Image forming apparatus

Abstract

To suppress deterioration of image quality of a print product due to image continuity at boundary nozzle positions.SOLUTION: The recording head includes a plurality of nozzle units, and end portions of two nozzle units in the plurality of nozzle units overlap each other in an overlapping region of a predetermined number of nozzles. The control unit determines nozzles corresponding to an image to be printed, and causes the recording head to eject ink from the nozzles. Then, the control unit sets boundary nozzle positions in the overlapping region, sets one side of the boundary nozzle positions in the main scanning direction as ink-not-discharging with respect to one of the two nozzle units, and sets the other side of the boundary nozzle positions in the main scanning direction as ink-not-discharging with respect to the other of the two nozzle units. Here, the boundary nozzle positions are set so as to be discontinuous in two lines adjacent in the sub-scanning direction.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] An inkjet type image forming device includes a plurality of nozzle rows, and the nozzle rows are arranged such that the ends of two nozzle rows overlap each other in the main scanning direction. A boundary nozzle position is set, and one of the two nozzle rows ejects ink to one side of the boundary nozzle position in the main scanning direction, and the other of the two nozzle rows ejects ink to the other side of the boundary nozzle position, and both nozzle rows eject ink at a small amount of ink to the boundary nozzle position.

[0003] Furthermore, if the border nozzle position is set fixedly in the main scanning direction, the border nozzle position will be noticeable in the print product, so in some image forming devices, the border nozzle position is made to vary continuously and linearly in the sub-scanning direction to prevent the border nozzle position from becoming noticeable (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-89629 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-described image forming apparatus, since the boundary nozzle positions change continuously, the boundary nozzle positions still stand out in the printed product, and the image quality of the printed product may not be good.

[0006] The present invention has been made in consideration of the above problems, and aims to provide an image forming device in which degradation of image quality of print products caused by image continuity at boundary nozzle positions is suppressed. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention includes a recording head having a plurality of nozzle units, which ejects ink corresponding to an image to be printed from nozzles arranged in the nozzle units, and a control unit which determines nozzles corresponding to the image to be printed and causes the recording head to eject ink from the nozzles. Ends of two nozzle units in the plurality of nozzle units overlap each other in an overlapping area of ​​a predetermined number of nozzles. The control unit sets a boundary nozzle position in the overlapping area, and for one of the two nozzle units, sets one side of the boundary nozzle position in the main scanning direction as non-ejection of ink, and for the other of the two nozzle units, sets the other side of the boundary nozzle position in the main scanning direction as non-ejection of ink. Here, the boundary nozzle position is set so as to be discontinuous in two adjacent lines in the sub-scanning direction. Effect of the Invention

[0008] According to the present invention, an image forming apparatus can be obtained in which degradation of image quality of print products caused by image continuity at boundary nozzle positions is suppressed.

[0009] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view illustrating the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing an example of the recording heads 1a, 1b, 1c, and 1d in the image forming apparatus 10 shown in FIG. [Diagram 3]FIG. 3 is a diagram illustrating an overlapping region of the nozzle units 11 of the recording heads 1a, 1b, 1c, and 1d in the image forming apparatus 10 shown in FIG. [Figure 4] FIG. 4 is a block diagram showing an electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram for explaining the fluctuation range of the boundary nozzle position (boundary fluctuation range). [Figure 6] FIG. 6 is a diagram showing an example of boundary nozzle positions for each line. [Figure 7] FIG. 7 is a diagram showing another example of the boundary nozzle positions for each line. [Figure 8] FIG. 8 is a diagram showing an example of dots formed by ink ejection in the case of the boundary nozzle position shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] 1 is a side view illustrating the internal mechanical configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus according to this embodiment is a device such as a printer, a copier, a facsimile machine, or a multifunction machine.

[0013] The image forming apparatus 10 shown in Fig. 1 includes a print engine 10a and a sheet conveying unit 10b. The print engine 10a physically forms a page image to be printed on a print sheet (e.g., a print sheet). In this embodiment, the print engine 10a is a line-type inkjet print engine.

[0014] In this embodiment, print engine 10a includes line-type recording heads 1a to 1d corresponding to four ink colors, namely cyan, magenta, yellow, and black.

[0015] Fig. 2 is a plan view showing an example of the recording heads 1a, 1b, 1c, and 1d in the image forming apparatus 10 shown in Fig. 1. For example, as shown in Fig. 2, in this embodiment, each of the recording heads 1a, 1b, 1c, and 1d has a plurality of nozzle units 11 (three in this example). These nozzle units 11 are arranged along the main scanning direction and are detachable from the main body of the apparatus. Each of the recording heads 1a, 1b, 1c, and 1d ejects ink corresponding to an image to be printed from nozzles arranged in the nozzle unit 11.

[0016] Fig. 3 is a diagram illustrating an overlapping region of nozzle units 11 of recording heads 1a, 1b, 1c, and 1d in image forming apparatus 10 shown in Fig. 1. For example, as shown in Fig. 3, each nozzle unit 11 has nozzles 12 (one or more nozzle rows) arranged in the main scanning direction. In each of recording heads 1a, 1b, 1c, and 1d, ends of two adjacent nozzle units 11 in the multiple nozzle units 11 overlap each other in an overlapping region of a predetermined number of nozzles (seven nozzles 12 in Fig. 3).

[0017] The sheet transport section 10b transports the print sheet before printing to the print engine 10a along a predetermined transport path, and transports the print sheet after printing from the print engine 10a to a predetermined discharge destination (such as a discharge tray 10c).

[0018] The sheet conveying section 10b includes a main sheet conveying section 10b1 and a circulating sheet conveying section 10b2. In double-sided printing, the main sheet conveying section 10b1 conveys print sheets used for printing a page image on the first side to the print engine 10a, and the circulating sheet conveying section 10b2 conveys print sheets from the rear stage to the front stage of the print engine 10a while retaining a predetermined number of print sheets.

[0019] In this embodiment, the main sheet transport section 10b1 includes a circular transport belt 2 arranged opposite the print engine 10a for transporting the print sheet, a drive roller 3 and a driven roller 4 on which the transport belt 2 is suspended, an adhesion roller 5 that nips the print sheet together with the transport belt 2, and a pair of discharge rollers 6, 6a.

[0020] A driving roller 3 and a driven roller 4 rotate the conveyor belt 2. Then, the suction roller 5 nips the print sheet conveyed from paper feed cassettes 20-1 and 20-2 (described later), and the nipped print sheet is conveyed by the conveyor belt 2 to the printing positions of the recording heads 1a to 1d in order, and the recording heads 1a to 1d print images of each color. Then, after color printing is completed, the print sheet is discharged to a discharge tray 10c or the like by a pair of discharge rollers 6 and 6a.

[0021] Furthermore, the main sheet transport section 10b1 includes a plurality of paper feed cassettes 20-1, 20-2. The paper feed cassettes 20-1, 20-2 store print sheets SH1, SH2, and the lift plates 21, 24 push the print sheets SH1, SH2 upward to abut against the pickup rollers 22, 25. The print sheets SH1, SH2 placed on the paper feed cassettes 20-1, 20-2 are picked up one by one from above by the pickup rollers 22, 25 to the paper feed rollers 23, 26. The paper feed rollers 23, 26 are rollers that transport the print sheets SH1, SH2, which are fed from the paper feed cassettes 20-1, 20-2 by the pickup rollers 22, 25, one by one onto the transport path. The transport roller 27 is a transport roller on the transport path common to the print sheets SH1, SH2 transported from the paper feed cassettes 20-1, 20-2.

[0022] The circulating sheet transport unit 10b2 returns the print sheet from a predetermined position downstream of the print engine 10a to a predetermined position upstream of the print engine 10a (here, a predetermined position upstream of a line sensor 31 described later) during double-sided printing. The circulating sheet transport unit 10b2 includes a transport roller 41 and a switchback transport path 41a that reverses the traveling direction of the print sheet to switch the side of the print sheet facing the print engine 10a from the first side to the second side.

[0023] The image forming apparatus 10 further includes a line sensor 31 and a sheet detection sensor 32. The line sensor 31 is an optical sensor that is arranged along a direction perpendicular to the conveying direction of the print sheet and detects the positions of both end edges (both side edges) of the print sheet. For example, the line sensor 31 is a CIS (Contact Image Sensor). In this embodiment, the line sensor 31 is arranged between the registration roller 28 and the print engine 10a. The sheet detection sensor 32 is an optical sensor that detects that the leading ends of the print sheets SH1 and SH2 have passed a predetermined position on the conveying path. The line sensor 31 detects the positions of both end edges of the print sheets when the leading ends of the print sheets SH1 and SH2 are detected by the sheet detection sensor 32.

[0024] For example, as shown in FIG. 1, the print engine 10a is disposed above or below the transport path of the print sheet (here, the upper side), the line sensor 31 is disposed above or below the transport path of the print sheet (here, the lower side), and the circulating sheet transport section 10b2 transports the print sheet by switching back from the downstream side of the print engine 10a to the upstream side of the line sensor 31.

[0025] Fig. 4 is a block diagram showing the electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. As shown in Fig. 4, the image forming apparatus 10 includes an image output unit 71 having the mechanical configuration as shown in Fig. 1 and Fig. 2, as well as an operation panel 72, a storage device 73, an image reader 74, and a controller 75.

[0026] The operation panel 72 is arranged on the surface of the housing of the image forming apparatus 10 and includes a display device 72a such as an LCD display, and an input device 72b such as hard keys or a touch panel. The display device 72a displays various messages to the user, and the input device 72b accepts user operations.

[0027] The storage device 73 is a non-volatile storage device (such as a flash memory or a hard disk drive) that stores data, programs, and the like required for controlling the image forming apparatus 10.

[0028] The image reading device 74 includes a platen glass and an automatic document feeder, and optically reads the image of a document placed on the platen glass or a document transported by the automatic document feeder, and generates image data of that image.

[0029] The controller 75 includes a computer that executes software processing according to a program, and an ASIC (Application Specific Integrated Circuit) that executes predetermined hardware processing, and operates as various processing units. The computer includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and operates as various processing units (together with the ASIC as necessary) by loading a program stored in the ROM, storage device 73, etc., into the RAM and executing it on the CPU. Here, the controller 75 operates as a control unit 81, an image processing unit 82, and a correction processing unit 83.

[0030] The control unit 81 controls the image output unit 71 (print engine 10a, sheet conveying unit 10b, etc.) to execute a print job requested by a user. In this embodiment, the control unit 81 causes the image processing unit 82 to execute a predetermined image processing, and controls the print engine 10a (nozzle unit 11) to eject ink to form a print image on a print sheet. The image processing unit 82 executes predetermined image processing such as RIP (Raster Image Processing), color conversion, and halftoning on the image data of the image to be printed on the print sheet. Specifically, the control unit 81 causes the print engine 10a to print a user original image based on the print image data specified by the user.

[0031] In this embodiment, the control unit 81 has an automatic centering function that (a) specifies the center position of the print sheet as the actual sheet center position based on the positions of both edge portions of the print sheet detected by the line sensor 31, and (b) adjusts the center position of the image to be printed based on the actual sheet center position, and executes the automatic centering function as hardware processing. Specifically, in the automatic centering function, the control unit 81 changes the drawing position of the image to be printed along the main scanning direction by the difference between the reference center position of the print engine 10a and the actual sheet center position. In this embodiment, the nozzles in the recording heads 1a to 1d do not move, so the nozzles corresponding to each pixel in the image to be printed are changed according to the drawing position of the image to be printed.

[0032] In this way, the control unit 81 determines the nozzles corresponding to the image to be printed (the nozzles corresponding to each pixel of the image) (here, according to the position on the print sheet), and causes the recording heads 1a to 1d to eject ink from the nozzles.

[0033] FIG. 5 is a diagram for explaining the variation range (boundary variation range) of the boundary nozzle position. Furthermore, as shown in FIG. 5, for example, the control unit 81 sets the boundary nozzle position 12b in the above-mentioned overlapping region of the nozzle unit 11, and for one of the above-mentioned two nozzle units, one side of the boundary nozzle position in the main scanning direction is set to non-eject ink, and for the other of the two nozzle units, the other side of the boundary nozzle position in the main scanning direction is set to non-eject ink, thereby maintaining the continuity of the formed image. In FIG. 5, a boundary variation range of 5 pixels (5 nozzles) is set, and the boundary nozzle position 12b varies within the boundary variation range depending on the position in the sub-scanning direction (i.e., the line). Also, in FIG. 5, the nozzle 12n1 on one side of the boundary nozzle position 12b in the nozzle unit 11A is set to be a nozzle that does not eject ink, and the nozzles 12n1 and 12n2 on the other side of the boundary nozzle position 12b in the nozzle unit 11B are set to be nozzles that do not eject ink.

[0034] Here, nozzle 12n1 is a nozzle that is set as a non-ink ejection nozzle according to the boundary nozzle position 12b, and nozzle 12n2 is a nozzle that is fixedly set as a non-ink ejection nozzle regardless of the boundary nozzle position 12b. In other words, the nozzles are fixedly set as non-ink ejection nozzles by the difference (2 in FIG. 5) between the number of nozzles in the overlapping region (7 in FIG. 5) and the number of nozzles in the boundary fluctuation range (5 in FIG. 5). Note that nozzles other than nozzles 12n1 and 12n2 are permitted to eject ink.

[0035] Furthermore, the boundary nozzle positions are set so as to be discontinuous between two adjacent lines in the sub-scanning direction.

[0036] Fig. 6 is a diagram showing an example of the boundary nozzle position for each line. For example, the control unit 81 may refer to a table showing the boundary nozzle positions for a predetermined number of lines (five lines in Fig. 6) and repeatedly set the boundary nozzle positions so that the two adjacent lines in the sub-scanning direction are discontinuous. The table is stored in advance in the storage device 73 or the like. In Fig. 6, the boundary variation range is nine pixels (nine nozzles), and in the five lines, the boundary nozzle position changes by two pixels (two nozzles) for each line.

[0037] In the example shown in FIG. 6, a table showing the boundary nozzle positions for five lines is used, but a table for another number of lines, such as 32 lines, may also be used.

[0038] FIG. 7 is a diagram showing another example of the boundary nozzle position for each line. For example, the control unit 81 may repeatedly set the boundary nozzle position so that two adjacent lines in the sub-scanning direction are discontinuous by calculating a predetermined calculation formula for the line number of each line. In FIG. 7, the boundary fluctuation range is 9 pixels (9 nozzles), and if the line number is n, the boundary nozzle position is calculated by mod(a×n, x). Here, mod(n1, n2) is a function (calculation formula) showing the remainder when n1 is divided by n2, x is the number of pixels (number of nozzles) in the boundary fluctuation range (here, x=9), and a is a coefficient (here, a=4). FIG. 8 is a diagram showing an example of dots formed by ink ejection in the case of the boundary nozzle position shown in FIG. 7. In FIG. 8, hatched dots are dots formed by one nozzle unit 11A, and non-hatched dots are dots formed by the other nozzle unit 11B.

[0039] Returning to Fig. 4, the correction processing unit 83 executes a correction process to reduce the amount of ink droplets ejected from the two nozzle units 11A, 11B at the boundary nozzle position. Specifically, in the correction process, the correction processing unit 83 identifies pixels in the image to be printed that correspond to the nozzles at the boundary nozzle position in the two nozzle units 11A, 11B, and corrects the pixel values ​​to reduce the amount of ink droplets ejected from those nozzles. This reduces the diameter of the dots at the boundary nozzle position, as shown in Fig. 8.

[0040] Here, for example, as shown in FIG. 5, when the boundary nozzle position 12b of one nozzle unit 11A is different from the boundary nozzle position 12b of the other nozzle unit 11B, the correction amount of the pixel value (i.e., the pixel value after correction) may be set according to the deviation between the two in the main scanning direction.

[0041] In this case, the pixel values ​​corresponding to each nozzle are appropriately determined by, for example, interpolation of pixel values ​​of pixels in the image to be printed, so that the pixel values ​​corresponding to each nozzle at boundary nozzle position 12b may be derived using a conversion table in which the pixel value for boundary nozzle position 12b of nozzle unit 11A and the pixel value for boundary nozzle position 12b of the other nozzle unit 11B are input, and the corrected pixel value for boundary nozzle position 12b of nozzle unit 11A and the corrected pixel value for boundary nozzle position 12b of the other nozzle unit 11B are output.

[0042] Next, the operation of the image forming apparatus 10 will be described.

[0043] When the control unit 81 receives a print request, the image processing unit 82 executes image processing on the image specified by the print request to obtain image data of the image to be printed, and the image output unit 71 transports a print sheet and prints the image to be printed on the print sheet based on the image data.

[0044] At this time, the control unit 81 sets the boundary nozzle position for each line in each of the recording heads 1a, 1b, 1c, and 1d so that the overlapping areas of the nozzle units 11 are discontinuous between the lines as described above, identifies the pixel corresponding to the boundary nozzle position, and the correction processing unit 83 performs a correction process on the pixel and adjusts the pixel value so as to reduce the amount of ink droplet.The control unit 81 then controls each of the recording heads 1a, 1b, 1c, and 1d to eject ink from the nozzle corresponding to each pixel with the ink droplet amount corresponding to the pixel value of each pixel in the corrected image.

[0045] As described above, according to the above embodiment, the recording heads 1a, 1b, 1c, and 1d include a plurality of nozzle units 11, and eject ink corresponding to an image to be printed from the nozzles 12 arranged in the nozzle units 11. The control unit 81 determines the nozzles 12 corresponding to the image to be printed, and causes the recording heads 1a, 1b, 1c, and 1d to eject ink from the nozzles 12. The ends of two nozzle units 11 in the plurality of nozzle units 11 overlap with each other in an overlapping area of ​​a predetermined number of nozzles. Then, the control unit 81 sets a boundary nozzle position in the overlapping area, and for one of the two nozzle units, one side of the boundary nozzle position in the main scanning direction is set to be ink non-ejection, and for the other of the two nozzle units, the other side of the boundary nozzle position in the main scanning direction is set to be ink non-ejection. Here, the boundary nozzle position is set so as to be discontinuous in two adjacent lines in the sub-scanning direction.

[0046] As a result, the dot positions corresponding to the boundary nozzle positions in the printed product become discontinuous, making it difficult to visually recognize the pixels corresponding to the boundary nozzle positions, and reducing the degradation of the image quality of the printed product due to the continuity of the boundary nozzle positions. For example, when an image of a constant density was printed with a resolution of 600 dpi and a boundary fluctuation width of 10 pixels or 20 pixels, the boundary nozzle positions were not visually recognized in the printed product.

[0047] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, such changes and modifications are intended to be included within the scope of the claims. [Industrial Applicability]

[0048] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0049] 1a~1d Recording head 10 Image forming device 11 Nozzle unit 12 Nozzles 81 Control Unit 83 Correction processing section

Claims

1. a recording head including a plurality of nozzle units, the recording head ejecting ink corresponding to an image to be printed from nozzles arranged in the nozzle units; a control unit that determines nozzles corresponding to the image to be printed and causes the recording head to eject ink from the nozzles; end portions of two nozzle units among the plurality of nozzle units overlap each other in an overlap region of a predetermined number of nozzles, the control unit sets a boundary nozzle position in the overlapping region, and for one of the two nozzle units, sets one side of the boundary nozzle position in the main scanning direction to be non-ejecting ink, and for the other of the two nozzle units, sets the other side of the boundary nozzle position in the main scanning direction to be non-ejecting ink; the boundary nozzle position is set so as to be discontinuous between two adjacent lines in the sub-scanning direction; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the control unit repeatedly sets the boundary nozzle positions so as to be discontinuous between two adjacent lines in the sub-scanning direction by referring to a table indicating the boundary nozzle positions for a predetermined number of lines.

3. 2. The image forming apparatus according to claim 1, wherein the control unit repeatedly sets the boundary nozzle position so that two adjacent lines in the sub-scanning direction are discontinuous by calculating a predetermined arithmetic expression for the line number of the line.

4. 4. The image forming apparatus according to claim 1, further comprising a correction processing unit that executes a correction process to reduce the amount of ink droplets ejected from the two nozzle units at the boundary nozzle position.

Images