JP2011201051A - Fine pattern position detection method and apparatus, defective nozzle detection method and apparatus, and liquid delivering method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of specifying a position of a line pattern with a higher accuracy than the resolution for reading an image (accuracy of a less than 1-pixel unit of a reading image pitch).SOLUTION: A test pattern (line pattern) on a recording medium is read (S80), and a corresponding position of the test pattern is acquired by a pixel unit of reading pixel pitch (S82). In addition, from read image data, a primary differentiated value of gradation value at the corresponding position of the test pattern and at an adjoining read pixel position is calculated (S84), and a test pattern arrangement possibility (adaptability) of the test pattern to a candidate position of the less than 1-pixel unit of the read pixel pitch is derived from the primary differentiated value (S86). From the adaptability related to the candidate position, a corresponding position of the less than 1-pixel unit of the test pattern is obtained (S88), and from the corresponding position of the pixel unit and the corresponding position of the less than 1-pixel unit of the read pixel pitch acquired from the results of S82 and S88, a recording position of the test pattern is calculated (S90).

Description

  The present invention relates to a fine pattern position detection method and apparatus, a defective nozzle detection method and apparatus, and a liquid ejection method and apparatus, and more particularly to a technique for specifying the position of a line pattern on a recording medium with an accuracy less than a reading pixel pitch.

  As a method for recording an image on a recording medium, there is an ink jet drawing method in which ink droplets ejected according to an image signal are landed on the recording medium. As an image drawing apparatus using this ink jet drawing method, an ejection unit (a plurality of nozzles) that ejects ink droplets is arranged in a line so as to correspond to the entire area of one side of the recording medium, and the recording medium is ejected. There is a full line head type image drawing apparatus that records an image on the entire area of a recording medium by conveying in a direction orthogonal to the recording medium. Full line head type image drawing device can draw an image over the entire area of the recording medium by transporting the recording medium without moving the ejection part, and is suitable for increasing the recording speed. ing.

  Since such a full-line type recording head has a length equal to or larger than the recording paper width, for example, when the recording resolution is 1200 DPI and the recording paper width is 27 inches, the recording head has 32400 nozzles for each type of ink. Elements are provided, and when there are four types of ink, a total of 129600 recording elements are provided.

  However, when a full line head type image drawing apparatus is used, the actual dot position recorded on the recording medium deviates from the ideal dot position due to manufacturing variations of the recording elements (nozzles) in the ejection section. May result in a recording position error. As a result, so-called streaks and unevenness occur in the image recorded on the recording medium, which may cause a reduction in image quality.

  That is, an ideal recording head records dots on recording paper at regular intervals by regularly arranged recording elements. However, in an actual recording head, the actual dot landing position has a positional error (landing position error) with respect to the ideal recording position due to manufacturing variations of recording elements, changes over time, or problems during maintenance. To have.

  Therefore, for example, if a recording element having a position error that is half or more than the interval between recording elements is driven, the effect on the image quality is increased. Therefore, it is advantageous to avoid using such a recording element in terms of image quality. is there.

  A technique for correcting an image based on a dot landing position is known as a technique for reducing image degradation by correcting streaks and unevenness. As a technique for measuring the dot landing position error, each nozzle is operated at a predetermined interval to form a test pattern (line pattern), and a test pattern image is read using an image reading device. There is a technique for detecting a position error by an algorithm. The test pattern here is a plurality of dot lines formed on the recording medium by the droplets ejected from the nozzles, and recording in which the ejection state (recording position error, density error, etc.) from the corresponding nozzles is reflected. It is a recording dot on the medium.

  When the recording head has a dot landing position error close to the adjacent dot interval (recording element interval) (for example, in a 1200 DPI recording head, the ideal dot interval is 20.8 μm, so 10.4 (= 20.20). 8/2) When the recording head has a dot landing position error of μm or more), the image quality is deteriorated. A recording element (nozzle) having a positional error close to such a recording element interval is temporarily called a defective ejection nozzle (defective recording element).

  There are various timings when the actual nozzle becomes such a defective ejection nozzle, a recording element with a large landing position error from the time of manufacturing the recording head, a recording element with a large landing position error that changes over time over a long period of time, A recording element that is normal at the start of printing, but the landing position error changes greatly from the middle of printing (some recording elements return to the normal range after maintenance), or a recording element that has a large landing position error due to poor maintenance (another maintenance) (Some recording elements return to the normal range later.) Are examples of defective ejection nozzles.

  In order to prevent degradation of image quality, it is necessary to stop ink ejection from such a defective recording element or to correct ink ejection control. As a method for detecting and correcting defective ejection nozzles in a timely manner, there is a method in which a test pattern is drawn on printing paper and an image of the test pattern is read during printing operation to detect the defective ejection nozzles and perform image correction.

(Advantage of test pattern composition)
When a recording sheet is used exclusively for the test pattern, a mechanism for separating the test pattern and the non-test pattern is required, or an extra recording sheet for the test pattern is consumed. In addition, if the time from the occurrence of a defective ejection nozzle to the detection is delayed, the printing result during this time includes a problem in image quality. In order to reduce this delay, it is necessary to increase the output frequency of the test pattern. In such a case, test pattern recording paper is further consumed, which is uneconomical. However, when a test pattern is created in the margin portion of the recording paper edge and detection correction is performed, waste of recording paper consumption can be suppressed and position errors can be constantly monitored. The problem basically doesn't happen.

(Test pattern design problem)
In order to detect a position error for each recording element, each recording element is independently operated at a predetermined interval, and continuous dots (lines, line patterns) formed by these recording elements are read by an image reading apparatus, and predetermined detection is performed. Calculation based on the algorithm is performed to calculate the position error.

  In order to improve the position error detection accuracy, it is desirable to increase the interval between line patterns forming the test pattern and lengthen continuous dots (line patterns). However, in such a case, the test pattern area increases, so it is necessary to secure a large margin for recording the test pattern, which causes another disadvantage such as a narrow print area usable by the user. There is. When the test pattern is formed in the margin part in this way, there is a demand to reduce the area used for the test pattern as much as possible, so the line pattern interval of the test pattern is narrowed to shorten the continuous dot (line pattern). It is desirable to do.

(Problem with image reading device)
An image reading apparatus that reads a test pattern is advantageous in terms of cost if it has a low-resolution configuration as much as possible. In a high-resolution reading apparatus, the overall cost increases with an increase in lens cost, illumination light amount, reading transfer clock, image data amount, and algorithm processing amount.

  There is a conflict between the requirement to use such a low-resolution image reading apparatus and the requirement to narrow the continuous dot (line pattern) of the test pattern described above.

(algorithm)
Therefore, in order to reduce the cost of the image reading apparatus while narrowing the test pattern, an algorithm for calculating the position error with high accuracy from the low resolution read image is required.

  Patent Document 1 discloses a method for calculating the center position of a ruled line figure read in the multi-value mode. In particular, FIG. 6 of Patent Document 1 describes the relationship between sampling points and ruled line density distribution. ing. However, since many reading apparatuses have an aperture size, an integrated value with an aperture size centered on a sampling point is obtained as an image reading result. Under reading conditions in which the interval between the reading object and the reading pixel pitch is close, the original density distribution cannot be estimated simply by connecting sampling points due to the influence of the aperture effect (the sampling phase and aperture size are related). Therefore, it is difficult for the technique of Patent Document 1 to accurately obtain the center position under reading conditions in which the interval between the reading target and the reading pixel pitch is close.

  Further, according to the technique described in Patent Document 2, the position of the raster that forms the gradation center of gravity is obtained from a plurality of rasters centered on the raster having the highest average gradation value (paragraph 0092 in Patent Document 2). reference). However, it is difficult to obtain the raster center position with respect to the gradation center of gravity under reading conditions in which the interval between the reading object and the reading pixel pitch is close.

  FIG. 34 shows a profile when the distance between the reading target and the reading pixel pitch is long (when the reading pixel pitch is fine) (2400 DPI). FIG. 35 shows a profile when the interval between the reading target and the reading pixel pitch is close (500 DPI). FIG. 36 shows profiles when the distance between the reading object and the reading pixel pitch is close (500 DPI) and when the distance between the reading object and the reading pixel pitch is far (when the reading pixel pitch is fine) (2400 DPI). 34 to 36, the horizontal axis represents the reading position (X coordinate (μm)), and the vertical axis represents the optical density (OD value).

  As shown in FIG. 34 to FIG. 36, regarding the reading results for the same profile, in the case of 2400 DPI, a state close to the original profile is shown, whereas in the case of 500 DPI (including the case of the sampling phase difference). It can be seen that a state far away from the original profile is shown. It can be seen that the expected value for the position is the same even if the sampling phase is changed, but it is difficult to accurately obtain the accurate position from the gradation center of gravity.

JP 2000-135818 A JP 2008-182352 A

  As described above, there is no high-reliability technology that can accurately calculate the nozzle ejection error from the scanned image of the fine test pattern. Especially, the droplet landing position error is highly accurate from the low-resolution scanned image. What is desired is a method and apparatus that can be calculated to:

  The present invention has been made in view of such circumstances, and has a relationship such that the resolution (read pixel pitch) of the image reading apparatus does not satisfy the sampling theorem with respect to the dot size (line width) to be detected. However, it is an object of the present invention to present a technique capable of detecting a change in dot landing position with a certain accuracy. For example, the resolution of the recording element is 1200 DPI (interval between recording elements is about 21 μm), the dot diameter is 40 to 50 μm, and the resolution in the main scanning direction of the reading device is 500 DPI (interval of reading pixels is about 50 μm). In addition, it is an object of the present invention to present a technique capable of accurately detecting changes in dot landing positions.

  According to one aspect of the present invention, a reading step of reading a recording medium on which a line pattern is formed at a predetermined reading pixel pitch in a predetermined reading direction to acquire read data, and correspondence between the line pattern based on the reading pixel pitch A read pixel position obtaining step for obtaining a position from the read data, a feature value at the corresponding position of the line pattern, and a feature value at an adjacent pixel position adjacent to the corresponding position based on the read pixel pitch, A plurality of feature value acquisition steps acquired from the read data, and a matching function prepared in advance for each of the corresponding position and the adjacent pixel position of the line pattern, and having a pitch shorter than the read pixel pitch And the feature value that is prepared for each of the candidate positions and represents the possibility of arrangement of the line pattern. Using the fitness function associated with the line pattern, the fitness derivation for deriving the fitness at each of the plurality of candidate positions from the feature value at the corresponding position of the line pattern and the feature value at the adjacent pixel position. A candidate position acquisition step for detecting a candidate position showing the best fitness based on the derived fitness at each of the plurality of candidate positions, and the line pattern based on the read pixel pitch. A fine pattern position, comprising: a corresponding position and a recording position acquisition step of calculating a recording position of the line pattern on the recording medium from the candidate position indicating the detected best matching degree. It relates to a detection method.

  According to this aspect, the position of the line pattern is accurately identified in units less than the read pixel pitch by detecting a position having a high degree of fitness from a plurality of candidate positions based on a feature value correlated with the line pattern. Can do.

  Here, the “feature value” is a value that reflects the correlation with the line pattern, and indicates the influence of the line pattern at each position (including the position corresponding to the line pattern and the adjacent pixel position) based on the read pixel pitch. The value to represent. Examples of the characteristic value include optical density (tone value) and numerical values related to these.

  Preferably, the plurality of candidate positions are set in the reading direction in units of less than one pixel based on the reading pixel pitch, and in the recording position acquisition step, the recording position of the line pattern is the reading pixel pitch unit. Is obtained from the corresponding position based on the read pixel pitch, and a position in units of less than one pixel based on the read pixel pitch is obtained from the candidate position showing the best matching degree.

  According to this aspect, the position of the unit of less than one pixel of the line pattern can be accurately identified from the plurality of candidate positions set in units of less than one pixel based on the read pixel pitch.

  Preferably, the goodness of fit is an index indicating the probability that the line pattern exists at a corresponding candidate position, and in the candidate position acquisition step, from the feature value at the corresponding position of the line pattern and the adjacent pixel position. Among the plurality of sets of goodness-of-fit derived at each of the plurality of candidate positions, the candidate position corresponding to the set of goodness-of-fit having the highest probability that the line pattern exists is the candidate position showing the best goodness of fit Detect as.

  According to this aspect, it is possible to specify a candidate position set in units of less than one pixel based on the read pixel pitch from the set of fitness having the highest probability that a line pattern exists.

  The line pattern formed on the recording medium may have a width substantially equal to the reading pixel pitch in the reading direction.

  The line pattern formed on the recording medium may have a width of 3 to 5 times the read pixel pitch in the reading direction.

  Even in these cases, according to the above aspect of the present invention, the position of the line pattern can be accurately identified in units of less than one pixel based on the read pixel pitch.

  Preferably, the feature value at the corresponding position of the line pattern and the feature value at the adjacent pixel position are read from the read data at the corresponding position of the line pattern and the corresponding position of the line pattern. Based on the pixel pitch, it is calculated from the read data at the two adjacent pixel positions adjacent to the front side and two adjacent to the rear side in the reading direction.

  According to this aspect, the feature value is derived in an integrated manner from the corresponding position of the line pattern and the read data at a total of four adjacent pixel positions, two before and after, and the position of the line pattern is less than one pixel based on the read pixel pitch. The unit can be specified with high accuracy.

  Preferably, in the reading step, read data relating to optical density is acquired, and the characteristic value is based on the optical density.

  According to this aspect, the position of the line pattern can be easily specified with accuracy in units of less than one pixel based on the read pixel pitch from the read data relating to the optical density.

  Preferably, the feature value is based on a first derivative value of the read data.

  In this way, by using the first derivative value of the read data, a value that more clearly reflects the feature of the line pattern may be used as the feature value.

  Preferably, the recording medium is formed with a detection bar extending continuously in the reading direction and having a predetermined width so as to correspond to the line pattern. In the reading step, the line pattern and the detection bar are read simultaneously. The read data relating to the optical density is obtained, and in the read pixel position obtaining step, the position of the detection bar is obtained from the change in the optical density indicated by the read data, and the relative positional relationship between the detection bar and the line pattern Then, the corresponding position of the line pattern is acquired from the obtained position of the detection bar.

  According to this aspect, the position of the line pattern can be accurately identified from the detection bar having a simple configuration.

  Another aspect of the present invention is a defective nozzle detection method including the fine pattern position detection method described above, wherein a plurality of the line patterns corresponding to each of the nozzles are recorded by the liquid ejected from the plurality of nozzles. A pattern forming step for forming on the medium, a reference position serving as a reference for a landing position of the liquid on the recording medium and set for each of the plurality of nozzles, and the recording position acquiring step. The present invention relates to a defective nozzle detection method, comprising: a defective nozzle detection step of detecting a defective ejection nozzle from the plurality of nozzles from the calculated recording position of the line pattern.

  According to this aspect, it is possible to accurately detect the defective ejection nozzle from the position of the line pattern and the reference position specified with high accuracy.

  Preferably, the reference position is calculated based on the recording position of the adjacent line pattern.

  According to this aspect, the reference position used for detecting the defective ejection nozzle can be easily obtained.

  Another aspect of the present invention is a liquid ejection method including the above defective nozzle detection method, wherein a reception step of receiving input data, a correction step of correcting the received input data, and the corrected input A discharge step of discharging the liquid from the plurality of nozzles based on data, and in the correction step, the discharge of the liquid from the defective discharge nozzle detected in the defective nozzle detection step is compensated by another nozzle In addition, the present invention relates to a liquid ejection method that corrects the input data so that the liquid is not ejected from the defective ejection nozzle.

  According to this aspect, it is possible to accurately correct the liquid discharge from the defective discharge nozzle that is detected accurately, and it is possible to accurately discharge the liquid that reflects the input data.

  According to another aspect of the present invention, there is provided a reading unit that reads a recording medium on which a line pattern is formed at a predetermined reading pixel pitch in a predetermined reading direction to obtain read data, and the line pattern based on the reading pixel pitch. Read pixel position acquisition means for acquiring a corresponding position from the read data, a feature value at the corresponding position of the line pattern, and a feature value at an adjacent pixel position adjacent to the corresponding position based on the read pixel pitch, Feature value acquisition means acquired from the read data, and a matching function prepared in advance for each of the corresponding position and the adjacent pixel position of the line pattern, and having a pitch shorter than the read pixel pitch Prepared for each of a plurality of candidate positions, and the degree of conformity indicating the arrangement possibility of the line pattern is associated with the feature value. A degree-of-fit deriving means for deriving the degree of fit at each of the plurality of candidate positions from the feature value at the corresponding position of the line pattern and the feature value at the neighboring pixel position using the obtained fit function; , Candidate position acquisition means for detecting a candidate position showing the best fitness based on the derived fitness at each of the plurality of candidate positions, and the corresponding position of the line pattern based on the read pixel pitch And a recording position acquisition means for calculating the recording position of the line pattern on the recording medium from the detected candidate position indicating the best matching degree. About.

  Another aspect of the present invention is a defective nozzle detection device including the fine pattern position detection device described above, wherein a plurality of line patterns corresponding to each of the nozzles are recorded by the liquid ejected from the plurality of nozzles. A pattern forming unit formed on a medium, a reference position which is a reference position of a landing position of the liquid on the recording medium and set for each of the plurality of nozzles, and the recording position acquiring unit The present invention relates to a defective nozzle detection device comprising: defective nozzle detection means for detecting a defective ejection nozzle from the plurality of nozzles from the calculated recording position of the line pattern.

  Another aspect of the present invention is a liquid ejecting apparatus including the above defective nozzle detection device, wherein the receiving unit receives input data, the correcting unit corrects the received input data, and the corrected input. Discharge means for discharging the liquid from the plurality of nozzles based on the data, and the correction means compensates the discharge of the liquid from the defective discharge nozzle detected by the defective nozzle detection means by another nozzle. In addition, the present invention relates to a liquid ejection apparatus that corrects the input data so that the liquid is not ejected from the defective ejection nozzle.

  According to the present invention, the position of the line pattern can be accurately identified in units less than the read pixel pitch by detecting a position having a high degree of fitness from a plurality of candidate positions based on a feature value correlated with the line pattern. Can do.

1 is an overall configuration diagram of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 2A is a plan perspective view showing an example of the structure of the head 50, and FIG. 2B is an enlarged view of a part of FIG. It is a plane perspective view which shows the other structural example of a head. It is sectional drawing which follows the 4-4 line in FIG. 2 (a) and (b). It is an enlarged view which shows the nozzle arrangement | sequence of a head. It is a block diagram which shows the system configuration | structure of an inkjet recording device. (A) is a plan view showing a line arrangement of a plurality of nozzles in the head, (b) is a diagram of a state in which ink droplets are ejected from the nozzles toward the recording paper, as viewed from the side, and (c). It is an upper view showing a test pattern (landing position) formed on the recording paper 16 by ink droplets ejected from a nozzle. (A)-(c) is a figure which illustrates typically the state from which the landing position on the recording medium of the ink droplet discharged from a nozzle deviates from an ideal landing position. It is a flowchart which shows an example of the process which detects a defective recording element (defective discharge nozzle). It is a functional block diagram of a system related to detection of defective ejection nozzles and correction processing of input image data. It is a figure which shows the basic form of the test pattern recorded on a recording paper. It is a figure which shows one specific example of a test pattern, and the test pattern containing a reference position detection bar is shown. FIG. 4 is a conceptual diagram of a read image of a test pattern when the reading resolution of the printing apparatus is 1200 DPI. FIG. 6 is a conceptual diagram of a read image of a test pattern when the reading resolution of the printing apparatus is 500 DPI. It is a flowchart which shows a series of flow which calculates | requires the position error of each line position of a test pattern. It is a figure explaining the method to detect the reference position for line position specification from a read image. It is a figure explaining extraction of a line block of a nozzle based on a reference position. It is a figure which shows an example of the test pattern which overlapped the analysis area | region in one part. It is a figure which shows the graph which digitized the density distribution profile in each line block. It is a flowchart which shows the process of calculating the position below a pixel about each line position of a test pattern. (A) is a table showing the relationship between the matching function table for determining the position of a line less than a pixel and the position in units of less than a pixel, and (b) schematically shows the arrangement relationship between a pixel position of a read image and a candidate position. FIG. It is a graph which shows the basic shape (basic concept) of a fitting function table, an X axis shows an input value, and a Y axis shows a fitting degree. It is a graph which shows the some adaptation function characteristic for performing position determination of a unit less than 1 pixel, and respond | corresponds to the first primary differential value tz1. It is a graph which shows the several adaptation function characteristic for performing the position determination of a unit less than 1 pixel, and respond | corresponds to the 2nd primary differential value tz2. It is a graph which shows the some adaptation function characteristic for performing the position determination of a unit less than 1 pixel, and respond | corresponds to the 3rd primary differential value tz3. It is a graph which shows the several adaptation function characteristic for performing the position determination of a unit less than 1 pixel, and respond | corresponds to the 4th primary differential value tz4. It is a figure which shows typically the calculation method of the relative position of the test pattern on a read image. It is a figure which shows an example of the calculation method of a reference position, Comprising: It is a figure which shows the method of calculating a reference position from the position of the adjacent line (test pattern) of both adjacent. It is a figure which shows the other example of the calculation method of a reference position, Comprising: It is a figure which shows the method of calculating a reference position from the position of the adjacent line (test pattern) of one side. It is a flowchart which shows the flow of image printing. It is a flowchart which shows the flow of defective discharge nozzle detection. It is a flowchart which shows an example of the algorithm which detects the position of a test pattern in the unit of less than the pixel of reading resolution (reading pixel pitch). It is a functional block diagram which shows the function structure of the defective discharge nozzle detection part which processes the algorithm of FIG. FIG. 4 is a layout diagram on a print sheet in a system that detects and corrects defective ejection nozzles. It is a figure which shows a profile when the space | interval of reading object and reading pixel pitch is far (when reading pixel pitch is fine) (2400 DPI). It is a figure which shows a profile when the space | interval of a reading object and a reading pixel pitch is near (500 DPI). It is a figure which shows a profile when the space | interval of reading object and a reading pixel pitch is near (500 DPI), and when the space | interval of reading object and a reading pixel pitch is far (when reading pixel pitch is fine) (2400 DPI).

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

  Here, an application example to the measurement of the ink dot landing position (that is, the dot position) by the image forming apparatus (inkjet recording apparatus) will be described. First, the overall configuration of the ink jet recording apparatus will be described.

(Inkjet recording device)
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention.

  As shown in the figure, the ink jet recording apparatus 10 includes a plurality of ink jet recording heads ("" provided corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. Corresponding to “liquid discharge head”, hereinafter referred to as “head”.) Ink storage / stores the printing unit 12 having 12K, 12C, 12M, and 12Y and the ink supplied to each of the heads 12K, 12C, 12M, and 12Y. A loading unit 14, a paper feeding unit 18 that supplies recording paper 16 as a recording medium, a decurling unit 20 that removes curling of the recording paper 16, and a nozzle surface (ink ejection surface) of the printing unit 12. A belt conveyance unit 22 that is arranged and conveys the recording paper 16 while maintaining the flatness of the recording paper 16 and a paper discharge unit 26 that discharges the recorded recording paper (printed matter) to the outside are provided.

  The ink storage / loading unit 14 has an ink tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has a head 12K, 12C, 12M, and 12Y through a required pipe line. Communicated with.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In the case where a plurality of types of recording media can be used, a means for specifying the type of recording medium to be used (media type) is provided, and ink is provided so as to realize appropriate ink ejection according to the media type. It is preferable to perform discharge control.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  After the decurling process, the recording paper 16 cut to a desired size by a cutting cutter (first cutter) 28 is sent to the belt conveyance unit 22. The belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 forms a horizontal plane (flat surface). ing.

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. An adsorption chamber 34 is provided inside the belt 33 spanned between the rollers 31 and 32 at a position facing the nozzle surface of the printing unit 12, and the adsorption chamber 34 is sucked by a fan 35 to be negative pressure. As a result, the recording paper 16 is sucked and held on the belt 33. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  When the power of the motor (reference numeral 88 in FIG. 6) is transmitted to at least one of the rollers 31 and 32, the belt 33 is driven in the clockwise direction in FIG. 1, and the recording paper 16 held on the belt 33 is It is conveyed from left to right in FIG.

  A belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the printing area). Although the detailed configuration of the belt cleaning unit 36 is not illustrated, for example, there are a method of niping a brush roll, a water absorbing roll, an air blow method of spraying clean air, or a combination thereof.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 2).

  The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side in the recording paper 16 feed direction. 12K, 12C, 12M, and 12Y are installed so as to extend along a direction substantially perpendicular to the conveyance direction of the recording paper 16.

  A color image can be formed on the recording paper 16 by discharging different colors of ink from the heads 12K, 12C, 12M, and 12Y while the recording paper 16 is being transported by the belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction). The image can be recorded on the entire surface of the recording paper 16 by performing the operation of relatively moving the 12 only once (that is, by one sub-scan). 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 the present embodiment, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to the configuration of the present 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 ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  A post-drying unit 42 is provided following the printing unit 12. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferable.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be originally printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. When the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by the cutter (second cutter) 48.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders. In addition, the ink jet recording apparatus 10 of this example includes a head maintenance unit that performs cleaning (wiping, purging, nozzle suction, etc. of the nozzle surface) of each head 12K, 12C, 12M, and 12Y, and the recording paper 16 on the paper transport path. A sensor for detecting the position and the like, a temperature sensor for detecting the temperature of each part of the apparatus, and the like are provided.

(Head structure)
Next, the structure of the head will be described. Since the structures of the respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  2A is a plan perspective view showing an example of the structure of the head 50, and FIG. 2B is an enlarged view of a part thereof. 3 is a plan perspective view showing another example of the structure of the head 50, and FIG. 4 is a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 51) serving as a recording element unit. FIG. 4 is a cross-sectional view (a cross-sectional view taken along line 4-4 in FIG. 2A).

  As shown in FIGS. 2A and 2B, the head 50 according to the present embodiment includes a plurality of inks including nozzles 51 that are ink discharge ports, pressure chambers 52 corresponding to the nozzles 51, and the like. The chamber units (droplet ejection elements) 53 have a structure in which the chamber units (droplet ejection elements) 53 are arranged in a staggered matrix (two-dimensionally), so that the chamber units (droplet ejection elements) are arranged along the longitudinal direction of the head (direction perpendicular to the paper feed direction) High density of substantial nozzle interval (projection nozzle pitch) to be projected (orthographic projection) is achieved.

  A mode in which nozzle rows having a length corresponding to the full width Wm of the recording paper 16 are configured in a direction (arrow M direction; main scanning direction) substantially orthogonal to the feeding direction of the recording paper 16 (arrow S direction; sub-scanning direction) It is not limited to this example. For example, instead of the configuration shown in FIG. 2A, as shown in FIG. 3, recording paper is obtained by arranging short head modules 50 'in which a plurality of nozzles 51 are two-dimensionally arranged in a staggered manner and joined together. You may comprise the line head which has a nozzle row of the length corresponding to the full width of 16.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIG. 2A and FIG. 2B), and is located at one of the diagonal corners. An outlet to the nozzle 51 is provided, and an inlet (supply port) 54 for supply ink is provided on the other side. The shape of the pressure chamber 52 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. 4, each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 52 via the common channel 55.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibrating plate that also serves as a common electrode) 56 constituting a part of the pressure chamber 52 (the top surface in FIG. 4). By applying a drive voltage between the individual electrode 57 and the common electrode, the actuator 58 is deformed and the volume of the pressure chamber 52 is changed, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. The actuator 58 is preferably a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate. After the ink is ejected, when the displacement of the actuator 58 returns to its original state, new ink is refilled into the pressure chamber 52 from the common channel 55 through the supply port 54.

  By controlling the driving of the actuator 58 corresponding to each nozzle 51 according to the dot arrangement data generated from the input image, ink droplets can be ejected from the nozzle 51. A desired image can be recorded on the recording paper 16 by controlling the ink ejection timing of each nozzle 51 in accordance with the transport speed while transporting the recording paper 16 in the sub-scanning direction at a constant speed.

  As shown in FIG. 5, the ink chamber unit 53 having the above-described structure is slanted in a fixed arrangement pattern along a row direction along the main scanning direction and an oblique column direction having a constant angle ψ not orthogonal to the main scanning direction. A high-density nozzle head is realized by arranging a large number in a grid pattern. That is, with the structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along the direction of an angle ψ with respect to the main scanning direction, each nozzle 51 is substantially at a constant pitch PN = It can be handled equivalently to a linear array of d × cos ψ.

  When driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the nozzles 51-11, 51-12, 51-13, 51-14, 51-15, and 51-16 are made into one block ( In addition, nozzles 51-21,..., 51-26 are set as one block, nozzles 51-31,..., 51-36 are set as one block,. Accordingly, the recording paper 16 is driven in the width direction (paper) by sequentially driving from one end to the other end (nozzles 51-11, 51-12,..., 51-16 are sequentially driven) for each block. One line (a line made up of a single row of dots or a line made up of a plurality of rows of dots) is printed in a direction perpendicular to the transport direction.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by such nozzle driving (main scanning) is referred to as the main scanning direction, and one line formed by this main scanning (a line by a single line or a plurality of lines). The repeated printing in the relative movement direction by the relative movement of the head and the recording paper 16 is called sub-scanning. In other words, in the present embodiment, the conveyance direction of the recording paper 16 is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  In the present embodiment, a piezoelectric element is applied as an ejection force generation unit for ink ejected from the nozzles 51 provided in the head 50. However, a unit for generating ejection pressure (ejection energy) is not limited to a piezoelectric element. First, various means and methods such as a heater (heating element) in the thermal method and various actuators by other methods can be applied.

  In the implementation of the present invention, the arrangement form of the nozzles 51 in the head 50 is not limited to the illustrated example, and various nozzle arrangement structures can be applied. For example, instead of the matrix arrangement described with reference to FIG. 2, a linear array of lines, a V-shaped nozzle arrangement, and a zigzag (W-shaped) nozzle having a V-shaped arrangement as a repeating unit An array or the like is also possible.

(Description of control system)
FIG. 6 is a block diagram showing a system configuration of the inkjet recording apparatus 10.

  As shown in the figure, the inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a ROM 75, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, and a head driver 84. I have.

  The communication interface 70 is an interface unit (image input unit) that receives image data sent from the host computer 86. For the communication interface 70, 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.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 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 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, and the like, and performs communication control with the host computer 86, read / write control of the image memory 74 and ROM 75, and the like. At the same time, a control signal for controlling the motor 88 and the heater 89 of the transport system is generated.

  The ROM 75 stores programs executed by the CPU of the system controller 72 and various data necessary for control. The ROM 75 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. The image memory 74 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 76 is a driver (driving circuit) that drives the conveyance motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print controller 80 has a signal processing function for performing various processes such as various processes and corrections for generating a print control signal from the image data (original image data) in the image memory 74 according to the control of the system controller 72. And a control unit that supplies the generated print data (dot data) to the head driver 84.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 6, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, for example, RGB image data is stored in the image memory 74.

  In the inkjet recording apparatus 10, a pseudo continuous tone image is formed by human eyes by changing the droplet ejection density and dot size of fine dots by ink (coloring material). It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and the print control unit 80 performs halftoning using a threshold matrix, error diffusion, and the like. It is converted into dot data for each ink color by processing.

  That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 80 is stored in the image buffer memory 82.

  The head driver 84 generates a drive signal for driving the actuator 58 corresponding to each nozzle 51 of the head 50 based on print data (that is, dot data stored in the image buffer memory 82) given from the print control unit 80. Output. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  When a drive signal output from the head driver 84 is applied to the head 50, ink is ejected from the corresponding nozzle 51. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head driver 84 based on the dot data generated through the required signal processing in the print controller 80. Thereby, a desired dot size and dot arrangement are realized.

  The print controller 80 performs various corrections on the head 50 based on dot position information acquired by a dot position measurement method described later, and cleaning operations such as preliminary ejection, nozzle suction, and wiping as necessary. Control to perform (nozzle recovery operation) is performed.

(Description of dot position measurement method)
Next, the dot position measurement method according to this embodiment will be described in detail.

(Overall flow of image correction)
FIGS. 7A to 7C are diagrams schematically illustrating a state where the landing position of the ink droplets ejected from the nozzle on the recording medium deviates from the ideal landing position. Specifically, FIG. 7A is a plan view showing a line arrangement of a plurality of nozzles 51 in the head 50. FIG. 7B is a diagram of a state in which ink droplets are ejected from the nozzles 51 toward the recording paper (recording medium) 16 as viewed from the lateral direction. Is shown schematically. FIG. 7C is an upper view showing a test pattern (landing position) 102 formed on the recording paper 16 by ink droplets ejected from the nozzle 51, and an ideal landing position 104 is indicated by a dotted line. The actual landing position 102 is indicated by a thick black line.

  7A and 7B show the head 50 in which a plurality of nozzles 51 are arranged in a row for simplification of illustration, but as described with reference to FIGS. Of course, the present invention can also be applied to a matrix head in which a plurality of nozzles are two-dimensionally arranged. That is, the two-dimensional array of nozzle groups can be handled as substantially equivalent to a single nozzle array by considering a substantial nozzle array that is orthogonally projected onto a straight line along the main scanning direction.

  As shown in FIG. 7A to FIG. 7C, the plurality of nozzles 51 of the head 50 include the normal nozzles exhibiting normal ejection characteristics and the ejection trajectory of the ejected ink droplets from the original trajectory. Included are defective discharge nozzles that are excessively removed. The line-shaped dot pattern (test pattern) 102 formed by the ink droplets ejected from the defective ejection nozzles and landed on the recording paper 16 deviates from the ideal landing position 104, which is a cause of image quality degradation. Become.

  In the single-pass recording method, which is a high-speed recording technology, the number of nozzles corresponding to the paper width of the recording paper 16 is tens of thousands per ink, and in full-color recording, the number of ink colors (for example, cyan, magenta, yellow and black) is further increased. There are recording elements corresponding to (four colors). The process shown in FIG. 8 is an example of a method for detecting a defective recording element (defective ejection nozzle) from hundreds of thousands of recording elements in such a single-pass recording method.

  That is, in order to detect variations in the ejection direction between the nozzles, as shown in FIGS. 7A to 7C, ink droplets are ejected from the nozzles 51 toward the recording paper 16, and the test pattern 102 is detected. Is printed on the recording paper 16 (S10 in FIG. 8).

  The test pattern 102 is read by a low-resolution scanner, and the image data of the read test pattern 102 is compared with a predetermined value according to a predetermined detection algorithm, whereby the test pattern 102 from the ideal landing position 104 is read. Landing position error is required. At this time, a nozzle having an excessive position error of a predetermined value or more is detected and specified as a defective ejection nozzle (S12). A specific flow for detecting the defective ejection nozzle will be described later.

  The defective ejection nozzle specified in this way is subjected to mask processing and treated as a non-ejection nozzle that does not eject ink droplets (S14). Then, the input image data is corrected by image processing in consideration of compensating for ink droplets not ejected from the non-ejection nozzles by ink droplets ejected from other ejection nozzles (for example, adjacent nozzles) (S16). A desired image is recorded on the recording paper 16 with good quality based on the input image data.

  Next, a series of processing flows including detection of defective ejection nozzles and input image data correction processing will be described. FIG. 9 is a functional block diagram of a system related to detection of defective ejection nozzles and correction processing of input image data.

  The following color conversion processing unit 110, non-ejection nozzle correction image processing unit 112, halftone processing unit 114, image memory 74, image analysis unit 124, test pattern synthesis unit 118, head driver 84, defect shown in FIG. The ejection nozzle detection unit 132, the defective ejection nozzle determination unit 130, the defective nozzle information accumulation unit 126, the defective ejection correction determination unit 122, and the correction information setting unit 120 may be a single unit or a combination of a plurality of units of the control unit of the inkjet recording apparatus 10. Configured.

  The print image data to be printed sent from the host computer via the communication interface is subjected to predetermined color conversion processing in the color conversion processing unit 110, and each plate corresponding to the recording ink (in this example, CMYK ink). Image data is obtained. The image data obtained in this way is sent from the color conversion processing unit 110 to the non-ejection nozzle corrected image processing unit 112.

  On the other hand, in the defective ejection correction determination unit 122, defective nozzle correction information is comprehensively acquired, and from the correspondence between the image position (image dot position) and the nozzle position, dots are normally recorded by the defective ejection nozzle. A corrected image position, which is a position on the displayed image, is specified. Since the defective discharge nozzle cannot appropriately record the image portion at the corrected image position, the defective discharge correction determination unit 122 stores the recording information of the corrected image position corresponding to the defective discharge nozzle. The nozzle is distributed to one or more normal nozzles in the vicinity including the nozzles on both sides of the discharge nozzle. Here, the distribution of the recording information corresponding to the defective ejection nozzle means that the recording from the corrected image position corresponding to the defective ejection nozzle is compensated for by the ink ejection from the other nozzle. Data processing for correction (correction processing) is meant. Further, the defective ejection correction determination unit 122 corrects the image information thus distributed according to the recording characteristics.

  The defective ejection correction determination unit 122 collates the information (image position information data) from the image analysis unit 124 with the defective ejection nozzle information from the defective ejection nozzle determination unit 130, and records an image portion to be recorded by the defective ejection nozzle. Correction information is created only for At this time, the defective ejection correction determination unit 122 is set in data indicating the necessity of correction provided from the correction information setting unit 120 (for example, data indicating a correction area set on the print image, or in a printing unit of the head 50). By referring to the correction area (nozzle unit data) to be corrected, it is also possible to create correction information only for a highly necessary area. The correction information created in this way is sent from the defective ejection correction determination unit 122 to the non-ejection nozzle correction image processing unit 112.

  In the non-ejection nozzle correction image processing unit 112, correction processing is performed on the image data sent from the color conversion processing unit 110 based on the correction information related to the defective ejection nozzle sent from the defective ejection correction determination unit 122. In this way, the corrected image data reflecting the non-ejection information from the defective ejection nozzle is sent from the non-ejection nozzle correction image processing unit 112 to the halftone processing unit 114.

  In the halftone processing unit 114, halftone processing is performed on the image data sent from the non-ejection nozzle correction image processing unit 112, and multivalued image data for driving the recording head 50 is generated. At this time, the generated multi-value image data (recording head driving multi-value) is smaller than the number of image gradation values (that is, satisfying the number of image gradation values> the recording head driving multi-value). Halftone processing is performed.

  The image data that has been subjected to the halftone process is sent from the halftone processing unit 114 to the image memory 74. The halftone processed image data sent to the image memory 74 is also sent to the image analysis unit 124. The image data subjected to the halftone process is stored in the image memory 74 and analyzed by the image analysis unit 124 to obtain information on the position where the image information exists (image position) and the position where the image information does not exist (image position information). Data) is generated. The image position information data generated in this way is sent from the image analysis unit 124 to the defective ejection correction determination unit 122 and is used to create correction information for the defective ejection nozzles in the defective ejection correction determination unit 122.

  The image data that has been subjected to the halftone process (halftone image data) is also sent from the image memory 74 to the test pattern synthesis unit 118.

  The test pattern synthesis unit 118 synthesizes the halftone image data sent from the image memory 74 and the image data (test pattern image data) related to the test pattern, and the synthesized image data is sent to the head driver (ejection unit) 84. Sent. Although the details will be described later, the test pattern is a dot pattern formed on the recording paper by each nozzle for the purpose of detecting defective ejection nozzles. The test pattern image data and the halftone image data are combined by the test pattern combining unit 118 so that the test pattern is printed on the edge of the recording paper.

  Image data obtained by combining the halftone image data and the test pattern image data is sent from the test pattern combining unit 118 to the head driver 84. The head driver 84 drives the head 50 based on the image data sent from the test pattern synthesizing unit 118 and records a desired image and a test pattern on the recording paper. As described above, the pattern forming means for forming a plurality of test patterns corresponding to each of the nozzles on the recording paper with the ink droplets ejected from the nozzles includes the test pattern combining unit 118 and the head driver 84. It will be.

  Note that, according to the method of the present embodiment in which the position of the test pattern can be specified in units less than the reading pixel pitch, the test pattern has a width substantially equal to the reading pixel pitch in the reading direction, Even when the width is 3 to 5 times or less, the position of the test pattern can be specified appropriately.

  The recording paper on which the image and the test pattern are recorded is sent toward the paper discharge unit along the conveyance path (see arrow B in FIG. 9). At this time, the test pattern reading unit (reading unit) 136 installed in the middle of the conveyance path reads the test pattern recorded on the recording paper and generates a test pattern read image. The test pattern reading unit 136 reads the recording paper 16 on which the test pattern 102 is formed in the longitudinal direction of the head 50 (nozzle row direction, main scanning direction, X direction) at a predetermined reading pixel pitch, and sets the reading pixel pitch. Based on the read test pattern image data. The test pattern read image data is sent from the test pattern reading unit 136 to the defective ejection nozzle detection unit 132.

  In the defective ejection nozzle detection unit 132, from the test pattern read image data sent from the test pattern reading unit 136, a defective ejection nozzle (defect nozzle and ink whose landing position error on the recording paper of the ink droplets to be ejected is larger than a predetermined value). A non-ejection nozzle that does not eject droplets) is detected. Information data regarding the detected defective ejection nozzle (defective ejection nozzle information) is sent from the defective ejection nozzle detection unit 132 to the defective ejection nozzle determination unit 130.

  The defective ejection nozzle determination unit 130 includes a memory (not shown) that can store defective ejection nozzle information sent from the defective ejection nozzle detection unit 132 a predetermined number of times. The defective ejection nozzle determination unit 130 refers to past defective ejection nozzle information stored in the memory, and determines the defective ejection nozzle depending on whether or not it has been detected as a defective ejection nozzle a predetermined number of times or more in the past. If it is determined that the nozzle is a normal nozzle that is not a defective ejection nozzle more than a predetermined number of times in the past, even if the nozzle has been treated as a defective ejection nozzle, the handling is changed so that it is treated as a normal nozzle. The defective ejection nozzle information is corrected.

  The defective ejection nozzle information determined in this way is sent from the defective ejection nozzle determination unit 130 to the head driver 84 and the defective ejection correction determination unit 122. Further, when a predetermined condition is satisfied (for example, after printing a predetermined number of sheets, after JOB, at the time of user instruction, etc.), the determined defective ejection nozzle information is sent from the defective ejection nozzle determination unit 130 to the defective nozzle information storage unit 126. It is done.

  The head driver 84 deactivates the nozzle corresponding to the defective ejection nozzle based on the defective ejection nozzle information sent from the defective ejection nozzle determination unit 130.

  Further, the defective ejection nozzle information sent to the defective nozzle information accumulation unit 126 is accumulated and stored in the defective nozzle information accumulation unit 126 and used as statistical information of the defective ejection nozzle. The defective ejection nozzle information stored in the defective nozzle information accumulation unit 126 is sent to the defective ejection nozzle determination unit 130 at an appropriate timing as initial defective nozzle information. The initial defective nozzle information here is information indicating which nozzles (corresponding to CMYK inks) are defective nozzles. The inspection information at the time of head shipment is used as the initial value of the initial defective nozzle information, and defective nozzles at a specific cycle. Based on the defective ejection nozzle information stored in the information storage unit 126, the initial defective nozzle information is updated in a timely manner. The defective discharge nozzle determination unit 130 stores necessary defective discharge nozzle information in the initial defective nozzle information in a memory (not shown) at the start of printing or the like, and uses the defective discharge nozzle determination process.

  The defective ejection correction determination unit 122 generates correction information for an image portion to be corrected (image portion recorded by the defective ejection nozzle) from the defective ejection nozzle information sent from the defective ejection nozzle determination unit 130, and the correction information is obtained. This is sent to the non-ejection nozzle correction image processing unit 112.

  Further, the defective ejection correction determination unit 122 compares the correction information generated in this way with the immediately preceding correction information, and a new defective ejection nozzle is generated (preferably a predetermined number or more) and the correction information increases. It is detected whether it is doing. When it is recognized that the correction information has increased, a predetermined instruction is sent from the defective ejection correction determination unit 122 to the defective ejection detection display unit 134.

  Upon receiving this predetermined instruction, the defective ejection detection display unit 134 identifies a defective ejection printed matter that has been recorded by the new defective ejection nozzle (that is, a printed matter that has been printed without correction for the new defective ejection nozzle). Perform the process to make it possible. Specifically, the defective ejection detection display unit 134 performs sticking on a printed material from the printed material (recording paper) in which the defect is detected until the corrected printing is started. Then, at the time of printing after the correction processing for the new defective ejection nozzle is completed (at the time of printing based on the image data (halftone image data) after the correction processing is completed), the predetermined instruction is invalidated. Then, an instruction signal is sent from the defective ejection correction determination unit 122 to the defective ejection detection display unit 134, and the defective ejection detection display unit 134 performs a normal operation (normal display).

  Based on the above-described series of processing flows, the defective ejection nozzle detection and input image data correction processing are appropriately performed. Depending on the stability of the recording head 50, the above detection and correction processing may be performed only on the first predetermined number of recording sheets at the start of printing (an offline scanner may be used), or the user A configuration that is implemented only when instructed by the user is also possible.

  Next, a test pattern read by the test pattern reading unit 136 will be described.

  FIG. 10 is a diagram showing a basic form of a test pattern recorded on a recording sheet (recording medium). FIG. 11 is a diagram showing a specific example of a test pattern, and shows a test pattern including a reference position detection bar. 10 and 11 show an enlarged end portion of the recording paper 16 on which the test pattern 102 is printed.

  By transporting the recording paper 16 to the recording head and driving a plurality of nozzles of the recording head at regular intervals, a basic portion of the line-shaped test pattern 102 is created on the recording paper 16. That is, ink droplets are ejected for each nozzle block composed of nozzle groups having a predetermined interval among a plurality of nozzles of the recording head to form a line-shaped test pattern 102, and ink droplets are ejected along with the conveyance of the recording paper 16 By sequentially changing the nozzle blocks, the test patterns 102 are formed in a staggered pattern as shown in FIG. Since each test pattern 102 corresponds to ink ejection from each nozzle, by determining whether each test pattern 102 is properly formed, ink droplets are properly ejected from the corresponding nozzle. It is possible to detect whether or not.

  In the present embodiment, as shown particularly in FIG. 11, the reference position detection bars 106a and 106b are also recorded in the upper and lower portions of the test pattern 102, respectively. The reference position detection bars 106a and 106b serve as a reference for detecting the position of the test pattern 102, as will be described later.

  FIG. 12 is a conceptual diagram of a read image of a test pattern when the reading resolution of the printing apparatus is 1200 DPI (dots / inch). In the read image of FIG. 12, the length in the longitudinal direction of each line-shaped test pattern 102 corresponds to 4 pixels at 100 DPI and 48 pixels at 1200 DPI.

  FIG. 13 is a conceptual diagram of a read image of a test pattern when the reading resolution of the printing apparatus is 500 DPI. As is clear from FIG. 13, at the reading resolution of 500 DPI, each line of the read image of the test pattern 102 is blurred, and it is difficult to identify a clear outline.

  Thus, while it is possible to clearly specify the position of each test pattern according to the high resolution read image, the outline is blurred in the low resolution read image, and the position of each test pattern is simply determined. It is difficult to identify. However, since the high-resolution image reading apparatus (scanner) itself is expensive, from the viewpoint of cost reduction, even a low-resolution image reading apparatus can accurately specify the position of the test pattern. Is desired.

  Therefore, an example of a method for accurately identifying the position of the test pattern from the low-resolution read image is shown below.

  In the following description, the image density (light / dark) distribution when the read image is cut in one direction (X direction) is called a profile. This profile does not necessarily indicate a density (shading) distribution of only one pixel. For example, a density (shading) distribution in the X direction may be adopted as a profile using density (shading) averaged in the Y direction.

  First, a method for obtaining the position error of each line position of the test pattern (line pattern) will be described.

  FIG. 14 is a flowchart showing a series of flows for obtaining the position error of each line position of the test pattern. FIG. 15 is a diagram illustrating a method for detecting a reference position for specifying a line position from a read image. FIG. 16 is a diagram illustrating the cutting out of the nozzle line block based on the reference position.

  The test pattern 102 printed on the recording paper 16 by the nozzles of the recording head is read as image data by the test pattern reading unit 136 (see FIG. 9), and image reading data of the test pattern 102 is generated (S20 in FIG. 14). ). As an example, the reading condition of the test pattern 102 at this time is set to 500 DPI in the X direction (main scanning direction) and 100 DPI in the Y direction (sub-scanning direction).

  Then, reference positions (reference position detection bars 106a and 106b) used when specifying the line position of each test pattern 102 are determined from the image reading data of the test pattern 102 (S22 in FIG. 14).

  Specifically, as shown in FIG. 15, the reference position detection window 140 that is a rectangular region that always includes the end of the test pattern 102 is set at each of both ends (left and right ends in the X direction) of the test pattern 102. To do. At this time, with respect to the read image (RGB color), the position of the test pattern 102 in the read image can be specified to some extent from the positional relationship among the test pattern 102, the recording paper 16, and the reading device (test pattern reading unit 136 in FIG. 9). It shall be. The reference position detection window 140 is set so as to always include one end of the test pattern 102 with respect to the test pattern position range that is known to some extent.

  The reference position detection window 140 is divided into two upper and lower regions, and optical density projection graphs 142a to 142d (X coordinate projection graph L1, X coordinate projection graph L2, Y coordinate) in the X direction and Y direction in each region. A projection graph L1, a Y coordinate projection graph L2, an X coordinate projection graph R1, an X coordinate projection graph R2, a Y coordinate projection graph R1, and a Y coordinate projection graph R2). The X-coordinate projection graph L1 (142a) and the Y-coordinate projection graph L1 (142c) here are projection graphs in the upper area of the reference position detection window 140 on the left end side in FIG. Similarly, an X-coordinate projection graph L2 (142b) and a Y-coordinate projection graph L2 (142d) indicate projection graphs in the lower region of the reference position detection window 140 on the left end side. Although not shown, the projection graph in the upper area of the reference position detection window 140 on the right end side is called the X coordinate projection graph R1 and the Y coordinate projection graph R1, and the projection graph in the lower area of the reference position detection window 140 on the right end side. Are called an X coordinate projection graph R2 and a Y coordinate projection graph R2. These projection graphs are created for each color of RGB, and the X (Y) coordinate projection graph having the highest contrast is used. Thereafter, the calculation is performed on the color image plane with the highest contrast.

  The Y coordinate projection graph L1 will be described as an example. The Y coordinate projection graph L1 is created by averaging density gradation values above the rectangular region (reference position detection window 140) on the left end side in the X-axis direction. This rectangular area includes the white paper background, the first reference position detection bar 106a of the test pattern 102, and each of the line-shaped test patterns 102. Therefore, in the Y coordinate projection graph L1 (142c), the white background portion (white color), the first reference position detection bar 106a (dark density), and the line portion (light density) are sequentially arranged. For this reason, the left upper end Y coordinate of the first reference position detection bar 106a can be obtained by detecting an edge that changes from white to dark density.

  Further, the X coordinate projection graph L1 (142a) is created by averaging the density gradation values in the Y axis direction above the rectangular region on the left end side (reference position detection window 140). This rectangular area includes the white paper portion and the first reference position detection bar 106a of the test pattern 102 (and the line-shaped test pattern 102 overlapping the first reference position detection bar 106a). Therefore, in the X coordinate projection graph L1 (142a), locations indicating the white background portion (white color), the reference position detection bar 1, and the line portion (dark density) are arranged in order. For this reason, the upper left X coordinate of the first reference position detection bar 106a can be obtained by detecting an edge that changes from white to dark density.

  Other projection graphs can be analyzed in the same manner. As a result, the XY coordinates of each corner (test pattern corners CL1, CL2, CR1, CR2) of the first reference position detection bar 106a and the second reference position detection bar 106b as shown in FIG. 16 are obtained. be able to. The test pattern corners CL1, CL2, CR1, and CR2 are used as reference positions.

  Even when the head 50 includes a non-ejection nozzle and the first reference position detection bar 106a and the second reference position detection bar 106b are printed by a nozzle group including the non-ejection nozzle, the first reference position is detected. Since the detection bar 106a and the second reference position detection bar 106b are solid portions that are continuous in the X direction (nozzle direction) and the Y direction, to the position detection result of the print location 51a corresponding to the defective ejection nozzle (non-ejection nozzle). Is less affected. The corresponding ink can also be determined by analyzing the RGB color for each portion of the first reference position detection bar 106a and the second reference position detection bar 106b.

  Next, the position of each line block 146 is obtained from the test pattern corners CL1, CL2, CR1, and CR2 which are reference positions (S24 in FIG. 14). Each line block 146 is constituted by a group of test patterns 102 arranged in the X direction as shown in FIG. 16, and the line blocks 146 adjacent in the Y direction are arranged from adjacent nozzles in a row of nozzle arrays (projection nozzle arrays). Printed with ink droplets. Accordingly, each test pattern 102 is assigned to one of the line blocks 146 sequentially arranged in the Y direction.

  First, from the positional relationship between the test pattern corners CL1, CL2, CR1, and CR2, the rotation angle of the test pattern 102 and the magnification error in the X direction and the Y direction (deviation between the actual magnification and the designed magnification) are calculated. Since the layout of the test pattern 102 is known information, the line block 146 is based on known test pattern design information (for example, the X direction pitch, Y direction pitch, X direction width, Y direction length, etc. of the test pattern 102). (Relative positions from the test pattern corners CL1, CL2, CR1, and CR2 and the four corner coordinates of the rectangle) are obtained. The relative position of each line block 146 on the read image is calculated from the test pattern corner CL1 based on the magnification error and the rotation angle obtained previously. At this time, even if the portion 51a printed by the defective ejection nozzle exists, the first reference position detection bar 106a and the second reference position detection bar 106b are hardly affected by the portion 51a corresponding to the defective ejection nozzle. The position of the line block 146 can be accurately calculated. In this way, the positions of all the line blocks 146 are specified.

  Next, the density in the line block 146 is binarized by a predetermined threshold value, and the line position of each test pattern 102 is determined in pixel units (read pixel pitch units) of the read image (S26 in FIG. 14). The predetermined threshold used at this time may be a relative value with respect to the white background gradation value or may be changed for each paper type of the recording paper 16. Further, when there is a density difference of a certain level or more depending on the paper, the threshold value can also be determined by analyzing the image. It is also possible to determine the threshold using a known determination method such as a discriminant analysis method or a P tile method. Alternatively, a relative value between the gradation value of the first reference position detection bar 106a and the second reference position detection bar 106b and the gradation value of the white background can be used. For example, the first reference position detection bar The gradation value of 106a and the second reference position detection bar 106b may be set to 100%, the gradation value of the white background may be set to 0%, and the gradation value corresponding to X% may be set as the threshold value.

  In the binarization of the density distribution in the line block 146 by this threshold value, after creating a profile of the portion (near the center) in the line block 146 that is not affected by other line blocks 146 adjacent to the upper and lower sides, On the other hand, binarization is performed. When the test pattern has an inclination, the portion that is regarded as a portion near the center that is not affected by the upper and lower other line blocks 146 gradually shifts in the vertical direction. The effect is likely to appear as an error. In such a case, as shown in FIG. 17, an analysis region 148 for creating a profile is overlapped in a part in the line block 146, and the overlap part is averaged to create a profile. The presence / absence of the inclination of the test pattern is detected from the test pattern corners CL1, CL2, CR1, and CR2.

  FIG. 18 shows a graph in which the density distribution profile in each line block 146 is binarized. The graph G1 in FIG. 18 uses the pixel position (reading position) of the read image of the test pattern 102 as the X axis, and the read signal value (8 bits) of the gradation value (optical density) of the read image of the test pattern 102 as the Y axis. (See the Y axis on the left side of FIG. 18). In the graph G2, the first-order differential value of the read signal value in the graph G1 is the Y axis (see the Y axis on the right side of FIG. 18). A threshold value T1 is set in the graph G1, and a threshold value T2 is set in the graph G2, which is below the threshold values T1 and T2 (the read signal value is smaller than the threshold value T1, and the first derivative value is lower than the threshold value T2. The (small) read pixel position indicates a corresponding position based on the read pixel pitch of each test pattern 102. When a plurality of continuous pixels are below the threshold value, the center pixel of the plurality of pixels is set as a line position, or, for example, when there are two continuous pixels, a smaller value (tone value) is shown. The pixel position may be a line position.

  Next, for each line position of the test pattern 102, the position of the read pixel in units of less than one pixel is calculated (S28 in FIG. 14). FIG. 19 is a flowchart showing a process of calculating a position in units of less than one pixel for the line position of each test pattern.

Signal value is smaller pixel reading position than the threshold value T1 in the graph G1 of FIG. 18 relates to _{(X i),} before and after the adjacent reading five pixels including two pixels of the pixel _{(X i - 2, X i} - 1, X i, Based on X _i + ₁ , X _i + ₂ ), first derivative values (dz1, dz2, dz3, dz4) of the graph G2 are calculated (S40 in FIG. 19). Thus, by obtaining the primary differential value, it is possible to grasp the gradation change information more clearly.

  In this example, the primary differential values dz1, dz2, dz3, and dz4 (strictly described later) obtained from the read image data as the feature values at the corresponding positions of the target test pattern and the feature values at the adjacent pixel positions. The gradation conversion differential values tz1, tz2, tz3, and tz4) in which the logarithm is adjusted are used.

If the profile image data (read signal value) of each live block LBk is represented by PFIk (X), the graph G2 obtained for a certain pixel position (X _i ) whose read signal value is smaller than the threshold value T1 in the graph G1. The primary differential values (dz1, dz2, dz3, dz4) are obtained as follows.

(Formula 1)
dz1 = PFIk (X _i-1 ) −PFIk (X _i-2 )
_{dz2 = PFIk (X i) -PFIk} (X i-1)
dz3 = PFIk (X _{i + 1} ) −PFIk (X _i )
dz4 = PFIk (X _{i + 2} ) −PFIk (X _{i + 1} )
Based on the first differential value thus obtained, the number of data is compressed by gradation tables TBL1, TBL2, TBL3, and TBL4 prepared in advance (preferably prepared for each ink (CMYK)). (Reduction of the number of gradations) and correction reflecting the characteristics of each ink are performed (S42 in FIG. 19). For each of the primary differential values (dz1, dz2, dz3, dz4), corresponding gradation tables TBL1, TBL2, TBL3, TBL4 are prepared.

(Formula 2)
tz1 = TBL1 (dz1)
tz2 = TBL2 (dz2)
tz3 = TBL3 (dz3)
tz4 = TBL4 (dz4)
Next, the suitability for the candidate positions of the four data sets is calculated with respect to these four corrected primary differential values (tz1, tz2, tz3, tz4).

  FIG. 20A is a table showing the relationship between the matching function table for determining the line position of less than one pixel and the position in units of less than one pixel. FIG. 20B shows the pixel position and candidate position of the read image. The arrangement relationship is shown schematically. In the example shown in FIG. 20A, the gradation tables TBL1_01 to TBL4_19 correspond to a total of 19 candidate positions in the range of −0.9 to +0.9 in increments of 0.1 pixels in the X direction. The candidate position is set in the reading direction in units of less than one pixel based on the reading pixel pitch, and includes the corresponding position (0) of the test pattern 102 in the reading pixel pitch unit. That is, “0” shown in FIGS. 20A and 20B indicates the pixel position of the read image, and the closer to “−0.9”, the closer to the pixel position of the read image adjacent to the left side in the X direction. This indicates a position closer to the pixel position of the read image adjacent to the right side in the X direction as it approaches “+0.9”.

  FIG. 21 is a graph showing the basic shape (basic concept) of the fitness function table TBLi_j (i = 1 to 4, j = 01 to 19), and the X-axis shows the input value (gradation value, first derivative value). The Y axis indicates the degree of fitness.

  The “degree of conformity” here is an index representing the possibility of arrangement of line patterns, and indicates the probability that the target line pattern exists at the corresponding candidate position. The fitness distribution with respect to the candidate position can be appropriately determined by various methods. For example, the fitness distribution can be obtained according to the following S1 to S6.

  S1) The line optical density distribution is determined on the computer based on the characteristics (drawing resolution, optical density, dot diameter, dot distribution, etc.) of the printer apparatus (inkjet recording apparatus 10).

  S2) Regarding an ideal line profile, based on the characteristics of the reader (reading resolution, aperture response, MTF, etc.), a read image is calculated from the optical density distribution on the computer, and the line profile is further determined on the computer. .

  S3) A predetermined feature amount is determined based on the line profile on the computer.

  S4) By executing S1 to S3 while changing the line position, a set of positions on the computer (correct position) for a predetermined feature amount is obtained.

  S5) Repeat calculation of S1 to S4 while changing disturbance factors (optical density fluctuation, dot diameter fluctuation, dot distribution fluctuation, reading noise, magnification fluctuation, etc.), and correct probability distribution (fitness) for a predetermined feature amount To decide. At this time, how to give the fluctuation is adjusted based on the characteristics of the printer / reader.

  S6) The probability distribution (goodness of fit) obtained in S5 is fitted according to the characteristics of the system. The system characteristics here are resources that can be allocated to maintain and use the probability distribution, and the reason for adopting a simple trapezoidal shape, as will be described later, is that data points can be reduced. It is. If resources are given, the distribution obtained by calculation can be used as it is.

  In this example, as shown in FIG. 21, the fitting function table TBLi_j has a trapezoidal shape, and four values fmin2, fmin1, fmax1, and fmax2 that define the trapezoid are respectively the lower left side, the upper side left, and the upper side of the trapezoid. The right side corresponds to the lower right side, and the upper side of the trapezoid corresponds to a goodness of fit. By using the fitness function table TBLi_j, the fitness (Pi) for the input value (Xi) of the primary differential value (tzi, i = 1 to 4) can be obtained.

  FIG. 22 is a graph showing a plurality of fitness function characteristics for performing position determination in units of less than one pixel, and corresponds to the first primary differential value tz1. The X axis indicates the position of the reading pixel pitch in units of less than one pixel, the Y axis indicates the input value (gradation value, first derivative value), and the above four values fmin2, fmin1, fmax1, and fmax2 that define the adaptation function table Is plotted. In FIG. 22, each of the 19 straight lines extending in the Y direction indicates a function table (fit function table) indicating the fitness (fit function characteristics) corresponding to candidate positions j = 01 to j = 19 in order from the left. A vertical section (vertical characteristics) at the candidate position j (j = 01,..., 19) indicates a trapezoidal shape (see FIG. 21) related to TBL1_j (j = 1,..., 19).

  Similarly, FIG. 23 to FIG. 25 are graphs showing a plurality of fitness function characteristics for determining the position of less than one pixel, FIG. 23 corresponds to the second primary differential value (tz2), and FIG. This corresponds to the third primary differential value (tz3), and FIG. 25 corresponds to the fourth primary differential value (tz4).

  In this way, the first to fourth primary differential values (tz1 to tz4) derived from the read data at the position of the test pattern 102 and the adjacent pixel positions are associated with each of the plurality of candidate positions. Calculated as described above. That is, a plurality of sets of goodness of fit are derived for each candidate position.

  Then, the product of the set of fitness (TBL1_j (tz1), TBL2_j (tz2), TBL3_j (tz3), TBL4_j (tz4)) of the first to fourth primary differential values (tz1 to tz4) thus obtained. From this, the total fitness Pj at each candidate position j (j = 01 to 19) is calculated (S44 in FIG. 19). At this time, the product of the fitness (TBL1_j (tz1), TBL2_j (tz2), TBL3_j (tz3), TBL4_j (tz4)) is calculated for each candidate position j (j = 01 to 19).

(Formula 3)
Pj = TBL1_j (tz1) × TBL2_j (tz2) × TBL3_j (tz3) × TBL4_j (tz4) (j = 01,..., 19)
Then, a candidate position corresponding to the set of fitness levels having the highest probability that the test pattern 102 exists is detected as a candidate position indicating the best fitness level. That is, in order to obtain the candidate position with the best adaptability, the maximum value Pm of the overall fitness Pj (j = 01,..., 19) calculated for each candidate position is obtained (FIG. 19). S46) A position m indicating the maximum value Pm (position Q in units of less than one pixel of the read pixel pitch) is determined from the candidate positions j (j = 01,..., 19) (S48 in FIG. 19). At this time, when there are a plurality of maximum values, the average value of the candidate positions indicating the maximum value is obtained. For example, when P4, P5, and P6 indicate the maximum value, (4 + 5 + 6) / 3 = 5 (average value) Is required. If the average value obtained at this time is not an integer, for example, the position of the read pixel pitch corresponding to the integer part of the average value is set to Q1, and the position of the read pixel pitch corresponding to the integer part +1 of the average value is defined as Q1. A position of less than one pixel can be determined by Q = Q1 × (1−s) + Q2 × s, where Q2 is a position in units of less than one pixel and s is a fractional part of the average value.

In this way, with respect to all “pixel positions X _i having a read signal value smaller than the threshold value T1 of the graph G1 (see FIG. 18)” in the line block 146, the position Q in units of less than one pixel of the read pixel pitch. Is calculated.

  Then, based on the relationship between the calculated line position of the test pattern 102 and the reference position (test pattern corners CL1, CR1, CL2, CR2 (see FIG. 16)), the relationship between the line position and the corresponding nozzle number is determined. Identified. The rotation angle of the test pattern 102 and the magnification error in the X direction and the Y direction are calculated from the positional relationship between the test pattern corners CL1, CR1, CL2, and CR2.

  Further, since the layout of the test pattern 102 can be handled as known information, the position of each nozzle within the line block position (relative position from the test pattern corner CL1 (corresponding)) from the known test pattern design information. Is required. As shown in FIG. 26, as the line position of the test pattern 102, the relative position Rd on the read image from the test pattern corner CL1 is calculated based on the previously obtained magnification error and rotation angle, and from this calculated value Rd. The coordinates on the profile can be obtained.

  The distance from the test pattern 102 line position (one pixel unit and less than one pixel) already obtained by profile binarization to the coordinates on the profile of each nozzle based on the test pattern design information obtained in this way And the line position of the test pattern 102 corresponding to each nozzle is obtained (S30 in FIG. 14).

  Next, an adjacent line position for each line of the test pattern 102 is obtained, and an average position of a plurality of adjacent lines is adopted as a reference position (S32 in FIG. 14).

  FIG. 27 is a diagram illustrating an example of a method for calculating the reference position, and illustrates a method for calculating the reference position from the positions of adjacent lines (test patterns) on both sides. FIG. 28 is a diagram showing another example of the method for calculating the reference position, and shows a method for calculating the reference position from the position of the adjacent line (test pattern) on one side.

  In this example, when the test patterns are arranged at substantially equal intervals, the average position of the test pattern 102 derived from the positions of the same number of nozzles on the left and right of the target nozzle is adopted as the reference position. For example, in the example shown in FIG. 27, the position of the target line (test pattern) 102c is P3 + e3, the positions of the two adjacent lines 102a and 102b on the left side are P1 + e1 and P2 + e2, and the two adjacent lines 102d and 102e on the right side. When the positions are P4 + e4 and P5 + e5, the reference position P3s of the line of interest 102c is obtained by the following equation.

(Formula 4)
P3s = (P1 + e1 + P2 + e2 + P4 + e4 + P5 + e5) / 4
= (P1 + P2 + P4 + P5) / 4 + (e1 + e2 + e4 + e5) / 4
For the test patterns at the end where the same number of adjacent test patterns do not exist on the left and right, multiple reference lines (reference nozzles) are set on the side where each line of the test pattern is a certain number or more, and the line average pitch Based on the (nozzle average pitch) and line number difference (nozzle number difference), obtain the expected position for each reference line (reference nozzle), and calculate the average value of the expected positions for multiple reference lines (reference nozzles). The reference position. For example, in the example shown in FIG. 28, the position of the target line (test pattern) 102a is P1 + e1, the position of the next adjacent reference line (reference nozzle) 102b is P2 + e2, and the next adjacent reference line (reference nozzle) 102c. If the position is P3 + e3, the position of the next adjacent reference line (reference nozzle) 102d is P4 + e4, and the position of the next adjacent reference line (reference nozzle) 102e is P5 + e5, the reference position P1s of the target line 102a is It is calculated by the formula.

(Formula 5)
P1s = ((P2 + e2-L) + (P3 + e3-L × 2) + (P4 + e4-L × 3) + (P5 + e5-L × 4)) / 4
In the above, e1 to e5 indicate error components, and assuming that a normal distribution is assumed, by averaging these error components (for example, by (e1 + e2 + e4 + e5) / 4), the influence of these errors is sufficiently reduced. Can be expected. If a line (test pattern 102) due to defective ejection nozzles (non-ejection nozzles) is included in the above calculation, the above calculation is performed using the expected value of each line (nozzle) instead of the actual measurement value. May be performed. Further, the number of test pattern lines (number of nozzles) used in the calculation can be changed, and the above calculation may be performed using data of three or more adjacent lines (adjacent nozzles). The above calculation may be performed using data of lines (nozzles) included in other adjacent nozzle blocks.

  Then, for each line position of the test pattern obtained in this way, the difference between the reference position and the measured position is calculated (S34 in FIG. 14). From this difference, it is determined whether or not the actual landing position (line position) of each test pattern is separated from the reference position by a predetermined distance or more, and if it is separated by a predetermined distance or more, it is detected as a defective ejection nozzle.

(Overall process flow)
As described above, according to the ink jet recording apparatus of the present embodiment, it is possible to accurately grasp the landing position of the ink droplet ejected from each nozzle on the recording paper, and thus a precise correction process for compensating for the landing position error. Can be applied to the input image data. The overall process flow based on the various processes described above will be described below.

  FIG. 29 is a flowchart showing the overall flow of image printing. When input image data of a desired image sent from the host computer 86 (see FIG. 6) is received via the communication interface (reception means) 70 (reception step in S60 of FIG. 29), color conversion processing (FIG. 9). Color conversion processing unit 110), defective ejection nozzle correction processing (non-ejection nozzle correction image processing unit 112), halftone processing (halftone processing unit 114), test pattern synthesis processing (test pattern synthesis unit 118), and the like. Data is corrected (correction step of S62). Therefore, in this example, the correction processing means for correcting the input image data includes the color conversion processing unit 110, the non-ejection nozzle correction image processing unit 112, the halftone processing unit 114, and the test pattern synthesis unit 118 of FIG. ing.

  Then, based on the corrected input image data, the head driver 84 ejects ink droplets from the nozzles 51 of the heads 50 toward the recording paper 16 (ejection step of S64), thereby clearly recording a desired image. It can be printed on paper 16.

  In the correction step (S62), the ejection of ink droplets from the defective ejection nozzle is compensated by other normal nozzles, and a defective ejection nozzle correction process (non-deletion) is performed to prevent the ejection of ink droplets from the defective ejection nozzle. A discharge nozzle correction image processing unit 112) is performed on the input image data. The defective ejection nozzle correction process is performed based on the read image data of the test pattern 102 sent from the test pattern reading unit 136 in the defective ejection nozzle detection unit 132 (see FIG. 9).

  FIG. 30 is a flowchart showing a flow of defective ejection nozzle detection. First, a plurality of test patterns 102 (see FIG. 10) corresponding to each of the nozzles 51 is printed on the recording paper 16 by ink droplets ejected from the nozzles 51 based on image data that has passed through the test pattern synthesis unit 118 (see FIG. 9). (The pattern forming step in S70 of FIG. 30). Then, the image of the test pattern 102 is read, and the recording position of each test pattern 102 is detected (pattern position detection step in S72). The detected recording position of the test pattern 102 is compared with the reference position (see FIGS. 27 and 28), and whether or not the test pattern 102 is separated from the reference position by a predetermined distance or not (whether the distance difference from the reference position is a predetermined threshold or more). ), It is detected whether or not the nozzle 51 corresponding to the test pattern 102 to be compared is a defective ejection nozzle (defective nozzle detection step in S74). Since the detection of the defective ejection nozzle is basically performed for all the nozzles 51 of the head 50, not only the nozzle that has changed from the normal state to the defective discharge state but also the nozzle that has changed from the defective discharge state to the normal state. Can also be detected appropriately (see the defective ejection nozzle determination unit 130 in FIG. 9). Note that the reference position serving as a reference for the landing position of the ink droplet on the recording paper 16 is set for each of the nozzles 51 (test pattern 102).

  Note that whether or not the nozzle is a non-ejection nozzle that cannot record a test pattern on a recording medium without ejecting ink droplets is also appropriately determined based on the presence or absence of the corresponding test pattern.

  In the pattern position detection step (S72), the corresponding position of the test pattern 102 is detected based on the reading resolution (reading pixel pitch) of the scanner (see the test pattern reading unit 136 in FIG. 9) which is a reading device. The position of the test pattern 102 cannot be directly detected in units smaller than one pixel of the reading resolution. Therefore, as described above, the position of the test pattern 102 is calculated in units of less than one pixel of the reading resolution (reading pixel pitch) based on a predetermined algorithm.

  FIG. 31 is a flowchart illustrating an example of an algorithm for detecting the position of the test pattern 102 in units of less than one pixel of reading resolution (reading pixel pitch). FIG. 32 is a functional block diagram showing a functional configuration of a defective ejection nozzle detection unit (see FIG. 9) that processes the algorithm of FIG.

  The recording paper 16 on which the test pattern 102 is formed is read in a predetermined reading direction (X direction) at a predetermined reading pixel pitch by a scanner (test pattern reading unit 136 in FIG. 9), and a test pattern based on the reading pixel pitch. The read data 102 is sent to the defective ejection nozzle detector 132 (reading step in S80 of FIG. 31).

  Then, in the pixel unit position specifying unit (read pixel position acquisition unit) 162 of the defective ejection nozzle detection unit 132, the corresponding position (corresponding position of the read pixel unit) of the test pattern 102 based on the read pixel pitch is acquired from the read data. (Reading pixel position acquisition step of S82). Specifically, the corresponding position of the test pattern 102 is obtained based on the gradation value change (optical density change) in the read image data (see FIG. 18).

  Then, in the differential value calculation unit (feature value acquisition unit) 164 of the defective ejection nozzle detection unit 132, the gradation at the corresponding position of the test pattern 102 and the adjacent pixel position adjacent to the corresponding position based on the read pixel pitch. A first derivative value (feature value) of the value is calculated from the read data (feature value acquisition step in S84). In this example, tone number conversion processing is applied to these primary differential values at this stage.

  Then, in the fitness level deriving unit (fit level deriving unit) 166 of the defective ejection nozzle detection unit 132, the fitness function table (gradation value (primary differential value) / satisfaction level table, FIG. 20A) and FIGS. Referring to FIG. 5), the fitness at each of the plurality of candidate positions is derived from the primary differential value of the gradation value at the corresponding position of the test pattern 102 and the adjacent pixel position (the fitness derivation step of S86). The matching function table used here is prepared in advance for each of the corresponding position and adjacent pixel position of the test pattern 102, and a plurality of candidate positions having a pitch shorter than the read pixel pitch (FIG. 20B). ) Reference), and the degree of conformity indicating the arrangement possibility of the test pattern 102 and the first derivative value are associated with each other.

  Then, the sub-pixel unit specifying unit (candidate position acquisition unit) 168 of the defective ejection nozzle detection unit 132 detects a candidate position indicating the best matching level based on the matching levels at each of the plurality of derived candidate positions. Then, the corresponding position of the test pattern 102 in units of less than one pixel of the read pixel pitch is acquired (candidate position acquisition step in S88).

  Then, in the recording position calculation unit (recording position acquisition unit) 170 of the defective ejection nozzle detection unit 132, the corresponding position (S82) of the line pattern based on the read pixel pitch and the candidate position (the best matching degree detected) From (S88), the recording position of the line pattern on the recording medium is calculated (recording position acquisition step of S90). That is, the position in units of the read pixel pitch among the recording positions of the test pattern 102 is acquired from the corresponding position (S82) based on the read pixel pitch obtained from the read data of the scanner, and is the position in units of less than one pixel based on the read pixel pitch. Is acquired from the candidate position (S88) indicating the best matching degree.

  In this way, the recording position of the test pattern 102 detected with high accuracy in units of less than one pixel of the reading pixel pitch is the reference position (FIG. 27) in the defective nozzle detection unit (defective nozzle detection means) 172 of the defective discharge nozzle detection unit 132. In addition, it is detected whether or not the nozzle is a defective ejection nozzle (see S74 in FIG. 30). Information relating to the defective ejection nozzle is sent as defective ejection nozzle data from the defective ejection nozzle detection unit 132 to the defective ejection nozzle determination unit 130, and is used for correction processing of input image data.

  Next, the print layout on the recording paper will be described. FIG. 33 is a diagram illustrating a layout on a print sheet in a system that detects and corrects defective ejection nozzles.

  The recording paper 16 is divided into a detection driving waveform area 150 and a normal driving waveform area 152 provided at the end of the paper. The detection drive waveform area 150 includes a test pattern area 154 and a blank area 156 for printing the test pattern 102 described above, and the normal drive waveform area 152 includes a user area 158 for printing a desired image. Consists of.

  A blank area 156 provided between the test pattern area 154 and the user area 158 is a transition section for switching from test pattern printing to normal printing, and is necessary for the switching based on the conveyance speed of the recording paper 16. The area is secured as a blank area 156. In particular, when a test pattern is formed in the test pattern area 154 using a special drive waveform signal, a blank area corresponding to the time required to switch from the special drive waveform signal to the normal drive waveform signal Is secured. It is preferable that the margin area 156 is provided at least as much as the nozzle area 160 of the head 50 with respect to the conveyance direction C of the recording paper. Note that a special drive waveform signal for printing the test pattern 102 is used to make it easy to distinguish between a defective discharge nozzle and a normal discharge nozzle. It is preferable to use a specially designed drive waveform signal that facilitates functioning as a non-ejection nozzle.

  As described above, according to the present embodiment, based on the gradation value (primary differential value) having a correlation with the test pattern 102, a position having a high degree of matching with the test pattern 102 is determined from the plurality of candidate positions with the read pixel pitch. It can be obtained with accuracy in units of less than one pixel. As a result, the position in units of less than one pixel can be determined from very little pixel information, and even if the reading resolution of the image reading device (test pattern reading unit 136) is low, it is higher than the reading resolution of the image reading device. The position of the test pattern 102 can be specified with the resolution of. Therefore, a relatively inexpensive low-resolution image reading apparatus can be used, and it is possible to achieve both cost reduction of the apparatus and high image reading accuracy.

  Then, it is possible to accurately detect a nozzle with defective ejection from the recording position of the test pattern 102 that can be accurately obtained in units of less than one pixel of the read pixel pitch. Therefore, it is possible to stop defective ejection nozzles that have large landing position errors and cause image quality problems, and to perform image correction for these defective ejection nozzles appropriately, resulting in high-quality images that more reliably prevent streaks and unevenness. It can be printed on a recording medium.

  In particular, in an ink jet recording apparatus (liquid ejecting apparatus) such as the present embodiment that detects defective ejection nozzles from the recording position of the test pattern 102, an image reading with a compact structure is possible because the arrangement space of each unit is limited. A device is desirable. Therefore, according to an image reading apparatus having a simple configuration with low resolution, the configuration of the apparatus can be simplified, and thus the technique according to the present embodiment is very useful.

  Note that the above-described embodiment only shows one aspect of the present invention, and the present invention can be applied to other methods and apparatuses.

  For example, in the above-described embodiment, an example in which the present invention is applied to an ink jet recording apparatus has been described. However, a coating apparatus, a coating apparatus, a wiring drawing apparatus, a fine structure forming apparatus, and the like that discharge liquid from a plurality of discharge units. The present invention can also be applied to other apparatuses, and can be widely applied as a technique for measuring the liquid landing position on the ejection target medium.

Moreover, although the example using the density gradation value (primary differential value) as the feature value correlated with the test pattern (line pattern) has been described, other factors may be used as the feature value. For example, various values calculated based on gradation values can be used as feature values. For example, (1) a value Y (Y = αR × R + αG ×) calculated by mixing values derived from RGB color data. G + αB × B + αC), and the gradation value D converted by a predetermined table (ScannerLUT: look-up table for removing individual differences in the gradation characteristics of the scanner) D ′: D ′ = ScannerLUT [D], adjacent to each other The ratio R _{(Di / Di + 1)} (R _{(Di / Di + 1)} = D _i / D _{i + 1} ) between the gradation values (D _i and D _{i + 1} ) of the adjacent pixels (i and i + 1) may be used as the feature value. Good. Of course, a ratio of values calculated based on the gradation value may be used as the feature value. Further, for example, the relationship between the read pixel pitch and the position in units of less than one pixel may be narrowed down by a statistical process such as a correlation coefficient, or a feature value having a high correlation may be used using a data mining technique. For example, when the feature amount D _i × D _{i + 1} ×... × D _{i + k} (k is a different candidate such as 1, 2, 3, 4) before being narrowed down by data mining, (D _i × D _{i + 1} ×... × D _{i + k} ) ^{1 / (k + 1)} (k is a different candidate such as 1, 2, 3, 4 respectively) can also be used as the feature value.

  In the above example, the candidate position indicating the best matching degree is specified based on the product of the matching degree at the corresponding position of the test pattern and the adjacent pixel position (see Equation 3). You may identify from the value (value which added inclination according to a position) which multiplied the predetermined coefficient.

  In the above example, the feature value is calculated from the read data at a total of four adjacent pixel positions at two positions before and after the corresponding position of the test pattern, but the read data at more adjacent pixel positions and fewer adjacent pixel positions. The feature value may be calculated from the read data.

  Further, the method for obtaining the fitness distribution is not limited to the above example, and various methods can be used. For example, the fitness distribution can be obtained by the following simple method. In other words, the line profile is defined as a simplified graphic (eg, triangle, trapezoid, etc.), and the graphic variation (eg, “graphic height” corresponds to the line profile density, and “graphic width” corresponds to the line profile width. “Graphic deformation” corresponds to the asymmetry of the dot distribution). Then, a feature amount is calculated by giving a variation to the defined figure, and a variation corresponding to noise at the time of reading is given to the feature amount. Then, the center position of the figure is defined as the center of gravity position before the change. As described above, the relationship between the feature amount and the center position can also be obtained as described above.

  The fine pattern position detection method, the defective nozzle detection method, and the liquid ejection method according to the present embodiment cause the system controller 64, the print control unit 80, or another control unit of the inkjet recording apparatus 10 to perform the above processing. The present invention can also be realized as a computer program, a recording medium on which the computer program is recorded, or a program product.

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feeding part, 20 ... Decal processing part, 22 ... Belt conveyance part, 26 ... Paper discharge part, 30 ... Heating drum, 31 ... roller, 33 ... belt, 34 ... adsorption chamber, 35 ... fan, 36 ... belt cleaning unit, 40 ... heating fan, 42 ... post-drying unit, 44 ... pressure unit, 45 ... pressure roller, 50 ... head, 51 ... nozzle, 52 ... pressure chamber, 53 ... ink chamber unit, 54 ... supply port, 55 ... common flow path, 57 ... individual electrode, 58 ... actuator, 70 ... communication interface, 72 ... system controller, 74 ... Image memory, 75 ... ROM, 76 ... Motor driver, 78 ... Heater driver, 80 ... Print control unit, 82 ... Image buffer memory, 84 ... Head driver, 86 ... Host Computer ... 88 ... motor 89 ... heater 102 ... test pattern 104 ... ideal landing position 106 ... reference position detection bar 110 ... color conversion processing unit 112 ... non-ejection nozzle correction image processing unit 114 ... half Tone processing unit 118 ... test pattern synthesis unit 120 ... correction information setting unit 122 ... defective ejection correction determination unit 124 124 image analysis unit 126 ... defective nozzle information storage unit 130 130 defective ejection nozzle determination unit 132 Defective ejection nozzle detection unit 134... Defective ejection detection display unit 136. Test pattern reading unit 140. Reference position detection window 142. Projection graph 144 144 Test pattern corner 146 Line block 148 Analysis region 150 ... Detection drive waveform area, 152 ... Normal drive waveform area, 154 ... Test pattern area, 56 ... margin area, 158 ... user area, 160 ... nozzle area, 162 ... pixel unit position specifying section, 164 ... differential value calculating section, 166 ... fitness degree deriving section, 168 ... sub-pixel unit specifying section, 170 ... recording position calculation Part, 172... Defective nozzle detection part

Claims (15)

A reading step of reading the recording medium on which the line pattern is formed at a predetermined reading pixel pitch in a predetermined reading direction to obtain read data;
A read pixel position acquisition step of acquiring a corresponding position of the line pattern based on the read pixel pitch from the read data;
A feature value acquisition step of acquiring, from the read data, a feature value at the corresponding position of the line pattern and a feature value at an adjacent pixel position adjacent to the corresponding position based on the read pixel pitch;
A matching function prepared in advance for each of the corresponding position and the adjacent pixel position of the line pattern, and prepared for each of a plurality of candidate positions having a pitch shorter than the read pixel pitch; From the feature value at the corresponding position of the line pattern and the feature value at the adjacent pixel position, using a matching function in which the degree of matching representing the arrangement possibility of the line pattern and the feature value are associated with each other. A fitness deriving step for deriving the fitness at each of a plurality of candidate positions;
A candidate position acquisition step of detecting a candidate position indicating the best matching degree based on the matching degree in each of the plurality of derived candidate positions;
A recording position acquisition step of calculating a recording position of the line pattern on the recording medium from the corresponding position of the line pattern based on the read pixel pitch and the candidate position indicating the best matching degree detected. ,
The fine pattern position detection method characterized by including. The plurality of candidate positions are set in the reading direction in units of less than one pixel based on the reading pixel pitch,
In the recording position acquisition step, the recording position of the line pattern is obtained from the corresponding position based on the read pixel pitch, and the position in units of less than one pixel based on the read pixel pitch. The fine pattern position detection method according to claim 1, wherein the fine pattern position detection method is obtained from the candidate position showing the best degree of matching. The fitness is an index indicating the probability that the line pattern exists at a corresponding candidate position,
In the candidate position acquisition step, the line pattern is present among a plurality of sets of the fitness values derived from the feature values at the corresponding position of the line pattern and the adjacent pixel positions at each of the plurality of candidate positions. 3. The fine pattern position detection method according to claim 1, wherein a candidate position corresponding to a set of matching degrees having the highest probability is detected as a candidate position showing the best matching degree.   4. The fine pattern position detection method according to claim 1, wherein the line pattern formed on the recording medium has a width substantially equal to the reading pixel pitch in the reading direction.   4. The fine pattern position according to claim 1, wherein the line pattern formed on the recording medium has a width of 3 to 5 times the reading pixel pitch with respect to the reading direction. 5. Detection method.   The feature value at the corresponding position of the line pattern and the feature value at the adjacent pixel position are set to the read pixel pitch with respect to the read data at the corresponding position of the line pattern and the corresponding position of the line pattern. 6. The fine data according to claim 1, wherein the fine data is calculated from the read data at the two adjacent pixel positions adjacent to the front side and two adjacent to the rear side based on the reading direction. Pattern position detection method. In the reading step, read data relating to optical density is acquired,
The fine pattern position detection method according to claim 1, wherein the feature value is based on an optical density.   The fine pattern position detection method according to claim 1, wherein the feature value is based on a first-order differential value of the read data. On the recording medium, a detection bar extending continuously in the reading direction and having a predetermined width is formed so as to correspond to the line pattern,
In the reading step, the line pattern and the detection bar are simultaneously read, and the reading data relating to optical density is acquired,
In the read pixel position acquisition step, the position of the detection bar is obtained from a change in optical density indicated by the read data, and from the relative positional relationship between the detection bar and the line pattern and the obtained position of the detection bar, The fine pattern position detection method according to claim 1, wherein the corresponding position of the line pattern is acquired. A defective nozzle detection method including the fine pattern position detection method according to claim 1,
A pattern forming step of forming a plurality of the line patterns corresponding to each of the nozzles on the recording medium by liquid discharged from the plurality of nozzles;
A reference position which is a reference position of the landing position of the liquid on the recording medium and set for each of the plurality of nozzles, and the recording of the line pattern calculated in the recording position acquisition step A defective nozzle detection step for detecting a defective discharge nozzle from the plurality of nozzles from a position;
A defective nozzle detection method comprising:   The defective nozzle detection method according to claim 10, wherein the reference position is calculated based on the recording positions of the adjacent line patterns. A liquid ejection method comprising the defective nozzle detection method according to claim 10 or 11,
A receiving step for receiving input data;
A correction step for correcting the received input data;
A discharge step of discharging the liquid from the plurality of nozzles based on the corrected input data,
In the correction step, the input data is corrected so that the discharge of the liquid from the defective discharge nozzle detected in the defective nozzle detection step is compensated by another nozzle and the liquid is not discharged from the defective discharge nozzle. A liquid discharge method characterized by that. Reading means for reading the recording medium on which the line pattern is formed in a predetermined reading direction at a predetermined reading pixel pitch, and acquiring read data;
Read pixel position acquisition means for acquiring a corresponding position of the line pattern based on the read pixel pitch from the read data;
Feature value acquisition means for acquiring, from the read data, a feature value at the corresponding position of the line pattern and a feature value at an adjacent pixel position adjacent to the corresponding position based on the read pixel pitch;
A matching function prepared in advance for each of the corresponding position and the adjacent pixel position of the line pattern, and prepared for each of a plurality of candidate positions having a pitch shorter than the read pixel pitch; From the feature value at the corresponding position of the line pattern and the feature value at the adjacent pixel position, using a matching function in which the degree of matching representing the arrangement possibility of the line pattern and the feature value are associated with each other. Goodness-of-fit deriving means for deriving the goodness of fit at each of a plurality of candidate positions;
Candidate position acquisition means for detecting a candidate position showing the best degree of matching based on the degree of matching at each of the derived candidate positions;
Recording position acquisition means for calculating the recording position of the line pattern on the recording medium from the corresponding position of the line pattern based on the read pixel pitch and the candidate position indicating the best matching degree detected. ,
A fine pattern position detection apparatus comprising: A defective nozzle detection device including the fine pattern position detection device according to claim 13,
Pattern forming means for forming a plurality of the line patterns corresponding to each of the nozzles on the recording medium by liquid discharged from the plurality of nozzles;
A reference position that is a reference position of the landing position of the liquid on the recording medium and is set for each of the plurality of nozzles, and the recording of the line pattern calculated by the recording position acquisition unit A defective nozzle detection means for detecting a defective ejection nozzle from the plurality of nozzles from a position;
A defective nozzle detection device comprising: A liquid ejection apparatus including the defective nozzle detection apparatus according to claim 14,
Receiving means for receiving input data;
Correction means for correcting the received input data;
Discharge means for discharging the liquid from the plurality of nozzles based on the corrected input data,
The correction unit compensates the discharge of the liquid from the defective discharge nozzle detected by the defective nozzle detection unit by another nozzle and corrects the input data so that the liquid is not discharged from the defective discharge nozzle. A liquid discharge apparatus characterized by: