changing the drive voltage also changes the ejection speed of the ink droplets that are ejected, which may change the landing position on the base material, which may affect the quality of the printed image. Problems may occur.

FIG. 3 is a measurement example of ink density data obtained by printing and reading a test pattern in the configuration shown in FIG. 1. In this example, the dark color density data example is the measurement data 7 and the light color density data. The measurement data 8 is an example, and the measurement data 7 and the regions 3 to 6 of the measurement data 8 correspond to the print regions of the printing material of FIG. In the example of FIG. 3, the ink density error in the inkjet head 1a is the largest, it is small in the inkjet head 1b, and it is almost nonexistent in the inkjet heads 1c and 1d. In this example, the average density in the inkjet head is higher than that of the other inkjet heads 1c.

Further, in this example, the ink density at the connecting portion between the inkjet heads 1a and 1b in FIG. 3 is high, and so-called black stripes appearing as a band on the printed image in which the ink density is high are generated. The ink density at the adjacent joints between 1b and 1c and between 1c and 1d is low, and so-called white stripes appearing as strips on the printed image in the area where the ink density is low.
Normally, the measured data 7 and the measured data 8 have the same tendency as long as they are printed by using the same inkjet head even if the measured data are of different color densities. Are often different. Therefore, a test pattern for each different density, which will be described separately, is used.

FIG. 4 is a graph showing the measured value of the color density and the target density value for explaining the relationship between the ink density correction and the target density value to be the target at the time of the correction. The horizontal axis shows the position in the print width direction, and the vertical axis shows the color density. The measurement data 10 indicates 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. By correcting this, correction data is created so as to obtain a uniform color density. First, it is necessary to determine the target color density reference value. In the example shown in FIG. 4, the target density value (target density) 9 shown by the solid line is the average value of the overall density. In this case, as the correction data 11, the measured value will be described in detail below, but a numerical value will be calculated by a predetermined method, but an outline will be given so that the portion where the color density value is high becomes low. The correction data is generated in such a manner that the correction data is generated so that the density value is low in the portion having the low density value, and the portion having the same density as the target density is not corrected.

Here, the target density value (target density) may 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 apparatuses of the same model that print using the same substrate and the same ink are installed in the production factory. In this case, it is necessary to print an image having the same color density value and tint regardless of which printing device is installed. For example, in a printed material such as a building material where a plurality of printed materials are arranged side by side, all color density values need to be uniform. If there is a slight error in the color density value of the printed material, the printed material will be regarded as a 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 apparatuses have the same color density value. For example, when there are printers 1 to 5 to be installed, the measurement value of the newly installed second machine is the measurement data 10, and the color density measured by printing the test pattern on the second machine alone. The correction value calculated from the average of the values is used as the correction data 11, and the corrected density value of the installed No. 1 machine itself is the target density value (target density) 9a. When the color density value of Unit 1 is used as the reference value, the target density value of Unit 2 is set as the target density value (target density) 9a. If the corrected density value of Unit 1 is the target density value (target density) 9b, the target density value of Unit 2 may be set to the target density value (target density) 9b in order to match it. Then, the correction value calculated from the average value of the overall densities of Unit 2 alone is further subjected to the process of adjusting to the predetermined target density at the same time, so that the ink density error and the inkjet head group which occur in the respective inkjet heads can be eliminated. It is possible to correct not only the ink density error between the respective inkjet heads constituting the ink density error, the density error in the adjacent portions of the inkjet heads configuring the inkjet head group, but also the ink density error caused by the individual difference between the apparatuses.

FIG. 5 shows an example of a test pattern in single-pass printing. The test pattern image has at least a color density pattern for measuring ink density and an alignment mark. The alignment mark 12a, the alignment mark 12b, the alignment mark 12c, and the alignment mark 12d each have a function of detecting the print position of the test pattern, the imaging resolution, the inclination of the image, and the like, and are shown in FIG. 5 and FIGS. Thus, the color density pattern is arranged on the outer peripheral portion. . The shape of the alignment mark is not limited to a circular shape as long as it is easy to use for computer processing. The imaging conditions and specific data processing are not directly related to the present invention, so a detailed description thereof will be omitted. However, the imaging resolution of the test pattern must be equal to or higher than the desired resolution and spatial frequency. Further, the dynamic range of the image pickup device needs to be saturated in a bright direction even in a non-printed portion and not saturated in a dark direction even in a maximum density portion.

Further, in the example of FIG. 5, the color density pattern has 16 levels of color density including the part where no printing is performed. The number of patterns is not limited to 16 patterns, and it is not necessary to arrange them in the order of color density steps. However, the purpose of having a plurality of color density patterns is wide because the occurrence status of an 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 area, and ink density errors that occur in multiple color densities are measured to generate correction data. By doing so, more accurate correction can be performed, and by setting a target density value for each of a plurality of color densities, even more accurate correction can be performed.

FIG. 6 shows the measurement values of the test pattern of FIG. 5 as measurement values 13 and 14 in the two color density regions of 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, which is caused by an optical blur phenomenon of the image pickup apparatus. As a result of the blurring phenomenon, the color density value at the end of the printing width cannot be accurately measured. This is inevitable no matter how expensive the imaging device is. The same phenomenon occurs when a test pattern used in a multi-pass inkjet printing apparatus shown in FIG. 16 described later is imaged. In this case, the optical problem of the image pickup apparatus can be avoided by applying the averaging process in the vicinity of the end to the end of the test pattern in FIG. Further, when the test pattern is imaged and the ink density error is calculated in the case of the multi-pass method shown in FIG. 16, different processing is performed, but 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 using a commercially available low-priced imaging device (scanner), the position coordinates of the pixel on the captured test pattern image and the position coordinates of the pixel on the actual test pattern image before printing are used due to the imaging accuracy of the scanner. Will explain how to perform practical-level imaging because a significant error occurs during measurement.

First, a commercially available scanner shown on the left side of FIG. 21 is used to image a glass mask, which is a high-precision measure, and an example of how much error occurs in the image captured by the scanner and how the error occurs will be shown below.
A rectangular glass mask of 140 mm × 350 mm was read, but the upper left origin 201. Of the upper right apex 202. Coordinates (140-0.639 mm, 0), and the lower right vertex 203. Has coordinates (140 + 0.166 mm, 350 + 0.139 mm), and the lower left apex 204. The coordinates of (0 + 0.974 mm, 350 + 0.182 mm) have errors in the coordinates of each vertex. For example, in the case of a 600 dpi head, the nozzle interval is about 42 ㎛ Therefore, if 5 nozzles are displaced, 42 ㎛ × = 210 ㎛ From the viewpoint of the density measurement for each nozzle of the present invention, the displacement of the measurement position by 210 ㎛ means that the nozzle position is displaced by 5 nozzles. This means that the 508th nozzle was corrected in an attempt to correct it.

In order to solve the above problem, a method of correcting the positional error of each pixel forming the test pattern image picked up by the image pickup apparatus (scanner) can be adopted 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 forming 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 of the alignment mark on the plane orthogonal coordinate system are read, and the deformation parameter for deforming the image is calculated so as to match the theoretical value.
(3) At least the color density pattern portion of the captured test pattern image is two-dimensionally deformed based on the calculated deformation parameter.
(4) The nozzle is cut out (specified) based on the deformed image, and the density is measured.

First, the above-mentioned "(1) Printing four or more alignment marks on the outer peripheral portion of the color density pattern forming the test pattern" will be described. In the example of FIG. 5, four or more marks, which are 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. The alignment marks are preferably 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) XY coordinates of the alignment mark on the plane orthogonal coordinate system are read and the deformation parameter for performing the image deformation process so as to match the theoretical value is calculated and calculated."
In the example of FIG. 5, which alignment mark is the alignment mark can be identified by the thickness of the solid black line, the solid white line, and the black circle. Then, the center of each alignment mark is labeled to obtain the center coordinates of the alignment mark, and the coordinates of the alignment mark can be read accordingly.
Here, the theoretical coordinates of the alignment mark on the plane orthogonal coordinate system are (X1, Y1), (X2, Y2), (X3, Y3), (X4, Y4), and the reading coordinates by the image pickup device (scanner) are , (X1, y1), (x2, y2), (x3, y3), (x4, y4).
Here, the following relational expression holds, and the deformation parameters a11, a12, a13, a14, b11, b12, b13, b14 are calculated by this relational expression.
X1 = a11 × x1 + a12 × y1 + a13 × x1 × y1 + a14
X2 = a11 × x2 + a12 × y2 + a13 × x2 × y2 + a14
X3 = a11 × x3 + a12 × y3 + a13 × x3 × y3 + a14
X4 = a11 × x4 + a12 × y4 + a13 × x4 × y4 + a14
Y1 = b11 × x1 + b12 × y1 + b13 × x1 × y1 + b14
Y2 = b11 × x2 + b12 × y2 + b13 × x2 × y2 + b14
Y3 = b11 × x3 + b12 × y3 + b13 × x3 × y3 + b14
Y4 = b11 × x4 + b12 × y4 + b13 × x4 × y4 + b14

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

In addition, when a test pattern of 600 dpi was printed using the above-mentioned glass mask and a predetermined position on the glass mask was verified by imaging at 600 dpi, the nozzle position error was 1-2 nozzles. It was within (42-84 μm). An error within this range 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.
In general, commercially available scanners are at most A3 size or A3 novi size. 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 mark arranged in the print width direction at a size of 40 cm which can be imaged by the scanner is imaged in three divisions so as to include both the alignment marks of the divided portions.
After that, the test pattern images captured by dividing the image on software may be combined at 0-40 cm, 40-80 cm, and 80-120 cm, respectively. By providing 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 in three steps, and the coordinates of the alignment marks shared by each image are set. By combining inside, it is possible to measure the ink density error even in an inkjet printing apparatus that requires a wide test pattern.

FIG. 7 is an explanatory diagram regarding the overlap processing of the inkjet heads. In this explanatory diagram 7, two adjacent ink jet heads overlap by 4 nozzles and overlap each other. The x shown in FIG. 7 indicates a pixel in charge of printing by the left ink jet head, and the □ shown in FIG. 7 indicates a pixel in charge of printing by the right ink jet head. In the printing of the width of four nozzles that overlap, the right inkjet head and the left inkjet head alternately take charge of printing, respectively, so that it is possible to reduce the ink density error in the overlapping portion. By performing the density correction means described above after reducing the overall density difference in this processing, it is possible to improve the image quality with higher accuracy.

Based on the above, an embodiment of the present invention in single-pass printing will be described as an embodiment 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 image data to be printed.

First, the creation of ink density error correction data will be described with reference to FIG. First, in the use condition adjusting step 31, a process of correcting an ink density error is performed on each of a plurality of inkjet heads forming an inkjet head group by adjusting an applied voltage which is a conventional method. The use condition adjusting step 31 corresponds to the processing described in FIG. Next, in an overlap processing step 32, an inkjet head group is formed, and overlap processing is performed on the connecting portions of the inkjet heads that are adjacent to and overlap each other. The specific content of the overlap processing corresponds to the processing described in FIG. 7. By the processes up to step 2, the ink density error between the inkjet heads forming 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. 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 step 34 performs print gamma correction on the test pattern image. The printer gamma correction, which will be described in detail later, refers to a means for correcting image data to be printed so that the change in the color density of the actual printed matter becomes linear for each density.

Then, in a test pattern printing step 35, a test pattern for 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. The width of the test pattern to be printed is, as described above, the ink density error of the nozzles in one ink jet head, the ink density error between the individual ink jet heads forming the ink jet head group, and the connecting portion of adjacent ink jet heads. From the viewpoint of collectively correcting all of the ink density errors and the ink density errors caused by individual differences between manufactured individual inkjet printing apparatuses, the printable width is preferably the full width.

Then, in the test pattern imaging step 36, the printed test pattern is imaged. The image pickup means may be a scanner or another image pickup means, but it is necessary to take an image of the entire test pattern with required accuracy such as a predetermined resolution. Further, at this time, by applying the average processing shown in FIG. 6 to obtain the color density of the print width end portion of the captured test pattern image in the vicinity of the end portion, the optical problem of the above-described image pickup apparatus is avoided, This 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 calculated numerical value is used to create the ink density error correction data.

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

FIG. 9 is an example of measurement of ink density data different from that of FIG. 3, and is an example of measurement of ink density when there are a total of nine levels of color density input for printing. The width of the color density of the input data is one of 256 levels from 0 to 255, and the larger the number is, the higher the color density is. In FIG. 9, the input data 255 has the highest color density, and the smaller the color density becomes 224, 192, 160, 128, 96, 64, 32, 0, the lower the color density becomes. 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 in the print width direction of the image as in the above example, in other words, the position of the nozzle. The position of n nozzles is shown on the horizontal axis of FIG. The vertical axis represents the density, and in the figure, the density at the time of the input data 255 is shown as the highest density, 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 may be composed of different numbers of bits such as 16 bits. FIG. 9 shows the respective densities, in this case, the densities of all nozzles and all areas in nine stages. This is the whole picture of the measurement data. In FIG. 9, the measured 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 possible.

FIG. 10 shows a graph obtained by cutting out and plotting the ink density error data for the n nozzles and the peripheral nozzles in FIG. In FIG. 10, ink density error data of three nozzles, n nozzles and adjacent n + 1 nozzles and n + 2 nozzles, are plotted. The position may be identified by the nozzle number or the image position number. 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 density of the n + 2 nozzles is low, and the n nozzles are the darkest. For example, when printing a 500 mm width at 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, one graph can be made with two or more nozzles, and from the viewpoint of improving the resolution, it can be made one graph with two nozzles or more. In the case of 2 nozzles 1 graph, the number of graphs is 5,905, and in the case of 1 nozzle 2 graphs, it is 23622.

FIG. 11 explains 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 for correction are shown. In converting the measurement data of the n nozzles into the target density value, it is understood from FIG. 11 that the ink density output from the n nozzles when the input data Di is P1 and the target density value is P2. Therefore, in order to output the ink density of P2 using n nozzles, it is necessary to set the input data to Do. Therefore, it is possible to output the ink density of P2 from the n nozzles by creating a table for converting Di into Do.

By performing the above steps, not only the ink density error that occurs in each inkjet head itself that configures the inkjet head group, but also the ink density error between the individual inkjet heads that configure the inkjet head group and the adjacent inkjet heads Ink density error correction data capable of collectively correcting all of the ink density errors at the joint portion and the ink density errors caused by individual differences between the manufactured individual inkjet printing devices can be executed in a single procedure. It can be calculated.

Next, referring to FIG. 12, an 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 in step 39, the RGB image is converted into a CMYK image and the color profile is converted. Then, in step 40, print gamma conversion is performed for the image data. Run against.

Here, an example of the processing of the image data performed in steps 38 to 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 also assumed, and different data formats such as palettes are also assumed. The image data is converted into multivalued data (usually 8 bits) of ink colors CMYK via the color profile. If the printing device is a different model, the mounted ink and other functions are different, so even if the same image data is printed, there is the problem that the tint will be different.Therefore, in general, a standard profile called the ICC profile is used. As a result, color reproducibility independent of the printing device is realized.

The printer gamma conversion is a means for correcting the image data to be printed so that the change in the color density of the actual printed matter becomes linear, and the actual condition is often a table conversion. Further, since the ink density error correction according to the present invention is also often performed by making full use of a plurality of table conversions, it is also assumed that the printer gamma conversion table and the ink density error correction table are combined to be performed in one table. it can. By using one table, the amount of information to be processed can be minimized, and the speed of data processing can be increased.

After the above steps 40 are completed, in the image conversion (ink density error correction) step 41, the entire print 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 for an 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 and printed using the corrected output data plotted in FIG. 13, the n nozzles can perform printing with the same ink density as the target density value. By performing this process for all nozzles or all position data, it is possible to correct the ink density error in all areas and all color density areas. Note that 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 density after correction will eventually change due to the conversion processing of steps 38 to 40. Therefore, it is desirable to execute the image conversion (ink density error correction) step 41 after the steps up to step 40 are completed.

Then, finally, the gradation reduction processing is executed on the corrected print image as the gradation reduction processing step 42 in FIG. Here, the gradation reduction process will be described in detail. FIG. 14 is an explanatory diagram of an example of the gradation reduction processing. Generally, image data has 8 bits and 256 density gradations, but the gradation that can be realized by an inkjet head is not ejected in the case of a model capable of ejecting droplets of three sizes, for example, small droplet, medium droplet, and large droplet. Since there are only 4 gradations including the case, it is necessary to reduce the gradation data of 256 gradations to 4 gradations. The horizontal axis of FIG. 14 represents the input data and has 256 gradations from 0 to 255. The vertical axis represents the printing rate of each droplet, and 100% indicates a state in which all dots are printed in a predetermined area, and in the case of 50%, dots are printed in 50% of the predetermined area. Shows the state. In FIG. 14, while the input data is 0-a, only the small droplets change the printing rate from 0% to 100%. While the input data is ab, the printing rate of small drops changes to 100% -0%, and the printing rate of medium drops changes to 0% -100%. While the input data is b-255, the printing rate of medium drops changes to 100% -0%, and the printing rate of large drops changes to 0% -100%. That is, it can be said that 100% of the printing rate of the small drops corresponds to the input data a, 100% of the printing rate of the medium drops corresponds to the input data b, and 100% of the large drops corresponds to the input data 255. Of course, this relationship depends on the characteristics of the base material and the ink, and if 100% of large drops are used, the density of the printed ink may be too high. In this case, adjust so that 100% of large drops are not used. In some cases.

After performing all of the above steps, the corrected print image data is printed by the inkjet printing apparatus to obtain the ink density error of the nozzles of the individual inkjet heads that configure the inkjet head group, and the individual inkjet heads that configure the inkjet head group. The ink density error between the inkjet heads, the ink density error at the connecting portion of the adjacent ink jet heads, and the ink density error caused by the individual difference between the manufactured individual inkjet printing apparatuses can be collectively and highly corrected. 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 an example of a general printing configuration in normal multi-pass printing. As described above, the multi-pass method is a method in which the same portion is divided into a plurality of times for printing. In FIG. 15, the first scan 16 represents the first drawing scan, in which the ink is discharged while drawing while moving in the X direction indicated by the arrow, and this operation is repeated as the second scan 17 and the third scan 18. Be done. This example is a method called a 3-pass method in which the same portion is divided into three parts and printed, and shows a method in which a part of the print image is completed by three times of overlapping 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 of the inkjet head shown in FIG. Usually, one scan prints about one third of the final density, which is the ink density of the finally completed printed image.

The second scan 17 indicates the second drawing scan, and printing is performed using the lower two thirds of the head. As in the case of the first scan 16, the portion overprinted twice becomes about ⅔ of the final density and the lower half becomes about ⅓ of the final density.

The third scan 18 indicates the third drawing scan, and printing is performed using the entire inkjet head. The portion overlaid three times becomes the final image that has achieved the final density, and the printing of that portion is completed. After that, multipass printing is performed by repeating the drawing scans to form the entire image, such as the fourth scan 19 and the fifth scan 20. Here, the relationship between the printed material and the head is relative, and the head may move in the X direction of the arrow and the printed material may move in the Y direction.

It should be noted that in FIG. 15, an image having a length that is one-third of that of the inkjet head is printed in one scan, but the basic unit in the multi-pass printing in the present invention is printing in one scan. The length of the image to be displayed is shown. In this example, the length of one third of the ink jet head is the basic unit, but of course, the basic unit becomes relatively shorter as the number of divisions of printing is increased, and the basic unit becomes relatively longer as the number of divisions is decreased. The basic unit is not necessarily limited to a fraction of the length of the inkjet head in the nozzle row direction.

FIG. 16 shows an example of the test pattern corresponding to FIG. The printing width is more than twice the basic printing unit. FIG. 16A shows an example in which the print width is twice the basic unit, and FIG. 16B shows an example in which the print width is 5 times the basic unit. In FIG. 15, it is assumed that the head moves in the X direction and the printing material moves in the Y direction. A whitish or blackish streak may appear between the Nth scan and the (n + 1) th scan. This cause may be a physical phenomenon due to the accuracy of the amount of movement of the printed material or an error in how the ink spreads on the base material due to the physical effect of the ink and the base material at the boundary of the basic unit. It is described by the term banding in the inkjet printing device industry. In the present invention, banding also becomes an ink density error to be solved. In this regard, in FIG. 16A, banding may occur by inserting two basic printing units and printing the test pattern such that the boundary between the scans is included in the test pattern. The area is secured. In FIG. 16B, five basic print units are inserted to further increase the amount of information. When the basic unit amount is increased, the information amount is increased, so that more detailed ink density error measurement can be performed, but there is a problem that the information amount is increased and the processing load is increased.

Regarding the processing of the blurring phenomenon at the print width end portion of the captured test pattern image described in the above description of FIG. 6 when the ink density error is calculated by capturing the multi-pass test pattern of FIG. explain. In the case of the multi-pass method, the existence of the ink density error in the connecting part of the basic units to be printed is directly linked to the occurrence of banding as described above, and therefore it is necessary to calculate the ink density error more accurately. The processing of parts becomes particularly important. Therefore, in this case, the numerical value of the ink density error calculated from both end portions of the adjacent portion of the basic unit printed on the captured test pattern is applied to the print width end portion. That is, to explain using the example of FIG. 16A, the printing in each basic unit is performed by dividing the nozzles used by the same inkjet head in all the passes by the same dividing method, and thus printing each basic unit. The occurrence status of the ink density error within the unit is theoretically the same or similar. Therefore, in the example of FIG. 16A, the numerical value of the upper end of the lower basic unit that is in contact with the basic unit adjacent portion of FIG. 16A in the blurring occurrence portion in the uppermost print width end of FIG. Apply. 16A, the numerical value of the lower end of the upper basic unit that is in contact with the basic unit adjacent portion of FIG. 16A is applied to the blurring occurrence portion in the lowermost printing width end portion. By the same processing, theoretically, more accurate processing of the end portion of the printing width can be executed.

In addition, here, the imaging conditions for imaging the test pattern of FIG. 16 will be described in detail. In multi-pass printing, the resolution of the image printed on the substrate is not uniform. Also, due to the banding problem peculiar to the multi-pass printing and the need to match the nozzles used with the image to be printed as described below, the resolution of the imaged test pattern is different from that of the printed test pattern. It is necessary to match the resolution with the resolution of the captured test pattern image. Therefore, when capturing the test pattern, it is necessary to set conditions 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 nozzles and the print image is fixed in the multi-pass printing. The inkjet head 1 in FIG. 17 is an inkjet head having 1000 nozzles, and the nozzles for ejecting the inks to which the numbers are assigned are shown therein. Assuming that four-pass multi-pass printing is performed using this inkjet head, printing of each pass starts from the nozzle 201b, which is the partition of the inkjet head nozzles starting from nozzle 201a and having nozzle numbers 1 to 250. It is divided into four sections of the sections of nozzle numbers 251 to 500, the sections of nozzle numbers 501 to 750 starting from the nozzle 201c, and the sections of nozzle numbers 751 to 1000 starting from the nozzle 201d. ..

17A and 17B are diagrams showing the correspondence between nozzles used for printing and printed pixels. Image data is shown with the upper left reference, and the numbers of nozzles 201 and the numbers of pixels 204 are used. , Shows the correspondence between printed pixels and nozzles used for printing. Although FIG. 17 shows the same 4-pass printing, two types of 4-pass printing examples of FIGS. 17A and 17B are shown. 17A shows four passes for quadrupling the resolution in the nozzle row direction, one pixel line is printed by one nozzle, and FIG. 17B shows doubling the resolution in the nozzle direction. One pixel line is printed by 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. 17 (a), the left-side writing position is the 1st nozzle, the 2nd nozzle is the 251 nozzle, the 3rd nozzle is the 501 nozzle, and the 4th nozzle is the 751 nozzle. The numbers of the pixels that have been printed and form the image correspond to the nozzle numbers. In the example of FIG. 17B, the first line, which is the left-side writing position, is the first nozzle and nozzle 501, the second line is the nozzle 251 and nozzle 751, and the third line is the nozzle 502 and nozzle 502. The number of a pixel forming an image, such as the No. nozzle, corresponds to the nozzle number.

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 constant the positional relationship between the pixels that form the image and the relationship between the ink density error caused by the nozzles, the connecting portion between adjacent inkjet heads, and the like.

In the case of the single-pass printing, as described above, the printing is performed on the printing object by ejecting ink from the nozzles when the printing object passes directly below the nozzle surface of the inkjet head. Since the drawing method is used and the resolution depends on the nozzle of the inkjet head, in the example of the inkjet head of FIG. 17, the line of the first pixel is printed by the first nozzle and the second line is printed. This means that the pixel line of No. 2 is printed by the second nozzle, and as a result, the positional relationship between the inkjet nozzles and the printed image is automatically made constant.

Based on the above, an embodiment of the present invention in multi-pass printing will be described as a second embodiment which is one of the best embodiments of the present invention.

FIG. 18 is a work procedure flow of the present invention in the multi-path method, and description will be given based on this flow. FIG. 18 shows a procedure for creating the ink density error correction data, and FIG. 19 shows a work procedure flow for converting the image data based on the correction data created for the image data to be printed. Since the procedure is basically the same as that in the case of the single path method described in the first embodiment, 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 use condition adjusting step 51, the applied voltage, which is a conventional method, is adjusted to perform the process of correcting the ink density error for each of the individual inkjet heads forming the inkjet head group, and then the overlap processing step. At 52, overlap processing of the connecting portion of the inkjet head is performed. Note that 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 in FIG. 16 is prepared, and the print gamma correction step 54 performs print gamma correction on the test pattern image.
Then, in a test pattern printing step 55, a test pattern for the entire printable width formed by the inkjet head group is printed. Further, it is desirable that the width of the test pattern to be printed has a width of two basic units or more as described in FIG.

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 processing for the blur phenomenon to the print width end portion of the captured test pattern image 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 case of 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 has occurred. Since the above calculation is performed, the correction data of the banding portion can be calculated at one time.

By performing 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 between the basic units, and the individual inkjet heads that make up the inkjet head group when multiple inkjet heads are used. Ink density error that can collectively correct all of the ink density errors between each other, the ink density errors of the connecting parts of adjacent ink jet heads, and the ink density errors caused by individual differences between the manufactured individual inkjet printing devices. The correction data can be calculated by executing the procedure once.

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

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

After the above steps 60 are completed, in the image conversion (ink density error correction) step 61, the entire print 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 changed by the conversion processing of steps 58 to 60. Therefore, it is similar to the first embodiment that the image conversion (ink density error correction) step 61 is desirably executed after the steps up to step 60. Then, finally, the gradation reduction processing is executed on the corrected print image as the gradation reduction processing step 62.

By performing the above procedure 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 the multiple In the case of using the above inkjet heads, it occurs due to an error in the ink density between the inkjet heads forming the inkjet head group, an error in the ink density at the connecting portion of adjacent inkjet heads, and individual differences between the manufactured individual inkjet printing apparatuses. All 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 print-out unit 101, a print unit 103, and a print-up unit 105. An ink jet 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 the scanner used as the imaging device 109 and processed by the computer. The imaging device 109 can be incorporated in an inkjet printing device to automatically print a test pattern, capture a test pattern, calculate correction data, correct print data, and the like.

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

After correcting the ink density error such as adjusting the applied voltage for each inkjet head, the print image is converted based on the correction data calculated based on the test pattern that was printed and read, so that the entire inkjet head group can be installed. On the other hand, it was possible to correct the ink density, and it was possible to realize high-quality, high-quality printing, which cannot be achieved by the conventional correction method, in an inkjet printing apparatus for industrial use.

After the correction of the connecting portion between the adjacent inkjet heads by the overlap processing described later, the print image correction is performed based on the correction data calculated based on the read test pattern, thereby achieving the completion degree in the inkjet printing apparatus for industrial use. Higher image quality was achieved.

In a single-pass inkjet printing device, a test pattern is printed using the entire print width of the inkjet head group for each ink type, and image conversion is performed based on the correction data calculated using the printed test pattern. Therefore, it is possible to collectively correct the difference in ink density between the nozzles of the inkjet heads, the difference in ink density between the inkjet heads that make up the inkjet head group, and the difference in ink density at the connection between the adjacent inkjet heads. It became possible.

By defining a reference value to be used as a reference in the ink density correction and switching the target value to be corrected for the ink density to the reference value, it becomes possible to correct the density difference between the apparatuses.

In a multi-pass inkjet printing device, based on a test pattern with a unit width of two basic units or more, which is the width to be printed by one moving scan of the inkjet head with the print image data and nozzle relationship fixed By generating correction data, it is possible to correct even in the multi-pass method, and it is now possible to print high-quality images with a smaller number of passes. Became.

1 Inkjet head 2 Printed material 9 Target density value (target density)
10 Measurement Data 11 Correction Data 12 Alignment Mark 15 Printing Width End 31 Use Condition Adjustment Step 32 Overlap Processing Step 35 Test Pattern Printing Step 36 Test Pattern Imaging Step 37 Correction Data Calculation Step 41 Image Conversion (Ink Density Error Correction) Step 42 Reduction gradation processing step 201 Nozzle 204 Pixel

Claims (8)

A method for correcting an error in ink density, which is the density of ink to be ejected from the inkjet head, in an inkjet printing apparatus that performs printing by relatively moving an inkjet head having a plurality of nozzles and an object to be printed, Adjusting the use conditions of the inkjet head to individually adjust the ink density; printing a color density pattern and a test pattern having alignment marks arranged at four or more points around the color density pattern; A test pattern imaging step of imaging a pattern to create a test pattern image; a deformation parameter calculation step including a step of reading coordinates of the alignment mark on the test pattern image and calculating a deformation parameter of the color density pattern; The test pattern image based on the deformation parameter A test pattern modification processing step including a step of modifying the color density pattern, a correction data calculation step of calculating correction data based on measurement data of the modified test pattern image, and printing based on the correction data. A step of correcting the ink density error in the entire image printed on the substrate by converting the entire image to be printed,
The deformation parameter calculation step calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
An ink density error correction method characterized in that the test pattern modification processing step corrects the coordinates of pixels constituting the color density pattern on the test pattern image on the plane orthogonal coordinate system based on the modification parameter. The correction data calculating step applies the density value of the color near the end portion in the print width direction to the density value of the color portion at the end portion in the print width direction that could not be accurately measured in the measurement data of the test pattern image. The ink density error correction method according to claim 1, further comprising: The step of capturing the test pattern includes a step of capturing the test pattern by dividing the test pattern into a plurality in the print width direction, and the step of combining the plurality of test pattern images captured by the parameter calculation step into adjacent portions to be divided. The ink density error correction method according to claim 1, further comprising: An inkjet head group configured to have a width corresponding to a printing width by mounting two or more inkjet heads is mounted for at least one type of ink, and a print object is once on the nozzle surface side of the inkjet head group. In an inkjet printing apparatus that is a single-pass method in which printing is completed only by passing through the ink jet head, the ink density, which is the density of ink to be ejected from each inkjet head, is adjusted by adjusting the usage conditions of the inkjet head. Means, a means for printing a test pattern having a color density pattern and alignment marks arranged at four or more points around the color density pattern, and a test pattern imaging means for imaging the test pattern to create a test pattern image. , Read the coordinates of the alignment mark on the test pattern image A deformation parameter calculation means including means for calculating a deformation parameter of the color density pattern; a test pattern deformation processing means including means for deforming the color density pattern on the test pattern image based on the deformation parameter; Correction data calculation means for calculating correction data based on the measured data of the processed test pattern image, and ink density error in the entire image printed on the printing object by converting the entire image to be printed based on the correction data Has a means for correcting
The deformation parameter calculation means calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
The ink jet printing apparatus, wherein the test pattern modification processing means corrects the coordinates of the pixels forming the color density pattern on the test pattern image on the plane orthogonal coordinate system according to the modification parameter. The printing material and the inkjet head are relatively moved in a direction parallel to the direction in which the nozzles of the inkjet head are aligned by a basic unit which is a width to be printed by one moving scan of the inkjet head, and the inkjet head and the printing object. The inkjet printing apparatus is a multi-pass system in which one or more inkjet heads are mounted, and the printing is completed by ejecting the ink while relatively moving and scanning the nozzles a plurality of times in the direction perpendicular to the direction in which the nozzles are arranged. 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 use conditions of the inkjet head, and a color density having a width of two or more of the basic units. Alignment mark with four or more points arranged around the pattern and the color density pattern Means for printing a test pattern, a test pattern imaging means for imaging the test pattern to create a test pattern image, and reading the coordinates of the alignment mark on the test pattern image and setting the deformation parameter of the color density pattern. Deformation parameter calculation means including calculation means, test pattern transformation processing means including means for transforming the color density pattern on the test pattern image based on the transformation parameters, and measurement of the transformed test pattern image A correction data calculation unit that calculates correction data based on the data; and a unit that corrects an ink density error in the entire image printed on the printing target by converting the entire image to be printed based on the correction data,
The deformation parameter calculation means calculates a parameter used for correction of coordinates on a plane orthogonal coordinate system of pixels forming the color density pattern on the test pattern image,
The ink jet printing apparatus, wherein the test pattern modification processing means corrects the coordinates of the pixels forming the color density pattern on the test pattern image on the plane orthogonal coordinate system according to the modification parameter. The correction data calculation means applies the density value of the color near the end portion in the print width direction to the density value of the color at the end portion in the print width direction that could not be accurately measured in the measured data of the captured test pattern. The inkjet printing apparatus according to claim 4, further comprising: An area adjacent to the basic unit in which the correction data calculation unit prints the imaged test pattern at the density value of the color at the end portion in the print width direction that could not be accurately measured in the imaged measurement data of the test pattern. The inkjet printing apparatus according to claim 5, further comprising a unit that applies a color density value calculated from both ends to a corresponding end in the print width direction. The unit for capturing the test pattern includes a unit for capturing the test pattern by dividing the test pattern into a plurality in the print width direction, and a unit for coupling the plurality of test pattern images captured by the parameter calculation unit to adjacent portions for division. The inkjet printing apparatus according to claim 4, further comprising: