Image formation device

Abstract

To provide an image formation device which suppresses unnecessary correction processing and makes printing quality good.SOLUTION: A recording head discharges ink corresponding to an image to be printed, by arrayed nozzles. A control part 81 determines a nozzle corresponding to the image to be printed, and discharges ink from the nozzle to recording heads 1a to 1d. A discharge failure nozzle detection part 83 performs nozzle discharge failure inspection, and detects a discharge failure nozzle. A correction processing part 84 executes correction processing corresponding to the detected discharge failure nozzle. The discharge failure nozzle detection part 83 performs the discharge failure inspection for each print of a predetermined number without performing the correction processing, in continuous printing, and updates the discharge failure nozzle performing the correction processing, on the basis of the result of the discharge failure inspection.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] An inkjet type image forming apparatus uses a recording head to print a test pattern on a print sheet, and based on a scanned image of the printed test pattern, detects nozzles in the recording head that are no longer capable of ejecting ink normally, and increases the amount of ink in adjacent dots as a correction process. Furthermore, the image forming apparatus periodically inspects the nozzles, disables the abnormal nozzle, and if the immediately following inspection determines that the disabled nozzle is not abnormal, it restores the nozzle to an enabled state, and if the disabled nozzle is determined to be abnormal in a predetermined number of inspections, it continues to disable the nozzle (see, for example, Patent Document 1). As a result, even if an abnormal nozzle is erroneously detected, the erroneous detection is eliminated in the immediately following inspection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-49631 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if an abnormal nozzle is detected as normal, foreign matter or dirt adhering to the nozzle may come off over time during subsequent printing operations.

[0005] In the above-mentioned device, if an abnormal nozzle is erroneously detected, the erroneous detection is eliminated in the next test immediately after the detection; however, if the nozzle is abnormal for a reason that is eliminated over time during printing operations, the nozzle will still be detected as an abnormal nozzle in the next test immediately after the detection, and therefore the nozzle will continue to be disabled for use even if the cause of the abnormality is subsequently eliminated.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide an image forming apparatus that suppresses unnecessary correction processing and improves print image quality. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention includes a recording head that ejects ink corresponding to an image to be printed from an arranged nozzle, a control unit that determines the nozzle corresponding to the image to be printed and causes the recording head to eject ink from the nozzle, a defective nozzle detection unit that performs a defective ejection inspection of the nozzles and detects defective nozzles among the nozzles, and a correction processing unit that executes a correction process corresponding to the detected defective nozzle.The defective nozzle detection unit performs the defective ejection inspection without performing the correction process every time a predetermined number of pages are printed in continuous printing, and updates the defective ejection nozzle for which the correction process is performed based on the result of the defective ejection inspection. Effect of the Invention

[0008] According to the present invention, an image forming apparatus that suppresses unnecessary correction processing and improves print image quality 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 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 block diagram showing an electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Figure 4] FIG. 4 is a flowchart illustrating the operation of the image forming apparatus shown in FIGS. 1 to 3 during continuous printing. [Diagram 5] FIG. 5 is a diagram for explaining an example of the number of nozzles to be corrected when continuously printing 50,000 pages in the image forming apparatus according to the embodiment of the present invention. 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 the 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 head units 11 (three in this embodiment). The head units 11 are arranged along the main scanning direction and are detachable from the main body of the apparatus. Note that the recording heads 1a, 1b, 1c, and 1d may each have only one head unit 11. The head units 11 of the recording heads 1a, 1b, 1c, and 1d each have nozzles arranged two-dimensionally corresponding to the ejection positions arranged in the main scanning direction, and eject 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 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[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 disposed along a direction perpendicular to the conveyance direction of the print sheet and detects the positions of both edge portions (both side edge portions) of the print sheet. For example, the line sensor 31 is a CIS (Contact Image Sensor). In this embodiment, the line sensor 31 is disposed 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 pass a predetermined position on the transport 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 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.

[0026] Fig. 3 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. 3, 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.

[0027] 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.

[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 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.

[0030] 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), ROM (Read Only Memory), RAM (Random Access Memory), 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, a defective nozzle detection unit 83, and a correction processing unit 84.

[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 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.

[0034] 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.

[0035] The discharge-faulty nozzle detection unit 83 performs discharge-fault inspections on the nozzles of the recording heads 1a to 1d and detects discharge-faulty nozzles among the nozzles of the recording heads 1a to 1d. Specifically, the discharge-faulty nozzle detection unit 83 (a) prints a test pattern on a print sheet using the recording heads 1a to 1d, and (b) detects discharge-faulty nozzles based on the density distribution of a read image of the test pattern. The discharge-faulty nozzle detection unit 83 also stores discharge-faulty nozzle data (such as nozzle number) indicating the detected discharge-faulty nozzles in the storage device 73 as setting data 73a.

[0036] The test pattern is an existing one, for example a band-shaped image of a single density, or an image including thin lines corresponding to each nozzle.

[0037] Furthermore, the read image of the above-mentioned test pattern is obtained as, for example, RGB image data using the line sensor 31 or the image reading device 74. When reading the image of the test pattern using the line sensor 31, a print sheet on which the test pattern is printed by the print engine 10a is transported to the position of the line sensor 31 using the circulating sheet transport unit 10b2.

[0038] Furthermore, the resolution of the read image (scanning resolution) is lower than the resolution of the test pattern printed on the print sheet by the recording heads 1a to 1d (printing resolution). For example, the resolution of the read image is set to be equal to or less than a quarter of the printing resolution. For example, the printing resolution is 1200 dpi, and the resolution of the read image is 300 dpi.

[0039] When a nozzle has a discharge defect, a density defect occurs in the test pattern. Therefore, in the density distribution of the above-mentioned read image, a density drop occurs at the density defect location of the test pattern. However, if the scan resolution of the above-mentioned read image is lower than the print resolution, the density drop does not peak, but becomes gentle. Therefore, the discharge-defective nozzle detection unit 83 identifies the pixel with the lowest density of the density drop in the density distribution of the above-mentioned read image, and identifies the discharge-defective nozzle from the nozzle corresponding to that pixel based on the shape of the density drop in the density distribution of the above-mentioned read image.

[0040] The correction processing unit 84 executes a correction process (here, a hardware process) for the image to be printed that corresponds to the nozzle to be corrected. In this correction process, for example, the image data (pixel value) of the pixel corresponding to the nozzle with the ejection failure is corrected so that ink is not ejected, and the image data (pixel value) of the pixel corresponding to the nozzle adjacent to the ejection failure nozzle is corrected so that the density of the pixel is increased.

[0041] Then, in continuous printing (i.e., a print job in which multiple pages are printed continuously), the non-ejecting nozzle detection unit 83 performs a non-ejecting inspection without performing correction processing (i.e., by printing a test pattern without performing correction processing) after printing a predetermined number of pages, and updates the non-ejecting nozzle for which correction processing is performed based on the results of the non-ejecting inspection.

[0042] For example, in continuous printing of 50,000 pages, a discharge defect inspection is performed every 10,000 pages printed. Note that the above-mentioned predetermined number of pages, which is the interval between discharge defect inspections, may be a fixed value or may be set by the user.

[0043] In the defective discharge inspection for each print of a predetermined number of pages, the defective discharge nozzle detection unit 83 determines which defective discharge nozzles are to undergo correction processing and which are not to undergo correction processing based on the results of the current defective discharge inspection.

[0044] In this embodiment, the number of defective nozzles for which correction processing is performed is limited to a predetermined upper limit (for example, 100). This upper limit is the limit number of defective nozzles for which correction processing can be performed during the time from when the nozzles corresponding to each pixel of the image to be printed are identified to when the nozzles are made to eject ink. The correction processing unit 84 may (a) if the number of defective nozzles in the current defective discharge inspection does not exceed the predetermined upper limit, set both defective nozzles for which correction processing is performed and defective nozzles for which correction processing is not performed based on the results of the current defective discharge inspection, regardless of the results of the previous defective discharge inspection, and (b) if the number of defective nozzles in the current defective discharge inspection exceeds the predetermined upper limit, set defective nozzles for which correction processing is performed based on the results of the previous defective discharge inspection and the results of the current defective discharge inspection.

[0045] In this case, for example, the results of the discharge defect test (such as the nozzle number of the discharge defect nozzle) are stored in the memory device 73 as historical data, and if the number of discharge defect nozzles found in the current discharge defect test exceeds a predetermined upper limit, then based on that historical data, nozzles that have been detected as discharge defect nozzles more frequently in a predetermined number of past tests are preferentially selected as discharge defect nozzles for which correction processing is performed.

[0046] Next, the operation of the image forming apparatus 10 will be described.

[0047] (a) Setting the nozzles to be corrected

[0048] The discharge-failure nozzle detection unit 83 performs a discharge-failure inspection at a predetermined timing. In the discharge-failure inspection, first, (a) the discharge-failure nozzle detection unit 83 uses the control unit 81 to cause the image output unit 71 to print the above-mentioned test pattern on a print sheet at a predetermined print resolution, and then uses the line sensor 31 and the image reading device 74 to obtain a read image (RGB image data, grayscale image data, etc.) of the test pattern printed on the print sheet at a predetermined scan resolution.

[0049] Then, the discharge-faulty nozzle detection unit 83 detects the discharge-faulty nozzle as described above from the density distribution in the main scanning direction for the read image of the test pattern, and determines the discharge-faulty nozzle as a nozzle to be corrected, and stores setting data 73a indicating the nozzle to be corrected (identification information such as nozzle number) in the storage device 73. At this time, history data indicating the discharge-faulty nozzle may also be stored in the storage device 73.

[0050] In this manner, the nozzles to be subjected to the correction process are set in the ejection failure nozzle data.

[0051] (b) Printing behavior

[0052] 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.

[0053] In this case, the correction processing unit 84 reads the setting data 73a from the storage device 73 before printing starts to identify the nozzles to be corrected, and when the line sensor 31 detects the position of the print sheet, (a) it identifies the nozzles corresponding to each pixel in the image, (b) it identifies the nozzles to be corrected used for the image, and (c) it executes the correction process corresponding to the nozzles to be corrected. As a result, the correction process is executed for the parts of the image that correspond to the nozzles to be corrected (and the nozzles adjacent to the nozzle with poor ejection in the main scanning direction). The control unit 81 then executes the printing described above based on the image data after the correction process.

[0054] (c) Operation during continuous printing

[0055] Fig. 4 is a flow chart for explaining the operation during continuous printing of the image forming apparatus shown in Fig. 1 to Fig. 3. For example, when the number of pages of continuous printing is equal to or greater than a predetermined value, the following process is executed.

[0056] First, when a print request is received, the correction processing unit 84 reads the setting data 73a from the storage device 73 before printing starts to identify the nozzles to be corrected (step S1), the control unit 81 selects a page image (step S2), and when the line sensor 31 detects the position of the print sheet, the correction processing is executed as described above (step S3).The control unit 81 then causes the print engine 10a to execute a print process based on the page image after the correction processing (step S4).

[0057] The control unit 81 determines whether printing has been completed up to the final page (step S5). If it is determined that printing has been completed up to the final page, the control unit 81 ends the continuous printing.

[0058] On the other hand, if it is determined that printing has not been completed up to the final page, the defective nozzle detection unit 83 determines whether the number of printed pages since the start of continuous printing or since the previous defective nozzle inspection has reached the above-mentioned specified number of pages (step S6).

[0059] If it is determined that the number of printed pages has not reached the above-mentioned predetermined number of pages, the process returns to step S2, and the process from step S2 onwards is executed for the next page.

[0060] On the other hand, if it is determined that the number of printed pages has reached the above-mentioned predetermined number of pages, the defective discharge nozzle detection unit 83 stops the continuous printing, performs a defective discharge inspection as described above (step S7), and updates the nozzles to be corrected (setting data 73a) (step S8). After that, the continuous printing is resumed, and the process returns to step S2, and the process from step S2 onwards is executed for the next page.

[0061] As described above, according to the above 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, and causes the recording heads 1a to 1d to eject ink from the nozzles. The defective nozzle detection unit 83 performs a defective ejection inspection of the nozzles and detects defective ejection nozzles. The correction processing unit 84 executes a correction process corresponding to the detected defective ejection nozzle. Then, in continuous printing, the defective ejection detection unit 83 performs a defective ejection inspection without performing a correction process every time a predetermined number of pages are printed, and updates the defective ejection nozzle for which the correction process is to be performed based on the result of the defective ejection inspection.

[0062] As a result, correction processing is not performed on nozzles whose ejection defects have been resolved during continuous printing, so unnecessary correction processing is suppressed and print image quality is improved. In particular, when an upper limit is set for the number of nozzles to be corrected, it is possible to reduce the number of nozzles with ejection defects that are not corrected.

[0063] FIG. 5 is a diagram for explaining an example of the number of nozzles to be corrected when continuously printing 50,000 pages in the image forming apparatus according to the embodiment of the present invention.

[0064] In the example shown in Fig. 5, under the condition that 5000 nozzles of only black ink are used at an output resolution of 1200 dpi, the image forming apparatus according to the present embodiment performs a discharge defect inspection and updates the nozzles to be corrected every 10,000 pages, and in the case of coated paper, 19 nozzles to be corrected are removed from the original nozzles to be corrected by the discharge defect inspection and updates of the nozzles to be corrected every 10,000 pages, leaving a final number of nozzles to be corrected of 13. In addition, in the case of plain paper, 35 nozzles to be corrected are removed from the original nozzles to be corrected by the discharge defect inspection and updates of the nozzles to be corrected every 10,000 pages, leaving a final number of nozzles to be corrected of 78. Compared to coated paper, plain paper is more likely to produce paper dust that causes discharge defects, and tends to have more discharge defect nozzles (i.e., nozzles to be corrected).

[0065] In the comparative example, the ejection failure inspection and the update of the nozzles to be corrected are not performed every 10,000 pages, and the initial nozzles to be corrected are corrected until the end, and in the case of coated paper, the number of nozzles to be corrected is 30. In addition, in the case of plain paper, of the 122 ejection failure nozzles, 100 nozzles (upper limit) are set as the nozzles to be corrected, and the correction process is not performed on the 22 ejection failure nozzles.

[0066] In addition, in Figure 5, "visual streaks" indicates whether or not white streaks in the print product can be visually recognized, with "◯" (good) indicating that white streaks are not visible and "×" (bad) indicating that white streaks are visible.

[0067] In addition, "Scanner streaks" in Figure 5 indicates whether or not white streaks are detected in the 1200 dpi scanned image of the print product, with "◯" (good) indicating that the maximum difference in RGB values ​​between the normal image and the image after correction processing is less than 10% of the normal value, "△" (medium) indicating that the maximum value is 10% or more and less than 20% of the normal value, and "×" (bad) indicating that the maximum value is 20% or more of the normal value.

[0068] In the example shown in Fig. 5, in this embodiment, the print image quality is good for both print sheet types ("visual streaks" is "good" and "scanner streaks" is "good"). On the other hand, in the comparative example, in the case of plain paper, defective ejection nozzles for which correction processing has not been performed continue to remain, resulting in poor print image quality ("visual streaks" is "bad" and "scanner streaks" is "bad").

[0069] 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.

[0070] For example, in the above embodiment, the above-mentioned predetermined number of pages may be set according to the type of print sheet used for printing. For example, the more likely a type of print sheet is to produce paper dust that can cause ejection defects, the smaller the above-mentioned predetermined number of pages is set.

[0071] In the above embodiment, the above-mentioned predetermined number of pages may be set depending on whether double-sided printing or single-sided printing is performed.

[0072] Furthermore, in the above embodiment, in the case of a discharge defect inspection during continuous printing, the inspection may be performed only on nozzles that were determined to be discharge defective nozzles in the previous discharge defect inspection. [Industrial Applicability]

[0073] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0074] 1a~1d Recording head 10 Image forming device 81 Control Unit 83 Defective nozzle detector 84 Correction processing section

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 nozzles corresponding to the image to be printed and causes the recording head to eject ink from the nozzles; a defective nozzle detection unit that performs a defective discharge inspection on the nozzles and detects defective nozzles among the nozzles; a correction processing unit that executes a correction process corresponding to the detected ejection defective nozzle, the discharge-failed nozzle detection unit performs the discharge failure inspection without performing the correction process every time a predetermined number of pages are printed in continuous printing, and updates the discharge-failed nozzle for which the correction process is performed based on a result of the discharge failure inspection; An image forming apparatus comprising:

2. In the ejection defect inspection, the ejection defective nozzle detection unit (a) prints a test pattern on a print sheet with the recording head, and (b) detects an ejection defective nozzle based on a density distribution of a read image of the test pattern, the discharge-failed nozzle detection unit performs the discharge failure inspection by printing the test pattern without performing the correction process every time a predetermined number of pages are printed in continuous printing, and updates the discharge-failed nozzle for which the correction process should be performed based on a result of the discharge failure inspection; 2. The image forming apparatus according to claim 1, wherein:

3. The image forming apparatus according to claim 1, characterized in that, in the ejection failure inspection for each print of the specified number of pages, the ejection failure nozzle detection unit sets the ejection failure nozzles for which the correction process is to be performed and the ejection failure nozzles for which the correction process is not to be performed based on the results of the current ejection failure inspection.

4. The number of the defective ejection nozzles subjected to the correction process is limited to a predetermined upper limit or less, the correction processing unit: (a) when the number of the discharge-fault nozzles in the current discharge defect inspection does not exceed a predetermined upper limit number, sets both the discharge-fault nozzles for which the correction process is to be performed and the discharge-fault nozzles for which the correction process is not to be performed based on the result of the current discharge defect inspection, regardless of the result of the previous discharge defect inspection; and (b) when the number of the discharge-fault nozzles in the current discharge defect inspection exceeds a predetermined upper limit number, sets the discharge-fault nozzles for which the correction process is to be performed based on the result of the previous discharge defect inspection and the result of the current discharge defect inspection.

2. The image forming apparatus according to claim 1,

Images