JP2005186381A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer that is simply structured and has a nondischarge detection means capable of detection the nondischarge of an ink for a plurality of print heads. <P>SOLUTION: The detection means 125 is composed of a light-emitting unit 125a, a light-receiving unit 125b and reflection units 125c and 125d. Light emitted from the light-emitting unit 125a advances in a scanning direction in a manner that an optical path is blocked by an ink discharged from the first print head 121 and reaches the reflection units 125c and 125d. At this point, the course is changed and the light takes a route in which the optical path is blocked by the ink discharged from a subsequent print head 121 and enters the light-receiving unit 125b. In the light-receiving unit 125b, since the amount of light received varies with prescribed timing, when the timing is off, the nondischarge of a nozzle 123 corresponding thereto can be known. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet printer that prints by ejecting ink onto a recording medium, and more particularly, to a technique for detecting ejection failure of nozzles.

  2. Description of the Related Art Inkjet printers that record ink by discharging ink from a print head to a recording medium such as paper or a plastic sheet based on input print data are known. In an ink jet printer, printing is performed by ejecting ink from nozzles while relatively moving between a recording medium and a print head. However, defective ejection of nozzles causes image defects.

  Therefore, in Patent Document 1 (Japanese Patent Laid-Open No. 2001-113725), in order to detect the occurrence of such an image defect, a light emitting element and a light receiving element are used so that an ink droplet ejected from a nozzle blocks an optical path. A method for detecting ink droplets and detecting ejection failure has been proposed. Here, the print head ejects ink toward the clogging prevention means at the rest position. A light emitting unit and a light receiving unit are provided at both ends of the print head, and the light emitted from the light emitting unit is shielded by the ink ejected from the nozzles of the print head and reaches the light receiving unit. The print head has a nozzle row composed of a number of nozzles, and each nozzle ejects ink one by one at a predetermined timing. Therefore, the light emitted from the light emitting unit is blocked by the ink ejected at a predetermined timing and reaches the light receiving unit, and the light receiving unit receives the light blocked at the predetermined timing. When there is a portion that does not block light at a predetermined timing, it can be determined that the nozzle corresponding to the portion that does not block light is non-ejection.

  By the way, the inkjet recording method includes a serial method in which printing is performed while the head is moving, and a line head method in which printing is performed by moving a recording medium with respect to a fixed head. In an ink jet printer configured to perform printing while moving the head as in Patent Document 1, one sensor is fixed at the pause position or the like, and ink non-ejection of nozzles is detected while moving a plurality of heads. It is possible.

  However, in the line head type ink jet printer, detecting the ink non-ejection while moving the print head has a problem that the configuration becomes complicated and large.

  In addition, the line head method requires a nozzle density equivalent to the print density to meet the desired print density. However, the low-density nozzle array is used in combination rather than manufacturing a high-density head. Can be manufactured inexpensively. For example, when printing at 600 dpi, an image of 600 dpi can be substantially obtained by arranging 300 dpi nozzle rows in parallel and shifting the phase in the nozzle row direction by a distance equivalent to 600 dpi.

If non-ejection detection is performed for each nozzle row with such a configuration, the non-ejection detection means further increases the number of movements and requires a lot of time for detection.
JP 2001-113725 A

  The present invention was conceived from the above facts, and an object of the present invention is to provide an ink jet printer provided with non-ejection detection means capable of detecting non-ejection of ink for a plurality of print heads with a simple configuration. It is said.

  In order to achieve the above object, a first aspect of the present invention is an ink jet printer that performs printing by ejecting ink from a nozzle array while relatively moving a recording medium and a print head, and includes two or more print heads. And detecting means for detecting whether or not the ink is normally ejected from each nozzle of the nozzle array formed in the scanning direction of each print head, and the detecting means includes a light emitting unit, a light receiving unit, and a reflecting unit. The light beam emitted from the light emitting unit travels in the scanning direction so that the light path is blocked by the ink ejected from the first print head of the two or more print heads, and the path is changed by the reflection unit. Follow the path that blocks the optical path from the ink ejected from the print head and repeat the path change by the next reflection unit. It is characterized in that incident on the light receiving unit out ink follow a path such as to block the optical path.

  The light from the light emitting unit travels while being blocked by ink ejected from each nozzle of the first print head, reaches the reflection unit, is reversed, and travels while being blocked by ink from the nozzles of the next print head. This is repeated and passes through the last print head and enters the light receiving unit. The light receiving unit outputs an output corresponding to the intensity of the incident light, and the incident light periodically changes its output by the ink ejected from each nozzle. Therefore, the periodically changing output can be checked, and the non-ejection nozzle can be identified from the portion lacking the cycle.

  The invention of claim 2 is characterized in that the print head has a plurality of nozzle rows obtained by dividing a predetermined print density.

  According to a third aspect of the present invention, the print head is a line head type in which nozzle rows are arranged over the entire scanning direction of the recording medium. The print head is divided into a plurality of print heads in the scanning direction, and the light from the light emitting unit It is characterized by proceeding so that the ink path is blocked by the ink ejected from a plurality of print heads arranged in the direction of the nozzle row.

  According to a fourth aspect of the present invention, the print head is composed of a plurality of pairs of print heads arranged in parallel, and one detection means detects ink ejection in units of one pair of print heads, and all of them are moved sequentially. The print head is detected.

  According to a fifth aspect of the present invention, the print head is movable from a print position to an upper detection position, and the detection means is opposed to the print head by moving in a direction parallel to the recording medium conveyance direction from the standby position. It is possible to move to a detection position.

  According to the first aspect of the present invention, in a line head type print head, it is possible to detect ink ejection failure with a simple configuration. In addition, a plurality of print heads can be detected by one detection means, and an inexpensive apparatus can be obtained.

  For manufacturing, for example, it is cheaper to combine two 300 dpi print heads than to create a 600 dpi print head. Therefore, such a print head is used. According to the invention of claim 2, even with the print head divided in this way, it is possible to detect non-ejection of ink by one detection means.

  The print head may be divided into a plurality of parts in the main scanning direction for convenience of manufacturing yield. When the print head is integrally formed over the entire width of the paper, if one nozzle is defective, the entire print head becomes a defective product, but if divided into a plurality of parts as in claim 3 Even if one nozzle is defective, the other print head can be used as a non-defective product, and the yield is improved. Also, one detection means can be used.

  According to a fourth aspect of the present invention, the print heads are a plurality of pairs of print heads, and one detection means detects ink ejection in units of one pair of print heads, and detects all print heads while sequentially moving. If it is set as the structure to perform, a detection means can be decreased. In this case, since the detection means is moved without moving the print head, the configuration is simplified.

  According to another aspect of the present invention, the print head moves from the print position to the upper detection position, and the detection means moves from the standby position in a direction parallel to the conveyance direction of the recording medium. Switching to non-ejection inspection can be performed in a short time.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall view showing the configuration of an ink jet printer. In FIG. 1, the inkjet printer 100 includes a cassette 110 in which sheets P as recording media are stacked and accommodated, a printing unit 120, a sheet conveyance unit 130, and a sheet discharge unit 140.

  The paper P in the cassette 110 is sent out one by one by the paper feed roller 111 and fed into the paper transport unit 130. A registration roller 131 is provided at the entrance of the paper conveyance unit 130, and an endless conveyance belt 133 wound around a plurality of conveyance rollers 132 is provided at a position passing through the registration roller 131. The paper P transported on the transport belt 133 is printed by the print head 121, and is discharged onto the paper discharge tray 142 by the paper discharge roller 141 when printing is finished. Four print heads 121 are provided corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black).

  FIG. 2 is an enlarged view of the nozzles of one print head 121. Arrows indicate the paper transport direction. The print head 121 is a line head type, and a large number of nozzles 123 corresponding to the print density such as 300 dpi or 600 dpi are arranged in a line in the scanning direction, and the length W is substantially the width direction of the paper (perpendicular to the transport direction). To match the size).

  The posture of the paper P sent out from the cassette 110 is corrected by the registration roller 131, and the registration roller 131 sends the paper under the print head 121 in accordance with the timing when the print head 121 ejects ink.

  The print head 121 is connected to a control device (not shown), and the control device drives each YMCK print head 121 based on the input print data to eject ink of each color at a necessary timing to form a color image.

  A detection unit 125 is provided below the print head 121 at a distance from the print head. The detection means 125 has a detection means drive mechanism (not shown), and the detection means 125 of each print head 121 can be moved simultaneously in the paper transport direction.

  The sheet is conveyed while being electrostatically attracted to the conveyance belt 133 while passing under the print head 121. The posture holding means of the paper P at the time of recording is not limited to the conveyance belt 133, and a drum winding method, an air suction method, or the like may be used. The paper P printed by the recording unit is discharged to the paper discharge tray 142. Alternatively, in the case of double-sided printing, the paper is sent to a reversing unit (not shown) and conveyed again to the recording unit, or sent to a post-processing machine (not shown) to perform predetermined post-processing such as punching and stapling.

  Next, non-ejection detection will be described. When the print head 121 is not used for a long time or when dust or the like adheres to the nozzle surface, ink may not be ejected from some of the nozzles 123 or may become insufficient. Particularly, in the line head printer as in the present embodiment, the nozzle ejection failure has a great influence on the image, so it is necessary to detect the occurrence at an early stage and recover or correct the image.

  FIG. 3 is a diagram illustrating a state in which ink ejection failure is detected. At the time of detection, all the print heads 121 are retracted upward, and the detection means 125 is moved from the standby position in the paper transport direction by the detection means driving mechanism to move to the detection position below the print head 121.

  FIG. 4 is an enlarged view schematically showing FIG. 3 as viewed from above. The detection unit 125 includes a light emitting unit 125a, a light receiving unit 125b, reflection units 125c and 125d, and a discharge ink collecting unit (not shown).

  The light emitting unit 125a has a lens, and emits parallel laser light through the lens. The emitted light beam passes under the print head 121 from one end to the other end, the path is changed by the reflection units 125c and 125d, and the U-turn enters the light receiving unit 125b. The light beam passes through a path such that ink ejected from the nozzle array of the Y print head 121 in the forward path interrupts the optical path, and is reflected by the reflection units 125c and 125d, and then the nozzle array of the M print head 121 in the return path. The ink ejected from the ink follows a path that blocks the light path.

  In the Y print head 121 in the first row, for example, one nozzle at a time sequentially ejects ink from the nozzle closest to the lower light emitting unit 125a in FIG. 4 to the nozzle closest to the reflection unit 125c. Next, the ink is moved to the M print head 121 in the second row, and ink is sequentially ejected from the nozzle closest to the light receiving unit 125b of this nozzle row to the nozzle closest to the reflection unit 125d.

  Since the ink ejected from each nozzle 123 blocks the light emitted from the light emitting unit 125a, the amount of light incident on the light receiving unit 125b decreases each time the ink crosses the optical path. Based on this change in the amount of light, it is possible to determine whether ink is ejected from each nozzle 123 or not.

  In the embodiment, the discharge order of the nozzles 123 is from bottom to top in FIG. 4, but may be top to bottom, Y may be bottom to top, and M may be top to bottom.

  5A and 5B show examples of the output of the light receiving unit 125b. FIG. 5A shows a case where there is no non-ejection nozzle, and FIG. 5B shows a case where there is a non-ejection nozzle 123. FIG. In (a), the ink discharged from all the nozzles is detected and the output decreases regularly. However, in (b), the output does not decrease as indicated by the arrow, and the corresponding nozzle does not discharge. You will see that there is.

  The color of ink ejected from each print head 121 is different from Y (yellow), M (magenta), C (cyan), and K (black). However, the intensity of the light transmitted through the ink is affected by the refractive index, not the color of the ink. In normal cases, the inks of the respective colors of YMCK have almost the same refractive index, so the intensity of the light received by the light receiving unit 125b Is considered to be almost unrelated to the color of the ink.

  However, there may be a case where the refractive index and transmittance are different for each color. In that case, it is possible to cope with this by setting in advance that the output of the light receiving unit 125b differs depending on the print head 121.

  In the embodiment, the reflecting units 125c and 125d use a roof-type mirror in which two reflecting mirrors are combined at a right angle, but a right-angle reflecting prism may be used instead. If there is any part between the light emitting unit 125a and the light receiving unit 125b or the adjacent print head 121, and this can block the light path and light cannot pass, this part can be bypassed using another reflecting mirror or the like. Is possible.

  The ink is ejected from the front end surface of the nozzle 123, and initially maintains a predetermined speed. However, when the distance from the nozzle increases, the speed decreases due to air resistance, and the straightness decreases. The detection is preferably performed in the vicinity of the nozzle tip surface, and it is desirable to detect within a range of about 5 mm.

  Here, one detection means 125 includes a light emitting unit 125a, a light receiving unit 125b, and reflection units 125c and 125d. In the above embodiment, there are four print heads 121 of YMCK, the first detection means 125 is used as a pair of print heads for Y and M, and the second print head is used as a pair of print heads for C and K. The detection means 125 is used. On the other hand, the number of detection means 125 is one, and first, the ejection of ink is detected for the two print heads 121 of YM, and then the detection means 125 is moved to the print head 121 of CK, The print head 121 may detect ink ejection.

  Alternatively, the four print heads 121 of YMCK may be detected by one detection device. In this case, in FIG. 4, a light emitting unit 125a is provided on the lower side of the first Y print head 121, and a light receiving unit 125b is provided on the lower side of the last K print head 121. the same). Reflecting units 125c and 125d are provided below the middle M and C print heads 121 in FIG. Thus, the light from the light emitting unit 125a passes through the four print heads 121 in the order of YMCK and reaches the light receiving unit 125b, and can be detected by one detection means 125.

  FIG. 6 is an overall view showing the configuration of the ink jet printer according to the second embodiment of the present invention. The inkjet printer 200 shown in FIG. 6 includes a cassette 210, a printing unit 220, a paper transport unit 230, and a paper discharge unit 240.

  There is a registration roller 231 at the entrance of the paper conveyance unit 230, and an endless belt 233 wound around a plurality of conveyance rollers 232 is passed through the registration roller 231. The paper P in the cassette 210 is sent out by the paper feed roller 211, printed, and then discharged onto the paper discharge tray 242 by the paper discharge roller 241.

  Four print heads 221 are provided corresponding to each color of (yellow), M (magenta), C (cyan), and K (black), and one group of print heads 221 includes a plurality of print heads. ing.

  FIG. 7 is an enlarged view of one print head 221. An arrow indicates the conveyance direction of the paper P. The print head 221 includes three sets of print heads 221a, 221b, and 221c. Further, the print head 221a is divided into two print heads 221a1 and 221a2, the print head 221b is divided into two print heads 221b1 and 221b2, and the print head 221c is divided into two print heads 221c1 and 221c2. ing.

  FIG. 8 is an enlarged view of the print head 221a of FIG. As shown in the figure, the print head 221a has a large number of nozzles 223 arranged in two rows, and its length w (FIG. 7) is approximately 1/3 of the paper width direction. Each of the two nozzles 221a1 and 221a2 has a 300 dpi nozzle row, which is arranged in parallel with a ½ pitch shift, so that an image of 600 dpi can be printed with two nozzles. The print heads 221b and 221c have the same configuration.

  In terms of manufacturing, it is cheaper to combine two 300 dpi print heads than to create a 600 dpi print head, so the configuration shown in FIG. 8 is often used. At this time, the nozzle array may be shifted by a distance smaller than the print density for the purpose of reducing the maximum instantaneous voltage and not being affected by the discharge of adjacent nozzles. Is considered to be a negligible distance, so that column can be regarded as one column.

  Further, the print head may be divided into a plurality of modules in the main scanning direction like the print heads 221a, 221b, and 221c in FIG. 7 for the convenience of manufacturing yield. When the print head is integrally formed over the entire width of the sheet, if one nozzle is defective, the entire print head becomes a defective product. However, if the line is divided into a plurality of modules as shown in FIG. 7, even if there is a nozzle failure, the remaining modules can be used as non-defective products, so that the manufacturing yield is improved.

  The print head 221 is connected to a control device (not shown), and the control device drives each YMCK print head 221 based on the input print data to eject ink of each color at a necessary timing to form a color image.

  In the lower part of the print head 221, as in the first embodiment, a detection means 125 is provided slightly apart from the print head. Although the detection means 125 shown in FIG. 1 has a detection means drive mechanism (not shown), the detection means 125 of each print head 221 can be moved simultaneously in the paper transport direction.

  FIG. 9 is a diagram showing the arrangement state of the detection means 125 in the print head of FIG. FIG. 9 corresponds to FIG. 4 of the first embodiment. Here, the detection means 125 is provided in each of the print heads 221a, 221b, and 221c constituting one module. Each detection means includes a light emitting unit 125a, a light receiving unit 125b, and reflection units 125c and 125d.

  FIG. 10 is a diagram illustrating a state where non-ejection is detected. When detecting, as in the case of the first embodiment, all the print heads 221 are raised, and the detection means 125 is moved so that the light of the light emitting unit 125a passes directly under the print heads 221. The non-ejection detection method is the same as that described in the first embodiment.

  FIG. 11 shows an embodiment in which the number of detection means 125 is reduced. In the embodiment of FIG. 9, since there are three detection means 125 for each color of YMCK, twelve detection means 125 are used as a whole. On the other hand, in the embodiment of FIG. 11, one detection means 125 is provided for each YMCK print head 221.

  That is, the light emitting unit 125a is arranged at one end of the print head 221a1, and the light receiving unit 125b is provided at one end of the print head 221b2. Then, reflection units 125c and 125d are arranged between the print heads and the print head. The light emitted from the light emitting unit 125a is shielded by the ink ejected from the nozzle row of the print head 221a1, and then shielded by the ink ejected from the nozzle row of the print head 221c1, and reaches the reflection unit 125c. The light reflected by the reflection unit 125c and the reflection unit 125d is shielded by the ink ejected from the nozzle array of the print head 221c2, and then is shielded by the ink ejected by the nozzle array of the print head 221a2 and reaches the reflection unit 125c. . Here, the light reflected by the reflection unit 125c and the reflection unit 125d is shielded by the ink ejected from the nozzle row of the print head 221b1, and reaches the reflection unit 125c. Here, the light reflected by the reflection unit 125c and the reflection unit 125d is shielded by the ink ejected from the nozzle row of the print head 221b2, and reaches the light receiving unit 125b. By detecting the output of the light receiving unit 125b while sequentially discharging ink from the six print heads 221a1 to 221b2, it is possible to detect which nozzle of which print head is not ejecting.

  Although the detection unit 125 is described with reference to FIG. 4, a plurality of print heads 221 can be detected by a single detection unit 125 in the embodiment of FIG. 9. However, since the ejection ink collecting means for collecting the non-ejection detection ink is shared with the suction cap as the recovery means when the non-ejection is detected, it may be provided corresponding to each head module. Necessary. This is because if the suction cap is shared, color mixing with other color inks may occur.

1 is an overall view illustrating a configuration of an inkjet printer. FIG. 2 is an enlarged view of nozzles of one print head. It is a figure which shows the state which detects ink non-ejection. FIG. 4 is an enlarged view schematically showing FIG. 3 as viewed from above. In the example showing the output of the light receiving unit, (a) shows a case where there is no non-ejection nozzle, and (b) shows a case where there is a non-ejection nozzle. It is a general view which shows the structure of the inkjet printer in 2nd Example of this invention. FIG. 7 is an enlarged view of one print head in FIG. 6. FIG. 8 is an enlarged view of the print head of FIG. 7. It is a figure which shows the arrangement | positioning state of a detection means in the print head of FIG. It is a figure which shows the state which detects non-ejection. This is an embodiment in which the number of detection means is reduced.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Inkjet printer 121 Print head 123 Nozzle 125 Detection means 125a Light emission unit 125b Light reception unit 125c, 125d Reflection unit 200 Inkjet printer 221 Print head

Claims (5)

An inkjet printer that prints by ejecting ink from a nozzle array while relatively moving a recording medium and a print head, and includes two or more print heads and nozzles of the nozzle array formed in the scanning direction of each print head Detecting means for detecting whether or not the ink has been ejected normally. The detecting means comprises a light emitting unit, a light receiving unit, and a reflecting unit, and the light emitted from the light emitting units is emitted from the two or more print heads. The ink travels in the scanning direction so that the optical path is blocked by the ink ejected from the first print head, the path is changed by the reflection unit, and the path is blocked by the ink ejected from the next print head. Repeatedly changing the path with the next reflection unit, following a path that blocks the light path from the ink ejected from the last print head. The ink jet printer, characterized in that entering the serial receiving unit. 2. The ink jet printer according to claim 1, wherein the print head has a plurality of nozzle rows obtained by dividing a predetermined print density. The print head is a line head type in which nozzle rows are arranged over the entire scanning direction of the recording medium, and is divided into a plurality of print heads in the scanning direction, and the light from the light emitting unit is arranged in the direction of the nozzle rows. 2. The ink jet printer according to claim 1, wherein the ink path is blocked by the ink ejected from the plurality of print heads. The print head is composed of a plurality of pairs of print heads arranged in parallel, and one detection means detects ink ejection in units of a pair of print heads, and detects all print heads while sequentially moving. The ink jet printer according to claim 1. The print head can move from the print position to an upper detection position, and the detection means can move from the standby position to a detection position facing the print head by moving in a direction parallel to the recording medium conveyance direction. The ink jet printer according to claim 1.

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