JP7537315B2 - Ejection data correction device, image forming apparatus, and ejection data correction method - Google Patents

Description

The present invention relates to an ejection data correction device, an image forming device, and an ejection data correction method.

Conventionally, there is an inkjet image forming device that forms an image on a recording medium by ejecting ink from the nozzle openings of a plurality of nozzles arranged on the recording medium, which is conveyed by a conveying device. In this inkjet image forming device, ink ejection defects (also called nozzle failure) can occur, such as the amount of ink ejected from the nozzle opening decreasing from the initial value, or even completely stopping ejection, or the ejection direction changing, due to nozzle clogging or the like.

In inkjet image forming devices, such ink ejection defects lead to a decline in the quality of the images formed. For this reason, conventionally, inkjet image forming devices periodically inspect the state of ink ejection from the nozzle openings. One method for inspecting the state of ink ejection involves capturing an image of a test image formed on a recording medium and analyzing the captured image data. Conventionally, this method judges whether ink ejection from each nozzle opening is defective by ejecting ink separately from each nozzle opening and checking the presence or absence of ejection and the density of the ink.

In addition, in inkjet recording devices, there is a complementation technology that, based on such test results, adjusts (complements) the amount of ink ejected from the nozzle opening adjacent to the defective nozzle causing the ink ejection defect, thereby suppressing the occurrence of image defects (white streaks) caused by the ink ejection defect (see, for example, Patent Document 1).

JP 2015-047725 A

However, even if the above-mentioned compensation technology is applied when ink ejection defects occur, there is a problem in that depending on how the ink ejection amount is adjusted (compensated), it may not be possible to sufficiently suppress the occurrence of image defects caused by ink ejection defects.

The object of the present invention is to provide an ejection data correction device, an image forming device, and an ejection data correction method that can sufficiently suppress the occurrence of image defects due to ink ejection defects.

The ejection data correction device according to the present invention comprises:
a specifying unit that specifies a first pixel position from which ink is ejected, which corresponds to a first nozzle having an ink ejection defect, and a second pixel position from which ink is not ejected, which corresponds to a second nozzle located in the periphery of the first nozzle and does not have an ink ejection defect, based on first ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to a plurality of nozzles that eject ink;
a change unit that changes an ink ejection position from the first pixel position to the second pixel position;
a spatial filter process execution unit that executes a spatial filter process on second ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to the second nozzle after changing the ejection position;
a correction unit that corrects the second ejection data based on the third ejection data obtained by executing the spatial filter process and the second ejection data;
Equipped with
The correction unit calculates, for each pixel position corresponding to the second nozzle, a difference value between the pixel value before the spatial filter processing is performed and the pixel value after the spatial filter processing is performed, and corrects the second ejection data by changing the ink ejection position from the pixel position where ink is ejected and the difference value is the largest to the pixel position where ink is not ejected and the difference value is the largest.

The ejection data correction method according to the present invention comprises the steps of:
identifying a first pixel position from which ink is ejected that corresponds to a first nozzle having an ink ejection defect and a second pixel position from which ink is not ejected that corresponds to a second nozzle located in the periphery of the first nozzle and having no ink ejection defect, based on first ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to a plurality of nozzles that eject ink;
changing an ink ejection position from the first pixel position to the second pixel position;
After changing the ejection position, a spatial filter process is performed on second ejection data indicating whether or not ink is ejected for each pixel position corresponding to the second nozzle;
Based on the third ejection data obtained by executing the spatial filter process and the second ejection data, a difference value between the pixel value before the spatial filter process is executed and the pixel value after the spatial filter process is executed is calculated for each pixel position corresponding to the second nozzle, and the ink ejection position is changed from the pixel position where ink is ejected and the difference value is the largest to the pixel position where ink is not ejected and the difference value is the largest, thereby correcting the second ejection data.

The present invention makes it possible to sufficiently suppress the occurrence of image defects caused by poor ink ejection.

FIG. 1 is a diagram illustrating a schematic configuration of an inkjet image forming apparatus. FIG. 2 is a schematic diagram illustrating a configuration of a head unit. FIG. 2 is a schematic cross-sectional view illustrating a configuration of an image reading unit. 1 is a block diagram showing a main functional configuration of an inkjet image forming apparatus; FIG. 13 is a diagram showing an example of a test chart used to detect defective nozzles. 6 is a flowchart illustrating an example of a faulty nozzle detection process according to the present embodiment. 10 is a flowchart illustrating an example of an ejection data correction process in the present embodiment. 10A to 10C are diagrams illustrating an example of ejection data correction processing in the present embodiment.

This embodiment will be described below with reference to the drawings.

Figure 1 is a diagram showing the schematic configuration of an inkjet image forming device 1. The inkjet image forming device 1 (functioning as the "image forming device" of the present invention) comprises a paper feed section 10, an image forming section 20, a paper discharge section 30, and a control section 40 (see Figure 4).

Under the control of the control unit 40, the inkjet image forming device 1 transports the recording medium P stored in the paper feed unit 10 to the image forming unit 20, forms an image on the recording medium P in the image forming unit 20, and transports the recording medium P with the image formed thereon to the paper discharge unit 30. As the recording medium P, various media capable of fixing the ink that has landed on the surface, such as paper such as plain paper or coated paper, fabric or sheet-like resin, can be used.

The paper feed unit 10 has a paper feed tray 11 that stores the recording medium P, and a media supply unit 12 that transports and supplies the recording medium P from the paper feed tray 11 to the image forming unit 20. The media supply unit 12 has a ring-shaped belt supported by two rollers on the inside, and transports the recording medium P from the paper feed tray 11 to the image forming unit 20 by rotating the rollers with the recording medium P placed on this belt.

The image forming unit 20 includes a conveying unit 21, a transfer unit 22, a heating unit 23, a head unit 24, a fixing unit 25, an image reading unit 26, and a delivery unit 28.

The transport unit 21 holds the recording medium P placed on the transport surface 211a (mounting surface) of the cylindrical transport drum 211, and transports the recording medium P on the transport drum 211 in the transport direction (Y direction) by rotating and moving around a rotation axis (cylindrical axis) extending in the X direction. The transport drum 211 has a claw portion and an air intake portion (not shown) for holding the recording medium P on the transport surface 211a. The recording medium P is held on the transport surface 211a by having its edge pressed by the claw portion and being sucked to the transport surface 211a by the air intake portion. The transport unit 21 is connected to a transport drum motor (not shown) for rotating the transport drum 211. The transport drum 211 rotates by an angle proportional to the amount of rotation of the transport drum motor.

The transfer unit 22 transfers the recording medium P transported by the medium supply unit 12 of the paper feed unit 10 to the transport unit 21. The transfer unit 22 is provided at a position between the medium supply unit 12 of the paper feed unit 10 and the transport unit 21, and holds and picks up one end of the recording medium P transported from the medium supply unit 12 with the swing arm unit 221, and transfers it to the transport unit 21 via the transfer drum 222.

The heating unit 23 is provided between the position of the transfer drum 222 and the position of the head unit 24, and heats the recording medium P transported by the transport unit 21 so that the temperature of the recording medium P falls within a predetermined temperature range. The heating unit 23 has, for example, an infrared heater, and energizes the infrared heater based on a control signal supplied from the control unit 40 (see FIG. 4) to cause the infrared heater to generate heat.

The head units 24 eject ink from nozzle openings provided on an ink ejection surface facing the transport surface 211a of the transport drum 211 at appropriate timing according to the rotation of the transport drum 211 holding the recording medium P, to form an image. The head units 24 are arranged so that the ink ejection surface and the transport surface 211a are separated by a predetermined distance. In the inkjet image forming device 1 in this embodiment, four head units 24 corresponding to four ink colors, yellow (Y), magenta (M), cyan (C), and black (K), are arranged at predetermined intervals from the upstream side in the transport direction of the recording medium P in the order of Y, M, C, and K.

Figure 2 is a schematic diagram showing the configuration of the head unit 24. Here, the surface of the head unit 24 that faces the transport surface 211a of the transport drum 211 is shown.

The head unit 24 has four recording heads 242 attached to a mounting member 244. Each of the recording heads 242 has a plurality of recording elements, each of which has a pressure chamber that stores ink, a piezoelectric element provided on the wall of the pressure chamber, and a nozzle 243. When a drive signal that causes the piezoelectric element to deform is input, the pressure chamber is deformed by the deformation of the piezoelectric element, changing the pressure within the pressure chamber, and ink is ejected from a nozzle that communicates with the pressure chamber.

In the recording head 242, two nozzle rows are formed, each consisting of nozzles 243 arranged at equal intervals in a direction intersecting the transport direction of the recording medium P (in this embodiment, a direction perpendicular to the transport direction, i.e., the X direction). These two nozzle rows are arranged such that the arrangement positions of the nozzles 243 are shifted from each other in the X direction by half the arrangement interval of the nozzles 243 in each nozzle row.

In addition, in the recording head 242, nozzles 243 that fail to eject ink (faulty nozzles) may occur due to processing variations during the formation of the nozzles 243, variations in the characteristics of the piezoelectric elements, clogging of the nozzles 243, or blockage due to the adhesion of foreign matter to the nozzle openings. A method for detecting faulty nozzles will be described later.

The four recording heads 242 are arranged in a staggered pattern so that the nozzle row's X-direction range is continuous without breaks. The X-direction range of the nozzles 243 included in the head unit 24 covers the X-direction width of the area on the recording medium P transported by the transport unit 21 where an image is formed, and the head unit 24 is used with its position fixed relative to the rotation axis of the transport drum 211 when forming an image. In other words, the head unit 24 has a line head capable of ejecting ink over the image-formable width in the X-direction relative to the recording medium P, and the inkjet image forming device 1 is a single-pass type inkjet image forming device.

The number of nozzle rows in the recording head 242 may be one or three or more, instead of two. The number of recording heads 242 in the head unit 24 may be three or less, or five or more, instead of four.

The ink ejected from the nozzles of the recording element is energy ray curable ink, which changes phase to a gel or sol depending on the temperature and hardens when exposed to energy rays such as ultraviolet light. In the present embodiment, ink is used that is gel-like at room temperature and becomes sol-like when heated. The head unit 24 includes an ink heating section (not shown) that heats the ink stored in the head unit 24. The ink heating section operates under the control of the control section 40, and heats the ink to a temperature at which it becomes sol-like.

The recording head 242 ejects ink that has been heated and turned into a sol. When this sol ink is ejected onto the recording medium P, the ink droplets land on the recording medium P, and then the ink quickly turns into a gel and solidifies on the recording medium P due to natural cooling.

The fixing unit 25 has a light-emitting unit arranged across the width of the transport unit 21 in the X direction, and irradiates the recording medium P placed on the transport unit 21 with energy rays such as ultraviolet rays from the light-emitting unit to cure and fix the ink ejected onto the recording medium P. The light-emitting unit of the fixing unit 25 is arranged opposite the transport surface 211a in the transport direction between the position of the head unit 24 and the position of the transfer drum 281 of the delivery unit 28.

In addition, the ink ejected from the nozzles of the recording element may be energy ray curable ink that changes phase to a gel or sol state depending on the temperature and hardens when irradiated with an electron beam (energy beam). In this case, the fixing unit 25 irradiates the recording medium P placed on the conveying unit 21 with an electron beam to harden and fix the ink ejected onto the recording medium P.

The image reading unit 26 is positioned so as to be able to read the surface of the recording medium P on the transport surface 211a at a position between the ink fixing position by the fixing unit 25 and the position of the transfer drum 281 in the transport direction. In this embodiment, the image reading unit 26 reads the surface of the recording medium P transported by the transport unit 21 within a predetermined reading range and outputs the captured image data to the control unit 40.

Figure 3 is a schematic cross-sectional view illustrating the configuration of the image reading unit 26. In Figure 3, the configuration of the image reading unit 26 in a cross section perpendicular to the X direction is shown. The image reading unit 26 includes a housing 261, a pair of light sources 262 housed inside the housing 261, mirrors 2631 and 2632, an optical system 264, and a line sensor 265.

The housing 261 is a rectangular parallelepiped member arranged so that one surface faces the transport surface 211a. The surface of the housing 261 facing the transport surface 211a is a light-transmitting surface 261a made of a light-transmitting material such as glass. In the following, the transport direction of the recording medium P at the position facing the light-transmitting surface 261a is the Y direction, and the direction perpendicular to the XY plane is the Z direction.

Each of the pair of light sources 262 is a line light source having a plurality of LEDs (Light Emitting Diodes) arranged in a range that includes the range in which an image can be formed by the head unit 24 in the X direction. The pair of light sources 262 are arranged at symmetrical positions with respect to a predetermined reference plane A perpendicular to the transport direction, and emit light to the recording medium P on the transport surface 211a through the light transmitting surface 261a of the housing 261. In addition, the angle of each light source 262 is adjusted so that light is irradiated at the same angle of incidence onto a line of the recording medium P that intersects with the reference plane A when the distance between the light transmitting surface 261a and the recording medium P on the transport surface 211a is a predetermined standard distance d.

Mirror 2631 has a length in the X direction corresponding to the range of arrangement of light source 262, and reflects light emitted from light source 262 and reflected by recording medium P, traveling along reference surface A, in the direction of mirror 2632. Mirror 2632 is provided at a position closer to light transmitting surface 261a than mirror 2631, and reflects the light reflected by mirror 2631 in the direction of optical system 264. By providing mirrors 2631 and 2632 in this manner, an appropriate optical path length is ensured within housing 261.

The optical system 264 focuses the incident light from the mirror 2632 at the position of the image sensor of the line sensor 265. The optical system 264 is adjusted so that when the distance between the light transmitting surface 261a and the recording medium P on the conveying surface 211a is a predetermined standard distance d, the surface of the recording medium P is imaged at the position of the image sensor of the line sensor 265, i.e., the focus is on the surface of the recording medium P. As the optical system 264, for example, one having a large number of gradient index lenses arranged to focus the incident light at a predetermined position by the refractive index distribution in the direction perpendicular to the optical axis can be used.

The line sensor 265 has a configuration in which multiple image pickup elements that output signals according to the intensity of incident light are arranged in the X direction. Specifically, the line sensor 265 has three rows of image pickup elements arranged in the X direction, and each row of image pickup elements outputs a signal according to the intensity of the R (red), G (green), and B (blue) wavelength components of the incident light. The image pickup elements corresponding to R, G, and B, respectively, can be, for example, a CCD (Charge Coupled Device) sensor having a photodiode as a photoelectric conversion element or a CMOS (Complementary Metal Oxide Semiconductor) sensor having a color filter that transmits light of the R, G, or B wavelength component arranged in the light receiving section. Note that an area sensor may be used in the image reading unit 26 instead of the line sensor 265.

The signal output from the line sensor 265 undergoes current-voltage conversion, amplification, noise removal, analog-to-digital conversion, etc. in an analog front end (not shown), and is output to the control unit 40 as imaging data indicating the luminance value of the read image. In this embodiment, the pixel value of the imaging data indicates the light detection intensity by the imaging element in 256 gradations from 0 to 255.

The delivery section 28 has a belt loop 282 with a circular belt supported by two rollers on the inside, and a cylindrical transfer drum 281 that transfers the recording medium P from the transport section 21 to the belt loop 282. The recording medium P transferred from the transport section 21 to the belt loop 282 by the transfer drum 281 is transported by the belt loop 282 and sent to the paper discharge section 30.

The paper discharge section 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent from the image forming section 20 by the delivery section 28 is placed.

Figure 4 is a block diagram showing the main functional configuration of the inkjet image forming device 1. The inkjet image forming device 1 includes a heating unit 23, a recording head driving unit 241 and a recording head 242, a fixing unit 25, an image reading unit 26, a control unit 40, a transport driving unit 51, an operation display unit 52, an input/output interface 53, and a bus 54.

The recording head driver 241 supplies a drive signal to the recording elements of the recording head 242 at an appropriate timing to deform the piezoelectric elements in accordance with the image data (and thus the ejection data), thereby ejecting an amount of ink from the nozzles 243 of the recording head 242 according to the pixel values of the image data. The ejection data (corresponding to the "first ejection data" of the present invention, hereinafter also referred to as "first ejection data") is halftone data obtained by executing a halftone process on the image data, and indicates the presence or absence of ink ejection (ink ejection: 1, ink not ejected: 0) and the density gradation at the time of ejection for each pixel position corresponding to each nozzle 243. Each pixel position corresponding to each nozzle 243 is a pixel position where ink is ejected only once by the nozzle 243.

The control unit 40 has a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a storage unit 44. The control unit 40 functions as an "ejection data correction device" that includes the "identification unit," "change unit," "spatial filter processing execution unit," and "correction unit" of the present invention.

The CPU 41 reads out various control programs and setting data stored in the ROM 43, stores them in the RAM 42, and executes the programs to perform various calculation processes. The CPU 41 also controls the overall operation of the inkjet image forming device 1.

RAM 42 provides working memory space for CPU 41 and stores temporary data. RAM 42 may include non-volatile memory.

The ROM 43 stores various control programs and setting data executed by the CPU 41. Note that a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used instead of the ROM 43.

The storage unit 44 stores print jobs (image formation commands) input from the external device 2 via the input/output interface 53, image data relating to the print jobs, test image data which is image data of a test chart (test image) used in the defective nozzle detection process described below, image data 44a captured by the image reading unit 26, defective nozzle data 44b which indicates defective nozzles with ejection problems, and the like. Of these, the print job includes information specifying the image data relating to the image to be formed, as well as information relating to the type of recording medium P on which the image is formed (for example, the size and thickness of the recording medium P). As the storage unit 44, for example, a HDD (Hard Disk Drive) is used, and a DRAM (Dynamic Random Access Memory) or the like may also be used in combination.

The transport drive unit 51 supplies a drive signal to the transport drum motor of the transport drum 211 based on a control signal supplied from the control unit 40 to rotate the transport drum 211 at a predetermined speed and timing.

Here, the transport drive unit 51 rotates the transport drum 211 at a first speed or a second speed greater than the first speed based on the control signal. The first speed is a speed that is preset as the speed when reading is performed by the image reading unit 26. The second speed is a speed that is preset as the speed when an image is formed by the head unit 24.

The transport drive unit 51 also supplies drive signals to motors for operating the medium supply unit 12, the transfer unit 22, and the delivery unit 28 based on control signals supplied from the control unit 40, thereby supplying the recording medium P to the transport unit 21 and discharging it from the transport unit 21.

The operation display unit 52 includes a display device such as a liquid crystal display or an organic EL display, and an input device such as operation keys and a touch panel arranged over the screen of the display device. The operation display unit 52 displays various information on the display device, and converts user input operations on the input device into operation signals and outputs them to the control unit 40.

The input/output interface 53 mediates the transmission and reception of data between the external device 2 and the control unit 40. The input/output interface 53 is, for example, composed of any one of various serial interfaces, various parallel interfaces, or a combination of these.

The bus 54 is a path for transmitting and receiving signals between the control unit 40 and other components.

The external device 2 is, for example, a personal computer, and supplies print jobs, image data, etc. to the control unit 40 via the input/output interface 53.

Next, we will explain how to detect defective nozzles in the inkjet image forming device 1.

In the inkjet image forming device 1 of this embodiment, defective nozzles are detected at a predetermined timing or based on a predetermined input operation by the user on the operation display unit 52. Defective nozzles are detected by recording a predetermined test chart on the recording medium P and analyzing the image data obtained by imaging this test chart with the image reading unit 26.

Figure 5 shows an example of a test chart used to detect defective nozzles. The test chart 60 shown in Figure 5 is an image formed on the recording medium P by the head unit 24, and includes a line pattern consisting of multiple lines 61 extending in the transport direction.

Figure 5 shows a portion of the test chart 60 recorded by one recording head 242. Similar line patterns are also recorded by the other recording heads 242 of the head unit 24.

Each line 61 of the test chart 60 is formed by ink ejected from a single nozzle 243 of the head unit 24. Furthermore, in this test chart 60, the lines 61 recorded by nozzles 243 that are adjacent in position in the X direction are recorded with a shift in the Y direction, and the Y direction positions of the lines 61 recorded by every seventh nozzle 243 are aligned with each other.

Since each of the multiple lines 61 in this test chart 60 corresponds to one of the multiple nozzles 243, if an abnormality is found in a specific line 61 in the image data captured by the image reading unit 26 of the test chart 60, the nozzle 243 corresponding to that specific line 61 can be identified as a defective nozzle. For example, if the line 61a shown in FIG. 5 is missing in the image data of the test chart 60, the nozzle 243 corresponding to that line 61a is identified as a defective nozzle that does not eject ink.

In addition, if the density of a particular line 61 in the image data of the test chart 60 is outside a predetermined reference range, the nozzle 243 corresponding to that particular line 61 is identified as a defective nozzle having an abnormality in the amount of ink ejected.

In addition, if a specific line 61 in the image data of the test chart 60 is not formed within a predetermined range corresponding to the position of the nozzle 243, the nozzle 243 corresponding to the specific line 61 is identified as a defective nozzle having an abnormality in the direction of ink ejection. When a defective nozzle is identified, defective nozzle data 44b indicating the array number of the defective nozzle in the head unit 24 is stored in the memory unit 44.

After the faulty nozzle has been identified, the print job is stored in the memory unit 44, and when an image forming operation is performed to form an image related to the print job on the recording medium P, the faulty nozzle data 44b is referenced and the ejection data is corrected so as to compensate for the ink ejection defects of the faulty nozzle. The image is then formed based on the corrected ejection data. This makes it possible to form an image with appropriate image quality even when there is a faulty nozzle.

Next, we will explain the defective nozzle detection process that detects defective nozzles, and the ejection data correction process that uses the defective nozzle detection results.

Figure 6 is a flowchart showing an example of a faulty nozzle detection process. This faulty nozzle detection process is executed when a predetermined input operation is performed on the operation display unit 52 by the user to instruct the execution of faulty nozzle detection. The faulty nozzle detection process may also be executed at a predetermined timing, for example, when the inkjet image forming device 1 is manufactured or shipped, or when the inkjet image forming device 1 has formed images on a predetermined number of recording media P.

First, the control unit 40 controls the head unit 24 to form the test chart 60 on the recording medium P (step S101). That is, the control unit 40 causes the transport drive unit 51 to output a drive signal to the transport drum motor of the transport drum 211, causing the transport drum 211 to rotate at the second speed described above. Then, the control unit 40 causes the recording head drive unit 241 to supply test image data (ejection data) related to the test chart 60 stored in the memory unit 44 to the recording head 242, thereby causing the head unit 24 to eject ink onto the recording medium P and form the test chart 60 on the recording medium P.

In addition, when the recording medium P to which the ink has been applied moves to the position of the fixing unit 25, the control unit 40 causes the fixing unit 25 to irradiate the ink with a predetermined energy beam, thereby fixing the ink to the recording medium P.

Next, the control unit 40 causes the image reading unit 26 to read the recording medium P on which the test chart 60 is formed (step S102). That is, the control unit 40 causes the conveying drive unit 51 to output a drive signal to the conveying drum motor of the conveying drum 211 to rotate the conveying drum 211 at a first speed. The control unit 40 also causes the image reading unit 26 to repeatedly read the test chart 60 on the recording medium P at an appropriate timing according to the rotation of the conveying drum 211, and acquires and stores the imaging data 44a in the memory unit 44.

Finally, the control unit 40 detects the faulty nozzle based on the image data of the test chart 60 (step S103). That is, the control unit 40 identifies the line 61 where an abnormality is found from the image data of the test chart 60, and identifies the nozzle 243 corresponding to the line 61 as a faulty nozzle. The control unit 40 generates faulty nozzle data 44b indicating the array number in the head unit 24 of the identified faulty nozzle, and stores it in the storage unit 44. When the process of step S103 is completed, the control unit 40 ends the faulty nozzle detection process.

Figure 7 is a flowchart showing an example of an ejection data correction process (corresponding to the "ejection data correction method" of the present invention) using the defective nozzle detection results. This ejection data correction process is performed for each pixel position corresponding to each nozzle 243 after halftone processing is performed on the image data input from the external device 2 to the control unit 40.

First, the control unit 40 refers to the first ejection data and the defective nozzle data 44b, and determines whether the pixel position corresponds to a defective nozzle (corresponding to the "first nozzle" of the present invention, hereinafter also referred to as the "defective nozzle") where an ink ejection defect is occurring, and whether the pixel position is where the ink is to be ejected (step S201).

If the result of the determination is that the data does not correspond to a defective nozzle causing an ink ejection defect, or that the data corresponds to a defective nozzle causing an ink ejection defect but is not a pixel position from which ink is ejected (step S201, NO), the control unit 40 ends the ejection data correction process.

On the other hand, if the pixel position corresponds to a defective nozzle having an ink ejection defect and from which ink is ejected (corresponding to the "first pixel position" of the present invention, hereinafter also referred to as the "first pixel position") (step S201, YES), the control unit 40 identifies a pixel position (corresponding to the "second pixel position" of the present invention, hereinafter also referred to as the "second pixel position") from which ink is not ejected that corresponds to a nozzle (corresponding to the "second nozzle" of the present invention, hereinafter also referred to as the "peripheral nozzle") located around the defective nozzle and from which ink is not ejected. The control unit 40 then changes the ink ejection position from the first pixel position to the second pixel position, i.e., corrects the first ejection data (step S202).

Next, the control unit 40 performs spatial filtering on the first ejection data, which indicates whether or not ink is ejected for each pixel position corresponding to the surrounding nozzles (corresponding to the "second ejection data" of the present invention, also referred to as "second ejection data" hereinafter) (step S203). In this embodiment, the spatial filtering is performed using a filter designed to retain the spatial frequency components of the halftone pattern (dot pattern) formed based on the first ejection data. In the spatial filtering, the sum of the products of the pixel values of the surrounding pixel positions corresponding to the pixel position of interest and the filter size of the filter and the filter coefficient is calculated as the spatial filtering result (pixel value) for the pixel of interest.

Next, the control unit 40 corrects the second ejection data based on the ejection data obtained by executing the spatial filter process (corresponding to the "third ejection data" of the present invention, hereinafter also referred to as the "third ejection data") and the second ejection data.

Specifically, the control unit 40 calculates the difference between the pixel value before the spatial filter process is performed and the pixel value after the spatial filter process is performed for each pixel position corresponding to the peripheral nozzles. The control unit 40 then identifies pixel position A, from among all pixel positions corresponding to the peripheral nozzles, where ink is ejected and the difference value is the largest (step S204). The control unit 40 also identifies pixel position B, from among all pixel positions corresponding to the peripheral nozzles, where ink is not ejected and the difference value is the largest (step S205).

Then, the control unit 40 changes the ink ejection position from pixel position A, where ink is ejected and the difference value is the largest, to pixel position B, where ink is not ejected and the difference value is the largest, i.e., corrects the second ejection data (step S206). By completing the process of step S206, the control unit 40 ends the ejection data correction process shown in FIG. 7.

Figure 8 is a diagram illustrating an example of the processing of the flowchart shown in Figure 7, particularly steps S202 and S203.

Figure 8A shows an image 80, which is a part of an image corresponding to the ejection data (first ejection data) before the processing of step S202 is performed. As shown in Figure 8A, the image 80 is composed of a plurality of dots (pixels) formed on the recording medium P by ejecting ink from a plurality of nozzles 243 provided in the recording head 242. In the example shown in Figure 8A, only the nozzle 243A of the plurality of nozzles 243 provided in the recording head 242 is a defective nozzle that is causing an ink ejection defect. In the first ejection data, the presence or absence of ink ejection is set for each pixel position included in the pixel region 82 (dot line) corresponding to the nozzle 243A. Specifically, the pixel positions 82A, 82B, and 82C included in the pixel region 82 are set as pixel positions at which ink is ejected, while the pixel positions other than the pixel positions 82A, 82B, and 82C are set in the first ejection data as pixel positions at which ink is not ejected.

As shown in FIG. 8B, the control unit 40 is located in the vicinity of the nozzle 243A (faulty nozzle), specifically, adjacent to the nozzle arrangement direction (the up-down direction in the figure), and identifies pixel position 84A from which ink is not ejected among pixel positions included in pixel region 84 corresponding to nozzle 243B (peripheral nozzle) that is not experiencing ink ejection defects. The control unit 40 then changes the ink ejection position, i.e., the dot formation position, from pixel position 82B included in pixel region 82 to pixel position 84A included in pixel region 84.

Next, as shown in FIG. 8C, the control unit 40 performs spatial filtering on the ejection data (second ejection data) indicating the presence or absence of ink ejection for each pixel position of pixel region 86 (excluding pixel region 82 corresponding to nozzle 243A (faulty nozzle), the same applies below) corresponding to multiple nozzles 243B-243G (peripheral nozzles) that are located around nozzle 243A (faulty nozzle) and are not experiencing ink ejection defects. In this embodiment, three nozzles 243B-243D above nozzle 243A (faulty nozzle) and three nozzles 243E-243G below nozzle 243A (faulty nozzle) are selected in the nozzle arrangement direction (up and down in the figure) as multiple nozzles that are located around nozzle 243A (faulty nozzle) and are not experiencing ink ejection defects.

The control unit 40 calculates the difference between the pixel value before spatial filter processing is performed and the pixel value after spatial filter processing is performed for each pixel position in the pixel region 86 corresponding to the multiple nozzles 243B-243G (peripheral nozzles). The control unit 40 then identifies, among all the pixel positions corresponding to the peripheral nozzles 243B-243G, pixel position A where ink is ejected and the difference value is the largest, and pixel position B where ink is not ejected and the difference value is the largest, and changes the ink ejection position from pixel position A to pixel position B, i.e., corrects the second ejection data. The process described with reference to FIG. 8 is also performed on pixel positions 82A and 82C included in the pixel region 82 corresponding to the nozzle 243A (faulty nozzle).

By the above process, after the ink ejection position is changed from pixel positions 82A, 82B, and 82C included in pixel region 82 corresponding to nozzle 243A (defective nozzle) to pixel region 84 corresponding to nozzle 243B (peripheral nozzle), the pixel positions (dot formation positions) where ink is ejected are distributed at uniform intervals without bias in pixel region 86 corresponding to multiple nozzles 243B to 243G (peripheral nozzles). In simple terms, the image is blurred (density is made uniform), and the user's visibility of the pixel positions where the ink ejection position has been changed is reduced. Therefore, even if a compensation technique is applied when an ink ejection defect occurs, the occurrence of image defects (white stripes) due to ink ejection defect may not be sufficiently suppressed depending on the method of adjusting (complementing) the ink ejection amount, which is a problem of the conventional technology.

As described above in detail, the ejection data correction device (control unit 40) in this embodiment includes a determination unit that determines the first pixel position 82B from which ink is ejected, which corresponds to the first nozzle 243A (faulty nozzle) having an ink ejection defect, and the second pixel position 84A from which ink is not ejected, which corresponds to the second nozzle 243B (peripheral nozzle) that is located around the first nozzle 243A and does not have an ink ejection defect, based on the first ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to the multiple nozzles 243 that eject ink; a change unit that changes the ink ejection position from the first pixel position 82B to the second pixel position 84A; a spatial filter processing execution unit that executes spatial filter processing on the second ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to the second nozzles 243B to 243G (peripheral nozzles) after the ejection position is changed; and a correction unit that corrects the second ejection data based on the third ejection data and the second ejection data obtained by executing the spatial filter processing.

Specifically, the correction unit calculates the difference between the pixel value before the spatial filter process is performed and the pixel value after the spatial filter process is performed for each pixel position corresponding to the second nozzles 243B to 243G (peripheral nozzles) based on the second and third ejection data. The correction unit then corrects the second ejection data by changing the ink ejection position from pixel position A, where ink is ejected and the difference value is the largest, to pixel position B, where ink is not ejected and the difference value is the largest.

In this embodiment, which is configured in this manner, in the pixel region 86 corresponding to the multiple nozzles 243B-243G (peripheral nozzles), the pixel positions (dot formation positions) where ink is ejected are distributed at uniform intervals without bias, which, in simple terms, blurs the image, thereby reducing the user's visibility of the pixel positions where the ink ejection position has been changed. Therefore, even if compensation technology is applied when ink ejection defects occur, depending on how the ink ejection amount is adjusted (complemented), this can suitably solve the problem of the conventional technology that the occurrence of image defects (white streaks) due to ink ejection defects may not be sufficiently suppressed.

In addition, in this embodiment, the spatial filter process is performed using a filter designed to retain the spatial frequency components of the halftone pattern (halftone dot pattern) formed based on the first ejection data. This makes it possible to match the spatial frequency between the halftone pattern formed based on the second ejection data (local portion) and the halftone pattern formed based on the first ejection data (whole portion), ensuring that the user does not feel uncomfortable with the corrected second ejection data, and therefore the image formed based on the first ejection data.

In addition, in this embodiment, the ink used in the inkjet image forming apparatus 1 has energy ray curing properties, which means that the ink is cured by irradiating it with energy rays (ultraviolet rays or electron beams). In other words, the ink fixed to the recording medium P by the fixing unit 25 is an ink that undergoes almost no change in deposition (specifically, height change) even after fixing. Therefore, in the event of ink discharge defects, the occurrence of image defects, particularly three-dimensional gloss streaks (uneven streaks), can be effectively suppressed.

In the above embodiment, the spatial filter process is performed using a filter designed to leave the spatial frequency components of the halftone pattern formed based on the first ejection data, but the present invention is not limited to this. For example, the spatial filter process may be performed using a filter designed to leave the spatial frequency components of blue noise characteristics. The spatial filter process may be performed using a filter designed to leave the spatial frequency components of low frequencies. In this way, the spatial frequency of the image formed based on the second ejection data can be matched to the blue noise characteristics or low spatial frequency, that is, the pixel positions (dot formation positions) where the ink is ejected can be distributed at uniform intervals without bias, and the user's visibility of the pixel positions where the ink ejection position has been changed can be reduced. As a result, it is possible to reliably prevent the user from feeling unnatural about the corrected second ejection data and therefore the image formed based on the first ejection data.

Note that the head unit 24 can form an image by ejecting ink with different dot diameters (large dots and small dots), and when the destination of the ink ejection position is a small dot, the control unit 40 may change the dot diameter of the destination to a large dot and increase the gradation value.

In addition, in the above embodiment, an example of detecting defective nozzles using a test chart 60 including multiple lines 61 has been described, but the present invention is not limited to this. For example, a gray chart consisting of gradation patterns formed by each nozzle 243 may be formed as a test image, and defective nozzles may be detected from uneven density in the reading results of the gray chart. With such a gray chart, it is possible to detect abnormalities in the ink ejection direction of the nozzle 243, as well as easily and appropriately detect abnormalities in the amount of ink ejected from the nozzle 243.

In the above embodiment, the recording medium P moving due to the rotation of the transport drum 211 is read by the image reading unit 26, and ink is ejected from the head unit 24 onto the moving recording medium P. However, the present invention is not limited to this. For example, the reading of the recording medium P by the image reading unit 26 and the ejection of ink onto the recording medium P by the head unit 24 may be performed while the rotation of the transport drum 211 is temporarily stopped.

In the above embodiment, the recording medium P is transported by the transport drum 211, but the present invention is not limited to this. For example, the recording medium P may be transported by a transport belt supported by two rollers and moving in response to the rotation of the rollers. The recording medium P may also be transported by a transport member that moves back and forth on the same plane.

In the above embodiment, the inkjet image forming device 1 is described as an example in which ink that is in a gel state at room temperature and becomes a sol state when heated is heated to a sol state and then ejected, but the present invention is not limited to this, and various known inks, including inks that are in a sol state or liquid state at room temperature, may be used.

Furthermore, the above-mentioned embodiments are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be interpreted in a limiting manner based on these. In other words, the present invention can be implemented in various forms without departing from its gist or main features.

REFERENCE SIGNS LIST 1 Inkjet image forming apparatus 2 External device 10 Paper feed section 11 Paper feed tray 12 Medium supply section 20 Image forming section 21 Transport section 211 Transport drum 211a Transport surface 22 Delivery unit 23 Heating section 24 Head unit 241 Recording head driving section 242 Recording head 243, 243A, 243B, 243C, 243D, 243E, 243F, 243G Nozzle 244 Mounting member 25 Fixing section 26 Image reading section 261 Housing 261a Light transmitting surface 262 Light source 2631, 2632 Mirror 264 Optical system 265 Line sensor 28 Delivery section 30 Paper discharge section 31 Paper discharge tray 40 Control section 41 CPU
42 RAM
43 ROM
44 Memory section 44a Image data 44b Defective nozzle data 51 Conveyor driving section 52 Operation display section 53 Input/output interface 54 Bus 60 Test chart 61, 61a Line 80 Image 82, 84, 86 Pixel area 82A, 82B, 82C, 84A Pixel position P Recording medium

Claims (11)

a specifying unit that specifies a first pixel position from which ink is ejected, which corresponds to a first nozzle having an ink ejection defect, and a second pixel position from which ink is not ejected, which corresponds to a second nozzle located in the periphery of the first nozzle and does not have an ink ejection defect, based on first ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to a plurality of nozzles that eject ink;
a change unit that changes an ink ejection position from the first pixel position to the second pixel position;
a spatial filter process execution unit that executes a spatial filter process on second ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to the second nozzle after changing the ejection position;
a correction unit that corrects the second ejection data based on the third ejection data obtained by executing the spatial filter process and the second ejection data;
Equipped with
the correction unit calculates, for each pixel position corresponding to the second nozzle, a difference value between a pixel value before the spatial filter process is performed and a pixel value after the spatial filter process is performed, and corrects the second ejection data by changing an ink ejection position from a pixel position where ink is ejected and the difference value is the largest to a pixel position where ink is not ejected and the difference value is the largest.
Discharge data correction device. the spatial filtering process is performed so as to leave spatial frequency components of a halftone pattern formed based on the first ejection data;
The ejection data correction device according to claim 1 . The spatial filtering is performed in such a way as to leave spatial frequency components characteristic of blue noise.
The ejection data correction device according to claim 1 . The spatial filtering is performed to retain low spatial frequency components.
The ejection data correction device according to claim 1 . The ejection data correction device according to any one of claims 1 to 4 ,
an image forming unit that forms an image on a recording medium based on the corrected second ejection data;
An image forming apparatus comprising: The ink used in the image forming apparatus has energy ray curing properties and is cured by irradiation with energy rays.
The image forming apparatus according to claim 5 . The energy ray is ultraviolet light.
The image forming apparatus according to claim 6 . The energy beam is an electron beam.
The image forming apparatus according to claim 6 . The image forming apparatus forms an image by a single pass method.
The image forming apparatus according to any one of claims 6 to 8 . Each pixel position corresponding to the plurality of nozzles is a pixel position to which ink is ejected only once by each of the plurality of nozzles.
The image forming apparatus according to claim 9 . identifying a first pixel position from which ink is ejected that corresponds to a first nozzle having an ink ejection defect and a second pixel position from which ink is not ejected that corresponds to a second nozzle located in the periphery of the first nozzle and having no ink ejection defect, based on first ejection data indicating the presence or absence of ink ejection for each pixel position corresponding to a plurality of nozzles that eject ink;
changing an ink ejection position from the first pixel position to the second pixel position;
After changing the ejection position, a spatial filter process is performed on second ejection data indicating whether or not ink is ejected for each pixel position corresponding to the second nozzle;
a difference value between a pixel value before the spatial filter process is performed and a pixel value after the spatial filter process is performed is calculated for each pixel position corresponding to the second nozzle based on the third ejection data obtained by executing the spatial filter process and the second ejection data, and the second ejection data is corrected by changing the ink ejection position from the pixel position where ink is ejected and the difference value is the largest to the pixel position where ink is not ejected and the difference value is the largest.
Dispensing data correction method.