JP2005067191A - Image recording apparatus and method for specifying defective image recording element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately specify a position and a status of a defective image recording element showing defective recording in an image recording apparatus having a full-line recording head. <P>SOLUTION: Printing is made on a recording sheet by using a print head 50 in which a plurality of nozzles to discharge ink are arranged according to an entire width of a printing medium along a main scanning direction, and a thus printed image is read by a line sensor 120. Integration data by integrating a plurality of read pixel data obtained from a plurality of light-sensitive elements of the line sensor 120, in a certain width in a recording sheet feeding direction, are compared with an integrated value of expected read data expected from normally droplet-struck image to specify a defective nozzle. Thus, a position and a status of the defective nozzle are determined from a plurality of data values obtained from the respective pixels and their neighboring pixels. Based on the specification result of the defective nozzle, a droplet-striking control is made to correct the nozzle. Further, the correction accuracy is improved by referring to history information of the correction treatment, and by deciding a next correction method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and more particularly to a method for detecting a recording failure of an image recording element in an ink jet recording apparatus or other image recording apparatus that records an image on a print medium with a recording head having a plurality of image recording elements, and the recording failure It is related with the coping technology to compensate.

  An ink jet recording apparatus has an ink jet head (print head) in which a large number of nozzles are arranged. By ejecting ink from the nozzles while relatively moving the print head and the recording paper, an image is formed on the recording paper. Form. For some of the many nozzles, ink stops being ejected for some reason, or the ink ejection amount (dot size to be ejected on the recording paper) and the ejection position are inappropriate (the flight direction is inappropriate, There may be a case where ejection failure such as nozzle position is not uniform. The presence of such an inappropriate nozzle causes a reduction in the quality of the recorded image, and thus countermeasures are necessary.

  Conventionally, as a method of detecting defective ejection of nozzles, (1) a method of measuring a test pattern print, (2) measuring a practical print (printing a target image that actually requires print output) There are known methods and (3) a method of measuring the ejection characteristics inside the head.

Patent Document 1 discloses an example of the method (2) described above, and corrects dot missing due to ejection failure by comparing droplet ejection image data with data to be originally recorded.
JP-A-5-301427

  However, in the method of measuring the print of the test pattern, it is necessary to print a dedicated test pattern separately from the target image to be actually printed. Further, there is a problem that it is difficult to specify an inappropriate nozzle due to the influence of the measurement position error in a simple pattern. In addition, there is a problem that it is affected by variations in the output of the line sensor that images the test pattern.

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

  According to Patent Document 1, the dots on the recording paper are read by the photoelectric conversion elements arranged at the same pitch as the nozzle pitch of the recording head, and it is detected whether ink non-ejection has occurred. In the method, when the image becomes high density, the difference in sensor output from the surroundings becomes small. Therefore, there is a drawback that improper droplet ejection cannot be specified accurately by individual comparison for each dot. In particular, in the case of high-density nozzles used for high-resolution image recording, the observation area of each pixel of the line sensor is greater than or equal to the nozzle pitch. It becomes difficult.

  Further, the method of measuring the ejection characteristics inside the head can accurately identify an inappropriate nozzle, but there is a problem that the degree of inappropriateness is difficult to understand.

  The present invention has been made in view of the above circumstances, and provides an image recording device capable of accurately specifying an inappropriate image recording element that causes recording failure and a method for identifying the inappropriate image recording element. The purpose is to provide.

  In order to achieve the above object, an image recording apparatus according to the present invention comprises a printing means comprising a full-line recording head in which a plurality of image recording elements are arranged over a length corresponding to the entire width of a printing medium, and the recording head. And at least one of the print media is conveyed in a direction substantially orthogonal to the width direction of the print medium, and the recording head and the print medium are moved relative to each other, and the recording head records the print medium on the print medium. Based on image reading means in which a plurality of sensors for reading an image are arranged over a length corresponding to the entire width of the print medium and a plurality of read pixel data obtained from the plurality of sensors, the read pixel data of the sensor for each sensor And the read pixel data obtained from the neighboring sensor and the expected read data expected from the image to be recorded. It was carried out, to the improper image recording element specifying means for specifying the image-recording element of the recording failure based on the calculation result, characterized by comprising a.

  According to the present invention, a full-line type recording head having an image recording element array covering the entire width of the printing medium in a direction (main scanning direction) substantially orthogonal to the relative feeding direction (sub-scanning direction) of the printing medium. On the other hand, an image is formed on the print medium by the action of the image recording element of the recording head while relatively moving the print medium in the sub-scanning direction. When the printed image is read by the image reading unit, a signal corresponding to the amount of received light is output from each sensor (photoelectric conversion sensor) constituting the pixel of the image reading unit, and reading for one line in the main scanning direction is performed. Pixel data (data relating to actual measurement) is obtained. On the other hand, expected read data expected as read data of the image is obtained from the information of the image to be originally recorded, and an operation using the expected read data and the actually measured read pixel data is performed. Then, based on the calculation result, an image recording element (inappropriate image recording element) with poor recording is specified. At this time, the read pixel data of each sensor is not evaluated individually, but the evaluation is performed in consideration of the change (correlation) of the data value while comparing the read pixel data obtained from a plurality of neighboring sensors.

  As a result, the number of sensors (the number of pixels of the image reading means) does not match the number of image recording elements, or the sensor position and the dot position of the image (that is, the center position of the image recording element projected in the main scanning direction). ), Or when the arrangement pitch of the sensors projected in the main scanning direction is different from the arrangement pitch of the image recording elements projected in the main scanning direction. The position of the element can be specified accurately.

  Further, in order to identify an inappropriate image recording element using a plurality of data values including read pixel data obtained from neighboring sensors of each sensor as well as individual read pixel data obtained from each sensor, The influence of individual variations can be reduced, and determination with high accuracy is possible, and recording defects such as dot position variations (recording position deviation) can be efficiently determined from a plurality of pixel data. .

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

  The “full-line type recording head” is usually arranged along a direction perpendicular to the relative feeding direction (relative movement direction) of the print medium, but with respect to a direction perpendicular to the relative movement direction. There may also be a mode in which the recording head is arranged along an oblique direction having the angle. Further, the arrangement of the image recording elements in the recording head is not limited to a single line arrangement, but may be a matrix arrangement consisting of a plurality of columns. Further, by combining a plurality of short recording head units each having an image recording element array that is less than the length corresponding to the full width of the print medium, an image recording element array corresponding to the full width of the print medium is configured as the whole unit. There can also be a form.

  A “print medium” is a medium that can be printed by a recording head (which can be called an image forming medium, a recording medium, an image receiving medium, etc.), a continuous sheet, a cut sheet, a sealing sheet, a resin sheet such as an OHP sheet, a film Regardless of material, shape, cloth, etc., various media are included.

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

  As an example of the calculation in the inappropriate image recording element specifying unit, there is an aspect in which the actual measurement data based on the read pixel data is compared with the expected read data.

  In addition to the above configuration, an image recording apparatus according to an aspect of the present invention includes an expected read data generation unit that generates the expected read data based on dot data generated from data of an image to be recorded. The read data generation means includes a filter processing means for performing a filtering process on the dot data.

  In this case, further, the filter processing means is a filter processing means for performing a filtering process on the dot data using a filter having a plurality of types of coefficients corresponding to the types of dot sizes, and having a dot size indicated by the dot data. Accordingly, it is preferable that the filter processing unit selectively select the coefficient of the filter.

  By selecting an appropriate coefficient according to the difference in dot size, an inappropriate image recording element can be accurately identified even when the size of the dot to be recorded is changed. The filter coefficient is preferably determined by reflecting the area of dots included in the reading range of each sensor.

  According to another aspect of the present invention, there is provided an integration calculation unit that integrates the read pixel data in the relative movement direction in a unit having a width of a predetermined length or more with respect to the relative movement direction of the print medium with respect to the recording head; Comparing image characteristic values in the vicinity of at least two places in the main scanning direction substantially orthogonal to the relative movement direction from the integral data obtained by the calculation means, with the image characteristic values of the integral values of the expected read data, the two places An image position specifying means for specifying the positional relationship between the position of the sensor corresponding to the expected read data, and the correspondence between the sensor position corresponding to the two locations found by the image position specifying means and the image recording element position Position relation grasping means for grasping the correspondence between each sensor position and image recording element position, and each sensor grasped by the position relation grasping means Based on the correspondence between the location and the image recording element position, characterized by comprising a sensor reading expected value calculating means obtains the sensor readings expected value at each sensor position by interpolation.

  According to this aspect, the positional relationship between the sensor position and the image recording element position is associated, and the positional deviation in the image recording element array direction projected in the main scanning direction can be corrected.

  For example, there is a mode in which the sensor positions corresponding to both ends of the image are associated with the image recording element positions and the correspondence between each sensor position and the image recording element position is grasped.

  Various methods can be applied to the interpolation calculation. As an example, for each sensor, the reciprocal of the distance in the main scanning direction from the sensor position to the neighboring image recording element is used as a weighting coefficient, and the expected reading value of the neighboring image recording element position is calculated. There is a mode in which a sensor reading expectation value at each sensor position is obtained by calculating a weighted average.

  According to still another aspect of the present invention, an integrated value obtained by integrating read pixel data obtained from each sensor in the relative movement direction, and an expected sensor read value obtained by the expected sensor read value calculating unit are calculated as the relative value. An inappropriate image recording element position candidate specifying unit that specifies an approximate position of an inappropriate image recording element using an integrated value obtained by integrating in the moving direction is provided.

  By integrating the data values in the relative movement direction of the print medium, the influence of the sensor reading timing can be reduced, and reading errors can be averaged to detect a minute difference in data values. Furthermore, the light quantity of the light source that illuminates the print medium can be reduced.

  In this aspect, by integrating the read pixel data value obtained from each sensor directly (without performing an interpolation calculation or the like), inappropriate data having a high frequency can be detected without being dulled by interpolation.

  In another aspect of the present invention, expected read data expected from a recorded image when including an improper image recording element in an assumed defective state is compared with read pixel data obtained from the plurality of sensors. Thus, image recording element state determining means for determining the state of the inappropriate image recording element is provided.

  The “defective state” includes modes such as recording failure, dot size abnormality, and dot recording position abnormality. The “defective state” in the case of an inkjet recording apparatus that employs a nozzle that ejects ink as an image recording element includes aspects such as non-ejection, abnormal droplet ejection size, and abnormal landing position.

  Further, according to another aspect of the present invention, there is provided correction means for correcting an image recording operation based on a result of specifying an inappropriate image recording element by the inappropriate image recording element specifying means, and the inappropriate image recording element specifying means. It comprises at least one of cleaning means for cleaning the recording head based on the result of specifying an inappropriate image recording element or the result specified by the inappropriate image recording element candidate specifying means. To do.

  Furthermore, in the image recording apparatus according to the present invention, a correcting unit that corrects an image recording operation based on a result of specifying an inappropriate image recording element by the inappropriate image recording element specifying unit, and at least a previous inappropriate image recording History information storage means for storing element specific information and correction information for the image recording operation, information stored in the history information storage means and information obtained by reading the corrected image with the image reading means, A mode provided with history control means for determining correction contents is preferable.

  Thereby, even if correction of an inappropriate image recording element is mistaken in the previous process, the information is referred to in the next process, and an appropriate correction process is performed. Thus, the accuracy of correction can be improved by performing feedback control based on history information.

  As another more specific aspect of the present invention, the printing unit includes a recording head capable of printing at least each color of cyan (C), magenta (M), and yellow (Y), while the image reading unit includes: It is composed of RGB sensor rows that can be read by splitting red (R) light, green (G) light, and blue (B) light, and the same image section in which the respective colors are overlapped and recorded by the printing means is described above. A process of reading with the RGB sensor row and specifying an inappropriate image recording element in the color order of C, M, and Y is performed, and a portion determined to be an inappropriate image recording element in the preceding color processing is removed, and the subsequent It is characterized by performing processing.

  The printing unit may include a recording head for each color corresponding to each color of cyan (C), magenta (M), and yellow (Y), or may be configured to print a plurality of colors with one recording head. .

  Further, in addition to the above three colors (C, M, Y), an aspect having a recording head capable of printing black (K) color is also possible. In this case, a process for specifying an inappropriate image recording element in the color order of K, C, M, and Y is performed, and a portion determined as an inappropriate image recording element in the preceding color process is removed to perform a subsequent process. I do.

  According to this aspect, it is possible to specify an inappropriate image recording element of each color from a practical image with high accuracy and efficiency.

  The configuration of the printing unit may be a configuration in which a recording head for black (K) corresponding to the color of black (K) (by color) is added, or includes black (K) in combination with other colors. A recording head capable of printing in multiple colors may be used.

  The present invention also provides a method invention for achieving the above object. That is, the method for identifying an inappropriate image recording element in the image recording apparatus according to the present invention uses the full-line recording head in which a plurality of image recording elements are arranged over a length corresponding to the entire width of the print medium. A printing step of printing on a medium, an image reading step of reading an image recorded on the printing medium by an image reading means in which a plurality of sensors are arranged over a length corresponding to the entire width of the printing medium, Based on a plurality of read pixel data obtained from a sensor, calculation is performed for each sensor using the read pixel data of the sensor, read pixel data obtained from its neighboring sensors, and expected read data expected from an image to be originally recorded. And an inappropriate image recording element specifying step for specifying an image recording element having a recording failure based on the calculation result. To.

  According to the present invention, an image printed by a full-line type recording head in which a plurality of image recording elements are arranged over a length corresponding to the entire width of the print medium in the main scanning direction substantially orthogonal to the relative movement direction of the print medium. Since an image reading unit in which a plurality of sensors are arranged over a length corresponding to the entire width of the print medium is read, an inappropriate image recording element is specified based on a plurality of read pixel data obtained from each sensor. In addition, not only when the number of sensors and the number of image recording elements match, but also when the number of sensors and the number of image recording elements do not match, an inappropriate image recording element can be identified with high accuracy. Further, when the sensor position does not match the dot position of the image, or the arrangement pitch of the sensors projected in the main scanning direction is different from the arrangement pitch of the image recording elements projected in the main scanning direction. Cases can also be handled.

  Furthermore, in the present invention, since an inappropriate image recording element is specified by using a plurality of read pixel data obtained from a plurality of sensors that are adjacent to each other, it is possible to reduce the influence of individual variations of the sensors, In addition to being able to determine with high accuracy, it is also possible to efficiently determine recording defects such as recording position variations (recording position deviation) from a plurality of read pixel data.

  Further, in the present invention, by integrating the data value in the relative movement direction of the print medium, it is possible to reduce the influence of the reading timing of the sensor, average the reading error, and detect a minute difference in the data value. This makes it possible to improve the determination accuracy of inappropriate image recording elements.

  The method for identifying an inappropriate image recording element according to an aspect of the present invention is determined not only by a test pattern (test print) but also by a practical print because the determination is based on comparison between originally recorded data and actually measured data. It is possible.

  In another aspect of the present invention, since feedback control for correcting the next correction method using at least the previous history information is added, even if an erroneous correction is performed in the previous correction process, the next process is performed. In the process, it is possible to avoid performing the same erroneous correction and perform appropriate correction.

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

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside.

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

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

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

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

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, 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.

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

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

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

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

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

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

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is 1. The image can be recorded on the entire surface of the recording paper 16 only by performing it once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

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

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

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 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 is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like. Details of discharge detection will be described later.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

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

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

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

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

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

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

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

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

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

  When the nozzles are driven by a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, , 51-36 as one block, and the nozzles 51-11, 51-12,..., 51-16 are sequentially driven in accordance with the conveyance speed of the recording medium (recording paper 16). Thus, one line is printed in the width direction of the recording medium.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, 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 repeatedly performed. This is defined as sub-scanning.

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

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

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

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

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

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

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

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

  During printing or standby, when the frequency of use of a specific nozzle 51 decreases and the ink viscosity in the vicinity of the nozzle increases, dummy ejection is performed toward the cap 64 to discharge the deteriorated ink.

  Further, when air bubbles are mixed in the ink in the print head 50 (in the pressure chamber 52), the cap 64 is applied to the print head 50, and the ink in the pressure chamber 52 (ink in which the bubbles are mixed) is sucked by the suction pump 67. The ink removed and sucked and removed is sent to the collection tank 68. In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface.

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

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

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

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

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

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 7, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with a single processor.

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

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

  In the example shown in FIG. 1, the print detection unit 24 is provided on the print surface side, and the print surface is illuminated by a light source (not shown) such as a cold cathode tube disposed in the vicinity of the line sensor. Although the configuration is such that the reflected light is read by the line sensor, in the practice of the present invention, as shown in FIG. 8, the line sensor 90 and the light source 92 are arranged facing each other across the conveyance path of the recording paper 16. A configuration is also possible in which the light from the light source 92 is irradiated from the back side of the recording paper 16 (opposite the ink ejection surface) and the transmitted light quantity is read by the line sensor 90. The configuration of the transmission type detection shown in FIG. 8 has an advantage that the blur of the image captured by the line sensor can be reduced as compared with the configuration of the reflection type detection.

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

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

[Problems in detecting inappropriate nozzles]
Before describing a method for detecting inappropriate nozzles in the inkjet recording apparatus 10 according to the present embodiment, first, a technical problem that is a problem in detecting inappropriate nozzles will be discussed with reference to FIGS. 9 to 12.

  FIG. 9 is a diagram illustrating the relationship between the position of the nozzle, the position of the dot that is ejected onto the recording paper by each nozzle, the position of the sensor (pixel) that reads an image formed by the dot, and the output value of the sensor. is there. In the figure, the number of nozzles 101 and the number of sensors 102 (number of pixels of the line sensor) match (nozzle pitch Pn and sensor pitch Ps are equal), and nozzle 101 and sensor 102 are in a one-to-one correspondence. A related example is shown.

  In the case of a high-density nozzle, as shown in FIG. 9, the size of the dot 104 is larger than the nozzle pitch Pn, and the dots ejected by neighboring nozzles partially overlap each other.

  Each sensor 102 has a relatively large reading range as indicated by a double-pointed arrow 106 in the figure, and the output value of each sensor 102 is discharged from a nozzle in the vicinity of the corresponding nozzle. Influenced by dots.

  In FIG. 9, the third nozzle N3 from the left is the nozzle that does not eject, and the dots that should be ejected from the nozzle N3 are missing on the print. As shown in the figure, the sensor output value when the image formed by the nozzle row including the inappropriate nozzle N3 is captured by the line sensor has the highest output value of the third sensor S3 from the left. The output values of the sensors in the vicinity (second and fourth sensors S2, S4) are also high.

  Therefore, if only the output values of the sensors S1 to S5 are evaluated independently, the second and fourth nozzles N2 and N4 are determined to be defective in discharge, and which nozzles are actually actually inappropriate. It is not possible to specify whether it is a nozzle.

  FIG. 10 shows an example in which the number of sensors does not match the number of nozzles. In the figure, the sensor pitch Ps is 1.5 times the nozzle pitch Pn. For example, the case where the number of nozzles projected in the main scanning direction is 2400 per inch (2400 npi) and the number of pixels of the line sensor is 1600 per inch (1600 dpi) corresponds to this example.

  As shown in FIG. 10, when the third nozzle N3 from the left is a non-ejection nozzle, the output value of the line sensor is a sensor close to the non-ejection nozzle (the second and third from the left in FIG. 10). The output from the sensors S2, S3) is relatively high. However, as apparent from comparison with the graph of FIG. 9, in FIG. 10, the change in the waveform of the sensor output value is small overall, and it is difficult to detect a clear peak. Therefore, it is difficult to accurately determine which nozzle is inappropriate.

  FIG. 11 shows an example in which the number of sensors and the number of nozzles match, but the center position of the nozzle and the center position of the sensor (pixel) when viewed in the main scanning direction are shifted. . That is, in FIG. 11, the sensor is positioned in the middle of the adjacent nozzles when viewed in the main scanning direction.

  As shown in FIG. 11, when the third nozzle N3 from the left is a non-ejection nozzle, the output values of the line sensor are the same as the output values of the third sensor S3 and the fourth sensor S4 from the left. The output values of the sensors S2 and S5 adjacent to them are slightly higher than the normal output level. Therefore, it is not possible to specify which nozzle is an inappropriate nozzle only by evaluating the sensor output value individually.

  FIG. 12 shows an example in which variations in landing positions (ink flight direction deviation) and ejection amount abnormalities occur, although the relationship between the number of sensors, the number of nozzles, and the center positions thereof coincides. Yes. According to FIG. 12, the ink droplet ejected from the third nozzle N3 from the left is landed at a position shifted to the right by one pixel from the normal landing position. In this case, the output value of the second sensor from the left is the highest, as indicated by the solid line in FIG.

  Therefore, if attention is paid only to the second sensor output, there is a possibility that it is erroneously determined that the discharge amount of the corresponding nozzle N2 is small (dot size is small). If correction control is performed to increase the discharge amount of the corresponding nozzle based on such a misjudgment, streak unevenness (straight streak unevenness along the sub-scanning direction) is emphasized by the correction. there is a possibility.

  Further, as shown by the dotted line in FIG. 12, there may be a case where the landing position variation and the discharge amount decrease simultaneously. The line sensor output value in such a case is the one indicated by the dotted line in FIG.

  In this case as well, there is a possibility that the second nozzle is erroneously determined as an inappropriate nozzle, and not only the second sensor but also the third sensor output shows a relatively high value. There is a possibility of erroneous determination as an inappropriate nozzle.

  As described with reference to FIGS. 9 to 12, it is difficult to accurately determine the position and state of a defective nozzle only by individually determining the output of each pixel of the line sensor.

  Based on the above consideration, the inkjet recording apparatus 10 according to the present embodiment evaluates the state of the nozzle from the output of a plurality of pixels (sensors) in consideration of the overlapping state of neighboring dots and the reading range of each sensor, It is configured to identify the inappropriate nozzle and its state.

[Inappropriate nozzle detection method]
Hereinafter, a method for detecting an inappropriate nozzle in the inkjet recording apparatus 10 will be described.

  FIG. 13 is a diagram showing an example in which a test pattern is printed and the printing result is read by a line sensor. The test pattern is formed by a command to eject droplets with a predetermined discharge amount from all the nozzles for each of the print heads 12K, 12C, 12M, and 12Y so as to fill a predetermined print area with only one color for each ink color. . That is, “solid printing” in a certain range is performed in the sub-scanning direction over the entire recordable width for each color.

  As shown in the drawing, a rectangular filling pattern (having the maximum recordable width) in the order of K, C, M, Y from the downstream side on the recording paper 16 in the order of arrangement of the print heads 12K, 12C, 12M, 12Y. A solid print pattern for each color) is formed. As shown on the right side of FIG. 13, the pattern portion of each color is a dot pattern in which droplets are ejected from all nozzles in the main scanning direction, and droplets in a plurality of rows are continuous in the sub-scanning direction (paper transport direction). .

  Such a test pattern is read by the line sensor 120 (printing detection unit 24). The reading start timing of the line sensor 120 is determined from the distance between the sensor (pixel) and the nozzle and the conveyance speed of the recording paper 16.

  FIG. 14 is a block diagram showing a main configuration of nozzle detection in the inkjet recording apparatus 10. In the figure, parts corresponding to those in the block diagram shown in FIG. 7 are denoted by the same reference numerals or the same reference numerals with parentheses. FIG. 20 shows a detailed configuration example of the inappropriate nozzle (unsuitable image recording element) specifying unit 140 and the droplet ejection control unit 132 in FIG.

  Data of an image to be printed is input from the outside via the communication interface 70 described in FIG. 7 and stored in the first frame memory 130 shown in FIG. At this stage, RGB image data is stored in the first frame memory 130.

  The image data stored in the first frame memory 130 is sent to the droplet ejection control unit 132, and the halftone processing unit 213 (see FIG. 20) of the droplet ejection control unit 132 uses a known error diffusion algorithm or the like as an ink. Converted to dot data for each color. That is, the droplet ejection control unit 132 performs a process of converting the input RGB image data into KCMY four-color dot data. The dot data generated by the droplet ejection control unit 132 is stored in the second frame memory 134.

  At this time, the dot data of the portion used for inappropriate nozzle detection correction is also stored in the third frame memory 136.

  The head driver 84 takes in the dot data stored in the second frame memory 134 and generates a drive control signal for the print head 50. By applying a drive control signal generated by the head driver to the print head 50, ink is ejected from the print head 50. An image is formed on the recording paper 16 by controlling ink ejection from the print head 50 in synchronization with the conveyance speed of the recording paper 16.

  After droplet ejection by the print head 50, the droplet ejection image is read by the line sensor 120. Data output from the line sensor 120 is stored in the fourth frame memory 138. Based on the data stored in the fourth frame memory 138 and the data stored in the third frame memory 136, the inappropriate nozzle specifying unit 140 performs steps 1 to 5 and history control described later. Since the actual correction operation is performed by the droplet ejection control unit 132, the inappropriate nozzle specifying unit 140 only gives a correction instruction to the droplet ejection control unit 132.

  When performing the cleaning operation based on the result of the inappropriate nozzle specifying process by the inappropriate nozzle specifying unit 140, a command is sent from the print control unit 80 to the cleaning control unit 142. In accordance with a command from the print control unit 80, the cleaning control unit 142 performs the dummy discharge described in FIG. 6, suction by the suction pump, wiping by the cleaning blade 66 (wiping), or a cleaning operation (the nozzle operation) by an appropriate combination thereof. Control the execution of recovery action.

  In addition, a command is sent to the operation display unit 144 when warning display for notifying the presence of an inappropriate nozzle is performed. In accordance with this command, predetermined warning information is displayed on the operation display unit 144.

  The process of detecting and correcting inappropriate nozzles in the inappropriate nozzle specifying unit 140 includes the following steps 1 to 5 and history control based on the correction result.

[Step 1]: Creation of Expected Reading 1 Line Data from Dot Data First, as Step 1, the expected reading value of the sensor for one line expected at the center position of each nozzle from the droplet ejection command data (at each nozzle position) The data indicating the sensor output value of (the predicted value that should be about this) is created. This is because the data of the droplet ejection command (dot data) is what kind of data, and in order to estimate the expected value of what the sensor reading will be when droplet ejection is performed normally according to this command. This is the process of creating data. This step is performed by the expected read data generation unit 216 in FIG. Specifically, the following processes (1-1) and (1-2) are performed.

1-1. filtering
Based on a droplet ejection pattern including peripheral droplet ejection dots included in the sensor (pixel) reading range, a filtering process is performed using a filter as shown in FIG. FIG. 15 exemplifies a filter whose calculation target is a 5 × 5 pixel range in the nozzle arrangement direction and the paper conveyance direction. Each coefficient is determined based on the area of the dots included in the sensor reading range. That is, the area contribution rate (coefficient) of the target nozzle in the center of the filter is large, and the area contribution rate (coefficient) decreases as it goes to the left, right, top, and bottom. This data is held in the filter pattern 200 of FIG. 20, and filtering processing is performed by the filter processing unit 201.

  In FIG. 15, three coefficients are shown in each cell of the filter. When the droplet ejection size (dot size) is controlled to three types, the coefficient is selected according to the droplet ejection size. This corresponds to three types of droplet ejection: no droplet ejection / small size dots / large size dots. The droplet ejection size can be controlled by changing the waveform of the drive pulse applied to the actuator. The mode of selecting the filter coefficient in accordance with the droplet ejection size is particularly effective when processing an actual image.

  Thus, the data obtained as a result of the filtering process is a value reflecting the actual area (droplet ejection area) of dots formed on the recording paper 16 by the ink ejected from each nozzle.

1-2. Conversion to sensor reading value Next, conversion for converting the value after filtering processing obtained in (1-1) above into a sensor reading value is performed. A photoelectric conversion sensor such as a CCD can obtain a linear signal output value with respect to the amount of light (even when gamma is applied, a certain value multiplied by the gamma coefficient is obtained). Therefore, it is necessary to convert what reading value is returned to the actual droplet ejection area by the conversion LUT. This conversion process is performed by the table conversion unit 202 in FIG. 20, and a lookup table (conversion LUT) to be used is experimentally determined.

  That is, the conversion LUT is determined on the basis of the experimental result of executing several droplet ejections in advance, reading the dots with a sensor, and what reading value is obtained. For example, a table defining the relationship of the graph shown in FIG. 16 is provided, and the output value of (1-1) is converted into a sensor reading value according to this conversion table.

  By performing the processing (1-1) and (1-2) for the droplet ejection of all the nozzles of each print head, the sensor reading expectation value corresponding to each nozzle center position for one line is obtained.

[Step 2]: Position correction of sensor read data It is assumed that the positional deviation between the line sensor 120 and the nozzle array may exist up to about 100 μm in the nozzle array direction and the paper transport direction. Step 2 is a step of correcting the displacement in the nozzle row direction. In general, the line sensor is disposed relatively close to the head, so that the relative positional relationship between the pixel (sensor) and the nozzle is substantially constant during one reading period. Therefore, a certain correction is performed for the reading period. Specifically, the following processes (2-1) to (2-4) are performed.

  2-1. First, an image is read in units of a certain length or more in the sub-scanning direction (paper transport direction). If an image (dot) is read in units of one line, the accuracy of position detection decreases due to the influence of reading errors and noise. Therefore, in the inkjet recording apparatus 10 of this example, an image is read in a predetermined width unit (unit of a plurality of lines) having a certain length or more in the paper conveyance direction, and the integration calculation unit 203 in FIG. The droplet ejection image data is integrated (averaged).

  2-2. Next, the image position specifying unit 204 detects the rising positions at both ends of the image. That is, the edge profile near the both ends of the integrated data obtained in (2-1) is compared, and the boundary position corresponding to the edge of the image is determined. Specifically, a position where the difference between the output values of the adjacent pixels is maximized is determined, and the position is determined as the end of the image and associated with the nozzle position (number). The reason for using the difference between the pixels on both sides is that the influence of the error is less than when using the absolute value. It should be noted that the range to be compared is limited to about 2 to 3 times the assumed amount of misalignment in order to avoid a large mistake (false judgment).

  FIG. 17 is a graph showing the difference between the sensor output value near the left end portion of the image and the output values of both adjacent pixels. In order to represent the position of the light receiving element (pixel) of the line sensor 120, a number is assigned in order from the end of the pixel, and the position of the pixel is specified by this sensor number. The blank portion of the recording paper 16 (the region where ink droplets are not ejected) is bright and dark when an image by droplet ejection starts (when dots are formed), so the sensor output corresponding to the margin portion is high, and the sensor of the image portion The output decreases (graph a in FIG. 17).

  The difference between the pixels adjacent to sensor number k means the difference between the output value of the (k−1) th sensor and the output value of the (k + 1) th sensor, and graph b showing the difference between the adjacent pixels According to the above, the peak of the difference is at the 14th sensor.

  FIG. 18 is a graph showing the sensor reading expectation value at each nozzle position and the difference between the nozzle positions on both sides. The sensor output value expected at each nozzle position is obtained in the above [Step 1].

  In order to represent the nozzle position, a number is assigned to the nozzle row of the print head in order from the end, and the center position of the nozzle is specified by the nozzle number. The actual nozzle number starts from No. 0 of the reference end nozzle, but the reason why the negative nozzle number is assigned on the graph of FIG. If the dot is formed and the dot located outside the nozzle is within a certain reading range, it means that a detection signal can be obtained from the sensor.

  By comparing the graphs shown in FIGS. 17 and 18, the sensor No. 14 that is the peak of the difference between the adjacent pixels can be associated with the nozzle of the nozzle number “0”. 17 and 18, the processing for the left end portion of the image has been described. However, the same processing is performed for the right side portion of the image, and the correspondence between the nozzle number and the sensor number is obtained for both ends of the image.

2-3. Identification of nozzle position The nozzle position is specified by the positional relationship grasping unit 205 of FIG. If the set of the sensor number and nozzle number at both ends of the image obtained in (2-2) above is (S0, N0), (Sm, Nm), the position of the i-th sensor is converted to the nozzle position (number). Then, the nozzle position (number) Pi can be expressed by the following equation.

[Equation 1]
Pi = (Nm-N0) / (Sm-S0) * (i-S0) + N0 (1)
2-4. Calculation of Expected Reading Value at Sensor Position In the sensor reading expectation value calculation unit 206 in FIG. 20, a weighted average (distance of distance) is calculated with the reading expectation values of the two (two) nozzle numbers adjacent to each other across the nozzle position Pi obtained from Equation (1). (Weighted by reciprocal number) is calculated, and the i-th sensor reading expected value Ei is obtained.

[Step 3]: Inappropriate Nozzle Rough Identification Using the sensor number i-th read value Di and the expected value Ei obtained in [Step 2] above, an improper nozzle is first roughly identified. Here, the reason why Di is not converted into nozzle position data is to avoid dulling inappropriate data having a high frequency by the interpolation operation. Specifically, an inappropriate nozzle is roughly specified by the following steps (3-1) to (3-3).

3-1. Integration of data values in the paper conveyance direction Since it is difficult to accurately identify which nozzle has ejected droplets with only one line of data, the i th Integrate (average) the data. As a result, reading errors such as noise are also averaged, and minute data value changes due to inappropriate nozzles can be detected. If the read data is a solid image such as the test pattern described with reference to FIG. 13, the positional deviation in the paper conveyance direction is hardly a problem unless the reading position is out of the solid range. This integration is performed by the integration calculation unit 203 in FIG. 20 for the read value and by the sensor read expected value integration calculation unit 207 for the expected value.

  When using a practical technique, since the image data value is not constant, integration is performed longer in the paper conveyance direction (longer than when using the test pattern). Further, by integrating for a long time, the frequency of the image data in the nozzle array direction can be lowered. Since the data change caused by the inappropriate nozzle has a high frequency, it is easy to find the data change by the above integration.

  The integrated value of the i-th read value Di thus obtained is Dsi, and the integrated value of the expected value Ei is Esi.

3-2. Picking up inappropriate nozzle candidates Next, picking up inappropriate nozzle candidates is performed by the inappropriate image recording element position candidate specifying unit 208 in FIG. For two adjacent nozzles (i-th and i-1-th), the difference between the reading values (normalized difference) and the expected value difference (normalized difference) according to the following equations (2) and (3) Find and compare these.

[Expression 2] ΔDsi = (Dsi−Ds (i−1)) / (Dsi + Ds (i−1)) (2)
[Equation 3] ΔEsi = (Esi−Es (i−1)) / (Esi + Es (i−1)) (3)
If the difference between the read value difference ΔDsi obtained by the equation (2) and the expected value difference ΔEsi obtained by the equation (3) exceeds a predetermined threshold, the number “ i ”is registered. The threshold value that serves as a determination criterion at this time may be determined experimentally from data obtained by actually reading a droplet ejection pattern of an inappropriate nozzle.

3-3. Summary of Peripheral Data Since a defect of one nozzle affects the readings of a plurality of sensors in the vicinity of the corresponding position, “i” registered as an inappropriate nozzle candidate in (3-2) above. (I + 1), “i−1”, etc.) can also be extracted as inappropriate nozzle candidates. However, since these are caused by a common (single) nozzle defect, when there are inappropriate nozzle candidates around “i”, these are collectively “i” in order to avoid duplication. ".

[Step 4]: Identification of inappropriate nozzle and determination of inappropriate level The image recording element state determination unit 210 in FIG. In step 4, a process is performed to identify which position of the nozzle is actually inappropriate and how it is inappropriate for the inappropriate nozzle candidate detected in step 3.

  That is, an inappropriate nozzle is assumed in advance, and the actual sensor output is compared for each pattern. In the case of a high-density ink jet head, sufficient print quality can be obtained without strict correction for inappropriate nozzles. For example, when the droplet ejection size from a certain nozzle is about 3/4 of the normal value, no irregularities are recognized in the print result without performing correction to cover such ejection failure, and deterioration in image quality is recognized. Not. From such a viewpoint, it is assumed that correction processing is performed only for a few patterns that may cause problems in print quality.

  The registered patterns are the following seven types. These patterns are registered in the element state pattern 209 shown in FIG.

[1] Nozzle dead (no discharge) (illustrated in Fig. 9)
[2] Discharge amount 1/2 (However, there is no deviation of the droplet ejection position)
[3] Position shift to the right of one nozzle (illustrated by solid line in Fig. 12)
[4] Position shift to the left of one nozzle (symmetrical with the solid line in Fig. 12)
[5] Displacement 1/2 to the right of 1 nozzle (example shown with dotted line in FIG. 12)
[6] Displacement 1/2 to the left of one nozzle with displacement (symmetrical with dotted line in FIG. 12)
[7] No inappropriateness The following (4-1) and (4-2) operations are performed for the neighboring nozzles near Pi in the patterns [1] to [7] above, and the evaluation values match best. Is picked up with a combination of inappropriate nozzle number and pattern.

  4-1. The expected sensor output at the nozzle position is obtained for the configuration of the nozzle row including the assumed inappropriate nozzle. That is, the operation described in step 1 is calculated assuming that there is an inappropriateness of each pattern. For example, when the discharge amount (volume of the discharge liquid) changes, the coefficient is changed so that the change is about 2/3 power in terms of the dot area (cross-sectional area).

  Thus, assuming that there is an inappropriate nozzle in a certain position, the expected sensor output value is calculated once again according to the calculation procedure of [Step 1].

  Thereafter, alignment with the sensor and integration in the paper transport direction are similarly performed to obtain a new Esi.

4-2. Calculation of Evaluation Value Using Esi of the expected sensor output value obtained in (4-1) above, the absolute value of the following equation is calculated over the width of the pattern around the position of the inappropriate nozzle candidate, and the calculated value is The evaluation value.

[Equation 4] j
Evaluation value = | Σ {(Dsj−Esj) − (Dsi−Esi)} | (4)
In this evaluation value, the absolute value reference is calculated over the width of the pattern with the absolute value reference as the position of “i”. According to the example described with reference to FIGS. 9 and 12, the “pattern width” means 7 points (or 5 points) around the center position, and these 7 points (or 5 points) become j. Equivalent to.

  Thus, according to the equation (4), a total of 35 evaluation values of the number of patterns (7 types) × nozzle position (5 types for the size of the filter size) are calculated, and the one showing the minimum value is matched. Pick up as you want.

  Through the process (4-2), the position of the inappropriate nozzle is specified, and the inappropriate level is specified (whether the state is any of the patterns [1] to [7]). ).

[Step 5]: Correction or Cleaning Based on the result of specifying the inappropriate nozzle and determining the inappropriate level in Step 4 described above, correction control is performed by the correction unit 214 in FIG. 20 as necessary. The correction is performed by changing the discharge amount or discharge frequency of the peripheral nozzles. Specifically, correction methods are registered in the correction patterns 215 corresponding to the patterns [1] to [7], respectively. The contents of the correction process associated with each pattern are as follows.

  [1] With respect to nozzle dead (not ejected), when a nozzle of the nozzle dead is to be ejected, control is performed to add 1/2 of the dead nozzle ejection amount to the ejection amount of the two nozzles on both adjacent sides. . If the discharge amount cannot be added (for example, when the maximum discharge amount is commanded), the error is taken over in the paper transport direction and corrected for the next discharge opportunity.

  [2] For an inappropriate nozzle with a discharge amount of 1/2, when the inappropriate nozzle is ejected, control is performed to add 1/4 of the discharge amount of the inappropriate nozzle to the discharge amount of the two adjacent nozzles on both sides. I do. If the discharge amount cannot be added, the error is taken over in the paper transport direction and corrected for the next discharge opportunity.

  [3] Inappropriate nozzles that cause misalignment to the right of one nozzle will not be corrected. This is because the high-density head is not visually recognized on the print.

  [4] As with [3], inappropriate nozzles that cause misalignment to the left of one nozzle shall not be corrected.

  [5] For improper nozzles that are misaligned to the right of one nozzle and have a discharge rate of 1/2, when the improper nozzle is ejected, the improper nozzle discharge amount Add 1/2 of the nozzle discharge amount. When the addition cannot be performed, the error is taken over in the paper transport direction and corrected for the next ejection opportunity.

  [6] For improper nozzles that are misaligned to the left of one nozzle and have a discharge rate of ½, when the improper nozzle is ejected, the improper nozzle discharge rate Add 1/2 of the nozzle discharge amount. When the addition cannot be performed, the error is taken over in the paper transport direction and corrected for the next ejection opportunity.

  [7] If there are no inappropriate nozzles, no correction will be made.

  In addition, when the presence of an inappropriate nozzle is detected, if the cleaning (nozzle function recovery operation) is possible in the sequence, ink suction or wiping of the corresponding portion is performed, and the above correction operation is not performed. possible. This instruction is given by the cleaning control unit 142 in FIG.

  In the above description, the case where the number of nozzles and the number of sensors coincide as shown in FIG. 9 has been described. However, when the present invention is implemented, the case where the number of nozzles and the number of sensors do not coincide is also described above [ By correcting the filter of the filtering process in step 2], basically the same method as described above can be applied.

In the above description, the example in which the cleaning operation is controlled based on the determination result of the image recording element state determination unit 210 in FIG. 20 is described. However, the result of specifying by the inappropriate image recording element position candidate specifying unit 208 is described. It is also possible to perform cleaning based on this.
[Explanation about history control]
According to the methods in steps 1 to 5 described above, it is possible to identify an inappropriate nozzle with relatively high accuracy. However, even if the data in the paper conveyance direction is integrated, there is a certain limit to the detection accuracy of unevenness. Yes, the possibility of erroneous detection and correction of inappropriate nozzles cannot be completely excluded. A slight streak with a density of 0.01 or less causes unevenness, and an error may occur in specifying the positional relationship between the sensor and the nozzle.

  For this reason, it is preferable to store information on improper nozzle detection and correction performed last time and add history control to increase accuracy of next improper nozzle detection and correction using the history information.

  Here, as an example of history control, a description will be given of a response when an inappropriate nozzle is mistakenly corrected with a nearby nozzle.

  FIG. 19 shows an example in which an inappropriate nozzle is erroneously determined and corrected. The figure shows a state where the previous nozzle “N3” was not ejected (nozzle dead) was erroneously determined as “N4” and correction was performed when the next line was ejected. As a result of erroneously determining that the nozzle of “N4” is the nozzle dead, the discharge amount of the nozzles of “N3” and “N5” on both sides is increased by the correction.

  As a result of this correction, the discharge amount of the nozzle “N5” increases by the amount of dots indicated by the dotted line in FIG. 19, but since the nozzle of “N3” is originally unable to discharge, a droplet ejection increase command by correction is received. But no droplets are ejected.

  Therefore, the dotted line in FIG. 19 is detected from the sensor output obtained by reading this correction result. In this case, the same inappropriate nozzle detection and correction processing as before is performed, but it may be determined that the nozzle of “N4” is nozzle dead again, and as a result, the correction does not function effectively. obtain.

  In order to avoid this situation, the history information is used as follows.

  <1.> The expected output value of the sensor is calculated without including the correction amount up to the previous time, and steps 1 to 4 are performed. In this case, droplet ejection image data not including correction is stored in the third frame memory 136 shown in FIG.

  <2.> At this time, if the inappropriate nozzle is identified as the same nozzle as the previous one, the one with the smaller evaluation value of the same pattern of the adjacent nozzle is selected again as the inappropriate nozzle.

  Instead of <2 '.> Or <2.> above, if an inappropriate nozzle is identified as the same nozzle as the previous one, the nozzle and pattern combination with the second smallest evaluation value is selected again.

  If these steps <1.> to <2.> (or <2 '.>) Are not improved even after being repeated, a plurality of neighboring nozzles are considered inappropriate, and a cleaning operation is performed. If the correction process and cleaning operation do not improve, a warning is issued.

  These instructions are executed by the history control unit 212 to the image recording element state determination unit 210 based on the previous evaluation value recorded in the history information recording unit 211 in FIG. 20 and the specified inappropriate nozzle information. To do. In addition, accumulation | storage of log | history information is not restricted to the last information, You may memorize | store the information for the past several times including the last information at least.

[Intercolor processing when reading practical images]
In the above description, the case of reading an image using a test pattern for each color as shown in FIG. 8 has been described. However, in the implementation of the present invention, not only an embodiment using a test pattern but also an actual image may be used. Is possible.

  When reading a practical image, the same (overlapping) section ejected by the print heads 12K, 12C, 12M, and 12Y of each color is read by a plurality of color (RGB) line sensors and processed in the following ink order. .

  [Processing Procedure 1] First, an inappropriate nozzle is detected for the K ink nozzle. For the evaluation of the K ink nozzle, the average value of the outputs of all RGB sensors is used.

  [Processing procedure 2] Next, an inappropriate nozzle is detected for the C ink nozzle. For the evaluation of the C ink nozzle, the output of the R sensor is used. However, an inappropriate portion of the K ink nozzle is removed and detection correction is performed for the other range.

  [Processing procedure 3] Next, an inappropriate nozzle is detected for the M ink nozzle. For the evaluation of the M ink nozzle, the output of the G sensor is used. However, inappropriate portions of the K ink nozzle and the C ink nozzle are removed, and detection correction is performed for the other ranges.

  [Processing procedure 4] Next, an inappropriate nozzle is detected for the Y ink nozzle. For the evaluation of the Y ink nozzle, the output of the B sensor is used. However, inappropriate portions of the K ink nozzle, the C ink nozzle, and the M ink nozzle are removed, and detection correction is performed for the other ranges.

  The reason why the processing is performed in the order of K → C → M → Y according to the above processing procedures 1 to 4 is due to the relationship between the spectral sensitivity of the sensor and the spectral absorption of the color material. That is, the K ink gives almost the same output change to the RGB sensors. Therefore, accurate detection is possible by first performing processing using these average values. In addition, since the color material normally has secondary absorption on the short wavelength side, the C ink has absorption on the R side and absorption on the shorter wavelength side, that is, on the G and B regions. That is, C ink affects the detection of M ink and Y ink. Similarly, the M ink affects the detection of the Y ink. Therefore, in order to eliminate such influence, it is preferable to perform processing in order of increasing influence range (that is, in order from the long wavelength side). By doing so, processing between colors can be performed efficiently.

  In the above embodiment, an inkjet recording apparatus has been described as an example of an image recording apparatus, but the scope of application of the present invention is not limited to this. Besides the ink jet system, the present invention can be applied to various types of image recording apparatuses such as a thermal transfer recording apparatus having a line head, an LED electrophotographic printer, and a silver salt photographic printer having an LED line exposure head.

1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of print head Sectional view along line 4-4 in FIG. FIG. 3 is an enlarged view showing the nozzle arrangement of the print head shown in FIG. Schematic diagram showing the configuration of an ink supply system in the inkjet recording apparatus according to the present embodiment Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. The figure which shows the other example of arrangement | positioning of the light source for illumination The figure which illustrated the relationship between the nozzle position, dot position, sensor (pixel) position, and sensor output value when the number of sensors, the number of nozzles, and their arrangement pitch are equal The figure which illustrated the relationship between the nozzle position, the dot position, the sensor position, and the sensor output value when the number of sensors and the number of nozzles do not match The figure which illustrated the relationship between the nozzle position, the dot position, the sensor position, and the sensor output value when the nozzle position and the sensor position are deviated The figure which illustrated the relation of the nozzle position, the dot position, the sensor position, and the sensor output value when the dispersion of the landing position and the abnormality of the discharge amount occur Diagram showing an example of reading a test pattern with a line sensor The block diagram which showed the principal part structure of the nozzle detection in the inkjet recording device which concerns on this embodiment. The figure which showed the example of the filter used for filtering processing The graph which illustrated the conversion table used when converting the output value of filtering processing into the reading value of a sensor A graph showing the sensor output value near the left edge of the image and the difference between the output values of both adjacent pixels A graph showing the expected sensor reading at each nozzle position and the difference between the nozzle positions on both sides The figure which shows the example which corrected by misjudging an inappropriate nozzle 14 is a block diagram showing a detailed configuration example of an inappropriate nozzle (unsuitable image recording element) specifying unit and a droplet ejection control unit in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Print head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feed part, 20 ... Decal processing part, 22 ... Adsorption Belt transport unit 24 ... Print detection unit 28 ... Cutter 33 ... Belt 50 ... Print head 51 ... Nozzle 52 ... Pressure chamber 53 ... Ink chamber unit 54 ... Supply port 58 ... Actuator 64 ... Cap , 66 ... cleaning blade, 67 ... suction pump, 72 ... system controller, 76 ... motor driver, 80 ... print controller, 84 ... head driver, 90, 120 ... line sensor, 92 ... light source, 132 ... droplet ejection controller, 140: Inappropriate nozzle specifying unit, 142: Cleaning control unit

Claims (12)

Printing means comprising a full-line recording head in which a plurality of image recording elements are arranged over a length corresponding to the entire width of the printing medium;
Transport means for transporting at least one of the recording head and the print medium in a direction substantially perpendicular to the width direction of the print medium and moving the print head and the print medium relative to each other;
Image reading means in which a plurality of sensors for reading an image recorded on the print medium by the recording head are arranged over a length corresponding to the full width of the print medium;
Based on a plurality of read pixel data obtained from the plurality of sensors, for each sensor, read pixel data of the sensor, read pixel data obtained from its neighboring sensors, and expected read data expected from an image to be originally recorded are used. Inappropriate image recording element specifying means for specifying an image recording element of recording failure based on the calculation result,
An image recording apparatus comprising:   The image recording apparatus according to claim 1, wherein the inappropriate image recording element specifying unit performs a calculation process of comparing actual measurement data based on the read pixel data and the expected read data.   Expected read data generating means for creating the expected read data based on dot data generated from image data to be recorded, and the expected read data generating means performs filtering processing on the dot data. The image recording apparatus according to claim 1, further comprising:   The filter processing unit is a filter processing unit that performs a filtering process on the dot data using a filter having a plurality of types of coefficients corresponding to the types of dot sizes, and the filter processing unit performs the filtering according to the dot size indicated by the dot data. 4. The image recording apparatus according to claim 3, wherein the coefficient is a filter processing means for selectively determining the coefficient of the image. Integration calculation means for integrating the read pixel data in the relative movement direction in a unit having a width of a predetermined length or more with respect to the relative movement direction of the print medium with respect to the recording head;
Comparing image characteristic values in the vicinity of at least two locations in the main scanning direction substantially orthogonal to the relative movement direction from the integral data obtained by the integral calculation means, with the image characteristic value of the integral value of the expected read data, Image position specifying means for specifying the positional relationship between the position of the sensor corresponding to two places and the expected read data;
A positional relationship grasping means for associating a sensor position and an image recording element position corresponding to the two positions found by the image position identifying means, and grasping a correspondence relationship between each sensor position and the image recording element position;
Based on the correspondence between each sensor position and the image recording element position grasped by the positional relation grasping means, a sensor reading expectation value calculating means for obtaining a sensor reading expectation value at each sensor position by interpolation calculation;
The image recording apparatus according to claim 1, further comprising:   An integral value obtained by integrating the read pixel data obtained from each sensor in the relative movement direction, and an integral obtained by integrating the sensor read expectation value obtained by the sensor read expectation value calculating means in the relative movement direction. 6. The image recording according to claim 1, further comprising inappropriate image recording element position candidate specifying means for specifying an approximate position of the inappropriate image recording element using a value. apparatus.   By comparing expected read data expected from a recorded image when including an improper image recording element in an assumed defective state with read pixel data obtained from the plurality of sensors, the state of the inappropriate image recording element The image recording apparatus according to claim 1, further comprising an image recording element state determination unit that determines whether or not   Correction means for correcting an image recording operation based on an inappropriate image recording element specifying result by the inappropriate image recording element specifying means, and an inappropriate image recording element specifying result by the inappropriate image recording element specifying means or 8. The apparatus according to claim 1, further comprising at least one of cleaning means for cleaning the recording head based on a result specified by the inappropriate image recording element candidate specifying means. The image recording apparatus described in the item. Correction means for correcting the image recording operation based on the result of specifying the inappropriate image recording element by the inappropriate image recording element specifying means;
History information storage means for storing at least the previous specific information of the inappropriate image recording element and the correction information of the image recording operation;
History control means for determining the next correction content from the information stored in the history information storage means and information obtained by reading the corrected image with the image reading means;
The image recording apparatus according to claim 1, further comprising: The printing unit includes a recording head capable of printing at least each of cyan (C), magenta (M), and yellow (Y),
The image reading means is composed of an RGB sensor array that can split and read red (R) light, green (G) light, and blue (B) light,
Read the same image section recorded by overlapping each color by the printing means with the RGB sensor row,
A process of specifying an inappropriate image recording element in the color order of C, M, and Y is performed, and a subsequent process is performed by removing a portion determined as an inappropriate image recording element in the preceding color process. The image recording apparatus according to any one of claims 1 to 9. The printing means includes a recording head capable of printing black (K) color,
A process for specifying an inappropriate image recording element in the color order of K, C, M, and Y is performed, and a subsequent process is performed by removing a portion determined as an inappropriate image recording element in the preceding color process. The image recording apparatus according to claim 10. A printing step of printing on the print medium using a full-line type recording head in which a plurality of image recording elements are arranged over a length corresponding to the full width of the print medium;
An image reading step of reading an image recorded on the print medium by an image reading means in which a plurality of sensors are arranged over a length corresponding to the full width of the print medium;
Based on a plurality of read pixel data obtained from the plurality of sensors, for each sensor, read pixel data of the sensor, read pixel data obtained from its neighboring sensors, and expected read data expected from an image to be originally recorded are used. Inappropriate image recording element specifying step of specifying an image recording element having a recording failure based on the calculation result,
A method for identifying an inappropriate image recording element in an image recording apparatus, comprising:

Images