Image forming device

Abstract

In accordance with the position of a print sheet, a control unit (81) determines a nozzle corresponding to an image to print, and causes a recording head to eject ink from the nozzle. A correction processing unit (83) performs, in the above-mentioned image, correction processing corresponding to each of a plurality of ejection defect positions. The correction processing unit (83) uses recording heads (1a-1d) to print a test pattern, identifies an ejection defect position and an ejection defect type on the basis of a read image of said test pattern, and performs correction processing with the ejection defect position where the ejection defect type is misfiring being prioritized over the ejection defect position where the ejection defect type is ejection misdirection.

Description

[Technical Field]

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

[0002] One inkjet image forming device detects defective nozzles that are no longer able to eject ink normally among the nozzles in a recording head, and changes the ejection amount of adjacent dots based on the occurrence of defective nozzles (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-142807 Summary of the Invention [Problem to be solved by the invention]

[0004] When printing on cut paper, the state of paper transport varies for each paper, and the nozzles used to draw each pixel in the image to be printed may be determined depending on the position of the paper as it is transported (the position perpendicular to the transport direction). As mentioned above, when correcting the amount of ink ejection due to a faulty nozzle, the pixel in the image to be printed that corresponds to the faulty nozzle must be identified and correction processing performed on the surrounding area of ​​that pixel in the short time between when the paper position is identified and when ink is ejected, so the correction processing must be performed within that short time, but software correction processing is not enough.

[0005] Therefore, the correction process is performed using high-speed hardware, but as the number of defect positions stored increases, the storage capacity of the storage device increases, resulting in higher costs.

[0006] The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus that effectively performs correction processing to address ejection defects. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention includes a print head that ejects ink corresponding to an image to be printed from an array of nozzles, a control unit that determines the nozzles corresponding to the image to be printed according to a position on a print sheet and causes the print head to eject ink from the nozzles, and a correction processing unit that executes a correction process corresponding to each of a plurality of ejection defect positions in the image. The correction processing unit (a) prints a test pattern with the print head, (b) identifies the ejection defect positions and types based on a read image of the test pattern, and (c) executes the correction process by giving priority to the ejection defect positions where the ejection defect type is non-ejection over the ejection defect positions where the ejection defect type is deviation. [Effects of the Invention]

[0008] According to the present invention, an image forming apparatus that effectively performs correction processing to address ejection defects can be obtained.

[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 explanation 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. [Figure 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. [Figure 3] FIG. 3 is a block diagram showing the electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining detection of a defective ejection position based on the density distribution of a read image of a horizontal band test pattern. [Figure 5]FIG. 5 is a diagram for explaining detection of a defective ejection position based on the density distribution of a read image of a vertical line test pattern. [Figure 6] FIG. 6 is a diagram illustrating the correspondence between the detection result of the discharge defect position, the discharge defect type, and the correction process. DETAILED DESCRIPTION OF THE INVENTION

[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 10 according to an embodiment of the present invention. The image forming apparatus 10 according to this embodiment is a device such as a printer, a copier, a facsimile machine, or a multifunction peripheral.

[0013] 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 is equipped with line-type recording heads 1a to 1d corresponding to four ink colors: 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. 2. For example, as shown in FIG. 2, in this embodiment, each of the recording heads 1a, 1b, 1c, and 1d has a plurality of (three in this example) head units 11. These head units 11 are arranged along the main scanning direction and are detachable from the apparatus main body. Note that each of the recording heads 1a, 1b, 1c, and 1d may have only one head unit 11. The head unit 11 of each of the recording heads 1a, 1b, 1c, and 1d has nozzles arranged two-dimensionally, and ejects ink corresponding to the image to be printed from the nozzles.

[0016] 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).

[0017] The sheet transport unit 10b includes a main sheet transport unit 10b1 and a circulating sheet transport unit 10b2. In double-sided printing, the main sheet transport unit 10b1 transports print sheets to be used for printing the page image on the first side to the print engine 10a, and the circulating sheet transport unit 10b2 transports print sheets from the rear stage to the front stage of the print engine 10a while retaining a predetermined number of print sheets.

[0018] In this embodiment, the main sheet conveying section 10b1 includes a circular conveying belt 2 arranged opposite the print engine 10a to convey the print sheet, a drive roller 3 and a driven roller 4 on which the conveying belt 2 is suspended, an adsorption roller 5 that nips the print sheet together with the conveying belt 2, and a pair of discharge rollers 6, 6a.

[0019] A drive roller 3 and a driven roller 4 rotate the conveyor belt 2. Then, an attraction roller 5 nips a 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 recording heads 1a to 1d in order, where images of each color are printed by the recording heads 1a to 1d. After color printing is completed, the print sheet is discharged onto a discharge tray 10c or the like by a pair of discharge rollers 6 and 6a.

[0020] Furthermore, the main sheet transport section 10b1 is equipped with a plurality of paper feed cassettes 20-1 and 20-2. The paper feed cassettes 20-1 and 20-2 store print sheets SH1 and SH2, and lift plates 21 and 24 push the print sheets SH1 and SH2 upward to contact pickup rollers 22 and 25. The print sheets SH1 and SH2 placed in the paper feed cassettes 20-1 and 20-2 are picked up one by one from above by the pickup rollers 22 and 25 onto paper feed rollers 23 and 26. The paper feed rollers 23 and 26 transport the print sheets SH1 and SH2, which have been fed from the paper feed cassettes 20-1 and 20-2 by the pickup rollers 22 and 25, onto a transport path one by one. Transport roller 27 is a transport roller on a transport path shared by the print sheets SH1 and SH2 transported from the paper feed cassettes 20-1 and 20-2.

[0021] During double-sided printing, 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 (here, a predetermined position upstream of the line sensor 31, which will be described later). 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 in order to switch the side of the print sheet facing the print engine 10a from the first side to the second side.

[0022] Furthermore, the image forming apparatus 10 includes a line sensor 31 and a sheet detection sensor 32 .

[0023] The line sensor 31 is an optical sensor that is arranged along a direction perpendicular to the conveyance direction of the print sheet and detects the positions of both edge portions (edges on both sides) 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 rollers 28 and the print engine 10a.

[0024] The sheet detection sensor 32 is an optical sensor that detects when the leading edges of the print sheets SH1 and SH2 have passed a predetermined position on the conveyance path. The line sensor 31 detects the positions of both edge portions of the print sheets SH1 and SH2 when the leading edges of the print sheets SH1 and SH2 are detected by the sheet detection sensor 32.

[0025] For example, as shown in FIG. 1, the print engine 10a is arranged above or below (here, above) the print sheet transport path, the line sensor 31 is arranged above or below (here, below) the print sheet transport path, 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.

[0026] Fig. 3 is a block diagram showing the electrical configuration of image forming apparatus 10 according to the embodiment of the present invention. As shown in Fig. 3, image forming apparatus 10 includes image output unit 71 having the mechanical configuration shown in Figs. 1 and 2, as well as operation panel 72, storage device 73, image reader 74, and controller 75.

[0027] The operation panel 72 is arranged on the surface of the housing of the image forming device 10 and is equipped with a display device 72a such as an LCD display and an input device 72b such as hard keys or a touch panel, and displays various messages to the user on the display device 72a and accepts user operations on the input device 72b.

[0028] 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.

[0029] The image reading device 74 is equipped with 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.

[0030] The controller 75 includes a computer that executes software processing according to a program, an ASIC (Application Specific Integrated Circuit) that executes predetermined hardware processing, and the like, and operates as various processing units. The computer includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like, and operates as various processing units (together with the ASIC as necessary) by loading programs stored in the ROM, storage device 73, etc. into the RAM and executing them on the CPU. Here, the controller 75 operates as a control unit 81, an image processing unit 82, and a correction processing unit 83.

[0031] 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 predetermined image processing, and controls the print engine 10a (head 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.

[0032] Specifically, the control unit 81 causes the print engine 10a to print a user document image based on print image data designated by the user.

[0033] In addition, in this embodiment, the control unit 81 has an automatic centering function that (a) identifies the center position of the print sheet as the actual sheet center position based on the positions of both end edges 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.

[0034] 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.

[0035] In this way, the control unit 81 determines the nozzles (nozzles corresponding to each pixel) corresponding to the image to be printed according to the position on the print sheet, and causes the recording heads 1a to 1d to eject ink from the nozzles.

[0036] The correction processing unit 83 executes, as hardware processing, correction processing corresponding to each of the multiple discharge defect positions in the image to be printed. Note that in this correction processing, for example, the image data (pixel value) of a pixel adjacent to the discharge defect position is corrected so that the density of that pixel is increased.

[0037] Specifically, the correction processing unit 83 (a) prints a test pattern using the recording heads 1a to 1d described above, (b) identifies the location and type of defective discharge based on the scanned image of the test pattern, and (c) performs correction processing by prioritizing defective discharge locations where the type of defective discharge is non-discharge over defective discharge locations where the type of defective discharge is deviation. Note that "deviation of discharge" refers to a state in which the landing position of droplets discharged from a nozzle is misaligned in the main scanning direction.

[0038] In this embodiment, the correction processing unit 83 (a) prints, using the above-mentioned recording heads 1a to 1d, a first test pattern (hereinafter also referred to as a horizontal band test pattern) in the form of continuous bands in the main scanning direction and a second test pattern (hereinafter also referred to as a vertical line test pattern) including independent thin lines (straight thin lines along the sub-scanning direction) for each nozzle of the recording heads 1a to 1d, (b) identifies the defective discharge position based on each of the read images of the first test pattern and the read images of the second test pattern, and (c) identifies the defective discharge type of the defective discharge position identified in both the read images of the first test pattern and the read images of the second test pattern as non-discharge, and identifies the defective discharge type of the defective discharge position identified only in the read image of the first test pattern out of the read images of the first test pattern and the read images of the second test pattern as misaligned discharge.

[0039] Fig. 4 is a diagram for explaining detection of a discharge defect position based on the density distribution of a read image of a horizontal band test pattern. Fig. 5 is a diagram for explaining detection of a discharge defect position based on the density distribution of a read image of a vertical line test pattern. Note that the arrangement order of the vertical lines in the vertical line test pattern is not limited to that shown in Fig. 5. Fig. 6 is a diagram for explaining the correspondence between the detection result of the discharge defect position, the discharge defect type, and the correction process.

[0040] In this embodiment, a line sensor 31 is provided to detect the position of the print sheet. For example, the above-mentioned test pattern is printed on the print sheet, the print sheet is transported by the circulating sheet transport section 10b2, the image of the printed test pattern is read by the line sensor 31, and the position of the defective ejection is detected based on the density distribution of the image in the main scanning direction.

[0041] For example, as shown in FIG. 4, in a scanned image of a horizontal band test pattern, the position where a dip appears in the density distribution is detected as the ejection failure position.

[0042] Also, as shown in FIG. 5, for example, in a scanned image of a vertical line test pattern, a missing position of a peak in the density distribution corresponding to the set arrangement of vertical lines is detected as a defective ejection position.

[0043] Furthermore, in this embodiment, as shown in FIG. 6, for example, if the number of defective discharge positions identified only in the read image of the first test pattern among the read images of the first test pattern and the read images of the second test pattern is equal to or greater than a predetermined upper limit, the correction processing unit 83 performs correction processing on the defective discharge positions whose type of defective discharge is non-discharge, but does not perform correction processing on the defective discharge positions whose type of defective discharge is deviation.

[0044] The read image of the test pattern described above is acquired using the line sensor 31 or the image reading device 74. When the line sensor 31 is used to detect the position of the discharge defect as described above, the position of the discharge defect is automatically detected and a print sheet on which the test pattern is printed is discharged. Alternatively, instead of using the line sensor 31, the print sheet on which the test pattern is printed may be immediately discharged, and the image of the print sheet set in the image reading device 74 by the user may be read by the image reading device 74.

[0045] Next, the operation of the image forming apparatus 10 will be described.

[0046] (a) Determining the position of the defective discharge to be corrected

[0047] The correction processing unit 83 causes the image output unit 71 to print the above-described horizontal band test pattern and vertical line test pattern on a print sheet.

[0048] As described above, the correction processing unit 83 uses the line sensor 31 and the image reading device 74 to obtain read images (image data for each ink color) of the horizontal band test pattern and the vertical line test pattern.

[0049] The correction processing unit 83 detects the defective discharge position and the defective discharge type at the defective discharge position based on the density distribution of the read image in the main scanning direction for each of the horizontal band test pattern and vertical line test pattern read images, as described above, and identifies the nozzle corresponding to the defective discharge position.

[0050] Then, the correction processing unit 83 determines whether the number of detected defective ejection positions (here, the sum of the number of misaligned nozzles and the number of non-ejecting nozzles) exceeds an upper limit value (the limit number of defective ejection positions for which correction processing is performed within the short period of time described above).

[0051] If the number of detected defective discharge positions does not exceed the upper limit value, the correction processing unit 83 determines all currently detected defective discharge positions as targets for correction processing, and stores the defective discharge positions and nozzle data in the memory device 73.

[0052] On the other hand, if the number of detected defective ejection positions exceeds the upper limit, the correction processing unit 83 determines that only the defective ejection positions with no ejection (excluding the defective ejection positions with distortion) are to be subjected to correction processing from among the defective ejection positions currently detected, and stores the defective ejection positions and nozzle data in the memory device 73.

[0053] In this way, the nozzles (poor ejection positions) that are the targets of the correction process are set.

[0054] (b) Printing behavior

[0055] 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.

[0056] In this case, the correction processing unit 83 reads out data on the discharge defect positions and nozzles from the storage device 73 before printing begins to identify the discharge defect positions and nozzles, and when the position of the print sheet is detected by the line sensor 31, (a) identifies the nozzles corresponding to each pixel in the image, (b) identifies the discharge defect positions (corresponding nozzles) in the image, and (c) performs correction processing for the discharge defect positions.The control unit 81 then performs the printing described above based on the image data after the correction processing.

[0057] As described above, according to the embodiment, the recording heads 1a to 1d eject ink corresponding to the image to be printed from the arranged nozzles. The control unit 81 determines the nozzles corresponding to the image to be printed according to the position of the print sheet, and causes the recording heads 1a to 1d to eject ink from the nozzles. The correction processing unit 83 performs correction processing corresponding to each of the multiple ejection defect positions in the image. The correction processing unit 83 then (a) prints a test pattern using the recording heads 1a to 1d, (b) identifies the ejection defect position and the ejection defect type based on the read image of the test pattern, and (c) performs correction processing by prioritizing the ejection defect position where the ejection defect type is non-ejection over the ejection defect position where the ejection defect type is deviation.

[0058] This means that when there are many locations of ejection defects, correction processing for minor ejection defects can be omitted, making it possible to correct all fatal white streaks caused by non-ejection, thereby reducing the number of complaints.

[0059] 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, it is intended that such changes and modifications be included within the scope of the claims.

[0060] For example, in the above embodiment, for nozzles that have distortion, the amount of distortion (i.e., the amount of deviation in the landing position of droplets) is detected based on the above-mentioned read image (particularly the read image of the vertical line test pattern), and the type of defective ejection of the nozzle that has distortion is classified into multiple sub-types, such as large distortion and small distortion, based on the detected amount of distortion.Of the nozzles that have distortion, only nozzles in the sub-type with a small amount of distortion are excluded from the correction process.By doing so, if the number of nozzles that are subject to the correction process (the number of defective ejection positions) is below the above-mentioned upper limit value, other nozzles in the sub-type with a large amount of distortion may not be excluded from the correction process. [Industrial Applicability]

[0061] The present invention is applicable to, for example, an inkjet type image forming apparatus.

Claims

1. a print head that ejects ink corresponding to an image to be printed from an array of nozzles; a control unit that determines the nozzles corresponding to the image to be printed according to the position of the print sheet and causes the recording head to eject ink from the nozzles; a correction processing unit that executes a correction process corresponding to each of a plurality of ejection failure positions in the image, the correction processing unit (a) prints a test pattern with the recording head, (b) identifies the discharge defect position and the discharge defect type based on a read image of the test pattern, and (c) performs the correction processing by giving priority to the discharge defect position where the discharge defect type is non-discharge over the discharge defect position where the discharge defect type is deviation. An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the correction processing unit (a) prints, with the recording head, a first test pattern in the form of continuous bands in the main scanning direction and a second test pattern including an independent thin line for each nozzle, (b) identifies the defective ejection position based on the read image of the first test pattern and the read image of the second test pattern, and (c) identifies the defective ejection type of the defective ejection position identified in both the read image of the first test pattern and the read image of the second test pattern as non-ejection, and identifies the defective ejection type of the defective ejection position identified only in the read image of the first test pattern out of the read image of the first test pattern and the read image of the second test pattern as misaligned ejection.

3. The image forming apparatus according to claim 1, wherein the correction processing unit (a) prints, with the recording head, a first test pattern in the form of continuous bands in the main scanning direction and a second test pattern including independent thin lines for each nozzle, and (b) when the number of defective ejection positions identified only in the read image of the first test pattern out of the read image of the first test pattern and the read image of the second test pattern is equal to or greater than a predetermined upper limit, performs the correction processing on the defective ejection positions whose type of defective ejection is non-ejection, and does not perform the correction processing on the defective ejection positions whose type of defective ejection is deviation.

4. 2. The image forming apparatus according to claim 1, wherein the correction processing section executes the correction processing as hardware processing.

5. Further provided is a line sensor for detecting the position of the print sheet, the line sensor generates a read image of the test pattern; 2. The image forming apparatus according to claim 1, wherein:

Images