JP2011020460A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration in an image quality by the change of a gap between an ink discharge nozzle and a recording medium. <P>SOLUTION: An ink jet recorder includes a recording head 25 in which a plurality of ink discharge nozzles are arranged, a conveying belt which conveys the recording medium of a sheet of paper, etc. to conduct image recording by this recording head, a gap detecting unit 43 which detects the gap between the ink discharge nozzle of the recoding head and a recording medium surface to be fixed with the ink, an image processing program 332 which converts the input image data of 8 bits per pixel to the image data of 3 bits per pixel by dither processing, and a switching means which switches a dither pattern used for the dither processing to a dither pattern to generate dots in a direction different from the conveying direction of the recording medium, such as, for example, a diagonal direction when the gap to be detected by the gap detecting unit becomes larger. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus having a recording head in which a plurality of ink discharge nozzles are arranged.

  As an ink jet recording apparatus, for example, an on-demand line ink jet recording apparatus is known. For example, as shown in FIGS. 13 and 14, the line ink jet recording apparatus has a nozzle unit 2 provided with a large number of ink chambers 1 and a main body unit 4 provided with a common ink chamber 3 for supplying ink to each ink chamber 1. And a recording head provided with an ink supply path 5 for supplying ink to the common ink chamber 3, and ink droplets are ejected from the ink ejection ports 6 of the ink chamber 1 by applying a volume variation in the ink chamber 1. Printing is to be performed. Further, the ink consumed in the ink chamber 1 is replenished from the common ink chamber 3. As a control method for giving a volume variation in the ink chamber 1, there are a piezoelectric control method using distortion deformation of a piezoelectric member and a heat control method using heat generation of a heating element.

  In such an ink jet recording apparatus, there are variations in the direction of ink ejection from the nozzles, variations in the amount of ink ejection, etc., so if recording is performed using a fixed dot pattern for each gradation, the effect of variation for each nozzle is affected. As a result, there is a problem that unevenness occurs and the image quality is remarkably lowered. In order to solve this, a dot pattern table for storing a plurality of different dot patterns is provided for each of the gradation values, and one dot pattern table is selected from the N dot pattern tables based on the gradation value information of each pixel. And a dot pattern selected from the dot pattern table selected based on the position information indicated by the pixel, and recording is performed using the selected dot pattern (for example, patents). Reference 1).

JP 2001-54956 A

  However, in the conventional ink jet recording apparatus, when the gap between the nozzle and the recording medium on which the ink is landed is constant, even if it is possible to prevent the image quality from being deteriorated due to the occurrence of unevenness due to the variation of each nozzle, the nozzle and the recording can be performed. It has not been possible to cope with a decrease in image quality due to a change in the gap with the medium.

  That is, as shown in FIG. 15A, for example, a relatively thick recording medium 11 is conveyed by the conveying belt 10, and recording is performed by ejecting ink from the ink ejection nozzles 13 of the recording head 12 onto the recording medium 11. When performing, since the gap Vgap between the nozzle 13 and the recording medium 11 becomes small, even if there is a variation in the ink ejection direction, the recording medium is hardly affected as shown in FIG. The dots 14 can be formed by landing ink on the ink 11. Therefore, the image quality does not deteriorate so much.

  On the other hand, as shown in FIG. 16A, for example, a relatively thin recording medium 15 is transported by the transport belt 10, and ink is ejected from the ink ejection nozzles 13 of the recording head 12 onto the recording medium 15. When recording is performed, the gap Vgap between the nozzle 13 and the recording medium 15 becomes large, so that a gap is formed between adjacent dots as shown in FIG. For example, the image quality is greatly reduced. In particular, in the type in which a line recording head is used and one line is recorded at a time without moving the head from side to side, it is greatly affected by variations in the ink ejection direction, and the image quality is significantly reduced. However, the conventional inkjet recording apparatus cannot cope with such a decrease in image quality.

  The present invention has been made to solve such problems, and provides an ink jet recording apparatus capable of preventing a decrease in image quality due to a change in a gap between an ink discharge nozzle and a recording medium.

  The present invention provides a recording head in which a plurality of ink ejection nozzles are arranged, a recording medium such as a belt, a drum, and a roller for conveying a recording medium such as paper in order to perform image recording with the recording head, Gap detection means for detecting a gap between the ink ejection nozzle and the surface of the recording medium on which ink is landed, and image data of 1 pixel N (where M> N ≧ 1) bits by dithering the input image data of 1 pixel M bits When the gap detected by the pseudo halftone processing means and the gap detection means becomes large, the dither pattern used by the pseudo halftone processing means for the dither processing is affected by the ink ejection characteristics of the print head generated by the increase in the gap. In an inkjet recording apparatus provided with a switching means for switching to a dither pattern in which dots are generated in the direction to cancel .

  According to the present invention, when the gap between the ink discharge nozzle and the surface of the recording medium on which the ink is landed becomes large, the dither pattern used by the pseudo halftone processing unit for the dither processing is generated by the ink discharge of the print head generated by the increase in the gap. Since switching to a dither pattern in which dots are generated in a direction that cancels the influence of the characteristics, it is possible to provide an ink jet recording apparatus that can prevent deterioration in image quality due to a change in the gap between the ink discharge nozzle and the recording medium.

1 is a perspective view illustrating a configuration of a main part of an ink jet recording apparatus according to an embodiment of the present invention. The side view which shows the principal part structure of the inkjet recording device based on the embodiment. The block diagram which shows the control part structure of the inkjet recording device based on the embodiment. The figure for demonstrating the basic algorithm of a dither process in the embodiment. The figure which shows the example of a dither pattern used for a dither process when a gap is large in the embodiment. The figure which compares and shows the example which switched the dither pattern and printed without switching the dither pattern when the gap is large in the embodiment. The figure which shows the dither pattern actually switched and used when the gap is large in the same embodiment. The figure which shows the dither pattern actually switched and used when the gap becomes still larger in the same embodiment. The perspective view which shows the principal part structure of the inkjet recording device based on other embodiment of this invention. The functional block diagram which shows the image processing function which the image processing program in the embodiment performs. FIG. 9 is a perspective view of a recording head according to another embodiment of the invention. FIG. 3 is a diagram illustrating an arrangement of ink discharge nozzles of the recording head according to the embodiment. FIG. 3 is a cross-sectional view illustrating a configuration example of a recording head of an on-demand type line inkjet recording apparatus. FIG. 3 is a diagram illustrating an arrangement of ink discharge nozzles of a recording head of the same line inkjet recording apparatus. The figure which shows the dot formation state on a recording medium when the gap of the nozzle of a recording head and a recording medium is small in the same line inkjet recording device. The figure which shows the dot formation state on a recording medium in case the gap of the nozzle of a recording head and a recording medium is large in the same line inkjet recording device.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to an ink jet recording apparatus that performs monochromatic printing.
FIG. 1 and FIG. 2 are diagrams showing the main configuration of the ink jet recording apparatus. A transport belt 23 is installed between a pair of drive rollers 21 and 22 to transport a recording medium 24 such as paper in the direction of the arrow in the figure. Forming means.

  A long recording head 25 in which a large number of ink discharge nozzles are arranged at predetermined intervals in the center of the conveying belt 23 in a direction orthogonal to the conveying direction of the recording medium 24 is arranged on the surface of the conveying belt 23. Are arranged at a predetermined distance from each other. A fixing device 26 for drying and fixing ink landed on the recording medium 24 is disposed behind the recording head 25 in the conveying direction of the conveying belt 23.

  FIG. 3 is a block diagram showing the configuration of the control unit of the ink jet recording apparatus. In the figure, 31 is a CPU (central processing unit) constituting the control unit main body, and 32 is a ROM (read only memory) in which the CPU 31 stores a program for controlling each unit for printing operation and maintenance processing. , 33 is a RAM (random access memory) provided with a memory used when the CPU 31 performs data processing, 34 is a pixel processing parameter table, 35 is an I / O port, and 36 is in communication with the host computer 37. I / F (interface).

  The ROM 32 also stores a dither pattern selection program 321 for selecting a dither pattern and an image processing program 322 for performing image processing. In particular, the RAM 33 has an image processing parameter area 331 for temporarily storing a table and a program necessary for image processing for converting an input image for printing and recording into an image suitable for the apparatus, and an input for printing and recording. An input / output image area 332 for storing an image and an output image converted into an image optimal for the apparatus by an image processing program, and a reception buffer 333 for temporarily storing print data received from the host computer 37 are provided. Yes. A table necessary for image processing temporarily stored in the image processing parameter area 331 is read from the pixel processing parameter table 34.

  The I / O port 35 includes a head driver 38 that drives and controls the recording head 25, a motor driver 40 that drives and controls the conveyance motor 39 that rotationally drives the driving rollers 21 and 22, and operates during maintenance of the recording head 25. A maintenance driver 42 for driving and controlling the maintenance mechanism 41 is connected.

  In addition, the I / O port 35 detects a temperature in the vicinity of the recording head 25, a gap detection unit 43 as a gap detection unit that detects a gap between the ink ejection nozzles of the recording head 25 and the surface of the recording medium 24. A head temperature sensor 44 and a power switch 45 are connected. As the gap detection unit 43, for example, a unit that detects a gap based on a moving distance when the recording head 25 is moved from a fixed position and is brought into contact with the recording medium 25 is used.

  The CPU 31 performs dither processing based on the image processing program 322 stored in the ROM 32, and converts input 1-pixel M-bit image data into 1-pixel N (where M> N ≧ 1) -bit image data. (Pseudo halftone processing means). For example, 8-bit input image data is converted into 3-bit image data having a smaller number of gradations.

Next, a basic algorithm for dither processing will be described.
As shown in FIG. 4, threshold means TH having a different threshold value Tij for each pixel is provided, and the threshold value TH compares the original pixel value Xij of the input signal with the threshold value Tij to determine whether the pixel is on or off. , And output as an output signal Yij. That is, in the case of 256 gradations from 0 to 255, Yij = 255 when Xij ≧ Tij, and Yij = 0 when Xij <Tij.

  Dither methods can be classified into systematic dither methods and random dither methods depending on how dither signals are added, but they are broadly divided into conditional decision methods and independent decision methods. There are also taxonomies that fall into the area.

  A method for multi-leveling the organized dither method will be described. As the simplest example, consider a case where the output values are three values of 0, 127, and 255. In this case, when the pixel value of the original image is 0 to 127, the corresponding pixel is 0 or 127, and when the pixel value is 127 to 255, the corresponding pixel is 127 or 255. Therefore, two types of threshold matrix T0 corresponding to pixels having an input pixel value of 0 to 127 and threshold matrix T1 corresponding to pixels having an input pixel value of 127 to 255 are prepared, and these threshold values are prepared according to the input pixel value. The output value can be made ternary by switching the matrix. If this method is used, the output value can be easily increased to four or more.

  When performing the dither processing based on the image processing program 322, the CPU 31 uses the dither pattern selection program 321 based on the gap between the ink ejection nozzles of the recording head 25 and the recording medium 24 detected by the gap detection unit 43. The dither pattern used for dither processing is switched (switching means). That is, when the detected gap is small, as shown in FIG. 15, even if there is a variation in the ink ejection direction, the ink is landed on the recording medium 24 from the ink ejection nozzle of the recording head 25 with little influence. be able to. For example, even if the ink ejection directions are adjacent to each other between adjacent ink ejection nozzles, the ink lands before the separation increases, so that the image quality does not deteriorate so much.

  However, when the detected gap is large, as shown in FIG. 16, if there is a variation in the ink ejection direction, it is greatly affected, for example, the direction in which the ink ejection directions are separated from each other between adjacent ink ejection nozzles. In this case, the inks that have landed on both sides are separated on both sides from the position where they should be. That is, the characteristics of the recording head 25 appear in a direction orthogonal to the conveyance direction of the recording medium 24.

  In order to cancel such an influence, the CPU 31 sets the dither pattern used for the dither processing in a direction where the dot generation direction due to ink landing is different from the conveyance direction of the recording medium 24, for example, as shown in FIG. The dither pattern is switched so that dots are generated in an oblique direction.

  The recording head 25 performs dot recording on the recording medium 24 based on the output image data obtained by performing dither processing using such a dither pattern, whereby a printing result as shown in FIG. Obtained. On the other hand, when the recording head 25 performs dot recording on the recording medium 24 based on the output image data obtained by performing the dither processing without switching the dither pattern even when the gap becomes large, the state shown in FIG. As shown.

  Further, when the gap between the ink ejection nozzle of the recording head 25 and the recording medium 24 is further increased, not only the recording characteristics of the recording head 25 are emphasized but also the ink between the recording head 25 and the recording medium 24 is increased. When the ejection amount is small, the flying ink droplets are caused to flow under the influence of the airflow generated by the relative movement of the recording head 25 and the recording medium 24, and the ink landing accuracy is extremely deteriorated.

  Therefore, when the dither pattern is switched and used, the CPU 31 shows the three values of the output image as shown in (a), (b), and (c) of FIG. 7 when the gap is not extreme. The dither pattern is switched to use, but when the gap becomes extremely large, the dither pattern shown in FIGS. 8A, 8B, and 8C is used for the three values of the output image. Switch as follows. That is, by switching the output value of 3 bits to 2 bits and increasing one ink discharge amount when the gradation value is small, it is possible to prevent the ink droplets in flight from flowing. That is, the dither pattern shown in FIG. 7A is switched to the dither pattern shown in FIG. 8A, and the dither pattern shown in FIG. 7B is changed to the dither pattern shown in FIG. 7C and FIG. 8C are the same.

  As described above, when the gap between the ink discharge nozzles of the recording head 25 and the recording medium 24 becomes large, the dither pattern used for the dither processing is switched to land in a direction in which the recording characteristics of the recording head 25 are visually improved. Doing dots can be corrected, and deterioration in image quality can be prevented.

  In the above-described embodiment, the present invention is applied to an inkjet recording apparatus that performs monochromatic printing. However, it is needless to say that the present invention can also be applied to an inkjet recording apparatus that performs color printing.

  As shown in FIG. 9, the inkjet recording apparatus that performs color printing includes recording heads 251, 252, 253, which eject inks of yellow (Y), magenta (M), cyan (C), and black (K). 254 are arranged at a predetermined distance from the surface of the conveyor belt 23 at a predetermined interval.

  In this inkjet recording apparatus, yellow dots are printed by the yellow recording head 251 and magenta dots are printed by the magenta recording head 252 on the recording medium 24 conveyed by the conveying belt 23, and cyan. The recording head 253 prints cyan dots. A color image is recorded by superimposing these dots. In the case of black, recording is performed using a dedicated recording head 254.

  In this case, the image processing functions executed by the image processing program stored in the ROM are shown in functional blocks as shown in FIG. That is, it includes a color conversion unit 51, a BG / UCR processing unit 52, a gradation correction unit 53, and a pseudo gradation processing unit 54.

  In this function, first, input 1-pixel M-bit color image data, for example, a standard RGB image signal of 8 bits for each color is input to the color converter 51, and the color converter 51 Thus, the color reproduction color of the ink jet recording apparatus is converted into CMY colors.

  Next, the BG / UCR processing unit 52 extracts the black component from the CMY color, determines the subsequent CMY color, and finally converts it to the CMYK color. Next, the gradation correction unit 53 performs correction according to the substantial output characteristics of the ink jet recording apparatus. Finally, the pseudo gradation processing unit 54 performs dither processing for each color, and multi-value image data of N bits for each color, for example, 3 bits for each color, in which data for one pixel is matched with the printing capability of the inkjet recording apparatus. Convert to C′M′Y′K ′.

  Therefore, the pseudo gradation processing unit 54 performs dither processing for each color, and the ink ejection of the recording head 25 detected by the gap detection unit 43, as in the above-described embodiment, is used for the dither pattern used in the dither processing. When the gap between the nozzle and the recording medium 24 increases, the dither pattern shown in FIG. 7 or 8 is switched.

  As a result, even in an ink jet recording apparatus that performs color printing, it is possible to visually correct dots that land in a direction in which the recording characteristics of the recording heads 251 to 254 are improved, and to prevent image quality from deteriorating. be able to.

  Each of the above-described embodiments has been described with respect to a recording head configured with a single head module. However, the present invention is not limited to this, and the present invention can also be applied to a recording head using a plurality of head modules. It is. That is, it becomes more difficult to manufacture a long line recording head having a large number of ink ejection nozzles as the number of ink ejection nozzles increases. Therefore, for example, as shown in FIGS. 11 and 12, three head modules 61, 62, 63 in which a large number of ink discharge nozzles 60 are arranged at a predetermined pitch are arranged on both sides of a substrate 64. The head modules 61 and 63 are positioned at both ends on the other surface side and bonded to each other at the central portion on the one surface side. This facilitates the production of a long recording head 65 having a large number of ink ejection nozzles.

  The ink discharge ports of the head modules 61 and 63 and the ink discharge ports of the head module 62 do not line up in a straight line with respect to the line direction orthogonal to the recording medium conveyance direction. By adjusting the ink discharge timing of the head module 62, the same printing result as that arranged on a straight line in the line direction can be obtained. And it is easy to perform such control.

  In this embodiment, the recording medium is transported in a plane by the transport belt. However, the recording medium transport method is not limited to this, and the recording medium may be transported by winding the recording medium around a drum. Good. In this case, since ink is ejected from the recording head arranged opposite to the drum surface and recording is performed on the recording medium, the gap between the ink ejection nozzle of the recording head and the recording medium wound around the drum is detected. Become.

  DESCRIPTION OF SYMBOLS 23 ... Conveyance belt, 24 ... Recording medium, 25 ... Recording head, 31 ... CPU, 32 ... ROM, 321 ... Dither pattern selection program, 322 ... Image processing program, 38 ... Head driver, 43 ... Gap detection part.

Claims (2)

A recording head in which a plurality of ink discharge nozzles are arranged;
Conveying means for conveying a recording medium to perform image recording by the recording head;
Gap detecting means for detecting a gap between the ink discharge nozzle of the recording head and the surface of the recording medium on which the ink is landed;
Pseudo halftone processing means for converting 1-pixel M-bit input image data into 1-pixel N (where M> N ≧ 1) -bit image data by dither processing;
When the gap detected by the gap detecting unit becomes large, the dither pattern used for the dither processing by the pseudo halftone processing unit generates dots in a direction that cancels the influence of the ink ejection characteristics of the recording head generated by the increase in the gap. Switching means for switching to a dither pattern to be
An ink jet recording apparatus comprising:   The switching means switches the dither pattern used for the dither processing by the pseudo halftone processing means to a dither pattern in which dots are generated in an oblique direction different from the conveyance direction of the recording medium when the gap detected by the gap detection means becomes large. The ink jet recording apparatus according to claim 1.

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