JP2005096447A - Inkjet recording apparatus and discharge fault detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus and a discharge fault detecting method which quickly detect a discharge fault of a nozzle such as non-discharge of ink, and correct the poorly discharging nozzle. <P>SOLUTION: Test patterns in respective colors are printed by respective print heads 12 in a test printing area of a recording sheet 16. The test patterns are read with sensors 41 provided just behind the respective print heads 12, and a poorly discharging nozzle in the print heads 12 is detected with the images. When the poorly discharging nozzle is detected, an image correction and a recovery operation of the poorly discharging nozzle are made. Thus, the poorly discharging is detected immediately after printing, which enables an early aid for the image. The poorly discharging nozzle is detected in such a way that the sensors 41 are disposed opposite to the print heads 12 respectively, a test printing is carried out between a current practical printing and the next practical printing, and an image formed in the test printing is read out with a sensor 41. When the poorly discharging nozzle is detected in the test printing, its correction is applicable to the first practical image thereafter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inkjet recording apparatus and a discharge failure detection method, and more particularly to a discharge failure detection technique of an inkjet recording apparatus using a line head in which a plurality of recording elements are arranged in one direction.

  In recent years, inkjet recording apparatuses (inkjet printers) have become widespread as recording apparatuses that print and record images taken by digital still cameras. The ink jet recording apparatus is relatively inexpensive and not only easy to handle, but also has an advantage that an image with good image quality can be obtained. An ink jet recording apparatus includes a plurality of recording elements in a head, and scans the recording head while ejecting ink droplets from the recording elements onto the recording medium. When an image is recorded for one line on the recording paper, the recording medium is recorded for one line. By conveying and repeating this process, an image is formed on the recording paper.

  Inkjet printers use a single serial head and perform recording while scanning the head in the width direction of the recording medium, or a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium Some use In the case of using a line head, image recording can be performed on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements. A printer using a line head does not require a carriage system such as a carriage that scans a short head, and does not require complicated scanning control between the movement of the carriage and the recording medium. Further, since only the recording medium moves, the recording speed can be increased as compared with a printer using a serial head.

  On the other hand, in an inkjet recording apparatus equipped with a full line head, streaks and unevenness may occur in the sub-scanning direction, which is the conveyance direction of the print medium, and the print quality may deteriorate. This is an ink jet recording with a full line head that can perform printing for one line in the main scanning direction orthogonal to the sub scanning direction at a time, and prints the entire printing area in one scanning in the sub scanning direction. In the device, if there are nozzles that do not eject ink droplets, or nozzles that vary in the direction and amount of ink droplet ejection, the dots that should be ejected from that nozzle may not be ejected, or the droplet ejection position may be shifted. It is a phenomenon that occurs because of Various methods have been proposed for finding such an inappropriate nozzle and suppressing the influence on the printing result.

  In the image recording method and apparatus and the recorded product and processed product thereof disclosed in Patent Document 1, the shuttle head scans with the recording head and reads the recorded image recorded on the recording medium, and the reading unit reads the recorded image. And a determination unit that determines a defective recording position from the recorded image, and is configured to supplement the recording defective position determined by the determination unit by subsequent scanning by the supplementary recording unit.

In addition, the ink jet recording apparatus disclosed in Patent Document 2 has a reading unit disposed rearward with respect to the recording scanning direction of the recording head, and an ink discharge state by an identification unit from an image read by the reading unit. And a predetermined recovery operation is performed on the recording element determined to be non-ejection by the determining means.
JP-A-5-301427 JP-A-6-143548

  However, when the nozzle density is increased, it is difficult to accurately determine ink droplet ejection, non-ejection, ejection direction, and ejection amount for each nozzle, and which nozzle is inappropriate. It is difficult to determine accurately. If there is an erroneous detection of an inappropriate nozzle, the recovery operation is not performed on the nozzle that originally needs the recovery operation, and the nozzle may not recover in the predetermined recovery operation. In addition, if a recovery operation is performed on a nozzle that originally does not require a recovery operation, ink is wasted.

  In the image recording method and apparatus disclosed in Patent Document 1, and the recorded product and processed product thereof, a shuttle head that performs printing while scanning in the main scanning direction is applied to the recording head. Since there is no subsequent scanning in the scanning direction, the defective recording position cannot be corrected.

  In the ink jet recording apparatus disclosed in Patent Document 2, the light receiving element and the recording element have the same resolution. For example, when large droplets are ejected from all nozzles, the ink is ejected from adjacent nozzles. It is difficult to read dots one by one because the dots overlap. In addition, the case where two or more colors are used is not disclosed, and two or more colors cannot be distinguished.

  The present invention has been made in view of such circumstances, and provides an inkjet recording apparatus and an ejection failure detection method capable of quickly detecting ejection failure of nozzles such as ink non-ejection and correcting the ejection failure nozzle. Objective.

  In order to achieve the above object, an inkjet recording apparatus according to the present invention includes one or more nozzle rows in which a plurality of nozzles that eject ink are arranged over the entire width of the recording medium in a direction substantially perpendicular to the feeding direction of the printing medium. A full-line recording head corresponding to a plurality of ink colors is provided for each color, and an image formed on the print medium by ejecting ink from the plurality of recording heads provided for the respective colors. A plurality of image reading means for reading is arranged on the downstream side in the feeding direction of the print medium with respect to the recording head of the corresponding color for each color.

  According to the present invention, the recording head provided for each ink color is provided with image reading means for reading an image formed by ink droplets ejected from the corresponding recording head on the downstream side in the print medium conveyance direction. Therefore, immediately after printing, the image on the image forming medium can be read for each color by the image reading means.

  The recording head corresponding to each color includes a recording head for each color of black (K), cyan (C), magenta (M), and yellow (Y), and a recording head of light ink for the four colors. There are several aspects.

  The image reading unit may have a configuration in which a plurality of light receiving element groups are arranged along the main scanning direction. Further, the reading unit may include an illuminating unit that irradiates an image to be read with illumination light.

  As the image reading means, a line sensor in which photoelectric conversion elements are arranged in a line or an area sensor in which photoelectric conversion elements are two-dimensionally arranged in a matrix are used. For these sensors, a CCD solid-state imaging device may be applied, or another imaging device such as a MOS type imaging device may be applied.

  Also, illumination means for illuminating the ink droplets ejected from each nozzle onto the print medium, and an optical member for enlarging the ink droplets ejected from each nozzle onto the print medium and correcting the optical path difference Etc. may be provided.

  In this specification, the term “printing” represents not only the formation of characters but also the concept of forming an image in a broad sense including characters.

  A full-line type recording head is usually arranged along a direction perpendicular to the conveyance direction (sub-scanning direction) of the print medium, but has a predetermined angle with respect to the direction perpendicular to the conveyance direction. There may be a mode in which the recording head is arranged along an oblique direction.

  The print medium is a medium (image-forming medium) that is subjected to printing by a recording head, and is not limited to a continuous sheet, a cut sheet, a seal sheet, a resin sheet such as an OHP sheet, a film, a cloth, or any other material or shape. Includes media.

  The transport means is a mode for transporting the print medium to the stopped (fixed) recording head, a mode for moving the recording head relative to the stopped print medium, or a mode for moving both the recording head and the print medium. Any of these are included.

  Further, the image includes dots (dots), pictures represented by a plurality of dots, characters, and the like.

  According to an aspect of the present invention, the plurality of recording heads include two or more same-color recording heads corresponding to the same-color dark and light inks, and for reading an image ejected by the same-color recording head. The image reading means to be used is common.

  According to this aspect, a part of the image reading means can be shared, and the number of image reading means can be reduced.

  According to this aspect, since the same color recording head can share the image reading means, the number of the image reading means can be reduced, and the control burden can be reduced.

  As an embodiment having dark and light inks, there are six color inks in which light cyan and light magenta, which are light colors of cyan and magenta, in addition to black, cyan, magenta and yellow are added.

  According to another aspect of the present invention, the sensitivity of the common image reading means used for reading an image ejected by the same color recording head is set in accordance with the reading of light ink. It is said.

  According to another aspect of the present invention, a detection unit that detects a discharge failure nozzle from an image read by the image reading unit, and at least an image correction or discharge when a discharge failure nozzle is detected by the detection unit. Discharge defect handling means for performing processing including any one of the recovery operations of the defective nozzle is provided.

  According to this aspect, since the defective ejection nozzle in the recording head can be detected from the image read by the image reading unit, and the predetermined processing is performed when the defective ejection nozzle is detected, the printing is performed. Immediately after that, a defective discharge nozzle can be detected, and correction processing can be performed immediately after the defective discharge nozzle is detected.

  The ejection failure includes non-ejection in which ink droplets are not ejected, ejection amount failure in which the ejection amount of ink droplets is different from a predetermined ejection amount, and abnormal flight direction in which the flight direction of ink droplets deviates from a predetermined direction. Further, these ejection failures can be determined from the position and size of the dots formed by the ink droplets.

  In image correction, there are a mode in which correction is performed immediately after a defective ejection nozzle is detected, and a mode in which printing is stopped and correction is performed from the beginning of the printing.

  For recovery operation of defective ejection nozzles, suction operation for sucking out ink containing bubbles in the nozzle using suction means, preliminary ejection for ejecting ink with increased viscosity in the nozzle to an ink receiver, etc. There is. As the recovery operation, it is preferable to apply a recovery operation suitable for the stage of ejection failure.

  According to still another aspect of the invention, the detection unit detects a defective nozzle in each print head based on a practical print read by the image reading unit, and the defective discharge nozzle handling unit detects the nozzle. It is characterized in that the control is performed to substitute droplets with other normal nozzles for the defective ejection nozzles.

  According to this aspect, the nozzle abnormality is determined at an early stage during practical printing, and immediately recovered by substitution droplet ejection using another normal nozzle, so that the printed matter being printed can be relieved. Further, the nozzle abnormality can be determined without performing the test print, and the print medium is not wasted.

  The practical skill print includes a print (printing) for obtaining a desired print result.

  In the substitute droplet ejection, dots larger than a predetermined size may be ejected, or ink droplets may be ejected obliquely from adjacent nozzles. Substitute droplet ejection is preferably performed by proximity nozzles of the same color.

  According to still another aspect of the present invention, there is provided test print control means for performing control to print a test image in a blank area on the print medium, and the detection means reads the test image by the image reading means. A defective discharge nozzle is detected based on the read result, and the defective discharge nozzle handling means performs a control for ejecting a substitute with another normal nozzle for the detected defective discharge nozzle.

  Since the test print is executed in the blank area, the test print is read by the image reading means, and the ejection failure nozzle is detected by the detection means from the read result, the comparison is made with respect to the print subsequent to the test print. Relief can be made as soon as possible.

  The margin area indicates an area between the actual skill print area and the next actual skill print area.

  The test image is printed in order to determine whether the dot position, size, color, and the like are correctly printed by printing a test image such as a test dot or test pattern. In general, a dedicated test image different from the practical print is printed.

  It is preferable that the test image is printed by filling each color.

  Still further, according to another aspect of the present invention, the test print control means has a value n times a minimum dot interval in a direction substantially perpendicular to the print medium feed direction, where n is a positive integer of 2 or more. When printing a dot having a diameter of 5 mm, a droplet is ejected every (n-1) nozzles in the case of droplet ejection in which one dot row is formed in a direction substantially orthogonal to the print medium feed direction. Control is performed to print a test image for forming n dot rows at a pitch corresponding to n times the minimum dot interval in the print medium feeding direction while changing.

  According to this aspect, when n is a positive integer, dots are ejected every n−1 dots in a direction substantially orthogonal to the print medium feeding direction, and this dot row is ejected by n rows. In addition, droplets can be ejected from all nozzles so that adjacent dots do not overlap, and reading errors can be prevented.

  Another aspect of the present invention is characterized in that the image reading means has a sensor array arranged over the entire width of the print medium in a direction substantially perpendicular to the feeding direction of the print medium.

  According to this aspect, it is possible to read one line in a direction substantially perpendicular to the feeding direction of the print medium by one reading. In order to read the image one dot at a time, the resolution of the image reading means needs to be smaller than the printing resolution of one line in the direction substantially orthogonal to the feeding direction of the printing medium.

  According to another aspect of the present invention, the image reading unit includes a sensor array having a width smaller than the entire width of the print medium in a direction substantially orthogonal to the feeding direction of the print medium. The present invention is characterized in that traveling means for traveling the entire width of the print medium in a direction substantially perpendicular to the medium feeding direction is provided.

  According to this aspect, the image reading means has a sensor array having a width smaller than the entire width of the recording medium in a direction substantially orthogonal to the print medium feeding direction, and the image reading means is substantially orthogonal to the print medium conveyance direction. Since the traveling means for traveling in the direction is provided, even when the number of reading pixels of the image reading means is reduced, ejection defects for the total number of nozzles can be detected by the traveling means.

  The present invention also provides a method invention for achieving the above object. That is, the ejection failure detection method in the ink jet recording apparatus according to the present invention provides the recording in a direction in which a plurality of nozzles that eject ink for each color corresponding to a plurality of ink colors are substantially orthogonal to the feeding direction of the print medium. An ejection failure detection method in an inkjet recording apparatus including a full-line type recording head having one or more nozzle rows arranged over the entire width of a medium, wherein the ink droplets ejected from the nozzles are applied onto the print medium. An image forming process for forming an image, and an image formed on the print medium by the image reading unit disposed on the downstream side in the print medium feeding direction with respect to the recording head of the corresponding color by the image forming process. Image reading process for reading out each color, and detection for detecting defective ejection nozzles from the image read by the image reading process It is characterized in that it comprises a degree, the.

  A mode including an ejection failure coping process that performs image correction processing and nozzle recovery operation processing when a ejection failure nozzle is detected is preferable.

  In order to achieve the above object, an ink jet recording apparatus according to the present invention includes at least one row in which a plurality of nozzles that eject ink are arranged over the entire width of the print medium in a direction substantially perpendicular to the feed direction of the print medium. A full-line type recording head provided for each of a plurality of ink colors having a nozzle row, a test image printing medium arranged to face the nozzle surface of the recording head, and to print a test image from the recording head; An image reading unit that reads the test image formed on the test image print medium and a cleaning unit that removes ink droplets that form the test image on the test image print medium are provided.

  According to the present invention, since the test image printing medium for printing the test image is provided, a printing medium for test printing is unnecessary.

  It is preferable to use a print medium that has been cut to a standard length.

  A transparent or translucent member may be applied to the test image printing medium so that ink droplets (dots) deposited on the front surface can be read by a reading means provided on the back surface side.

  An embodiment is possible in which an optical member is provided between the test image printing medium and the image reading means, and a reading assist function such as enlargement of ink droplets is added by the optical member.

  Further, the print surface of the test image print medium may be disposed substantially parallel to the print surface of the print medium, or may be disposed at an angle with the print surface of the print medium.

  An aspect including a collecting unit that collects ink droplets or the like removed from the test image printing medium by the cleaning unit is preferable.

  The cleaning unit may be a mode in which ink droplets are blown by air, or a mode using a cleaning member such as a blade.

  According to an aspect of the present invention, there is provided a save unit that moves the test image print medium to a predetermined save position.

  According to this aspect, the test image printing means can be placed at a position facing the recording head at the time of test printing, and can be moved to a predetermined retracted position at the time of practical printing, thereby realizing a compact mechanism.

  The retracting means is composed of a transport mechanism including a support guide, a carriage, etc., a motor for driving the transport mechanism, a drive system including a belt, a control system including a microcomputer and a recording element for controlling the drive system, and the like. .

  According to another aspect of the present invention, a full-line type has a plurality of nozzle rows in which a plurality of nozzles that eject ink are arranged over the entire width of the print medium in a direction substantially orthogonal to the feed direction of the print medium. A plurality of recording heads are provided for each color corresponding to a plurality of ink colors, and a plurality of inks are ejected from a plurality of recording heads provided for the respective colors to read an image formed on the test image printing medium. The image reading means is arranged for each color with respect to the recording head of the corresponding color.

  According to this aspect, since the image reading means is provided for each recording head, the image can be read for each color and can be read immediately after printing each color.

  The present invention also provides a method invention for achieving the above object. That is, the ejection failure detection method in the ink jet recording apparatus according to the present invention includes one or more nozzle rows in which a plurality of nozzles that eject ink are arranged over the entire width of the print medium in a direction substantially perpendicular to the feed direction of the print medium. An ejection failure detection method in an ink jet recording apparatus having a full line type recording head provided for each of a plurality of ink colors, wherein the ink droplets ejected from the nozzles face the nozzle surface of the recording head A test printing process for forming a test image on the test image printing medium arranged in the same manner, and a test image formed on the test image printing medium by the test printing process. Read by the image reading means read by the image reading means arranged in the direction, and the image reading process A detection step of detecting an ejection failure nozzle from the image, is characterized by comprising a cleaning step of removing the ink droplets forming a test image on the test image print medium.

  An aspect including a step of retracting the test image printing medium at a predetermined position when the test printing is completed is preferable.

  According to the present invention, in the ink jet recording apparatus provided with the full line head, the image reading means is provided immediately downstream of the color-specific recording heads in the print medium conveying direction, and the print results by the respective recording heads are displayed on the image. It can be read by reading means. Therefore, an image can be read for each color immediately after printing.

  Further, a defective ejection nozzle can be detected from the read result, and when a defective ejection nozzle is detected, a predetermined countermeasure process is performed. The coping processing includes processing such as image correction and ejection failure nozzle recovery operation, and preferable correction processing is performed. Therefore, it is possible to detect defective ejection nozzles for each color, and it is possible to perform preferable correction processing at an early stage, and a defective image is immediately repaired.

  The reading means can be shared by two or more recording heads. For example, in a recording head using dark and light inks, the reading means can be shared. The image reading means may be configured by arranging a plurality of light receiving element groups in the main scanning direction.

  Detection of defective ejection nozzles may be performed by practical printing or by test printing. If the ejection failure nozzle is detected in the practical print, the print medium is not wasted. If the ejection failure nozzle is detected in the test print, the ejection failure nozzle can be corrected from the immediately following print. For the correction process for the ejection failure nozzle, a mode in which droplet substitution is performed from the adjacent nozzle of the same color is preferable.

  In addition, the ink jet recording apparatus having a full line head includes a test image printing medium that is provided at a position facing the recording head for each color and that ejects ink droplets from each nozzle during test image printing. The medium is not wasted.

  A test image deposited on the test image print medium is detected by image reading means provided at a position facing the recording head with the test image print medium interposed therebetween, and between the actual print and the actual print. Since the test image is read and the ejection failure is detected, the correction process for the ejection failure nozzle can be performed from the subsequent print immediately after the test printing, and the head portion of the print can be relieved. The test image printing medium is preferably configured to be retractable.

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

[Overall configuration of inkjet recording apparatus]
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 inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt conveyance unit 22 arranged to face the surface (ink ejection surface) and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, a print detection unit 41 for reading a printing result by the printing unit 12, A paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside.

  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.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  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.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction 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 and the sensor surface of the printing detection unit 41 is horizontal ( Flat surface).

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 41 inside the belt 33 spanned between the rollers 31 and 32. By sucking the suction chamber 34 with a fan 35 to make it a negative pressure, the recording paper 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, described as reference numeral 88 in FIG. 7) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording paper 16 held on the belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction 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.

  The printing unit 12 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording paper of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the paper transport direction). , 12C, 12M, 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording paper 16 only by performing it (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, 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 this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  The print detection unit 41 includes an image sensor for imaging the droplet ejection result of each printing unit 12, and functions as means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  The print detection unit 41 of this example includes a line sensor 41K, 41C, 41M, 41Y provided for each of the print heads 12K, 12C, 12M, 12Y, and each line sensor 41K, 41C, 41M, 41Y includes Arranged on the downstream side in the paper conveyance direction between the print heads. It is preferable that each line sensor is placed closer to the sensor side of the color to be read than the intermediate position between the print heads.

  Further, the line sensors (image sensors) 41K, 41C, 41M, and 41Y are configured by line sensors having a light receiving element array that is wider than at least the ink ejection width (image recording width) of each print head. The line sensors 41K, 41C, 41M, and 41Y are provided with an R sensor array in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, and a green (G) color filter. And a color separation line CCD sensor including a G sensor array and a B sensor array provided with a blue (B) color filter. Note that the line sensor may be a monochrome sensor, and an area sensor in which light receiving elements are two-dimensionally arranged may be used instead of the line sensor.

  The print detection unit 41 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like. Details of discharge detection will be described later.

  A post-drying unit 42 is provided following the print detection unit 41. 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 preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by blocking the paper holes by pressurization. There is an effect to.

  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. The main image to be originally printed (printed target image, practical print) and test print are separated by switching the paper discharge path by the conveyance switching 47. The practical print is conveyed to the accumulation tray 26A, and the test print is discharged to the dust tray 26B.

  Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the image collecting tray 26 </ b> A is provided with a sorter for collecting images according to orders.

  The inkjet recording apparatus 10 further includes a maintenance unit (recovery unit) 69 that performs a recovery process on the print heads 12K, 12C, 12M, and 12Y. In FIG. 1, the maintenance unit 69 is illustrated downstream of the print heads 12K, 12C, 12M, and 12Y in the recording sheet conveyance direction. However, the maintenance unit 69 recovers immediately below the ink ejection surface of the print heads 12K, 12C, 12M, and 12Y. It is configured to be movable between the operation execution position and the retracted position.

  Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  FIG. 3A is a plan perspective view showing an example of the structure of the print head 50, and FIG. 3B is an enlarged view of a part thereof. 4 is a cross-sectional view (a cross-sectional view taken along line 4-4 in FIG. 3) showing a three-dimensional configuration of the ink chamber unit. In order to increase the dot pitch printed on the recording paper surface, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 3 and 4, the print head 50 of this example includes a plurality of ink chamber units 53 including nozzles 51 for ejecting ink droplets and pressure chambers 52 corresponding to the nozzles 51. In this way, a high density of the apparent nozzle pitch is achieved.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the nozzle 51 and the supply port 54 are provided at both corners on the diagonal line. Each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54.

  An actuator 58 having an individual electrode 57 is joined to the pressure plate 56 constituting the top surface of the pressure chamber 52, and the actuator 58 is deformed by applying a driving voltage to the individual electrode 57, and the nozzle 51 Ink is ejected. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The structure is arranged in a lattice pattern. With a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. .

  That is, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction. Hereinafter, for convenience of explanation, it is assumed that the nozzles 51 are linearly arranged at a constant interval (pitch P) along the longitudinal direction (main scanning direction) of the head.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the full width of the paper, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially driven from one side to the other (3) ) The nozzle is divided into blocks, and each block is driven sequentially from one side to the other. One line or one band is printed in the paper width direction (direction perpendicular to the paper transport direction). Such nozzle driving is defined as main scanning.

  In particular, when the nozzles 51 arranged in the matrix as shown in FIG. 5 are driven, the main scanning as described in the above (3) is preferable. That is, the nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, The nozzles 51-31,..., 51-36 are set as one block,..., And the recording paper 16 is driven by sequentially driving the nozzles 51-11, 51-12,. One line is printed in the width direction.

  On the other hand, repetitively moving the above-described full line head and the paper to repeatedly perform one line or one band-like printing formed by the above-described main scanning is defined as sub-scanning.

  That is, nozzle driving that prints a line formed by a single line of dots or a line formed by a plurality of lines in the width direction of the paper is referred to as main scanning, and a line or a plurality of lines formed by a single line formed by the main scanning. Repeatedly printing a line made up of dots is called sub-scanning.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. However, in the practice of the present invention, the method of ejecting ink is not particularly limited. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

  FIG. 6 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10.

  The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of ink supply tank 60: a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the ink remaining amount is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink supply tank 60 in FIG. 6 is equivalent to the ink storage / loading unit 14 in FIG. 1 described above.

  As shown in FIG. 6, a filter 62 is provided between the ink supply tank 60 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  Although not shown in FIG. 6, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a nozzle surface cleaning means.

  A maintenance unit (recovery unit) 69 including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and can be moved from a predetermined retraction position to a position below the print head 50 as required. Moved to the maintenance position. Of course, a moving mechanism for moving the print head 50 may be provided so that the print head 50 moves to the position of the maintenance unit 69.

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 64 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle 51 surface (ink ejection surface) with the cap 64.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the actuator 58 operates.

  Before such a state is reached (within the range of the viscosity that can be discharged by the operation of the actuator 58), the actuator 58 is operated, and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged. Preliminary ejection (purging, idle ejection, brim ejection) is performed toward the ink receiver.

  Further, when air bubbles are mixed into the ink in the print head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the actuator 58 is operated. In such a case, the cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 67, and the suctioned and removed ink is sent to the collection tank 68. .

  In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

  FIG. 7 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and 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 temporarily 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 is a control unit that controls each unit such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling is generated.

  The motor driver 76 is a driver (drive circuit) that drives the 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 control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (print data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the print head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  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. 7, the image buffer memory 82 is shown in a mode 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 a single processor.

  The head driver 84 drives the actuators 58 of the print heads 12K, 12C, 12M, and 12Y of the respective colors based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  As described with reference to FIG. 1, the print detection unit 41 is a block including line sensors 41K, 41C, 41M, and 41Y. The print detection unit 41 reads an image printed on the recording paper 16, performs necessary signal processing, and the like. (Ejection presence / absence, variation in droplet ejection, etc.) is detected, and the detection result is provided to the image correction control unit 87 in the print control unit 80.

  That is, the print control unit 80 detects a defective discharge nozzle based on the detection result of the print detection unit 41, and a nozzle recovery process is performed on the defective discharge nozzle so as to execute a recovery operation using the recovery unit 69. The In other words, the print detection unit 41 functions as a detection unit that detects ejection failure nozzles.

  Further, the image correction control unit 87 performs various operations for the print head 50 such as image correction and discharge correction for performing substitute discharge using nozzles other than defective discharge nozzles based on information obtained from the print detection unit 41 as necessary. Correction is performed to suppress image deterioration due to the occurrence of ejection failure nozzles.

  In the example shown in FIG. 1, the print detection unit 41 is provided on the print surface side, and is provided by a light source (not shown) such as a cold cathode tube disposed in the vicinity of the line sensors 41K, 41C, 41M, and 41Y. The print surface is illuminated and the reflected light is read by a line sensor. However, when the present invention is implemented, for example, as shown in FIG. 41C, 41M, 41Y and the light source 92 are arranged to face each other, the light of the light source 92 is irradiated from the back side of the recording paper 16 (opposite side of the ink ejection surface), and the amount of transmitted light is measured by the line sensors 41K, 41C, A configuration of reading by 41M and 41Y is also possible. The configuration of the transmission type detection shown in FIG. 8 has an advantage that the blur of the image captured by the line sensor can be reduced as compared with the configuration of the reflection type detection.

  However, in the case of the transmission type, the amount of light incident on the line sensor is smaller than that of the reflection type. Further, it is assumed that the incident light quantity is small even in the reflection type. In any case, if the amount of light incident on the line sensor is small, a sufficient detection signal cannot be obtained. However, when the image is read by the line sensor, the resolution in the paper feed direction is not required. Or by integrating the read data in the paper feed direction.

  The reading start timing of the line sensor is determined from the distance between the sensor and the nozzle and the conveyance speed of the recording paper 16.

  In addition, in this example, although the aspect provided with the light source 92 for every line sensor 41K, 41C, 41M, 41Y was shown, you may comprise so that one light source may be moved to the detection position of each line sensor, A large light source corresponding to the detection position of the line sensors 41K, 41C, 41M, 41Y may be used.

[First Embodiment]
Next, detection of defective ejection nozzles and correction processing thereof in the ink jet recording apparatus according to the first embodiment of the present invention will be described.

  In a full line head type ink jet recording apparatus, ink droplets are ejected by the same nozzle in one line in the paper transport direction, so if there are defective ejection nozzles such as non-ejection, ejection direction abnormality, ejection amount abnormality, etc. As a result, streaks and unevenness in the paper conveyance direction may occur. In order to suppress a decrease in print quality due to streaks, unevenness, etc., it is necessary to quickly detect ejection failure nozzles and perform correction processing according to ejection failures.

  First, a method for detecting defective ejection nozzles by test printing will be described.

  FIG. 9 shows an example in which roll paper is used as the recording paper 16 and the test patterns 100 and 102 are printed in the test print area 16A of the recording paper 16. The arrows in FIG. 9 indicate the paper conveyance direction.

  In the test patterns 100 and 102, ink droplets are ejected from all the nozzles so as to form one line along the main scanning direction for each color. The test pattern droplet ejection is performed for each color in order to quickly feed back the detection result to the discharge failure countermeasure means and to prevent erroneous detection between colors.

  Further, the dot size applied to the test patterns 100 and 102 is a size equal to or smaller than the minimum dot interval. However, there is a mode in which dots having a size larger than the minimum dot size are printed, and the test pattern is printed in a plurality of rows while changing the droplet ejection nozzle. This is done for the purpose of preventing erroneous detection of dots, and each dot must be printed so that adjacent dots do not overlap.

  As shown in FIGS. 16 (a) and 16 (b), the minimum dot interval referred to here is the inter-nozzle pitch of the projection nozzle row 300 projected in the main scanning direction so as to be aligned in the main scanning direction (FIG. 16 ( Pmin) is shown in a) and (b).

  For example, as shown in FIG. 16A, when printing dots 302, 304, 306,..., 312, 314, 316,... Having a size (diameter D) twice the minimum dot interval Pmin (diameter). D = 2 × Pmin dots), the odd nozzles (for example, nozzles 321 and 323) with respect to the adjacent nozzles (for example, the nozzle 321 and the nozzle 322) that are projected so as to be aligned in the main scanning direction. , 325), dots 302, 304, 306,... Are ejected in the main scanning direction, and then the recording paper 16 is n times the minimum dot interval Pmin in the sub scanning direction (where n is an integer of 2 or more). Are ejected in the main scanning direction by even-numbered nozzles (for example, nozzles 322, 324, and 326).

  In other words, in droplet ejection that forms dot rows in the sub-scanning direction, droplet ejection is performed at the same timing every 1 (= n−1) nozzles, and 2 (= n) dot rows are formed in the main scanning direction. .

  Further, as shown in FIG. 16B, dots 342, 344, 346,..., 352, 354, 356,..., 362, 364, 366,. In this case, first, the dots 342, 344, 346,... Are ejected simultaneously (at the same ejection timing) from every other nozzle (321), 324, 327,. .

  Next, at the timing when the recording paper 16 is conveyed in the sub-scanning direction by 3 times the minimum dot interval Pmin, the nozzles 322, 325, and 328 adjacent to the nozzle used for the previous droplet ejection are used as dots 352, 354, and 356. , ..., simultaneously.

  Further, at the timing when the recording paper 16 is conveyed in the sub-scanning direction by three times the minimum dot interval Pmin, the nozzles 323, 326, and 329 adjacent to the nozzle used for the previous droplet ejection are used as dots 362, 364, 366, ... and drop at the same time.

  That is, when droplets having a diameter D that is n times the minimum dot interval Pmin (where n is an integer of 2 or more) are ejected, in the sub-scanning direction, every (n-1) nozzles are at the same timing. Droplet ejection is performed to form n rows of dots in the main scanning direction. Therefore, since ink droplets are ejected so that the dots are arranged in a staggered pattern (diagonally), even if the dot diameter is large, they do not overlap each other, and erroneous detection can be prevented.

  Furthermore, when the above is expanded, when printing with a dot diameter n times as large as the minimum dot interval, every n-1 nozzles are projected with respect to adjacent nozzles when projected so as to be aligned in the main scanning direction. In the same manner as in the case of n = 2 above, dots are ejected in the main scanning direction, and n-line dots are ejected in a staggered manner in the sub-scanning direction, so that they do not overlap each other even with a large dot diameter. False detection can be prevented.

  In the test pattern 100, ink droplets are ejected from the print heads of all four colors, and in the test pattern 102, ink droplets are ejected from the print out of the four colors. In the test pattern 102, the ink droplets are ejected from the three color print heads. However, the test pattern may be formed by the two color print heads or may be one color. The selection of one to three colors from the four colors may be arbitrarily controlled according to the usage frequency of the nozzles.

  In other words, nozzles that are frequently used are unlikely to increase in ink viscosity in the vicinity of the nozzles, and are less likely to contain bubbles from the nozzles. High color heads can reduce ink consumption if test (pattern) printing is omitted. Further, it is more preferable to perform test (pattern) printing only on nozzles that are not frequently used, not on a head-by-color basis. In this case, the line sensors 41K, 41C, 41M, and 41Y determine ejection or non-ejection only for dots that are ejected from nozzles that are less frequently used for test printing.

  When test printing is performed for only three of the four colors as in the test pattern 102, ink consumption can be reduced. If one test print is made of two colors or one color, the ink consumption can be further reduced.

  The test print area 16A may be arranged on the front side in the conveyance direction of the recording paper 16 of the practical print area 16B, or may be arranged on the rear side. Also, as shown in FIG. 9, one may be arranged in one practical printing area 16B, or one may be arranged in a plurality of printing areas. Reference numeral 16 </ b> C denotes a marginal margin area of the recording paper 16.

  FIG. 10 shows test patterns 104 and 106 during borderless printing. Similarly to FIG. 9, the test patterns 104 and 106 can be printed in the test print area 16A during borderless printing without the edge portion blank area 16C shown in FIG.

  The test patterns 100, 102, 104, and 106 printed on the recording paper 16 in this way are read for each color by the line sensors 41K, 41C, 41M, and 41Y provided in each print head.

  Each of the line sensors 41K, 41C, 41M, and 41Y is provided with illumination means (not shown), and the illumination light is irradiated onto the test pattern 100 by the illumination means, and the reflected light is transmitted to the line sensors 41K, 41C, and 41Y. It can be read by each of the light receiving elements 41M and 41Y. The illumination means may be provided separately from the line sensor, but is preferably provided in the vicinity.

  The reading start timing is determined from the distance between the sensor and the nozzle and the conveyance speed of the recording paper 16.

  In order to accurately read the test pattern 100 dot by dot, the reading resolution of the line sensors 41K, 41C, 41M, and 41Y is preferably sufficiently higher than the printing resolution on the recording paper 16. Further, it is preferable that the reading resolution of the line sensors 41K, 41C, 41M, and 41Y is m times the printing resolution (m is a positive integer).

  For the line sensors 41K, 41C, 41M, and 41Y, a shuttle scan type that reads a test pattern 100 while moving a sensor having a width smaller than the printable width by a traveling means that scans (runs) in the width direction of the recording paper 16 is applied. In this case, even when the reading resolution of the sensor is not sufficiently larger than the printing resolution, the reading resolution of the sensor can be supplemented by reducing the scanning resolution of the sensor.

  The travel means includes a motor controlled by the control of the system controller 72 shown in FIG. 7, a transport means such as a ball screw and a transport belt for moving (moving) a carriage with a sensor attached by driving the motor, and the travel means. It is composed of a guide member for instructing.

  In this way, at least the dot position and the dot size are read by the line sensors 41K, 41C, 41M, and 41Y, and this dot information is sent to the print controller 80 shown in FIG. The print control unit 80 compares the calculated dot that is originally ejected for all dots with the actually ejected dot, and detects a defective ejection nozzle based on the comparison result.

  The ejection failure nozzle includes non-ejection that does not eject ink droplets, ejection amount abnormality in which the ejection amount of the ink droplet is different from the original ejection amount, and ejection direction abnormality in which the flying direction of the ink droplet is different from the original flight direction. Of course, other discharge defects may be detected.

  When an ejection failure nozzle is detected, a preferred correction process is performed according to the ejection failure mode and the degree of ejection failure.

  The correction processing includes an image correction in which an image is corrected in the next printing, a nozzle recovery operation in which the next printing is stopped, and a recovery operation is performed on the ejection failure (non-ejection) nozzle.

  In image correction, there is a mode in which droplets are substituted from other normal nozzles. Substitute droplet ejection includes a mode in which dots are ejected larger than the size originally ejected from the proximity nozzle, and a mode in which the ejection direction of the proximity nozzle is changed. A mode in which the nozzle recovery operation is performed at an appropriate time after the image correction is preferable.

  In addition, the recovery operation includes, for example, tsunami that discharges the clogged ink in the nozzle 51 to the cap 64, wiping for wiping and cleaning the nozzle surface, and ink suction for sucking out the clogged ink by the suction pump 67. When the predetermined recovery operation is completed, the next printing can be performed.

  When a defective ejection nozzle is detected, streaks and unevenness may occur in the practical print immediately before the test print. Therefore, it is preferable that the actual skill print immediately before the test print is reprinted. Practical print to which reprinting is applied is not limited to immediately before test printing, but can be applied to any practical printing after the previous test printing.

  FIG. 11 is a flowchart showing a flow of defective ejection nozzle detection control of the inkjet recording apparatus 10.

  When a print instruction is sent from the system controller 72 to the print controller 80 (step S10), a black test pattern is printed on the test print area 16A of the recording paper 16 from the first head 12) (step S12). The black test pattern is read by the line sensor 41K (step S14), and the reading result is determined (printing determination) (step S16). If it is determined in step S16 that there is a defective ejection nozzle in the first head (NO determination), it is determined whether or not dot correction is possible (step S18).

  An example of a criterion for determining whether or not dot correction is possible is to determine that dot correction is possible if there are two or less ejection abnormal nozzles in a nozzle array projected so as to be aligned in the main scanning direction. If there are three or more ejection abnormal nozzles in succession, it becomes very difficult to perform alternative ejection by increasing the diameter of the dots ejected by the normal nozzle adjacent to the ejection abnormal nozzle. If there are two or less ejection abnormal nozzles, it is relatively easy to perform alternative droplet ejection by increasing the dot diameter of adjacent normal nozzles.

  In step S18, it is determined whether the nozzle is a non-ejection nozzle or an ejection amount abnormality or ejection direction abnormality nozzle. If it is determined that the dot correction operation is not possible (non-ejection nozzle) (NO determination), the second head (Print head 12C), 3rd head (print head 12M), 4th head (print head 12Y), only test printing is performed, a test pattern is read for every head, and the ejection failure nozzle in each head is judged. (Step S20).

  When step S20 is completed, the recording paper 16 is sent in the paper conveyance direction, the test print area 16A is cut by the cutter 48 (step S22), and the conveyance direction is switched to the dust tray 26B side by the conveyance switching 47 (step S24). The cut test print area 16A is stored in the dust tray 26B (step S28).

  The recovery operation described above is performed on the nozzles determined to be ejection failure nozzles in each head (step S28), and the process proceeds to step S30.

  In step S30, it is determined whether or not reprinting is performed. If reprinting is not performed (NO determination), the process proceeds to step S48, and it is determined whether or not there is a next printing.

  When reprinting is performed in step S30 (YES determination), reprinting is executed (step S32), and the process proceeds to step S48.

  In step S48, if there is no subsequent print data (NO determination), the print job is ended (step S31). If the subsequent print data is sent (YES determination), the process proceeds to step S12. Next print is executed.

  On the other hand, if it is determined in step S18 that the correction operation is possible, correction calculation is performed in the print controller 80 (step S34), and black printing is performed by the first head (step S36).

  In step S16, when there is no nozzle determined to be an ejection failure nozzle in the first head (YES determination), black printing by the first head is executed (step S36).

  Subsequently, test printing of the second head is performed (step S38). Thereafter, the same control as the control in the first head is performed in the third head and the fourth head.

  Although not shown in the flowchart of FIG. 11, if it is determined that correction is not possible in the second test printing in step S38, the test printing for the third and subsequent heads is performed so as to correspond to step S20. Proceed to implementation and judgment.

  When cyan printing is executed by the fourth head (step S40), the practical print is finished, and the recording paper 16 is fed in the paper transport direction and cut to a predetermined size by the cutter 48 (step S42). At this time, the transport switching 47 is switched to the stacking tray 26A side (step S44), and the practical print is discharged to the stacking tray 26A (step S46).

  After the nozzle recovery operation, the process from the test print is executed again. However, when the nozzle recovery operation is performed, the test print is not executed and the actual print is executed. May be.

  In the aspect in which the piezoelectric element is used for the actuator 58 shown in FIG. 4, the size of the dot can be changed stepwise depending on the ejection amount of the ink droplet. If a small droplet can be ejected, a large droplet can also be ejected, so that only a small droplet needs to be detected. In this case, however, the line sensor must have high resolution (high density).

  On the other hand, when determining with a large droplet, it is necessary to configure the test pattern 102 so that dots do not overlap, but in this case, the line sensor may not have high resolution.

  In this embodiment, the line sensors 41K, 41C, 41M, and 41Y, which are reading means, are provided for each print head corresponding to each color, but reading of two or more colors may be performed by a common line sensor. In this case, if the distance between each print head and the line sensors 41K, 41C, 41M, and 41Y is shorter than the distance between images, printing stop, reprinting, and nozzle recovery operation are possible, but dot (image) correction is possible. I can't.

  In the present embodiment, a mode in which test printing is performed to detect defective ejection nozzles is shown, but a mode in which a practical print is read to detect defective ejection nozzles is also possible.

  When reading a practical print, a multi-color (RGB) line sensor is applied to the reading sensor of the print detection unit 41. Black (K) detection uses the average output value of all RGB sensors, and cyan (C) detection uses the output of the R sensor for an area where K is not originally ejected. Further, for detection of magenta (M), the output of the G sensor is used for an area where K and C are not originally ejected. For detection of yellow (Y), the output of the B sensor is used for a region where K, C, and M are not originally ejected.

  K ink gives almost the same output change to each RGB sensor. Therefore, accurate detection is possible by first performing processing using these average values. In addition, since the color material usually has secondary absorption on the short wavelength side, the C ink has absorption on the R side and absorption on the shorter wavelength side, that is, on the G and B regions. That is, C ink affects the detection of M ink and Y ink. Therefore, in order to eliminate such influence, it is preferable to perform processing in order of increasing influence range (that is, in order from the long wavelength side). By doing so, processing between colors can be performed efficiently. The above-described practical print detection method is merely an example, and other detection methods may be used.

  When an ejection failure nozzle is detected, the same correction operation as that for reading the test print described above is performed.

  In the ink jet recording apparatus 10 configured as described above, each color print head includes line sensors 41K, 41C, 41M, and 41Y on the downstream side in the paper transport direction, and a test pattern printed for each color is displayed for each color. Reading is performed by the line sensors 41K, 41C, 41M, and 41Y provided in the print head, and an ejection failure nozzle is determined from the reading result. It is possible to immediately determine the ejection failure nozzle, and it is possible to issue a print change instruction for subsequent printing. A series of control operations such as dot reading, ejection failure nozzle detection, and correction operation can be performed for each color.

[Second Embodiment]
Next, an ink jet recording apparatus according to a second embodiment of the present invention will be described.

  FIG. 12 is a main part configuration diagram of an inkjet recording apparatus 200 according to the second embodiment. 12 shows the main part of the ink jet recording apparatus 200. The parts not shown in FIG. 12 are basically the same as those in FIG. 1, and the same or similar parts as FIG. 1 in FIG. Are denoted by the same reference numerals, and the description thereof is omitted.

  The ink jet recording apparatus 200 is provided at a position facing the nozzle surface of each print head for each print head and a print unit 12 having print heads 12K, 12C, 12M, and 12Y for each ink color. A test pattern printing medium 202 (202K, 202C, 202M, 202Y) on which ink droplets are ejected from the print head and an image sensor 204 (204K, 204C) that reads the ink droplets (dots) ejected on the test pattern printing medium 202. 204M, 204Y), and the print detection unit 41 that determines nozzle ejection failure from the read image and the recording paper (cut paper) 16 filled in the paper feeding unit (paper feeding tray) 18 downstream in the paper conveyance direction. The transport unit 210 to be transported to the side (from left to right in FIG. 12) and the printed printed matter (printed matter) are stored. It includes a product tray 26A, a.

  Although not shown in FIG. 12, a cleaning unit (reference numeral 220 in FIG. 13) that cleans the ink that has been ejected onto the test pattern print medium 202 is provided close to the test pattern print medium 202.

  Although cut paper is applied to the recording paper 16, roll paper can also be applied. When roll paper is used, a cutter for cutting the roll paper at a predetermined position is required. The details of the cutter are as described with reference to FIG.

  FIG. 12 shows a state in which test printing is performed in the print head 12C. In the ink jet recording apparatus 200, each print head completes printing on the previous recording paper, the recording paper is conveyed in the downstream direction, and the test printing is performed until the next recording paper arrives below the head. Executed.

  That is, the test print is performed before the practical print is finished and the next practical print is executed, and the image sensor 204C provided in the print detection unit 41 with the dots ejected onto the test pattern print medium 202C by the test print. By this, it is possible to detect defective nozzles of the nozzles in the print head 12C. Of course, the same test printing is performed in the print heads 12K, 12M, and 12Y, and the ejection failure nozzles in each print head are detected.

  The image sensor 204 may be a line sensor or an area sensor. A plurality of sensors may be arranged in the main scanning direction.

  The transport unit 210 includes drive rollers 212 and 214 and driven rollers 216 and 218. The driving roller 212 and the driving roller 214 are rotated by the driving force of the motor 88 shown in FIG. 7 and are sent out to the downstream side in the paper conveyance direction with the recording paper 16 sandwiched between the driving roller 212 and the driving roller 214. It has become.

  The driven rollers 216 and 218 are arranged between the upstream drive rollers 212A and 214A and the downstream drive rollers 212B and 214B, and convey the recording paper 16 so that the recording paper 16 is not bent and the transport direction is not shifted. It is provided to assist. As with the driving rollers 212 and 214, the recording paper 16 is conveyed while being sandwiched between the driven rollers 216 and 218.

  Although not shown in FIG. 12, the transport unit 210 includes a support member such as a guide in order to ensure the flatness of the portion of the recording paper 16 that faces the print unit 12 and the print detection unit 41. It has been.

  In this embodiment, roller / nip conveyance is applied to the conveyance unit 210, but feed conveyance other than roller / nip conveyance may be applied. However, it is necessary to ensure the flatness of the recording paper 16 described above. Further, it is possible to apply a mode in which the recording paper 16 is conveyed while holding both edges, or a belt conveyance by a conveyance belt having a slit through which ink droplets pass.

  Details of the print detection unit 41 of the inkjet recording apparatus 200 will be described with reference to FIG. The print detection units for the respective colors have the same configuration.

  The print detection unit 41 includes a test pattern printing medium 202 on which ink droplets are ejected at the time of test printing, an image sensor 204 that reads dots formed by ink droplets deposited on the test pattern printing medium 202, and a test pattern printing medium. And cleaning means 220 for removing ink droplets on 202.

  The image sensor 204 includes illumination means (not shown) that irradiates the test pattern with illumination light. The illumination unit may be provided on the print head side.

  The cleaning unit 220 is provided in an ink receiver 224 that collects ink droplets on the test pattern print medium 202 blown out by air sent from the compressor 222 via the air nozzle 223, and a mechanism that collects air in the compressor 222. The filter 226 and the tube 228 are included. If the compressor 222 does not need a mechanism for collecting air, the filter 226 and the tube 228 are unnecessary.

  The test pattern printing medium 202 is made of a transparent member such as glass or resin or a translucent member having good light transmission so that the ink deposited on the front surface can be read by the image sensor 204 on the back side. It is done. In addition, it is preferable to use a material that allows ink droplets to be fixed on the test pattern printing medium 202 at the time of reading by the image sensor 204 and that can be easily removed at the time of cleaning by the cleaning means 220.

  In the present embodiment, the cleaning unit 220 has a mode in which ink droplets on the surface of the test pattern print medium 202 are blown by air, but a mode in which the surface of the test pattern print medium 202 is wiped with a blade or the like may be used.

  In the ejection failure nozzle detection control in the present embodiment, the same control and processing as in the first embodiment described above are performed. That is, test pattern droplet ejection control, test pattern reading control, resolution of the image sensor 204, determination of ejection failure nozzles, and correction operations are the same as in the first embodiment, and description thereof is omitted here.

  FIG. 14 shows a modification of the print detection unit 41 according to the second embodiment. In the present embodiment, the image sensor 204 that is a reading unit is opposed to the print head and is provided on the back side of the test pattern print medium 202 (opposite side of the print head). It may be provided on the downstream side (or upstream side) of the test pattern print medium 202 in the paper conveyance direction, or may be provided on the side surface side of the test pattern print medium 202 so as to be substantially orthogonal to the paper conveyance direction. FIG. 14 shows an aspect provided on the downstream side of the test pattern printing medium 202 in the paper conveyance direction.

  In the present modification, the test pattern printing medium 202 is provided at an angle θ from a surface 240 parallel to the printing surface of the recording paper 16, and the test pattern printing medium 202 is printed by the image sensor 204 provided downstream in the paper transport direction. An ink droplet ejected on the medium 202 can be read.

  Further, it is necessary to set the angle θ so that ink droplets do not fall from the surface of the test pattern printing medium 202. A preferable range of the angle θ is about 5 degrees to 30 degrees. Further, if the ink affinity is increased so that the ink droplets do not fall from the test pattern print medium 202, the ink droplets cannot be removed from the test pattern print medium 202 during cleaning, so the contact angle between the test pattern print medium 202 and the ink droplets is About 30 to 150 degrees is preferable. The contact angle indicates the degree of hydrophilicity of the ink droplet. When the contact angle is large, the ink affinity is low, and when the contact angle is small, the hydrophilicity is high.

  When ink droplets landed two-dimensionally on the surface of the test pattern printing medium 202 are read using the image sensor 204, as shown in FIG. 15, the ink droplets (dots) 248, the image sensor 204, Therefore, it is necessary to provide an optical correction means (correction plate) 250 between the test pattern printing medium 202 and the image sensor 204.

  FIG. 15 shows a state in which the test pattern print medium 202, the image sensor 204, and the optical correction means 250 are viewed from the print head side.

  It is preferable that the test pattern printing medium 202 includes a retracting mechanism (not shown) so that the test pattern printing medium 202 can move to a predetermined retracted position except during test printing. The retracting mechanism may be configured such that a mechanism system such as a support guide and a carriage is operated by a drive system including a motor and a belt, and the drive system is controlled by a control system including a CPU and a memory. .

  In the present embodiment, the test pattern printing medium 202 is illustrated as being provided in each color head, but these may be integrated.

  The ink jet recording apparatus 200 configured as described above includes the print detection unit 41 directly below the print head, and can perform test printing between the actual print image and the actual print image to detect ejection failure nose. Since the recording paper 16 is not used for test printing, the recording paper 16 is not wasted.

  In the first embodiment and the second embodiment described above, the number of ink droplets that are ejected for detection may not be suitable, and in order to increase the reading accuracy (to improve S / N), Ink may be ejected. In the ink jet recording apparatus 10 shown in the first embodiment in which the paper feeding cannot be stopped, the droplet ejection result is an ellipse, and the position of the print head and the reading means (image sensor) 204 does not change. In the ink jet recording apparatus 200 shown in the form, the printing result is a single point in a range where the distance between adjacent droplets does not overlap.

  In the present embodiment, a piezo-type inkjet recording apparatus that performs ink ejection control using a piezo element is illustrated, but the present invention is also applicable to a bubble-type inkjet recording apparatus.

1 is a basic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of the main part around the printing of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of print head Sectional view along line 4-4 in FIG. FIG. 3 is an enlarged view showing the nozzle arrangement of the print head shown in FIG. Schematic diagram showing the configuration of the ink supply unit in the inkjet recording apparatus according to the present embodiment Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. The figure which shows the example of arrangement | positioning of the light source for illumination The figure explaining the test printing of the inkjet recording device which concerns on 1st Embodiment of this invention. The figure explaining the test printing in the borderless printing of the inkjet recording device which concerns on this embodiment The flowchart which showed the flow of control of the discharge defect nozzle detection of the inkjet recording device which concerns on this embodiment. FIG. 5 is a configuration diagram of a main part of an ink jet recording apparatus according to a second embodiment of the invention. Configuration diagram of a main part of a print detection unit of the ink jet recording apparatus according to the present embodiment. The figure which shows the modification of the print detection part of the inkjet recording device which concerns on this embodiment. The figure explaining the aspect provided with the optical correction means in the print detection part shown in FIG. Diagram showing an example of test pattern

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 16 ... Recording paper, 22,210 ... Conveyance part, 24 ... Print detection part, 41, 204 ... Image sensor, 50 ... Print head, 51 ... Nozzle, 202 ... Test pattern printing Medium 220 ... Cleaning means 206 ... System controller 208 ... Print control unit

Claims (14)

A full-line type recording head having one or more nozzle rows in which a plurality of nozzles for ejecting ink are arranged over the entire width of the recording medium in a direction substantially perpendicular to the feeding direction of the printing medium corresponds to a plurality of ink colors. Provided for each color,
A plurality of image reading means for reading an image formed on the print medium by ejecting ink from a plurality of recording heads provided for the respective colors is provided for each color recording head. An ink jet recording apparatus, wherein the ink jet recording apparatus is disposed downstream of the print medium in the feeding direction. The plurality of recording heads include two or more same color recording heads corresponding to the same color dark and light inks,
2. The ink jet recording apparatus according to claim 1, wherein the image reading means used for reading an image ejected by the same color recording head is shared.   3. The ink jet recording apparatus according to claim 2, wherein sensitivity of the common image reading means used for reading an image ejected by the same color recording head is set in accordance with reading of light ink. . Detection means for detecting defective ejection nozzles from the image read by the image reading means;
When a defective discharge nozzle is detected by the detection unit, a discharge failure handling unit that performs processing including at least one of image correction and recovery operation of the defective discharge nozzle;
The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is provided.   The detecting means detects defective nozzles in each print head by a practical print read by the image reading means, and the defective discharge nozzle handling means detects other normal discharge defects for the detected defective nozzles. The ink jet recording apparatus according to claim 1, wherein the nozzle performs a droplet ejection using a nozzle. Test print control means for performing control to print a test image in a margin area on the print medium;
The detecting means detects a defective discharge nozzle based on the result of reading the test image by the image reading means, and the defective discharge nozzle handling means substitutes another normal nozzle for the detected defective discharge nozzle. 6. The ink jet recording apparatus according to claim 1, wherein the ink droplet is controlled to be dropped.   When the test print control means prints dots having a diameter n times the minimum dot interval in a direction substantially perpendicular to the print medium feeding direction when n is a positive integer of 2 or more, the print medium In droplet ejection in which one dot row is formed in a direction substantially orthogonal to the feed direction, droplet ejection is performed every (n-1) nozzles, and the minimum dot interval is set in the print medium feed direction while changing the nozzles to be ejected. 7. An ink jet recording apparatus according to claim 6, wherein control is performed to print a test image for forming n dot rows at a pitch of n times.   The said image reading means has a sensor row | line | column arrange | positioned over the full width of the said printing medium in the direction substantially orthogonal to the feed direction of the said printing medium, The any one of Claim 1 thru | or 6 characterized by the above-mentioned. Inkjet recording device. The image reading means has a sensor array having a width smaller than the entire width of the print medium in a direction substantially orthogonal to the feed direction of the print medium,
The inkjet according to any one of claims 1 to 6, further comprising traveling means for causing the image reading means to travel over the entire width of the printing medium in a direction substantially orthogonal to the feeding direction of the printing medium. Recording device. A full nozzle having at least one nozzle array in which a plurality of nozzles for ejecting ink corresponding to a plurality of ink colors are arranged over the entire width of the recording medium in a direction substantially perpendicular to the feeding direction of the printing medium. An ejection failure detection method in an inkjet recording apparatus including a line-type recording head,
An image forming step of forming an image on the print medium with ink droplets discharged from the nozzle;
An image reading step for reading the image formed on the print medium by color by an image reading unit disposed on the downstream side in the print medium feeding direction with respect to the recording head of the corresponding color by the image forming step;
A detection step of detecting an ejection failure nozzle from the image read by the image reading step;
A discharge failure detection method comprising: A full line type recording in which a plurality of nozzles for ejecting ink are provided for each of a plurality of ink colors having one or more nozzle rows arranged over the entire width of the printing medium in a direction substantially orthogonal to the feeding direction of the printing medium. Head,
A test image printing medium that is arranged to face the nozzle surface of the recording head and prints a test image from the recording head;
Image reading means for reading the test image formed on the test image printing medium;
Cleaning means for removing ink droplets forming a test image on the test image printing medium;
An ink jet recording apparatus comprising:   12. The ink jet recording apparatus according to claim 11, further comprising a retracting unit that moves the test image print medium to a predetermined retracted position. A full-line recording head having one or more nozzle rows in which a plurality of nozzles for ejecting ink are arranged over the entire width of the print medium in a direction substantially orthogonal to the feed direction of the print medium corresponds to a plurality of ink colors. Provided for each color,
A plurality of image reading means for reading an image formed on the test image printing medium by ejecting ink from a plurality of recording heads provided for each color is provided for each color recording head. The ink jet recording apparatus according to claim 11, wherein the ink jet recording apparatus is disposed with respect to the ink jet recording apparatus. A full line type recording in which a plurality of nozzles for ejecting ink are provided for each of a plurality of ink colors having one or more nozzle rows arranged over the entire width of the printing medium in a direction substantially orthogonal to the feeding direction of the printing medium. An ejection failure detection method in an inkjet recording apparatus including a head,
A test printing step of forming a test image on a test image printing medium disposed opposite to the nozzle surface of the recording head by ink droplets ejected from the nozzle;
A test image reading step of reading a test image formed on the test image printing medium by the test printing step by an image reading means in which a plurality of light receiving elements are arranged in the print medium feeding direction;
A detection step of detecting an ejection failure nozzle from the image read by the image reading step;
A cleaning step of removing ink droplets forming a test image on the test image printing medium;
A discharge failure detection method comprising:

Images