Image forming device

Abstract

To provide an image forming device that can properly read out a synchronization mark for synchronizing a test pattern image for detecting a nozzle failing in discharging with a nozzle.SOLUTION: A test pattern image 201 includes a synchronization mark 203 formed by a nozzle at a predetermined reference position. A line sensor 41 comprises a plurality of sensor units 51a and 51b. The plurality of sensor units 51a and 51b respectively read out the test pattern image 201 partially to generate partial test pattern read-out images. A region read out of the image by the sensor units 51a and 51b have an overlapping section. The synchronization mark 203 is formed on a print sheet 101 so that the mark passes on the overlapping section. A discharge failure determining part identifies a position corresponding to a nozzle, in the partially read-out test pattern image, on the basis of a position of the synchronization mark 203, and determines whether the nozzle fails in discharging or not, on the basis of a density of the identified position.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] One inkjet image forming device prints a test pattern on a print sheet by forming a thin line with each nozzle, and while transporting the print sheet, reads the printed test pattern with a line sensor. If a density defect occurs in a thin line in the read image of the test pattern, it determines that an ejection abnormality has occurred in the nozzle corresponding to that thin line. In this case, the image forming device includes a synchronization mark in the test pattern, forms the synchronization mark with a specified nozzle, and identifies the nozzle corresponding to that thin line based on the relative position of the thin line with respect to the synchronization mark in the read image of the test pattern (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-6025 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, by arranging a plurality of sensor units (contact image sensors, etc.) with a specified width as line sensors for reading the test pattern image, the line sensors can be installed inexpensively.

[0005] As described above, when using a line sensor equipped with multiple sensor units, if the synchronization mark passes through the gap between the reading areas of two adjacent sensor units when reading a test pattern image with the line sensor, the synchronization mark may not be read properly.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an image forming device that can properly read synchronization marks for synchronizing (associating) test pattern images with nozzles to detect nozzle ejection abnormalities. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention includes an inkjet recording unit that prints by ejecting ink onto a sheet using an array of nozzles, a sheet transport unit that transports the sheet, a line sensor that reads a test pattern image printed on the sheet using the nozzles and generates a test pattern read image, and an ejection abnormality determination unit that determines, for each nozzle of the plurality of nozzles, whether the nozzle has an ejection abnormality based on the density distribution of the test pattern read image corresponding to that nozzle. The test pattern image includes a synchronization mark formed by a nozzle at a predetermined reference position among the plurality of nozzles. The line sensor includes a plurality of sensor units that generate a plurality of partial test pattern read images by partially reading the test pattern image as the test pattern read image. The reading areas of the multiple sensor units have an overlapping section in a direction perpendicular to the conveying direction of the sheet, and the synchronization mark is formed on the sheet so as to pass through the overlapping section, and the ejection abnormality determination unit (a) identifies positions in the partial test pattern read image corresponding to each of a portion of the multiple nozzles based on the position of the synchronization mark in the partial test pattern read image, and (b) determines whether the nozzle corresponding to the positions is an ejection abnormality nozzle based on the density of the identified positions. [Effects of the Invention]

[0008] According to the present invention, an image forming apparatus can be obtained that can properly read a test pattern image for detecting nozzle ejection abnormalities and a synchronization mark for synchronizing the nozzles.

[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 front view showing the line sensor 41 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 showing an example of a test pattern image. [Figure 5] FIG. 5 is a diagram for explaining the position of the main scanning synchronization mark 203 in the test pattern image 201 shown in FIG. [Figure 6] FIG. 6 is a diagram showing a portion 201a of the test pattern image shown in FIGS. 4 and 5 that is read by the sensor unit 51a. [Figure 7] FIG. 7 is a diagram showing a portion 201b of the test pattern image shown in FIGS. 4 and 5 that is read by the sensor unit 51b. [Figure 8] FIG. 8 is a diagram showing an example of a partial test pattern read image generated by the sensor unit 51a as shown in FIGS. [Figure 9] FIG. 9 is a diagram showing an example of a partial test pattern read image generated by the sensor unit 51b as shown in FIGS. [Figure 10] FIG. 10 is a diagram showing an example of a color adjustment chart. 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 according to an embodiment of the present invention. The image forming apparatus 10 according to this embodiment is a device such as a printer, copier, facsimile machine, or multifunction device, and in this embodiment is equipped with a line-head inkjet color printing mechanism.

[0013] The image forming apparatus 10 shown in FIG. 1 includes a print engine 10a and a sheet transport unit 10b. The print engine 10a physically prints an image to be printed on a print sheet (such as print paper). An ink cartridge is detachably attached to the print engine 10a, and the print engine 10a performs printing using ink supplied from the ink cartridge. The sheet transport unit 10b transports the print sheet along a transport path.

[0014] In this embodiment, print engine 10a is equipped with line-head type inkjet recording units 1a-1d corresponding to four ink colors: cyan, magenta, yellow, and black. Each inkjet recording unit 1a-1d ejects ink of the corresponding color onto print sheet 101 using an array of nozzles to perform printing.

[0015] In this embodiment, the sheet conveying section 10b includes a circular conveying belt 2 arranged opposite the print engine 10a to convey the print sheet, a drive roller 3, a driven roller 4, and a tension roller 4a around which the conveying belt 2 is suspended, an adsorption roller 5 that nips the print sheet together with the conveying belt 2, a downstream conveying belt 6, and a dryer 7.

[0016] A drive roller 3, a driven roller 4, and a tension roller 4a rotate the conveyor belt 2. The print sheet 101 conveyed from a paper feed cassette 20 (described later) is nipped by an attraction roller 5, and the nipped print sheet 101 is conveyed by the conveyor belt 2 to the printing positions of the inkjet recording units 1a-1d in order, where an image of each color is printed by the inkjet recording units 1a-1d. The sheet sensor 2a detects the passage of the print sheet, and the current position of the print sheet on the conveyance path is determined based on the detection timing. The image is then printed at the appropriate position on the print sheet. After printing, the print sheet is discharged to a discharge tray or the like by a subsequent conveyor belt 6. At this time, a dryer 7 dries the print sheet on which the ink has been discharged.

[0017] Ink receivers 8a to 8d are provided below the inkjet recording units 1a to 1d. When the flushing openings of the conveyor belt 2 are located directly below the inkjet recording units 1a, 1b, 1c, and 1d, flushing (line flushing) is performed in accordance with a flushing timing signal. During flushing, ink is ejected in lines from the inkjet recording units 1a, 1b, 1c, and 1d and received by the corresponding ink receivers 8a, 8b, 8c, and 8d through the flushing openings, and then collected in a waste ink tank. The flushing timing signal specifies the flushing timing for the inkjet recording units 1a to 1d, and is generated by a control unit 81 based on the position of the conveyor belt 2 determined by a sensor signal from a belt sensor 29.

[0018] The sheet suction units 9 are arranged along the sheet transport path at a location other than the ink receiving units 8a to 8d. A negative pressure is applied to the sheet suction units 9, which causes the print sheet to adhere to the transport belt 2. A negative pressure lower than that applied to the ink receiving units 8a to 8d is applied to the sheet suction units 9.

[0019] Furthermore, the sheet transport unit 10b is equipped with a paper feed cassette 20 as a paper feed source. The paper feed cassette 20 stores print sheets 101, and a lift plate 21 pushes the print sheets 101 upward to abut against a pickup roller 22. The print sheets 101 placed in the paper feed cassette 20 are picked up one by one from above by the pickup roller 22 onto a paper feed roller 23. The paper feed roller 23 is a roller that transports the print sheets 101 fed from the paper feed cassette 20 by the pickup roller 22 onto a transport path one by one.

[0020] The transport rollers 27 are rollers that transport the print sheet 101 on a predetermined transport path. When the transported print sheet 101 is detected by the resist sensor 28a, the resist rollers 28 temporarily stop the print sheet 101 and transport the print sheet 101 to the print engine 10a (specifically, to the nip position between the attraction roller 5 and the transport belt 2) at the secondary paper feed timing. The secondary paper feed timing is specified by the control unit 81, which will be described later, so that an image is formed at a specified position on the print sheet 101.

[0021] Furthermore, the sheet transport unit 10b includes a circulating sheet transport unit 31. When performing double-sided printing or the like, the circulating sheet transport unit 31 returns the print sheet along the transport path using transport rollers from a predetermined position downstream of the print engine 10a to a predetermined position upstream.

[0022] As shown in FIG. 1, the circulating sheet transport section 31 includes a line sensor 41 and a switchback transport path .

[0023] The line sensor 41 is provided at a predetermined position (downstream of the switchback conveying path 42) on the conveying path of the circulating sheet conveying section 31, and optically reads the image on the print sheet 101 passing through the conveying path.

[0024] In particular, during the operation of detecting nozzles with ejection abnormalities, the line sensor 41 reads a test pattern image (described later) from the print sheet 101 that is conveyed and passes the reading position of the line sensor 41, and generates a test pattern read image.

[0025] The test pattern image is an image printed on the print sheet 101 by multiple nozzles in the inkjet recording units 1a to 1d, and in this case includes thin lines (lines of 1 dot width along the sub-scanning direction) formed by each of the multiple nozzles being tested that are not abnormal ejection nozzles.

[0026] 2 is a front view showing the line sensor 41 in FIG. 1. The line sensor 41 includes multiple sensor units 51a and 51b. Here, the sensor units 51a and 51b are CIS (Contact Image Sensors). Each of the sensor units 51a and 51b includes imaging elements arranged one-dimensionally and is disposed along a direction perpendicular to the transport direction of the print sheet 101. The multiple sensor units 51a and 51b generate multiple partial test pattern read images by partially reading the test pattern image, and the reading areas of the multiple sensor units 51a and 51b have an overlapping section in the direction perpendicular to the transport direction of the print sheet 101, as shown in FIG. 2.

[0027] Here, the width of the overlapping section is set to be wider than the maximum positional deviation in the direction perpendicular to the conveying direction of the print sheet 101 during conveyance.

[0028] The switchback conveying path 42 reverses the direction of travel 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.

[0029] Fig. 3 is a block diagram showing the electrical configuration of image forming apparatus 10 according to an embodiment of the present invention. As shown in Fig. 3, image forming apparatus 10 includes a printing device 71 having the mechanical configuration shown in Figs. 1 and 2, as well as an operation panel 72, a storage device 73, and an arithmetic processing device 74.

[0030] 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.

[0031] 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.

[0032] The arithmetic processing device 74 includes a computer that operates according to a program, an ASIC (Application Specific Integrated Circuit) that executes predetermined operations, 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.

[0033] Here, the arithmetic processing device 74 operates as a control unit 81, an image processing unit 82, a discharge abnormality determination unit 83, and a color adjustment unit 84.

[0034] 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 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.

[0035] Specifically, the control unit 81 causes the print engine 10a to print a user document image based on print image data specified by the user, and forms a test pattern image on a single print sheet 101 to detect nozzles with abnormal ejection.

[0036] For example, a line sensor is used for the sheet sensor 2a, and the control unit 81 uses the sheet sensor 2a to detect the range of the print sheet 101 in the direction perpendicular to the transport direction (the positions of both edge edges), and when forming a test pattern image on the print sheet 101, excludes nozzles outside the range of the print sheet 101 in the direction perpendicular to the transport direction from the inspection target described below. This prevents ink from being ejected outside the print sheet 101. In other words, the control unit 81 masks the portions of the test pattern image that correspond to the nozzles outside the range of the print sheet 101.

[0037] The ejection abnormality determination unit 83 controls the line sensor 41 to acquire the test pattern read image from the line sensor 41, and for each of the multiple nozzles to be inspected in the inkjet recording units 1a to 1d for each ink color, determines whether or not the nozzle is an ejection abnormality nozzle (such as a non-ejecting nozzle) based on the density distribution of the test pattern read image corresponding to that nozzle. Note that the correspondence between the nozzle and its position in the test pattern read image is identified based on a synchronization mark included in the test pattern image, as will be described later.

[0038] 4 is a diagram showing an example of a test pattern image 201. For example, as shown in FIG. 4, a test pattern image 201 includes a sub-scanning synchronization mark 202, a main-scanning synchronization mark 203, and a thin line 204.

[0039] The test pattern image 201 is printed individually for each of the inkjet recording units 1a to 1d. The control unit 81 controls each of the inkjet recording units 1a to 1d so that a thin line 204 is printed for each of the nozzles to be tested, as shown in Fig. 4, for example, and if there are no ejection abnormalities in the nozzles to be tested, the thin line 204 is printed without any defects.

[0040] For example, each thin line 204 in Fig. 4 is a linear image formed by one nozzle. For example, as shown in Fig. 4, thin lines formed by two adjacent nozzles are formed so as not to be connected in the main scanning direction (for example, at different positions in the sub-scanning direction), and for one position in the sub-scanning direction, multiple thin lines 204 are formed by multiple nozzles at a predetermined period (16-pixel period in Fig. 4) along the main scanning direction.

[0041] In addition, the sub-scanning synchronization mark 202 is an image that indicates the start position of forming the thin line 204 in the sub-scanning direction, and is a band-shaped solid image of a predetermined number of lines along the main scanning direction, and is formed by multiple nozzles to be inspected.

[0042] FIG. 5 is a diagram illustrating the position of the main scanning synchronization mark 203 in the test pattern image 201 shown in FIG. 4. The main scanning synchronization mark 203 is a linear image along the sub-scanning direction formed by a predetermined reference position nozzle among the nozzles to be tested. The reference position nozzle may be a single nozzle or multiple nozzles consecutive in the main scanning direction. Here, one or multiple nozzles in the center of the nozzle range in the main scanning direction in each of the inkjet recording units 1a to 1d are set as the reference position nozzles. The main scanning synchronization mark 203 is formed on the print sheet 101 so as to pass through the overlapping section described above, as shown in FIG. 5, for example. The main scanning synchronization mark 203 is formed so as not to be continuous with any of the thin lines 204.

[0043] Fig. 6 is a diagram showing a portion 201a of the test pattern image shown in Fig. 4 and Fig. 5 that is read by the sensor unit 51a. Fig. 7 is a diagram showing a portion 201b of the test pattern image shown in Fig. 4 and Fig. 5 that is read by the sensor unit 51b.

[0044] 6 and 7, the plurality of sensor units 51a and 51b generate a plurality of partial test pattern read images by reading portions 201a and 201b of the test pattern image 201. At this time, the sub-scanning synchronization mark 202 and the main-scanning synchronization mark 203 are included in each of the partial test pattern read images of the plurality of sensor units 51a and 51b.

[0045] Then, the ejection abnormality determination unit 83 (a) identifies positions in each partial test pattern read image corresponding to some of the above-mentioned multiple nozzles based on the position of the main scanning synchronization mark 203 in that partial test pattern read image, and (b) determines whether the nozzle corresponding to that position is an ejection abnormality nozzle based on the density of the identified position.

[0046] Fig. 8 is a diagram showing an example of a partial test pattern read image generated by sensor unit 51a as shown in Fig. 5 and Fig. 6. Fig. 9 is a diagram showing an example of a partial test pattern read image generated by sensor unit 51b as shown in Fig. 5 and Fig. 7.

[0047] 8 and 9, each partial test pattern read image is generated with the end of the overlapping section in the main scanning direction as the origin. That is, one partial test pattern read image (here, the partial test pattern read image shown in FIG. 9) is generated with the main scanning direction reversed. In this embodiment, the ejection abnormality determination unit 83 searches for the main scanning synchronization mark 203 and the thin line 204 in each of these partial test pattern read images along the main scanning direction from the origin, as shown in FIG. 8 and 9, for example.

[0048] Specifically, as shown by the dashed lines in Figures 8 and 9, when a sub-scanning synchronization mark 202 is detected in a partial test pattern read image, a search is made for a main-scanning synchronization mark 203 along the main-scanning direction at a position a predetermined number of lines away from that position in the sub-scanning direction, the position of the main-scanning synchronization mark 203 (the center position of the main-scanning synchronization mark 203 in the main-scanning direction) is identified, and at each position in the sub-scanning direction based on the sub-scanning synchronization mark 202 in the sub-scanning direction, a thin line 204 is searched for along the main-scanning direction from the position of the main-scanning synchronization mark 203.

[0049] Then, in the partial test pattern read image, the position where each nozzle should form the thin line 204 is identified using the position of the main scanning synchronization mark 203 as a reference, and if the density at that position is equal to or greater than a predetermined threshold, it is determined that the nozzle is not experiencing an ejection abnormality, and if the density at that position is less than the predetermined threshold, it is determined that the nozzle is experiencing an ejection abnormality.

[0050] For example, when thin lines 204 are formed as shown in FIG. 4, if there are no ejection abnormalities, thin lines 204 are formed every 16 pixels, starting from a position 8 pixels away from the center position of the main scanning synchronization mark 203 in FIG. 8. If the reference position nozzle (the central nozzle) is the Nth nozzle, ejection abnormalities are inspected based on the density at pixel position (N+8+16×m (m=0, 1, 2, . . .)). In other words, approximately 1 / 16th of the nozzles to be inspected are inspected in one scan in the main scanning direction. After this inspection is completed, approximately 1 / 16th of the nozzles to be inspected are inspected in the same way in the next scan in the main scanning direction, at positions a predetermined number of lines away in the sub-scanning direction. At that time, because the position of the thin line 204 in the main scanning direction is shifted by one pixel, in the partial test pattern read image shown in Fig. 8, an ejection abnormality inspection is performed based on the density of the pixel position (N+9+16×m), and in the partial test pattern read image shown in Fig. 9, an ejection abnormality inspection is performed based on the density of the pixel position (N+7+16×m). In this way, by performing 16 scans, an inspection is performed for all nozzles to be inspected that correspond to the test pattern image.

[0051] In this way, by setting the end of the overlapping section of the partial test pattern read image as the origin of the image, all partial test pattern read images can be processed in the same way, with only the offset amount of the start position of each scan being different.

[0052] As described above, when the control unit 81 identifies the range of the print sheet 101, it identifies the nozzle range corresponding to that range and excludes nozzles outside the identified nozzle range from the nozzles to be inspected. At that time, the control unit 81 stores data on that nozzle range in the storage device 73, RAM, etc., and the ejection abnormality determination unit 83 reads that data to identify the nozzle range to be inspected and determines whether or not there is an ejection abnormality only for the nozzles within the nozzle range to be inspected, and does not determine whether or not there is an ejection abnormality for the other nozzles.

[0053] 3, the color adjustment unit 84 performs color adjustment (chromatic aberration correction, gamma correction for each RGB color, etc.) of the line sensor 41. A predetermined color adjustment chart for color adjustment is used for color adjustment.

[0054] FIG. 10 is a diagram showing an example of a color adjustment chart. As shown in FIG. 10, the color adjustment chart 301 is a sheet on which a plurality of color patch images 311 are pre-printed. For chromatic aberration correction, the plurality of color patch images 311 have a fixed length in the main scanning direction. For gamma correction, a plurality of color patch images 311 corresponding to a plurality of gradation levels are used for one color.

[0055] During color adjustment, the color adjustment chart 301 is set in the paper feed cassette 20 or a manual feed tray (not shown), and the sheet conveying unit 10b conveys the color adjustment chart 301 along the conveying path. The color adjustment unit 84 passes the color adjustment chart 301 without operating the print engine 10a and performs color adjustment based on the scanned image of the color adjustment chart 301 generated by the line sensor 41. At this time, the sensor units 51a and 51b generate multiple partial color adjustment chart scanned images by partially scanning the color adjustment chart 301. Similar to the scanning of the partial test pattern image described above, each partial color adjustment chart scanned image is generated with the end of the overlapping section in the main scanning direction as the origin. The color adjustment unit 84 then individually performs color adjustment on each of the partial color adjustment chart scanned images using the sensor units 51a and 51b along the main scanning direction from the origin toward the other end of the partial color adjustment chart scanned image.

[0056] Furthermore, if the width of the color adjustment chart 301 is narrower than the reading area of the line sensor 41, The correction characteristics (such as chromatic aberration correction and gamma correction) obtained by color adjustment as described above may be extrapolated and applied to the portions of the line sensor 41 that the color adjustment chart 301 does not pass through.

[0057] Next, the operation of the image forming apparatus 10 will be described.

[0058] (a) Identifying nozzles with abnormal discharge

[0059] The ejection abnormality determination unit 83 uses the control unit 81 to cause the image output unit 71 to print the test pattern image 201 on the print sheet 101 .

[0060] The print sheet 101 on which the test pattern image is printed is conveyed by the circulating sheet conveying section 31, switched back by the switchback conveying path 42, and conveyed to the reading position of the line sensor 41.

[0061] Each of the sensor units 51a and 51b of the line sensor 41 optically reads a part of the test pattern image on the print sheet 101, and generates a partial test pattern read image.

[0062] The ejection abnormality determination unit 83 then detects the synchronization marks 202, 203 in each of the multiple partial test pattern read images, identifies the position where the thin line 204 should be formed by each nozzle corresponding to the position of the synchronization marks 202, 203, and determines whether the nozzle is an ejection abnormality nozzle based on the density at that position.

[0063] The discharge abnormality determination unit 83 stores in the storage device 73 discharge abnormality nozzle data (nozzle number, etc.) indicating the nozzle determined to be the discharge abnormality nozzle.

[0064] In this way, the nozzle having the ejection abnormality is identified. The print sheet 101 on which the test pattern image is printed is discharged to a discharge tray or the like by the sheet conveying section 10b.

[0065] (b) Printing behavior

[0066] 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.

[0067] Before printing begins, the control unit 81 reads out the abnormal-ejection nozzle data from the storage device 73 and identifies the abnormal-ejection nozzle, and then, when the position of the print sheet 101 (position in the direction perpendicular to the transport direction) is detected by the sheet sensor 2a or the like, (a) it identifies the nozzle corresponding to each pixel in the image described above according to that position, (b) it identifies the abnormal-ejection nozzle to be used for the image described above, and (c) it executes a correction process corresponding to that abnormal-ejection nozzle. For example, in this correction process, the image data (pixel value) of the pixel corresponding to the abnormal-ejection nozzle is corrected so that ink is not ejected, and the image data (pixel value) of the pixel corresponding to the nozzle adjacent to the abnormal-ejection nozzle is corrected so that the density of that pixel is increased.

[0068] As described above, according to the above embodiment, the test pattern image 201 for inspecting ejection abnormalities of the multiple nozzles in the inkjet recording units 1a to 1d includes a synchronization mark 203 formed by a nozzle at a predetermined reference position among the multiple nozzles. The line sensor 41 includes multiple sensor units 51a and 51b, which generate multiple partial test pattern read images by partially reading the test pattern image 201. The reading areas of the multiple sensor units 51a and 51b have an overlapping section in a direction perpendicular to the conveyance direction of the print sheet 101, and the synchronization mark 203 is formed on the print sheet 101 so as to pass through the overlapping section. The ejection abnormality determination unit 83 (a) identifies positions in the partial test pattern read image that correspond to each of the multiple nozzles based on the positions of the synchronization mark 203 in the partial test pattern read image, and (b) determines whether the nozzle corresponding to the identified position is an ejection abnormality nozzle based on the density of the identified position.

[0069] As a result, the synchronization mark 203 is included in each partial test pattern read image, and the synchronization mark 203 for synchronizing the test pattern image (thin lines 204) with the nozzles is properly read. As a result, nozzle testing based on the partial test pattern read image is properly performed for each partial test pattern read image.

[0070] 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.

[0071] For example, in the above embodiment, the line sensor 41 has two sensor units 51a and 51b, but the number of sensor units 51a and 51b may be any number as long as it is a multiple of two.

[0072] Furthermore, in the above embodiment, the sheet sensor 2a may identify and store the above-mentioned nozzle ranges at multiple positions on the print sheet 101 along the transport direction (for example, the leading edge, center, and trailing edge of the print sheet 101), and switch the range of nozzles to be inspected depending on the position of the test pattern image in the sub-scanning direction.

[0073] Furthermore, in the above embodiment, a mechanism may be provided that intentionally misaligns the print sheet 101 in a direction perpendicular to the transport direction, and if the width of the print sheet 101 is narrower than the nozzle range of all the nozzles (for example, if the print sheet 101 is A4 size and the nozzle range of all the nozzles is 12 inches), the mechanism may shift the position of the print sheet 101 so that one end of the nozzle range of all the nozzles is included in the range of the print sheet 101 in the first test, and shift the position of the print sheet 101 so that the other end of the nozzle range of all the nozzles is included in the range of the print sheet 101 in the second test, thereby performing the above-mentioned test on all the nozzles in two tests.

[0074] Furthermore, in the above embodiment, if multiple paper feed cassettes 20 are provided and print sheets of multiple sizes can be used, the print sheet of the largest size may be used for the above-mentioned inspection (i.e., printing of the test pattern image).In this case, the print sheet of the size specified by the user may be used.

[0075] Furthermore, in the above embodiment, if multiple destinations for the print sheet are provided, the print sheet used for the above-mentioned inspection may be discharged to a destination (e.g., a specific tray such as a proof tray) different from the destination for the print product of the user's print job.

[0076] Furthermore, in the above embodiment, if head capping mechanisms are provided for the inkjet recording units 1a to 1d, the control unit 81 may control the head capping mechanisms when transporting the color adjustment chart 301 so that the color adjustment chart 301 passes through the print engine 10a with the heads of the inkjet recording units 1a to 1d capped. In this case, the color adjustment chart 301 does not come into contact with the heads of the inkjet recording units 1a to 1d and is not deteriorated. Furthermore, the control unit 81 may discharge the color adjustment chart 301 without operating the dryer 7. In this case, the color adjustment chart 301 is not deteriorated by the heat of the dryer 7. [Industrial Applicability]

[0077] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0078] 1a to 1d Inkjet recording unit 10 Image forming device 10b Sheet transport section 41 Line Sensor 51a Sensor unit 51b Sensor unit 83 Discharge abnormality determination section 84 Color adjustment section

Claims

1. an inkjet recording unit that performs printing by ejecting ink onto a sheet using a plurality of arranged nozzles; a sheet conveying section that conveys the sheet; a line sensor that reads a test pattern image printed on the sheet by the plurality of nozzles and generates a test pattern read image; an ejection abnormality determination unit that determines, for each of the plurality of nozzles, whether or not the nozzle is an ejection abnormality nozzle based on a density distribution of the test pattern read image corresponding to the nozzle; the test pattern image includes a synchronization mark formed by a nozzle at a predetermined reference position among the plurality of nozzles, the line sensor includes a plurality of sensor units; the plurality of sensor units generate a plurality of partial test pattern read images by partially reading the test pattern image, respectively, as the test pattern read images; the reading areas of the plurality of sensor units have an overlapping section in a direction perpendicular to the conveying direction of the sheet, the synchronization mark is formed on the sheet so as to pass through the overlapping section, the ejection abnormality determination unit (a) identifies positions in the partial test pattern read image corresponding to each of some of the plurality of nozzles based on the positions of the synchronization marks in the partial test pattern read image, and (b) determines whether or not the nozzle corresponding to the positions is an ejection abnormality nozzle based on the density of the identified positions; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the width of the overlapping section is greater than the maximum value of the positional deviation in a direction perpendicular to the conveying direction of the sheet.

3. the test pattern image includes thin lines formed by nozzles that are not abnormal ejection nozzles among the plurality of nozzles, the plurality of partial test pattern read images are generated with an end portion on the overlapping section side in the main scanning direction as an origin; the ejection abnormality determination unit searches for the synchronization mark and the thin line from the origin along a main scanning direction for each of the plurality of partial test pattern read images; 2. The image forming apparatus according to claim 1, wherein:

4. a color adjustment unit that performs color adjustment of the line sensor, the sheet conveying unit conveys a color adjustment chart; the color adjustment unit performs the color adjustment based on a read image of the color adjustment chart generated by the line sensor, the plurality of sensor units generate a plurality of partial color adjustment chart read images by partially reading the color adjustment chart, the plurality of partial color adjustment chart read images are generated with the end of the overlapping section in the main scanning direction as the origin; the color adjustment unit individually performs color adjustment of the plurality of sensor units along a main scanning direction from the origin toward the other end of the partial color adjustment chart read image for each of the plurality of partial color adjustment chart read images; 2. The image forming apparatus according to claim 1, wherein:

Images