JP2005111892A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of color variation on a recording medium in an inkjet recorder that has an inkjet head having formed thereon a nozzle array consisting of a plurality of nozzles which are arranged in a line in a direction diagonal to the conveyance direction of the recording medium on a face opposite to the recording medium conveyed in a predetermined direction, and records a halftone image on the recording medium by allowing each nozzle to eject ink on the recording medium. <P>SOLUTION: A head section has the plurality of inkjet heads juxtaposed in a sub-scanning direction. The nozzle array is formed on a nozzle plate of the inkjet head such that the nozzles are arranged in a line in a direction diagonal to the conveyance direction of the recording paper by 20 degrees. A screen angle of each color is set to be different from the inclination angle of the respective nozzle array. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides an ink jet head in which a nozzle array composed of a plurality of nozzles arranged in a line in a direction inclined with respect to the transport direction of the recording medium is formed on a surface facing the recording medium transported in a predetermined direction. And an ink jet recording apparatus that records a halftone image on the recording medium by ejecting ink from each of the nozzles to the recording medium.

  2. Description of the Related Art Conventionally, a line type ink jet recording apparatus including an ink jet head arranged to be inclined with respect to a recording medium conveyance direction is known (see, for example, Patent Document 1). On the nozzle surface of the ink jet head, a nozzle row composed of a plurality of nozzles arranged in a line in the inclination direction of the ink jet head is formed. According to this type of ink jet recording apparatus, since the nozzle row is inclined with respect to the recording medium conveyance direction, the apparent nozzle density during printing can be increased, and as a result, the printing density is increased. be able to. This configuration is particularly effective when applied to a line type ink jet recording apparatus in which a plurality of ink jet heads are arranged in the width direction of the recording medium.

  In addition, halftone processing is generally known as one of image processing (for example, Patent Document 2). Halftone processing is processing for dividing a continuous tone of an image into points of various sizes. By applying this halftone process to the image, gray or color continuous tone can be reproduced on the recording medium.

  Here, the process of traditional graphic halftone processing for a grayscale image will be described. First, the original image is mounted on a copy board of a camera and irradiated with light. At this time, the bright part (highlight) on the original picture reflects light well, while the dark part (shadow) on the original picture does not reflect (absorbs) light much. Next, the reflected light enters the camera and passes through a halftone screen (details of the halftone screen will be described later). Thereby, the original picture is divided into dot patterns, and as a result, a halftone negative is formed on the film. At this time, on the negative film, the dot corresponding to the above-mentioned highlight becomes large, while the dot corresponding to the above-mentioned shadow becomes small. Finally, a positive image is created using a negative film. At this time, on the positive image, the dot corresponding to the above-mentioned highlight becomes small, while the dot corresponding to the above-mentioned shadow becomes large.

  Here, details of the halftone screen will be described. The halftone screen is configured by crossing two thin plates formed with a plurality of lines extending in parallel at equal intervals. Then, reflected light of various luminances passes through the halftone screen, so that halftone dots of various sizes are formed in portions corresponding to the gaps of the halftone screen on the film.

  By the way, the precision of a halftone image differs depending on the number of screen lines of a halftone screen. The number of screen lines refers to the number of lines of a halftone dot pattern on a halftone screen or image. As the number of screen lines increases, an image with clear details can be reproduced.

  In creating a halftone image, it is necessary to consider the screen angle in addition to the number of screen lines. Here, in order to make the halftone dot pattern on the image inconspicuous, the screen angle is preferably 45 degrees.

  Also, the traditional graphic halftone processing principle described above for grayscale images can be applied to color images. However, in order to reproduce a color image, four color inks (that is, cyan (C), magenta (M), yellow (Y), and black (K)) and four halftone screens (that is, half-cyan for cyan) are used. Tone screen, magenta halftone screen, yellow halftone screen and black halftone screen). Printing for reproducing such a color image is called process printing or CMYK printing.

Here, in order to prevent the occurrence of a moire pattern on a color image subjected to halftone processing, the screen angles of the respective colors are generally set as follows (see FIG. 8).
C = 15 °, M = 75 °, Y = 90 °, K = 45 °

Further, the above-described traditional graphic halftone processing technology is the basis of digital halftone processing.
JP-A-6-344627 JP-A-8-237396

  By the way, when the inclination angle of the inkjet head and the screen angle are the same, the ink ejection timing of each nozzle is substantially the same. Therefore, when the inclination angle of the inkjet head is the same as the screen angle and the conveyance speed of the recording medium is uneven, color unevenness extending in the inclination direction of the inkjet head occurs on the recording medium. , Resulting in degradation of image quality. For example, when the inclination angle of the inkjet head is the same as the cyan screen angle and the conveyance speed of the recording medium temporarily decreases, the recording medium in the cyan halftone dot pattern 100 on the recording medium A dark diagonal line 101 extending in the direction of inclination of the ink jet head is generated in a portion where the transport speed is temporarily reduced (see FIG. 9).

  The present invention has been made in view of the above points, and an object of the present invention is to line up a surface inclined to a recording medium transport direction in a direction opposite to the recording medium transported in a predetermined direction. An ink jet head having an ink jet head formed with a nozzle array composed of a plurality of nozzles arranged in a line, and recording a halftone image on the recording medium by ejecting ink from each of the nozzles to the recording medium An object of the present invention is to provide a technique for preventing the occurrence of color unevenness on a recording medium in a type recording apparatus.

  In a first aspect of the present invention, an ink jet in which a nozzle array composed of a plurality of nozzles arranged in a line in a direction inclined with respect to the transport direction of the recording medium is formed on a surface facing the recording medium transported in a predetermined direction. An ink jet recording apparatus that includes a head and records a halftone image on the recording medium by ejecting ink from each of the nozzles to the recording medium, the transport direction of the recording medium and the nozzles The angle formed by the inclination direction of the row is different from the screen angle based on the conveyance direction of the recording medium in the halftone image.

  As a result, the angle formed between the conveyance direction of the recording medium and the inclination direction of the nozzle row is different from the screen angle based on the conveyance direction of the recording medium in the halftone image. In the recording, the ink ejection timings of the nozzles are different from each other. Therefore, even when there is unevenness in the conveyance speed of the recording medium, color unevenness extending in the inclination direction of the nozzle row is unlikely to occur on the recording medium.

  In a second aspect based on the first aspect, the halftone image includes at least first and second halftone dot patterns having different screen angles and colors, and the transport direction of the recording medium. And the inclination direction of the nozzle row is larger than the screen angle based on the conveyance direction of the recording medium in the first halftone dot pattern and the recording medium in the second halftone dot pattern The screen angle is smaller than the screen angle based on the transport direction.

  Thereby, the angle formed between the conveyance direction of the recording medium and the inclination direction of the nozzle row is larger than the screen angle based on the conveyance direction of the recording medium in the first halftone dot pattern and the second halftone dot pattern. Therefore, when the halftone image is recorded on the recording medium, the ink ejection timings of the nozzles are different from each other. Therefore, even if the halftone image includes at least the first and second halftone dot patterns and the conveyance speed of the recording medium is uneven, the color that extends in the inclination direction of the nozzle row on the recording medium Unevenness is unlikely to occur.

  According to the present invention, the angle formed between the recording medium conveyance direction and the nozzle row inclination direction is different from the screen angle based on the recording medium conveyance direction in the halftone image. When recording a halftone image, the ink ejection timing of each nozzle is different. For this reason, even when there is unevenness in the conveyance speed of the recording medium, color unevenness extending in the direction of inclination of the nozzle row is unlikely to occur on the recording medium. Therefore, it is possible to prevent the occurrence of color unevenness on the recording medium regardless of the accuracy of the conveyance speed of the recording medium, thereby improving the printing performance.

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

  As shown in FIG. 1, a line-type ink jet recording apparatus 1 according to an embodiment of the present invention includes a head block unit 2 for ejecting ink droplets onto a recording sheet 6 and an ink tank unit for containing ink. 3, a head control unit 4 that controls the head block unit 2, a recovery system mechanism unit 5 that performs a recovery operation to be described later on the head block unit 2, and a conveyance device that conveys a recording sheet 6 as a recording medium (see FIG. And an adjusting mechanism (not shown) that adjusts the positional relationship between the heads 2a, 2b, 2c, and 2d described later.

  The head block unit 2 includes a cyan (C) head unit 2 a for ejecting cyan ink droplets onto the recording paper 6, and magenta (M) for ejecting magenta ink droplets onto the recording paper 6. Head portion 2b, yellow (Y) head portion 2c for ejecting yellow ink droplets onto recording paper 6, and black (K) for ejecting black ink droplets onto recording paper 6 Head portion 2d. These head portions 2a, 2b, 2c, and 2d are arranged side by side in the conveyance direction of the recording paper 6, that is, the main scanning direction X. The head block unit 2 is configured to be movable in the sub-scanning direction Y perpendicular to the main scanning direction X.

  As shown in FIG. 2, the cyan head section 2 a includes a plurality of inkjet heads 7 that are arranged side by side in the sub-scanning direction Y so as to cover the entire print area in the sub-scanning direction Y (width direction) of the recording paper 6. , 7,... And a head holding plate 8 that holds the inkjet heads 7, 7,. In the present embodiment, the cyan head unit 2a includes, for example, nine inkjet heads 7 (the number of the heads 7 varies depending on the print width). Further, as shown in FIG. 3, each inkjet head 7 is disposed so as to be inclined at the same angle with respect to the conveyance direction of the recording paper 6. In the present embodiment, each inkjet head 7 is arranged so as to be inclined by, for example, 20 degrees with respect to the conveyance direction of the recording paper 6 (this angle varies depending on the arrangement of the nozzles 9a and the printing resolution). .

  4, each inkjet head 7 has a plurality of nozzles 9a, 9a,... (In this embodiment, for example, 400 pins arranged in a line in a direction inclined with respect to the conveyance direction of the recording paper 6. A nozzle plate 10 formed with a nozzle row 9 (see FIG. 3), and an ink flow path formed on the upper surface of the nozzle plate 10 and in which a common ink chamber 11 and the like are formed. A plurality of pressure chambers 13, 13,... That are formed on the upper surface of the member 12 and the ink flow path forming member 12 and communicate with the nozzles 9 a, 9 a,. The formed pressure chamber forming member 14, the diaphragm 15 provided so that a part of the lower surface thereof faces the plurality of pressure chambers 13, 13,..., And the pressure chambers 13, 13, Part corresponding to… A plurality of piezoelectric actuators 16 that are provided above and apply a pressure to cyan ink in each of the pressure chambers 13, 13,... And discharge cyan ink droplets from the nozzles 9 a, 9 a,. , 16,... As shown in FIG. 3, the nozzle row 9 extends on the nozzle plate 10 of the inkjet head 7 in the same direction as the inclination direction of the inkjet head 7 with respect to the conveyance direction of the recording paper 6. In other words, in this embodiment, the nozzle row 9 is inclined by, for example, 20 degrees with respect to the conveyance direction of the recording paper 6 (hereinafter, an angle formed by the conveyance direction of the recording paper 6 and the inclination direction of the nozzle row 9). "Inclination angle of the nozzle row 9"). The other head portions 2b, 2c, 2d have substantially the same configuration as the cyan head portion 2a. Further, the surface facing the recording medium in the present invention corresponds to the nozzle plate 10.

  As shown in FIG. 1, the ink tank unit 3 is installed on one side of the head block unit 2 in the main scanning direction X, and stores cyan ink and supplies the cyan head unit 2a with the ink. A cyan ink tank portion 3a, a magenta ink tank portion 3b for containing magenta ink and supplying the ink to the magenta head portion 2b, and a yellow ink portion for containing the yellow ink in the yellow head portion 2c. On the other hand, a yellow ink tank portion 3c for supplying the ink and a black ink tank portion 3d for containing black ink and supplying the ink to the black head portion 2d are provided. These ink tank portions 3a, 3b, 3c, 3d are arranged side by side in the main scanning direction X.

  The head control unit 4 corrects positional deviations of the head units 2a, 2b, 2c, and 2d in the main scanning direction X and the sub-scanning direction Y, which cannot be mechanically adjusted. It is installed above the head block portion 2. Specifically, the head control unit 4 corrects the positional deviation of each head unit 2a, 2b, 2c, 2d with respect to the main scanning direction X by correcting each of the image data and the ejection timing, while in the sub-scanning direction. The positional deviation of each head unit 2a, 2b, 2c, 2d with respect to Y is corrected by correcting the image data.

  The recovery system mechanism unit 5 is installed on one side of the head block unit 2 in the sub-scanning direction Y, and has a cap, a blade, a pump, and the like. The recovery system mechanism unit 5 is configured to be movable in the vertical direction and the main scanning direction X, respectively. Then, when performing a recovery operation on the head block unit 2, specifically, a process for forcibly ejecting ink from the nozzle 9a or a purge (suction) process for the nozzle 9a, the head block unit 2 is used as a recovery system mechanism. Move above part 5.

  The transport device transports the recording paper 6 to one side in the main scanning direction X at a constant speed. The recording paper 6 is, for example, roll paper.

  The adjustment mechanism unit mechanically finely adjusts the positional relationship between the head units 2a, 2b, 2c, and 2d in the main scanning direction X and the sub-scanning direction Y, respectively.

  The ink jet recording apparatus 1 is connected to a computer (not shown). This computer is connected to a digital camera, a scan (not shown), and the like. Then, the digital camera or the like outputs image data captured by the digital camera to the computer. The computer performs halftone processing on the input image data and outputs halftone image data formed by performing the halftone processing to the ink jet recording apparatus 1. In this embodiment, the computer separates an image into four color components of cyan (C), magenta (M), yellow (Y), and black (B), and performs color separation on each of the separated images. Halftone processing.

  Here, the screen angle of each color is determined in accordance with the inclination angle of the nozzle row 9. Specifically, the screen angle of each color is set to be different from the inclination angle of the nozzle row 9. In this embodiment, for example, when the inclination angle of the nozzle row 9 is 20 degrees, the cyan screen angle is 5 degrees, the black screen angle is 35 degrees, the magenta screen angle is 65 degrees, and the yellow screen angle is 5 degrees. The screen angle is set to 80 degrees (see FIG. 5). In other words, the screen angle of each color is set so that the inclination angle of the nozzle row 9 is larger than the cyan screen angle and smaller than the black screen angle.

-Operation of computer and ink jet recording apparatus-
Here, the operation steps of the computer and the ink jet recording apparatus 1 will be described with reference to FIG. First, the computer reads information on the inclination angle of the nozzle row 9 (step S1). In the present embodiment, the inclination angle of the nozzle row 9 is, for example, 20 degrees. Further, for example, color image data taken by a digital camera is input to the computer (step S2).

  Next, the computer determines the screen angle of each color according to the inclination angle of the nozzle row 9 (step S3). Specifically, the computer sets the screen angle of each color to be different from the inclination angle of the nozzle row 9. In this embodiment, when the inclination angle of the nozzle row 9 is 20 degrees, the computer sets the cyan screen angle to 5 degrees, the black screen angle to 35 degrees, the magenta screen angle to 65 degrees, and yellow. The screen angle is set to 80 degrees.

  Next, the computer performs a halftone process on the input image data to create a halftone image (step S4). At this time, the inclination angle of the nozzle row 9 is different from the screen angle of the created halftone image. Specifically, the inclination angle of the nozzle row 9 is different from the screen angle in the halftone dot (halftone dot) pattern of each color included in the created halftone image. In other words, the inclination angle of the nozzle row 9 is different from the angle formed by the conveyance direction of the recording paper 6 and the direction in which the halftone dot patterns of each color are arranged. In the present embodiment, the inclination angle of the nozzle array 9 is, for example, 20 degrees, the screen angle of the cyan halftone dot pattern is 5 degrees, the screen angle of the black halftone dot pattern is 35 degrees, and magenta The halftone dot pattern has a screen angle of 65 degrees, and the yellow halftone dot pattern has a screen angle of 80 degrees (see FIG. 5).

  Next, the user issues an output command for the formed halftone image to the computer (step S5). Next, the computer outputs the data of the halftone image to the ink jet recording apparatus 1, and then the ink jet recording apparatus 1 records the halftone image on the recording paper 6 (step S6). At the time of recording, the head block unit 2 is fixed at a predetermined position, while the recording paper 6 is conveyed to one side in the main scanning direction X by a conveying device. Then, by ejecting ink droplets of the respective colors from the respective nozzles 9a of the respective head portions 2a, 2b, 2c, and 2d onto the recording paper 6, a halftone dot (halftone dot) pattern of each color is formed on the recording paper 6. Form. As a result, a halftone image is printed on the recording paper 6. At this time, the inclination angle of the nozzle row 9 and the screen angle of the halftone image on the recording paper 6 are different. Specifically, the inclination angle of the nozzle row 9 is different from the screen angle in each color halftone dot pattern included in the halftone image on the recording paper 6. In other words, the inclination angle of the nozzle row 9 is different from the angle formed by the conveyance direction of the recording paper 6 and the direction in which the halftone dot patterns of the respective colors on the recording paper 6 are arranged. In the present embodiment, the inclination angle of the nozzle array 9 is, for example, 20 degrees, the screen angle of the cyan halftone dot pattern is 5 degrees, the screen angle of the black halftone dot pattern is 35 degrees, and magenta The halftone dot pattern has a screen angle of 65 degrees, and the yellow halftone dot pattern has a screen angle of 80 degrees (see FIG. 5). These screen angles are based on the conveyance direction of the recording paper 6. The predetermined direction in the present invention corresponds to one side of the main scanning direction X, the first halftone dot pattern corresponds to the cyan halftone dot pattern, and the second halftone dot pattern corresponds to the black halftone dot pattern. Corresponds to the halftone dot pattern.

-Effect-
As described above, according to the present embodiment, since the inclination angle of the nozzle row 9 and the screen angle of the halftone dot pattern of each color in the halftone image are different, the recording of the halftone image on the recording paper 6 is performed. At this time, the ink ejection timing of each nozzle 9a is different from each other. For this reason, even when the conveyance speed of the recording paper 6 is uneven, color unevenness extending on the recording paper 6 in the tilt direction of the nozzle row 9 hardly occurs. For example, when the inclination angle of the nozzle array 9 is 20 degrees and the cyan screen angle is 5 degrees as shown in FIG. 7, that is, when the two are different, the inclination angle of the nozzle array is as shown in FIG. Consider a case in which the screen angle is 15 degrees and the cyan screen angle is 15 degrees, that is, both are equal. In the case of FIG. 9, when the conveyance speed of the recording paper temporarily decreases, a dark diagonal line 101 extending in the inclination direction of the nozzle row is generated in the cyan halftone dot pattern 100 on the recording paper. However, in the case of FIG. 7, even when the conveyance speed of the recording paper 6 temporarily decreases, a dark diagonal line as in the conventional case is generated in the cyan halftone dot pattern 17 on the recording paper 6. Difficult (see the vicinity of the dashed line in FIG. 7). The same applies to the black, magenta, and yellow halftone dot patterns on the recording paper 6. Therefore, regardless of the accuracy of the conveyance speed of the recording paper 6, it is possible to prevent the occurrence of color unevenness on the recording paper 6, thereby improving the printing performance.

(Other embodiments)
In this embodiment, the inclination angle of the nozzle array 9 is 20 degrees, but the inclination angle of the nozzle array 9 is any value as long as the nozzle array 9 is inclined with respect to the conveyance direction of the recording paper 6. Also good.

  In this embodiment, the inclination angle of the nozzle array 9 is larger than the cyan screen angle and smaller than the black screen angle. However, the present invention is not limited to this. For example, it is larger than the black screen angle and the magenta screen angle. May be smaller.

  In this embodiment, the cyan screen angle is set to 5 degrees, the black screen angle is set to 35 degrees, the magenta screen angle is set to 65 degrees, and the yellow screen angle is set to 80 degrees. As long as the screen angle of each color is different from the inclination angle of the nozzle row 9, the screen angle of each color may be any value.

  In the present embodiment, the screen angle of each color is set to be different from the tilt angle of the nozzle row 9 with respect to the tilt angle of the nozzle row 9. The angle may be set to be different from the inclination angle of the nozzle row 9.

  In this embodiment, the screen angle of each color is determined according to the tilt angle of the nozzle row 9, but the tilt angle of the nozzle row 9 may be determined according to the screen angle of each color.

  In the present embodiment, the present invention is applied to recording of a halftone image subjected to digital halftone processing, but is applied to recording of a halftone image subjected to traditional graphic halftone processing. May be.

  In this embodiment, the image is color-separated into four color components, but may be color-separated into an arbitrary number of color components.

  In this embodiment, the computer performs halftone processing, but the ink jet recording apparatus 1 may perform halftone processing.

  In this embodiment, the recording paper 6 is a roll paper, but is not limited thereto, and may be a cut paper, for example.

  In the present embodiment, the recording medium referred to in the present invention is configured by the recording paper 6, but is not limited thereto, and may be, for example, a building material, a sheet metal, a cardboard, or the like.

  In the present embodiment, the present invention is applied to the line type ink jet recording apparatus 1, but may be applied to a so-called serial type.

  In the present embodiment, each of the head portions 2a, 2b, 2c, and 2d has nine inkjet heads 7. However, as long as the entire print area in the width direction of the recording paper 6 can be covered, The number of inkjet heads 7 may be an arbitrary number.

  In this embodiment, the piezoelectric actuator 16, that is, a so-called piezo-type actuator is used as means for applying pressure to the ink in the pressure chamber 13, but so-called bubble jet (registered trademark) is used as the pressure applying means. A mold or a so-called electrostatic type may be used.

  As described above, the present invention is useful when applied to a printer such as a computer, a facsimile machine, and a copying machine.

1 is a perspective view of a line-type ink jet recording apparatus according to an embodiment of the present invention. It is the perspective view which looked at the head part from the lower part. It is a top view of a nozzle plate. It is a cross-sectional perspective view of an inkjet head. It is the figure which showed the screen angle of the halftone dot pattern of each color. It is a figure which shows the process of operation | movement of a computer and an inkjet recording device. It is the figure which showed the relationship between the inclination angle of a nozzle row, and the screen angle of a cyan halftone dot pattern. It is the figure which showed the screen angle of the halftone dot pattern of each color in the past. It is the figure which showed the relationship between the inclination angle of the conventional inkjet head, and the screen angle of the halftone dot pattern of cyan.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 2 Head block part 6 Recording paper 7 Inkjet head 9 Nozzle row

Claims (2)

An inkjet head having a nozzle array composed of a plurality of nozzles arranged in a row in a direction inclined with respect to the transport direction of the recording medium on a surface facing the recording medium transported in a predetermined direction, An ink jet recording apparatus that records a halftone image on a recording medium by discharging ink from each of the nozzles to the recording medium,
An ink jet recording apparatus, characterized in that an angle formed by the transport direction of the recording medium and the inclination direction of the nozzle row is different from a screen angle based on the transport direction of the recording medium in the halftone image. . The ink jet recording apparatus according to claim 1,
The halftone image includes at least first and second halftone dot patterns having different screen angles and colors.
The angle formed between the transport direction of the recording medium and the tilt direction of the nozzle row is larger than a screen angle based on the transport direction of the recording medium in the first halftone dot pattern, and the second halftone. An ink jet recording apparatus having a dot pattern smaller than a screen angle based on a transport direction of the recording medium.

Images