Inkjet recording device

Abstract

An inkjet recording apparatus capable of suppressing deterioration in image quality is provided. [Solution] The inkjet recording device includes a recording unit, an image reading unit, and a control unit. When executing a correction mode, the control unit records a second check chart that has been halftoned using a selected pattern on a sheet, the image reading unit reads the recorded second check chart to obtain second density information for the recording head, corrects the head drive conditions according to the second density information, and when determining a pattern for halftoning when executing a normal image formation mode, excludes patterns for which the drive voltage applied to the piezoelectric element under the corrected head drive conditions exceeds a limit value.

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording apparatus. [Background technology]

[0002] A conventional inkjet recording device includes a recording unit, an image processing unit, and a control unit. The recording unit ejects ink from a plurality of nozzles of a plurality of recording heads to record an image on a sheet. The image processing unit processes image data input to the recording unit. The control unit controls the recording unit and the image processing unit.

[0003] The control unit performs image processing on the image data input to the recording unit, thereby suppressing uneven density of the image recorded on the sheet and suppressing deterioration of image quality. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-268337 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional inkjet recording devices, the degree to which ink droplets penetrate into a recording medium varies depending on the type of recording medium. Therefore, when recording images on different types of recording media, even if image processing is performed on the image data, there is a possibility that uneven density of the image recorded on the sheet will not be eliminated, which may result in a deterioration of image quality.

[0006] The present invention has been made in view of the above points, and has as its object to provide an inkjet recording apparatus that can suppress deterioration in image quality. [Means for solving the problem]

[0007] In order to solve the above problems, the inkjet recording apparatus of the present invention includes a recording unit, an image reading unit, and a control unit. The recording unit ejects ink from a plurality of nozzles of a plurality of recording heads to record an image on a sheet. The image reading unit reads the density of the image recorded on the sheet. The control unit controls the recording unit and the image reading unit. The recording head has a piezoelectric element that can adjust the amount of ink ejected from the nozzle by deforming in response to a drive voltage. The control unit has an image processing unit and a limit determination unit. The image processing unit is capable of halftone processing image data input to the recording unit using a plurality of patterns with different concentrations. The limit determination unit determines whether the drive voltage applied to the piezoelectric element exceeds a preset limit value. The control unit determines a halftone processing pattern when executing a normal image formation mode, and is capable of executing a correction mode that corrects the drive conditions of the recording head. When the correction mode is executed, the control unit records a first check chart for density measurement on a sheet, the image reading unit reads the recorded first check chart to obtain first density information of the recording head, selects a halftone processing pattern according to the first density information, records a second check chart halftone processed using the selected pattern on the sheet, the image reading unit reads the recorded second check chart to obtain second density information of the recording head, corrects the driving conditions of the recording head according to the second density information, and excludes patterns in which the driving voltage applied to the piezoelectric element under the corrected driving conditions of the recording head exceeds a limit value from the halftone processing patterns when the normal image formation mode is executed. [Effects of the Invention]

[0008] According to the configuration of the present invention, it is possible to provide an inkjet recording apparatus that can suppress deterioration in image quality. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an inkjet recording apparatus 100 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the recording unit 104 of the inkjet recording apparatus 100 of FIG. [Figure 3] 1 is a block diagram of an inkjet recording apparatus 100 according to an embodiment of the present invention. [Figure 4] FIG. 10 is an enlarged plan view of a portion of an image A1 recorded using image data that has been halftoned. [Figure 5] FIG. 10 is an enlarged plan view of a portion of an image A2 recorded using image data that has been halftoned. [Figure 6] 1 is a plan view showing an example of a check chart 20 for measuring concentration according to an embodiment of the present invention. [Figure 7] 5 is a flowchart showing an example of execution of a correction mode in the inkjet recording apparatus 100 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] <1. Configuration of Inkjet Recording Apparatus> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic configuration of an inkjet recording apparatus 100 to which a method for detecting density unevenness in nozzles according to an embodiment of the present invention is applied. Fig. 2 is a plan view of a recording unit 104 of the inkjet recording apparatus 100 shown in Fig. 1.

[0011] The inkjet recording apparatus 100 is, for example, an inkjet recording printer. The inkjet recording apparatus 100 includes a main body (apparatus main body) 101, a sheet supply unit 102, a sheet conveying unit 103, a recording unit 104, a drying unit 105, a sheet discharge unit 106, and a control unit 107.

[0012] The sheet supply unit 102 stores multiple sheets (recording media) P and separates and sends out the sheets P one by one during recording. The sheet supply unit 102 includes a cassette CA. The cassette CA stores the sheets P. That is, the inkjet recording apparatus 100 is equipped with the sheet supply unit 102 including the cassette CA that stores the sheets P. The cassette CA is detachable from the main body 101. The operation of storing the sheets P in the cassette CA is performed by the user. When performing the storage operation, the user pulls out the cassette CA from the main body 101, stores the sheets P in the cassette CA, and then attaches the cassette CA to the main body 101.

[0013] The ink permeability (degree of penetration) and drying property of the sheet P differ depending on the type of paper. Examples of the sheet P include gloss coated paper, silk coated paper, satin coated paper, semi-gloss coated paper, fine paper, plain paper, and inkjet matte paper.

[0014] The sheet conveying unit 103 conveys the sheet P sent out from the sheet supply unit 102 to the recording unit 104 and the drying unit 105, and further discharges the sheet P after printing and drying to the sheet discharge unit 106. The sheet conveying unit 103 has a first belt conveying unit 1031 and a second belt conveying unit 1032. The first belt conveying unit 1031 and the second belt conveying unit 1032 adsorb and hold the sheet P on the upper surface of an endless belt and convey it. When double-sided printing is performed, the sheet conveying unit 103 distributes the sheet P after printing and drying on the first side to the reversing conveying unit 1034 by the branching unit 1033, and further switches the conveying direction to reverse the sheet P and convey it again to the recording unit 104 and the drying unit 105.

[0015] The recording unit 104 faces the sheet P, which is attracted to and held on the upper surface of the first belt conveyor 1031 and conveyed, and is disposed above the first belt conveyor 1031 at a predetermined distance. The recording unit 104 has, for example, line-type inkjet recording heads 1041. The recording heads 1041 include recording heads 1041B, 1041C, 1041M, and 1041Y corresponding to four colors: black, cyan, magenta, and yellow. A plurality (e.g., three) of the recording heads 1041 for each color are arranged in a staggered pattern along the sheet width direction (arrow Dm in FIG. 2 = main scanning direction) perpendicular to the sheet conveyance direction (arrow Ds in FIG. 2 = sub-scanning direction). The number and arrangement of the recording heads 1041 are not limited to the example described above.

[0016] The multiple nozzles 1042 are arranged in a row along the sheet width direction (main scanning direction) Dm, and can eject ink over the entire printing area. The printing unit 104 sequentially ejects ink from four color printing heads 1041B, 1041C, 1041M, and 1041Y toward the sheet P conveyed by the first belt conveying unit 1031, and records a full-color image or a monochrome image on the sheet P.

[0017] More specifically, the print head 1041 is an inkjet head having a plurality of print elements including a plurality of nozzles 1042. The nozzles 1042 are arranged at the bottom of the print head 1041.

[0018] In addition to the nozzles 1042, the recording elements include pressure chambers (not shown) that store ink and piezoelectric elements (not shown) that are provided on the side walls of the pressure chambers, and the pressure chambers communicate with the nozzles 1042. The recording head 1041 is supplied with a driving voltage as a driving condition from the control unit 107 that causes the piezoelectric elements to deform in accordance with the pixel values ​​of the image data.

[0019] This causes the piezoelectric element to deform, and the pressure chamber to deform in accordance with the drive voltage. At this time, the pressure inside the pressure chamber changes, and ink is ejected from the nozzle 1042 that communicates with the pressure chamber. As a result, from each of the nozzles 1042, a liquid amount of ink corresponding to the pixel value of the image data is ejected toward the sheet P, and an image is formed on the sheet P. In other words, the recording head 1041 has a piezoelectric element that deforms in accordance with the drive voltage and can adjust the amount of ink ejected from the nozzle. Furthermore, increasing the drive voltage increases the amount of ink ejected, and decreasing the drive voltage decreases the amount of ink ejected.

[0020] The drying unit 105 is disposed downstream of the recording unit 104 in the sheet conveying direction, and is provided with a second belt conveying unit 1032. The sheet P on which an ink image has been recorded in the recording unit 104 is adsorbed and held by the second belt conveying unit 1032 in the drying unit 105, and the ink is dried while being conveyed.

[0021] The control unit 107 includes a CPU, a memory unit, and other electronic circuits and electronic components (not shown). The CPU controls the operation of each component provided in the inkjet recording apparatus 100 based on control programs and data stored in the memory unit to perform processing related to the functions of the inkjet recording apparatus 100. The sheet supply unit 102, the sheet conveying unit 103, the recording unit 104, and the drying unit 105 each receive individual commands from the control unit 107 and perform recording on the sheet P in cooperation with each other. The memory unit is configured by a combination of a non-volatile storage device such as a program ROM (Read Only Memory) or a data ROM (not shown), and a volatile storage device such as a RAM (Random Access Memory).

[0022] 3 is a reading area diagram showing a schematic configuration of the inkjet recording apparatus 100. The inkjet recording apparatus 100 further includes a display unit 2, an operation unit 3, and an image reading unit 4. The density unevenness detection unit 1 can execute various processes for detecting density unevenness of the nozzles 1042. The display unit 2, the operation unit 3, and the image reading unit 4 are connected to a control unit 107.

[0023] The display unit 2 is configured, for example, by a liquid crystal display panel or the like, and can display various information related to the control unit 107, information about processing results, etc. The operation unit 3 is an input device configured, for example, by a keyboard, a touch panel, etc., and can input operation information, setting information, etc. to the control unit 107.

[0024] The image reading unit 4 includes an image sensor such as a line sensor, optically reads the image on the sheet P, generates image data corresponding to the image, and transmits the image data to the control unit 107. The control unit 107 executes various processes for detecting density unevenness of the nozzles 1042 based on the image data of the check chart 20.

[0025] The image sensor has, for example, a plurality of detection elements 41, a light source, a lens, etc. The detection elements 41 are a plurality of photoelectric conversion elements arranged in the sheet width direction, with approximately the same number of detection elements 41 corresponding to the plurality of nozzles 1042. The image reading unit 4 detects ink ejected onto the sheet P by receiving reflected light from the light source irradiated onto the sheet P via the lens at the detection elements 41.

[0026] The image reading unit 4 can acquire the formed image of the sheet P on which the check chart 20 is recorded, for each of a plurality of wavelength components, for example, three wavelengths of red (R), green (G), and blue (B). The detection element of the line sensor can be a CCD (Charge Coupled Device) type imaging element or a CMOS (Complementary Metal Oxide Semiconductor) type imaging element. Note that the image reading unit 4 is not limited to the above configuration, and for example, instead of a line sensor, an area sensor in which imaging elements are arranged two-dimensionally can be used.

[0027] The control unit 107 controls the printing operation by the multiple nozzles 1042. The control unit 107 has a density information acquisition unit 1075, a determination unit 1077, an image processing unit 1071, a discharge control unit 1072, a correction unit 1073, and a limit determination unit 1074. The functions of each of these components are realized by performing arithmetic processing in accordance with a predetermined program.

[0028] The density information acquisition unit 1075 acquires the density values ​​of the check chart 20 based on the read data acquired from the image reading unit 4. In addition, the density information acquisition unit 1075 acquires the density information of the recording head 1041 corresponding to the check chart 20 based on the acquired density values.

[0029] The determination unit 1077 determines the density information of the print head 1041 acquired by the density information acquisition unit 1075 using a threshold value stored in advance in a storage unit. This makes it possible to determine whether density unevenness exceeding a predetermined threshold value has occurred in a portion of the check chart 20 in the main scanning direction. If the determination unit 1077 determines that density unevenness exceeding the predetermined threshold value has occurred in a portion of the check chart 20 in the main scanning direction, it identifies the defective nozzle that is causing the density unevenness from the determination result. A defective nozzle is, for example, a nozzle 1042 that is clogged and cannot eject ink droplets, or a nozzle 1042 where the landing position of ejected ink droplets is shifted.

[0030] The image processing unit 1071 generates print data to be actually printed on the sheet P based on the image data for printing input to the inkjet printing apparatus 100. The image processing unit 1071 can also perform halftone processing on the image data input to the printing unit 104 using a dither threshold matrix. The image processing unit 1071 can halftone the image data input to the printing unit 104 using a plurality of patterns with different degrees of concentration. A plurality of dither threshold matrix patterns are stored in advance in a storage unit (not shown). Examples of halftone processing include a concentrated pattern and a dispersed pattern.

[0031] 4 and 5 are enlarged plan views of a portion of an image recorded with halftone-processed image data. In FIGS. 4 and 5, black dots represent ink droplets. In FIGS. 4 and 5, each pixel area is represented by a solid rectangle, but such solid rectangles are not actually recorded on the sheet P. Also, FIG. 4 shows image A1 of a dispersed pattern, and FIG. 5 shows image A2 of a concentrated pattern. Compared to image A1 of the dispersed pattern, image A2 of the concentrated pattern has a higher concentration and more ink droplet dot clusters. Increasing the concentration reduces resolution, but reduces the likelihood of ink droplets interfering with each other in adjacent pixel areas.

[0032] When using a sheet P made of paper with low ink droplet penetration, ink droplets are prone to landing interference in adjacent pixel areas. By processing the image data using a highly concentrated pattern, density unevenness caused by defective nozzles becomes less noticeable. This reduces density unevenness in the image recorded on the sheet P, preventing degradation of image quality.

[0033] On the other hand, when using a sheet P of paper type that has a high degree of ink droplet penetration, it is difficult for ink droplets to land and interfere with each other in adjacent pixel areas. In response to this, by halftone processing the image data with a dispersed pattern with low concentration, it is possible to reduce density unevenness while suppressing a decrease in resolution of the image recorded on the sheet P.

[0034] Furthermore, the image processing unit 1071 generates print data for printing a check chart 20 for density measurement onto a sheet P when identifying the nozzle 1042 that is causing density unevenness.

[0035] The ejection control unit 1072 controls the ink ejection operation of each of the multiple nozzles 1042 so that an image corresponding to the print data generated by the image processing unit 1071 is recorded on the sheet P. More specifically, the ejection control unit 1072 controls the drive voltage to the print head 1041 based on the set drive conditions of the print head 1041, thereby controlling the ejection amount of ink droplets ejected from each of the nozzles 1042.

[0036] The correction unit 1073 performs various correction processes when an abnormal nozzle 1042 is identified by the determination unit 1077. For example, the correction unit 1073 receives information from the determination unit 1077 that density unevenness has occurred in a part of the check chart 20 in the main scanning direction Dm, and density information about the print head 1041 that is the cause of the density unevenness.

[0037] The correction unit 1073 corrects the driving conditions of the recording head 1041 that are the cause of the density unevenness based on the density information. This increases or decreases the amount of ink droplets ejected from each nozzle 1042 of the recording head 1041 that is the cause of the density unevenness, thereby suppressing the occurrence of density unevenness. By further correcting the driving conditions of the recording head 1041 for the halftone processed image data, the occurrence of density unevenness can be further suppressed.

[0038] The driving conditions of the print head 1041 are, for example, the magnitude of the voltage value (voltage amplitude) or application time of the driving voltage applied to the print head 1041. By correcting the driving conditions of the print head 1041, the amount of ink droplets ejected from each nozzle 1042 can be adjusted.

[0039] The limit determination unit 1074 determines whether the drive voltage applied to the piezoelectric element exceeds a preset limit value. Continuing to apply a drive voltage exceeding the limit value to the piezoelectric element may cause the piezoelectric element to deteriorate. This may cause the amount of ink ejected from the nozzle to vary depending on the applied drive voltage, which may result in uneven density. Therefore, by having the limit determination unit 1074 determine the drive voltage applied to the piezoelectric element, the drive voltage applied to the piezoelectric element can be suppressed, preventing deterioration of the piezoelectric element.

[0040] 6 is a plan view showing an example of a check chart 20 for detecting density unevenness according to an embodiment. Note that, unless otherwise required, the identification symbols "B," "C," "M," and "Y" representing each color may be omitted.

[0041] The check chart 20 includes check patterns 21Y, 21B, 21C, and 21M drawn with ink droplets of yellow, black, cyan, and magenta, respectively.

[0042] In this embodiment, the check patterns 21Y, 21B, 21C, and 21M are halftone patterns, each of which is a band-shaped pattern having a predetermined length in the sub-scanning direction Ds and extending across the entire area in the main scanning direction Dm. Fig. 6 shows an example in which the check patterns 21Y, 21B, 21C, and 21M are arranged in the order of yellow (21Y), black (21B), cyan (21C), and magenta (21M) from the upstream side in the sub-scanning direction, but the present invention is not limited to this order.

[0043] The density values ​​of check patterns 21Y, 21B, 21C, and 21M are measured across the main scanning direction Dm by the image reading unit 4. When ink droplets are ejected from the multiple nozzles 1042 of each print head 1041 in response to the same drive voltage, it is desirable that the amount of ink droplets ejected be uniform. However, variations in the temperature within the print head 1041, variations in the characteristics of the print elements of the print head 1041, defective nozzles, etc. may cause variations in the amount of ink droplets ejected.

[0044] If there is variation in the amount of ink droplets ejected among the multiple nozzles 1042, density unevenness occurs in the check patterns 21Y, 21B, 21C, and 21M. The density unevenness can be detected by fluctuations in the density values ​​measured by the image reading unit 4 in the main scanning direction Dm.

[0045] This density unevenness can be addressed by performing halftone processing on the image data input to the recording unit 104 and correcting the drive conditions of the recording head 1041. However, the degree to which ink droplets penetrate into the sheet P differs depending on the type of sheet P. For this reason, the density information of the recording head 1041 acquired from the check patterns 21Y, 21B, 21C, and 21M may also vary depending on the type of sheet P. As a result, even if halftone processing is performed on the image data, there is a possibility that the density unevenness will not be eliminated and image quality will deteriorate if the type of sheet P changes.

[0046] In this embodiment, the pattern of halftone processing is changed depending on the type of sheet P. This makes it possible to prevent density unevenness from occurring when the normal image forming mode is executed even after the type of sheet P has been changed.

[0047] Specifically, the control unit 107 determines a halftone processing pattern when the normal image formation mode is executed, and can execute a correction mode that corrects the drive conditions of the recording head 1041. When the correction mode is executed, the control unit 107 records a check chart (first check chart) 20 for density measurement on the sheet P, and the image reading unit 4 reads the recorded check chart (first check chart) 20 to obtain first density information of the recording head 1041. The halftone processing pattern is selected according to the obtained first density information.

[0048] In this embodiment, multiple patterns with different concentrations are selected according to the acquired first density information. Furthermore, the first density information of the print head 1041 is a density distribution in the main scanning direction Dm, and multiple patterns with different concentrations are selected when a density value exceeding a preset threshold is read. That is, when the correction mode is executed, the control unit 107 (determination unit 1077) determines the first density information of the print head 1041 using a threshold, and determines whether density unevenness exceeding a predetermined threshold has occurred in a part of the check chart (first check chart) 20.

[0049] On the other hand, if no density value exceeding the preset threshold is read, halftone processing is not performed on the image data when the normal image forming mode is executed. In other words, if the determination unit 1077 determines that no density unevenness exceeding the predetermined threshold has occurred in a part of the check chart 20, halftone processing is not performed on the image data when the normal image forming mode is executed.

[0050] Furthermore, after performing halftone processing on the image data, the control unit 107 (correction unit 1073) identifies the nozzle 1042 that is causing the density unevenness and performs various correction processes, thereby further reducing the density unevenness in the main scanning direction Dm.

[0051] Specifically, a check chart (second check chart) 20 that has been halftoned using the selected pattern is recorded on the sheet P for each pattern. The image reading unit 4 reads the recorded check chart (second check chart) 20 to obtain second density information for each recording head 1041. The driving conditions of the recording head 1041 are corrected according to the second density information. In this embodiment, the second density information for the recording head 1041 is the density distribution in the main scanning direction Dm, and the driving conditions of the recording head 1041 are corrected so that density unevenness in the main scanning direction Dm is reduced. For example, the driving voltage applied to the piezoelectric element (not shown) is changed for each recording head 1041 to adjust the amount of ink droplets ejected.

[0052] This makes it possible to suppress density unevenness in image data after halftone processing by increasing or decreasing the amount of ink droplets ejected from each nozzle 1042 of the print head 1041, which causes density unevenness. Therefore, the drive conditions of the print head 1041 can be corrected in accordance with the sheet P. This makes it possible to further suppress density unevenness in accordance with the type of sheet P when performing normal image formation mode, and reduce degradation in the image quality of the formed image.

[0053] Furthermore, the control unit 107 excludes from the halftone processing patterns when the normal image forming mode is executed any pattern in which the drive voltage applied to the piezoelectric element exceeds a limit value under the corrected drive conditions of the print head 1041. This makes it possible to suppress the drive voltage applied to the piezoelectric element when the normal image forming mode is executed, and to prevent deterioration of the piezoelectric element.

[0054] Furthermore, if there are multiple patterns in which the drive voltage applied to the piezoelectric element under the corrected drive conditions of the print head 1041 is equal to or less than the limit value, the control unit 107 selects the halftone process pattern that produces the smallest density unevenness in the main scanning direction Dm under the corrected drive conditions of the head from among the multiple selected halftone process patterns as the halftone process pattern to be used in the normal image formation mode. This allows the drive conditions of the print head 1041 to be corrected for the image data after halftone processing, thereby further suppressing density unevenness during execution of the image formation mode.

[0055] FIG. 7 is a flowchart showing an example of execution of the correction mode of the inkjet recording apparatus 100. In this embodiment, the correction mode is executed when the cassette CA is installed in the apparatus main body 101. As a result, when the sheet P is replaced, the halftone processing pattern is switched according to the type of sheet P. Therefore, when the image formation mode is executed, it is possible to suppress the occurrence of density unevenness and reduce degradation in the quality of the formed image. The correction mode may also be executed by the user inputting through the operation unit 3.

[0056] When the correction mode starts, the drive conditions of the print head 104 are set (step S1). If the drive conditions of the print head 1041 have never been corrected, the drive conditions of the print head 104 are returned to the initial settings. The initial setting drive conditions are, for example, all of the drive voltages to the print heads 1041 being the same.

[0057] Next, a check chart (first check chart) 20 for density measurement is recorded on a sheet P based on the driving conditions of the recording head 104 set in step S1 (step S2). Specifically, image data of the check chart (first check chart) 20 is sent to the image processing unit 1071, and recording data of the image data is generated. The discharge control unit 1072 controls the recording head 1041 based on the recording data to record the check chart (first check chart) 20 on the sheet P. At this time, the driving voltage to the recording head 1041 is controlled based on the driving conditions of the recording head 1041 set in step S1. The image data of the check chart (first check chart) 20 is stored in advance in a storage unit or the like within the inkjet recording apparatus 100.

[0058] Next, the check chart (first check chart) 20 recorded on the sheet P is optically read by the image reading unit 4 (step S3). Specifically, the check chart (first check chart) 20 is read by a plurality of detection elements 41 arranged along the main scanning direction Dm. The image reading unit 4 generates read data corresponding to the read image and transmits the image data to the density information acquisition unit 1075.

[0059] The density information acquiring unit 1075 acquires density information (first density information) of the recording head 1041 based on the read data of the check chart (first check chart) 20 received from the image reading unit 4.

[0060] The determination unit 1077 determines the density information (first density information) of the recording head 1041 acquired by the density information acquisition unit 1075 using a threshold value stored in advance in a storage unit (not shown) (step S4). This makes it possible to determine whether density unevenness exceeding a predetermined threshold value has occurred in a part of the check chart (first check chart) 20 in the main scanning direction Dm. If the determination unit 1077 determines that the density information (first density information) of the recording head 1041 exceeds the threshold value and that density unevenness exceeding the predetermined threshold value has occurred in a part of the check chart 20 in the main scanning direction Dm (NO in step S4), the process proceeds to step S5.

[0061] On the other hand, if the judgment unit 1077 determines that the density information (first density information) of the recording head 1041 is below the threshold value and that no density unevenness exceeding the predetermined threshold value has occurred in a part of the main scanning direction Dm of the check chart 20 (YES in step S4), it sets the halftone processing not to be performed in the normal image formation mode and ends the correction mode.

[0062] In step S4, fixed threshold values ​​stored in advance in a storage unit or the like are used to detect density unevenness. Threshold values ​​are stored in advance for each of the colors yellow, black, cyan, and magenta.

[0063] In step S5, image data of the check chart 20 is sent to the image processing unit 1071, and recording data of the image data is generated. For example, the image data sent to the image processing unit 1071 is the same as the image data sent in step S2.

[0064] In step S5, the image data sent to the image processing unit 1071 is divided into a plurality of patterns with different degrees of concentration using a dithering threshold matrix and halftoned. In this embodiment, the image data is halftoned using a first pattern with a high degree of concentration (see FIG. 5), a third pattern with a low degree of concentration (see FIG. 4), and a second pattern with a degree of concentration intermediate between the first and second patterns. The first, second, and third patterns are pre-stored in a storage unit or the like within the inkjet recording apparatus 100.

[0065] In step S6, the check charts (second check charts) 20 of the first, second, and third patterns that have been halftoned in step S5 are recorded on the sheet P, respectively.

[0066] In step S7, each of the check charts (second check charts) 20 of the first, second, and third patterns recorded on the sheet P is optically read by the image reading unit 4. Specifically, each of the check charts (second check charts) 20 of the first, second, and third patterns is read by a plurality of detection elements 41 aligned along the main scanning direction Dm. The image reading unit 4 generates read data corresponding to the read image and transmits the image data to the density information acquisition unit 1075.

[0067] In step S8, the density information acquisition unit 1075 acquires density information (second density information) of the recording head 1041 based on the read data of each check chart (second check chart) 20 of the first pattern, second pattern, and third pattern received from the image reading unit 4. Furthermore, the determination unit 1077 determines the density information (second density information) of the recording head 1041 acquired by the density information acquisition unit 1075 using a threshold value stored in advance in a storage unit (not shown) (step S8). Note that the threshold value used in step S8 is different from the threshold value used in step S4.

[0068] This makes it possible to determine whether or not density unevenness exceeding a predetermined threshold value has occurred in a part of the main scanning direction Dm of each check chart (second check chart) 20 of the first, second, and third patterns. Furthermore, when the determination unit 1077 determines that the density information of the recording head 1041 exceeds the threshold value and that density unevenness has occurred in a part of each check chart 20 of the first, second, and third patterns (NO in step S8), it identifies the nozzle 1042 that is causing the density unevenness from the result of the determination, and proceeds to step S9.

[0069] On the other hand, if the judgment unit 1077 determines that the density information (second density information) of the recording head 1041 is below the threshold value and that no density unevenness exceeding the predetermined threshold value has occurred in any part of the main scanning direction Dm of each check chart 20 of the first pattern, second pattern, and third pattern (YES in step S8), it proceeds to step S11.

[0070] In step S9, the correction unit 1073 executes various correction processes. For example, the correction unit 1073 receives information from the determination unit 1077 that density unevenness has occurred in a portion of each check chart (second check chart) 20 of the first, second, and third patterns, and density information about the recording head 1041 that is causing the density unevenness. The correction unit 1073 corrects the driving conditions of the recording head 1041 that is causing the density unevenness based on the density information. This increases or decreases the amount of ink droplets ejected from each nozzle 1042 of the recording head 1041 that is causing the density unevenness, thereby suppressing the occurrence of density unevenness.

[0071] In step S10, limit determination unit 107 determines whether the drive voltage applied to the piezoelectric element exceeds a preset limit value under the corrected drive conditions of print head 1041. The limit determination unit 107 makes a determination regarding the drive conditions of print head 1041 for image data halftoned with the first pattern, the drive conditions of print head 1041 for image data halftoned with the second pattern, and the drive conditions of print head 1041 for image data halftoned with the third pattern.

[0072] In step S11, the halftone processing pattern for execution in the normal image formation mode is determined to be the halftone processing pattern with the smallest density unevenness in the main scanning direction Dm from among the first, second, and third patterns for which the drive conditions of the print head 1041 have been corrected. At this time, among the first, second, and third patterns, any pattern for which the drive voltage applied to the piezoelectric element exceeds the limit value is excluded from the halftone processing patterns for execution in the normal image formation mode.

[0073] For example, if the density unevenness in the main scanning direction Dm under the corrected head driving conditions increases in the order of the first pattern, the second pattern, and the third pattern, and the drive voltage applied to the piezoelectric element in the image data after halftone processing of the first pattern exceeds the limit value, but the drive voltage applied to the piezoelectric element in the image data after halftone processing of the second and third patterns does not exceed the limit value, then the second pattern is determined to be the halftone processing pattern when executing the normal image formation mode.

[0074] As a result, even after changing the type of sheet P, when the normal image forming mode is executed, the image data is halftoned using a pattern that corresponds to the type of sheet P. Therefore, it is possible to reduce uneven density of the image depending on the type of sheet P. Furthermore, when the normal image forming mode is executed, it is possible to suppress the drive voltage applied to the piezoelectric element and prevent deterioration of the piezoelectric element.

[0075] In step S11, the halftone processing pattern with the lowest concentration may be determined as the halftone processing pattern for execution in the normal image forming mode from among the first, second, and third patterns in which the drive conditions of the recording head 1041 have been corrected. This makes it possible to suppress a decrease in image resolution while reducing uneven density in the image according to the type of sheet P.

[0076] In this embodiment, the image data of the check chart 20 is divided into three patterns with different concentrations using a dithering threshold matrix and then halftoned. However, the image data may be divided into two patterns and then halftoned. This can shorten the execution time of the correction mode. The image data may also be divided into four or more patterns and then halftoned.

[0077] In this embodiment, it is determined whether or not density unevenness exceeding a predetermined threshold occurs in a portion of the main scanning direction Dm in each of the check patterns 21Y, 21B, 21C, and 21M drawn with ink droplets of each color, and image data is halftoned in the check patterns 21Y, 21B, 21C, and 21M of the color in which density unevenness exceeding the predetermined threshold occurs in a portion of the main scanning direction Dm. However, if density unevenness exceeding the predetermined threshold occurs in a portion of the main scanning direction Dm in any of the check patterns 21Y, 21B, 21C, and 21M, the image data in the check patterns 21Y, 21B, 21C, and 21M of all colors may be halftoned.

[0078] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

[0079] For example, in this embodiment, the image reading unit 4 is included in the inkjet recording apparatus 100, but the image reading unit 4 may be a separate device separate from the inkjet recording apparatus 100. Also, in this embodiment, halftone processing is performed on image data using a threshold matrix of the dither method, but halftone processing may be performed using another method. [Industrial Applicability]

[0080] The present invention can be used when the type of sheet P of the inkjet recording device is changed. [Explanation of symbols]

[0081] 1 Density unevenness detection unit 2 Display section 3 Control section 4 Image reading unit 20 Check Chart 21Y, 21B, 21C, 21M check pattern 41 Detector element 100 Inkjet recording device 101 Main Unit 101 Device body 102 Sheet supply unit 103 Sheet transport unit 104 Recording section 104 Recording head 105 Drying section 106 Sheet discharge section 107 Control Unit 1031 First belt conveyor 1032 Second belt conveyor 1033 Branch 1034 Reversing conveying section 1041 Recording head 1041B, 1041C, 1041M, 1041Y recording head 1042 nozzle 1071 Image Processing Unit 1072 Discharge control section 1073 Correction Unit 1074 Limit judgment section 1075 Concentration information acquisition unit 1077 Judgment section CA cassette Dm Main scanning direction Ds Sub-scanning direction P-sheet

Claims

1. a recording unit that ejects ink from a plurality of nozzles of a plurality of recording heads to record an image on a sheet; an image reading unit that reads the density of the image recorded on the sheet; a control unit that controls the recording unit and the image reading unit, the recording head has a piezoelectric element that is deformed in response to a drive voltage to adjust the amount of ink discharged from the nozzle; The control unit an image processing unit capable of performing halftone processing with a plurality of patterns having different degrees of concentration on the image data input to the recording unit; a limit determination unit that determines whether or not the drive voltage applied to the piezoelectric element exceeds a preset limit value, the control unit determines a pattern of halftone processing when a normal image forming mode is executed, and is capable of executing a correction mode for correcting a driving condition of the recording head; an image reading unit reading the recorded second check chart to obtain second density information of the recording head; a drive condition of the recording head according to the second density information; and an ink jet recording device, wherein, when the correction mode is executed, the control unit records a first check chart for density measurement on the sheet; the image reading unit reads the recorded first check chart to obtain first density information of the recording head; a halftone processing pattern is selected according to the first density information; a second check chart halftone processed using the selected pattern is recorded on the sheet; the image reading unit reads the recorded second check chart to obtain second density information of the recording head;

2. 2. The inkjet recording device according to claim 1, wherein, when the correction mode is executed, the control unit determines, from among the multiple selected halftone processing patterns, the halftone processing pattern that has the smallest density unevenness in the main scanning direction under the driving conditions of the recording head after correction, as the halftone processing pattern to be used when executing the normal image formation mode.

3. 3. The inkjet recording apparatus according to claim 1, wherein the image processing unit is capable of halftone processing the image data into a concentrated pattern or a dispersed pattern.

4. 3. The inkjet recording apparatus according to claim 1, wherein the image processing section performs halftone processing on the image data using a threshold matrix of a dither method.

5. a sheet supply unit including a cassette for storing the sheets; 3. The inkjet recording apparatus according to claim 1, wherein the control unit executes the correction mode when the cassette is attached to a main body of the apparatus including the recording unit.

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