JP2008087287A - Method for detecting fault of ink delivering and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting fault of ink delivering accurately detecting a fault of the delivery of ink including white ink. <P>SOLUTION: The method for detecting the fault of ink delivering has an image reading process, a reference image calculating process, a difference image calculating process, a process for detecting a position of a nozzle with the fault of delivery, and a process for detecting a color of the ink with the fault of delivery. The image reading process reads a transmitted image and a reflecting image of the image formed by hitting the ink on a light-transmissive medium 16. The reference image calculating process calculates a reference transmission image and a reference reflecting image when the ink normally hits to form the image. The difference image calculating process calculates a difference transmission image between the transmitted image and the reference transmitted image and a difference reflecting image between a reflecting image and a reference reflecting image. The process for detecting the position of the nozzle with the fault of delivery detects the position of the nozzle with the fault of delivery from the difference transmission image and the difference reflecting image. The process for detecting the color of the ink with the fault of delivery detects the color of the ink with the fault of delivery from the difference transmission image and the difference reflecting image by using different correlation tables when the image is formed by hitting a chromatic ink by overlapping white ink hit on a light-transmissive medium and when the image is formed by hitting only the chromatic ink on the light-transmissive medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink discharge failure detection method and an image forming apparatus, and more particularly to a discharge failure detection method for detecting discharge failure information of white ink and colored ink even when white ink is ejected and a mechanism for realizing the method. The present invention relates to an ink jet recording apparatus including

  The printer device of Patent Document 1 performs template matching on each image data stored in the print image storage unit and the inspection image storage unit, and determines that the printing is defective when the difference exceeds a predetermined value.

Further, the image recording apparatus of Patent Document 2 includes a CCD having photoelectric conversion elements arranged at the same pitch as the nozzles of the recording head. This CCD scans an image recorded by scanning from the back of the recording head at the same speed as the recording head. Then, the presence or absence of a defective ejection nozzle is determined by comparing the image data to be recorded with the result read by the CCD.
JP-A-9-136411 JP-A-5-301427

  In recent years, inkjet printing has been actively performed on media other than paper, such as film, instead of paper media, and it has become possible to print images on transparent resin films. In this case, it is common to use a so-called white ink in order to apply a ground that reflects light to the printed image. That is, a part of the image has a function of printing white ink and applying a background, and another part has a function of maintaining transparency without ejecting the white ink. In this case, it is desirable to detect ink ejection defects including white ink.

  Here, “ejection failure” includes various forms of ejection failure such as “non-ejection” in which no ink is ejected from the nozzles, ejection variation, and variation in ejection amount.

  However, when light is applied to a light-transmitting medium on which a base with white ink is printed, the light is all reflected without passing through the light-transmitting medium. On the other hand, when light is applied to a translucent medium that is not printed with a white ink base, the light is translucent even if colored ink is printed over the white ink. Transparent media. As described above, the optical characteristics of the image change depending on whether the base with white ink is printed on the translucent medium or not.

  For this reason, when an image on a medium is read by a reading means such as a CCD line camera, it is considered that the read image changes depending on whether or not the background with white ink is present. It is considered that it becomes difficult to accurately detect the ink ejection failure by using it.

  Here, in the prior arts of Patent Document 1 and Patent Document 2, there is no suggestion of printing with white ink, and an image on the medium is read by a reading unit such as a CCD line camera, and the ink is determined based on the difference from the reference image. It merely determines the presence or absence of ejection failure. For this reason, when ink jet printing is performed on a translucent medium other than paper, such as a transparent film, it is necessary to form a base by printing white ink. It is considered that ink discharge failure including ink cannot be accurately detected.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an ejection failure detection method and an image forming apparatus having an ejection failure detection function that can accurately detect ejection failure of ink including white ink. And

  In order to achieve the above object, according to the first aspect of the present invention, in the ink ejection failure detection method, one surface side of the translucent medium with respect to an image formed by ejecting ink onto the translucent medium Irradiating with light, an image reading step for reading the transmission image of the image and the reflection image of the image, and the transmission image of the image and the image when the ink is normally ejected to form the image A reference image calculation step for calculating a reference transmission image and a reference reflection image to be predicted as a reflection image, and a difference image between the transmission image read in the reading step and the reference transmission image calculated in the reference image calculation step. A differential transmission image and a differential reflection image that is a difference image between the reflection image read in the reading step and the reference reflection image calculated in the reference image calculation step are calculated. A divided image calculation step, a defective discharge nozzle position detection step for detecting the position of a defective discharge nozzle from the differential transmission image and the differential reflection image, and colored ink is applied to the white ink deposited on the translucent medium. Incorrect ejection from the differential transmission image and the differential reflection image using a correlation table that differs between when an image is formed by droplets and when an image is formed by ejecting only colored ink on a translucent medium An ejection failure ink color detecting step for detecting the color of the ink.

  According to the present invention, different correlation tables are used when white ink is ejected and when it is not ejected. Therefore, it is possible to accurately detect ink ejection defects including white ink in response to changes in image characteristics that occur when white ink is ejected and not.

  The invention according to claim 2 is the ink ejection failure detection method according to claim 1, wherein in the ejection failure ink color detection step, the colored ink is ejected on the white ink deposited on the translucent medium. When an abnormality is detected in both the differential transmission image and the differential reflection image in the case of forming an image by the above method, the ejection failure ink is detected as white ink, and the abnormality is detected only in the differential reflection image. The ejection failure ink is detected as colored ink.

  According to the present invention, it is possible to easily detect ejection failure ink from the differential transmission image and the differential reflection image, and it is possible to simplify the ink ejection failure detection method.

  According to a third aspect of the present invention, in the image forming apparatus, light source means for irradiating light from one surface side of the translucent medium to an image formed by ejecting ink onto the translucent medium. A transmission image reading unit that reads a transmission image of the image from the other surface side of the translucent medium; a reflection image reading unit that reads a reflection image of the image from one surface side of the translucent medium; Reference image calculation means for calculating a reference transmission image and a reference reflection image predicted as the transmission image and reflection image to be read when ink is ejected normally, and the transmission image and the reference read by the transmission image reading means A differential transmission image, which is a difference image from the reference transmission image calculated by the image calculation means, and the reflection image and the base read by the reflection image reading means A difference image calculation unit that calculates a differential reflection image that is a difference image from the reference reflection image calculated by the image calculation unit, and a defective discharge nozzle that detects a position of a defective discharge nozzle from the differential transmission image and the differential reflection image Position detection means, a white ink ejection head that ejects white ink, a droplet ejection means that includes a colored ink ejection head that ejects colored ink, and a colored ink that is superimposed on the white ink that is ejected onto a translucent medium. When the image is formed by ejecting droplets, the differential transmission image calculated by the differential image calculation means and the correlation image different from the case where the image is formed by ejecting only colored ink on the translucent medium, And a discharge failure ink color detection means for detecting the color of discharge failure ink from the differential reflection image.

  According to the present invention, the correlation table is provided differently depending on whether or not the white ink is ejected. Therefore, it is possible to accurately detect ink ejection defects including white ink in response to changes in image characteristics that occur when white ink is ejected and not.

  According to the present invention, it is possible to accurately detect ink discharge failure including white ink.

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

[Outline of image forming apparatus]
FIG. 1 is a schematic diagram of an image forming apparatus according to this embodiment. As shown in FIG. 1, the image forming apparatus of this embodiment mainly includes a printing unit 11, a control unit 12, a transmission type measurement unit 13, a reflection type measurement unit 14, a conveyance unit 17, and the like.

  The printing unit 11 includes a plurality of inkjet recording heads (hereinafter referred to as heads) provided corresponding to white (W), black (K), cyan (C), magenta (M), and yellow (Y) inks. ) 21W, 21K, 21C, 21M, 21Y.

  A transmissive measurement unit 13 is provided behind the printing unit 11, and the light source 22 and the optical sensor 23 (CCD line sensor in the present embodiment) are arranged so as to face each other with the medium 16 interposed therebetween. Further, a reflection type measurement unit 14 is provided behind the transmission type measurement unit 13, and a light source 24 and an optical sensor 26 (CCD line sensor in the present embodiment) are arranged on the same side with respect to the medium. The medium 16 is transported by the transport unit 17 in the direction indicated by the arrow in FIG.

  Details of the image forming apparatus of the present embodiment will be described later.

[System configuration of image forming apparatus]
FIG. 2 shows a block diagram of a system configuration of the ink jet recording apparatus.

  As shown in FIG. 2, 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. Yes.

  The host computer 86 functions as an image output unit that transmits image data to the communication interface 70.

  The communication interface 70 is an interface unit (image input unit) that functions as an image input unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied.

  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 stores an image input via the communication interface 70, and data is read and written through the system controller 72.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, the measurement unit controller 90, and the like, and performs communication control with the host computer 86 and read / write control of the image memory 74. Control signals for controlling the motor 88, the heater 89, the transmissive sensor 23, and the reflective sensor 26 of the transport system are generated.

  The image memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver (driving circuit) that drives the conveyance 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 measurement unit controller 90 is a driver that drives the transmissive sensor 23 and the reflective sensor 26 of the sensor system in accordance with instructions from the system controller 72. The present invention proposes a method for detecting an ink ejection failure using the two sensors of the transmission type sensor 23 and the reflection type sensor 26. Details of the method of detecting an ink ejection failure will be described later.

  Under the control of the system controller 72, the print control unit 80 performs various processes such as processing and correction for generating a droplet ejection control signal from image data (multi-value input image data) in the image memory 74. In addition to functioning as signal processing means, it also functions as drive control means for controlling the ejection drive of the head 50 by supplying the generated ink ejection data to the head driver 84.

  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. 2, 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 one processor.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, for example, RGB multivalued image data is stored in the image memory 74.

  In the inkjet recording apparatus 10, a pseudo continuous tone image is formed by human eyes by changing the droplet ejection density and dot size of fine dots by ink (coloring material). It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. For this reason, the original image (RGB) data stored in the image memory 74 is sent to the print controller 80 via the system controller 72 and converted into dot data for each ink color.

  That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 80 is stored in the image buffer memory 82. The dot data for each color is converted into CMYK droplet ejection data for ejecting ink from the nozzles of the head 50, and the ink ejection data to be printed is determined.

  The head driver 84 outputs a drive signal for driving the actuator corresponding to each nozzle of the head 50 according to the print contents based on the ink ejection data and the drive waveform signal given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  In this way, when the drive signal output from the head driver 84 is applied to the head 50, ink is ejected from the corresponding nozzle 51. By controlling ink ejection from the head 50 in synchronization with the conveyance speed of the medium 16, an image is formed on the medium 16.

  As described above, based on the ink discharge data and the drive signal waveform generated through the required signal processing in the print control unit 80, control of the discharge amount and discharge timing of the ink droplets from each nozzle via the head driver 84. Is done. Thereby, a desired dot size and dot arrangement are realized.

[Description of detection method of defective ejection ink]
First, the reflected light and transmitted light detection patterns, which are the basic concept of the ink ejection failure detection method of the present invention, will be described. For the sake of simplicity, a description will be given of a case where ejection failure is non-ejection (the liquid does not eject from the nozzle and does not adhere to the medium). FIG. 3 is a diagram illustrating a relationship between a printing state on a medium and the presence or absence of generation of reflected light and transmitted light when light is irradiated from one direction of the medium.

As shown in FIG. 3, in an image on a medium such as a transparent film (a) when both white ink and colored ink are absent, (b) when there is no white ink and colored ink is present,
(C) Consider four patterns when there is white ink and no colored ink, and (d) when both white ink and colored ink are present.

  When both the white ink and colored ink shown in (a) are absent, if light is irradiated from one side of the media, there is no white ink underlayer, so no light is reflected, and there is no colored ink, so there is no transmission. To do. Therefore, reflected light is not generated, but transmitted light is generated.

  In addition, when there is no white ink as shown in (b) and there is colored ink, when light is irradiated from the colored ink side, there is no white ink underlayer, so light is not reflected, and light depends on the color of the colored ink. Through. Therefore, reflected light is not generated, but transmitted light is generated. However, the transmitted light has characteristics according to the color of the colored ink.

  Further, in the case where white ink is present and color ink is not present as shown in (c), when light is irradiated from the white ink side, the light is totally reflected and does not pass through the white ink underlayer. Therefore, reflected light is generated, but transmitted light is not generated.

  Further, when both the white ink and the colored ink shown in (d) are present, when light is irradiated from the colored ink side, the light is reflected by the base layer of the white ink according to the colored ink and is not transmitted. Therefore, reflected light is generated, but transmitted light is not generated. However, the reflected light has characteristics corresponding to the color of the colored ink.

  The detection patterns as described above are summarized in FIG. FIG. 4 is a table summarizing the contents shown in FIG. As shown in FIG. 4, it can be seen that the presence or absence of reflected light and transmitted light differs depending on the presence or absence of white ink on the medium, and the characteristics of reflected light or transmitted light differ depending on the presence or absence of colored ink. Therefore, it can be seen that both the reflected light and the transmitted light need to be measured by the sensor in order to detect the non-ejection of the ink on the medium printed with the white ink and the colored ink. Therefore, in the present invention, as shown in FIG. 1 and FIG. 2, the transmission type measurement unit 13 and the reflection type measurement unit 14 are provided.

  Therefore, a method for specifying the color of the non-ejection ink by measuring the reflected light and the transmitted light using the transmission type measurement unit 13 and the reflection type measurement unit 14 as shown in FIGS. 1 and 2 will be described. .

  FIG. 5 shows a transmissive sensor 23 and a reflective sensor in a region where an image is formed by normally ejecting white ink and cyan ink when the cyan ink is printed on the medium 16 over the white ink. 26 is a list of reference signal values calculated as signal values predicted to be measured by H.26. FIG. 5 shows the filter R, the filter G, and the filter B of each sensor.

  Since the light is reflected and does not pass through the printing of the white ink, the transmissive sensor 23 cannot measure the transmitted light. Therefore, as shown in FIG. 5, the reference signal values of all the filters of the transmissive sensor 23 are values close to zero.

  Further, light is reflected by printing with cyan ink as colored ink with characteristics corresponding to the color of cyan ink. Therefore, the reflected light having the characteristics corresponding to the color of the cyan ink is measured by the reflective sensor 26. Therefore, as shown in FIG. 5, in the reflective sensor 26, the filter G and the filter B calculate the reference signal value near the maximum value 255, whereas the filter R has a characteristic corresponding to the color of the cyan ink. 49 reference signal values are calculated.

  Therefore, based on the reference signal value shown in FIG. 5, the actual measurement signal values shown in FIGS. 6 to 8 are compared to verify the ink ejection state.

  In the measurement result (1) shown in FIG. 6, the measurement signal values of the transmission type sensor 23 and the reflection type sensor 26 substantially match the reference signal value shown in FIG. Therefore, it can be determined that white ink and cyan ink are ejected normally.

  In the measurement result (2) shown in FIG. 7, the measurement signal value is almost close to 0 in all the filters of the transmission sensor 23. Therefore, it can be determined that the white ink is ejected normally. On the other hand, in all the filters of the reflection type sensor 26, the measured signal value is near the maximum value 255. Therefore, the signal value of the filter R is greatly different from the reference signal value shown in FIG. Therefore, it can be determined that cyan ink is not ejected.

  Further, in the measurement result (3) shown in FIG. 8, in all the filters of the reflection type sensor 26, the measurement signal value is substantially different from the reference signal value shown in FIG. Therefore, it can be determined that white ink is not ejected. On the other hand, in the transmission sensor 23, the filter G and the filter B have a measurement signal value of 46 near the maximum value 255, whereas the filter R has 46 measurement signal values. Therefore, when compared with the reference signal value shown in FIG. 5, the signal value has almost the same tendency as the reference signal value of the reflective sensor 26. Therefore, it can be determined that the cyan ink is ejected normally.

  As described above, by using the signal values of a total of six channels for the filters R, G, and B of the transmission type sensor 23 and the reflection type sensor 26, and comparing the reference signal value and the measurement signal value, Non-ejection ink can be detected. Similarly, it is possible to detect a case where there is a discharge and is different from the original attachment position, or that the discharge amount is different (a measurement signal value is different). The present invention detects defective ejection ink using such a method.

[Explanation of defective ejection ink detection flow]
Therefore, the method for detecting defective ejection ink according to the present invention will be described in detail. FIG. 9 is a flowchart illustrating a method for detecting defective ejection ink. First, an image is input (step S1). Specifically, as described above, image data to be printed is input from the outside via the communication interface 70 of the control unit 12 and stored in the image memory 74.

  Next, ink amount data for each color is generated (step S2). Specifically, the image data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and the print control unit 80 generates ink amount data for each color.

  Next, the print control unit 80 reflects the transmissive sensor 23 and the reflection when the white ink and the colored ink are normally ejected and printed on the medium 16 based on the ink amount data of each color generated in step S2. Density data measured by the mold sensor 26 is predicted and calculated as transmission density reference data and reflection density reference data (step S3). In the calculation, the spectral absorption characteristics of the ink and the medium are taken into consideration.

  Next, the print controller 80 generates print data from the ink amount data of each color (step S4), and drives the head driver 84 based on the generated print data to drive the heads 21W, 21K, 21C, 21M, 21Y. Then, ink is ejected from the image to print an image on the medium 16 (step S5).

  Next, transmission density measurement data is obtained by irradiating the print image with the light source 22 and measuring with the transmission sensor 23, and further irradiating the print image with the light source 24 and measuring with the reflection sensor 26. Thus, reflection density measurement data is acquired (step S6).

  Specifically, as shown in FIG. 10, data is acquired by providing measurement areas for the transmission sensor 23 and the reflection sensor 26 in a direction perpendicular to the conveyance direction of the medium 16 on which an image is printed.

  Next, the transmission density difference data and the reflection density difference data obtained by collating the calculated transmission density reference data with the measured transmission density measurement data, and the calculated reflection density reference data with the measured reflection density measurement data, respectively. Is calculated (step S7).

  Here, Steps S <b> 3 to S <b> 7 will be specifically described with reference to FIGS. 11 and 12. FIG. 11 is a schematic diagram of the difference in signal value of the transmission sensor 23 when cyan ink is poorly ejected when white ink is ejected. FIG. 12 is a schematic diagram of the difference in signal value of the reflective sensor 26 when cyan ink is poorly discharged when white ink is discharged. In both FIGS. 11 and 12, the horizontal axis represents the sensor longitudinal direction and the vertical axis represents the signal value.

  Assume that the signal waveform of the transmission density reference data calculated in step S3 is represented as shown in FIG. 11A, and the signal waveform of the reflection density reference data is represented as shown in FIG. Further, it is assumed that the transmission density measurement data acquired in step S6 is expressed as shown in FIG. 11B and the reflection density measurement data is expressed as shown in FIG. Then, the signal waveform of the transmission density difference data calculated in step S7 is expressed as shown in FIG. 11C, and the signal waveform of the reflection density difference data is expressed as shown in FIG.

  Next, from the calculated transmission density difference data and reflection density difference data, the position of the nozzle with ink ejection failure is specified (step S8).

  In the example shown in FIG. 11 and FIG. 12, a sag portion is generated in the signal waveform of the filter R in FIG. 11C, and the sag portion is considered to be an ink ejection failure portion, and from the position in the longitudinal direction of the sensor. It is possible to specify the position of the nozzle of defective ejection ink. This drop can be automatically determined by performing determination based on an appropriate threshold.

  Next, in order to identify the color of ink with defective ejection, first, the channel in which the differential waveform shows an abnormal value (measurement data of the filters R, G, and B of each of the transmission type sensor and the reflection type sensor) Is specified (step S9).

  Next, it is determined whether or not to print white ink (step S10). When printing white ink, the correlation table A is used (step S11), and the color of the ink with defective ejection is specified (step S12). On the other hand, when the white ink is not printed, the correlation table B is used (step S13), and the color of the ink with defective ejection is specified (step S14).

  Here, the correlation table A is a table as shown in FIG. 13, and the correlation table B is a table as shown in FIG. 11 and 12 corresponds to the case where white ink is printed, the correlation table A shown in FIG. 13 is used in steps S9 and S10.

  And as shown in FIG.12 (c), the signal waveform of the transmission density difference data is a normal value in all the filters. On the other hand, as shown in FIG. 11C, the signal waveform of the reflection density difference data is normal in the filters G and B, but the signal waveform of the reflection density difference data in the filter R is an abnormal value. It has become. Accordingly, “cyan ink is poorly discharged” is specified from FIG. As described above, the ejection failure ink detection method of the present invention is performed.

[Configuration of inkjet recording apparatus]
Next, an ink jet recording apparatus will be described as a specific application example of the image forming apparatus provided with the above-described ink discharge failure detection function.

  FIG. 15 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. As shown in the figure, the ink jet recording apparatus 10 includes a plurality of inks provided corresponding to white (W), black (K), cyan (C), magenta (M), and yellow (Y) inks. Ink storage / loading that stores ink to be supplied to each of the heads 21W, 21K, 21C, 21M, and 21Y, and the printing unit 21 having ink jet recording heads (hereinafter referred to as heads) 21W, 21K, 21C, 21M, and 21Y. A portion 18, a supply portion 19 that supplies a medium 16 made of a transparent resin film, a decurling processing portion 20 that removes curl of the media 16, and a nozzle surface (ink ejection surface) of the printing portion 21. A belt conveyance unit 27 that is arranged and conveys the medium 16 while maintaining the flatness of the medium 16, and a transmission type that constitutes the ink ejection failure detection mechanism of the present invention. It includes a constant unit 13 and the reflection measuring unit 14, and a discharge portion 38 for discharging the recorded media (printed matter) to the outside.

  The ink storage / loading unit 18 includes ink tanks that store inks of colors corresponding to the heads 21W, 21K, 21C, 21M, and 21Y, and the tanks 21W, 21K, and 21C are connected to the respective tanks via necessary pipelines. , 21M, 21Y.

  The media 16 delivered from the supply unit 19 retains curl due to having been loaded in the magazine. In order to remove the curl, heat is applied to the medium 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 a roll-shaped medium, a cutter (first cutter) 28 is provided as shown in FIG. 15, and the medium is cut into a desired size by the cutter 28. Note that the cutter 28 is not necessary when a cut-shaped medium is used.

  After the decurling process, the cut medium 16 is sent to the belt conveyance unit 27. The belt conveyance unit 27 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 21 forms a horizontal surface (flat surface). ing.

  The belt 33 has a width that is greater than the width of the medium 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 16, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 21 inside the belt 33 spanned between the rollers 31 and 32, and this suction chamber 34 is connected to the fan 35. The medium 16 is sucked and held on the belt 33 by suctioning to negative pressure. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  The power of the motor (reference numeral 88 in FIG. 2) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The held medium 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorption roll, etc., an air blow method of blowing clean air, or a combination thereof.

  A heating fan 40 is provided on the upstream side of the printing unit 21 on the media conveyance path formed by the belt conveyance unit 27. The heating fan 40 blows heated air on the medium 16 before printing to heat the medium 16. By heating the medium 16 immediately before printing, the ink is easily dried after landing.

  Each of the heads 21W, 21K, 21C, 21M, and 21Y of the printing unit 21 has a length corresponding to the maximum paper width of the medium 16 targeted by the ink jet recording apparatus 10, and has a maximum size recorded on the nozzle surface. This is a full-line head in which a plurality of nozzles for ejecting ink are arranged over a length (full width of the drawable range) exceeding at least one side of the medium (see FIG. 16).

  The heads 21W, 21K, 21C, 21M, and 21Y are arranged in the order of white (W), black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the medium 16. The heads 21 </ b> W, 21 </ b> K, 21 </ b> C, 21 </ b> M, and 21 </ b> Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the medium 16.

  By ejecting different color inks from the heads 21W, 21K, 21C, 21M, and 21Y while transporting the medium 16 by the belt transport unit 27, it is possible to form a color image on a background with white ink.

  As described above, according to the configuration in which the full line type heads 21W, 21K, 21C, 21M, and 21Y having nozzle rows covering the entire width of the media are provided for each color, the media 16 and the paper 16 in the paper feeding direction (sub-scanning direction) An image can be recorded on the entire surface of the medium 16 by performing the operation of relatively moving the printing unit 21 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 recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of the standard colors (4 colors) of KCMY in addition to the white ink (W) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink is used as necessary. , Dark ink and special color ink may be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta.

  A post-drying unit 42 is provided following the printing unit 21. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used.

  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 pressurizing the paper holes with pressure. There is an effect to.

  Subsequent to the post-drying unit 42, a transmission type measurement unit 13 and a reflection type measurement unit 14 constituting the ink ejection failure detection mechanism of the present invention are provided.

  A heating / pressurizing unit 44 is provided following the reflective measurement unit 14. 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 output unit 38. 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) for switching the discharge path in order to sort the printed matter of the main image and the printed matter of the test print and send them to the sorting and discharging sections 38A and 38B. Yes. When the main image and the test print are simultaneously formed on a large medium in parallel, the test print portion is separated by the cutter (second cutter) 48. Although not shown in FIG. 15, the sorter / discharge unit 38A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the heads 21W, 21K, 21C, 21M, and 21Y for each color are the same, the heads are represented by the reference numeral 50 in the following.

  FIG. 16A is a plan perspective view showing a structural example of the head 50, and FIG. 16B is an enlarged view of a part thereof. 16C is a plan perspective view showing another structure example of the head 50, and FIG. 17 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 151). FIG. 17 is a cross-sectional view taken along line 17-17 in FIG.

  In order to increase the dot pitch printed on the medium 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIGS. 16A and 16B, the head 50 of this example includes a plurality of ink chamber units (liquid chambers) each including a nozzle 51 serving as an ink discharge port, a pressure chamber 52 corresponding to each nozzle 51, and the like. The droplet discharge elements 53 are arranged in a staggered matrix (two-dimensionally), and are thereby projected substantially in a line along the head longitudinal direction (direction perpendicular to the paper feed direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are formed over a length corresponding to the entire width of the media 16 in a direction substantially orthogonal to the feeding direction of the media 16 is not limited to this example. For example, instead of the configuration of FIG. 16 (a), as shown in FIG. 16 (c), short head modules 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged are arranged in a staggered manner and connected. A line head having a nozzle row having a length corresponding to the entire width of the medium 16 may be configured.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIGS. 16A and 16B), and the nozzle 51 is located at one of the diagonal corners. An outlet for supplying ink (supply port) 54 is provided on the other side. The shape of the pressure chamber 52 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon and other polygons, a circle, and an ellipse.

  As shown in FIG. 17, each pressure chamber 52 communicates with a common channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 52 via the common channel 55.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibrating plate that also serves as a common electrode) 56 constituting a part of the pressure chamber 52 (the top surface in FIG. 18). By applying a drive voltage between the individual electrode 57 and the common electrode, the actuator 58 is deformed and the volume of the pressure chamber 52 is changed, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. The actuator 58 is preferably a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate. After the ink is ejected, when the displacement of the actuator 58 returns to its original state, new ink is refilled into the pressure chamber 52 from the common channel 55 through the supply port 54.

  As shown in FIG. 18, the ink chamber units 53 having the above-described structure are arranged in a constant arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern.

  That is, with a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  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 the nozzles 51 arranged in a matrix as shown in FIG. 18 are driven, the main scanning as described in the above (3) 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, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. Print one line in the width direction.

  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.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as a main scanning direction, and the direction in which the sub scanning is performed is referred to as a sub scanning direction. That is, in this embodiment, the conveyance direction of the medium 16 is the sub-scanning direction, and the direction orthogonal to the medium 16 is the main scanning direction.

  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.

  Although the ink ejection method and the image forming apparatus of the present invention have been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

1 is a schematic diagram of an image forming apparatus according to an exemplary embodiment. 1 is a block diagram of a system configuration of an ink jet recording apparatus. It is a figure which shows the relationship between the printing state on a medium, and the presence or absence of generation | occurrence | production of the reflected light and transmitted light when light is irradiated from the one direction of the said medium. It is the table | surface which put together the content shown in FIG. It is a figure showing the list | wrist of a reference signal value. It is a figure showing the list of the measurement signal value of a measurement result (1). It is a figure showing the list of the measurement signal value of a measurement result (2). It is a figure showing the list of the measurement signal value of a measurement result (3). 5 is a flowchart illustrating a method for detecting defective ejection ink. It is a conceptual diagram which shows the conveyance direction of a medium, and the measurement direction of a sensor. It is a schematic diagram about the difference in the signal value of the reflection type sensor when cyan ink is poorly discharged when discharging white ink. It is a schematic diagram about the difference of the signal value of a transmissive | pervious sensor at the time of discharging a white ink, when cyan ink has a discharge defect. It is a figure showing the correlation table A. It is a figure showing the correlation table B. 1 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image recording apparatus according to the present invention. It is a plane perspective view which shows the structural example of a head. It is a partial enlarged view of a plan perspective view showing a structural example of a head. It is a plane perspective view which shows the other structural example of a head. It is sectional drawing which shows the three-dimensional structure of one droplet discharge element. FIG. 17 is an enlarged view showing a nozzle arrangement of the head shown in FIG. 16.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Printing part, 12 ... Control part, 13 ... Transmission type measurement unit, 14 ... Reflection type measurement unit, 16 ... Media, 17 ... Conveyance part, 21 ... Head, 22 ... Light source, 23 ... Transmission type sensor, 24 ... Light source , 26 ... reflection type sensor, 80 ... print control unit

Claims (3)

An image for reading a transmission image of the image and a reflection image of the image by irradiating light from one surface side of the light transmission medium to an image formed by ejecting ink onto the light transmission medium Reading process;
A reference image calculation step of calculating a transmission image of the image when ink is normally ejected and forming the image, a reflection image of the image, a predicted reference transmission image, and a reference reflection image;
A differential transmission image that is a difference image between the transmission image read in the reading step and the reference transmission image calculated in the reference image calculation step, and the reflection image and the reference image calculation step read in the reading step A difference image calculation step of calculating a difference reflection image that is a difference image from the reference reflection image calculated by
A defective ejection nozzle position detection step of detecting a position of a defective ejection nozzle from the differential transmission image and the differential reflection image;
There is a different correlation between the case where an image is formed by depositing colored ink over white ink deposited on a translucent medium and the case where an image is formed by ejecting only colored ink on a translucent medium. Using a table, an ejection failure ink color detection step of detecting a color of ejection failure ink from the differential transmission image and the differential reflection image;
An ink ejection defect detection method comprising: The ink ejection failure detection method according to claim 1,
In the ejection failure ink color detection step, when an image is formed by depositing colored ink on a white ink deposited on a translucent medium, both the differential transmission image and the differential reflection image are abnormal. , The ejection failure ink is detected as white ink, and when the abnormality is detected only in the differential reflection image, the ejection failure ink is detected as colored ink.
An ink ejection defect detection method characterized by the above. Light source means for irradiating light from one surface side of the translucent medium to an image formed by ejecting ink onto the translucent medium;
Transmission image reading means for reading the transmission image of the image from the other surface side of the translucent medium;
Reflected image reading means for reading the reflected image of the image from one surface side of the translucent medium;
A reference image calculation means for calculating a reference transmission image and a reference reflection image that are predicted as the transmission image and the reflection image to be read when ink is normally ejected;
A differential transmission image that is a difference image between the transmission image read by the transmission image reading unit and the reference transmission image calculated by the reference image calculation unit, and the reflection image and the reference image calculation unit read by the reflection image reading unit A difference image calculation means for calculating a difference reflection image that is a difference image from the reference reflection image calculated by:
A defective ejection nozzle position detecting means for detecting a position of a defective ejection nozzle from the differential transmission image and the differential reflection image;
A white ink ejection head for ejecting white ink; and a droplet ejection means including a colored ink ejection head for ejecting colored ink;
When an image is formed by depositing colored ink over white ink deposited on a translucent medium, a different correlation table is used when forming an image by ejecting only colored ink on the translucent medium. An ejection failure ink color detection unit that detects a color of ejection failure ink from the difference transmission image and the difference reflection image calculated by the difference image calculation unit;
An image forming apparatus comprising:

Images