JP5343469B2 - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents decrease of an image quality in the case of monochrome (black or gray) printing in the image forming apparatus with a line type recording head capable of performing color printing. <P>SOLUTION: In the image forming apparatus with the line type recording head equipped with two head unit arrays, the head unit includes a black nozzle array in which black nozzles each for delivering a black ink are arranged at equal intervals (the interval is made one pitch) in a main scanning direction, and color nozzle arrays arranged while shifted by half of the pitch to the black nozzle array. Nozzles (called overlapping nozzles) arranged in adjacent head units disposed in different head unit arrays are placed overlapping each other on a sub-scanning line. The ink delivered from the overlapping nozzles arranged overlapping forms an image (the same pixel) to almost the same region on a recording medium. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method.

  Image formation in an ink jet recording apparatus scans (main scans) the head in a direction perpendicular to the recording paper conveyance direction while discharging droplets from the ink discharge ports (nozzles) of the head onto the recording paper, and images are formed on the recording paper. When recording for one line, a predetermined amount of recording paper is conveyed in the sub-scanning direction, and an image is recorded for one line on the recording paper again as described above, and this is repeated to form an image.

As another configuration, there is a line head system in which the discharge ports of the head are arranged at an equal interval pitch at the length of almost the maximum recording width of the recording paper and a fixed line head is used.
According to this configuration, scanning of the head (main scanning) is unnecessary, and image formation can be performed only by transporting the recording paper in the direction orthogonal to the scanning direction (sub scanning). High speed recording can be performed as much as necessary.

  However, in the line head method, when the recording head is long, it is difficult to manufacture with high accuracy due to variations in processing of the discharge ports. Therefore, in such a case, a method of arranging a plurality of small unit heads that can be manufactured with relatively high accuracy in the width direction is used, and a method of connecting a plurality of heads in a straight line, or a head connecting portion overlaps each other. There is a method to make it.

  In a printer using a line head having a structure having such a connecting portion, the positioning accuracy of the seam between the head members is important in order to record a high-quality image without streaky density unevenness or whiteout. It is.

On the other hand, monochrome (black or gray) printing is frequently used in actual printing applications. It is an important issue to enable high-speed printing that does not cause deterioration in image quality of monochrome printing while suppressing an increase in cost. On the other hand, in the image forming method disclosed in Patent Document 1, during monochrome (black or gray) printing, a pseudo black printing raster using color ink is provided between adjacent rasters in printing with black ink. By substantially doubling the raster and halving the raster interval, both image quality improvement and high-speed printing are achieved.
JP 2007-030198 A

  If a line type recording head is configured by connecting a plurality of recording heads having a relatively short recording width, a line type recording head compatible with high-speed printing can be obtained without increasing the manufacturing cost of the recording head. However, when the configuration is such that a plurality of recording heads are connected, there is a problem in that the recording heads are likely to be misassembled and the print quality is deteriorated. Further, if the assembly accuracy of a plurality of adjacent recording heads is to be extremely increased, it is not practical due to an increase in manufacturing cost.

  Above all, in order to speed up monochrome (black or gray) printing, which has a high printing frequency, and to improve image quality, the data for printing black or gray includes black data for black dots and pseudo black for pseudo black dots. Even if printing is divided into data, in a line type recording head in which a plurality of recording heads are assembled, white streaks occur due to misalignment or the like, especially when the recording heads are separated from each other, and the print quality is greatly reduced. There was a problem.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus and an image forming method for preventing deterioration in image quality when monochrome (black or gray) printing is performed in an image forming apparatus having a line-type recording head capable of color printing. Is to provide.

The present invention is an image forming apparatus capable of forming a color image and a monochrome image by ejecting ink onto the recording medium from a line-type recording head disposed facing the recording medium conveyed in the sub-scanning direction. The line-type recording head includes a plurality of head units arranged along the main scanning direction, and among the plurality of head units, head units adjacent to the main scanning direction partially overlap in the sub-scanning direction. In the case where a monochrome image is formed, the ink ejected from the color nozzle at the end of one head unit and the ink ejected from the color nozzle at the end of the other head unit are formed in the overlap region. The ink is an image forming apparatus in which pseudo black dots are formed overlappingly on the recording medium.
A reference invention is an image forming apparatus that forms an image by ejecting ink onto a recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction. The type recording head has a duplication region in which a plurality of head units are arranged in two rows along the main scanning direction, and two head units adjacent in the sub scanning direction partially overlap in the main scanning direction The head unit includes a black nozzle row in which black nozzles that discharge black ink are arranged at an equal pitch in the main scanning direction, and a color nozzle that discharges color ink in the main scanning direction at the same pitch. A plurality of color nozzle rows, and black nozzles arranged in the black nozzle row and the same head as the black nozzle row. The color nozzles arranged in at least two of the color nozzle rows arranged in the unit are arranged shifted by a half pitch in the main scanning direction, and are arranged in different head units in the overlapping region. The color nozzles arranged to overlap in the scanning direction are image forming apparatuses that discharge different color inks for each head unit.

Preferably, the present invention is characterized in that the nozzle arrangement of the black nozzle array and the nozzle arrangement of the color nozzle array in which the color nozzles forming the pseudo black dots are shifted by a half pitch in the main scanning direction. The image forming apparatus.
The reference invention is characterized in that at least one set of the color nozzles arranged to overlap in the main scanning direction has an ink ejection amount different from other color nozzles in the same color nozzle row. Forming device.

In a preferred aspect of the present invention, the color nozzle at the end of the head unit has a larger amount of ink ejection than other color nozzles in the same color nozzle row.
The reference invention is the image forming apparatus, wherein the color nozzles arranged overlapping in the sub-scanning direction have a larger ink ejection amount than other color nozzles in the same color nozzle row.

In a preferred embodiment of the present invention, when the image end is formed by ink ejection from the color nozzle at the end of the head unit, the end of the head unit on the side provided with the color nozzles other than the image end is provided. In the image forming apparatus, the ink is ejected from the arranged color nozzles, and the ink is not ejected from the color nozzles arranged at the end of the other head unit.
The image is characterized in that, when the image end portion is formed by ink ejection from the color nozzles arranged overlapping with respect to the sub-scanning direction, the ink is ejected from different color nozzles of the same head unit. Forming device.

In a preferred aspect of the present invention, the combination of color inks forming the pseudo black dots is variable.
A reference invention is an image forming apparatus that forms an image by ejecting ink onto a recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction. The type recording head has a head unit row in which a plurality of head units are arranged in two rows along the main scanning direction, and two head units adjacent in the sub scanning direction partially overlap in the main scanning direction. The plurality of head units each include a black nozzle row in which black nozzles that discharge black ink are arranged at an equal pitch in the main scanning direction, and a color nozzle that discharges color ink at the same pitch in the main scanning direction. A plurality of arranged color nozzle rows, the color nozzles arranged in a predetermined color nozzle row, and the same as the predetermined color nozzle row The black nozzles arranged in the black nozzle row arranged in the head unit and the color nozzles arranged in at least one color nozzle row excluding the predetermined color nozzle row are shifted by a half pitch in the main scanning direction. Color nozzles arranged in at least one color nozzle row excluding black nozzles and the predetermined color nozzle row, arranged in adjacent head units arranged in different head unit rows. Among the combinations of black nozzles and / or color nozzles selected from the above, at least one set of black nozzles and / or color nozzles are arranged overlapping in the main scanning direction, and the color nozzles arranged overlapping in the main scanning direction Is an image forming apparatus that discharges ink of different colors

The reference invention is characterized in that, among the black nozzles and the color nozzles arranged overlapping in the main scanning direction, the ink discharge amount of the color nozzles is smaller than the ink discharge amount of the black nozzles. It is.

When the reference invention is formed by ejecting ink from the black nozzles and / or the color nozzles whose image end portions are overlapped in the main scanning direction, the color nozzles of different colors in the same head unit row Alternatively, the image forming apparatus is characterized in that ink is ejected from the black nozzle.

In the reference invention, the combination of the color nozzle and / or the black nozzle is variable in at least one combination among the combinations of the black nozzle and / or the color nozzle arranged overlapping in the main scanning direction. The image forming apparatus is characterized.

According to the present invention, a monochrome image is formed by a device capable of forming a color image and a monochrome image by ejecting ink onto the recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction. In the image forming method to be formed, the line-type recording head includes a plurality of head units arranged along a main scanning direction, and among the plurality of head units, a head unit adjacent to the main scanning direction includes: There is an overlap area that partially overlaps in the sub-scanning direction, and in the overlap area, the discharge ink from the color nozzle at the end of one head unit and the discharge from the color nozzle at the end of the other head unit An image forming method, wherein pseudo black dots are formed by overlapping ink on the recording medium.
The reference invention is an image forming method for forming an image by ejecting ink onto a recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction. The type recording head includes two head unit rows each having a plurality of head units arranged along the main scanning direction, and the line type recording head has a plurality of head units arranged in two rows along the main scanning direction. And a head unit row having an overlapping region in which two head units adjacent in the sub-scanning direction partially overlap in the main scanning direction, and each of the plurality of head units has a black nozzle for discharging black ink. Black nozzle rows arranged at equal pitches in the scanning direction and color nozzles that discharge color ink are arranged at the same pitch in the main scanning direction. A plurality of color nozzle rows, the black nozzles arranged in the black nozzle row, and the color nozzles arranged in at least two color nozzle rows arranged in the same head unit as the black nozzle row; Are arranged with a half-pitch shift in the main scanning direction, and at least one set of the color nozzles arranged in adjacent head units arranged in different head unit rows overlaps in the main scanning direction. In the image forming method, at least one set of the color nozzles arranged in an overlapping manner in the main scanning direction ejects different color inks.

The reference invention is an image forming method for forming an image by ejecting ink onto a recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction. The type recording head has a head unit row in which a plurality of head units are arranged in two rows along the main scanning direction, and two head units adjacent in the sub scanning direction partially overlap in the main scanning direction. The plurality of head units each include a black nozzle row in which black nozzles that discharge black ink are arranged at an equal pitch in the main scanning direction, and a color nozzle that discharges color ink at the same pitch in the main scanning direction. A plurality of arranged color nozzle rows, the color nozzles arranged in a predetermined color nozzle row, and the same as the predetermined color nozzle row The black nozzles arranged in the black nozzle row and the color nozzles arranged in at least one color nozzle row excluding the predetermined color nozzle row arranged in the head unit are half pitch in the main scanning direction. Are arranged in a shifted manner and arranged in adjacent head units arranged in different head unit rows and arranged in at least one color nozzle row excluding black nozzles and the predetermined color nozzle row. Among the combinations of black nozzles and / or color nozzles selected from the color nozzles, at least one set is arranged overlapping in the main scanning direction, and the color nozzles arranged overlapping in the main scanning direction are different from each other. An image forming method is characterized by discharging ink.

  According to the present invention, when monochrome (black or gray) printing is performed in an image forming apparatus having a line-type recording head capable of color printing, it is possible to provide an image forming apparatus and an image forming method that prevent deterioration in image quality. .

  The present invention relates to an image forming apparatus that forms an image by ejecting ink onto a recording medium from a line-type recording head arranged to face the recording medium conveyed in the sub-scanning direction. The recording head includes two head unit rows in which a plurality of head units are arranged along the main scanning direction (direction parallel to the width direction of the recording medium). These two head unit rows form a set of line type recording heads, and form an image (dot pattern line) for one line in the main scanning direction on the recording medium. Note that the actual recording head may be a line-type recording head that includes a plurality of line-type recording head units composed of the above-described two head unit rows and simultaneously forms a plurality of dot pattern lines.

  Each head unit has a black nozzle row in which black nozzles for ejecting black ink are arranged at equal intervals along the main scanning direction (this interval is 1 pitch) so as to be compatible with color printing. A color nozzle array in which color nozzles that discharge color inks of the same color are arranged at intervals of one pitch along the main scanning direction for each color of the color ink; and at least black nozzles arranged in the black nozzle array; The color nozzles arranged in the two color nozzle rows are shifted by a half pitch in the main scanning direction. The color nozzle that is shifted from the black nozzle by half a pitch is called a complementary color nozzle, and the color nozzle row in which the complementary color nozzles are arranged is called a complementary color nozzle row. For example, there are three types of color ink, cyan, magenta, and yellow. The cyan color nozzle row and the magenta color nozzle row are shifted from the black nozzle row by half a pitch in the main scanning direction, and the yellow color nozzle row is black. There is an array that is not displaced from the nozzle row.

  Further, at least one nozzle on adjacent head units arranged in different head unit rows, for example, black nozzles, at least one color nozzle, or a combination of black nozzles and color nozzles, etc. They are arranged so as to overlap each other on the same sub-scanning line (sub-scanning direction). These overlapping nozzles are called overlapping nozzles. The ink ejected from a set of overlapping nozzles that overlap on the same sub-scanning line forms an image of one pixel (one dot) by attaching ink dots on substantially the same area (dot pattern line) on the recording medium. Designed to be. Here, the substantially identical region refers to a region between an end black nozzle of a predetermined head unit and an end black nozzle of a head unit arranged adjacently, and is also referred to as an overlap region. In this image forming apparatus, an image of one pixel input to the image forming apparatus is formed because the ink that is arranged in different head units and the ink ejected from a set of overlapping nozzles corresponds to one pixel is formed. Information can be transmitted to two head units as a dot pattern signal, and the two head units can be controlled simultaneously.

  The ink ejected from the complementary color nozzle preferably forms a pseudo black ink that complements the black ink, and the ink ejected from at least one set of the complementary color nozzles may be a pseudo black ink. The present invention has an object of preventing image quality degradation during monochrome printing. For this reason, the ink ejected from the overlapping nozzles forms a pseudo black ink that complements the black ink, thereby improving the image quality of monochrome printing. The pseudo black ink is preferably dark in terms of brightness.

  It is preferable that the complementary color nozzle and the black nozzle have different ink discharge amounts. Normally, the black nozzle preferably has a larger ink discharge amount than the complementary color nozzle. The ink ejected from the complementary color nozzle complements the precise image formation of the black ink and improves the image quality. However, since the color and brightness are different from the black ink, monochrome (black or gray) printing is performed. Is preferably less than black ink.

  The overlapping nozzles preferably have different ink discharge amounts from other nozzles in the same nozzle row, and preferably have a larger ink discharge amount than the other nozzles. As will be described in detail later, the image forming area by the overlapping nozzles corresponds to the image forming area from the nozzles at the connection portion of the two head units, and therefore the dot pattern line width may be wider than the other image forming areas. There are areas where white lines are likely to occur. For this reason, it is preferable to increase the amount of ink ejected in this region to form large dots and suppress the occurrence of white streaks. In monochrome (black or gray) printing, since white streaks are particularly noticeable, it is more preferable that the ink dots from the overlapping nozzles are larger than the ink dots from the other nozzles.

  When the ink dots from the overlapping nozzles form an image end on the recording medium, it is preferable to stop ink ejection from the overlapping nozzles arranged on the side where the image disappears among the overlapping nozzles. In monochrome (black or gray) printing, the color of an image edge tends to be noticeable. As described above, the image forming area formed by the overlapping nozzles may have a wider dot line width than the other areas. Therefore, when the ink dots from the overlapping nozzles form the image end portion, the image forming area is more conspicuous. Become. For this reason, among the overlapping nozzles, the ink discharge from the overlapping nozzles arranged in the head unit on which the image disappears is stopped so that the dot line width does not widen, and the image quality at the edge of the image is reduced. prevent. It should be noted that if the ink is ejected only from the nozzles belonging to one head unit, the white streak problem does not occur at the edge of the image. Further, it is preferable to stop the ink ejection from the overlapping nozzle on the image disappearing side and form the end with the overlapping nozzle on the image existing side (cyan and magenta of the head unit 51b).

  A black nozzle can also be selected as the overlapping nozzle. When a black nozzle is selected as one of the overlapping nozzles, it is preferable that the ink discharge amount of the black nozzle as the overlapping nozzle is larger than the ink discharge amount of the corresponding other overlapping nozzle. This is because in monochrome (black or gray) printing, an image with as much black ink as possible is preferable in terms of brightness and color.

  The combination of overlapping nozzles is variable and is preferably changeable depending on the image forming time, the transport distance in the sub-scanning direction of the recording medium in image formation, or the number of image forming dots. Usually, a color image forming apparatus uses four colors of ink of black, cyan, magenta, and yellow. Also in the present invention, the four colors of ink can be assigned to each nozzle. In this case, when the combination of overlapping nozzles is two colors, combinations of cyan and magenta, black and yellow, magenta and yellow, black and cyan, cyan and yellow, and black and magenta are possible. For example, three color nozzles of cyan, magenta, and yellow can be used as overlapping nozzles on the same sub-scan line. By changing the combination of overlapping nozzles at a short timing or making it a preferable combination according to the situation, the image quality of the area where the head unit is switched can be improved. In addition, the amount of ink used can be adjusted.

  Also, if the overlapping part of adjacent head units in two head unit rows is increased so that a plurality of overlapping nozzles are formed in the same nozzle row, even if the combination of overlapping nozzles in the same nozzle row remains, The combination of overlapping nozzles can be changed.

  An image forming method of the present invention is a method for forming an image by ejecting ink onto a recording medium from a line type recording head arranged facing the recording medium conveyed in the sub-scanning direction. The recording head includes a plurality of head units arranged in two rows along the main scanning direction (direction parallel to the width direction of the recording medium). The plurality of head units each include a black nozzle row in which black nozzles that discharge black ink are arranged at equal intervals in the main scanning direction (the interval is 1 pitch) and a color nozzle that discharges color ink of the same color. A plurality of color nozzle rows arranged at intervals of 1 pitch in the main scanning direction are provided. The black nozzles arranged in the black nozzle row and the color nozzles (called complementary color nozzles) arranged in at least one color nozzle row (referred to as complementary color nozzle rows) are each half pitch in the main scanning direction. They are misaligned.

  Furthermore, in the image forming method of the present invention, at least two nozzles (referred to as overlapping nozzles) arranged in adjacent head units arranged in different head unit rows are, for example, black nozzles or color nozzles. The ink ejected from the overlapping nozzles can be formed on substantially the same position on the recording medium.

[Specific Embodiment]
Specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of the entire mechanism portion of an ink jet image recording apparatus which is an aspect of the image forming apparatus of the present invention. As shown in FIG. 1, this image forming apparatus is a line type image forming apparatus, and a paper feed tray 2 that stacks and feeds paper P on a main body 1, and discharges and stacks printed paper P. A paper discharge tray 3, a transport unit 4 that transports the paper P from the paper feed tray 2 to the paper discharge tray 3, a head array unit 5 that discharges and prints droplets on the paper P transported by the transport unit 4, A cleaning device 6 is provided as a maintenance / recovery mechanism that performs maintenance / recovery of each head of the head array unit 5 after the end of printing or at a required timing.

  The apparatus main body 1 includes front and rear side plates and stays (not shown), and the sheets P stacked on the sheet feed tray 2 are fed one by one to the transport unit 4 by the separation roller 21 and the sheet feed roller 22. The

  The transport unit 4 includes a transport drive roller 41a, a transport driven roller 41b, and an endless transport belt 43 wound around these rollers 41a and 41b. A plurality of holes (not shown) are formed on the surface of the transport belt 43, and a suction fan 44 that sucks the paper P is disposed below the transport belt 43. Further, conveyance guide rollers 42a and 42b are respectively held on guides (not shown) on the conveyance driving roller 41a and conveyance driven roller 41b and are in contact with the belt 43 by their own weight.

  The conveyance driving roller 41 a is rotated by a motor (not shown), so that the conveyance belt 43 rotates. The paper P is sucked onto the conveyance belt 43 by the suction fan 44 and is conveyed by the circular movement of the conveyance belt 43. The transport driven roller 41 b and the transport guide rollers 42 a and 42 b rotate following the transport belt 43.

  A head array unit 5 composed of a head array unit that discharges droplets to be printed on the paper P is disposed above the transport unit 4 so as to be movable in the arrow A direction. The head array unit 5 slides up to above the cleaning device 6 during the maintenance and recovery operation (during cleaning).

  FIG. 2 is a plan view of the mechanism portion of the image forming apparatus shown in FIG. 1. As shown in FIG. 2, the head array unit 5 has two head unit rows, and five head array rows per row. The head unit 51 is provided. The five head units 51 of each head unit row are fixedly arranged on an array member (holding member) 55 over almost the entire width of the paper in the main scanning direction. The head unit row on the upstream side in the paper transport direction is a first row (also referred to as a row), and includes head units 51a1, 51a2, 51a3, 51a4, and 51a5, and a second row (also referred to as b row) head unit row. Includes head units 51b1, 51b2, 51b3, 51b4, and 51b5. The head units 51a and 51b in the first row and the second row are alternately arranged in a staggered manner. The head units 51 are collectively referred to as the head units 51. When the head units in each row are collectively referred to, for example, the head units 51 in the a row are represented as “head unit 51a”.

  Each head unit 51 has four nozzle rows in which a plurality of nozzles are arranged, and each nozzle row has a discharge nozzle for ejecting the same color ink, a nozzle row, a yellow (Y) nozzle row, A magenta (M) nozzle row, a cyan (C) nozzle row, and a black (K) nozzle row are arranged. The nozzles in each nozzle row are arranged at equal intervals in the main scanning direction (paper width direction) (this interval is 1 pitch), and the nozzles in the adjacent nozzle rows are 1 / in the main scanning direction. It is shifted by 2 pitches. A color image for one pixel can be formed with a set of nozzles arranged in four rows. On the other hand, at the time of monochrome (black or gray) image formation, the black nozzle and the nozzle shifted by 1/2 pitch can form an image for one pixel. For this reason, at the time of monochrome (black or gray) image formation, the pixel density of the print image in the main scanning direction can be double that of the print image at the time of color image formation.

  In the head array unit 5, distributors 52 a to 52 d that are distributors for supplying ink of a desired color to each head unit 51 are arranged above each head unit 51, and a supply tube is provided between the distributor 52 and the head unit 51. 53 is connected. Further, a sub tank 54 is disposed in the distributor 52, and ink is supplied to the head of the head unit 51 due to a water head difference. Further, an ink main tank (not shown) is disposed on the upstream side of the sub tank 54, and ink is supplied to each through a supply tube.

  On the downstream side of the transport unit 4, a transport guide portion 7 that discharges the paper P to the paper discharge tray 3 is provided. The paper P guided and conveyed by the conveyance guide unit 7 is discharged to the paper discharge tray 3. The paper discharge tray 3 includes a pair of side fences 31 that regulate the width direction of the paper P and an end fence 32 that regulates the front end of the paper P.

  The maintenance / recovery mechanism (cleaning device) 6 corresponds to the head units 51 in the first to second rows of the head array unit 5, and includes five cleaning units 61a1 to 61a5 in the first row to the second row, respectively. 61b1 to 61b5 are arranged in a staggered pattern. The notation of each part of the cleaning device 6 is the same as that of the head array unit 5.

  Under each cleaning means 61, suction pumps 62 (62a, 62b) for sucking ink from the head of the head unit 51 are arranged.

  Further, in this image forming apparatus, after the printing is finished, when the ink of the head unit 51 that discharges droplets is capped by the cleaning unit 61 and ink is sucked from the nozzles, or the nozzle surface of the head of the head unit 51 When the ink adhering to the ink is cleaned by the cleaning means 61, after the printing is stopped, the entire transport unit 4 rotates in the direction of arrow B in FIG. 1 with the transport driven roller 41 b as a fulcrum, and the space between the head array unit 5 Is made larger than that at the time of image formation, so that the movement space of the head array unit 5 is secured. At this time, the conveyance guide portion 7 disposed on the upper portion of the cleaning device 6 is also rotated upward in the direction of the arrow C at the fulcrum 71, and the upper portion of the cleaning device 6 is opened.

  Then, after the transport unit 4 and the transport guide portion 7 are released (released), the head array unit 5 moves in the paper transport direction (arrow A direction), stops above the cleaning device 6, and the cleaning means 61 The head moves up and shifts to the head cleaning operation (maintenance recovery operation) of each head unit 51.

  FIG. 3 is a block diagram showing the configuration of the control unit of the image forming apparatus of the present invention. The control unit 100 includes a CPU 101 that controls the entire apparatus, a ROM 102 that stores programs executed by the CPU 101 and other fixed data, a RAM 103 that temporarily stores image data, and the like, while the apparatus is powered off. 1 also includes a non-volatile memory (hereinafter abbreviated as NVRAM) 104 for holding data, and an ASIC 105 for processing input / output signals for controlling the entire apparatus. As for the ASIC 105, an image forming apparatus classified as a “high-speed machine” to be described later may be provided with a function for taking part in image processing.

  The control unit 100 includes a host I / F 106 for transmitting and receiving data and signals to and from the host side, a head drive control unit 107 and a head driver 108 for driving and controlling each head unit 51, and movement of the head array unit. A head array moving motor driving unit 110 for driving the motor 109, a conveying belt moving motor driving unit 112 for driving the conveying belt moving motor 111, and a suction fan motor driving for driving the suction fan motor 116 for the suction fan 44. Part 117, environmental sensor 113 for detecting environmental temperature and / or environmental humidity, and I / O 114 for inputting detection signals from various sensors (not shown).

  An operation panel 115 for inputting and displaying information necessary for the apparatus is connected to the control unit 100.

  Here, the control unit 100 is an information processing apparatus such as a personal computer (hereinafter referred to as a PC), an image reading apparatus such as an image scanner, print data including image data from a host such as an imaging apparatus such as a digital camera, or the like. Is received by the host I / F 106 via a cable or a network.

  Then, the CPU 101 reads out and analyzes the print data in the reception buffer included in the host I / F 106 and performs data rearrangement processing or the like (in some cases, part of image processing described later in some cases) by the ASIC 105. The image data is transferred to the drive control unit 107. Note that conversion of print data for image output into bitmap data (print raster data) may be performed by storing font data in the ROM 102, for example, or image data may be converted into bitmap data by a printer driver on the host side. In this case, the print raster data may be transferred to this apparatus after the bitmap data (print raster data) of the print data is created.

  Upon receiving the print raster data data, the head drive control unit 107 sends the dot pattern data (print raster data data) to the head driver 108 as serial data in synchronization with the clock signal, and latches at a predetermined timing. A signal is sent to the head driver 108.

  The head drive control unit 107 includes a ROM (can be configured by the ROM 102) storing pattern data of a drive waveform (drive signal) and D / A-converted D of drive waveform data read from the ROM. A waveform generation circuit including an A converter and a drive waveform generation circuit including an amplifier and the like are included.

  The head driver 108 also receives a clock signal from the head drive control unit 107 and serial data as image data, and a latch circuit that latches the register value of the shift register using a latch signal from the head drive control unit 107. A level conversion circuit (level shifter) that changes the output value of the latch circuit, an analog switch array (switch means) that is controlled to be turned on / off by the level shifter, and the like, and controls on / off of the analog switch array. Thus, a required drive waveform included in the drive waveform is selectively applied to the actuator means of the head unit 51 to drive the head, print image data, and form a dot pattern line.

An example of processing performed on the host PC side will be described with reference to FIG. FIG. 4 shows a “general machine” (general-purpose image processing apparatus) that processes all image processing on the PC side and a “high-speed machine” that shares a part of the processing with an ASIC built in the recording apparatus. Yes. In the "high speed machine" shown in this figure, image processing can be shared between the host side and the recording apparatus side, so that not only can the time required for image processing be shortened, but also the opening of the host PC can be accelerated. The outline of image processing is CMM (Color Management Module) processing that converts input image data from a color space for monitor display to a color space for a recording device (RGB color system → CMY color system) Sections 201 and 301, BG / UCR (Black Generation / Under Color Removal) for generating / removing black color from CMY values, and γ correction for performing input / output correction reflecting the characteristics of the recording apparatus and user's preference. BG / UCR / γ correction units 202 and 302 to be performed, zooming (enlargement processing according to the resolution of the recording apparatus) (Zooming) processing units 203 and 303, and halftone processing (multi-value / low-value matrix) units 204 and 304 for replacing the image data with the pattern arrangement of dots ejected from the recording apparatus.

  The present invention has a feature relating to a process for replacing the image data among them with a pattern arrangement of dots ejected from the recording apparatus. Here, processing of a monochrome (black or gray) image in the present invention will be described.

  FIG. 5 is a plan view showing an arrangement of nozzles in each head unit 51 of the line type recording head of the ink jet recording apparatus according to the embodiment of the present invention. As shown in FIG. 5, the nozzle row 402 in the head unit 51 of the ink jet recording apparatus according to the present embodiment includes cyan (C) and black in a direction substantially perpendicular to the paper transport direction (sub-scanning direction) (main scanning direction). (K), magenta (M), and yellow (Y) are composed of four rows arranged in one row for each color. The four nozzle rows 402 of the head unit 51 are arranged at the same raster position (position overlapping the sub-scan line) in the paper transport direction with the black (K) nozzle row and the black (K) nozzle row. A first nozzle row 404 comprising a yellow (Y) nozzle row, a cyan (C) nozzle row, and a magenta (M) nozzle row are arranged at the same raster position in the paper transport direction; and The second nozzle array 403 is arranged with a half-pitch shift in the main scanning direction with respect to the nozzles of the first nozzle array 404.

  The colors used by the nozzles are not limited to the four colors of black (K), cyan (C), yellow (Y), and magenta (M), and other colors may be added. Further, the arrangement order of the colors on the head unit 51 is not limited to the order shown in FIG. Furthermore, since the raster nozzles (here, the second nozzle row 403) without black nozzles form pseudo black dots instead of black dots, a combination of nozzles having a high density and a color close to black is preferable. Depending on the combination, that is, two colors of cyan (C), yellow (Y), and magenta (M), the alternative dots are green and cyan (C) in the case of cyan (C) and yellow (Y). And magenta (M) are blue, and yellow (Y) and magenta (M) are red. Generally, cyan (C) and magenta (M) depending on the characteristics of the mounted ink. ) Is preferred.

  In the following description, as shown in the arrangement shown in FIG. 5, the pseudo black dots are cyan (C) and magenta (M) blue, and are described as an arrangement in the order of CKMY. The density corresponding to one pitch in the main scanning direction of each nozzle is 150 dpi. As shown in FIG. 5, the yellow nozzle row is arranged at the same raster position (on the same sub-scan line) as the black nozzle row, and the cyan nozzle row and the magenta nozzle row are half a pitch from the black nozzle row in the sub-scan direction. That is, they are arranged at raster positions shifted by 300 dpi.

  A conventional image forming method using the head unit 51a1 belonging to the first head unit row and the head unit 51b1 belonging to the second head unit row will be described with reference to FIGS. 6 and 7, the left figure shows the arrangement of the nozzles in the head unit 51a1 and the head unit 51b1, and the right figure shows a monochrome (black or gray) image written on the recording paper. The upper half of the monochrome image is written by the head unit 51b1, and the lower half is written by the head unit 51a1. In this image, one dot indicates 300 dpi, and six dot pattern lines are written in the sub-scanning direction, and one dot pattern line image is formed in one image formation. Further, this head array unit (line type recording head) shows a case where the head units 51a1 and 51b1 have no assembly position deviation.

  Raster dot (dot pattern) signals without black nozzles are assigned to cyan and magenta. As a result, in addition to the ink ejection by the black nozzle, the ejection by the cyan nozzle and the magenta nozzle arranged at a position shifted by 300 dpi is also performed, so that the dot pattern composed of black dots formed by the black ink, the cyan ink and the magenta Dot patterns composed of pseudo black dots formed of ink are alternately arranged. The dots (C + M dot pattern) in the black (K dot pattern) gap of the image have a color close to blue due to the mixture of cyan ink and magenta ink. Although the gray balance becomes closer to blue by filling the black gap with blue, the image is formed at a density of 300 dpi, the resolution of the image in the main scanning direction is doubled, and the density of the image is also increased. Here, the alternate arrangement direction of the K and C + M dot patterns is the same main scanning direction as the nozzle arrangement direction of each color of the head unit.

  An image for one dot pattern line is recorded at a position on the recording sheet facing the head unit 51a1 (lower side of the recording sheet in the figure), and 1 is also recorded at a position facing the head unit 51b1 (upper side of the recording sheet in the figure). Records an image of dot pattern lines. As a whole, an image for one dot pattern line over the entire width of the recording paper is obtained. At this time, if there is no assembly position deviation between the head units 51a1 and 51b1, as shown in FIG. 6, there is no position deviation in the image of one dot pattern line over the entire width of the recording paper, and no white streak occurs. A good image is obtained.

  In the conventional image forming apparatus, a head array unit in which the head unit 51a1 and the head unit 51b1 have almost no overlapping portion and no nozzle overlap (overlapping nozzle) has been used. For example, as shown in FIG. 6, even if there is an overlap of nozzles in the head unit 51a1 and the head unit 51b1, nozzles of the same raster arranged in different head units are based on the same print raster data. Ink was not ejected to form an image (pixel) at the same position. In the example of FIG. 6, the cyan (C) nozzle row of the head unit 51a1, the uppermost nozzle of the magenta (M) nozzle row, the black (K) nozzle row of the head unit 51b1, and the yellow (Y) nozzle row. The lowermost nozzle is a dummy nozzle that does not discharge ink.

  The head array unit shown in FIG. 7 shows an example in which the head unit 51a1 has an assembly position shift and is assembled in a direction in which the nozzles are separated from the head unit 51b1. In this case, the image at the upper end of the image area recorded by the head unit 51a1 and the image at the lower end of the image area recorded by the head unit 51b1 are recorded separately. A non-image forming area (white streak) may occur between the image area and the lower image area in the sub-scanning direction, resulting in an undesirable image quality.

  In the image forming apparatus of the present invention, as shown in the nozzle arrangement diagram of the head units 51a1 and 51b1 in FIG. 8, in the overlapping portion of the nozzle in the sub-scanning direction at the overlapping portion of the head unit 51a1 and the head unit 51b1, An image (dot) of one pixel is formed on the recording paper by the nozzle belonging to the unit 51a1 and the nozzle belonging to the head unit 51b1 arranged on the same sub-scan line (ignoring misalignment of assembly). Assign to the discharge nozzle. In other words, in the image forming apparatus of the present invention, nozzles of the same raster arranged in different head units eject inks based on the same print raster data to form images (dots) in substantially the same area. . These nozzles are called overlapping nozzles.

  Referring to the example of FIG. 8, the lowermost cyan color nozzle belonging to the cyan (C) nozzle row of the head unit 51b1 and the uppermost magenta color nozzle belonging to the magenta (M) nozzle row of the head unit 51a1 are: An image is formed at a position where the recording areas of the head unit 51a1 and the head unit 51b1 overlap on the recording paper. This image (dot) forms an image (dot) corresponding to one pixel by strictly shifting the dot of the head unit 51a1 and the dot of the head unit 51b1 due to the displacement of the assembly position of the head unit 51a1. . However, since black dots are arranged on both the upper and lower sides thereof, white streaks do not occur and the image quality is not affected if the assembly position deviation of the head unit 51a1 is less than the allowable value.

  In the image forming apparatus of the present invention, as a method for preventing the gray balance from being close to blue, it is preferable to relatively reduce the discharge amount of the pseudo black dots compared to the black dots. FIG. 9A shows an image example in which the cyan and magenta ink ejection amounts forming the pseudo black dot dot pattern are reduced and the black ink ejection amount is increased in the black dot dot pattern. When the discharge amount of cyan and magenta forming the pseudo black dot pattern is reduced, the area ratio of the black dots in the entire image increases, so that a good monochrome (black or gray) image is obtained.

  However, as shown in FIG. 10A, the “allowable assembling position deviation amount that does not generate white streaks” is up to “the sum of the cyan and magenta dot diameters that form pseudo black dots”. When the dot diameter of the ink is reduced, the “allowable assembling position deviation amount that does not cause white streaks” for naturally preventing white streaks is also reduced.

  On the other hand, as shown in FIG. 9B and FIG. 10B, the dot diameter of the pseudo black dot of the image in the overlap portion of the writing area formed by the ink ejected from the overlapping nozzles of both the head unit 51 a 1 and the head unit 51 b 1. Is larger than the dot diameter of the pseudo black dot that forms the writing area where the nozzles do not overlap, even if the overall gray balance is adjusted by suppressing the discharge amount of the entire pseudo black dot An allowable amount of assembly position deviation can be secured. Further, as shown in FIG. 10C, the size of individual dots ejected from the unit 51a1 and the head unit 51b1 constituting the pseudo black dots can be changed alternately.

  A description will be given of a preferable process in the case where the image formed in the overlapping portion of the writing area formed by the ink ejected from the overlapping nozzle forms the image end portion. FIG. 11A to FIG. 12 are explanatory diagrams in the case where the image end portion is an overlap portion between the writing area of the head unit 51a1 and the writing area of the head unit 51b1. In the printing examples shown in FIGS. 11A to 11C, image formation is completed in the writing area of the head unit 51b1. The white circle in the figure indicates that no image is formed at a virtual image forming position by the head unit 51a1.

  FIG. 11A shows a state in which the assembly position is not shifted between the head unit 51a1 and the head unit 51b1, and the image end portion is normally printed. In this case, as described above, there is no problem even if the magenta and cyan inks are respectively ejected from the overlapping nozzles of the head unit 51a1 and the head unit 51b1 to form an image (dot) at the edge of the image. .

  However, when the assembly position shift occurs between the head unit 51a1 and the head unit 51b1 and the overlap portion is widened, as shown in FIG. The width of the pseudo black dot becomes wider. If the width of the pseudo black dot is wide and not adjacent to the black dot at the edge of the image, the difference in color and brightness of the pseudo black dot in the monochrome image tends to be noticeable, which is not preferable in terms of image quality.

  Therefore, when the image end portion overlaps the overlap portion of the writing area of the head unit 51, as shown in FIG. 11C, the head unit 51 corresponding to the area that is not the image forming area (in FIG. 11C, the head unit 51a1). It is preferable that the ink to be ejected from the overlapping nozzles belonging to (1) is not ejected. Furthermore, it is preferable to eject magenta ink from the head unit 51b magenta nozzle in the same raster as the cyan nozzle of the head unit 51b1. Then, ink dots are ejected only from the overlapping nozzles belonging to the head unit 51b1 at the image end portion, and the image end portion having a wide pseudo black dot as shown in FIG. 11B is not formed. In this way, the image quality at the image edge can be improved. It should be noted that the description below applies to the lower end of the image, but the same applies to the upper end of the image.

  FIG. 12 shows a flow chart of data processing in the control unit when the image edge and the overlap part of the writing area overlap. With reference to FIG. 12, the data processing of the overlap part will be described. First, the top position of the overlap portion is set as a target pixel (step S1). It is determined whether or not the target pixel is an image portion (step S2). If it is not an image portion (N in step S2), the target pixel is moved to the next position (step S7). If it is an image portion (Y in step S2), bitmap data corresponding to the window is acquired (step S3). Then, matching is performed with a predetermined pattern (step S4), and if matched (Y in step S5), overlap portion data is generated (step S6), and the target pixel is moved to the next position (step S7). If it does not match the predetermined pattern (N in step S5), the target pixel is moved to the next position as it is (step S7). If the next pixel of interest is not the data end of the overlap portion (N in step S8), the process returns to step S2 and the data of the overlap portion in steps S2 to S7 is similarly applied to the next pixel of interest. Repeat generation and movement of target pixel. If the pixel of interest is a data end (Y in step S8), the process ends.

  In the overlap portion data generation, if the target pixel is not the image end portion and both the black dots exist in the adjacent pixels, pattern matching with a predetermined pattern is performed, and overlap portion data is generated, Control is performed so that the pseudo black dots in the overlap portion are formed by two head units. If the pixel of interest is at the edge of the image, the overlap portion data is not generated, and a pseudo black dot is formed only by the nozzle on the side where the image exists.

  A description will be given of a change in nozzle row, a change in nozzle arrangement, and a change in combination of overlapping nozzles in adjacent head units of different head unit rows. FIG. 13 changes the arrangement of the nozzle rows of the head unit shown in FIG. That is, the nozzle row is arranged from the right end in the order of the black nozzle row, the cyan nozzle row, the magenta nozzle row, and the yellow nozzle row. The black nozzle and the magenta nozzle are arranged at the same raster position, and the cyan nozzle and the yellow nozzle are arranged at a raster position shifted by a half pitch from the nozzle arrangement pitch. For this reason, a combination of overlapping nozzles can be a black nozzle and a magenta nozzle or a cyan nozzle and a yellow nozzle.

  Here, when a black nozzle is used for one of the overlapping nozzle combinations, a white and black streak does not occur as described above, and a preferable monochrome image can be obtained.

  In FIG. 14, the arrangement of the nozzle rows of the head unit shown in FIG. 5 is changed to a form different from that shown in FIG. That is, the arrangement of the nozzle rows is the same as that of the head unit shown in FIG. 5, but cyan nozzles, magenta nozzles, and yellow nozzles are arranged at raster positions shifted by a half pitch with respect to the black nozzle arrangement pitch. For this reason, the cyan nozzle, the magenta nozzle, and the yellow nozzle can be used as a combination of overlapping nozzles. As the combination of overlapping nozzles, for example, a maximum of 6 overlapping nozzles including a combination of cyan, magenta, and yellow nozzles can be used. A combination of nozzles, a cyan nozzle and a magenta nozzle, a combination of a cyan nozzle and a yellow nozzle, a combination of nozzles of the same color, and the like can be selected.

  If pseudo black ink dots are formed as overlapping nozzles combining the cyan nozzle, the magenta nozzle, and the yellow nozzle, the color and brightness close to that of the black ink dots can be achieved, and a high quality monochrome image can be obtained. Furthermore, by selecting the ink head to which the nozzle to be ejected belongs, the combination of these three colors of ink can be changed in units of pixels. These colors may be changed according to the situation of the surrounding image and a request in image formation. In this example, cyan and magenta + yellow dots are alternately formed for two dot pattern lines (see FIG. 15), and cyan, magenta, yellow, magenta + yellow, cyan + yellow, and magenta + cyan Examples of dots formed on the surface layer in order (see FIG. 16) are shown. In this way, white lines can be made inconspicuous.

  In particular, when recording on a recording medium that is difficult to bleed, misalignment of the head tends to be conspicuous. From the combination of a plurality of overlapping nozzles, the combination at a predetermined timing (time, distance, number of drops) as described above. This misalignment can be made inconspicuous by switching. Furthermore, by ejecting three colors of ink at substantially the same position, pseudo black dots that are almost black can be obtained.

1 is a schematic cross-sectional view of a mechanism portion of an image forming apparatus according to the present invention. The top view of the mechanism part of the image forming apparatus which concerns on this invention 1 is a block diagram showing a configuration of a control unit of an image forming apparatus according to the present invention. Block diagram showing the configuration of the image processing unit on the PC (personal computer) side Plan view showing the arrangement of nozzles in the head unit Operation status and normal printing example of discharge nozzles without overlapping discharge in the overlapping part of the head unit Operation example of discharge nozzles without overlapping discharge in the overlapping part of the head unit and printing example when the head unit is displaced in the sub-scanning direction Printing example that covers the operating status of the discharge nozzles including the overlapping discharge nozzles in the overlapping part of the head unit and the positional deviation of the head unit in the sub-scanning direction Example of printing with all pseudo black dots reduced in size Example of printing with pseudo black dots smaller than the edges Example of printing with all pseudo black dots reduced (when the head unit is displaced in the sub-scanning direction) Printing example in which the size of the pseudo black dots other than the edges is reduced (when the head unit is displaced in the sub-scanning direction) Example of printing with some pseudo black dots reduced (when the head unit is displaced in the sub-scanning direction) Example of normal image edge printing Example of printing at the edge of the image when misalignment occurs in the head unit Example of printing the edge of the image after edge processing (when the head unit is displaced in the sub-scanning direction) Flow chart of image processing at the edge Printing example (1) in which the nozzle arrangement is changed with respect to the configuration of the head unit shown in FIG. Printing example (2) in which the nozzle arrangement is changed with respect to the configuration of the head unit shown in FIG. Printing example (1) in which the combination of ejection nozzles of the head unit configured as shown in FIG. 14 is changed Printing example (2) in which the combination of ejection nozzles of the head unit configured as shown in FIG. 14 is changed

Explanation of symbols

1: Device main body (image forming apparatus)
2: Paper feed tray 3: Paper discharge tray 4: Transport unit 5: Head array unit 6: Cleaning device 7: Transport guide unit 21: Separation roller 22: Paper feed roller 31: Side fence 32: End fence 41a: Transport drive roller 41b: transport driven rollers 42a, 42b: transport guide roller 43: transport belt 44: suction fan 51: head units 51a, 51a1, 51a2, 51a3, 51a4, 51a5: head units (row a)
51b, 51b1, 51b2, 51b3, 51b4, 51b5: head unit (row b)
52, 52a, 52b, 52c, 52d: Distributor 53: Supply tube 54: Sub tank 55: Array member (holding member)
61, 61a-61a5, 61b1-61b5: Cleaning means 62, 62a, 62b: Suction pump

Claims (6)

An image forming apparatus capable of forming a color image and a monochrome image by discharging ink onto the recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction,
The line-type recording head includes a plurality of head units arranged along the main scanning direction ,
Among the plurality of head units, a head unit adjacent in the main scanning direction has an overlapping region that partially overlaps in the sub-scanning direction,
When a monochrome image is formed, in the overlap region, the ink ejected from the color nozzle at the end of one head unit and the ink ejected from the color nozzle at the end of the other head unit are on the recording medium. An image forming apparatus characterized by forming pseudo black dots overlappingly . A nozzle array of the black nozzle array, wherein the pseudo black to form dots of the color nozzle rows are arranged in the color nozzle nozzle arrangement, to claim 1, characterized in that in the main scanning direction are shifted by a half pitch The image forming apparatus described. The image forming apparatus according to claim 1, wherein the color nozzles at the end of the head unit have a larger amount of ink ejection than other color nozzles in the same color nozzle row. When the image end portion is formed by the ink ejection from the color nozzle end of the head unit, the color nozzle disposed at an end portion on the side of a head unit including a color nozzles that form other than the image edge portion 4. The image forming apparatus according to claim 1, wherein the ink is ejected from the ink and no ink is ejected from a color nozzle disposed at an end of the other head unit . The image forming apparatus according to any one of claims 1 to 4, characterized in that a variable combination of the color ink forming the pseudo black dot. Image formation in which a monochrome image is formed by a device capable of forming a color image and a monochrome image by ejecting ink onto the recording medium from a line-type recording head disposed opposite to the recording medium conveyed in the sub-scanning direction A method,
The line-type recording head includes a plurality of head units arranged along the main scanning direction,
Among the plurality of head units, a head unit adjacent in the main scanning direction has an overlapping region that partially overlaps in the sub-scanning direction,
In the overlapping area, the ink ejected from the color nozzle at the end of one head unit and the ink ejected from the color nozzle at the end of the other head unit are overlapped on the recording medium to form pseudo black dots. An image forming method.

Images