JP2011079199A - Inkjet recorder and method for detecting abnormal state - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder that enables an accurate determination of an abnormal nozzle based on read data obtained from a means for reading a resolution lower than a recoding resolution, and to provide a method for detecting an abnormal state. <P>SOLUTION: A nozzle detection pattern, which has one-on and N-offs, is formed taking the relation between the recording resolution R<SB>1</SB>and reading resolution R<SB>2</SB>into consideration. The number N of offs is determined so as to satisfy ä(N+1)×R<SB>2</SB>}R<SB>1</SB>=P (P is an integer of 2 or greater) and (N/R<SB>1</SB>)>R<SB>2</SB>. If the recording resolution R<SB>1</SB>and reading resolution R<SB>2</SB>are set to 1,200 dpi and 500 dpi respectively, N=11 when P=5; therefore, a nozzle detection pattern 202 that has one on and eleven offs (12 stages) are formed. The read data of such a nozzle detection pattern 202 is prevented from variation in data value, resulting from reading. Accordingly, a data value corresponding to a dot line and data corresponding to an inter-dot-line are reliably determined. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inkjet recording apparatus and an abnormality detection method, and more particularly to an abnormality detection technique for an inkjet head in which a plurality of nozzles are arranged in a matrix.

  2. Related Art An ink jet recording apparatus that forms a desired image on a recording medium by an ink jet method is known. Sub-heads with a two-dimensional nozzle array are arranged in the paper width direction, and equipped with a full-line inkjet head corresponding to the full width of the paper, and the full-line head and the paper are scanned only once to form an image on the entire paper. High productivity is realized by the single pass image recording.

  In an ink jet recording apparatus, an abnormal nozzle in which the ink ejection state is unstable causes various problems. Therefore, when an abnormal nozzle is detected, it is necessary to correct the abnormal nozzle. is there. Regarding the detection of abnormal nozzles, a configuration that captures a recorded image with a reading resolution equivalent to the output resolution of the recorded image using a line-type CCD image pickup device in which imaging elements such as CCDs are arranged in a line determines whether there is an abnormal nozzle. It is possible to detect with high accuracy.

  FIG. 13 shows read data for one stage when a 1-on 10-off detection pattern with a recording resolution of 1200 dpi is read by a line CCD imaging device with a reading resolution of 1200 dpi.

  The horizontal series in the figure represents nozzle numbers (nozzle positions), and the vertical series represents data values. The data value is 8-bit data (0 to 255), the vicinity of the data value “150” corresponds to the dot row (ON), and the vicinity of the data value “230” corresponds to the interval between the dot rows (OFF). . Since the read data shown in the figure has an on / off pattern corresponding to the detection pattern, it is determined that there is no abnormal nozzle among the nozzles forming the detection pattern at this stage.

  On the other hand, the higher the reading resolution of the line type CCD imaging device, the slower the data transfer speed. When the image output is inlined using the high resolution type line type CCD imaging device, the reading in the conveyance direction of the recording medium is performed. Due to the extremely low resolution, effective inspection becomes difficult.

  Therefore, at the time of in-line inspection due to the data transfer speed using a line CCD image pickup apparatus having a reading resolution (sufficiently high transfer speed) sufficiently lower than the recording resolution of the so-called “1 on N off type detection pattern”. There has been proposed a technique for avoiding an extreme decrease in reading resolution in the recording medium conveyance direction.

  Here, the “1 ON N OFF detection pattern” described above has (N + 1) stages of dot rows arranged at an (N + 1) dot pitch, and the nozzle rows at each stage are shifted with respect to the arrangement direction. It is an arranged pattern.

  That is, a dot row for one stage is formed by continuously driving every (N + 1) nozzles, and a dot row for (N + 1) stages is formed while switching the nozzles to be driven simultaneously. A 1 on N off type detection pattern including s is formed. Based on the read information of the 1-on-N-off detection pattern formed using all the nozzles, it is possible to determine whether there is an abnormality for all the nozzles.

JP 2005-205649 A

  FIG. 14 shows read data for one stage when a 1-on 10-off detection pattern with a recording resolution of 1200 dpi is read by a line CCD imaging device with a reading resolution of 500 dpi. The horizontal series value representing the nozzle number in the figure is a value obtained by multiplying the nozzle number in FIG. 13 by 5/12. The read data shown in the figure includes data having an intermediate value between the data value 150 corresponding to ON and the data values 200 to 230 corresponding to OFF, and the data having this intermediate value is the discharge amount. It is considered that the data value is decreased due to an insufficient amount or a landing position deviation, or data of a dot row located in the middle of adjacent imaging pixels. The former is data that should be determined as abnormal nozzles, and the latter should be determined as normal nozzles, but it is extremely difficult to accurately distinguish these from the read data shown in FIG.

  FIG. 15 shows a distribution using the data value of the read data shown in FIG. 14 as an index. The vertical series in FIG. 15 represents the appearance frequency of the data value, and the data value 150 has a peak corresponding to the normal nozzle. On the other hand, a value corresponding to an abnormal nozzle also appears in an area of a data value larger than the data value corresponding to a normal nozzle. It can be said that the nozzle corresponding to the data value in the section shown by the double arrow line from the peak corresponding to the normal nozzle in the vicinity of the data value 150 has a data value that is likely to be erroneously determined normal or abnormal.

  The present invention has been made in view of such circumstances, and an inkjet recording apparatus and an abnormality detection method capable of accurately determining an abnormal nozzle based on read data obtained from reading means having a resolution lower than the recording resolution. The purpose is to provide.

In order to achieve the above object, an ink jet recording apparatus according to the present invention includes an ink jet head provided with a plurality of nozzles for discharging droplets onto a recording medium, and the ink jet head and the recording medium along the sub-scanning direction. In (N + 1) (N is a positive integer) every moving means for relatively moving and a projection nozzle row in which the plurality of nozzles are projected so as to be aligned along the main scanning direction orthogonal to the sub-scanning direction. The nozzles are continuously driven simultaneously to form a dot row for one stage arranged at (N + 1) dot intervals along the main scanning direction, and all the nozzles are used while sequentially switching the driven nozzles. (N + 1) stages of dot rows are formed in the sub-scanning direction parallel to the moving direction of the recording medium, and dot rows arranged at intervals of N dots in the main scanning direction are arranged in the sub-scanning direction (N And drive control means for driving and controlling the plurality of nozzles to form a nozzle detection pattern having 1) stage, has a recording resolution smaller reading resolution R ₂ than R ₁ of the nozzle detection pattern, the nozzle detection pattern Reading means, data processing means for performing statistical processing on the image data read by the reading means, and whether each nozzle is an abnormal nozzle based on the processing result of the data processing means comprising determination means for determining, wherein the drive control unit includes a recording resolution R ₁ of the nozzle detection pattern, the reading resolution R ₂ of the reading means, arranged in the main scanning direction of the nozzle detection pattern pitch (N + 1) When the integer of 2 or more P, the relationship is to satisfy the following formula _{{(N + 1) × R} 2} / R 1 = P, and meet the following equation _{(N / R 1)> 1} / R 2 Characterized by driving and controlling the plurality of nozzles to form said nozzle detection pattern.

  According to the present invention, the interval (N + 1) between the dot rows in the main scanning direction of the nozzle detection pattern read by the reading unit is set to an integer multiple of 2 or more of the reading resolution of the reading unit, and (N + 1) is set to the reading resolution. By making it larger than the ratio of the recording resolution, all the dot rows constituting the nozzle detection pattern are reliably read. Therefore, data omission of data obtained from the reading unit is avoided, and preferable abnormal nozzle detection is realized.

1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a perspective plan view showing the structure of an ink jet head mounted on the ink jet recording apparatus shown in FIG. Enlarged view of FIG. Plane perspective view showing nozzle arrangement of the sub head shown in FIG. Sectional drawing which shows the three-dimensional structure of the subhead shown in FIG. 1 is a block diagram showing the configuration of a control system of the ink jet recording apparatus shown in FIG. Schematic configuration diagram showing an example configuration of an inline sensor Plan view of recording medium on which nozzle detection pattern is formed The figure explaining the relationship between the recording resolution, the reading resolution, and the pattern interval of the nozzle detection pattern The figure which shows the reading data of the nozzle detection pattern shown in this example Flowchart showing the flow of abnormal discharge nozzle detection and image correction control The figure showing the appearance frequency of the read data of the detection pattern The figure which shows the reading data at the time of reading with the same reading resolution as recording resolution The figure which shows the reading data at the time of reading with reading resolution lower than recording resolution The figure which shows distribution of the reading data read with the reading resolution lower than recording resolution

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

[Description of overall configuration of inkjet recording apparatus]
FIG. 1 is a configuration diagram showing the overall configuration of the ink jet recording apparatus according to the present embodiment. The ink jet recording apparatus 10 shown in the figure forms an image on the recording surface of the recording medium 14 based on predetermined image data using an ink containing a color material and an aggregating treatment liquid having a function of aggregating the ink. This is a two-liquid aggregation type recording apparatus.

  The ink jet recording apparatus 10 mainly includes a paper supply unit 20, a treatment liquid application unit 30, a drawing unit 40, a drying processing unit 50, a fixing processing unit 60, and a discharge unit 70. Transfer cylinders 32, 42, 52, and 62 are provided as means for delivering the recording medium 14 conveyed upstream of the treatment liquid application unit 30, the drawing unit 40, the drying processing unit 50, and the fixing processing unit 60, and the treatment liquid. As means for conveying the recording medium 14 while holding the recording medium 14 in each of the coating unit 30, the drawing unit 40, the drying processing unit 50, and the fixing processing unit 60, impression cylinders 34, 44, 54, and 64 having a drum shape are provided. .

  The transfer cylinders 32, 42, 52, 62 and the impression cylinders 34, 44, 54, 64 are provided with grippers 80 </ b> A, 80 </ b> B that hold the front end portion (or rear end portion) of the recording medium 14 at predetermined positions on the outer peripheral surface. It has been. The gripper 80A and the gripper 80B have the same structure for holding the tip of the recording medium 14 sandwiched between them, and the structure for transferring the recording medium 14 between grippers provided in other impression cylinders or transfer cylinders, and The gripper 80 </ b> A and the gripper 80 </ b> B are arranged at symmetrical positions that are moved 180 ° in the rotation direction of the pressure drum 34 on the outer peripheral surface of the pressure drum 34.

  When the transfer cylinders 32, 42, 52, 62 and the impression cylinders 34, 44, 54, 64 are rotated in a predetermined direction with the gripper 80A, 80B holding the tip of the recording medium 14, the transfer cylinders 32, 42 are rotated. , 52, 62 and the outer circumference of the impression cylinders 34, 44, 54, 64, the recording medium 14 is rotated and conveyed.

  In FIG. 1, only the grippers 80 </ b> A and 80 </ b> B provided in the impression cylinder 34 are denoted by reference numerals, and the reference numerals of the other impression cylinders and the transfer cylinder grippers are omitted.

  When the recording medium (sheet) 14 accommodated in the paper supply unit 20 is fed to the treatment liquid application unit 30, the aggregation process is performed on the recording surface of the recording medium 14 held on the outer peripheral surface of the impression cylinder 34. A liquid (hereinafter simply referred to as “treatment liquid”) is applied. The “recording surface of the recording medium 14” is an outer surface in a state where the impression cylinders 34, 44, 54, 64 are held, and is a surface opposite to the surface held by the impression cylinders 34, 44, 54, 64. It is.

  Thereafter, the recording medium 14 to which the aggregation treatment liquid has been applied is sent to the drawing unit 40, and color ink is applied to the area of the recording surface to which the aggregation treatment liquid has been applied, thereby forming a desired image.

  Further, the recording medium 14 on which the image of the color ink is formed is sent to the drying processing unit 50, where the drying processing unit 50 performs the drying processing, and after the drying processing, the recording medium 14 is sent to the fixing processing unit 60 to perform the fixing processing. Applied. By performing the drying process and the fixing process, the image formed on the recording medium 14 is hardened. In this way, a desired image is formed on the recording surface of the recording medium 14, and after the image is fixed on the recording surface of the recording medium 14, it is conveyed from the discharge unit 70 to the outside of the apparatus.

  Hereinafter, each unit (the paper feeding unit 20, the processing liquid coating unit 30, the drawing unit 40, the drying processing unit 50, the fixing processing unit 60, and the discharging unit 70) of the inkjet recording apparatus 10 will be described in detail.

(Paper Feeder)
The paper feeding unit 20 is provided with a paper feeding tray 22 and a feeding mechanism (not shown), and the recording medium 14 is configured to be fed one by one from the paper feeding tray 22. The recording medium 14 sent out from the paper feed tray 22 is positioned by a guide member (not shown) so that its tip is positioned at a gripper (not shown) of the transfer drum (paper feed drum) 32 and temporarily stops.

(Processing liquid application part)
The processing liquid application unit 30 includes a pressure drum (processing liquid drum) 34 that holds the recording medium 14 delivered from the paper feeding cylinder 32 on the outer peripheral surface and conveys the recording medium 14 in a predetermined conveying direction, and a processing liquid drum. And a processing liquid coating device 36 for applying a processing liquid to the recording surface of the recording medium 14 held on the outer peripheral surface 34 of the recording medium 14. When the processing liquid drum 34 is rotated counterclockwise in FIG. 1, the recording medium 14 is rotated and conveyed in the counterclockwise direction along the outer peripheral surface of the processing liquid drum 34.

  The processing liquid coating apparatus 36 shown in FIG. 1 is provided at a position facing the outer peripheral surface (recording medium holding surface) of the processing liquid drum 34. As a configuration example of the processing liquid coating device 36, a processing liquid container in which the processing liquid is stored, a pumping roller that is partially immersed in the processing liquid in the processing liquid container, and pumps up the processing liquid in the processing liquid container, and a pumping roller An embodiment including an application roller (rubber roller) that moves the pumped processing liquid onto the recording medium 14 is exemplified.

  In addition, there is provided an application roller moving mechanism that moves the application roller in the vertical direction (the normal direction of the outer peripheral surface of the treatment liquid drum 34), and an aspect in which collision between the application roller and the grippers 80A and 80B can be avoided. preferable.

  The treatment liquid applied to the recording medium 14 by the treatment liquid application unit 30 contains a color material aggregating agent that aggregates the color material (pigment) in the ink applied by the drawing unit 40, and the treatment liquid is applied on the recording medium 14. And the ink come into contact with each other, the separation of the color material and the solvent in the ink is promoted.

  The treatment liquid application device 36 is preferably applied while measuring the amount of the treatment liquid to be applied to the recording medium 14, and the film thickness of the treatment liquid on the recording medium 14 is an ink droplet ejected from the drawing unit 40. It is preferable to make it sufficiently smaller than the diameter.

(Drawing part)
The drawing unit 40 holds an impression cylinder (drawing drum) 44 that holds and transports the recording medium 14, a sheet pressing roller 46 for bringing the recording medium 14 into close contact with the drawing drum 44, and an inkjet that applies ink to the recording medium 14. Heads 48M, 48K, 48C, and 48Y are provided. The basic structure of the drawing drum 44 is the same as that of the processing liquid drum 34 described above, and a description thereof is omitted here.

  The sheet pressing roller 46 is a guide member for bringing the recording medium 14 into close contact with the outer peripheral surface of the drawing drum 44, faces the outer peripheral surface of the drawing drum 44, and delivers the recording medium 14 between the transfer drum 42 and the drawing drum 44. It is disposed downstream of the position in the transport direction of the recording medium 14 and upstream of the ink jet heads 48M, 48K, 48C, and 48Y in the transport direction of the recording medium 14.

  The recording medium 14 transferred from the transfer drum 42 to the drawing drum 44 is pressed by the sheet pressing roller 46 when being rotated and conveyed with the leading end held by a gripper (reference numeral omitted), and the outer periphery of the drawing drum 44. Adhere to the surface. After the recording medium 14 is brought into close contact with the outer peripheral surface of the drawing drum 44 in this way, the recording medium 14 is sent to the print area immediately below the ink jet heads 48M, 48K, 48C, 48Y without being lifted from the outer peripheral surface of the drawing drum 44. It is done.

  The inkjet heads 48M, 48K, 48C, and 48Y correspond to inks of four colors, magenta (M), black (K), cyan (C), and yellow (Y), respectively, and the rotation direction of the drawing drum 44 (see FIG. 1 are arranged in order from the upstream side in the counterclockwise direction in FIG. 1, and the ink discharge surfaces (nozzle surfaces, denoted by reference numeral 114A in FIG. 5) of the ink jet heads 48M, 48K, 48C, 48Y are drawn drums. The recording medium 14 is held so as to face the recording surface of the recording medium 14. Note that the “ink ejection surface (nozzle surface)” is a surface of the inkjet heads 48M, 48K, 48C, and 48Y that faces the recording surface of the recording medium 14, and is a nozzle that ejects ink described later (reference numeral in FIG. 4). This is a surface on which is formed.

  In addition, in the inkjet heads 48M, 48K, 48C, and 48Y shown in FIG. In such a manner, it is arranged to be inclined with respect to the horizontal plane.

  The inkjet heads 48M, 48K, 48C, and 48Y are full-line heads having a length corresponding to the maximum width of the image forming area in the recording medium 14 (the length in the direction orthogonal to the conveyance direction of the recording medium 14). The recording medium 14 is fixedly installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 14.

  On the nozzle surfaces of the inkjet heads 48M, 48K, 48C, and 48Y, nozzles for ejecting ink are formed in a matrix arrangement over the entire width of the image forming area of the recording medium 14.

  When the recording medium 14 is conveyed to the printing area immediately below the ink jet heads 48M, 48K, 48C, 48Y, the image data is converted into the area where the aggregation processing liquid of the recording medium 14 is applied from the ink jet heads 48M, 48K, 48C, 48Y. Based on this, ink of each color is ejected (droplet ejection).

  When droplets of the corresponding color ink are ejected from the inkjet heads 48M, 48K, 48C, and 48Y toward the recording surface of the recording medium 14 held on the outer peripheral surface of the drawing drum 44, processing is performed on the recording medium 14. The liquid and the ink come into contact with each other, and an aggregation reaction of the color material (pigment-based color material) dispersed in the ink or the color material (dye-based color material) to be insolubilized appears, and a color material aggregate is formed. As a result, movement of the color material in the image formed on the recording medium 14 (dot misalignment, dot color unevenness) is prevented.

  In addition, since the drawing drum 44 of the drawing unit 40 is structurally separated from the processing liquid drum 34 of the processing liquid application unit 30, the processing liquid does not adhere to the ink jet heads 48M, 48K, 48C, and 48Y. In addition, the cause of abnormal ink ejection can be reduced.

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

(Dry processing part)
The drying processing unit 50 holds an impression cylinder (drying drum) 54 that holds and conveys the recording medium 14 after image formation, and a solvent drying device 56 that performs a drying process for evaporating moisture (liquid component) on the recording medium 14. It has. The basic structure of the drying drum 54 is the same as that of the processing liquid drum 34 and the drawing drum 44 described above, and a description thereof is omitted here.

  The solvent drying device 56 is a processing unit that is disposed at a position facing the outer peripheral surface of the drying drum 54 and evaporates moisture present in the recording medium 14. When ink is applied to the recording medium 14 by the drawing unit 40, the liquid component (solvent component) of the ink and the liquid component (solvent component) of the processing liquid separated by the aggregation reaction between the processing liquid and the ink are placed on the recording medium 14. Since it remains, it is necessary to remove such a liquid component.

  The solvent drying device 56 performs a drying process for evaporating the liquid component existing on the recording medium 14 by heating with a heater, blowing with a fan, or a combination thereof, and removing the liquid component on the recording medium 14. Part. The amount of heating and the amount of air supplied to the recording medium 14 are appropriately set according to parameters such as the amount of moisture remaining on the recording medium 14, the type of the recording medium 14, and the conveyance speed (interference processing time) of the recording medium 14. Is done.

  When the drying process is performed by the solvent drying device 56, the drying drum 54 of the drying processing unit 50 is structurally separated from the drawing drum 44 of the drawing unit 40, and therefore, the inkjet heads 48M, 48K, 48C, and 48Y. In this case, it is possible to reduce the cause of abnormal ink ejection due to drying of the head meniscus by heat or air blowing.

  In order to exhibit the cockling correction effect of the recording medium 14, the curvature of the drying drum 54 is preferably 0.002 (1 / mm) or more. Further, in order to prevent the recording medium from being curved (curled) after the drying process, the curvature of the drying drum 54 is preferably 0.0033 (1 / mm) or less.

  In addition, a means (for example, a built-in heater) for adjusting the surface temperature of the drying drum 54 may be provided, and the surface temperature may be adjusted to 50 ° C. or higher. By applying heat treatment from the back surface of the recording medium 14, drying is promoted and image destruction during the subsequent fixing process is prevented. In this embodiment, it is more effective to provide means for bringing the recording medium 14 into close contact with the outer peripheral surface of the drying drum 54. Examples of the means for bringing the recording medium 14 into close contact include vacuum suction and electrostatic suction.

  The upper limit of the surface temperature of the drying drum 54 is not particularly limited, but from the viewpoint of safety of maintenance work such as cleaning ink adhering to the surface of the drying drum 54 (preventing burns due to high temperature). It is preferably set to 75 ° C. or lower (more preferably 60 ° C. or lower).

  The recording drum 14 is held on the outer peripheral surface of the drying drum 54 configured in this manner so that the recording surface of the recording medium 14 faces outward (that is, in a state in which the recording surface of the recording medium 14 is convex). By performing the drying process while rotating and transporting, drying unevenness due to wrinkling and floating of the recording medium 14 is surely prevented.

(Fixing processing part)
The fixing processing unit 60 includes a pressure drum (fixing drum) 64 that holds and conveys the recording medium 14, a heater 66 that heats the recording medium 14 on which an image is formed and liquid is removed, and the recording And a fixing roller 68 that presses the medium 14 from the recording surface side. Since the basic structure of the fixing drum 64 is common to the processing liquid drum 34, the drawing drum 44, and the drying drum 54, description thereof is omitted here. The heater 66 and the fixing roller 68 are disposed at a position facing the outer peripheral surface of the fixing drum 64, and are sequentially disposed from the upstream side in the rotation direction of the fixing drum 64 (counterclockwise direction in FIG. 1).

  In the fixing processing unit 60, the recording surface of the recording medium 14 is subjected to a preheating process by the heater 66 and a fixing process by the fixing roller 68. The heating temperature of the heater 66 is appropriately set according to the type of recording medium, the type of ink (the type of polymer fine particles contained in the ink), and the like. For example, a mode in which the glass transition temperature and the minimum film forming temperature of the polymer fine particles contained in the ink are considered.

  The fixing roller 68 is a roller member for heating and pressurizing the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 14. The Specifically, the fixing roller 68 is disposed so as to be in pressure contact with the fixing drum 64, and constitutes a nip roller with the fixing drum 64. As a result, the recording medium 14 is sandwiched between the fixing roller 68 and the fixing drum 64 and nipped at a predetermined nip pressure, and a fixing process is performed.

  As an example of the configuration of the fixing roller 68, there is an embodiment in which the fixing roller 68 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity. By heating the recording medium 14 with such a heating roller, when thermal energy equal to or higher than the glass transition temperature of the polymer fine particles contained in the ink is applied, the polymer fine particles are melted to form a transparent film on the surface of the image. Is done.

  When pressure is applied to the recording surface of the recording medium 14 in this state, the polymer fine particles melted into the unevenness of the recording medium 14 are pressed and fixed, and the unevenness of the image surface is leveled, so that preferable glossiness can be obtained. A configuration in which a plurality of fixing rollers 68 are provided in accordance with the thickness of the image layer and the glass transition temperature characteristics of the polymer particles is also preferable.

  The surface hardness of the fixing roller 68 is preferably 71 ° or less. By making the surface of the fixing roller 68 softer, a follow-up effect can be expected for the unevenness of the recording medium 14 caused by cockling, and fixing unevenness due to the unevenness of the recording medium 14 can be more effectively prevented. .

  In the ink jet recording apparatus 10 shown in FIG. 1, an inline sensor 82 is provided at a subsequent stage (downstream in the recording medium conveyance direction) of the processing area of the fixing processing unit 60. The inline sensor 82 is a sensor for reading an image formed on the recording medium 14 (or a nozzle detection pattern formed in a blank area of the recording medium 14), and a CCD line sensor (image sensor) is preferably used.

  Details of the inline detection unit including the inline sensor 82 (illustrated with reference numeral 172 in FIG. 7) will be described later. However, the inline sensor 82 has a resolution lower than the recording resolution, and each pixel has a plurality of dots ( The dot row is read while changing the timing.

  In the ink jet recording apparatus 10 shown in this example, the presence or absence of ejection abnormality of the ink jet heads 48M, 48K, 48C, and 48Y is determined based on the reading result of the inline sensor 82. Further, the in-line sensor 82 may include a measuring unit for measuring the moisture content, the surface temperature, the glossiness, and the like. In such an embodiment, parameters such as the processing temperature of the drying processing unit 50, the heating temperature of the fixing processing unit 60, and the pressure pressure are appropriately adjusted based on the moisture content, surface temperature, and gloss reading result, and the temperature inside the apparatus. The control parameter is adjusted as appropriate in accordance with the change and the temperature change of each part.

(Discharge part)
As shown in FIG. 1, a discharge unit 70 is provided following the fixing processing unit 60. The discharge unit 70 includes an endless conveyance belt 74 wound around the stretching rollers 72A and 72B, and a discharge tray 76 that stores the recording medium 14 after image formation.

  The recording medium 14 after the fixing process sent out from the fixing processing unit 60 is transported by the transport belt 74 and discharged to the discharge tray 76.

[Description of structure of inkjet head]
FIG. 2 is a schematic configuration diagram of an ink jet head applied to the present invention. FIG. 2 is a diagram (a plan perspective view of the head) of the recording surface of the recording medium viewed from the ink jet head. In addition, since the inkjet heads 48M, 48K, 48C, and 48Y shown in FIG. 1 have the same structure, in the following description, when it is not necessary to distinguish the inkjet heads 48M, 48K, 48C, and 48Y, these are used. Collectively, they are described as “inkjet head 100” or simply “head 100”.

  The head 100 shown in the figure forms a multi-head by connecting n sub-heads 102-i (i is an integer from 1 to n) in a line. Each sub head 102-i is supported by head covers 104 and 106 from both sides of the head 100 in the short direction. It is also possible to configure a multi-head by arranging the sub-heads 102 in a staggered manner.

  As an application example of a multi-head configured by a plurality of sub-heads, a full-line head corresponding to the entire width of a recording medium can be given. The full-line head has a plurality of nozzles (corresponding to the length (width) in the main scanning direction of the recording medium along the direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the recording medium. 4 is illustrated with reference numeral 108.) is arranged. An image can be formed on the entire surface of the recording medium by a so-called single-pass image recording method in which image recording is performed by scanning the head 100 having such a structure and the recording medium only once relatively.

  FIG. 3 is a partially enlarged view of the head 100. As shown in the figure, the sub head 102 has a substantially parallelogram-shaped planar shape, and an overlap portion is provided between adjacent sub heads. The overlap portion is a connecting portion of the sub heads, and is formed by nozzles in which dots adjacent to the sub heads 102-i are arranged in different sub heads in the arrangement direction of the sub heads 102-i (the horizontal direction in FIG. 2, the main scanning direction X shown in FIG. 3). The

  FIG. 4 is a plan view showing the nozzle arrangement of the sub head 102-i. As shown in the figure, each sub head 102-i has a structure in which nozzles 108 are arranged two-dimensionally, and a head including such a sub head 102-i is a so-called matrix head.

  In the sub-head 102-i shown in FIG. 4, a large number of nozzles 108 are arranged along a row direction W that forms an angle α with respect to the sub-scanning direction Y and a row direction V that forms an angle β with respect to the main scanning direction X. The substantial nozzle arrangement density in the main scanning direction X is increased. In FIG. 4, nozzle groups (nozzle rows) arranged along the row direction V are denoted by reference numeral 110, and nozzle groups (nozzle rows) arranged along the column direction W are denoted by reference numeral 112. ing.

In such matrix arrangement, when the adjacent nozzle spacing in the sub-scanning direction and L _s, the main scanning direction that substantially each nozzle 108 are arranged linearly at a fixed pitch P = L s _/ tanθ equivalent Can be handled.

  FIG. 5 is a cross-sectional view showing a three-dimensional configuration of one channel of droplet discharge elements (ink chamber units corresponding to one nozzle 108) serving as a recording element unit. As shown in the figure, in the head 100 of this example, a nozzle plate 114 formed with nozzles 108 and a flow path plate 120 formed with flow paths such as a pressure chamber 116 and a common flow path 118 are laminated and joined. Consists of structure. The nozzle plate 114 forms a nozzle surface 114A of the head 100, and a plurality of nozzles 108 communicating with the pressure chambers 116 are two-dimensionally formed.

  The flow path plate 120 constitutes a side wall portion of the pressure chamber 116 and a flow path forming a supply port 122 as a throttle portion (most narrowed portion) of an individual supply path that guides ink from the common flow path 118 to the pressure chamber 116. It is a forming member. For convenience of explanation, the flow path plate 120 has a structure in which one or a plurality of substrates are stacked, although it is illustrated schematically in FIG.

  The nozzle plate 114 and the flow path plate 120 can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common flow path 118 communicates with an ink tank (not shown) serving as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 116 via the common flow path 118.

  A diaphragm 124 constituting a part of the pressure chamber 116 (the top surface in FIG. 5) includes an individual electrode 126 and a lower electrode 128, and the piezoelectric body 130 is interposed between the individual electrode 126 and the lower electrode 128. A piezo actuator 132 having a sandwiched structure is joined. When the diaphragm 124 is formed of a metal thin film or a metal oxide film, it functions as a common electrode corresponding to the lower electrode 128 of the piezoelectric actuator 132. In the aspect in which the diaphragm is formed of a non-conductive material such as resin, a lower electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member.

  By applying a driving voltage to the individual electrode 126, the piezo actuator 132 is deformed to change the volume of the pressure chamber 116, and ink is ejected from the nozzle 108 due to a pressure change accompanying this. When the piezo actuator 132 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 116 from the common flow path 118 through the supply port 122.

  As shown in FIG. 4, the ink chamber unit having such a structure is latticed in a fixed arrangement pattern along a row direction V that forms an angle β with the main scanning direction X and a column direction W that forms an angle α with respect to the sub-scanning direction Y. The high-density nozzle head of this example is realized by arranging a large number in the shape.

[Explanation of control system]
FIG. 6 is a block diagram showing a system configuration of the inkjet recording apparatus 10. As shown in FIG. 6, the inkjet recording apparatus 10 includes a communication interface 140 and a system control unit 142, and overall control of each part of the apparatus is performed by the system control unit 142.

  The communication interface 140 is an interface unit (image input unit) that receives image data sent from the host computer 154. 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 140. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  The system control unit 142 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. To do. Further, it generates a control signal for controlling the conveyance control unit 144, the image processing unit 146, the head driving unit 148, and the like, and has a function as a memory controller of the storage unit 150 and the temporary storage unit 52.

  The image processing unit 146 is a processing block that performs predetermined processing on image data, and includes a processor having an image processing function. The image data sent from the host computer 154 is taken into the inkjet recording apparatus 10 via the communication interface 140 and temporarily stored in the image memory (for example, the temporary storage unit 152). The image memory is a storage unit that stores an image input via the communication interface 140, and data is read and written through the system control unit 142. The image memory is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The storage unit 150 stores programs executed by the CPU of the system control unit 142 and various data necessary for control (including data for ejecting test charts, abnormal nozzle information, and the like). The storage unit 150 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM.

  The temporary storage unit 152 is used as a temporary storage area for image data and various data, and is also used as a program development area and a calculation work area for the CPU. Further, it can also be used as a primary storage area for read data processed by the read data processing unit 168 and a calculation work area for the read data processing unit 168.

  The image processing unit 146 performs processes such as various processes and corrections for generating a droplet ejection control signal from image data (multi-valued input image data) in the image memory, under the control of the system control unit 142. It functions as a signal processing means. A droplet ejection control signal (ink ejection data) generated by the image processing unit 146 is supplied to the head driving unit 148.

  In other words, the image processing unit 146 includes functional blocks such as a density data generation unit, a correction processing unit, and an ink ejection data generation unit. Each of these functional blocks can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit is a signal processing unit that generates initial density data for each ink color from input image data, and includes density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion processing. I do.

  The correction processing unit is a processing unit that performs density correction using the density correction coefficient, and performs unevenness correction processing.

  The ink ejection data generation unit is a signal processing unit including a halftoning processing unit that converts the corrected image data (density data) generated by the correction processing unit into binary or multivalued dot data. Multi-value processing is performed. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into binary or multi-value gradation image data smaller than M. In the simplest example, the image data is converted into binary (dot on / off) dot image data. However, in the halftone process, the dot size type (for example, three types such as a large dot, a medium dot, and a small dot) is converted. It is also possible to perform corresponding multi-level quantization.

  The image processing unit 146 includes an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the image processing unit 146. Note that the image buffer memory may be in the form associated with the image processing unit 146 or may be used as the image memory. Further, the image processing unit 146 may be integrated with the system control unit 142 and configured by one processor.

  The ink discharge data generated by the image processing unit 146 (ink discharge data generation unit) is given to the head drive unit 148, and the ink discharge operation of the head 100 is controlled.

  The head drive unit 148 functions as a means for controlling the ejection drive of the head 100 and generates a drive signal waveform for driving an actuator (piezo actuator 132 shown in FIG. 5) corresponding to each nozzle 108 of the head 100. A drive waveform generator is included. The signal output from the drive waveform generation unit may be digital waveform data or an analog voltage signal.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 140 and stored in an image memory. At this stage, for example, RGB multi-valued image data is stored in the image memory.

  In the inkjet recording apparatus 10, a pseudo continuous tone image is formed by human eyes by changing the droplet ejection density and dot size of fine dots by ink (coloring material). It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory is sent to the image processing unit 146 via the system control unit 142, and is processed by the density data generation unit, the correction processing unit, and the ink ejection data generation unit. Converted to dot data for each ink color.

  That is, the image processing unit 146 performs processing for converting the input RGB image data into dot data of M, K, C, and Y colors. The dot data thus generated by the image processing unit 146 is stored in the image buffer memory. This dot data for each color is converted into MKCY droplet ejection data for ejecting ink from the nozzles of the head 100, and ink ejection data to be printed is determined.

  The head driving unit 148 outputs a driving signal for driving the actuator 132 corresponding to each nozzle 108 of the head 100 according to the printing content based on the ink ejection data and the driving signal (driving waveform). The head driving unit 148 may include a feedback control system for keeping the head driving conditions constant.

  In this way, when the drive signal output from the head drive unit 148 is applied to the head 100, ink is ejected from the corresponding nozzle 108. An image is formed on the recording medium 14 by controlling ink ejection from the head 100 in synchronization with the conveyance speed of the recording medium 14.

  As described above, based on the ink discharge data and the drive signal waveform generated through the required signal processing in the image processing unit 146, the discharge amount and discharge timing of the ink droplets from each nozzle via the head drive unit 148. Control is performed. Thereby, a desired dot size and dot arrangement are realized.

  Further, the system control unit 142 performs a predetermined data process on the read data of the nozzle detection pattern (shown with reference numeral 202 in FIG. 8) read from the inline sensor 82. And an inline detection unit 172 including a determination unit 170 that determines whether each nozzle is an abnormal nozzle based on the processing result of the read data processing unit 168. Examples of data processing by the read data processing unit 168 include binarization processing, normalization processing, comparison processing using a threshold value, and statistical processing. Data subjected to these processes is stored in a predetermined memory and referred to as appropriate.

  The abnormal nozzle determination unit 170 refers to the data processed by the read data processing unit 168, and determines whether there is an abnormal nozzle and the position of the abnormal nozzle (based on the printing status such as the presence / absence of ejection, variation in droplet ejection, and optical density). Number). Information on the determination result of the abnormal nozzle determination unit 170 is provided to the system control unit 142.

  That is, the inline detection unit 172 illustrated in FIG. 6 provides a function block that provides information related to the abnormal nozzle to the system control unit 142 through reading of an image (nozzle detection pattern), processing of read data, and processing of determining an abnormal nozzle. It is.

  The system control unit 142 performs various corrections on the head 100 based on information related to the abnormal nozzle obtained from the inline detection unit 172 and other information, and also performs cleaning operations (nozzle, preliminary ejection, suction, wiping, etc. as necessary) Control to implement recovery operation).

  Although not shown, a maintenance processing unit including members necessary for head maintenance, such as an ink receiver, a suction cap, a suction pump, and a wiper blade, is provided as means for executing the above-described cleaning operation.

  In addition, an operation unit as a user interface is provided, and the operation unit includes an input device for an operator (user) to perform various inputs and a display unit (display). Various forms such as a keyboard, a mouse, a touch panel, and buttons can be adopted as the input device. By operating the input device, the operator can input printing conditions, select image quality mode, input / edit attached information, search information, and display various information such as input contents and search results. It can be confirmed through the display of the department. This display unit also functions as means for displaying a warning such as an error message.

  The ink jet recording apparatus 10 of the present embodiment has a plurality of image quality modes, and the image quality mode is set by a user's selection operation or by automatic selection by a program. The criterion for determining an abnormal nozzle is changed according to the output image quality level required in the set image quality mode. The higher the required quality, the more severe the criteria.

  Information relating to printing conditions and abnormal nozzle determination criteria for each image quality mode is stored in the storage unit 150.

[Configuration example of inline detection unit (inline sensor)]
FIG. 7 is a schematic configuration diagram showing a configuration example of the inline sensor 82 (reading unit including the CCD image sensor 166). The in-line sensor 82 includes a reading sensor unit 274 in which a line CCD 270, a lens 272 that forms an image on the light receiving surface of the line CCD 270, and a mirror 273 that bends the optical path are arranged in parallel, and the image on the recording medium is arranged. Read each. The line CCD 270 has a photocell (pixel) array for each color provided with RGB color filters, and a color image can be read by RGB color separation. For example, a CCD analog shift register for separately transferring the charges of even-numbered pixels and odd-numbered pixels in one line is provided next to the photocell array for each of RGB3 lines.

  Specifically, a line CCD “μPD8827A” (trade name) manufactured by NEC Electronics Corporation having a pixel pitch of 9.325 μm, 7600 pixels × RGB, and an element length (sensor width in the photocell array direction) of 70.87 mm is used. it can.

  The line CCD 270 is fixed so that the arrangement direction of the photocells and the axis of the drum on which the recording medium is conveyed are parallel to each other.

  The lens 272 is a lens of a reduction optical system that forms an image on a recording medium wound on a conveyance drum (an impression cylinder 64 in FIG. 1) at a predetermined reduction ratio. For example, when a lens that reduces an image by 0.19 times is employed, a 373 mm width on the recording medium is imaged on the line CCD 270. At this time, the reading resolution on the recording medium is 518 dpi.

  As shown in FIG. 7, the reading sensor unit 274 in which the line CCD 270, the lens 272, and the mirror 273 are integrated can be moved and adjusted in parallel with the axis of the transport drum, and the positions of the two reading sensor units 274 are adjusted, respectively. The image read by the reading sensor unit 274 is slightly overlapped. Although not shown in FIG. 7, as an illuminating means for detection, for example, a xenon fluorescent lamp is arranged on the back surface of the bracket 275, on the recording medium side, and a white reference plate is periodically placed between the image and the illumination. To measure the white reference. In this state, the lamp is turned off and the black reference level is measured.

  The reading width of the line CCD 270 (the range that can be inspected at one time) can be designed in various ways in relation to the width of the image recording area on the recording medium. From the viewpoint of lens performance and resolution, for example, the reading width of the line CCD 270 is about ½ of the width of the image recording area (the maximum width that can be inspected).

  Image data obtained by the line CCD 270 is converted to digital data by an A / D converter or the like, stored in a temporary memory, processed through the system control unit 142 (see FIG. 6), and stored in the image memory. Is done.

[Description of nozzle detection]
Next, detection of abnormal nozzles will be described. In the ink jet recording apparatus 10 shown in this example, the nozzle detection pattern in which the blank portion of the recording medium 14 is formed is read by the inline sensor 82 shown in FIG. 1, and the discharge of each nozzle is performed based on the read data obtained from the read result. Nozzle positions (numbers) are stored for nozzles whose status has been grasped and which have been determined to be abnormal.

  FIG. 8 is a view of the recording surface of the recording medium 14 in which the nozzle detection patterns 202 for one head are formed in the leading edge blank area 204. The leading edge blank area 204 is provided between the leading edge of the recording medium 14 and the image area 206 where a recorded image is formed. Further, a dummy jet area 210 to which the ink 208 ejected by the dummy jet adheres is provided behind the image area 206. The leading margin area 204 and the dummy jet area 210 are cut and discarded after image recording in the image area 206.

  The nozzle detection pattern 202 shown in FIG. 8 is a so-called “1 on N off” pattern and is provided in each of the inkjet heads 48M, 48K, 48C, and 48Y provided in the inkjet recording apparatus 10 (see FIG. 1). It is formed using all the nozzles 108 (see FIG. 4).

  That is, the nozzle detection pattern 202 includes a dot row group 202B in which dot rows (vertical lines) 202A having a predetermined length in the sub-scanning direction Y are arranged every (N + 1) pixels along the main scanning direction X ( N + 1) stages of dot row groups 202B of (N + 1) stages are arranged with their positions shifted in the sub-scanning direction, and the phases of the dot row groups in the main scanning direction X are shifted from each other.

  In other words, in the projection nozzle row in which the nozzles 108 (see FIG. 4) arranged in a matrix are projected so as to be arranged in the main scanning direction X, the dot row group for one stage is continuously driven every (N + 1) nozzles. 202B is formed, and all the nozzles 108 are driven so as to sequentially form dot row groups for (N + 1) stages while switching the driven nozzles 108.

FIG. 9 shows a pixel corresponding to OFF between the recording resolution R ₁ of the inkjet head 100 (see FIG. 6), the reading resolution R ₂ of the in-line sensor 82, and the adjacent dot row 202 A in the main scanning direction of the nozzle detection pattern 202. It is explanatory drawing which shows the relationship with the number N (however, N is a positive integer). FIG. 9 illustrates a case where the nozzle detection pattern 202 having a 1 on 11 off pattern is formed when the ratio of the recording resolution R ₁ to the reading resolution R ₂ is 500/1200.

  In the case shown in the figure, a group of 12 stages of the nozzle detection pattern 202 (a group of dot rows formed from 12 nozzles continuous in the projection nozzle row) using five consecutive pixels of the in-line sensor 82. Is read. That is, one pixel of the in-line sensor 82 changes the reading timing and reads two or three dot rows.

  When P is an integer of 2 or more, these relationships satisfy Expression (1) and also satisfy Expression (2).

{(N + 1) × R ₂ } / R ₁ = P (1)
(N / R ₁ )> R ₂ (2)
That is, the pitch between dot rows ((2.54 / R ₁ ) × (N + 1)) of the nozzle detection pattern 202 is P times the pixel pitch (2.54 / R ₂ ) of the inline sensor 82 (P is an integer of 2 or more) ), The nozzle detection pattern “N” is determined. For example, when the recording resolution R ₁ is 1200 dpi, the reading resolution R ₂ is 500 dpi, and the value of N when P = 5 is obtained, N = 11 from the above equation (1), and 1 on 11 off (12 steps). A nozzle detection pattern is formed. N = 11 also satisfies the above equation (2).

Here, if the value of P is an integral multiple of the numerator value obtained by dividing R ₂ / R ₁ into an irreducible fraction, both the value of P and the value of N are always integers. In the example shown in FIG. 9, a multiple of the value “5” of the 5/12 numerator obtained by making R ₂ / R ₁ an irreducible fraction becomes the value of P.

  When the value of P is increased, the value of N (interval between dot rows of the nozzle detection pattern 202) is increased, and the occurrence of reading errors is more effectively suppressed. On the other hand, if the value of P is increased, the number of stages (N + 1) of the nozzle detection pattern 202 increases, leading to an increase in reading time and an increase in the required memory amount. The value of P is appropriately determined in consideration of the accuracy required for reading, the read time that can be secured, and the amount of memory.

  FIG. 10A to FIG. 10L illustrate the read data of 12 stages of the detection pattern of 1 on 11 off.

  10A shows the first stage read data, FIG. 10B shows the second stage read data,..., And FIG. 10L shows the twelfth stage read data. Read one by one and output (stored) one by one.

  The vertical series in FIGS. 10A to 10L are data values, and the horizontal series are the positions (nozzle numbers) of the projection nozzles projected in the main scanning direction. The maximum value of the vertical series (upper end of the vertical series) corresponds to between dot rows, and the minimum value (center of the vertical series) corresponds to dot rows. If all the nozzles are normal, a minimum value corresponding to the total number of nozzles appears at a position corresponding to each nozzle.

  In this way, the read data obtained from the in-line sensor 82 is subjected to predetermined data processing (details will be described later), and the presence or absence of abnormality is determined for each nozzle based on the read data after processing.

  FIG. 11 is a flowchart showing a control flow of nozzle detection (in-line inspection) shown in this example. When the recording medium 14 (see FIG. 8) on which the nozzle detection pattern 202 is formed reaches the reading position of the inline sensor 82 shown in FIG. 1, the inline sensor 82 images (reads) the nozzle detection pattern 202 (step S12). ).

  In the read data processing step shown in step S14, the read data obtained from the inline sensor 82 is binarized. When the binarization processing is performed on the read data of each stage shown in FIGS. 10A to 10L, the data value “0” corresponding to the dot row (nozzle) position and the data corresponding to the space between the dot rows. Binary data such as “011111111111011111111111011...” In which the value “1” is arranged can be obtained.

  In the detection step shown in step S16, the binary data is counted in the order of output, and the presence / absence of a dot row (data “0”) is detected. In other words, the continuously output binary data is divided into data for each stage, and the data value “0” corresponding to the dot row formation position and the data value “1” corresponding to the position between the dot rows. The number of data in the section where “

In the determination step shown in step S18, it is determined whether there is an abnormality for each nozzle.
For example, in the above binary data, when “... 110111...” That should originally be “... 1111011...” Is “... 1111011...”, A dot row is not formed at a position where the corresponding nozzle should originally form a dot row. A dot row is formed at a position shifted laterally. In such a case, it is determined that “there is an abnormal ejection nozzle”, and the nozzle number of the abnormal ejection nozzle is specified.

  That is, when the number of data in the interval in which the data value “1” corresponding to the dot rows continues is larger or smaller than the original number of data, it is determined that “abnormal nozzle exists”. In addition, the position of the abnormal nozzle is grasped from the position of the data value “0” in the section where the data value “1” originally continues. In addition, when the data value “0” appears in the middle of the section in which the data value “1” is originally continuous, the nozzles on both sides of the data value “0” are processed as abnormal nozzles.

  In the correction step shown in step S20, the abnormal nozzle is masked so that ink is not ejected from the nozzle specified as the “abnormal nozzle” in the determination step, and the dot formation position by the abnormal nozzle is applied. Correction of output data of the nozzle adjacent to the abnormal nozzle is performed.

  Examples of the correction processing by the adjacent nozzle include a mode in which the size of dots formed by the adjacent nozzle is increased and a mode in which nozzles of other heads are used. It is also possible to form dot data (ink ejection data) that takes into account the presence of abnormal nozzles during halftone processing. In addition, it is preferable that the configuration is such that when the number of abnormal nozzles exceeds a predetermined number, a recovery process such as wiping or capping is executed by entering the maintenance mode.

[Variations of read data processing]
(Use of concentration data)
Among abnormal nozzles, although the recording position is normal, the amount of ink discharged is too small or too large, so that the dots formed by the nozzle may not have an appropriate density. In such a case, it is effective to determine the abnormal nozzle using the density value. Since the read data obtained from the in-line sensor 82 correlates with the density value, the data value of the read data can be used. In such a case, it is effective to use density information of peripheral nozzle detection patterns and density information of dot rows formed by other nozzles belonging to the same stage.

  When density information is used, statistical processing for creating a frequency distribution using data values as parameters is performed on the read data (see FIG. 10).

  FIG. 12 shows the appearance frequency of data values in one stage of read data. As shown in the figure, a peak corresponding to a normal nozzle data value appears near the data value 172/255, whereas a peak corresponding to an abnormal nozzle forming a dot having a low density has a data value of 100. Appears near / 255.

  Therefore, in order to detect a data value corresponding to a dot row having a low density, it is possible to extract an abnormal nozzle by a simple process if a determination is made by providing a threshold value. For example, a data value “128/255” is set as a threshold value, and a nozzle having a data value larger than this threshold value and having a dot row having an intermediate data value between on and off is defined as an abnormal nozzle. Can be determined.

  As shown in FIG. 1, in an apparatus configuration including a head corresponding to each of a plurality of colors, a different threshold value can be set for each color (each head). It is also possible to change (reset) the threshold value in view of the occurrence state of abnormal nozzles.

(Normalization processing)
The correlation of the frequency distribution shown in FIG. 12 changes due to the ink color and the set density. Therefore, if the read data is normalized (for example, 255/255) and the abnormal nozzle is determined based on the normalized data value, the determination using the same reference is made between data having different ink colors and set densities. Thus, the determination difference for each color or density setting can be further suppressed.

  For example, yellow ink tends to have a lower density than cyan ink, magenta ink, and black ink. If an abnormal nozzle is determined based on the same reference (threshold), it may be determined that the yellow ink is abnormal even though the yellow ink is normal. Therefore, when normalization processing is performed on the read data, it is possible to avoid a situation in which the maintenance of only a specific head is repeated more frequently due to the determination difference for each color (density), and the maintenance between the heads is uneven. It is effective to prevent the

  As an example of the normalization process, there is a process in which the read data value of each color is multiplied by a coefficient, and the maximum value for each color on the read data is set to the same value.

  Further, a difference (density difference) in data value between the read data also appears between the dot row read at the center position of the read pixel and the dot row read at a position away from the center of the read pixel. The normalization process is also effective for compensating for the difference in data value caused by the position in the read pixel.

(High accuracy detection process)
Regarding the read data shown in FIGS. 10A to 10L, there may be a periodic change in the data value in the read data for one stage. Further, shading (periodic unevenness) may occur in the sheet width direction due to the lighting condition when reading by the inline sensor 82 in the reading data for one stage. If there is a periodic change in the portion corresponding to the normal nozzle output in the paper width direction in the read data for one stage, the read data may be detected and processed for each area divided in the paper width direction.

  For example, it is divided into areas corresponding to the period of change of the data value, the read data of the output image is processed, the density distribution of the pixel value is obtained for each range, and the abnormal nozzle is detected, thereby improving the detection accuracy. It becomes possible to increase.

(Statistical processing)
As another aspect of the data processing of the read data shown in FIGS. 10A to 10L, a statistical distribution is analyzed for each color, and a nozzle having a deviation greater than a predetermined value is determined as an abnormal nozzle. Is possible. For example, it is possible to determine an abnormal nozzle by obtaining a standard deviation from a statistical distribution. The standard deviation in the example according to the prior art shown in FIG. 13 is 9.1, the standard deviation in the example shown in this example is 6.7, and the standard deviation in the conventional example is larger than that in this example. An increase in standard deviation (variation) means that the probability of confusion between reading of abnormal ejection and reading of normal ejection is increased.

  Further, a difference (density difference) in data values between the read data also appears between the dot row read at the center position of the read pixel and the dot row read at a position away from the center of the read pixel. Statistical processing is also effective for compensating for the difference in data value caused by the position in the read pixel. For example, it can be considered that a nozzle corresponding to a data value having a large deviation of a certain value or more from the maximum value of the data value distribution is determined as an abnormal nozzle. It is good to comprise so that a level may be set statistically for every stage.

  The binarization process and the density value comparison process described above may be combined to determine non-ejection, ejection amount abnormality, and ejection direction abnormality collectively, or the binarization process and density value comparison process may be performed. It may be executed in stages. Further, a binarization process and a density value comparison process may be performed on the read data after the normalization process.

  According to the ink jet recording apparatus configured as described above, the interval between the dot rows in the main scanning direction (interval of the read nozzle detection pattern) (N + 1) of the 1 on N off nozzle detection pattern used for detecting the abnormality of the nozzle. ) Is an integer multiple of 2 or more of the reading resolution, and (N + 1) is made larger than the ratio of the recording resolution to the reading resolution, all the dot rows constituting the nozzle detection pattern change the amount of fluctuation of the reading data value. It can be made small, and erroneous determination of abnormal nozzles based on the read data is suppressed.

  In addition, the abnormal nozzle is detected after the binarization process is performed on the read data, thereby realizing efficient and accurate detection of the abnormal nozzle. Furthermore, by setting a threshold value for the read data and determining an abnormal nozzle by comparing with the threshold value, it is possible to detect an abnormal discharge amount of ink droplets. By using these processes in combination, an abnormal nozzle is detected with higher accuracy.

  By performing normalization processing on the read data, erroneous detection of abnormal nozzles due to density differences is prevented. In particular, in an aspect including a head corresponding to a plurality of colors, an erroneous determination due to a density difference between colors is prevented by detecting an abnormal nozzle based on read data after normalization processing.

  By performing the abnormal nozzle determination after performing the statistical processing, the detection accuracy of the abnormal nozzle can be increased.

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

<Appendix>
As can be understood from the description of the embodiment described in detail above, the present specification includes disclosure of various technical ideas including the invention described below.

(Invention 1): an inkjet head provided with a plurality of nozzles for discharging droplets to a recording medium, a moving means for relatively moving the inkjet head and the recording medium along a sub-scanning direction, and the plurality of the plurality of nozzles In the projected nozzle row in which the nozzles are projected so as to be aligned along the main scanning direction orthogonal to the sub-scanning direction, every (N + 1) nozzles (N is a positive integer) are continuously driven simultaneously to perform main scanning. A one-stage dot row arranged at (N + 1) dot intervals along the direction is formed, and all nozzles are used while sequentially switching the driven nozzles, and the sub-scanning direction parallel to the moving direction of the recording medium (N + 1) stages of dot rows are formed, and the nozzle detection pattern having (N + 1) rows of dot rows arranged at intervals of N dots in the main scanning direction is formed. And drive control means for driving and controlling the number of nozzles, has a recording resolution R smaller reading resolution R ₂ than ₁ of the nozzle detection pattern, and reading means for reading said nozzle detection pattern, read by the reading means A data processing means for performing statistical processing on the image data; and a judgment means for judging whether each nozzle is an abnormal nozzle based on a processing result of the data processing means, the drive control means Is the relationship between the recording resolution R ₁ of the nozzle detection pattern, the reading resolution R _{2 of the} reading means, the arrangement pitch (N + 1) in the main scanning direction of the nozzle detection pattern, and an integer P of 2 or more. to satisfy the following formula _{{(N + 1) × R} 2} / R 1 = P, and the following formula _(N / R 1)> the plurality of to form said nozzle detection pattern satisfying 1 / _{R 2} Bruno An ink jet recording apparatus characterized by controlling the driving of the Le.

  According to the present invention, the interval (N + 1) between the dot rows in the main scanning direction of the nozzle detection pattern read by the reading unit is set to an integer multiple of 2 or more of the reading resolution of the reading unit, and (N + 1) is set to the reading resolution. By making it larger than the ratio of the recording resolution, all the dot rows constituting the nozzle detection pattern are reliably read. Therefore, data omission of data obtained from the reading unit is avoided, and preferable abnormal nozzle detection is realized.

  The inkjet head includes a plurality of liquid chambers provided corresponding to the plurality of nozzles, and a plurality of discharge elements provided corresponding to the plurality of liquid chambers, and the liquid chambers and discharge elements corresponding to the arrangement of the nozzles There is a mode in which the is arranged. In addition, in an apparatus that records a color image using a plurality of colors of ink, an aspect in which an inkjet head is provided for each color is preferable.

  The ink jet head may be configured to form a desired pattern by ejecting a liquid such as a resist liquid or a resin liquid from the nozzle, in addition to the form in which the color ink is ejected from the nozzle.

  (Invention 2): In the ink jet recording apparatus according to Invention 1, the data processing means includes binarization processing means for performing binarization processing on the read data obtained from the reading means, and the determination means includes And determining whether each nozzle is an abnormal nozzle based on the interval corresponding to the dot rows of the nozzle detection pattern in the binary data obtained by the binarization processing means, and the binary data It is characterized in that it is determined which of the plurality of nozzles is abnormal based on a value corresponding to a dot row of the nozzle detection pattern.

  In this aspect, by performing binarization processing on the read data obtained from the reading unit, the number of data in the section where “1” between the data “0” of the binarized data continues (the width of the section). ) Is larger or smaller than the original number of data, it can be determined that there is an abnormal nozzle.

  (Invention 3): In the ink jet recording apparatus according to Invention 1, the determination means uses a density value indicated by a data value of a dot row formed by another nozzle belonging to the same stage of the nozzle detection pattern. It is characterized by determining whether each nozzle is an abnormal nozzle.

  According to this aspect, since the dot rows belonging to the same stage of the nozzle detection pattern have the same reading condition, the density value indicated by this data value is used, and therefore, it is affected by an error caused by the reading condition. There is nothing.

  (Invention 4): In the ink jet recording apparatus according to Invention 1 or 3, the determination means is a density value corresponding to a dot row of the detection pattern based on a density value indicated by data obtained from the data processing means. And a nozzle corresponding to an intermediate value between the density values corresponding to the dot rows of the detection pattern is determined as an abnormal nozzle.

  According to this aspect, it is possible to determine whether or not there is a nozzle having an abnormal ink discharge amount.

  (Invention 5): In the ink jet recording apparatus according to Invention 1, threshold setting means for setting a threshold for determining an abnormal nozzle with respect to data obtained from the data processing means; and the determination means Is characterized by comparing the data obtained from the data processing means with the threshold value to determine which of the plurality of nozzles is abnormal.

  In such an aspect, an aspect in which a threshold is set for each stage or for each head is preferable.

  (Invention 6): In the ink jet recording apparatus according to Invention 1, the data processing means includes statistical distribution calculation means for calculating a statistical distribution for the read data obtained from the reading means, and the determination means includes the data Based on the statistical distribution obtained from the processing means, a nozzle corresponding to a data value exceeding a predetermined deviation is determined as an abnormal nozzle.

  In such an aspect, an aspect in which the standard deviation of the read data value is obtained based on the statistical distribution is also preferable.

  (Invention 7): In the ink jet recording apparatus according to any one of Inventions 1 to 6, the data processing means includes normalization processing means for performing normalization processing on the read data obtained from the reading means. Features.

  According to this aspect, the difference in the data value for each head in the configuration including the plurality of inkjet heads is compensated for each stage of the nozzle detection pattern.

  A mode in which the binarization process is performed on the read data subjected to the normalization process by combining the invention 7 and the invention 2 is preferable. Further, it is preferable to determine whether or not there is an abnormal nozzle based on the density value indicated by the read data subjected to the normalization process by combining the invention 7 and the inventions 3 and 4.

  (Invention 8): In the ink jet recording apparatus according to Invention 7, the normalization processing unit normalizes the read data obtained from the reading unit for each region obtained by dividing the projection nozzle row into a plurality of regions. It is characterized by processing.

  According to this aspect, the reading error in the dot row for one stage due to the reading condition (illumination or the like) of the nozzle detection pattern is compensated.

  (Invention 9): In the ink jet recording apparatus according to any one of inventions 1 to 8, the reading unit is provided on the downstream side in the recording medium moving direction of the image recording unit including the ink jet head.

  According to this aspect, in-line inspection is possible, and if an abnormal nozzle is found, it can be dealt with early.

  (Invention 10): The ink jet recording apparatus according to any one of Inventions 1 to 9, further comprising correction means for correcting ejection data for the nozzle determined to be an abnormal nozzle by the determination means.

  In the ejection data correction in such an aspect, ejection data is generated from image data in consideration of an aspect in which droplet ejection data of a neighboring nozzle is changed so that alternative ejection is performed from a nozzle in the vicinity of the abnormal nozzle, or an abnormal nozzle is considered There are aspects.

(Invention 11): The plurality of nozzles are sub-scanned while relatively moving the ink-jet head provided with a plurality of nozzles for discharging droplets onto the recording medium and the recording medium along the sub-scanning direction. In the projection nozzle row projected so as to be aligned along the main scanning direction orthogonal to the direction, every (N + 1) (N is a positive integer) nozzles are continuously driven simultaneously along the main scanning direction ( N + 1) A dot row for one stage arranged at a dot interval is formed, and all nozzles are used while sequentially switching the driven nozzles, and the sub-scanning direction parallel to the moving direction of the recording medium is (N + 1) A nozzle detection pattern forming step of forming a dot detection pattern for forming a row of dot rows and having (N + 1) rows of dot rows arranged in the main scanning direction at intervals of N dots in the sub-scanning direction; Has a resolution R ₂ reading less than nozzle detection pattern recording resolution R ₁ of the a reading step reading a nozzle detection pattern, the reading performing statistical processing on the image data read in step data processing step And a determination step of determining whether each nozzle is an abnormal nozzle based on a processing result of the data processing step, wherein the detection pattern forming step includes a recording resolution R _{1 of the} nozzle detection pattern and The relationship between the reading resolution R _{2 of the} reading unit, the arrangement pitch (N + 1) of the nozzle detection pattern in the main scanning direction, and an integer P of 2 or more is represented by the following expression {(N + 1) × R ₂ } / R An abnormality detection method comprising: forming the nozzle detection pattern satisfying ₁ = P and satisfying the following formula (N / R ₁ )> 1 / R ₂ .

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording apparatus, 48M, 48K, 48C, 48Y, 100 ... Head, 82 ... Inline sensor, 108 ... Nozzle, 142 ... System control part, 168 ... Read data processing part, 170 ... Abnormal nozzle determination part, 172 ... Inline Detection unit, 202 ... Nozzle detection pattern

Claims (11)

An inkjet head provided with a plurality of nozzles for discharging droplets to a recording medium;
Moving means for relatively moving the inkjet head and the recording medium along the sub-scanning direction;
In the projected nozzle row in which the plurality of nozzles are projected so as to be aligned along the main scanning direction orthogonal to the sub-scanning direction, every (N + 1) (N is a positive integer) nozzles are continuously driven simultaneously. A dot row for one stage arranged at an interval of (N + 1) dots along the main scanning direction is formed, and all nozzles are used while sequentially switching the driven nozzles, and parallel to the moving direction of the recording medium. A plurality of (N + 1) stages of dot rows are formed in the sub-scanning direction, and the plurality of nozzle detection patterns having (N + 1) stages of dot rows arranged at intervals of N dots in the main scanning direction are formed. Drive control means for driving and controlling the nozzle;
A reading unit having a reading resolution R ₂ smaller than a recording resolution R _{1 of the} nozzle detection pattern and reading the nozzle detection pattern;
Data processing means for performing statistical processing on the image data read by the reading means;
Determination means for determining whether each nozzle is an abnormal nozzle based on the processing result of the data processing means;
With
Said drive control means includes a recording resolution R ₁ of the nozzle detection pattern, the reading resolution R ₂ of said reading means, the arrangement pitch (N + 1) in the main scanning direction of the nozzle detection pattern, and an integer of 2 or more P, Is represented by the following expression {(N + 1) × R ₂ } / R ₁ = P
And the following formula (N / R ₁ )> 1 / R ₂
An inkjet recording apparatus that drives and controls the plurality of nozzles so as to form the nozzle detection pattern that satisfies the above. The inkjet recording apparatus according to claim 1, wherein
The data processing means includes binarization processing means for performing binarization processing on the read data obtained from the reading means,
The determination unit determines whether each nozzle is an abnormal nozzle based on an interval corresponding to the dot rows of the nozzle detection pattern in the binary data obtained by the binarization processing unit, and An inkjet recording apparatus that determines which of the plurality of nozzles is abnormal based on a value corresponding to a dot row of the nozzle detection pattern in the binary data. The inkjet recording apparatus according to claim 1, wherein
The determination means determines whether each nozzle is an abnormal nozzle by using a density value indicated by a data value of a dot row formed by another nozzle belonging to the same stage of the nozzle detection pattern. An ink jet recording apparatus. In the ink jet recording apparatus according to claim 1 or 3,
The determination means is an intermediate value between the density value corresponding to the dot rows of the detection pattern and the density value corresponding to the space between the dot rows of the detection pattern, based on the density value indicated by the data obtained from the data processing means. An ink jet recording apparatus characterized in that a nozzle corresponding to 1 is determined as an abnormal nozzle. The inkjet recording apparatus according to claim 1, wherein
Threshold setting means for setting a threshold for determining an abnormal nozzle for the data obtained from the data processing means;
The ink jet recording apparatus, wherein the determination unit determines which of the plurality of nozzles is abnormal by comparing the data obtained from the data processing unit with the threshold value. The inkjet recording apparatus according to claim 1, wherein
The data processing means includes statistical distribution calculation means for calculating a statistical distribution for the read data obtained from the reading means,
The determination unit determines an nozzle corresponding to a data value exceeding a predetermined deviation as an abnormal nozzle based on a statistical distribution obtained from the data processing unit. The inkjet recording apparatus according to any one of claims 1 to 6,
The inkjet recording apparatus, wherein the data processing means includes normalization processing means for performing normalization processing on the read data obtained from the reading means. The inkjet recording apparatus according to claim 7.
The ink jet recording apparatus, wherein the normalization processing unit performs normalization processing on the read data obtained from the reading unit for each region obtained by dividing the projection nozzle row into a plurality of regions. The inkjet recording apparatus according to any one of claims 1 to 8,
The inkjet recording apparatus, wherein the reading unit is provided on a downstream side of a recording medium moving direction of an image recording unit including the inkjet head. The inkjet recording apparatus according to any one of claims 1 to 9,
An ink jet recording apparatus comprising: a correction unit that corrects ejection data for a nozzle that is determined to be an abnormal nozzle by the determination unit. While the ink jet head provided with a plurality of nozzles for discharging droplets to the recording medium and the recording medium are relatively moved along the sub-scanning direction, the plurality of nozzles are orthogonal to the sub-scanning direction. In the projection nozzle row projected so as to be aligned along the scanning direction, every (N + 1) nozzles (N is a positive integer) are continuously driven at the same time, with an interval of (N + 1) dots along the main scanning direction. An aligned dot row for one stage is formed, and all nozzles are used while sequentially switching the nozzles to be driven, and the dot row for (N + 1) stages in the sub-scanning direction parallel to the moving direction of the recording medium. Forming a nozzle detection pattern having (N + 1) stages of dot rows arranged in the main scanning direction at intervals of N dots in the sub-scanning direction; and
Has a recording resolution R smaller reading resolution R ₂ than ₁ of the nozzle detection pattern, the reading process reads the nozzle detection pattern,
A data processing step of performing statistical processing on the image data read in the reading step;
A determination step of determining whether each nozzle is an abnormal nozzle based on a processing result of the data processing step;
Including
The detection pattern forming step includes a recording resolution R ₁ of the nozzle detection pattern, a reading resolution R _{2 of the} reading unit, an arrangement pitch (N + 1) in the main scanning direction of the nozzle detection pattern, and an integer P of 2 or more. , The following expression {(N + 1) × R ₂ } / R ₁ = P
And the following formula (N / R ₁ )> 1 / R ₂
An abnormality detection method comprising forming the nozzle detection pattern satisfying

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