JP2024046489A - Image formation device - Google Patents

Abstract

To provide an image formation device which can accurately detect a discharge failure nozzle regardless of a degree of ink bleeding of a print sheet.SOLUTION: A recording head allows aligned nozzles to discharge ink corresponding to an image to be printed. A control part 81 determines nozzles corresponding to each pixel of the image to be printed among the nozzles of the recording head, and allows the recording head to discharge ink from the nozzles. A discharge failure nozzle detection part 83 drives the recording head by a drive signal having a plurality of different drive waveforms and prints a plurality of test patterns, and detects a discharge failure nozzle by a test pattern having the highest detection sensitivity of the discharge failure nozzle among the plurality of test patterns, on the basis of concentration distribution of the plurality of test patterns.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus.

One inkjet type image forming device supplies a drive signal with a specific drive waveform for detecting defective nozzles to the recording head, prints a test pattern with the recording head, and based on the image of the printed test pattern, detects defective nozzles that are no longer able to eject ink normally among the nozzles in the recording head that eject ink, and changes the ejection amount of adjacent dots based on the occurrence of defective nozzles (see, for example, Patent Document 1).

JP2011-212932A

However, since the degree of ink bleeding differs depending on the print sheet on which the test pattern is printed, the density distribution in the test pattern image changes depending on the print sheet, and the detection sensitivity of defective ejection nozzles may decrease.

The present invention was made in consideration of the above problems, and aims to provide an image forming device that can accurately detect nozzles with poor ejection performance regardless of the degree of ink bleeding on the print sheet.

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 array of nozzles, a control unit that determines which nozzles of the recording head correspond to each pixel of the image to be printed and causes the recording head to eject ink from the nozzles, and a defective nozzle detection unit that (a) prints a test pattern on a print sheet with the recording head and (b) detects defective nozzles based on a read image of the test pattern. The defective nozzle detection unit drives the recording head with drive signals of multiple different drive waveforms to print multiple test patterns, and detects the defective nozzle from among the multiple test patterns using the test pattern with the highest detection sensitivity for the defective nozzle based on the density distribution of the multiple test patterns.

According to the present invention, it is possible to obtain an image forming apparatus that accurately detects a defective ejection nozzle regardless of the degree of ink bleeding on a print sheet.

These and other objects, features and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings.

FIG. 1 is a side view illustrating the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. 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. FIG. 3 is a block diagram showing the electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of a plurality of test patterns. FIG. 5 is a diagram illustrating a density defect caused by a defective ejection nozzle in a test pattern. FIG. 6 is a diagram illustrating an example of a read image of a test pattern printed on a print sheet with little bleeding and in which a density defect occurs due to ejection deviation. FIG. 7 is a diagram showing an example of a read image of a test pattern that is printed on a print sheet with a lot of bleeding and has density loss caused by ink ejection deviation. FIG. 8 is a flowchart illustrating the operation of the image forming apparatus 10 shown in FIGS.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a side view illustrating the mechanical internal 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, a copy machine, a facsimile machine, or a multifunction device.

The image forming apparatus 10 shown in FIG. 1 includes a print engine 10a and a sheet conveying section 10b. The print engine 10a physically forms a page image to be printed on a print sheet (print sheet, etc.). In this embodiment, the print engine 10a is a line-type inkjet print engine.

In this embodiment, the print engine 10a includes line-type recording heads 1a to 1d that correspond to four ink colors: cyan, magenta, yellow, and black.

Figure 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 Figure 1. For example, as shown in Figure 2, in this embodiment, each of the recording heads 1a, 1b, 1c, and 1d has multiple (here, three) head parts 11. The head parts 11 are arranged along the main scanning direction and are detachable from the device body. Note that the recording heads 1a, 1b, 1c, and 1d may have only one head part 11. The head part 11 of the recording heads 1a, 1b, 1c, and 1d includes multiple nozzles arranged two-dimensionally, multiple pressure chambers connected to the multiple nozzles and supplied with ink, and multiple piezoelectric actuators provided in the pressure chambers, which are driven by a drive signal corresponding to the image data of the image to be printed, to push ink from the pressure chambers to the nozzles and eject the ink from the nozzles, and eject ink corresponding to the image to be printed from the nozzles.

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

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 the print sheet used to print the page image on the first side to the print engine 10a, and the circulating sheet transport unit 10b2 transports the print sheets from the rear stage to the front stage of the print engine 10a while retaining a predetermined number of print sheets.

In this embodiment, the main sheet conveying section 10b1 includes an annular conveying belt 2 that is disposed opposite to the print engine 10a and conveys the print sheet, a driving roller 3 and a driven roller 4 on which the conveying belt 2 is suspended. It includes a suction roller 5 that nips the print sheet together with the conveyor belt 2, and a pair of discharge rollers 6, 6a.

The drive roller 3 and driven roller 4 rotate the conveyor belt 2. The suction roller 5 nips the print sheet conveyed from paper feed cassettes 20-1 and 20-2 (described below), 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, where images of each color are printed by the recording heads 1a to 1d. After color printing is completed, the print sheet is discharged to the discharge tray 10c or the like by the pair of discharge rollers 6, 6a.

Further, the main sheet conveyance section 10b1 includes a plurality of paper feed cassettes 20-1 and 20-2. The paper feed cassettes 20-1 and 20-2 contain print sheets SH1 and SH2, and lift plates 21 and 24 push the print sheets SH1 and SH2 upward to abut against 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 the upper side by the pick-up rollers 22 and 25 onto the paper feed rollers 23 and 26, respectively. The paper feed rollers 23 and 26 are rollers that transport the print sheets SH1 and SH2 fed by the pickup rollers 22 and 25 from the paper feed cassettes 20-1 and 20-2 one by one onto the transport path. The conveyance roller 27 is a conveyance roller on a common conveyance path for the print sheets SH1 and SH2 conveyed from the paper feed cassettes 20-1 and 20-2.

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 described below) during double-sided printing. The circulating sheet transport unit 10b2 includes a transport roller 41 and a switchback transport path 41a that reverses the travel 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.

The image forming device 10 further includes a line sensor 31 and a sheet detection sensor 32.

The line sensor 31 is an optical sensor that is arranged along the direction perpendicular to the conveyance direction of the print sheet and detects the positions of both end edges (both side edges) of the print sheet. For example, the line sensor 31 is a CIS (Contact Image Sensor). In this embodiment, the line sensor 31 is arranged between the registration roller 28 and the print engine 10a.

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

For example, as shown in FIG. 1, the print engine 10a is disposed above or below the print sheet conveyance path (in this case, at the top), and the line sensor 31 is disposed above or below the print sheet conveyance path. The circulating sheet conveyance section 10b2 is arranged at the other side (lower side in this case) of the print engine 10a, and conveys the print sheet by switching back from the downstream side of the print engine 10a to the upstream side of the line sensor 31.

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

The operation panel 72 is disposed on the surface of the housing of the image forming device 10 and includes a display device 72a such as a liquid crystal 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.

The storage device 73 is a non-volatile storage device (such as a flash memory or a hard disk drive) that stores data, programs, etc. necessary for controlling the image forming device 10.

The image reading device 74 includes a platen glass and an automatic document feeder, and optically reads an image of a document placed on the platen glass or a document conveyed by the automatic document feeder, and reads the image. Generate image data.

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 operates as various processing units. The computer is equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and programs stored in the ROM, storage device 73, etc. are loaded into the RAM and executed by the CPU. As a result, it operates as various processing units (together with ASIC as necessary). Here, the controller 75 operates as a control section 81 , an image processing section 82 , a defective ejection nozzle detection section 83 , and a correction processing section 84 .

The control unit 81 controls the image output unit 71 (print engine 10a, sheet conveyance unit 10b, etc.) and executes a print job requested by the user. In this embodiment, the control unit 81 causes the image processing unit 82 to perform predetermined image processing, and controls the print engine 10a (head unit 11) to eject ink to form a print image on the print sheet. . Specifically, the control unit 81 supplies drive signals to each piezoelectric actuator of the head unit 11 to cause ink to be ejected from the nozzles. The image processing unit 82 performs predetermined image processing such as RIP (Raster Image Processing), color conversion, and halftoning on image data of an image to be printed on a print sheet.

In this way, the control unit 81 causes the print engine 10a to print a user document image based on the print image data specified by the user.

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 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.

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

The defective nozzle detection unit 83 uses the control unit 81 to (a) print a test pattern on a print sheet using the recording heads 1a to 1d, and (b) detect defective nozzles based on the read image of the test pattern. Note that the test pattern is printed independently for each ink color.

Specifically, in the test pattern, density defects occur in pixels corresponding to the nozzles with poor ejection, and the nozzles with poor ejection are identified based on the position of the density defects (position of poor ejection). In this embodiment, a line sensor 31 is provided to detect the position of the print sheet, so that, for example, the above-mentioned test pattern is printed on a print sheet, the print sheet is transported by the circulating sheet transport unit 10b2, the image of the printed test pattern is read by the line sensor 31, and the position of poor ejection is detected based on the density distribution of the image in the main scanning direction.

In particular, the faulty nozzle detection unit 83 uses the control unit 81 to drive the recording heads 1a to 1d with drive signals having multiple drive waveforms that are different from one another to print multiple test patterns, and detects the faulty nozzle using the test pattern that has the highest detection sensitivity for faulty nozzles among the multiple test patterns based on the density distribution (density distribution in the main scanning direction) of the multiple test patterns.

Here, the drive waveform is a pulse-like waveform, and the multiple drive waveforms differ in at least one of the pulse height, pulse width, rising slope, and falling slope, and this difference causes a difference in the amount of ink ejected. In other words, the multiple drive waveforms eject different amounts of ink droplets from the nozzles so that the dots in the multiple test patterns have different dot diameters.

FIG. 4 is a diagram showing an example of multiple test patterns. Each test pattern consists of a first strip-shaped test pattern (horizontal strip test pattern) that is continuous in the main scanning direction with a constant density, and a 1-dot thin line that is arranged every N dots and is independent for each nozzle (a linear strip along the sub-scanning direction). (vertical line test pattern). Test patterns #1, #2, and #3 in FIG. 4 are images printed with mutually different drive waveforms, and are drawn with dots having mutually different dot diameters.

FIG. 5 is a diagram illustrating a density defect caused by a defective ejection nozzle in a test pattern. Here, the ejection failure nozzle is a nozzle that is not ejecting or has ejection deviation. For example, as shown in FIG. 5, in a read image of a horizontal band test pattern, the position where a dip appears in the density distribution (in the case of RGB data, the position where the peak of pixel value appears, as shown in FIG. 5) is the ejection failure position. Detected. Furthermore, in the read image of the vertical line test pattern, the position of a peak defect in the density distribution corresponding to the set vertical line arrangement is detected as the ejection failure position.

Note that "distorted ejection" refers to a state in which the landing position of droplets ejected from a nozzle is misaligned in the main scanning direction. For example, as shown in Figure 5, for nozzles with defective ejection, particularly those with irregular ejection, the width of the density loss in the test pattern is narrower than in cases of no ejection, so appropriate detection sensitivity is required.

In this embodiment, the faulty nozzle detection unit 83 identifies the test pattern with the highest sensitivity for detecting faulty nozzles based on the difference in density between the pixel density of the faulty nozzle and the pixel density of the pixel density of the normal nozzle in the density distribution described above.

FIG. 6 is a diagram illustrating an example of a read image of a test pattern printed on a print sheet with little bleeding and in which a density defect occurs due to ejection deviation. FIG. 7 is a diagram illustrating an example of a read image of a test pattern printed on a print sheet with a lot of bleeding and in which a density defect occurs due to ejection deviation.

For example, in FIGS. 6 and 7, the test patterns are printed with a driving waveform such that the dot diameter of test pattern #1>the dot diameter of test pattern #2>the dot diameter of test pattern #3.

Further, when printed on a print sheet with little bleeding, the dot diameter becomes smaller than when printed on a print sheet with much bleeding.

For example, in the case shown in Figure 6, the density difference H1 of test pattern #1 > the density difference H2 of test pattern #2 > the density difference H3 of test pattern #3, so test pattern #1 is identified as the test pattern with the highest sensitivity for detecting nozzles with defective ejection.

For example, in the case shown in Figure 7, the density difference H1 of test pattern #1 < the density difference H2 of test pattern #2 < the density difference H3 of test pattern #3, so test pattern #3 is identified as the test pattern with the highest sensitivity for detecting nozzles with defective ejection.

The correction processing unit 84 executes correction processing corresponding to each detected ejection failure nozzle in the image to be printed. In this correction process, for example, the image data is corrected so as to make the ejection failure nozzle non-ejection and to increase the ink ejection amount of the nozzle adjacent to the ejection failure nozzle.

The read image of the test pattern described above is obtained using the line sensor 31 or the image reading device 74. When the line sensor 31 is used to detect nozzles with defective ejection as described above, the nozzles with defective ejection are automatically detected and a print sheet with the test pattern printed on it is discharged. Also, instead of using the line sensor 31, the print sheet with the test pattern printed on it 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.

Next, the operation of the image forming apparatus 10 will be explained.

(a) Detection of defective discharge nozzle

FIG. 8 is a flowchart illustrating the operation of the image forming apparatus 10 shown in FIGS. 1 to 3.

The defective nozzle detection unit 83 uses the control unit 81 to cause the image output unit 71 to print multiple test patterns as described above on a print sheet. At that time, the control unit 81 supplies drive signals of multiple drive waveforms to the recording heads 1a to 1d to print the multiple test patterns on the print sheet (step S1).

Then, as described above, the ejection failure nozzle detection unit 83 uses the line sensor 31 and the image reading device 74 to obtain read images of a plurality of test patterns (image data of each ink color) (step S2). .

The ejection failure nozzle detection unit 83 identifies the density distribution of the read images in the main scanning direction for each of the read images of a plurality of test patterns, and selects the test pattern with the highest detection sensitivity based on the density distribution as described above. The ejection failure position is identified based on the read image of the test pattern, and the nozzle corresponding to the ejection failure position is identified as the ejection failure nozzle (step S4).

Thereafter, the ejection failure nozzle detection unit 83 uses the control unit 81 to cause the image output unit 71 to print a confirmation pattern (test pattern or specific image) after the correction process (step S5). By visually checking the printed confirmation pattern, the user can confirm that the correction process has been performed appropriately.

In this way, the defective ejection nozzle to be subjected to the correction process is identified.

(b) Operation when printing

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.

At this time, the correction processing unit 84 reads the data of the ejection failure position and the nozzle from the storage device 73 before starting printing to specify the ejection failure position and the nozzle, and the position of the print sheet is detected by the line sensor 31. and (a) identify the nozzle corresponding to each pixel in the above image, (b) identify the pixel corresponding to the defective ejection nozzle in the above image, and execute correction processing for that pixel and its adjacent pixels. . Then, the control unit 81 executes the above-described printing based on the image data after the correction process.

As described above, according to the above embodiment, the non-ejecting nozzle detection unit 83 drives the recording heads 1a to 1d with drive signals having multiple drive waveforms that are different from each other to print multiple test patterns, and detects non-ejecting nozzles using the test pattern that has the highest detection sensitivity for non-ejecting nozzles among the multiple test patterns based on the density distribution of the multiple test patterns.

This allows the location of the defective ejection to be identified using multiple test patterns with different dot diameters, so that the defective nozzle can be accurately detected regardless of the degree of ink bleeding on the print sheet.

Note that various changes and modifications to the embodiments described above 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. It is intended that such changes and modifications be included within the scope of the claims.

The present invention can be applied to, for example, inkjet type image forming devices.

Reference Signs List 1a to 1d Recording head 10 Image forming apparatus 81 Control unit 83 Discharge defective nozzle detection unit

Claims (4)

a print head that ejects ink corresponding to an image to be printed from an array of nozzles;
a control unit that determines, among the nozzles of the recording head, a nozzle that corresponds to each pixel of the image to be printed, and causes the recording head to eject ink from the nozzle;
(a) printing a test pattern on a print sheet by the recording head; (b) detecting a nozzle that is malfunctioning based on a read image of the test pattern;
the faulty nozzle detection unit drives the recording head with a drive signal having a plurality of drive waveforms different from one another to print a plurality of test patterns, and detects the faulty nozzle by a test pattern having the highest detection sensitivity for the faulty nozzle among the plurality of test patterns based on density distribution of the plurality of test patterns;
An image forming apparatus comprising: The image forming apparatus according to claim 1, characterized in that the defective nozzle detection unit identifies a test pattern with the highest detection sensitivity for the defective nozzle based on the difference in density between the density of the pixel corresponding to the defective nozzle and the density of the pixel corresponding to the normal nozzle in the density distribution. The image forming device according to claim 2, characterized in that the defective nozzle is a nozzle that is experiencing misaligned ejection. The image forming device according to any one of claims 1 to 3, characterized in that the multiple drive waveforms cause the nozzles to eject different amounts of the ink droplets so that the dots in the multiple test patterns have different dot diameters.

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