JP2005313625A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect non discharging without the need of a recording medium exclusive for detection, and to obtain recording images corrected without the recording medium wasted even if non discharging is brought about. <P>SOLUTION: There are set a full line type printing head where a plurality of nozzles are arranged for every color of ink over a length corresponding to a total width of the recording medium, a selecting means which selects nozzles for printing to the recording medium printing data as dots for non discharging detection among the plurality of nozzles for printing the printing data, a non discharging detecting means for detecting discharging failures by reading the dots for non discharging detection printed to the recording medium, and a reverse feeding means for returning the recording medium after detected to a printing position of the printing head. After the detection by the non discharging detecting means, the recording medium is returned to the printing position of the printing head, and printing to obtain a final output image is carried out by the printing head to the recording medium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus, and more particularly, to a technique for repairing a recording defect due to non-ejection of ink during image recording in the ink jet recording apparatus.

  An image forming apparatus of an ink jet recording system has an ink jet head (printing head) in which a plurality of nozzles are arranged. By ejecting ink from the nozzles while relatively moving the print head and a recording medium, a target is formed. An image is formed on a recording medium.

  In such an ink jet recording method, printing is lost due to ejection failure such as ink ejection failure or abnormal ejection direction of the ink due to nozzle clogging of the print head or dirt on the ink meniscus surface. There are things to do. Such printing leakage is not noticeable due to the large multiplicity in the shuttle scan method, but in the case of a line head, this printing defect unevenness becomes remarkable.

  Therefore, various methods have been proposed for detecting a printing defect due to such a discharge failure, and for repairing this when a printing defect is detected.

  For example, it is known to detect whether ink particles are normally ejected by comparing dots printed using an image sensor with print data (see, for example, Patent Document 1). ).

  In addition, when a test pattern is recorded on the recording medium, read by the non-ejection detection means, and it is detected that ink non-ejection has occurred in some of the plurality of ejection openings, ink is ejected from the ejection openings. By changing the supply of drive data for the ejection ports other than the ejection ports causing non-ejection, even if non-ejection occurs in some of the ejection ports of the recording head, It is known that the drive data can be made to correspond to the discharge port so that recording can be performed even by a recording head in which non-discharge occurs in a part of the discharge data (for example, Patent Document 2) reference).

  The recording state of the image recorded on the dedicated test recording member is read by the reading unit, and the driving of the recording unit is controlled based on the read image information, and the test recording member erases the recorded image. Are known to be used again (see, for example, Patent Document 3).

In addition, based on the bitmap data of the black ink recording head, there is an area in which dots are formed with black ink in a line corresponding to at least the nozzle opening that needs to be ejected, among the nozzle openings of the color recording head. When the nozzle opening that needs to be ejected from the color ink recording head in addition to the print data faces the position where the black ink dots are formed, the ejection from the color ink recording head is performed. A single color ink drop is ejected from a nozzle opening that requires printing, and black dots based on the print data are printed over the color dots formed by this idle ejection, and the color dots are produced by idle ejection. It is known that the nozzles are clogged with black dots so that nozzles are not clogged by empty discharge during printing without interrupting the printing operation. Are (e.g., see Patent Document 4).
JP-A-63-260448 JP-A-5-338199 JP-A-6-340063 JP-A-9-216388

  However, in the system described in the above-mentioned Patent Document 1, in a system without multiplicity writing such as a single pass, or a system in which nozzles are increased in density or multi-nozzles, adjacent dots overlap each other when detecting dots. Therefore, there is a problem that non-ejection cannot be detected accurately.

  Further, the one described in Patent Document 2 has a problem in that the recording medium is wasted because a test pattern is recorded on the recording medium to detect non-ejection. 3 requires a dedicated recording medium for detection separately, which is reusable, but in order to be reused, a cleaning device for this dedicated recording medium is required. There is a problem that the configuration becomes complicated.

  Furthermore, the thing of the said patent document 4 prevents nozzle clogging by performing idle discharge during printing, does not detect non-discharge, and when non-discharge occurs However, there is a problem in that it is impossible to cope with the problem during printing, and it is necessary to stop printing and perform a nozzle recovery operation.

  The present invention has been made in view of such circumstances, and can detect non-ejection accurately without requiring a recording medium dedicated to detection, and can repair a recording medium without wasting it even if non-ejection occurs. An object of the present invention is to provide an ink jet recording apparatus capable of obtaining a recorded image.

  In order to achieve the above object, the invention described in claim 1 is directed to a full-line type print head in which a plurality of nozzles are arranged for each ink color over a length corresponding to the entire width of the recording medium, and print data. Selection means for selecting a nozzle to be printed on the recording medium from among the plurality of nozzles to be printed, as a dot for non-ejection detection, and a non-ejection detection dot printed on the recording medium. A non-ejection detection means for reading and detecting ejection failure; and a reverse feed means for returning the detected recording medium to the print position of the print head; after detection by the non-ejection detection means, by the reverse feed means An ink jet comprising: returning the recording medium to a printing position of the print head, and performing printing for obtaining a final output image by the print head on the recording medium. To provide a recording apparatus.

  This eliminates the need for test printing paper for non-ejection detection, makes it possible to perform non-ejection detection without wasting a recording medium, and prevents reduction in throughput.

  According to a second aspect of the present invention, the gap between dots of the non-ejection detection dots on the recording medium is ½ or more of the minimum dot diameter of dots printed by the print head. Features. Thereby, the detection accuracy of non-ejection detection dots can be improved.

  According to a third aspect of the present invention, the selection unit selects the non-ejection detection dot from a low-visibility region of the final output image. Further, according to a fourth aspect of the present invention, the selection unit selects the non-ejection detection dot from a writing leading end portion or a trailing end portion of the final output image on the recording medium. According to these, even when the recording medium is shifted to the print position of the print head and printing for obtaining the final output image is performed, it is not noticeable.

  According to a fifth aspect of the present invention, the selection unit selects a nozzle that prints the non-ejection detection dots on the recording medium based on the history data for each nozzle. Accordingly, it is possible to reduce ink consumption by detecting ejection of nozzles that are expected to be non-ejection risk.

  Moreover, as shown in claim 6, in the ink jet recording apparatus according to any one of claims 1 to 5, the selection unit is a nozzle that prints the non-ejection detection dots on the recording medium. Is selected as a reference dot for positioning, and a reference position sensor for detecting the reference dot is provided in the vicinity of the print head, and the reference dot detected by the reference position sensor is selected. A final output image is printed using the position as a reference position.

  As a result, it is possible to prevent printing misalignment during printing of the final output image after non-ejection detection.

  Similarly, in order to achieve the above object, the invention according to claim 7 is a full-line type print head in which a plurality of nozzles are arranged for each ink color over a length corresponding to the entire width of the recording medium. Selection means for selecting a nozzle to be printed on the recording medium as non-ejection detection dots from among the nozzles that are not used for printing print data among the plurality of nozzles; and the non-ejection detection printed on the recording medium A non-ejection detection means for detecting ejection failure by reading the dots for use, and a reverse feed means for returning the detected recording medium to the print position of the print head. After printing outside and detecting this by the non-ejection detecting means, the recording medium is returned to the printing position of the print head by the reverse feeding means and the recording medium is moved to the printing position. Providing an ink jet recording apparatus characterized by performing printing to obtain a final output image by de.

  As a result, non-ejection detection can be performed without affecting the final output image.

  According to another aspect of the present invention, when non-ejection is detected by the non-ejection detection means, a complementary operation for the non-ejection dot is performed by a nozzle adjacent to the nozzle where non-ejection is detected. It is characterized by that. Thereby, it is possible to repair the ejection failure image without wasting the recording medium.

  As described above, according to the ink jet recording apparatus of the present invention, non-ejection can be accurately detected without the need for a recording medium dedicated to detection, and even when non-ejection occurs, the recording medium is not wasted. A repaired recorded image can be obtained.

  Hereinafter, an inkjet recording apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, a dot (nozzle that discharges the dot) used for non-ejection detection is selected from output print data to be recorded, printed on a recording medium, detected by a light source and a reading sensor, and the recording medium is detected after detection. The final output image is obtained by returning to the recording position and performing additional droplet ejection using the remaining print data.

  FIG. 1 is an overall configuration diagram showing an outline of an embodiment of an ink jet recording apparatus according to the present invention.

  As shown in FIG. 1, the ink jet recording apparatus 10 includes a print head 12 having a plurality of print units 12K, 12LC, 12LM, 12C, 12M, and 12Y provided for each ink color. An ink storage / loading unit 14 for storing ink to be supplied to the printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y for each ink color; a paper feeding unit 18 for supplying the recording paper 16; The decurling unit 20 that removes curl and the nozzle surface (ink ejection surface) of the print head 12 are arranged opposite to each other, and the recording paper 16 is moved in the forward and reverse directions while maintaining the flatness of the recording paper 16. ) A suction belt conveyance unit 22 to convey, a non-ejection detection unit 24 that reads a print result by the print head 12, and a non-ejection detection, the recording paper 16 is moved to the print head 12 A reference position sensor 25 for positioning so that the image does not shift when the final output image is printed after returning to the character position, and a paper discharge unit 26 for discharging the printed recording paper (printed matter) to the outside. I have.

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

  In the case of an apparatus configuration using roll paper, a 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 arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  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.

  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 print head 12 and the sensor surface of the non-ejection detection unit 24 is flat. (Flat surface).

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, an adsorption chamber 34 is provided at a position facing the nozzle surface of the print head 12 and the sensor surface of the non-ejection detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. The suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 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 blowing method of spraying 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 printing area, the roller comes into contact with the printing surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing region is preferable.

  A heating fan 40 is provided on the upstream side of the print head 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 print head 12 supports inks of six colors (K (black), LC (light (light) cyan), LM (light (light) magenta), C (cyan), M (magenta), Y (yellow))). Printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y.

  FIG. 2 shows a plan perspective view of the print head 12. In FIG. 2, the recording paper 16 is conveyed in the direction of the arrow (upward in the figure) below the print head 12. Each of the printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y has a plurality of ejection ports (nozzles) 51 that eject ink of each color. In FIG. 2, the nozzles 51 are displayed as arranged on the surface of the figure, but FIG. 2 is a perspective view, and each nozzle 51 faces the recording paper 16 conveyed under the print head 12. (Toward the back side of the drawing), the ink is disposed below the print head 12 so as to eject ink.

  Further, as shown in FIG. 2, the print head 12 has its longitudinal direction in the paper transport direction (sub-scanning direction) so that each print unit 12K, 12LC, 12LM, 12C, 12M, 12Y takes the full width of the recording paper 16. ) And arranged in the width direction (main scanning direction) of the recording paper 16 orthogonal to each other, has a length corresponding to the maximum paper width, and exceeds at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. This is a so-called full-line head in which a plurality of nozzles 51 are arranged in the longitudinal direction over the length.

  The print head 12 has K (black), LC (light (light) cyan), LM (light (light)) from the upstream side (lower side in FIG. 2) along the conveyance direction of the recording paper 16 (indicated by an arrow in FIG. 2). Printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y corresponding to each of the six colors of ink are arranged in the order of light (magenta), C (cyan), M (magenta), and Y (yellow). The print head 12 can form a color image on the recording paper 16 by ejecting ink of each color from each of the printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y while conveying the recording paper 16.

  Thus, according to the print head 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 print head 12 in the paper transport direction is performed once. It is possible to record an image on the entire surface of the recording paper 16 only by performing (that is, by one scanning). Accordingly, the print head mounted on the carriage can perform high-speed printing as compared with the shuttle type head in which the print head reciprocates in the direction orthogonal to the paper conveyance direction, and productivity can be improved.

  In this example, a six-color configuration in which two light inks of light cyan (LC) and light magenta (LM) are added to the four standard colors of KCMY is exemplified. The combination is not limited to this embodiment, and other inks may be added as necessary, or a configuration of only KCMY four standard colors may be used.

  As shown in FIG. 1, the ink storage / loading unit 14 includes tanks that store inks of colors corresponding to the respective printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y. The print units 12K, 12LC, 12LM, 12C, 12M, and 12Y communicate with each other through the pipelines. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. doing.

  The non-ejection detection unit 24 reads the droplet ejection result of the print head 12 and detects non-ejection due to clogging of the nozzle 51 and other ejection defects.

  FIG. 3 shows an enlarged view of the periphery of the non-ejection detection unit 24. As shown in FIG. 3, the non-ejection detection unit 24 is disposed in the subsequent stage of the print head 12 and includes a light source 24 a and a light receiving sensor (color sensor) 24 b. The light source 24a is not particularly limited, and for example, an LED (light emitting diode), an LD (laser diode), a halogen lamp, a fluorescent lamp, or the like can be used. The light receiving sensor 24b is not particularly limited, and for example, a CCD or a phototransistor can be used.

  In the present embodiment, the light receiving sensor 24b is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by each of the printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y. . 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 includes 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 non-ejection detection unit 24 detects non-ejection when the non-ejection detection ink dots 17 ejected from the print head 12 onto the recording paper 16 are conveyed in the arrow A direction when the non-ejection is detected. When the light source 24a irradiates the ink dot 17 with light, and the reflected light is detected by the light receiving sensor 24b, the presence / absence of ink dot 17 (ejection presence / absence), dot landing position, dot size , Non-ejection and ejection failure are detected from the dot shape and the like.

  After the non-ejection is detected, the recording paper 16 is conveyed reversely as indicated by an arrow B in FIG. 3 by the suction belt conveyance unit 22 (see FIG. 1), and is temporarily returned to the printing position of the print head 12. . That is, the suction belt conveyance unit 22 functions as a reverse feeding means for returning the detected recording medium to the print position of the print head.

  If no ejection failure is detected in the non-ejection detection, the print head 12 simply performs additional droplet ejection using print data to form a final output image. On the other hand, when the non-ejection is detected, the non-ejection portion is repaired (complemented) along with the formation of the final output image. A method for selecting the nozzle 51 for ejecting the non-ejection detection ink dots 17 and a method for repairing when ejection failure is detected will be described in detail later.

  Further, when the recording paper 16 is returned to the printing position of the print head 12 and the final output image is formed or the non-ejection dots are complemented by additional droplet ejection, the positions of the non-ejection detection dots previously ejected are determined. A reference position sensor 25 for detecting the reference position is installed in the vicinity of the print head 12 so as not to cause a deviation. The configuration of the reference position sensor 25 is not particularly limited, but a configuration having a light source 25a and a light receiving sensor 25b can be used as in the non-ejection detection unit 24.

  A post-drying unit 42 is provided following the non-ejection 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. Although not shown, the paper output unit 26 for printed matter is provided with a sorter for collecting images according to orders.

  Next, the structure of the print units 12K, 12LC, 12LM, 12C, 12M, and 12Y that discharge the inks of the respective colors that constitute the print head 12 will be described. Each of the printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y provided for each ink color has a common structure. As shown in FIG. 2, each of the nozzles 51 has a two-dimensional matrix in a staggered manner. Is arranged.

  As shown in FIG. 4, each nozzle 51 corresponds to a pressure chamber 52 communicating with the nozzle 51, and an ink supply port 53 that supplies ink is formed in the pressure chamber 52. The nozzles 51 and the ink supply ports 53 are respectively disposed at both corners of the diagonal line of the pressure chamber 52. A pressure chamber unit 54 is formed by the pressure chamber 52, the nozzle 51, and the ink supply port 53, and a plurality of pressure chamber units 54 are arranged in a two-dimensional matrix to form the respective printing units 12K, 12LC, 12LM, 12C, 12M, and 12Y. Has been.

  FIG. 5 is a sectional view taken along line 5-5 of the pressure chamber unit 54 shown in FIG.

  As shown in FIG. 5, an actuator 58 having individual electrodes 57 is joined to a diaphragm 56 that forms the top surface of the pressure chamber 52. The diaphragm 56 also serves as a common electrode. When a driving voltage is applied to the common electrode and the individual electrode 57 to apply an electric field to the actuator 58, the actuator 58 is deformed to deform the diaphragm 56 toward the pressure chamber 52, thereby reducing the volume of the pressure chamber 52, and the pressure chamber. The ink in 52 is ejected from the nozzle 51.

  On the other hand, the pressure chamber 52 communicates with the common flow path 55 through the ink supply port 53, the electric field applied to the actuator 58 is released after ink is ejected, and the actuator 58 and the diaphragm 56 return to their original states. When the volume of the pressure chamber 52 increases, new ink is supplied from the common channel 55 to the pressure chamber 52 via the ink supply port 53.

  As described above, the recording medium transport direction (for example, the arrow direction in FIG. 2) is the sub-scanning direction, and the recording medium width direction (printing unit longitudinal direction) is the main scanning direction. The concept of main scanning and sub-scanning, which is a nozzle drive control method, will be described here.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the entire width of the recording medium (recording paper 16), (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially driven from one side to the other, ( 3) There is a driving method such as dividing nozzles into blocks and sequentially driving the nozzles in each block from one side to the other, and the width direction of the recording medium (direction perpendicular to the recording medium conveyance direction). A nozzle driving method that prints one line or one band is defined as main scanning.

  Further, by relatively moving the above-described full line head and the recording medium, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeated. The nozzle driving method to be performed is defined as sub-scanning.

  FIG. 6 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10 of the present embodiment. 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 control unit 80, and ink droplet ejection amounts of the print units 12K, 12LC, 12LM, 12C, 12M, and 12Y of the print head 12 via the head driver 84 based on the image data. And the discharge timing is controlled. 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. 6, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor.

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

  The print control unit 80 also includes a selection unit (non-ejection inspection nozzle) that selects a nozzle 51 that ejects non-ejection detection ink dots based on image data prior to output of an output image (final output image). (Selection means) 81 and a discharge history data memory 83 for storing history data for each nozzle are additionally provided. The print controller 80 instructs the head driver 84 based on these pieces of information to cause the print head 12 to eject ink dots for non-ejection detection.

  The selection of the ink dots used for this non-ejection detection (same as the nozzle 51 that ejects the dots) is performed as follows.

  FIG. 7 shows an example of a recorded image to be formed on the recording paper 16 by the output print data. In the example shown in FIG. 7, a large number of circular dots 90 indicated by broken lines are densely arranged to form a rhombus.

  A dot used for non-ejection detection is selected from a large number of dots 90 based on the print data. First, a non-ejection detection dot ejected on the recording paper 16 is read by a reading sensor (light receiving sensor 24b). In order to ensure detection, it is necessary to separate the non-ejection detection dots so that they do not overlap with other dots. Therefore, non-ejection detection is performed so that a gap between dots on the recording paper 16 is ½ or more (0.5 dots or more) of the minimum dot diameter of dots formed on the recording paper 16 by the print head 12. Select a dot.

In FIG. 8, eight non-ejection detection dots 91 to 98 are arranged so that the gaps between the dots among the dots 90 output by the print data are at least ½ dot of the minimum dot diameter. The selected state is shown. That is, as shown in FIG. 8, when the minimum dot diameter is D among the diameters of each dot 90, the gap d between the dots is ½ or more of the minimum dot diameter D (d> D / 2). In this way, the non-ejection detection dots 91 to 98 are selected.
In this embodiment, the dot size is an ink droplet amount of 2 [pl] and a dot diameter of about 25 to 30 [μm].

  Next, it is preferable to select the non-ejection detection dots from a region where the visibility of the output print data is low. Alternatively, it is preferable to select from the vicinity of the leading edge or the trailing edge of the recorded image on the recording paper 16 when the image is written. This is to prevent the recording paper 16 from becoming noticeable even if the recording paper 16 is displaced later when it is returned to the recording position and subjected to additional droplet ejection (overwriting).

  When selecting non-ejection detection dots from a low-visibility area, the human eye has a higher discrimination ability for density changes than for color changes. It is considered good to choose. In general, it is said that the relationship between the spatial frequency and the density difference visible to humans is as shown in the graph of FIG. As shown in FIG. 9, the density difference that is visible when the spatial frequency is 1 to 1.5 [lines / mm] is minimized, and the density that is visible even when the spatial frequency is higher or lower than this. The difference grows. That is, even if the spatial frequency is higher or lower than 1 to 1.5 [lines / mm], the density difference is difficult to be visually recognized.

  After all, the range in which the density difference is easy to be visually recognized is a range where the spatial frequency is 1 to 1.5 [lines / mm], and the range avoiding this is a low visibility region. The non-ejection detection dots are selected from the image.

  Specifically, from an image region having a spatial frequency of 0.5 [lines / mm] or less, that is, an interval of 2 mm pitch or more, or a spatial frequency of 2 [lines / mm] or more, that is, an interval of 0.25 mm pitch or less. It is preferable to select non-ejection detection dots. The spatial frequency referred to here represents the spatial frequency (color density change or pattern change) of the image or pattern to be output and the dot interval.

  Further, past non-discharge detection data for each nozzle 51 and history data such as the elapsed time from the previous discharge are stored in the discharge history data memory 83, and the non-discharge inspection nozzle selection means 81 determines the non-discharge inspection nozzle selection unit 81 based on this data. You may make it select the nozzle 51 which discharges the dot for discharge detection. As a result, ink consumption can be reduced by intensively detecting ejection with high risk of non-ejection.

  Further, as described above, not only the non-ejection detection dots are selected from the output print data but also selected from the nozzles 51 other than the nozzles 51 that eject the print data, for example, as shown in FIG. The non-ejection detection dots 99 may be ejected outside the image range.

  However, in this case, the non-ejection detection dots 99 are selected from a range with low visibility on the recording paper 16 with respect to the output image. In this case, the low visibility range means that the spatial frequency is 0.5 [lines / mm] or less, that is, an interval of 2 [mm] pitch or more, as shown in FIG. ], That is, a range in which an interval of 0.25 [mm] pitch or less is separated from the end of the output image. Further, when a plurality of non-ejection detection dots are hit, the above-mentioned interval is similarly set. At this time, similarly to the above, the gap between the minimum dots is 0.5 dots or more.

  As described above, non-ejection detection dots are selected and ink is ejected from the print head 12 onto the recording paper 16 to form a non-ejection detection pattern as indicated by black circles in FIG. 8 or FIG.

  After ejecting the non-ejection detection dots, the recording paper 16 is conveyed to the bottom of the non-ejection detection unit 24, and the non-ejection detection unit 24 detects the non-ejection detection dots.

  After the detection, the suction belt conveyance unit 22 is driven in the reverse direction to return the recording paper 16 to the recording position of the print head 12 and perform additional droplet ejection based on the output print data. Returning the recording paper 16 to the printing position of the print head 12 is not limited to the switchback method in which the suction belt conveyance unit 22 is driven reversely to reverse the sub-scanning direction. A loop system may be used in which the recording paper 16 is conveyed as it is in the forward direction in the sub-scanning direction, and then goes around once and returns to the printing position.

  At this time, additional droplet ejection is performed by ejecting dots based on the remaining print data between the detected non-ejection detection dots. For example, when the non-ejection detection dots are as shown in FIG. 10, dots based on other print data excluding the dots 91 to 99 ejected in FIG. 10 are additionally ejected, as shown in FIG. An image is formed. Here, the non-ejection detection dots 99 that are distant from the output image have low visibility as described above, and therefore have little influence on the output image.

  The method of additional droplet ejection is not limited to the method of ejecting additional dots based on the print data between the non-ejection detection dots detected in this way, and additional droplet ejection is performed by other methods. May be.

  For example, as shown in FIG. 12, the non-ejection detection dots 90 to 98 are first ejected with a light ink having a certain density, and when an additional ejection is performed after the detection, the non-ejection detection is performed. Alternatively, an output image may be formed as shown in FIG.

  Alternatively, the ink color of the non-ejection detection dot and another color ink may be overlapped to perform additional droplets to obtain a final color to be output by mixing the inks of these colors. For example, when G (green) is finally desired, non-ejection detection dots may be printed in Y (yellow), and additional droplets may be overprinted in C (cyan). The reverse is also possible. Alternatively, when black (K) is finally desired, a non-ejection detection dot is shot with, for example, C (cyan), and M (magenta) and Y (yellow) are overprinted for additional droplets, respectively. Then, K (black) may be obtained.

  Further, in the present embodiment, as described above, non-ejection detection dots (non-ejection detection patterns) are printed by the print head 12 and the recording paper 16 is conveyed to the non-ejection detection unit 24 for non-ejection detection. After detecting the dots for printing, the recording paper 16 is again conveyed back to the print head 12 in the sub-scanning direction, and the ink droplets are again superimposed on the non-ejection detection dots by the print head 12. Therefore, especially when the non-ejection detection dot is selected from the print data for output, the non-ejection detection dot and the dot by the print data to be added later are not shifted. There is a need to.

  Therefore, when selecting non-ejection detection dots by the non-ejection inspection nozzle selection means 81 attached to the print controller 80, a reference dot serving as a positioning reference is determined, and a final output image is formed by additional droplet ejection. In this case, the reference position sensor 25 detects the reference dots to perform reference alignment of the image forming positions, and a high-quality final output image without deviation can be obtained. The selection of the reference dot serving as the positioning reference is not particularly limited, and any non-ejection detection dot can be used as the reference dot. However, the position is clear and the image is displayed for convenience during recording. It is preferable that the dot at the leading end of the writing is a reference dot.

  Further, in the non-ejection detection by the non-ejection detection unit 24, when non-ejection or other ejection failure is detected, the adjacent dot of the ejection failure dot is hit when writing the normal image by the additional ejection after the detection. An image is complemented by the nozzle 51.

  In this complement, when there is a discharge failure, printing cannot be performed with the nozzle 51 having the discharge failure, and therefore, for example, a complement operation is performed using the nozzle 51 adjacent to the nozzle 51 having the discharge failure.

  For example, as shown in FIG. 14, it is assumed that the non-ejection detection dot 98 has ejection failure. At this time, the recording paper 16 is returned to the recording position of the print head 12, and the print control unit 80 confirms the position of the defective ejection dot 98, and the ink from the nozzle 51 that ejects a dot adjacent thereto is ejected. The head driver 84 is controlled to increase the discharge amount.

  Then, as shown in FIG. 15, the size of the dots 100, 101, and 102 around the non-ejection detection dot 98 that was an ejection failure is increased to complement the dot 98.

  The method for complementing defective ejection dots is not limited to this, and other complementing methods may be applied. For example, the print head 12 may be moved in the main scanning direction and printed by another nozzle 51 of the same color, or may be complemented by using the nozzle 51 of another color depending on the case.

  As described above, according to the present embodiment, the gap between dots on the recording paper for non-ejection detection dots is set to a predetermined value or more, so that ejection can be detected with high accuracy. Also, after printing the non-ejection detection dots (non-ejection detection pattern) on the recording paper and performing the detection operation, the recording paper was returned to the recording position of the print head, and normal printing was overprinted again. In addition, a recording medium dedicated to detection is not required, and the recording medium is not wasted.

  Although the ink jet recording apparatus of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

1 is a configuration diagram showing a schematic configuration of an embodiment of an ink jet recording apparatus according to the present invention. FIG. 2 is a plan perspective view illustrating a configuration of a print head according to the present embodiment. It is a side view which shows the non-ejection detection part periphery of this embodiment. It is a top view which expands and shows the printing unit of this embodiment. FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 1 is a block diagram illustrating a schematic configuration of a control system of an ink jet recording apparatus according to an embodiment. It is a top view which shows typically the recording dot by the output print data in this embodiment. It is explanatory drawing which shows a mode that the dot for non-ejection detection was selected from the output print data shown in FIG. It is a diagram which shows the relationship between a density | concentration difference and a spatial frequency. It is explanatory drawing which shows the other selection method of the non-ejection detection dot. It is explanatory drawing which shows a mode that printing data was additionally ejected with respect to the non-ejection detection dot of FIG. It is explanatory drawing which shows the other example of the non-ejection detection dot. It is explanatory drawing which shows the state which recorded the printing data with respect to the non-ejection detection dot of FIG. It is explanatory drawing which shows a mode that the discharge failure nozzle was detected. It is explanatory drawing which shows a mode that the discharge failure nozzle is complemented.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Print head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feeding part, 20 ... Decal processing part, 22 ... Adsorption belt conveyance part, 24 ... Non-ejection detection part, 25: Reference position sensor, 26: Paper discharge unit, 28: Cutter, 30 ... Heating drum, 31, 32 ... Roller, 33 ... Belt, 34 ... Suction chamber, 35 ... Fan, 36 ... Belt cleaning unit, 40 ... Heating fan , 42 ... post-drying section, 44 ... heating / pressurizing section, 45 ... pressure roller, 51 ... nozzle, 52 ... pressure chamber, 53 ... ink supply port, 54 ... pressure chamber unit, 55 ... ink common flow path, 56 ... Diaphragm, 58 ... Actuator, 70 ... Communication interface, 72 ... System controller, 74 ... Image memory, 76 ... Motor driver, 78 ... Heater driver, 80 ... Print controller, 1 ... non-discharge test nozzle selecting unit, 82 ... image buffer memory, 83 ... discharge history data memory, 84 ... head driver, 86 ... host computer, 88 ... motor, 89 ... heater, 90 to 99 ... non-ejection detection dot

Claims (8)

A full-line print head in which a plurality of nozzles are arranged for each ink color over a length corresponding to the entire width of the recording medium;
Selecting means for selecting a nozzle to be printed on the recording medium as a non-ejection detection dot from among the plurality of nozzles for printing print data;
Non-ejection detection means for detecting ejection failure by reading the non-ejection detection dots printed on the recording medium;
Reverse feed means for returning the detected recording medium to the print position of the print head;
After the detection by the non-ejection detection means, the recording medium is returned to the printing position of the print head by the reverse feeding means, and printing for obtaining a final output image by the print head is performed on the recording medium. An ink jet recording apparatus.   2. The inkjet according to claim 1, wherein a gap between dots of the non-ejection detection dots on the recording medium is ½ or more of a minimum dot diameter of dots printed by the print head. Recording device.   The inkjet recording apparatus according to claim 1, wherein the selection unit selects the non-ejection detection dots from a low-visibility region of the final output image.   3. The ink jet recording apparatus according to claim 1, wherein the selection unit selects the non-ejection detection dot from a leading end portion or a trailing end portion of the final output image on the recording medium.   The inkjet recording apparatus according to claim 1, wherein the selection unit selects a nozzle that prints the non-ejection detection dots on the recording medium based on history data for each of the nozzles.   The inkjet recording apparatus according to any one of claims 1 to 5, wherein the selection unit selects one of the nozzles for printing the non-ejection detection dots on the recording medium. In addition to designating as a reference dot for positioning, a reference position sensor for detecting the reference dot is provided in the vicinity of the print head, and a final output image is printed using the position of the reference dot detected by the reference position sensor as a reference position. An ink jet recording apparatus. A full-line print head in which a plurality of nozzles are arranged for each ink color over a length corresponding to the entire width of the recording medium;
Selecting means for selecting nozzles to be printed on the recording medium as non-ejection detection dots from nozzles that are not used for printing print data in the plurality of nozzles;
Non-ejection detection means for detecting ejection failure by reading the non-ejection detection dots printed on the recording medium;
Reverse feed means for returning the detected recording medium to the print position of the print head;
The non-ejection detection dots are printed outside the image area, detected by the non-ejection detection means, and then returned to the printing position of the print head by the reverse feeding means. An ink jet recording apparatus that performs printing for obtaining a final output image on a medium by the print head.   2. The non-ejection detecting unit detects a non-ejection, and a complementary operation for the non-ejection dot is performed by a nozzle adjacent to the non-ejection detected nozzle. The inkjet recording device according to any one of?

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