JP3838251B2 - Inkjet recording apparatus and ejection failure detection method - Google Patents

Description

  The present invention relates to an ink jet recording apparatus and a discharge failure detection method, and more particularly to a technique for detecting discharge failure of a nozzle that discharges ink droplets.

  In recent years, inkjet recording apparatuses (inkjet printers) have become widespread as recording apparatuses that print and record images taken by digital still cameras. 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.

  In an inkjet printer, some of the many nozzles may not be ejected for some reason, or the ink ejection amount (dot size to be ejected onto the recording paper) and flight direction (droplet ejection position) will be inappropriate. In some cases, ejection failure such as The presence of such an inappropriate nozzle causes a reduction in the quality of the recorded image, and thus countermeasures are necessary.

  Conventionally, as a method of detecting ejection failure of nozzles, a method of measuring a print of a test pattern, a method of measuring a practical print (printing a target image for which print output is actually required), or ejection inside the head A method for measuring a characteristic (a physical property value such as a resistance value) is known.

  In the ink jet recording apparatus and the ink jet recording method disclosed in Patent Document 1, a non-ejection nozzle is detected by a detection electrode provided in the recording head, and a change in driving voltage is detected via ink on the recording head substrate. Done.

  In the inkjet recording apparatus described in Patent Document 2, a continuous line composed of all nozzles of one head is formed on a test ejection sheet at a position where each of a plurality of heads does not interfere with each other, and the presence or absence of an intermittent portion of the line is determined. Optically or electrically detected.

In the color filter manufacturing method and manufacturing apparatus described in Patent Document 3, laser light is performed based on a state when ink ejected from an inkjet head passes.
JP 2001-315318 A Japanese Patent Laid-Open No. 6-24008 Japanese Patent Laid-Open No. 9-101410

  However, in the method of measuring the print of the test pattern, it is necessary to print a dedicated test pattern separately from the target image to be actually printed. In addition, there is a problem that it is difficult to detect defective nozzles due to measurement position errors in simple patterns. Furthermore, there is a problem in that it is affected by output variations of the line sensor that images the test pattern.

  In the case of a method for measuring a practical print, since the practical print to be measured is generally a complex image, it is difficult to determine whether it is an image defect due to a nozzle defect or the original image content, and the influence of the measurement position error is affected. Therefore, there is a problem that it is difficult to accurately identify the defective nozzle. Further, as in the case of the test pattern, it is affected by the variation of the line sensor.

  In the ink jet recording apparatus and the ink jet recording method disclosed in Patent Document 1, non-ejection due to bubbles in the nozzle can be detected, but non-ejection due to other causes such as dust adhesion cannot be detected.

  The inkjet recording apparatus described in Patent Document 2 requires a test ejection sheet, and the sheet is wasted.

  In the color filter manufacturing method and manufacturing apparatus described in Patent Document 3, detection takes time when the number of nozzles increases. Further, it is necessary to dispose the light emitting element and the light receiving element below the nozzle, and a mechanism for retracting the head when the head is long is required.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an inkjet recording apparatus and an ejection failure detection method that can detect ejection failure nozzles without reducing productivity.

In order to achieve the above object, an ink jet recording apparatus according to the present invention is compatible with cyan ink, magenta ink, and yellow ink, and ejects ink droplets from nozzles. A conveying means having a holding and conveying member for holding a predetermined area for printing a test image, holding the printing medium and conveying the printing medium, and moving the printing medium relative to each other in the feeding direction; cyan ink in a predetermined area, are printed and the test printing control means for controlling to print a test image magenta and yellow inks are ejected in the same droplet ejection point, the holding conveyance member by the test printing control means cyan ink in the test image, take read the mixed color dots of magenta and yellow inks RG A sensor, cyan ink, R sensor output of the RGB sensor by the relationship of the spectral absorption of the magenta and yellow inks, G sensor, cyan ink obtained by processing in the order of B sensor, magenta ink, dot information of yellow ink Detecting means for detecting a discharge failure nozzle from the magenta so as to detect the discharge failure nozzle of cyan ink using the output of the R sensor and to exclude the influence of the secondary absorption of cyan ink. The correction amount of the ink component and the correction amount of the yellow ink are calculated, and the ejection amount of the magenta ink is detected using the output of the G sensor in consideration of the correction amount of the magenta ink component. The correction amount of the yellow ink component is calculated so as to exclude the influence, and the B center It is characterized by detecting the ejection failure nozzles in yellow ink in consideration of the correction amount of the yellow ink components according to the correction amount and the magenta ink of yellow ink components of the cyan ink using the output.

According to the present invention, a test image in which cyan ink, magenta ink, and yellow ink are ejected onto the same ejection point is printed on a predetermined area of a holding and conveying member used for conveying a print medium in the conveying means, and the test is performed. Since the image is read by the RGB sensor and the dot information of each color is acquired from one dot of the mixed color of cyan ink, magenta ink, and yellow ink, the print area of the test image can be minimized and read. Can reduce the time it takes . In addition, the output of the RGB sensor is processed in the order of the R sensor, G sensor, and B sensor in accordance with the spectral absorption relationship of cyan ink, magenta ink, and yellow ink. Color separation processing can be executed. Furthermore, since the ejection failure nozzle is detected from the mixed color dots of cyan ink, magenta ink and yellow ink in the test image, the time required for detection can be shortened. When a defective ejection nozzle is detected, image correction by another nozzle and recovery operation for the defective ejection nozzle can be performed, and the image quality can be improved.

  The print head may be a full-line print head in which nozzles are arranged over the entire printable area in a direction substantially perpendicular to the print medium conveyance direction, or a short print head is substantially orthogonal to the print medium conveyance direction. A shuttle scan type print head that ejects ink droplets while moving in the direction may be used.

  As the holding and conveying member, a conveying belt or a conveying drum may be used.

  The test image includes images, characters, and the like that are preferable for detecting defective ejection nozzles, and may be composed of multiple colors. Further, it may be controlled to print a test image for each color.

  The test image may be an image printed from all nozzles or an image printed from some nozzles. A mode in which some of the nozzles are selected may be nozzles that are used less frequently or nozzles in which ejection failures have occurred in the past.

  Further, the print medium may be held by the holding and conveying member at least in a print area where ink droplets are ejected, and is held so as to ensure a predetermined flatness in the print area.

  As the reading means, a line sensor or an area sensor may be used. Also, a monochrome sensor or a sensor corresponding to a plurality of colors may be used. Moreover, the aspect which reads a laser beam and reads the reflected light may be sufficient.

  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.

  “Print medium” is a medium (image-forming medium) that is subjected to printing by a recording head, regardless of the material or shape of a continuous sheet, cut sheet, sealing sheet, resin sheet such as OHP sheet, film, cloth, and the like. Includes various media.

  “Conveying means” means a mode in which the print medium is transported to a stopped (fixed) recording head, a mode in which the recording head is moved relative to the stopped printing medium, or a movement of both the recording head and the printing medium Any of the embodiments are included.

Before SL holding and conveying member, wherein the test image a predetermined area is provided for printing, the test printing control means, since the control for printing the test image in the predetermined region, the test in a predetermined area Since there is a region for printing an image, the holding force on the holding and conveying member is high, and the conveying performance is good .

  For example, when the print medium is held by the holding and conveying member by air suction, an area where the pitch of the air suction holes in the print medium feeding direction is wider than other areas is provided, and a test image is printed in this area. You may comprise.

  According to another aspect of the present invention, the holding conveyance member is provided with a plurality of predetermined areas for printing the test image, and the plurality of predetermined areas are used in the conveyance direction of the print medium. It is characterized by being arranged with a gap in accordance with a high print medium size.

According to this mode, improved productivity, improved transport performance of large size printing medium.

  For example, 10 L size prints having a width (direction substantially perpendicular to the conveyance direction) of 127 mm and a length (conveyance direction) of 89 mm are arranged at intervals of 5 mm, and a test print area having a length of 20 mm is provided for each 10 sheets. Therefore, since test print areas are set at intervals of 935 mm, it is possible to frequently check for discharge defects, and normal L size prints are arranged at narrow intervals of 5 mm in length. Productivity of L size print increases.

  The interval between the print media may be adjusted to the most frequently used print medium size, or may be adjusted to the least common multiple of the most frequently used print medium size and the next most frequently used print medium size. Further, the interval between the areas where the test image is printed may be determined so that a plurality of print media can be fixed.

Before SL holding and conveying member, in such a manner that a predetermined region for the test print between printing medium transported continuously by the transport means, relative to the predetermined region for the test printing and the printing medium aspect Ru comprising alignment means for aligning also preferred.

  It may be configured not to place the print medium in the area where the test image is printed, or it is detected that the print medium is placed in the area where the test image is printed, and the print medium is placed in the print area. Control may be performed so that the test image is not printed. This is particularly effective when a full-line type line head is provided.

  The alignment unit includes a detector (sensor) in at least one of the conveyance unit or the drive system that drives the conveyance unit, and a relative position between the print medium and a predetermined region for performing test printing according to a signal obtained from the sensor. Alternatively, the relative position between the print medium and a predetermined area where test printing is performed may be controlled based on a drive system control signal (for example, an operation command signal for the drive system motor).

  Furthermore, according to another aspect of the present invention, the test print control means controls to perform a test print in an area between the main images.

  According to this aspect, since a test image can be printed between the main image and the next main image, productivity does not need to be reduced. The main image includes a printing result in which target image data is printed.

Embodiments in which at least the test image is configured to have a easy color determines the ink color region to be printed out before Symbol holding conveyance member is also preferred.

  According to this aspect, it becomes easy to distinguish between the ink droplet and the holding and conveying member, and the reading accuracy is improved.

  Generally, cyan, magenta, yellow, and black are used as ink colors. A color in a wavelength region where these colors can be easily identified may be applied, or a brightness difference from the ink color may be applied. That is, it is only necessary that the sensor applied to the reading unit can reliably recognize the ink droplet.

  The holding and conveying member may be composed of not only one color but also a plurality of colors corresponding to printing colors, and may be transparent or translucent. If the holding and conveying member is transparent or translucent, an image can be read by transmitted light.

  Note that the color referred to here includes black and white (monochrome).

  According to another aspect of the present invention, at least an area on which the test image is printed out of the holding and conveying member is made of a material that stabilizes the landing elasticity of the ink droplets.

According to this aspect, it is possible to stabilize the landing elasticity of ink droplets when printing a test image, and the reading accuracy is improved. Furthermore, it is preferable that the holding and conveying member be made of a material that can be easily cleaned.

  In consideration of prevention of ink droplet aggregation and easy cleaning of the holding and conveying member, the holding and conveying member is preferably made of a material having a contact angle of about 40 °. More preferably, the holding and conveying member is made of a material having a contact angle of about 100 °. The contact angle refers to a contact angle after a predetermined time has elapsed since an ink droplet was ejected onto a predetermined printing medium (that is, a holding and conveying member). The angle formed by the surface of the ink droplet in the liquid portion and the holding and conveying member.

  According to still another aspect of the invention, a cleaning unit that cleans the holding and conveying member is provided on the downstream side of the reading unit in the print medium conveying direction.

  According to this aspect, when the test image is read by the reading unit, the holding and conveying member is cleaned, the print medium is not contaminated, and the subsequent test printing is possible.

  Examples of the cleaning means include a mode of wiping (peeling) with a roller or a blade, and a mode of immersing the belt in a cleaning liquid (solvent) to remove (dissolve) ink or the like.

  If the surplus ink cleaning member is used for full screen printing (edgeless image printing), the cleaning means can be simplified.

The present invention also provides a method invention for achieving the above object. That is, the ejection failure nozzle detection method in the ink jet recording apparatus according to the present invention corresponds to cyan ink, magenta ink, and yellow ink, and prints a print medium for ejecting ink droplets from the nozzles , and prints the print medium on the print head. Inkjet recording comprising: a conveying unit that is relatively moved in a medium feeding direction, holds the print medium, conveys the print medium, and includes a holding conveyance member provided with a predetermined region for printing a test image. a discharge failure detecting method of the device, for printing the cyan ink to the predetermined region from the print head before Kiho lifting conveying member, test image magenta and yellow inks are ejected in the same droplet ejection point A test printing process, and before the droplets are deposited on the holding and conveying member in the test printing process by the RGB sensor. Cyan ink of the serial test image, and magenta ink and read that read the mixed color dot by the yellow ink step, the cyan ink of the test image read in said reading step, a mixed color dots of magenta ink and yellow ink, cyan The ejection failure nozzle from the dot information of cyan ink, magenta ink, and yellow ink obtained by processing the output of the RGB sensor in the order of R sensor, G sensor, and B sensor according to the spectral absorption relationship of ink, magenta ink, and yellow ink And detecting the cyan ink ejection failure nozzle using the output of the R sensor and correcting the magenta ink component so as to eliminate the influence of the secondary absorption of the cyan ink. Calculating the amount of ink and the correction amount of yellow ink, In consideration of the correction amount of the magenta ink component using the output of the sensor, the ejection failure nozzle of the magenta ink is detected, and the correction amount of the yellow ink component is calculated so as to exclude the influence of the secondary absorption of the magenta ink. It is characterized in that a discharge failure nozzle of yellow ink is detected in consideration of the correction amount of the yellow ink component by cyan ink and the correction amount of the yellow ink component by magenta ink using the output of the B sensor .

  It is preferable to include a nozzle recovery unit that performs a recovery operation on the detected ejection failure nozzle and a correction unit that corrects a print image performed using the ejection failure nozzle.

  According to the present invention, since the test image is printed on the holding and conveying member having the conveying means, the test image printing print medium (paper) is not necessary, and the test image is placed between the images. Since printing is performed, productivity is not reduced. When an ejection failure nozzle is detected, a predetermined nozzle recovery operation and a predetermined image correction can be performed.

  Further, the ejection failure nozzle can be detected from the reading result of the reading unit, and the test image printed on the holding and conveying member is cleaned after the reading by the cleaning unit for cleaning the holding and conveying member.

  The holding and conveying member is made of a material that stabilizes the ink drop landing elasticity and has a color that makes it easy to determine the color of the ink drop, so that the ink drop landing elasticity is stable and the reading accuracy can be improved.

  In addition, since multiple color inks are printed on the same line and each color dot is read from the mixed color dots, the area for printing the test image can be minimized, and the conveyance performance is improved. .

  By providing alignment means for aligning the test image printing area for printing the test image on the holding conveyance member and the printing medium, ink drop landing elasticity is ensured in the test printing area, and the printing medium is printed in the printing medium conveyance area. The holding force can be increased, and the conveyance performance is improved. When the test print area is adjusted to the size of a frequently used print medium, the interval between the print media can be reduced, and the productivity is improved.

  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 transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads 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. Then, the round blade 28B is arranged on the printing surface side across the conveyance path. 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 portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are 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, an adsorption 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 24 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.

  Further, the belt 33 is provided with a test print area (not shown in FIG. 1 and shown as reference numeral 33A in FIG. 9) on which a test image is printed. The test image printed in the test print area is read by the print detection unit 24, and the ejection failure of the print heads 12K, 12C, 12M, and 12Y is determined from the read result. The detailed structure of the belt 33 and details of ejection failure detection of the print heads 12K, 12C, 12M, and 12Y will be described later.

  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 counterclockwise in FIG. The recording paper 16 driven in the direction and held on the belt 33 is conveyed from right to left in FIG. Details of the belt 33 will be described later.

  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, each of the print heads 12K, 12C, 12M, and 12Y has a length that exceeds at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10, as shown in FIG. A line type head in which a plurality of ink discharge ports (nozzles) are arranged is formed.

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

  The print detection unit 24 of this example is composed of a line sensor (reference numeral 24A in FIG. 9) having a light receiving element array wider than at least the ink discharge width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. Is done. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 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. Further, the print detection unit 24 includes a light source (reference numeral 24B in FIG. 9) that irradiates light onto the ejected dots.

  A post-drying unit 42 is provided following the print detection unit 24. 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. When the main image (printed target image) and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by the cutter (second cutter) 48. 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 paper output unit 26 for the target prints is provided with a sorter for collecting prints according to print orders.

  Next, the structure of the print head 50 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. 3 (a) is a plan perspective view showing an example of the structure of the print head 50, and FIG. 3 (b) is an enlarged view of a part thereof. 3C is a perspective plan view showing another example of the structure of the print head 50, and FIG. 4 is a cross-sectional view showing the three-dimensional configuration of the ink chamber unit (along line 4-4 in FIG. 3A). FIG. 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. 3A to 3C and FIG. 4, the print head 50 of this example includes a plurality of inks including nozzles 51 that eject ink droplets, pressure chambers 52 corresponding to the nozzles 51, and the like. The chamber units 53 have a structure in which the chamber units 53 are arranged in a staggered matrix, thereby achieving an increase in the apparent nozzle pitch density.

  That is, in the print head 50 according to the present embodiment, as shown in FIGS. 3A and 3B, the plurality of nozzles 51 that eject ink correspond to the entire width of the print medium in a direction substantially orthogonal to the print medium feed direction. This is a full line head having one or more nozzle rows arranged over a length of the same.

  Further, as shown in FIG. 3 (c), short two-dimensionally arranged heads 50 'may be arranged in a staggered manner and connected to form a length corresponding to the entire width of the print medium.

  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 arranged 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 entire width of the paper (recording paper 16), (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and each block is sequentially driven from one side to the other. One row of dots is formed in the paper width direction (direction perpendicular to the paper conveyance direction). The driving of the nozzle that prints a line by (or a line by a plurality of rows of dots) is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above 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, by moving the full line head and the paper relative to each other, it is possible to repeat the printing of a line (or a line consisting of a plurality of dots) formed by one row of dots formed by the main scanning described above as sub-scanning. Define.

  In the implementation of 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 employed. In implementing the present invention, an actuator other than the piezoelectric element can be applied to the actuator 58.

  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 remaining amount of ink 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 51 and a cleaning blade 66 as a means for cleaning the surface of the nozzle 51. Yes.

  The maintenance unit 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 is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  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. A serial interface such as USB (Universal Serial Bus) , IEEE 1394, Ethernet (registered trademark) , a wireless network, or a parallel interface such as Centronics can be applied to the communication interface 70. 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 of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data provided from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  In addition, the print control unit 80 includes a test print control unit 90 that performs test print control. The test print control unit 90 generates an image (print data) at the time of test printing (determination of the nozzle that discharges ink at the time of test printing, the ink discharge amount of the nozzle, the ink discharge position, etc.) and the test print. A discharge signal (a drive signal for the actuator 58 shown in FIG. 4) is generated.

  The test image data read by the print detection unit 24 is temporarily stored in the image buffer memory 82 via the print control unit 80 and sent to the image processing unit 92.

  The image processing unit 92 performs predetermined image processing such as RGB → CMY conversion on the image read by the print detection unit 24. The test image data subjected to the image processing is determined based on the test image data in the determination unit 94 while referring to the setting values (nozzle management data) of the nozzles recorded in the setting value holding unit 96. It is determined whether the discharge is normal or abnormal.

  The determination result is sent to the system controller 72, and recovery operations such as preliminary discharge and suction are performed on the nozzle determined to be defective.

(Discharge failure detection)
Next, detection of defective ejection nozzles in the inkjet recording apparatus 10 will be described.

  The ink jet recording apparatus 10 according to the present invention is configured to deposit a test pattern on the belt 33 shown in FIG. 1, read this pattern by the print detection unit 24, and detect an ejection failure nozzle from the read result. . The test pattern is ejected at different positions on the belt 33 for each ink color, and is read and detected for each color.

  FIG. 8 is a schematic diagram of a portion relating to ejection failure nozzle detection of the inkjet recording apparatus 10. 8 that are the same as or similar to those in FIG. 1 are assigned the same reference numerals, and descriptions thereof are omitted.

  The print detection unit 24 includes a line sensor 24A and a light source 24B. Light is emitted from the light source 24B to the test pattern ejected from each print head 50 onto the belt 33, and the reflected light is read by the line sensor 24A. In the present embodiment, the color separation line CCD sensor is used as the line sensor, but a line CCD sensor that does not include a color filter may be used. Furthermore, the shape of a dot may be taken in by irradiating a laser beam, reading the reflected light.

  A belt cleaning unit 36 for cleaning dirt on the belt 33 is provided on the downstream side in the sub-scanning direction of the print detection unit 24, and the belt 33 on which the test pattern is ejected is cleaned by the belt cleaning unit 36. The belt cleaning unit 36 is also used as a cleaning member that cleans excess ink during full-screen printing (marginless printing).

  In the present embodiment, the cleaning roll 36A is used for the belt cleaning unit 36, but a wiping member such as a blade may be used, or the belt 33 is immersed (sprayed) in a solvent to remove the attached ink. You may use the aspect to do.

  The cleaning roll 36A may always be in contact with the belt 33, or may be in contact only when necessary. When the cleaning roll 36A is constantly in contact with the belt 33, the load fluctuation is small and the conveyance speed is stable. When the cleaning roll 36A is brought into contact in synchronization with discharge, the cleaning roll 36A is prevented from being worn.

  FIG. 9 shows details of the belt 33. FIG. 9 is a view of the belt 33 as viewed from above in FIG. 8 (above the print head 50).

  The belt 33 includes a test print area 33A where a test pattern is ejected and a recording paper suction area 33C in which a large number of air suction ports 33B for fixing the recording paper 16 to the belt 33 (air suction) are arranged in a matrix. I have. The test print area 33A and the recording paper suction area 33C have a predetermined length in the sub-scanning direction and are alternately arranged.

  The phases of the test print area 33A and the recording paper suction area 33C are controlled so that the recording paper 16 is on the recording paper suction area 33C.

  That is, as shown in FIG. 12, the length Lc along the sub-scanning direction of the recording paper suction area 33C is set according to the size L2 of the recording paper 16 that is frequently used (in the embodiment shown in FIG. 12). , L2 times n, where n is a positive integer), a test print area 33A having a length LA along the sub-scanning direction is formed between the recording paper suction area 33C and the next recording paper suction area 33C. Is provided.

  In other words, the belt 33 is provided with the test print area 33A at the pitch L1 (the length LA of the test print area 33A in the direction along the sub-scanning direction + the length LC of the recording paper suction area in the direction along the sub-scan direction). The test print area pitch L1 satisfies the relationship of L1 = n * (L2 + L3) + L3.

  Here, n represents a positive integer, and L3 represents the distance between the sheets or the test print area and the sheet.

  Note that if the air suction port 33B is present in the test print area 33A, ink enters the air suction port 33B, so that the air suction port 33B is not arranged in the test print region 33A.

  In this example, conveyance control (positioning control) of the belt 33 is performed so that the ejection control of the print head 50 and the position of the belt 33 are matched. As a motor for driving the belt 33 (the roller around which the belt 33 is wound), a motor capable of controlling the rotation amount such as a stepping motor or a servo motor is used. By controlling the rotation amount of the motor, the position of the belt 33 is controlled. Can be controlled.

  The rotation amount of the motor may be calculated from the pulse signal (motor control signal) given to the motor driver 76 shown in FIG. 7, and the movement amount of the belt may be calculated, or the motor or the belt 33 may be detected by an encoder or a linear encoder. And a rotation amount of the motor or a movement amount of the belt 33 may be calculated from a detection pulse (detection signal) obtained from the detector.

  If the size of the recording paper adsorption area 33C is adjusted to the size of the recording paper 16 that is frequently used, test printing can be performed between images being printed, and productivity is not reduced. Further, if the recording paper suction area 33C is the size of the recording paper 16 with the highest usage frequency and the least common multiple of the size of the recording paper 16 with the next highest usage frequency, the recording papers 16 of different sizes may be used efficiently.

  The material of the belt 33 may be a plastic member such as polyimide or a metal. Various other members can also be used. However, the flatness of the recording paper 16 attracted to the belt 33 must be ensured. In addition, the test print region 33A is made of a member having ink drop landing elasticity (fixability) and easy cleaning by the belt cleaning unit 36. Of course, an embodiment in which the entire belt 33 including the recording paper suction area 33C is made of the material having the performance described above is preferable. FIG. 13 is a flowchart showing the flow of the test print control described above.

  When the test print control is started (step S10), the print detection unit 24 detects the rear end of the test print area 33A (the end on the downstream side in the traveling direction of the belt 33) (step S12), and the test print area 33A is detected. Using the rear end as a reference (origin position), counting of pulse signals given to the motor driver (motor driver 76 shown in FIG. 7) of the motor that drives the belt 33 is started (step S14), and the process proceeds to step S16.

  In step S16, it is determined whether or not the pulse count (number of pulses) is N1. If the pulse count is not N1 (less than N1) (NO determination), the pulse count is continued.

  On the other hand, when the pulse count reaches N1, test printing is started (step S18).

  Here, the number of pulses N1 indicates the movement of the belt 33 from the state in which the rear end of the test print area 33A is positioned in the detection area of the print detection unit 24 to the movement of the front end of the test print area 33A to the print area of the print head 50. The number of pulses corresponding to the quantity.

  When the test print is executed, the print detection unit 24 reads the test image (step S20), and after the predetermined image processing is performed on the read result (step S22), the nozzle is defective in ejection. It is determined whether or not (step S24).

  In step S24, recovery processing (cleaning) such as preliminary ejection and suction is performed on the nozzles determined to be defective in discharge (step S26), and normal nozzles that are not determined to be defective in discharge proceed to step S28 to perform the next test printing. The rear end of the area 33A is detected.

  When the trailing edge of the next test print area 33A is detected in step S28, the next pulse count is started (step S30), and it is determined whether or not the pulse count is N2 (step S32).

  The number of pulses N2 corresponds to the amount of movement of the belt 33 from the state in which the rear end of the test print area 33A is positioned in the detection area of the print detection unit 24 until the leading edge of the recording paper 16 moves to the print area of the print head 50. There is an aspect in which the number of pulses is used.

  In step 32, when the pulse count is not N2 (when the pulse count is N2 or less) (NO determination), the pulse count is continued. When the pulse count reaches N2, the conveyance of the recording paper 16 is started. Then, the conveyance control of the belt 33 is performed (step S34), and the process proceeds to step S36.

  During the pulse count, the recording paper 16 is temporarily stopped by a registration sensor (not shown) provided in the front stage of the belt, and when the pulse count reaches N2, the conveyance of the recording paper 16 is started. Also good.

  In step S36, it is determined whether or not the pulse count is N3. If the pulse count is not N3 (when the pulse count is N3 or less) (NO determination), the pulse count is continued and the pulse count is N3. If (YES determination), ink ejection (actual image printing) is started from the print head 50 (step S38).

  When actual image printing is started, it is determined whether or not the number of printed sheets is the set number (step S40). If the number of printed sheets is equal to or smaller than the set number (NO determination), the process proceeds to step S42, and the number of printed sheets is determined. It is determined whether or not the nozzle check set number is reached.

  If the number of prints is equal to or smaller than the nozzle check set number in step S42 (NO determination), the process proceeds to step S34, and printing is continued.

  On the other hand, when the number of printed sheets reaches the number of nozzle check sheets, printing is stopped, the process proceeds to step S12, and the trailing edge of the test print area 33A is detected.

  In step S40, when the number of printed sheets reaches the set number (YES determination), the printing control is terminated (step S44).

  The number of pulses N1, N2, and N3 may be determined in consideration of the reading error of the print detection unit 24 and the conveyance error of the belt 33.

  If a highly ink repellent member having low ink affinity with ink is used, the ink droplets deposited on the belt 33 may move without being fixed. Also, if the ink affinity with the ink is high, the fixing property to the belt 33 on the belt 33 becomes high, but the landing diameter becomes large and the ink droplets may be aggregated with other ink droplets that are ejected nearby. possible. Also, cleaning can be difficult.

  In this embodiment, the contact angle of the ink droplet is applied as a physical property value indicating the relative ink affinity between the ink droplet and the belt 33. As shown in FIG. 10, the contact angle θ of the ink droplet is expressed by an angle formed by the droplet ejection surface, the tangent line of the ink droplet, and the droplet ejection surface. When the contact angle is small, the ink affinity is high (the ink droplet fixing property is high).

A state in which the ink droplet has completely penetrated into the belt 33 is referred to as a contact angle of 0 °, and a state in which the ink droplet and the droplet ejection surface are in contact at one point is referred to as a contact angle of 180 °. Further, since the surface properties such as the surface roughness of the belt 33 are also related to the fixability of the ink droplets, when the test print region 33A is made of metal, the surface can be roughened to obtain a desired contact angle. .

  When the contact angle is about 90 °, it is easy to read ink droplets, and a preferable member for the test print region 33A is a member having a contact angle of 40 ° or more for the ink droplets. More preferably, the member has a contact angle of 100 ° or more.

  The test print area 33A is provided with a lightness difference from the ink color in order to easily recognize the test pattern that has been ejected. Of course, a color different from the ink color may be used. Furthermore, a transparent (semi-transparent) member is used for the test print area 33A, and the line sensor 24A is arranged at a position facing the print head 50 with the belt 33 interposed therebetween, so that the test pattern can be read by transmitted light. Become. Reading using transmitted light can improve reading accuracy compared to reading using reflected light.

  In the present embodiment, the material and physical property values of the test print area 33A are exemplified, but the entire belt 33 may be formed of the same member as the test print area 33A.

  In this embodiment, the recording paper 16 is fixed (adsorbed) to the belt 33 by air. However, the recording paper 16 may be fixed to the belt 33 by electrostatic force or the like. When electrostatic force is used for fixing the recording paper 16, the air suction port 33B is not necessary, and it is not necessary to distinguish between the test print area 33A and the recording paper suction area 33C. In other words, it is possible to perform test printing on all areas of the belt 33 and to adsorb the recording paper 16 to all areas.

  When the print head 50 becomes longer and becomes longer in the conveyance direction of the recording paper 16, the positional deviation between the nozzle on the upstream side and the nozzle on the downstream side becomes severe. In consideration of skew and the like, suction conveyance and conveyance by wrapping around a belt are performed.

  If the print head 50 is retracted and the test print paper is flowed, the productivity is affected. However, in this embodiment, the test print can be performed without flowing the test print paper, so the print head 50 needs to be retracted. Absent.

  If a mechanism for retracting the print head 50 in the opposite direction of the belt 33 (above the print head) is provided, the reading accuracy can be improved by using this to increase the distance between the print head 50 and the belt 33. Can be raised. When the print detection unit 24 is integrally formed, the distance between the line sensor 24A and the belt 33 (test print region 33A) is approximately 1 mm or less. In order to ensure a predetermined reading accuracy, the distance between the line sensor 24A and the belt 33 may be increased.

  When the nozzles are highly integrated, the inter-dot distance decreases accordingly. When the inter-dot distance is reduced, the ink droplets are likely to aggregate on the belt 33, and therefore it is preferable to discharge the ink droplets with a gap between the droplets.

  FIG. 11 shows a droplet ejection example of the test pattern of this embodiment. The conditions in this example are a resolution of 2400 dpi of the print head 50, an ink droplet contact angle of 40 °, and an ink droplet ejection amount of 10 pl. The landing diameter of the dots deposited under these conditions is from 30 μm to 40 μm.

The numbers in the dots (reference numerals 100 to 131) shown in FIG. 11 indicate the numbers of the nozzles on which the dots have been ejected, and are the nozzle rows that are projected so that the nozzle rows in the print head 50 are aligned in the main scanning direction. The arrangement order is shown. That is, in the projection nozzle row, the first nozzle, the second nozzle,..., The fifteenth nozzle, the sixteenth nozzle,.

  The dots 116 ejected from the 16th nozzle are arranged at positions adjacent to the dots 101 ejected by the first nozzle in the main scanning direction. Thereafter, the dots 132 are ejected from the 32nd nozzle, the dots 148 (not shown) ejected from the 48th nozzle,. The dot interval (dot pitch) in each dot row along the main scanning direction is 15/2400 inches.

  On the other hand, in the sub-scanning direction, dots 102 ejected from the second nozzle are arranged at an interval of 15/2400 inches from the dots 101. The interval in the main scanning direction between the dots 101 and 102 is 1/2400 inch. Thereafter, the dots 103 ejected from the third nozzle,..., The dots 115 ejected from the fifteenth nozzle, in the order of 15/2400 inches in the sub-scanning direction and 1/2400 inches in the main scanning direction. In this case, each dot is arranged.

  When the test pattern is ejected as described above, the distance between the centers of the adjacent dots in each dot is 15/2400 inches, that is, about 160 μm. In the case of proper ejection, ink aggregation cannot occur even if variations in nozzles and the like are taken into consideration.

  The test pattern data read by the print detection unit 24 is sent to the print control unit 80 shown in FIG. 7 and then temporarily stored in the image buffer memory 82 (storage unit). From this test pattern data, predetermined image processing is performed for each ink color by an image processing unit (not shown). In the image processing, the outline of each dot is extracted, and the diameter of each dot and the distance between the dots (center distance) are obtained. The information of each dot obtained in this way is compared with the information of the dot that should be ejected originally, such as nozzle non-ejection, ejection amount abnormality, ejection direction abnormality (ink droplet flight direction abnormality), etc. A discharge failure is detected.

  When an ejection failure nozzle is detected, droplet ejection correction (image correction) is performed for the next print job. In image correction, substitute droplet ejection is performed from a nozzle adjacent to a defective ejection nozzle. The substitute droplet ejection may be a mode in which dots larger than a predetermined size are ejected from a nozzle adjacent to the defective ejection nozzle, or a mode in which the ejection failure nozzle is displaced to cover the defective ejection nozzle. .

  Further, instead of the above-described image correction, control may be performed so as to perform a recovery operation on the ejection failure nozzle. The recovery operation includes a suction operation for forcibly sucking a defective nozzle, and a purge for preliminary discharge (tsubaki) to the cap 64 shown in FIG. 6, and the recovery operation is selectively performed according to the state of the nozzle. It is good to do. Of course, a plurality of recovery operations may be used in combination.

  In the present embodiment, an example in which a test pattern is printed for each ink color is illustrated. However, a plurality of inks having different colors other than black are ejected to the same droplet ejection point, and color information is discriminated to thereby configure a plurality of colors. It is possible to detect a defective ejection nozzle in the print head 50 corresponding to each color from one dot.

  Next, an example of a method for reading dot information for each color from dots composed of a plurality of colors other than black will be described with reference to FIG. A dot composed of a plurality of colors is read by a plurality of color (RGB) line sensors and processed in the following ink order.

  First, test printing is performed with C ink (step S100), and then test printing is performed with M ink at the same point (step S102). Further, test printing is performed at the same point with Y ink (step S104), and the test printing is read by the print detection unit 24 (step S106).

  The test print read by the print detection unit 24 is decomposed into CMY components (step S110), and CMY colors are detected according to the following procedure.

  [Processing Procedure 1] First, an inappropriate nozzle is detected for the C ink nozzle (step S112). For the evaluation of the C ink nozzle, the output of the R sensor is used.

  [Processing procedure 2] The correction amount of the M component is calculated so as to exclude the influence of C ink (step S114).

  [Processing procedure 3] Next, in consideration of the correction amount of the M component, an inappropriate nozzle is detected for the M ink nozzle (step S116). For the evaluation of the M ink nozzle, the output of the G sensor is used. However, an inappropriate portion of the C ink nozzle is removed and detection correction is performed for the other range.

  [Processing procedure 4] The correction amount of the Y component is calculated so as to exclude the influence of C ink and M ink (step S118).

  [Processing procedure 5] Next, in consideration of the correction amount of the Y component, an inappropriate nozzle is detected for the Y ink nozzle (step S120). For the evaluation of the Y ink nozzle, the output of the B sensor is used. However, inappropriate portions of the C ink nozzle and the M ink nozzle are removed, and detection correction is performed for the other ranges.

  The reason why the processing is performed in the order of C → M → Y according to the above processing procedures 1 to 5 is due to the relationship between the spectral sensitivity of the sensor and the spectral absorption of the color material. That is, since the color material normally 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. Similarly, the M ink affects the detection of the 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.

  Thereafter, in step S122, it is determined whether or not each nozzle has a discharge failure, and the nozzles determined to have a discharge failure (YES determination) are subjected to recovery processing (cleaning) such as preliminary discharge and suction. (Step S124) Thereafter, the process proceeds to step S112.

  On the other hand, when the nozzle is normal (NO determination), the ejection failure detection is terminated (step S126).

  If dot information for each color can be read from one dot composed of a plurality of colors in this way, the time required for reading and detection can be reduced, and the length of the test print area 33A along the sub-scanning direction can be reduced. can do.

  In the inkjet recording apparatus 10 configured as described above, a test print area 33A is provided on the belt 33 that conveys the recording paper 16, and a test pattern is printed on the test print area 33A. Therefore, it is possible to improve the image quality by detecting an inappropriate nozzle and recovering the nozzle or replacing it with another nozzle. Furthermore, the recording paper 16 for test printing need not be wasted.

  Since the print detection unit 24 can be fixed and the landing ink is captured, it is not necessary to retract the print head 50, and productivity is expected to improve. Furthermore, ejection failure can be detected by utilizing the gap between papers, and can be detected without reducing productivity even during printing.

  Further, there is no need to retract the long head, the structure can be simplified, and the cost can be reduced.

  In the present embodiment, an ink jet recording apparatus provided with a full line type print head has been exemplified, but the scope of application of the present invention is not limited to this, and the present invention can also be applied to a shuttle scan type ink jet recording apparatus.

  Further, in the present embodiment, a piezo-type inkjet recording apparatus is illustrated, but the scope of application of the present invention is not limited to this, and a bubble-type inkjet recording apparatus that ejects ink by bubbles generated by rapidly heating ink. It can also be applied to.

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 Enlarged view of the main part of Fig. 3 (a) Plane perspective view showing another structural example of the print head Sectional view along line 4-4 in Fig. 3 (a) 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. Schematic diagram of the part related to defective discharge nozzle detection Diagram showing belt configuration Diagram explaining contact angle Diagram explaining an example of test pattern Diagram showing the positional relationship between the belt and recording paper Flow chart showing the flow of control for detecting defective discharge FIG. 13 is a flowchart showing a control flow of an application example of the ejection failure control shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 22 ... Adsorption belt conveyance part, 24 ... Print detection part, 33 belt, 33A ... Test printing area, 36 ... Belt cleaning part, 50, 50 '... Print head, 72 ... System Controller, 80 ... print control unit

Claims (6)

A print head that discharges ink droplets from nozzles, corresponding to cyan ink, magenta ink, and yellow ink ;
A holding and conveying member provided with a predetermined region for printing a test image by moving the printing medium relative to the print head in a feeding direction of the printing medium, holding the printing medium and conveying the printing medium; and transport means was,
Cyan ink to the predetermined region of the holding conveyance member, and the test printing control means for controlling the magenta and yellow inks are printed test image are ejected onto the same droplet ejection point,
And RGB sensor taking read the mixed color dots of cyan ink, magenta ink and yellow ink printed on said test image on said holding conveyance member by the test printing control means,
Ejection failure based on dot information of cyan ink, magenta ink, and yellow ink obtained by processing the output of the RGB sensor in the order of R sensor, G sensor, and B sensor according to the spectral absorption relationship of cyan ink, magenta ink, and yellow ink Detecting means for detecting a nozzle;
With
The detection means detects the cyan ink ejection failure nozzle using the output of the R sensor and calculates the correction amount of the magenta ink component and the correction amount of the yellow ink so as to exclude the influence of the secondary absorption of the cyan ink. Then, a correction amount of the yellow ink component is calculated so as to detect a magenta ink ejection failure nozzle in consideration of the correction amount of the magenta ink component using the output of the G sensor and to eliminate the influence of the secondary absorption of the magenta ink. An inkjet recording apparatus for detecting a discharge failure nozzle of yellow ink in consideration of a correction amount of a yellow ink component by cyan ink and a correction amount of a yellow ink component by magenta ink using the output of the B sensor .   The holding and conveying member includes a plurality of predetermined areas for printing the test image, and the plurality of predetermined areas are spaced in accordance with a frequently used print medium size in the print medium conveyance direction. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is disposed.   3. The ink jet recording apparatus according to claim 1, wherein the test print control means controls to perform test print in an area between the main images. It said region at least a test image is printed out of the holding conveyance member, an ink jet recording apparatus according to claim 1, 2 or 3, wherein the landing of the ink droplets is characterized by comprising a material that stably.   5. The inkjet recording apparatus according to claim 1, further comprising a cleaning unit that cleans the holding and conveying member on the downstream side of the reading unit in the print medium conveying direction. 6. Corresponding to cyan ink, magenta ink, and yellow ink, a print head that ejects ink droplets from nozzles , a print medium relative to the print head in the feed direction of the print medium, and holding the print medium A discharge means for detecting an ejection failure of an ink jet recording apparatus, comprising: a transfer unit including a holding transfer member configured to transfer a print medium and to provide a predetermined region for printing a test image ;
A test printing process cyan ink to the predetermined region before Kiho lifting conveying member, magenta and yellow inks are printed a test image to be ejected on the same droplet ejection point from the print head,
The RGB sensor, and the test printing cyan ink of the test image that has been ejected into the holding conveyance member in step, reading that read the mixed color dot by magenta and yellow inks step,
The mixed color dots of the test image read in the reading step by cyan ink, magenta ink, and yellow ink are converted into R sensor, G sensor output of the RGB sensor according to the spectral absorption relationship of cyan ink, magenta ink, and yellow ink. , A detection step of detecting a discharge failure nozzle from dot information of cyan ink, magenta ink, and yellow ink obtained by processing in the order of B sensor ;
Including
In the detection step, the discharge amount of cyan ink is detected using the output of the R sensor, and the correction amount of the magenta ink component and the correction amount of the yellow ink are calculated so as to exclude the influence of the secondary absorption of the cyan ink. Then, a correction amount of the yellow ink component is calculated so as to detect a magenta ink ejection failure nozzle in consideration of the correction amount of the magenta ink component using the output of the G sensor and to eliminate the influence of the secondary absorption of the magenta ink. And detecting a defective nozzle for discharging yellow ink in consideration of the correction amount of the yellow ink component by cyan ink and the correction amount of the yellow ink component by magenta ink using the output of the B sensor. Method.

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