Inkjet image forming device

Abstract

To prevent white stripes and density unevenness from occurring.SOLUTION: An inkjet image forming device 1, which has a plurality of line head rows of the same color and can select a high-resolution printing mode and a low-resolution / high-speed printing mode, comprises a printing data sorting part 71 that when the high-speed printing mode is set, sorts printing data showing the number of drops that are discharged from a nozzle into the plurality of line head rows of the same color to create data on one pixel. The printing data sorting part 71 determines the number of drops on the basis of the number of drops, nozzle density property data, information on sub-scanning positions in printing data, nozzle density property in the printing data on adjacently arranged nozzles, and the number of drops.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inkjet image forming apparatus that prevents the occurrence of white streaks and density unevenness. [Background technology]

[0002] A line-type inkjet image forming apparatus performs printing by ejecting ink from an inkjet head based on image data onto paper that is transported by a belt transport unit provided below the inkjet head.

[0003] Patent document 1 discloses technology relating to a printing device in which print modes are managed to enable selection of a high-speed print mode or a high-quality print mode depending on information read from a memory contained in an ink cartridge, and which generates print data that reproduces desired pixels for each of two nozzle rows, thereby improving print speed by expanding the range printed at one time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-130755 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the printing device described in Patent Document 1 does not take into account the differences in characteristics between the nozzles in the two nozzle rows, and there is a problem that white streaks and uneven density can occur depending on the characteristics of adjacent nozzles, reducing image quality.

[0006] The present invention has been made in view of the above problems, and has an object to provide an inkjet image forming apparatus that prevents the occurrence of white streaks and density unevenness. [Means for solving the problem]

[0007] In order to achieve the above object, the inkjet image forming apparatus according to the present invention is characterized in that: An inkjet image forming apparatus having a plurality of line head rows of the same color and capable of selecting a high-resolution printing mode and a low-resolution high-speed printing mode, a print data distribution unit that, when the high-speed print mode is set, divides and creates print data indicating the number of drops to be ejected from a nozzle onto one pixel among the plurality of line head rows of the same color; The print data allocation unit determines the number of drops based on the number of drops, nozzle density characteristic data, sub-scanning position information of the print data, and the nozzle density characteristics and the number of drops of the print data of adjacent nozzles. The point is... Effect of the Invention

[0008] According to the features of the inkjet image forming apparatus of the present invention, the occurrence of white streaks and density unevenness can be prevented. [Brief description of the drawings]

[0009]

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Figure 5

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings. However, it should be noted that the drawings are schematic and may differ from the actual product. In addition, the drawings may include parts with different dimensional relationships and ratios.

[0011] The embodiments described below are merely examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the arrangement of each component to that described below. Various modifications can be made to the technical idea of ​​the present invention within the scope of the claims.

[0012] (Configuration of Inkjet Image Forming Apparatus 1) An embodiment of an inkjet image forming apparatus 1 according to the present invention will be described in detail below with reference to the accompanying drawings.

[0013] FIG. 1 is a schematic diagram of an inkjet image forming apparatus 1 according to an embodiment of the present invention.

[0014] In the following description, the front side of the paper in Fig. 1 where the user is positioned is referred to as the left direction, and the back side of the paper is referred to as the right direction. Furthermore, in Fig. 1, the up and down directions from the user's perspective are referred to as the up and down directions. Furthermore, the path indicated by the dashed line in Fig. 1 is the transport path R along which paper PA, which is the print medium, is transported. The transport direction of paper PA is referred to as the front-rear direction. In the following description, upstream means the forward direction, and downstream means the backward direction.

[0015] As shown in FIG. 1, the inkjet image forming apparatus 1 includes a paper feed section 2, a suction transport section 3, a printing section 4, and a paper discharge section 6.

[0016] The paper feed unit 2 feeds paper PA, which is a print medium, and includes a paper feed tray 11, a paper feed roller 12, and a registration roller 13.

[0017] The paper feed tray 11 is stacked with paper PA to be used for printing.

[0018] The paper feed roller 12 picks up the paper PA stacked on the paper feed tray 11 one by one and transports the paper PA toward the registration rollers 13. The paper feed roller 12 is disposed above the paper feed tray 11. The paper feed roller 12 is driven to rotate by a motor (not shown).

[0019] The registration rollers 13 temporarily stop the paper PA conveyed by the paper feed rollers 12, and then convey the paper PA toward the suction conveying section 3. The registration rollers 13 are disposed downstream of the paper feed rollers 12. The registration rollers 13 are rotated by a motor (not shown).

[0020] The suction transport section 3 transports the paper PA transported from the registration rollers 13 toward the printing section 4 and the paper discharge section 6. The suction transport section 3 includes a transport belt 21, a drive roller 22, driven rollers 23-25, a belt drive motor 26, a platen plate 27, and a suction fan 28.

[0021] The conveyor belt 21 is a circular endless belt stretched around a drive roller 22 and driven rollers 23 to 25. The conveyor belt 21 has intake holes, which are through holes for attracting and holding the paper sheet PA, formed at predetermined intervals along the conveying direction of the conveyor belt 21. The conveyor belt 21 attracts and holds the paper sheet PA on the conveyor belt 21 by a negative pressure (adsorption force) generated in the intake holes by driving the suction fan 28.

[0022] 1 by being rotated by the driving roller 22. As a result, the conveyor belt 21 moves endlessly to convey the paper PA to the right.

[0023] The conveyor belt 21 is stretched around the driving roller 22 and the driven rollers 23 to 25. The driving roller 22 is rotated by a belt driving motor 26 to rotate the conveyor belt 21. The driven rollers 23 to 25 are driven by the driving roller 22 via the conveyor belt 21. The driven roller 23 is disposed at substantially the same height as the driving roller 22 and spaced a predetermined distance from the driving roller 22 in the left-right direction. The driven rollers 24 and 25 are disposed below the driving roller 22 and the driven roller 23, spaced a predetermined distance from each other in the left-right direction, and at substantially the same height.

[0024] The belt drive motor 26 drives the drive roller 22 to rotate.

[0025] The platen plate 27 is disposed below the conveyor belt 21 between the drive roller 22 and the driven roller 23, and supports the lower surface of the conveyor belt 21 in a slidable manner.

[0026] The suction fan 28 is disposed below the platen 27 and generates a downward airflow.

[0027] The printing unit 4 prints on the paper PA transported by the suction transport unit 3. The printing unit 4 is provided above the suction transport unit 3. The printing unit 4 is fixed inside a housing (not shown) of the inkjet image forming apparatus 1. The printing unit 4 includes black (K) inkjet heads 31Ka, 31Kb, a cyan (C) inkjet head 31C, a magenta (M) inkjet head 31M, a yellow (Y) inkjet head 31Y, a gray (G) inkjet head 31G, and a head holder 32.

[0028] FIG. 2 is a plan view of the inkjet head 31 provided in the inkjet image forming apparatus 1 according to the present invention.

[0029] As shown in FIG. 2, inkjet heads 31Ka, 31Kb, 31C, 31M, 31Y, and 31G each have two rows of heads with nozzles that eject ink, arranged in a grid pattern. By ejecting ink from the nozzles onto paper PA that is being transported while being sucked by suction and transport unit 3, printing can be performed without gaps in the main scanning direction (left and right direction).

[0030] In addition, inkjet head 31Ka and inkjet head 31Kb are inkjet heads that eject the same black (K) ink, and are arranged so that the nozzle positions are shifted by half a pitch in the left-right direction (main scanning direction). During low-resolution printing, ink is ejected from only one of inkjet head 31Ka and inkjet head 31Kb, and during high-resolution printing, ink is ejected from both.

[0031] The head holder 32 holds the inkjet head 31 above the suction transport unit 3. The head holder 32 is formed in a hollow, substantially rectangular parallelepiped shape.

[0032] The paper discharge section 6 discharges the paper PA printed by the printing section 4.

[0033] The control unit 7 controls the paper feed unit 2, the suction transport unit 3, the paper discharge unit 6, and the like that are provided in the inkjet image forming apparatus 1.

[0034] Furthermore, the control unit 7 has a print data distribution unit 71 as a function thereof.

[0035] When the high-speed printing mode is set, i.e., when printing is performed using both inkjet head 31Ka and inkjet head 31Kb, the print data distribution unit 71 divides and creates print data indicating the number of drops to be ejected from a nozzle onto one pixel for inkjet head 31Ka and inkjet head 31Kb, which are multiple line heads of the same color.

[0036] At this time, the print data allocation unit 71 determines the number of drops based on the number of drops, the nozzle density characteristic data, sub-scanning position information of the print data, and the nozzle density characteristics and number of drops of the print data of adjacent nozzles.

[0037] For example, if the maximum drop number is 6 drops and the drop data is 4 drops or 6 drops, the print data allocation unit 71 allocates 1 / 2 of the drop data to each of the inkjet heads 31Ka and 31Kb so as to allocate the data evenly to the inkjet heads 31Ka and 31Kb.

[0038] When the drop data is 5 drops and the ejection volume of the nozzle adjacent to the high ejection nozzle NzA is 3 drops or more, the print data allocation unit 71 takes into account the size of the dots of the adjacent nozzles and sets the image data of the head on the high ejection nozzle NzA side to 2 drops and the drop data of the head on the low ejection nozzle NzB side to 3 drops.

[0039] When the drop data is 5 drops and the ejection volume of the nozzle adjacent to the high ejection nozzle NzA is 2 drops or less, in order to complement the dots of the adjacent nozzle, the print data allocation unit 71 sets the drop data of the inkjet head 31Ka to 3 drops and the drop data of the inkjet head 31Kb to 2 drops.

[0040] When the drop data is 3 drops or less and there is no ejection to the pixel in front of the inkjet heads 31Ka and 31Kb, the print data allocation unit 71 writes the drop data for the head on the high ejection nozzle NzA side.

[0041] When the drop data is 3 drops or less and ejection is to occur on pixels in front of the inkjet heads 31Ka, 31Kb, the print data allocation unit 71 writes the drop data to the pixels in front of the inkjet heads 31Ka, 31Kb so as to arrange them in a staggered pattern.

[0042] (Function of Inkjet Image Forming Apparatus 1) FIG. 3 is a flowchart showing the operation of the inkjet image forming apparatus 1 according to the embodiment of the present invention.

[0043] As shown in FIG. 3, in step S101, the control unit 7 acquires image data to be printed that is output from a computer or the like connected via a network (not shown), or image data to be printed that is output by reading an original image in an original reading device (not shown).

[0044] In step S103, the control unit 7 performs halftone processing on the image data of each color of K, C, M, Y, and G based on the image data to generate drop data for each color. As the halftone processing, an error diffusion process or a dither mask process is used. The drop data is data that indicates the number of ink drops for each print dot (print pixel) of each color.

[0045] In step S105, the control unit 7 executes a print data creation process to generate print data for controlling the inkjet heads 31Ka, 31Kb, 31C, 31M, 31Y, and 31G based on the drop data of each color.

[0046] In step S107, the control unit 7 executes printing based on the print data.

[0047] FIG. 4 is a flowchart showing details of the print data creation process in the flowchart shown in FIG. 3 in the inkjet image forming apparatus 1 according to the embodiment of the present invention.

[0048] In step S201, if there is an unread pixel in the image data (YES), the print data sorting unit 71 of the control unit 7 reads one pixel of the image data.

[0049] In step S203, the print data distribution unit 71 acquires the output nozzle positions of the inkjet heads 31Ka and 31Kb.

[0050] In step S205, the print data allocation unit 71 acquires density data indicating the density characteristics of nozzles in the inkjet heads 31Ka and 31Kb that output to the same pixel. Here, the high discharge nozzle is designated as NzA, and the low discharge nozzle is designated as NzB. The nozzle density characteristics may vary depending on the head position and the amount of adjustment within the head and between the heads, and the head to which the nozzle expected to discharge a large amount belongs. This shows such characteristics.

[0051] In step S207, the print data sorting unit 71 determines whether the drop data is 3 drops or less.

[0052] If it is determined that the drop data exceeds 3 drops (step S207; NO), in step S209, the print data sorting unit 71 determines whether the drop data is 5 drops or not.

[0053] If it is determined that the drop data is not 5 drops (step S209; NO), the drop data will be 4 drops or 6 drops, so in step S211, the print data allocation unit 71 writes 1 / 2 of the drop data to each of the inkjet heads 31Ka and 31Kb as new drop data so as to allocate it evenly to the inkjet heads 31Ka and 31Kb.

[0054] FIG. 5A is a diagram showing a schematic example of an ink landing state (dots) when half of the drop data is assigned to 31Ka and 31Kb.

[0055] As shown in Figure 5(a), when the drop data is 4 drops or 6 drops, it is evenly allocated to inkjet heads 31Ka and 31Kb, and dots 31Ka1 formed by ink ejected from inkjet head 31Ka and dots 31Kb1 formed by ink ejected from inkjet head 31Kb are printed without any gaps and without forming white streaks or the like.

[0056] On the other hand, if it is determined that the drop data is 5 drops (step S209; YES), then in step S213, the print data allocation unit 71 determines whether the discharge amount of the nozzle adjacent to the high discharge nozzle NzA is 3 drops or more or 2 drops or less.

[0057] If the ejection amount of the nozzle adjacent to the high ejection nozzle NzA is 3 drops or more (step S213; 3 drops or more), taking into account the size of the dots of the adjacent nozzles, in step S215, the print data allocation unit 71 sets the image data of the head on the high ejection nozzle NzA side to 2 drops, and the drop data of the head on the low ejection nozzle NzB side to 3 drops.

[0058] FIG. 5(b) is a diagram schematically showing an example of the ink landing state (dots) when the image data of the head on the high ejection nozzle NzA side is set to 2 drops and the drop data of the head on the low ejection nozzle NzB side is set to 3 drops.

[0059] As shown in FIG. 5(b), when the drop data is 4 drops or 6 drops, since the image data of the head on the high ejection nozzle NzA side is set to 2 drops and the drop data of the head on the low ejection nozzle NzB side is set to 3 drops, the dot diameter of the dot 31Kb1 formed by the ink ejected from the inkjet head 31Kb is larger than the dot diameter of the dot 31Ka2 formed by the ink ejected from the inkjet head 31Ka, and the dots of the adjacent nozzles are printed without gaps in accordance with the size of the dots.

[0060] Also, when the ejection amount of the nozzle adjacent to the high ejection nozzle NzA is 2 drops or less (step S213; 2 drops or less), in order to complement the dots of the adjacent nozzle, in step S217, the print data distribution unit 71 sets the drop data of the inkjet head 31Ka to 3 drops and the drop data of the inkjet head 31Kb to 2 drops.

[0061] On the other hand, when it is determined that the drop data is 3 drops or less (step S207; YES), in step S221, the print data distribution unit 71 determines whether there is ejection at the pixels in front of the inkjet heads 31Ka and 31Kb.

[0062] When it is determined that there is no ejection at the pixels in front of the inkjet heads 31Ka and 31Kb (step S221; NO), in step S223, the print data distribution unit 71 writes the drop data of the head with the high ejection nozzle on the NzA side.

[0063] On the other hand, if it is determined that ejection is occurring in the pixels in front of the inkjet heads 31Ka and 31Kb (step S221; YES), then in step S225, the print data allocation unit 71 writes drop data to the pixels in front of the inkjet heads 31Ka and 31Kb so as to be arranged in a houndstooth pattern.

[0064] FIG. 5C is a diagram showing an example of the landing state (dots) of ink when the drop data is three drops or less and ejection is performed on a pixel in the previous stage.

[0065] As shown in Figure 5 (c), when the drop data is three drops or less and there is ejection at the previous pixel, dots 31Ka3 formed by ink ejected from inkjet head 31Ka and dots 31Kb3 formed by ink ejected from inkjet head 31Kb are printed in a houndstooth pattern, thereby preventing the occurrence of white streaks even when the number of drops is small.

[0066] (Additional Note) This application discloses the following inventions.

[0067] (Appendix 1) An inkjet image forming apparatus having a plurality of line head rows of the same color and capable of selecting a high-resolution printing mode and a low-resolution high-speed printing mode, a print data distribution unit that, when the high-speed print mode is set, divides and creates print data indicating the number of drops to be ejected from a nozzle onto one pixel among the plurality of line head rows of the same color; The print data allocation unit determines the number of drops based on the number of drops, nozzle density characteristic data, sub-scanning position information of the print data, and the nozzle density characteristics and the number of drops of the print data of adjacent nozzles. 1. An ink-jet image forming apparatus comprising:

[0068] This makes it possible to determine the number of drops taking into consideration the difference in characteristics between the nozzles in the two nozzle rows, thereby making it possible to prevent the occurrence of white streaks and density unevenness and improve image quality. [Explanation of symbols]

[0069] 1. Inkjet image forming device 2 Paper feed section 3. Suction and transport section 4 Printing Department 6 Paper output section 7 Control section 31Ka, 31Kb, 31C, 31M, 31Y, 31G Inkjet head 32 Head Holder 71 Print data distribution unit

Claims

1. An inkjet image forming apparatus having a plurality of line head rows of the same color and capable of selecting a high-resolution printing mode and a low-resolution high-speed printing mode, a print data distribution unit that, when the high-speed print mode is set, divides and creates print data indicating the number of drops to be ejected from a nozzle onto one pixel among the plurality of line head rows of the same color; The print data allocation unit determines the number of drops based on the number of drops, nozzle density characteristic data, sub-scanning position information of the print data, and the nozzle density characteristics and the number of drops of the print data of adjacent nozzles.

1. An ink-jet image forming apparatus comprising:

Images