JP5783948B2 - Color image forming apparatus - Google Patents

Description

  Embodiments described herein relate generally to a color image forming apparatus that controls an ink drop amount per pixel using an inkjet head.

Conventionally, an image forming apparatus generally has recording pixel positions arranged in a grid pattern. However, because of the speed of the engine, the accompanying drive waveform and speed of image processing, ensuring the density, stabilizing the recording characteristics, etc., the image forming apparatus in which the recording pixel positions are arranged in a staggered manner,
It is also considered to switch between grid-like recording and staggered recording according to the recording mode.

  However, in these prior arts, there is no detailed description of the data handling method even though the recording pixel positions of the image forming apparatus are staggered.

  In some color ink jet printers, the paper is locally stretched due to the relative recording position of the ink on the medium, and even if the head and paper transport are physically correctly controlled, the ink is actually recorded on the medium. Deviation occurs at the ink landing position, and this may cause noise such as visualizing white stripes and deterioration of graininess due to pattern deviation.

Japanese Patent Laid-Open No. 04-142878 Japanese Patent No. 3339692

  The problem to be solved by the present invention is to provide a color image forming apparatus capable of appropriately controlling the ink landing position even when local elongation occurs in the recording medium.

In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention includes a plurality of nozzles arranged at predetermined equal intervals, a head that ejects ink, and a plurality of inks having different colors. The head is disposed such that the nozzle positions are shifted from each other by a predetermined interval, and a head unit that reciprocates in a main scanning direction orthogonal to the recording medium conveyance direction, and the head unit moves while ejecting the ink. When the recording medium is transported in the transport direction each time recording for one pass is performed, and when recording for one pass is performed, the recording timing is set in the main scanning direction as compared with the recording of the immediately preceding pass . A head unit control unit that records by shifting by one pixel , and forms dots by superimposing ink of each color by recording for a plurality of passes .

1 is a configuration diagram of an MFP according to the present embodiment. FIG. 3 is a cross-sectional view illustrating a configuration of a printer unit. FIG. 4 is a schematic diagram for explaining the operation of an inkjet head. The schematic diagram of zigzag pattern formation. The figure shown about the handling method of the image data by the side of a signal flow. The process figure shown about the handling method of image data. The schematic diagram which shows the nozzle arrangement between each color of a line inkjet head. The schematic diagram which shows the nozzle arrangement between each color of a line inkjet head. The figure which shows the row of a line inkjet head. The figure which shows the recording dot formation process of a line inkjet head. The figure which shows the row of a line inkjet head. The figure which shows the recording dot formation process of a line inkjet head. The figure which shows an example of the display on the operation panel which prompts selection of pixel recording density. The schematic diagram of pattern formation at the time of 200 dpi selection.

(This embodiment)
Hereinafter, embodiments will be described with reference to FIGS.

  Hereinafter, embodiments in which the present invention is applied to a color multifunction peripheral will be described. FIG. 1 schematically shows a general system configuration related to an MFP (multifunction peripheral) using an inkjet image forming apparatus.

  The multifunction device 100 includes a main control unit 101, a scanner unit 102, a printer unit 103, and an operation panel 104.

  A shared bus 111 shown in FIG. 1 connects CPUs (Central Processing Units) and the like to be described later, whereby program I / O transfer via the CPU or a peripheral device controls the bus as a bus master, and directly to a memory or the like. Data transfer by the accessing bus master is possible.

  The main control unit 101 includes a main CPU 110, a storage unit 112, an image processing unit 116, a page memory control unit 117, and a page memory 118.

  The main CPU 110 controls the entire main control unit 101.

  The storage unit 112 performs bidirectional communication between the main CPU 110 and a printer CPU 130 of the printer unit 103 described later, and stores a control program and various data for the main CPU 110. The storage unit 112 is an aggregate of a read-only memory (hereinafter referred to as ROM) and a rewritable memory (hereinafter referred to as RAM), and a process of performing the procedure of the embodiment together with a program and fixed data for performing the procedure of the present embodiment. Stores data that is generated or changed by.

  The image processing unit 116 performs image processing. The page memory control unit 117 stores or reads out image information in the page memory 118. The page memory 118 has an area where image information for a plurality of pages can be stored, and is formed so that data obtained by compressing image information from the scanner unit 102 can be stored for each page.

  The operation panel 104 includes various operation keys 141, a liquid crystal display unit 142 having soft keys (touch panel), and a panel CPU 140 to which these are connected, and a user performs an operation for changing parameters, which will be described later. Panel CPU 140 is connected to main CPU 110. Various commands are input from the operation keys 141 or the soft keys of the liquid crystal display unit 142 and transmitted from the panel CPU 140 to the main CPU 110.

  A scanner unit 102, which is an image reading unit, is connected to the main CPU 110, and under the control of the scanner unit 120, controls the scanner unit 102, a storage unit 122 that stores a control program and various data, and a document for reading documents and the like. A CCD driver 123 that drives a line sensor such as a CCD; a scanning motor driver 124 that controls the rotation of a scanning motor that moves a carriage (not shown) carrying a line sensor, an exposure lamp, a mirror, and the like; an image recognition unit 125; And an image correction unit 126.

  The printer unit 103 illustrated in FIG. 1 has, for example, a conventionally known configuration, and includes a printer CPU 130, a storage unit 132, an inkjet engine 133, a head unit control unit 134, a conveyance control unit 135, and a process control unit 136. The well-known configuration described below is not shown.

The printer CPU 130 is connected to the main CPU and controls the entire printer unit 103 under the control of the printer CPU 130.
The storage unit 132 stores a control program and various data.
The ink jet engine uses, for example, an element (piezo element) that is deformed by applying a voltage, the ink storage space in the head is increased / decreased by the deformation, and ink droplets are ejected by this pressure.

  The head unit control unit 134 drives a head unit having a plurality of nozzles, and controls landing points in the main scanning direction.

  The conveyance control unit 135 controls drive motors of various rollers to control conveyance of a recording medium accommodated in a known paper cassette from the paper cassette along the paper conveyance path.

  The process control unit 136 controls a known pressurizer, head unit control unit, and conveyance control unit, and adjusts the conveyance of the recording medium from the ejection of ink droplets according to the input image data.

  Hereinafter, image formation of the MFP 100 having the above-described configuration will be briefly described.

  FIG. 2 is a cross-sectional view illustrating a schematic configuration of an example of a printer unit.

  As shown in this figure, the recording medium is supplied to the printer unit 103 from a paper feed roller (not shown). Further, the main CPU 110 that controls the MFP 100 gives an image formation command according to the image data to the printer CPU 130. The recording medium 201 is wound around a rotating recording medium conveyance roller 202 and is fixed to the recording medium conveyance roller 202 by a fixed roller 203 while being conveyed in the conveyance direction indicated by an arrow, for example, Y (yellow), M An image is formed by ink droplets ejected from the head unit 204 having (magenta), C (cyan), and K (black) inkjet nozzles. This head unit 204 has nozzles for ejecting ink droplets corresponding to a plurality of ink storage chambers in the main scanning direction, and while the recording medium is conveyed by one rotation in the sub-scanning direction as shown in FIG. The nozzle moves by 42 μm (corresponding to one dot of 600 dpi) in the main scanning direction, and at the moved position, the nozzle discharges ink onto the recording medium to form an image.

  In this embodiment, the image formation uses a 600 dpi (dot per inch) engine to create a houndstooth pattern equivalent to 420 dpi.

  FIG. 4 is a schematic diagram for realizing 420 dpi by switching ON (ink ejection) and OFF (ink non-ejection) for each pixel of ink. After turning off pixels with grid-like hatching, the pixels that are turned on eject ink droplets along the center as shown by the black circle, and the direction indicated by the diagonal lattice as the reproduction density increases The printer CPU gives an instruction to enlarge the image point.

  FIG. 5 is a diagram illustrating a method for handling image data on the signal flow side with respect to the staggered arrangement on the image recording side. In general, it is most efficient for a digital imaging device to handle rasterized images in a grid pattern. This is the case, for example, when an image read by a scanner or the like is recorded by an image recording apparatus, or when a document is handled as an image converted into bitmap data by a RIP (Raster Image Processor), for example, software RIP as a printer.

  In the embodiment introduced here, a processing block as close to the engine as possible, that is, before gradation processing-specifically, other processing such as gamma conversion strongly related to gradation processing is also included in this gradation processing--600 × 300 dpi By performing the conversion, the 600 × 300 dpi conversion is performed while the symmetry of the 600 dpi image is ensured, and finally a symmetrical 420 dpi recording is realized.

  FIG. 5A shows 600 dpi image data subjected to upstream processing in the block shown in FIG. 2, and FIG. 5B shows how the resolution is converted to 600 × 300 dpi. It can be seen that the lines in the sub-scanning direction in the main scanning direction are to be converted in units of two pixels in each of the odd lines and the even lines. This shift is shifted so as to synchronize with the phase of the staggered 420 dpi recording shown in FIG. Next, the image internally converted in FIG. 5B is converted into a 600 × 300 dpi image that is easy to handle as data processing for digital processing shown in FIG. 5C. Thereafter, after performing gradation processing to be described later, the data arrangement is reconfigured by the driver (see FIG. 6) so that the staggered 420 dpi recording is performed, and the recording shown in FIG. 5D is performed.

  FIG. 6 is a process diagram showing the image data handling method for the staggered arrangement on the image recording side. When generating a houndstooth pattern, as shown in the process block diagram of this figure, after performing resolution conversion 302 after processing 301 such as compression / decompression, γ correction 303, 5-value halftoning 304, driver Through 305, image data is output to the engine 306, and position designation for realizing staggered arrangement is performed.

  7 and 8 show a part of the relative positional relationship of the nozzle arrangement between the colors ((C: cyan), (K: black), (M: magenta), (Y: yellow)) of the line inkjet head. It is shown. FIG. 7 shows an example in which the relative nozzle position between the colors is 600 dpi. In the example of FIG. 8, it is assumed that the nozzles are arranged at intervals of 150 dpi corresponding to the length corresponding to the effective maximum print width of the recording medium. By shifting the position of the head in the nozzle arrangement direction by 600 dpi for each pass recording and repeating this four times, an image of 600 dpi can be recorded in the nozzle arrangement direction. For example, as shown in FIG. 3, while the head unit moves on the recording medium in the main scanning direction, ink is ejected four times and recording is performed four times. In the direction perpendicular to the nozzle alignment direction (paper transport direction), a signal with the required resolution can be formed by controlling the drive signal. Thus, staggered recording can be realized by shifting the recording timing by 600 dpi and controlling each pass with a drive signal of 300 dpi.

  As described above, in FIG. 7 to FIG. 8, the head arrangement order is CKMY, but this is an example, and another arbitrary arrangement order may be used.

  In the case of ink-jet recording, depending on the type of recording medium, even if the paper stretches locally due to the relative relationship of the recording position of the ink on the medium, even if the head and paper transport are physically correctly controlled, the medium Deviation occurs in the landing position of the ink recorded on the recording medium, and this may cause noise such as visualization of white stripes and deterioration of graininess due to pattern deviation.

  When all the colors are recorded in the same row in the first pass in the first pass as in the conventional method, the remaining three pixels in the nozzle alignment direction 600 dpi are completely blank. In such a recording, if four colors of ink are printed locally in the same row, the paper is stretched and shifted to the landing position of the ink during the remaining two to four passes of recording. May occur, causing streaks and the like. This is especially true for plain paper and recycled paper.

  In order to cope with this, in the present embodiment, the above problem is solved by changing the relative positional relationship of the nozzle arrangement between the colors of the line inkjet head. For example, FIG. 7 shows an example in which the four color heads are shifted by 600 dpi in the nozzle arrangement direction. Note that the order of the colors may be any combination as long as the landing points of the respective colors of 600 dpi are shifted.

  In FIG. 8, the heads are divided into two systems, C and M are set to the same position in the nozzle arrangement direction, and K and Y are shifted from the C and M heads by 600 dpi in the nozzle arrangement direction. is there. Similarly, the order of the colors does not matter.

  FIG. 9 and FIG. 10 show examples in which the phases of all four colors of the staggered recording are adjusted in the head configuration shown in FIG. 7 and all four colors are recorded at the same staggered position. FIG. 9 shows the arrangement of the heads, and FIG. 10 shows how recording dots are formed each time the number of passes is repeated.

  FIG. 11 and FIG. 12 show actual recording examples in which the four colors are divided into two colors in the head configuration shown in FIG. 8 and the phases of the staggered recording positions are made different from each other. FIG. 11 shows the arrangement of the heads, and FIG. 12 shows how recording dots are formed each time the number of passes is repeated.

  From FIG. 10 and FIG. 12, it can be seen that a large amount of ink of a plurality of colors is not concentrated and ejected between the first and second passes at locally biased positions on the medium. In addition, there is no wide blank area of 600 dpi and a width of 3 pixels. Accordingly, it becomes difficult for the deviation of the physical landing position of the ink actually recorded on the medium due to the elongation of the paper to be generated, and it is possible to suppress the occurrence of unevenness of the streaks or the like.

  Further, in this embodiment, when the recording density is instructed on the printer driver or the operation panel, a screen for prompting selection of the recording density to be used again for printing appears as shown in FIG.

  For example, when 200 dpi is selected here, an image dot formation pattern as shown in the schematic diagram of FIG. 14 is switched between ON (ink ejection) and OFF (ink non-ejection) for each pixel of ink to realize 200 dpi. . In this case, similarly to the example shown in the schematic diagram of FIG. 4, after turning off the pixels that are lattice-shaped hatched, the pixels that are turned on are indicated by black circles along with the center position of the ink. A command is given from the printer CPU to eject droplets and enlarge the image point in the direction indicated by the diagonal grid as the reproduction density increases.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

100 ... MFP (MFP)
110 ... Main CPU
103: Printer unit 130 ... Printer CPU
131 ... Inkjet engine 132 ... Storage unit 133 ... Inkjet engine 134 ... Head unit control unit 135 ... Process control unit 202 ... Recording medium transport roller 204 ... Head unit 1300 ... Recording density switching instruction screen

Claims (3)

A head having a plurality of nozzles arranged at predetermined equal intervals and ejecting ink;
A plurality of heads having different color inks arranged such that the nozzle positions are shifted from each other by a predetermined interval, and a head unit that reciprocates in a main scanning direction perpendicular to the conveyance direction of the recording medium;
Transport means for transporting the recording medium in the transport direction each time recording is performed for one pass by moving the head unit while discharging the ink ;
When printing for one pass, printing is performed by shifting the printing timing by one pixel in the main scanning direction as compared with the printing of the previous pass, and by superimposing the ink of each color by printing for a plurality of passes. A head unit controller that forms
A color image forming apparatus comprising: The color image forming apparatus according to claim 1, further comprising an instruction unit that can specify switching of a pixel recording density, and switching a control method for shifting an ink ejection position according to the selected pixel recording density . The color image forming apparatus according to claim 1 , wherein the recording is performed while the amount of ink ejected by the nozzle is suppressed to be smaller than that in the case of recording by single pass .

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