JP2011152710A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and method suppressing deterioration of image quality (density unevenness, occurrence of mist) due to crosstalk, regardless of a single pass system or a multipath (serial) system. <P>SOLUTION: A nozzle position for discharging and the discharge timing are specified from first dot image data defining the dot arrangement of an image to be drawn and nozzle arrangement information, and a crosstalk evaluation value is calculated (S202) for evaluating the size of the crosstalk between the nozzles connected to the same flow path, on the basis of information of the specified information and information of the flow path communicating with the respective nozzles. The data of the specific pixel are replaced with the near pixel of the specific pixel, when the crosstalk evaluation value exceeds an allowable range, and second dot image data such that the crosstalk evaluation value settled in the allowable range can be obtained are generated (S208-S212), and droplet ejection is controlled on the basis of the second dot pixel data. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and method, and in particular, suppresses deterioration in image quality due to discharge variation caused by fluid interaction between nozzles in an image forming apparatus using an inkjet head having a large number of nozzles (droplet discharge ports). The present invention relates to image processing technology.

  Inkjet printers that eject ink droplets from nozzles by increasing the pressure in the ink chamber filled with ink liquid, depending on the presence or absence of ejection from nearby nozzles, ejected ink amount (droplet amount) and ejection speed (droplet flying speed) ) Is known to change. Such a phenomenon is hereinafter referred to as “crosstalk”. These are caused by a meniscus force caused by a decrease in the ink amount in the ink chamber at the time of ejection or a pressure wave accompanying the ejection.

  In recent years, due to demands for higher speed, lower power, and higher image quality of printing presses, single-pass printing presses using line heads in which a large number of nozzles are two-dimensionally arranged have attracted attention. The machine is easily affected by the above-described discharge error due to crosstalk due to the high density of nozzles and the miniaturization of the flow path in the head. Such a discharge error appears on a printed image as density unevenness, uneven stripes, or jaggy, particularly in a high density portion, and causes deterioration of image quality.

  Among the above problems, Patent Documents 1 and 2 are known as techniques for suppressing density unevenness. Patent Document 1 discloses a non-uniformity correction method for correcting density nonuniformity that occurs when a large number of ink droplets are ejected simultaneously. For the droplet amount error among the ejection errors, feedback is applied to the volume change of the ink passage. A method for improving the image quality by controlling the discharge amount is shown.

  On the other hand, Patent Document 2 discloses a density unevenness correction method that is mainly caused by a decrease in the amount of droplets generated when ink droplets are frequently ejected from the same nozzle in terms of time (continuous ejection). According to the document 2, a back pressure fluctuation is predicted from the created print data, a density fluctuation is predicted from the predicted back pressure, and the print data is corrected based on the fluctuation.

  Further, Patent Documents 3 and 4 are known as techniques for suppressing the above-described crosstalk. In Patent Document 3, in a multi-pass printing method (serial method) printer that completes an image by scanning a recording head a plurality of times in the same scanning area, a thinning mask pattern is used to simultaneously scan adjacent nozzles in a scan. A technique for suppressing discharge is disclosed.

  On the other hand, in Patent Document 4, by using a threshold matrix method and periodically inserting a pause element in the same direction (width direction) as the nozzle row, the discharge ports included in each of the discharge port groups that are not continuously paused are used. A method of setting the number to 1 or more and a predetermined number or less has been proposed, and a technique for suppressing crosstalk by setting the number of ejections to a predetermined number or less is disclosed.

JP 2000-218823 A JP 2007-237477 A JP 2003-266666 A JP 2008-290324 A

  However, incorporating the density unevenness correction mechanism disclosed in Patent Document 1 into the printing apparatus leads to an increase in manufacturing cost. In addition, since it is generally difficult to control the amount of droplets, there is a problem that density unevenness cannot be completely eliminated. On the other hand, in the case of the method disclosed in Patent Document 2, meniscus fluctuations should also occur due to the corrected print data, and in order to predict the density unevenness, it is necessary to make another prediction again. Have difficulty.

  In response to the problems of Patent Documents 1 and 2, Patent Document 3 proposes to suppress the simultaneous ejection of adjacent nozzles, but the technique of Patent Document 3 is based on a multi-pass (serial) system. Yes, not applicable to single-pass printers.

  In the case of the technique of Patent Document 4, in order to obtain a required density while limiting the number of ejections to a predetermined value or less, it is necessary to increase the number of nozzles or increase the droplet size, but increase the number of nozzles. This leads to an increase in cost, and an increase in droplet size leads to deterioration of the granularity.

  The present invention has been made in view of such circumstances, and an image capable of suppressing deterioration in image quality (density unevenness, occurrence of mist, etc.) due to crosstalk regardless of a single-pass method or a multi-pass (serial) method. It is an object to provide a forming apparatus and method.

  In order to achieve the above object, the following invention modes are provided.

  (Invention 1): An image forming apparatus according to Invention 1 stores a recording head having a plurality of nozzles arranged two-dimensionally and having a plurality of flow paths communicating with the plurality of nozzles, and nozzle arrangement information of the recording head. Storage means for storing flow path connection information indicating the connection relationship between the plurality of flow paths and the nozzles, and first dot image data for obtaining first dot image data defining a dot arrangement of image contents to be drawn From the acquisition means, the first dot image data and the nozzle arrangement information, the nozzle position of the recording head responsible for recording each pixel of the first dot image data and the ejection timing thereof are specified, and the specified information and the Based on the flow path connection information, the magnitude of the influence of crosstalk due to the interaction between nozzles connected to the same flow path is evaluated for a specific pixel in the image. Crosstalk evaluation value calculation means for calculating a Stoke evaluation value, the crosstalk evaluation value calculated for the specific pixel is compared with a predetermined criterion value, and the first dot image data needs to be corrected based on the comparison result. When it is determined by the determination unit that determines NO and the correction of the first dot image data is necessary by the determination unit, the data of the specific pixel and the data of the neighboring pixels of the specific pixel are switched, and after the replacement Dot arrangement change processing means for generating second dot image data for obtaining the crosstalk evaluation value within the allowable crosstalk range indicated by the determination reference value for each of the specific pixel and the neighboring pixels, and the second dot And a droplet ejection control means for controlling droplet ejection from each nozzle of the recording head based on image data. .

  According to the present invention, the first dot image data is analyzed, and the degree of the influence of crosstalk is evaluated by an index called a crosstalk evaluation value based on the nozzle arrangement information and the flow path connection information. If image quality deterioration due to crosstalk is predicted from the evaluation result, the dot image data is corrected, and the number of ejections is distributed between the flow paths or between ejection timings. Thereby, the number of ejections is averaged between the flow paths or between timings, and the occurrence of crosstalk is suppressed as a whole while maintaining the image density.

  Note that the determination reference value for evaluating and evaluating the crosstalk evaluation value can have both an aspect that defines the upper limit value of the evaluation value and an aspect that defines the lower limit value. That is, the determination reference value in the case of using the crosstalk evaluation value defined so that the evaluation value becomes larger as the influence of the crosstalk becomes larger indicates the upper limit of the allowable range. On the contrary, the determination reference value in the case of using the crosstalk evaluation value defined so that the evaluation value is smaller as the influence of the crosstalk is larger indicates the lower limit.

  (Invention 2) In the image forming apparatus according to Invention 2, in the invention 1, the crosstalk evaluation value calculated by the crosstalk evaluation value calculating means is simultaneously discharged from a group of nozzles connected to the same flow path. It is determined from the number of nozzles.

  As the number of simultaneous discharges in the same flow path increases, crosstalk tends to occur more easily. Therefore, the number of pixels simultaneously discharged from the same flow path can be obtained and this value can be used as the evaluation value.

  (Invention 3) In the image forming apparatus according to Invention 3, in the invention 1 or 2, the crosstalk evaluation value is determined from a distance between nozzles ejected simultaneously among nozzle groups connected to the same flow path. It is characterized by that.

  The closer the distance between nozzles that are simultaneously ejected in the same flow path, the greater the influence of crosstalk. Therefore, a mode in which the crosstalk evaluation value is determined as a function of the distance between the nozzles is also possible.

  (Invention 4): The image forming apparatus according to Invention 4 is the image forming apparatus according to any one of Inventions 1 to 3, wherein the crosstalk evaluation value calculating means is configured to perform ejection at each discharge timing of a nozzle group connected to the same flow path. With reference to the presence / absence of droplets, the presence / absence of ejection at a specific frequency in the same flow path is evaluated, and an operation for reflecting the evaluation result on the crosstalk evaluation value is performed.

  Due to the characteristics of the head, if ejection is performed at a specific frequency, the ejection performance may deteriorate due to crosstalk. Such specific frequency is experimentally grasped in advance, and the information is stored in a storage means such as a memory, so that the droplet ejection operation of the first dot image data includes ejection at the specific frequency. It can be determined whether or not. When ejection at a specific frequency is included, the influence of crosstalk becomes large. Therefore, it is possible to define an evaluation value so that the factor of the specific frequency is reflected in the crosstalk evaluation value.

  (Invention 5): The image forming apparatus according to Invention 5 is the image forming apparatus according to any one of Inventions 1 to 4, wherein the specific pixel when the data of the specific pixel and the data of the neighboring pixel of the specific pixel are replaced and Replacement for recalculating the crosstalk evaluation value for neighboring pixels, and evaluating whether or not to adopt the replacement by evaluating the crosstalk reduction effect by the replacement based on the recalculated crosstalk evaluation value It has a determination means.

  By comparing the crosstalk evaluation value before replacement of pixel data with the crosstalk evaluation value after replacement, the crosstalk reduction effect by the replacement can be determined.

  Based on this determination, it is preferable to replace a pixel with a high crosstalk reduction effect.

  (Invention 6): The image forming apparatus according to Invention 6 is the dispersibility evaluation means for evaluating the dispersibility of dots when the data of the specific pixel and the data of the neighboring pixels of the specific pixel are replaced in the invention 5. And the replacement determination unit determines whether or not to adopt the replacement based on an evaluation result by the dispersibility evaluation unit.

  It is desirable to change the ejection pixels so as not to deteriorate the granularity of the reproduced image. From such a viewpoint, in order to maintain the dispersibility of dots, a mode in which the dispersibility after the pixel data change (after the replacement) is evaluated and the change is not adopted depending on the evaluation result (the other pixels are changed) is preferable. . According to this aspect, it is possible to eliminate a replacement process that deteriorates the granularity. As a result, it is possible to reduce crosstalk while avoiding the deterioration of granularity. As the value for evaluating the dispersibility, for example, the number of dots adjacent to the particular pixel of interest (the number of ejection pixels) can be employed.

  (Invention 7): In the image forming apparatus according to Invention 7, in any one of Inventions 1 to 6, the neighboring pixel to be replaced with the specific pixel is a nozzle different from a nozzle responsible for recording the specific pixel. It is a thing corresponding.

  Even if data is exchanged between pixels that are ejected by nozzles belonging to the same flow path, the number of ejections in the same flow path does not decrease, and therefore such replacement has a low crosstalk reduction effect. Accordingly, it is desirable to replace and change the pixels that are ejected by different nozzles, particularly nozzles belonging to different flow paths.

  (Invention 8): The image forming apparatus according to Invention 8, in any one of Inventions 1 to 7, when the image content to be drawn is a line drawing, the replacement processing by the dot arrangement change processing means. It is characterized by not implementing.

  In the case of a line drawing, if the dot position is changed, the continuity of the line may be lost. Therefore, it is preferable to switch the processing contents so as not to perform the dot replacement (discharge pixel change) process.

  (Invention 9): The image forming apparatus according to Invention 9, in any one of Inventions 1 to 8, obtains the first dot image data by performing halftone processing on a multi-tone input image. It is a halftone processing means.

  The first dot image data acquisition unit may include a halftone processing unit that generates first dot image data from multi-valued input image data. Further, in place of or in combination with the halftone processing unit, there is also a mode in which the first dot image data generated by another external device is acquired by a communication unit or an external storage device.

  (Invention 10): The image forming apparatus according to Invention 10 according to any one of Inventions 1 to 9, wherein the first pixel corresponding to the specific pixel in the first dot image data, and recording of the first pixel. The crosstalk evaluation value of the first pixel is calculated based on the data of the second pixel discharged at the same timing as the first pixel by another second nozzle belonging to the same flow path as the first nozzle responsible for On the other hand, a third pixel recorded by a third nozzle connected to a flow path different from the first nozzle and the second nozzle corresponding to the first pixel and the second pixel, and the third pixel The crosstalk evaluation value of the third pixel is calculated based on the data of the fourth pixel recorded by the other fourth nozzle belonging to the same flow path as the third nozzle responsible for the recording of the first nozzle. Crosstalk evaluation value and the third Based crosstalk evaluation value of the unit, so as to average the crosstalk evaluation values of both pixels, and performs the process to replace the data with the third pixel and the first pixel.

  In addition, “averaging” in such an aspect means that the larger value is reduced and the smaller value is increased, thereby reducing the difference between the two. Absent.

  According to the aspect of the invention 10, since it becomes difficult to discharge simultaneously from adjacent pixels in the same flow path, crosstalk is suppressed, and the occurrence of density unevenness and mist can be suppressed.

  (Invention 11): In the image forming method according to Invention 11, a plurality of nozzles are two-dimensionally arranged, and nozzle arrangement information of a recording head having a plurality of flow paths communicating with the plurality of nozzles is stored in a storage unit, and A storage step of storing in the storage means flow path connection information indicating a connection relationship between a plurality of flow paths and the nozzles, and a first dot for obtaining first dot image data defining a dot arrangement of image contents to be drawn From the image data acquisition step, the first dot image data and the nozzle arrangement information, the nozzle position of the recording head responsible for recording each pixel of the first dot image data and the ejection timing thereof are specified, and the specified information And the magnitude of the influence of crosstalk due to the interaction between nozzles connected to the same flow path for a specific pixel in the image based on the flow path connection information. A crosstalk evaluation value calculation step for calculating a crosstalk evaluation value to be evaluated, and the crosstalk evaluation value calculated for the specific pixel is compared with a predetermined determination reference value, and from the comparison result, the first dot image data A determination step for determining whether or not correction is necessary, and when the determination step determines that the correction of the first dot image data is necessary, the data of the specific pixel and the data of neighboring pixels of the specific pixel are exchanged, A dot arrangement change processing step of generating second dot image data for obtaining the crosstalk evaluation value that falls within an allowable range of crosstalk indicated by the determination reference value for the specific pixel and the neighboring pixel after the replacement, And a droplet ejection control step for controlling droplet ejection from each nozzle of the recording head based on the second dot image data. And features.

  According to the present invention, it is possible to determine a dot arrangement in which crosstalk is unlikely to occur in accordance with the arrangement form of nozzles in the inkjet head and the flow path structure. As a result, density unevenness and mist generation due to crosstalk can be suppressed, and high-quality image formation is possible.

Plan view schematically showing the relationship between nozzle layout and image data address (pixel position) Explanatory diagram schematically showing the relationship between the ejection timing of each pixel and the nozzle number Explanatory drawing which showed the example by which simultaneous discharge is suppressed by replacement of pixel data 7 is a flowchart showing a processing procedure in the ink jet recording apparatus according to the embodiment of the invention. Flowchart of the dot arrangement optimization process in FIG. Explanatory drawing which shows the specific example of the replacement | exchange process of the pixel data which reduces crosstalk Explanatory drawing when the number of adjacent dots is used as an example of means for evaluating dot dispersibility Explanatory drawing which shows the example which replaced the data of the object pixel and optimized 1 is a configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. Diagram showing an example of the structure of an inkjet head Plane perspective view showing another structural example of the inkjet head Sectional drawing which follows the AA line in FIG. Main block diagram showing the system configuration of the inkjet recording apparatus The figure which looked at the head module which constitutes the ink jet head concerning other embodiments from the nozzle face side. The figure which showed the flow-path structure in the head module shown in FIG. Enlarged view showing the flow path structure inside the head module Sectional drawing which follows the BB line in FIG. FIG. 14 is a plan view showing the nozzle layout of the head module shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Explanation of the cause of crosstalk and its suppression method>
FIG. 1 is a plan view schematically showing the relationship between a nozzle layout in an inkjet head and image data addresses (pixel positions) at which tod printing is possible by droplet ejection from each nozzle of the layout. Here, in order to simplify the explanation, a 5 × 5 diagonal matrix array will be described as an example of a two-dimensional array of nozzle layouts, but the nozzle layout is not particularly limited when implementing the present invention.

  In FIG. 1, reference numerals 1-1, 1-2, 1-3, 1-4, 1-5, 2-1, 2-2,. Is shown. The ink jet head having the nozzle layout and the recording paper (recording medium) are moved relative to each other in the arrow S direction (+ y direction) in FIG. 1 and ink is ejected from the nozzles at an appropriate timing, thereby obtaining a desired pixel position. A dot can be formed (a desired image can be formed).

  An oblique solid line indicated by reference numeral 11 in the drawing is an ink flow path for supplying ink to the nozzles 1-1, 1-2, 1-3, 1-4, and 1-5. The nozzle group (nozzles 1-1 to 1-5) connected to the ink flow path 11 is referred to as a “first nozzle row”.

  Similarly, reference numeral 12 denotes an ink flow path for supplying ink to the nozzles 2-1, 2-2, 2-3, 2-4 and 2-5 belonging to the second nozzle row, and reference numeral 13 denotes a third nozzle row. Ink flow paths for supplying ink to the nozzles 3-1, 3-2, 3-3, 3-4, 3-5 belonging to, and reference numeral 14 denotes the nozzles 4-1, 4-2 belonging to the fourth nozzle row , 4-3, 4-4, 4-5, and ink flow paths 15 for the nozzles 5-1, 5-2, 5-3, 5-4, 5 belonging to the fifth nozzle row. This is an ink flow path for supplying ink to −5.

  Each of the ink flow paths 11 to 15 is connected to the supply-side common flow path 10, and a supply connection port 10 </ b> A that is an upstream end of the supply-side common flow path 10 is an ink tank (not shown) via a pipe line (not shown). Connected to. The ink introduced into the head from the supply connection port 10 </ b> A passes through the ink flow paths 11 to 15 corresponding to the branch flow paths branched from the supply-side common flow path (main flow path) 10 into the nozzles 1-1 to 5-5. 5 is supplied to a pressure chamber (not shown) corresponding to 5.

  In the nozzle layout shown in FIG. 1, the nozzles connected to the same ink flow path are arranged at a constant cycle in the xy coordinate system representing the pixel position of the image data (that is, the image data address). That is, the relative positional relationship between two adjacent nozzles belonging to the same ink flow path is arranged in a constant spatial cycle of 1 pixel interval in the + x direction and 4 pixel intervals in the -y direction. Assuming the arrangement period Tx in the x direction and the arrangement period Ty in the y direction, the nozzles are arranged at a period of (Tx, Ty) = (1, −4).

  The nozzles belonging to the same flow path are, for example, the nozzles 2-1 to 2-5 when referring to the ink flow path of reference numeral 12. Further, the adjacent nozzles in the same flow path are, for example, the nozzles 2-2 and 2-4 with respect to the nozzle 2-3.

  In the case of the flow channel structure shown in FIG. 1, the “same flow channel” in which the occurrence of crosstalk is a problem is the ink flow channels 11 to 15 in which the pressure chambers corresponding to the nozzles are in direct communication. The supply-side common flow channel 10 to which the ink flow channels 11 to 15 are connected does not correspond to a flow channel that mediates the interaction (crosstalk) between the nozzles.

  That is, crosstalk at the time of ink ejection occurs in the nozzle groups belonging to the same ink flow path 11-15. The nozzle groups belonging to the first nozzle row are connected to the same ink flow path 11, and crosstalk can occur between nozzles connected via the same ink flow path 11. The same applies to each of the ink flow paths 12 to 15, and the occurrence of crosstalk becomes a problem in the nozzle groups connected to the same ink flow path.

  Crosstalk is more likely to occur as the number of ejections increases in the same flow path. This is particularly likely when the number of simultaneous ejections from nozzles belonging to the same ink flow path is large. In addition, due to the characteristics of the flow path structure in the head, there is a tendency that it is likely to occur when discharge is continued from a specific nozzle or when the discharge frequency is a specific frequency. In view of such a tendency of occurrence of crosstalk, in order to suppress crosstalk, it is effective to change to dot image data having a dot arrangement in which crosstalk hardly occurs from the above viewpoint.

  This will be described more specifically with reference to FIG. FIG. 2 shows the correspondence between the four nozzles 31, 32, 33, and 34 (nozzle numbers 1, 2, 3, and 4 from the left) belonging to the same flow path and the dot image data for each ejection timing. It was. For the convenience of illustration, the positions of the nozzles 31 to 34 are drawn with circles superimposed on the upper left corner of the corresponding pixel cell.

  The correspondence between these nozzles and image data addresses depends on the nozzle layout. FIG. 2A shows the relationship between the nozzle layout and the image data address at each ejection timing.

  The numbers in parentheses described in each cell of the image data address represent the discharge timing T and the nozzle number N by (T, N). FIG. 2A shows that the image data is such that droplet ejection (discharge) is performed on the pixels (8, 1), (8, 2), (8, 3), and (8, 4). Yes. (8, 1), (8, 2), (8, 3), (8, 4) are ejection pixels, and pixel positions other than these are non-ejection pixels. That is, the image data indicates that all the nozzles of nozzle numbers 1, 2, 3, and 4 are ejected simultaneously at the ejection timing T = 8.

  The arrangement of the ejection pixels in the image data is 1 pixel period in the horizontal direction (x direction) and 4 pixel periods in the vertical direction (y direction), but the layout of the nozzles 31 to 34 belonging to the same flow path is the same. Due to the arrangement cycle, even pixels that are separated from each other on the image data are ejected by adjacent nozzles belonging to the same ink flow path on the nozzle layout.

  In the case of the discharge position shown in FIG. 2A, at the discharge timing T = 8, four nozzles belonging to the same flow path discharge simultaneously. In such a case, the number of simultaneous discharges in the same flow path is large. So crosstalk is likely to occur.

  On the other hand, FIG. 2B is a diagram in which ejection pixels (dots) are shifted little by little from the original image. Specifically, instead of the ejection pixels of (8, 1), (8, 2), and (8, 3) in the original image of FIG. 2A, (12, 2) in FIG. 2B, respectively. ), (7, 2), (9, 3) are discharge pixels, and (8, 1), (8, 2), (8, 3) are non-discharge pixels.

  In this manner, by slightly shifting the ejection pixels, in FIG. 2B, the droplets are dispersed at the ejection timings T = 7 to 9 and 12, and there are no dots that are ejected simultaneously at each ejection timing. . That is, the nozzle of nozzle number 2 is ejected at ejection timing T = 7, nozzle number 4 is ejected at T = 8, nozzle number 3 is ejected at T = 9, and nozzle number 2 is ejected at T = 12. Thus, the four dots corresponding to the ejection pixels (12, 2), (7, 2), (9, 3), (8, 4) are all ejected at different timings. In such a dot arrangement, crosstalk is suppressed as compared with FIG.

<Method of suppressing crosstalk by replacing pixel data>
As described above, if the number of ejections at the same timing is large for nozzles belonging to the same ink flow path, crosstalk is likely to occur. Therefore, when the number of simultaneous ejections is large, the pixel data is replaced so that the ink is ejected at different ink flow paths or at different timings.

  The schematic diagram is shown in FIG.

  FIG. 3 shows a part of binary image data that has been quantized (halftone processed). A numeral “1” shown in a cell representing a pixel indicates a discharge pixel (a pixel that discharges ink) for recording a dot, and a cell without a number is a non-discharge pixel that does not record a dot. Assuming that the nozzles 36 and 37 indicated by circles in FIG. 3 are connected to the same ink flow path, in FIG. 3A, image data in which these two nozzles belonging to the same flow path perform simultaneous ejection and It has become.

  In such a case, from the viewpoint of crosstalk suppression, the data of one of the ejection pixels (for example, reference numeral 40 in the figure) is shifted up by one pixel and replaced with the data of the non-ejection pixel immediately above (“0”). . Thereby, a dot arrangement (FIG. 3B) that avoids simultaneous ejection is obtained. In FIG. 3, the dot is moved to the pixel immediately above the pixel of interest (reference numeral 40). However, the dot may be moved to another neighboring pixel as long as simultaneous ejection in the same flow path can be avoided. By correcting the dot image data in this way, the number of ejections between the ink flow paths and the ejection timing is made uniform (because the number of ejections is excessively large), and crosstalk is suppressed.

  In an image such as a flat screen with a high recording resolution, the image quality rarely changes greatly even if the dot position changes by about one pixel. Although practically depending on the recording resolution, it is possible to change the dot position of about one pixel to several pixels within a range in which image quality that does not cause image quality degradation is practically maintained.

  Therefore, by simultaneously moving the dots within this allowable range (changing data), simultaneous discharge of the same flow path can be suppressed.

  Hereinafter, specific embodiments to which this method is applied will be described.

<Application to inkjet recording apparatus>
First, the overall configuration of the processing process in the ink jet recording apparatus according to the present embodiment will be described. FIG. 4 is a flowchart showing a processing procedure.

  A continuous tone image (for example, 8-bit, 256 tone image data) is input as an input image (step S102). Halftone processing is performed on the continuous tone image (step S104) to convert it into dot image data (binary image data indicating the presence or absence of dots). Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the means for halftone processing in step S104. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into gradation image data having an N value (N <M). In this example, it is converted into binary (dot on / off) dot image data, but in the halftone process, it corresponds to the dot size type (for example, three types such as large dot, medium dot, and small dot). It is also possible to perform multi-level quantization.

  Based on the dot image data (corresponding to “first dot image data”) obtained by the halftone process in step S104 and the nozzle layout, the presence / absence of droplet ejection from each nozzle at each timing is tentatively determined. The meaning of “provisional” is because the dot image data includes the possibility that the possibility of occurrence of crosstalk is evaluated and the data is corrected by the evaluation result. In the flowchart of FIG. 4, the generated dot image data is expressed as “half-toned crosstalk (CT) non-optimized image” (step S106).

  For the dot image data generated in this way, dot arrangement optimization processing (crosstalk suppression processing) for suppressing crosstalk is performed (step S108). Details of the dot placement optimization process will be described later, but this is a process of analyzing dot image data to evaluate the possibility of crosstalk occurrence, and correcting the dot placement to suppress the occurrence of crosstalk based on the evaluation result It is.

  By this process, the presence or absence of droplet ejection at each nozzle at each timing is corrected and converted into a dot arrangement in which crosstalk hardly occurs. This optimization process may be performed in parallel with the halftone process. However, as shown in FIG. 4, the processing time can be shortened by sequentially performing the pixel replacement process from the halftoned pixel.

  In this way, dot image data (a crosstalk optimized image) in which the dot arrangement is optimized so as to suppress the occurrence of crosstalk is obtained (step S110). Then, nozzle control data at each timing is generated from the dot image data, and printing is performed based on this data (step S112).

  Note that the signal processing means for performing the halftone process and its process shown in step S104 of FIG. 4 correspond to the “first dot image data acquisition means (process)”. A configuration in which halftone processing is performed in an external apparatus such as a host computer and halftone processed dot image data is provided to the inkjet recording apparatus is possible, as well as a mode in which the halftone processing is performed in the inkjet recording apparatus. In this case, image data input means for capturing dot image data from an external device, for example, a media interface that reads an external storage medium, a communication interface that exchanges information with the external device, and other information acquisition means This corresponds to “first dot image data acquisition means”.

  Further, the signal processing means and its process for performing the dot arrangement optimization process shown in step S108 of FIG. 4 are “crosstalk evaluation value calculation means (process)”, “determination means (process)”, “dot arrangement change process”. "Means (process)" and "storage means (process)" are included. The crosstalk optimized image (step S110) obtained by the dot arrangement optimization process corresponds to “second dot image data”, and printing is performed based on the optimized image data (step S112). The control means including the control circuit and the process thereof correspond to “droplet ejection control means (process)”.

  Each of these means (processes) includes a central processing unit (CPU) mounted on the device, electronic circuit hardware including a memory and other peripheral circuits, software such as a program that defines a procedure for arithmetic processing, and the like. Realized by a combination of

  Next, the dot arrangement optimization process will be described. FIG. 5 is a flowchart of the dot arrangement optimization process. FIG. 5 is a processing flow for the target pixel (specific pixel) in the image data, and the flow in FIG. 5 is repeated for all the pixels in the image.

  With respect to the image data obtained by the halftone process (step S104 in FIG. 4) (the “halftoned CT non-optimized image” shown in step S106 in FIG. 4), a target pixel (specific pixel to be processed) is predetermined. The crosstalk characteristic value of each pixel (corresponding to “crosstalk evaluation value”, sometimes referred to as “CT evaluation value”) is calculated while sequentially moving in accordance with the scanning direction and the processing order (step S202). For example, the pixels are sequentially processed (raster processing) one by one along the pixel arrangement order from left to right in the column direction and from top to bottom in the row direction.

  The “crosstalk characteristic value (CT evaluation value)” is an evaluation value that evaluates the degree of occurrence of crosstalk, and is defined, for example, by the number of nozzles that are discharged simultaneously in the same flow path. This value can be calculated from the quantized image data and the relationship between the nozzles corresponding to the ejection timing in the image data (that is, the relationship between the image data address, the nozzle and the ejection timing described with reference to FIG. 1). For example, as shown in FIG. 1, when the nozzle array period is constant, the number of simultaneous droplets can be easily calculated by shifting and adding the pixels in the array period.

  As the crosstalk characteristic value, in addition to the above-described simultaneous droplet ejection number (simultaneous ejection nozzle number), the following values can be employed. Examples of methods for calculating crosstalk characteristic values are summarized below.

[Example of how to calculate crosstalk characteristic values]
(Example 1) In view of the tendency that crosstalk occurs when there are a large number of dots hit at the same timing in the same flow path, the number of simultaneous discharges at the same flow path is evaluated as a crosstalk characteristic value.

  (Example 2) In view of the tendency that the closer the distance between the simultaneous discharge nozzles in the same flow path, the greater the influence on the crosstalk, the crosstalk characteristic value as a function of the distance between the simultaneous discharge nozzles in the same flow path. Define and evaluate. For example, the number of adjacent nozzles among the same channel simultaneous discharge nozzles is counted. Alternatively, the simultaneously ejecting nozzles in the same flow path are added as a decreasing function of the distance from the target nozzle.

  (Example 3) When the head characteristic is such that the ejection performance deteriorates when ejected at a specific frequency, the presence or absence of ejection at the specific frequency is reflected in the crosstalk characteristic value so as to avoid this. For example, it is determined whether or not the specific nozzle discharges continuously or at a specific pixel cycle.

  Furthermore, you may select two or more from said Examples 1-3. Moreover, you may make the evaluation value which weighted the some selected from said Examples 1-3. For example, a value obtained by linearly combining each value in Examples 1 to 3 with an appropriate weighting coefficient can be used as the evaluation value.

  The crosstalk characteristic value is calculated in this way (step S202), and the obtained crosstalk characteristic value is compared with a predetermined determination reference value to determine the possibility of occurrence of crosstalk (step S204). If it is determined in step S204 that the crosstalk characteristic value is greater than or equal to the determination reference value and the possibility of causing crosstalk is high, the same calculation is performed for neighboring pixels.

  Then, it progresses to step S206. In step S206, priorities are determined for a plurality of adjacent pixels (for example, eight pixels in contact with the periphery) located in the vicinity of the periphery of the target pixel (step S206). For example, the priority is set higher in the order in which the crosstalk reduction effect due to the replacement of the pixel value with the target pixel is predicted to be high based on the relative positional relationship between the target pixel and the adjacent pixel. This priority can be set in advance from the nozzle layout and the flow path structure. In the example of FIG. 1, among pixels in the vicinity of the target pixel, a pixel that is ejected by the same nozzle as the target pixel (a pixel having the same x coordinate as the target pixel, such as a pixel directly above or below the target pixel). Even if the pixels are exchanged, droplets are eventually ejected from the same nozzle, so the crosstalk reduction effect is low. On the other hand, if the pixel is replaced for a pixel that is ejected by a nozzle different from the pixel of interest (a pixel having an x coordinate different from the pixel of interest such as the right side or the left side of the pixel of interest), Therefore, the crosstalk reduction effect is high. From such a viewpoint, priority is set for neighboring pixels.

  In step S208, the data of the neighboring pixel and the target pixel is exchanged (change in dot arrangement) according to the above priority, and how the crosstalk characteristic value is changed by this exchange is calculated (step S208). ). That is, in step S208, the crosstalk evaluation value (crosstalk characteristic value) of each of the proximity pixel and the target pixel when the data of the proximity pixel and the target pixel is exchanged is calculated.

  The crosstalk evaluation value calculated here is compared with the crosstalk evaluation value before dot replacement to determine whether or not the value has been improved (step S210). When it is determined that the crosstalk evaluation value is improved by replacing the pixel data, the process proceeds to step S212, and processing is performed to replace the target pixel (x, y) and the data of the neighboring pixels having high priority.

  Note that the pixel to be replaced is preferably a pixel close to the target pixel. Further, it is desirable to make the following determination when determining whether or not replacement is possible.

[Criteria for replacement judgment]
(Criteria 1): It is desirable not to deteriorate the graininess by pixel replacement (pixel change). From this point of view, in order to maintain the dispersibility of the dots, an arithmetic means (dispersion evaluation means) for evaluating the dispersibility of the dots after the pixel change is provided, and the change is not performed when the evaluation result becomes worse ( Change the pixel).

  (Criteria 2): Even if the pixels ejected by the nozzles belonging to the same flow path are replaced, they are not ejected in the end, so the effect of reducing crosstalk is low. From this point of view, the pixels that are ejected by different nozzles, particularly the pixels that are ejected by nozzles belonging to different flow paths, are changed (replaced) with priority.

  (Criteria 3): When the image content to be drawn is a line drawing, the line is broken by the pixel replacement process, so the replacement process is not performed. That is, when the input image data is analyzed or the image content to be drawn is detected from the tag information attached to the image data and the line drawing is drawn, the dot arrangement optimization process is prohibited.

  Further, in step S204 of FIG. 5, when it is determined that the crosstalk evaluation value is lower than the predetermined determination reference value and crosstalk does not occur (or an acceptable level), or after replacement in step S210. If no improvement is observed in the crosstalk characteristic value, the original data is maintained without replacing the pixels.

  As described above, by performing the processing of the flowchart of FIG. 5 for each pixel, a dot arrangement in which crosstalk hardly occurs can be obtained.

  The calculation processing means for calculating the crosstalk evaluation value shown in step S202 of FIG. 5 and the process thereof correspond to “crosstalk evaluation value calculation means (process)”. The processing means for performing the determination shown in step S204 and its process correspond to “determination means (process)”.

  The processing means and the process for performing the signal processing and determination shown in steps S208 to S210 correspond to “replacement determination means (process)”.

  A further specific example will be described below.

FIG. 6A shows the relationship between the quantized image (“1” in the cell represents droplet ejection), each nozzle, and the ink flow path of these nozzles. In the figure, at the discharge timing T = T ₀ , the nozzle of the target pixel (reference numeral 50) and two adjacent nozzles in the same flow path (that is, three nozzles including the nozzle of the target pixel) are discharged simultaneously.

  As one of the crosstalk characteristic values at this time, when the number of adjacent nozzles that simultaneously discharge in the same ink flow path is set, the crosstalk characteristic value of the target pixel becomes “2”. FIG. 6B shows the crosstalk characteristic value of each pixel (here, the number of adjacent simultaneous ejection nozzles in the same ink flow path). The crosstalk characteristic value of the target pixel is “2”, and the pixel is likely to cause crosstalk because adjacent nozzles in the same flow path discharge simultaneously. Therefore, the dot arrangement is changed by dot arrangement optimization.

  Next, search for a pixel to replace the dot. Here, an adjacent pixel and a next adjacent pixel (range of surrounding 8 pixels in contact with the target pixel) are set as candidates for replacement, and an optimal arrangement is searched for in consideration of dot dispersibility. As an example of an index for evaluating the dispersibility of dots, the number of adjacent dots of each pixel is used as an evaluation function. The dispersibility evaluation value at that time is shown in FIG.

  From the evaluation result of the dispersibility shown in FIG. 7 and the calculation result of the crosstalk characteristic value shown in FIG. 6B, the lower left pixel of the target pixel has no dot of the adjacent pixel on the image (that is, even if it is replaced, it is granular) Are not easily deteriorated), and there is no simultaneous discharge by adjacent nozzles in the same flow path. From the results in the upper right diagram, the pixel on the lower left of the target pixel has no dot of the adjacent pixel (on the image) (it is difficult to deteriorate the granularity by switching), and there is no simultaneous ejection from the adjacent nozzle in the same flow path. Therefore, data is exchanged between the target pixel and the lower left pixel (see FIG. 8).

  By sequentially performing such processing for each pixel, it is possible to suppress deterioration in image quality due to crosstalk while avoiding deterioration in graininess.

<Configuration example of inkjet recording apparatus>
FIG. 9 is a configuration diagram of the ink jet recording apparatus 100 according to the embodiment of the present invention. In the inkjet recording apparatus 100, a recording medium 124 (sometimes referred to as “paper” for convenience) held on the impression cylinder (drawing drum 170) of the drawing unit 116 is provided with a plurality of colors from the inkjet heads 172M, 172K, 172C, 172Y. Is an impression cylinder direct drawing type ink jet recording apparatus that forms a desired color image by applying ink droplets of the ink. A treatment liquid (in this case, an aggregating treatment liquid) is applied onto the recording medium 124 before ink ejection. This is an on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method for forming an image on a recording medium 124 by reacting a treatment liquid and an ink liquid is applied.

  As shown in the figure, the ink jet recording apparatus 100 mainly includes a paper feeding unit 112, a treatment liquid application unit 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a paper discharge unit 122.

(Paper Feeder)
The paper feeding unit 112 is a mechanism that supplies the recording medium 124 to the processing liquid application unit 114, and the recording medium 124 that is a sheet is stacked on the paper feeding unit 112. The paper feed unit 112 is provided with a paper feed tray 150, and the recording medium 124 is fed from the paper feed tray 150 to the processing liquid application unit 114 one by one.

  In the inkjet recording apparatus 100 of this example, a plurality of types of recording media 124 having different paper types and sizes (paper sizes) can be used as the recording medium 124. A mode is also possible in which a plurality of paper trays (not shown) for separately collecting various recording media are provided in the paper feeding unit 112 and the paper to be sent to the paper feeding tray 150 is automatically switched from among the plurality of paper trays. In addition, a mode is also possible in which the operator selects or replaces the paper tray as necessary. In this example, a sheet (cut paper) is used as the recording medium 124, but a configuration in which continuous paper (roll paper) is cut to a required size and fed is also possible.

(Processing liquid application part)
The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  As shown in FIG. 9, the treatment liquid application unit 114 includes a paper feed drum 152, a treatment liquid drum 154, and a treatment liquid application device 156. The processing liquid drum 154 includes a claw-shaped holding means (gripper) 155 on the outer peripheral surface thereof, and the recording medium 124 is sandwiched between the claw of the holding means 155 and the peripheral surface of the processing liquid drum 154. The tip can be held. The treatment liquid drum 154 may be provided with a suction hole on the outer peripheral surface thereof and connected to a suction unit that performs suction from the suction hole. As a result, the recording medium 124 can be held in close contact with the peripheral surface of the treatment liquid drum 154.

  A processing liquid coating device 156 is provided outside the processing liquid drum 154 so as to face the peripheral surface thereof. The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller partially immersed in the processing liquid in the processing liquid container, and the recording medium 124 on the anix roller and the processing liquid drum 154. And a rubber roller that transfers the measured processing liquid to the recording medium 124. According to the processing liquid coating apparatus 156, the processing liquid can be applied to the recording medium 124 while being measured.

  In the present embodiment, the configuration in which the application method using the roller is exemplified, but the present invention is not limited to this. For example, various methods such as a spray method and an ink jet method can be applied.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

(Drawing part)
The drawing unit 116 includes a drawing drum 170, a paper holding roller 174, and ink jet heads 172M, 172K, 172C, and 172Y. Similar to the treatment liquid drum 154, the drawing drum 170 includes a claw-shaped holding means (gripper) 171 on the outer peripheral surface thereof. The recording medium 124 fixed to the drawing drum 170 is conveyed with the recording surface facing outward, and ink is applied to the recording surface from the inkjet heads 172M, 172K, 172C, 172Y.

  The inkjet heads 172M, 172K, 172C, and 172Y are full-line inkjet recording heads (inkjet heads) each having a length corresponding to the maximum width of the image forming area on the recording medium 124. Is formed with a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  The droplets of the corresponding color ink are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held in close contact with the drawing drum 170, whereby the processing liquid application unit 114 performs the processing. The ink comes into contact with the treatment liquid previously applied to the recording surface, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. Thereby, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

  As described above, according to the configuration in which the full line head having the nozzle row covering the entire width of the image forming area of the recording medium 124 is provided for each ink color, the recording medium 124 is conveyed at a constant speed by the drawing drum 170. In this transport direction (sub-scanning direction), the recording medium 124 and each of the inkjet heads 172M, 172K, 172C, and 172Y are moved only once (that is, in one sub-scanning operation). Images can be recorded in 124 image forming areas. Single-pass image formation with such a full-line (page wide) head is a multi-pass with a serial (shuttle) type head that reciprocates in the direction (main scanning direction) orthogonal to the recording medium conveyance direction (sub-scanning direction). High-speed printing is possible as compared with the case where the method is applied, and print productivity can be improved.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special colors are used as necessary. Ink may be added. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  Further, the application range of the present invention is not limited to a printing method using a line type head, and a short head that is less than the length in the width direction (main scanning direction) of the recording medium 124 is scanned in the width direction of the recording medium 124. Printing in the width direction is performed, and when printing in one width direction is completed, the recording medium 124 is moved by a predetermined amount in the direction perpendicular to the width direction of the recording medium 124 (sub-scanning direction). A serial method in which printing is performed in the width direction and printing is performed over the entire printing area of the recording medium 124 by repeating this operation may be applied.

(Drying part)
The drying unit 118 is a mechanism for drying water contained in the solvent separated by the color material aggregating action, and includes a drying drum 176 and a solvent drying device 178, as shown in FIG.

  Similar to the processing liquid drum 154, the drying drum 176 includes a claw-shaped holding unit (gripper) 177 on the outer peripheral surface thereof, and the holding unit 177 can hold the leading end of the recording medium 124.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176, and includes a plurality of halogen heaters 180 and hot air ejection nozzles 182 disposed between the halogen heaters 180.

  Various drying conditions can be realized by appropriately adjusting the temperature and air volume of the hot air blown toward the recording medium 124 from each hot air ejection nozzle 182 and the temperature of each halogen heater 180.

  The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

(Fixing part)
The fixing unit 120 includes a fixing drum 184, a halogen heater 186, a fixing roller 188, and an inline sensor 190. Like the processing liquid drum 154, the fixing drum 184 includes a claw-shaped holding unit (gripper) 185 on the outer peripheral surface, and the leading end of the recording medium 124 can be held by the holding unit 185.

  With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  The fixing roller 188 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 124. The Specifically, the fixing roller 188 is disposed so as to be in pressure contact with the fixing drum 184 and constitutes a nip roller with the fixing drum 184. As a result, the recording medium 124 is sandwiched between the fixing roller 188 and the fixing drum 184 and nipped at a predetermined nip pressure (for example, 0.15 MPa), and the fixing process is performed.

  In addition, instead of the ink containing the high boiling point solvent and the polymer fine particles (thermoplastic resin particles), a monomer component that can be polymerized and cured by ultraviolet (UV) exposure may be contained. In this case, the inkjet recording apparatus 100 includes a UV exposure unit that exposes the ink on the recording medium 124 to UV light instead of the heat-pressure fixing unit (fixing roller 188) using a heat roller.

  The in-line sensor 190 is a measuring unit for measuring a check pattern, a moisture content, a surface temperature, a glossiness, and the like for an image fixed on the recording medium 124, and a CCD line sensor or the like is applied.

(Output section)
As shown in FIG. 9, a paper discharge unit 122 is provided following the fixing unit 120. The paper discharge unit 122 includes a discharge tray 192. Between the discharge tray 192 and the fixing drum 184 of the fixing unit 120, a transfer drum 194, a conveyance belt 196, and a stretching roller 198 are in contact with each other. Is provided. The recording medium 124 is sent to the conveyor belt 196 by the transfer drum 194 and discharged to the discharge tray 192.

  Although not shown in the drawing, the ink jet recording apparatus 100 of the present example has an ink storage / loading unit for supplying ink to each of the ink jet heads 172M, 172K, 172C, and 172Y in addition to the above-described configuration, and application of processing liquid. A means for supplying a processing liquid to the unit 114, and a head maintenance unit for cleaning each ink jet head 172M, 172K, 172C, 172Y (wiping, purging, nozzle suction, etc. of the nozzle surface), A position detection sensor for detecting the position of the recording medium 124, a temperature sensor for detecting the temperature of each part of the apparatus, and the like are provided.

  <Inkjet Head Structure> Next, the structure of the inkjet head will be described. Since the inkjet heads 172M, 172K, 172C, and 172Y corresponding to the respective colors have the same structure, the heads are represented by the reference numeral 250 in the following.

  FIG. 10A is a plan perspective view showing an example of the structure of the head 250, and FIG. 10B is an enlarged view of a part thereof. 11 is a perspective plan view showing another structural example of the head 250, and FIG. 12 is a three-dimensional configuration of one-channel droplet discharge elements (ink chamber units corresponding to one nozzle 251) serving as recording element units. It is sectional drawing (sectional drawing in alignment with the AA in FIG. 10) which shows this.

  As shown in FIG. 10, the head 250 of this example has a matrix of a plurality of ink chamber units (droplet discharge elements) 253 including nozzles 251 serving as ink discharge ports and pressure chambers 252 corresponding to the nozzles 251. The nozzle spacing (projection nozzle pitch) is projected (orthogonally projected) so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density is achieved.

  Nozzle rows having a length corresponding to the entire width Wm of the drawing area of the recording medium 124 are configured in a direction (arrow M direction; main scanning direction) substantially orthogonal to the feeding direction (arrow S direction; sub-scanning direction) of the recording medium 124. The form to do is not limited to this example. For example, instead of the configuration of FIG. 10A, as shown in FIG. 11A, short head modules 250 ′ in which a plurality of nozzles 251 are two-dimensionally arranged are arranged in a staggered manner and joined together. Thus, there are a mode in which a line head having a nozzle row having a length corresponding to the entire width of the recording medium 124 is configured, and a mode in which the head modules 250 ″ are arranged in a row and connected as shown in FIG.

  The pressure chamber 252 provided corresponding to each nozzle 251 has a substantially square planar shape (see FIGS. 10A and 10B), and the nozzle 251 is located at one of the diagonal corners. An outlet for supplying ink (supply port) 254 is provided on the other side. Note that the shape of the pressure chamber 252 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse. As shown in FIG. 12, the head 250 is formed with a flow path such as a nozzle plate 251A in which the nozzles 251 are formed, a pressure chamber 252 and a common flow path 255 (corresponding to the ink flow paths 11 to 15 described in FIG. 1). The flow path plate 252P and the like are laminated and joined. The nozzle plate 251A constitutes a nozzle surface (ink ejection surface) 250A of the head 250, and a plurality of nozzles 251 communicating with the pressure chambers 252 are two-dimensionally formed.

  The flow path plate 252P forms a side wall of the pressure chamber 252 and a flow path that forms a supply port 254 as a narrowed portion (most narrowed portion) of an individual supply path that guides ink from the common flow path 255 to the pressure chamber 252. It is a forming member. For convenience of explanation, the flow path plate 252P has a structure in which one or a plurality of substrates are stacked, although it is illustrated schematically in FIG.

  The nozzle plate 251A and the flow path plate 252P can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common flow channel 255 communicates with an ink tank (not shown) as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 252 via the common flow channel 255.

  A piezoelectric actuator 258 having an individual electrode 257 is joined to a diaphragm 256 that constitutes a part of the pressure chamber 252 (the top surface in FIG. 10). The diaphragm 256 of this example is made of silicon (Si) with a nickel (Ni) conductive layer functioning as a common electrode 259 corresponding to the lower electrode of the piezoelectric actuator 258, and is arranged corresponding to each pressure chamber 252. It also serves as a common electrode for the actuator 258. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (conductive material), such as stainless steel (SUS).

  By applying a driving voltage to the individual electrode 257, the piezo actuator 258 is deformed and the volume of the pressure chamber 252 is changed, and ink is ejected from the nozzle 251 due to the pressure change accompanying this. When the piezo actuator 258 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 252 from the common channel 255 through the supply port 254.

  As shown in FIG. 10B, the ink chamber units 253 having such a structure are arranged in a fixed manner along the row direction along the main scanning direction and the oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. By arranging a large number of patterns in a lattice pattern, the high-density nozzle head of this example is realized. In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 251 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  In the implementation of the present invention, the arrangement form of the nozzles 251 in the head 250 is not limited to the illustrated example, and various nozzle arrangement structures can be applied. For example, instead of the matrix array described in FIG. 10, a linear array of lines, a V-shaped nozzle array, and a zigzag (W-shaped) nozzle array having a V-shaped array as a repeating unit. Etc. are also possible.

  The means for generating the discharge pressure (discharge energy) for discharging the droplets from each nozzle in the inkjet head is not limited to the piezo actuator (piezoelectric element), but the thermal method (the pressure of film boiling due to the heating of the heater) Various pressure generating elements (energy generating elements) such as heaters (heating elements) and other actuators based on other systems can be applied. Corresponding energy generating elements are provided in the flow path structure according to the ejection method of the head.

<Description of control system>
FIG. 13 is a principal block diagram showing the system configuration of the inkjet recording apparatus 100. The inkjet recording apparatus 100 includes a communication interface 270, a system controller 272, a memory 274, a motor driver 276, a heater driver 278, a print control unit 280, an image buffer memory 282, a head driver 284, and the like.

  The communication interface 270 is an interface unit that receives image data sent from the host computer 286. As the communication interface 270, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. The image data sent from the host computer 286 is taken into the inkjet recording apparatus 100 via the communication interface 270 and temporarily stored in the memory 274.

  The memory 274 is a storage unit that temporarily stores an image input via the communication interface 270, and data is read and written through the system controller 272. The memory 274 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 272 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 100 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 272 controls the communication interface 270, the memory 274, the motor driver 276, the heater driver 278, and the like, performs communication control with the host computer 286, read / write control of the memory 274, and the like. Control signals for controlling the motor 288 and the heater 289 are generated.

  The ROM 290 stores various control programs, various parameters, and the like, and the control program is read and executed in accordance with a command from the system controller 272.

  The memory 274 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 276 is a driver that drives the motor 288 in accordance with an instruction from the system controller 272. In FIG. 13, various motors arranged in each unit in the apparatus are represented by reference numeral 288.

  The heater driver 278 is a driver that drives the heater 289 in accordance with an instruction from the system controller 272. In FIG. 13, various heaters arranged in each part in the apparatus are represented by reference numeral 289.

  The print control unit 280 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the memory 274 according to the control of the system controller 272, and the generated print data This is a control unit that supplies (dot image data) to the head driver 284.

  The dot image data is generally generated by performing color conversion processing and halftone processing on multi-gradation image data. In the color conversion process, image data expressed in sRGB or the like (for example, 8-bit image data for each RGB color) is converted into color data for each color of ink used in the inkjet recording apparatus 100 (in this example, KCMY color data). It is a process to convert.

  The halftone process is a process of converting the color data of each color generated by the color conversion process into dot data of each color (KCMY dot data in this example) by processes such as an error diffusion method and a threshold matrix.

  The required signal processing is performed in the print control unit 280, and the ejection amount and ejection timing of the ink droplets of the head 250 are controlled via the head driver 284 based on the obtained dot data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 280 includes an image buffer memory 282, and image data, parameters, and other data are temporarily stored in the image buffer memory 282 when image data is processed in the print control unit 280. Also possible is an aspect in which the print control unit 280 and the system controller 272 are integrated to form a single processor.

  The head driver 284 may include a feedback control system for keeping the driving conditions of the head 250 constant.

  The inkjet recording apparatus 100 shown in this example applies a common drive power waveform signal to each piezo actuator 258 of the head 250 and connects to the individual electrodes of each piezo actuator 258 according to the ejection timing of each piezo actuator 258. A driving method is employed in which ink is ejected from the nozzles 251 corresponding to the piezoelectric actuators 258 by switching on and off of the switch elements (not shown).

  In the case of this embodiment, the print control unit 280 shown in FIG. 13 corresponds to “droplet ejection control unit”. Further, the print controller 280 or a combination of this and the system controller 272 corresponds to means for performing the halftone process and the dot arrangement optimization process described with reference to FIGS. The ROM 290 or the memory 274 illustrated in FIG. 13 corresponds to a “storage unit” that stores the nozzle arrangement information of the head and the flow path connection information.

<About other nozzle layout examples>
FIG. 14 is a view of a head module according to another configuration example as viewed from the nozzle surface side. In FIG. 14, the y direction is the recording medium feed direction (sub-scanning direction), and the x direction is the recording medium width direction (main scanning direction). This head module 300 has an end face on the long side along the v direction having an inclination of angle γ with respect to the x direction and an end face on the short side along the w direction having an inclination of angle α with respect to the y direction. The plane shape of a parallelogram having A full line type line head can be configured by connecting a plurality of head modules 300 shown in FIG. 14 in the x direction. In FIG. 14, reference numeral 380 represents a nozzle.

  FIG. 15 is a perspective plan view showing a flow path structure inside the head module. As shown in FIG. 15, a supply-side ink flow path 310 and a recovery-side ink flow path 320 are provided for each nozzle line along the w direction in the drawing with the nozzle lines interposed therebetween. The supply-side ink flow path 310 provided along the w direction is a branch flow path branched from the supply-side common flow path main flow 330, and the supply-side common flow path main flow 330 is connected via a supply connection port (not shown). It is connected to an ink tank (not shown). The recovery-side ink flow path 320 is a branch flow path branched from the recovery-side common flow path main stream 340, and the recovery-side common flow path main flow 340 is connected to a recovery tank (not shown) through a connection port (not shown). The

  FIG. 16 is an enlarged view showing the flow path structure inside the head module, and FIG. 17 is a cross-sectional view taken along the line BB in FIG. In these drawings, reference numeral 400 denotes a pressure chamber, 402 denotes an individual supply passage that connects the supply-side ink flow path 310 and each pressure chamber 400, 404 denotes a nozzle flow path that connects the pressure chamber 400 to the nozzle 380, and 406 denotes a nozzle flow path. This is an individual recovery path that connects 404 and the recovery-side ink flow path 320. In FIG. 17, reference numeral 420 is a nozzle plate, 430 is a flow path substrate, 440 is a diaphragm, and 450 is a piezoelectric actuator (piezoelectric element). Reference numeral 460 denotes a cover plate that seals the periphery of the piezo actuator 450 while securing the movable space 454 of the piezo actuator 450.

  Although not shown in the drawing, a supply-side ink chamber and a recovery-side ink chamber are formed above the cover plate 460, and the supply-side common flow path main flow in the flow path substrate 470 is connected to each other via a communication path (not shown). 330, connected to the recovery-side common flow path main stream 340.

  The ink supplied from the supply side ink flow path 310 to the pressure chamber 400 via the individual supply path 402 is discharged from the nozzle 380 through the nozzle flow path 404. In addition, surplus ink that is not used for ejection is recovered from the nozzle flow path 404 to the recovery-side ink flow path 320 via the individual recovery path 406.

  FIG. 18 is a schematic plan view of the nozzle layout 500 in the head module 300. In FIG. 18, for convenience of illustration, the angle α formed by the nozzle rows along the sub-scanning direction (y direction) and the w direction is drawn larger than the angle α shown in FIG.

  In FIG. 18, each nozzle 380 is assigned a nozzle number (“1” to “162”) corresponding to the position in the x direction. The nozzle layout 500 is composed of four nozzle group regions, a first band 501, a second band 502, a third band 503, and a fourth band 504. The nozzle row in which the nozzles are arranged along the w direction has 32 nozzles arranged in each. In addition, the x-direction intervals (S1, S2, S3, S4) between the respective nozzle rows in the w direction are equal and constant values.

  As shown in the drawing, 32 nozzles 380 arranged in the w direction are divided into the respective bands (501 to 504). Therefore, the nozzle array in the w direction in each band is configured by 8 nozzles arranged side by side. The The nozzles 380 shown here are arranged in four different band patterns. That is, from the left to the right in the figure, "1-4-2-3", "1-3-4-2", "1-3-2-4", "1-2-4- 4 "band patterns.

  In the band pattern “1-4-2-3” shown on the left in the drawing, the nozzle number of the leftmost nozzle 380 in the x direction is “1”, and this nozzle number “1” is assigned to the first band 501. Belongs. From this point, the nozzles 380 that sequentially form dots adjacent in the + x direction are in the order of nozzle numbers “2”, “3”, and “4”, which are the fourth band 504, the second band 502, and the third band, respectively. 503. In this way, the order of the bands to which the nozzle numbers continuously arranged in the x direction belong is periodically repeated in the order of the first band 501 → the fourth band 504 → the second band 502 → the third band 503. Is called “1-4-2-3” band pattern.

  The nozzle next to the nozzle number “4” in the x direction is the nozzle number “5”, which belongs to the first band 501. Similarly, the band pattern “1-4-2-3” is repeated until the nozzle number “32” is reached.

  Subsequently, the nozzle layout shifts to the “1-3-4-2” band pattern. The nozzle number “33” belongs to the second band 502, and strictly speaking, it does not correspond to any of the patterns “1-4-2-3” and “1-3-4-2”. The arrangement of nozzles starting with “34” is a “1-3-4-2” band pattern. The “1-3-4-2” band pattern is repeated up to the nozzle number “64”.

  Subsequently, the nozzle layout shifts to the “1-3-2-4” band pattern. Strictly speaking, the nozzle numbers “65”, “66”, and “67” do not correspond to any of the patterns “1-3-4-2” and “1-3-2-4”. The array of nozzles starting with the number “68” is a band pattern “1-3-2-4”.

  After the nozzle number “95”, the pattern shifts to the “1-2-4-3” band pattern. Strictly speaking, the nozzle numbers “96”, “97”, and “98” do not correspond to any of the patterns “1-3-2-4” and “1-2-4-3”. The nozzle array starting with "" is a band pattern of "1-2-4-3".

  After the nozzle number “126”, the process proceeds to the “1-4-2-3” band pattern. Strictly speaking, nozzle numbers “127” and “128” do not correspond to any of the patterns “1-2-4-3” and “1-4-2-3”, but nozzles starting from nozzle number “129” The line pattern is a band pattern of “1-4-2-3”.

  As described above, a large number of nozzles are two-dimensionally arranged while repeating four types of band patterns in the x direction.

  Also for such a nozzle layout 500, the number of simultaneous discharges in the same flow path can be grasped from the relationship between each nozzle 380 and the flow path structure described with reference to FIGS. 15 and 16, and the present invention can be applied. It is.

<Application examples to other devices>
In the above embodiment, the application to an inkjet recording apparatus for printing has been described as an example of an image forming apparatus, but the scope of application of the present invention is not limited to this example. For example, a wiring drawing apparatus for drawing a wiring pattern of an electronic circuit, a manufacturing apparatus for various devices, a resist printing apparatus that uses a resin liquid as a functional liquid for ejection, a color filter manufacturing apparatus, and a material deposition material. The present invention can be widely applied to inkjet systems that obtain various shapes and patterns using a liquid functional material, such as a fine structure forming apparatus for forming a structure.

  DESCRIPTION OF SYMBOLS 10 ... Supply side common flow path, 11, 12, 13, 14, 15 ... Ink flow path, 31, 32, 33, 34 ... Nozzle, 40 ... Pixel of interest, 100 ... Inkjet recording device, 124 ... Recording medium, 172M, 172K, 172C, 172Y ... inkjet head, 251 ... nozzle, 272 ... system controller, 274 ... memory, 290 ... ROM, 280 ... print controller, 300 ... head module, 310 ... supply side ink flow path, 320 ... collection side ink Flow path, 380 ... Nozzle, 400 ... Pressure chamber, 402 ... Individual supply path, 406 ... Individual recovery path, 500 ... Nozzle layout

Claims (11)

A plurality of nozzles two-dimensionally arranged, and a recording head having a plurality of flow paths communicating with the plurality of nozzles;
Storage means for storing nozzle arrangement information of the recording head and storing flow path connection information indicating a connection relationship between the plurality of flow paths and the nozzles;
First dot image data acquisition means for acquiring first dot image data defining a dot arrangement of image content to be drawn;
From the first dot image data and the nozzle arrangement information, the nozzle position of the recording head responsible for recording each pixel of the first dot image data and the ejection timing thereof are specified, and the specified information and the flow path connection information Crosstalk evaluation value calculation means for calculating a crosstalk evaluation value for evaluating the magnitude of the influence of crosstalk due to the interaction between nozzles connected to the same flow path for a specific pixel in the image, ,
A determination unit that compares the crosstalk evaluation value calculated for the specific pixel with a predetermined determination reference value, and determines whether or not the first dot image data needs to be corrected based on the comparison result;
When the determination unit determines that the correction of the first dot image data is necessary, the data of the specific pixel and the data of the neighboring pixel of the specific pixel are replaced, and the specific pixel and the neighboring pixel after the replacement Dot arrangement change processing means for generating second dot image data for obtaining the crosstalk evaluation value falling within the crosstalk tolerance range indicated by the determination reference value for
Droplet ejection control means for controlling droplet ejection from each nozzle of the recording head based on the second dot image data;
An image forming apparatus comprising: In claim 1,
The image forming apparatus according to claim 1, wherein the crosstalk evaluation value calculated by the crosstalk evaluation value calculating means is determined from the number of nozzles ejected simultaneously from a group of nozzles connected to the same flow path. In claim 1 or 2,
The crosstalk evaluation value is determined from a distance between nozzles ejected simultaneously among a group of nozzles connected to the same flow path. In any one of Claims 1 thru | or 3,
The crosstalk evaluation value calculation means evaluates the presence / absence of ejection at a specific frequency in the same flow path with reference to the presence / absence of droplet ejection at each ejection timing of the nozzle group connected to the same flow path, and the evaluation result An image forming apparatus characterized by performing an operation for reflecting the value in the crosstalk evaluation value. In any one of Claims 1 thru | or 4,
Recalculating the crosstalk evaluation value for the specific pixel and the neighboring pixel when the data of the specific pixel and the data of the neighboring pixel of the specific pixel are exchanged, and based on the recalculated crosstalk evaluation value An image forming apparatus comprising a replacement determination unit that evaluates a crosstalk reduction effect by the replacement and determines whether or not the replacement is adopted. In claim 5,
Dispersibility evaluation means for evaluating the dispersibility of dots when the data of the specific pixel and the data of neighboring pixels of the specific pixel are replaced,
The image forming apparatus according to claim 1, wherein the replacement determination unit determines whether or not the replacement is accepted based on an evaluation result by the dispersibility evaluation unit. In any one of Claims 1 thru | or 6,
The image forming apparatus according to claim 1, wherein the neighboring pixel to be replaced with the specific pixel corresponds to a nozzle different from a nozzle responsible for recording the specific pixel. In any one of Claims 1 thru | or 7,
When the image content to be drawn is a line drawing, the replacement processing by the dot arrangement change processing unit is not performed. In any one of Claims 1 thru | or 8,
The first dot image data acquisition unit is a halftone processing unit that obtains the first dot image data by performing a halftone process on a multi-tone input image. In any one of Claims 1 thru | or 9,
The first pixel corresponding to the specific pixel in the first dot image data and the other second nozzle belonging to the same flow path as the first nozzle responsible for recording the first pixel at the same timing as the first pixel. Calculating the crosstalk evaluation value of the first pixel based on the data of the second pixel discharged
A third pixel recorded by a third nozzle connected to a flow path different from the first nozzle and the second nozzle corresponding to the first pixel and the second pixel, and recording of the third pixel Calculating the crosstalk evaluation value of the third pixel based on the data of the fourth pixel recorded by another fourth nozzle belonging to the same flow path as the third nozzle responsible for
Based on the crosstalk evaluation value of the first pixel and the crosstalk evaluation value of the third pixel, the crosstalk evaluation value of both the pixels is averaged between the first pixel and the third pixel. An image forming apparatus that performs a process of exchanging data in step (b). A plurality of nozzles are two-dimensionally arranged, and nozzle arrangement information of a recording head having a plurality of flow paths communicating with the plurality of nozzles is stored in a storage unit, and a flow indicating a connection relationship between the plurality of flow paths and the nozzles A storage step of storing road connection information in the storage means;
A first dot image data acquisition step of acquiring first dot image data defining a dot arrangement of image contents to be drawn;
From the first dot image data and the nozzle arrangement information, the nozzle position of the recording head responsible for recording each pixel of the first dot image data and the ejection timing thereof are specified, and the specified information and the flow path connection information A crosstalk evaluation value calculation step for calculating a crosstalk evaluation value for evaluating the magnitude of the influence of crosstalk due to the interaction between nozzles connected to the same flow path for a specific pixel in the image, ,
A determination step of comparing the crosstalk evaluation value calculated for the specific pixel with a predetermined determination reference value, and determining whether or not the first dot image data needs to be corrected based on the comparison result;
When the determination step determines that the correction of the first dot image data is necessary, the data of the specific pixel and the data of the neighboring pixel of the specific pixel are replaced, and the specific pixel and the neighboring pixel after the replacement A dot arrangement change processing step for generating second dot image data for obtaining the crosstalk evaluation value that falls within an allowable range of crosstalk indicated by the determination reference value for each of
A droplet ejection control step of controlling droplet ejection from each nozzle of the recording head based on the second dot image data;
An image forming method comprising:

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