Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the occurrence of an image defect caused by burr when performing image formation on a perforated sheet.SOLUTION: When the type of a sheet is a perforated sheet and an image to be formed in a perforation area is an image in a single K toner color (Yes in both S1 and S3), a control unit determines whether a single color replacement function is effective (S4). When the single color replacement function is effective (Yes in S4), the control unit replaces the single K toner color being black with the combination of CMY toners reproducing black in the perforation area (S5). In the perforation area where the single color replacement is performed, since dots of the CMY toners are arranged at different screen angles to form an image, even if unintentional electric discharge occurs in the perforation area, the randomness of the shape and arrangement of dots hardly becomes apparent. An image defect caused by burr of the sheet thus hardly occurs.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an electrophotographic image forming apparatus such as a printer, a copier, a facsimile, or a multifunction machine. [Background technology]

[0002] The image forming apparatus is equipped with a cassette or a manual feed tray on which sheets can be set, and forms an image by transferring a toner image onto various sheets conveyed from the cassette or the manual feed tray. In some cases, a sheet with perforations (called a perforated sheet) is used as the sheet (Patent Document 1). In addition, an image forming apparatus has been proposed that can selectively execute either a screen process or an error diffusion process as a halftone process in order to generate image data for output with a lower gradation than input image data (Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-71751 [Patent Document 2] Japanese Patent Application Publication No. 9-331450 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the past, there was a risk of image defects occurring when a toner image was formed on a perforated sheet. That is, in the case of a perforated sheet, unevenness called burrs occurs on the sheet when the perforations are processed, and when a toner image is transferred to the perforated sheet, unintended discharge may occur in a specific area (called a perforation area) where the burrs occur. If this happens, the toner may be transferred to an unintended location, and the shape and arrangement of the dots forming the image may become disordered, resulting in image defects such as a change in the color of the toner image. In particular, when AM screen processing was performed on a monochrome image, image defects due to burrs on the sheet were likely to occur.

[0005] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing image defects caused by burrs on a sheet when forming an image on a perforated sheet. [Means for solving the problem]

[0006] An image forming apparatus according to an embodiment of the present invention is an image forming apparatus capable of forming an image on a perforated sheet, and includes an image carrier carrying toner images of first, second, third and fourth colors that are different from one another, a first image forming unit that forms a toner image of the first color to be carried on the image carrier, a second image forming unit that forms a toner image of the second color to be carried on the image carrier, a third image forming unit that forms a toner image of the third color to be carried on the image carrier, a fourth image forming unit that forms a toner image of the fourth color to be carried on the image carrier, a transfer unit that transfers the toner image formed on the image carrier to a sheet, an image processing unit that performs AM screen processing on acquired image data of the first, second, third and fourth colors, and a transfer unit that performs AM screen processing on the first, second, third and fourth colors based on the image data of each color processed by the image processing unit. and a control unit which causes the second, third and fourth image forming units to form toner images of each color, wherein the control unit is capable of replacing the toner image of the first color with a replacement toner image formed using two or more of the first color, the second color, the third color and the fourth color, and the image processing unit is capable of executing a mode in which, when a sheet on which a toner image is formed is a perforated sheet and a toner image formed in a predetermined area where a burr is formed by perforation is a toner image of the first color, image data of the first color located in all areas is replaced with image data of two or more of the first color, the second color, the third color and the fourth color so that the toner image of the first color formed in all areas including the image data located in the predetermined area is the replacement toner image.

[0007] An image forming apparatus according to an embodiment of the present invention is an image forming apparatus capable of forming an image on a perforated sheet, and includes an image carrier carrying toner images of first, second, third and fourth colors that are different from one another, a first image forming unit that forms a toner image of the first color to be carried on the image carrier, a second image forming unit that forms a toner image of the second color to be carried on the image carrier, a third image forming unit that forms a toner image of the third color to be carried on the image carrier, a fourth image forming unit that forms a toner image of the fourth color to be carried on the image carrier, a transfer unit that transfers the toner image formed on the image carrier to a sheet, an image processing unit that performs AM screen processing on acquired image data of the first, second, third and fourth colors, and image data of each color processed by the image processing unit. and a control unit that causes the first, second, third and fourth image forming units to form toner images of each color based on a toner image data of the first color, the second color, the third color and the fourth color, wherein the control unit is capable of replacing the toner image of the first color with a replacement toner image formed using two or more of the first color, the second color, the third color and the fourth color, and wherein when a sheet on which a toner image is formed is a perforated sheet and a toner image formed in a predetermined area where a burr is formed due to perforation is a toner image of the first color, the image processing unit is capable of executing a mode in which image data of the first color located in the predetermined area is replaced with image data of two or more of the first color, the second color, the third color and the fourth color so that the toner image of the first color formed in the predetermined area is the replacement toner image. Effect of the Invention

[0008] According to the present invention, when an image is formed on a perforated sheet, the occurrence of image defects caused by burrs in the sheet can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a control block diagram showing a control configuration of the image forming apparatus. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] 4 is a flowchart showing an image forming process according to the first embodiment. [Figure 6] FIG. 13 is a diagram showing a replacement / non-replacement selection screen. [Figure 7] FIG. [Figure 8] FIG. 4 is a schematic diagram showing an image formed using a single color K toner. [Figure 9] Schematic diagram showing an image formed using CMY toners. [Figure 10] 10 is a flowchart showing an image forming process according to a second embodiment. [Figure 11] FIG. 13 is a diagram showing a perforation position setting screen. [Figure 12] FIG. 13 is a diagram showing a replacement range setting screen. [Figure 13] 13 is a schematic diagram showing an image in which single-color replacement is performed in a perforated region and single-color replacement is not performed in a region other than the perforated region. [Figure 14] FIG. 2 is a schematic diagram showing an image formed using CMYK toners. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [First embodiment] <Image forming device> The image forming apparatus of this embodiment will be described with reference to FIG. 1. The image forming apparatus 100 is a tandem-type full-color printer of an electrophotographic system. The image forming apparatus 100 has image forming units Pa, Pb, Pc, and Pd that form images of yellow, magenta, cyan, and black, respectively. The image forming unit Pd corresponds to a first image forming unit that forms a toner image of black (first color), the image forming unit Pa corresponds to a second image forming unit that forms a toner image of yellow (second color), the image forming unit Pc corresponds to a third image forming unit that forms a toner image of magenta (third color), and the image forming unit Pd corresponds to a fourth image forming unit that forms a toner image of cyan (fourth color). The image forming apparatus 100 forms a toner image on a sheet S based on image data sent from an external device 1000 such as a document reading device 130 connected to the image forming apparatus 100 or a personal computer. Examples of the sheet S include sheet materials such as plain paper, thick paper, rough paper, textured paper, and coated paper.

[0011] The document reading device 130 serving as a document reading section is disposed on the upper portion of the image forming apparatus 100, and has an image reading section 131 that reads an image on a sheet S on which an image has been formed in advance, and a document transport section 132 that automatically transports the sheet S to the image reading section 131. The image reading section 131 irradiates light onto the sheet S transported onto a platen glass 133 using an irradiation section 131a, receives reflected light from the sheet S of the irradiated light using a light receiving section 131b, and is capable of reading the image on the sheet S at a predetermined dot density.

[0012] The conveying process of the sheet S in the image forming apparatus 100 will be described. The sheet S can be set in a form stacked in the cassette 10. Alternatively, the sheet S can be set in a form stacked on the manual feed tray 17. The sheet S set in the cassette 10 or the manual feed tray 17 is sent out by the supply roller 13 in accordance with the image formation timing. The cassette 10 and the manual feed tray 17 are provided so as to be openable and closable, and may be opened and closed at the user's discretion.

[0013] The sheet S sent out by the supply roller 13 is conveyed to the registration roller 12 arranged in the conveying section 114 capable of conveying the sheet S. Then, after the registration roller 12 performs skew correction and timing correction on the sheet S, the sheet S is conveyed to the secondary transfer nip T2. The secondary transfer nip T2 is a transfer nip portion formed by the secondary transfer inner roller 14 and the secondary transfer outer roller 11, and a toner image is transferred onto the sheet in response to a secondary transfer voltage applied by a power source 90 to the secondary transfer outer roller 11 as a transfer section. Although only one cassette 10 is shown in FIG. 1, there may be multiple cassettes 10. The conveying section 114 conveys the sheet S from the cassette 10 or the manual feed tray 17 to the secondary transfer nip T2.

[0014] The image forming process in which the image is sent to the secondary transfer nip T2 at the same timing as the above-mentioned conveying process of the sheet S to the secondary transfer nip T2 will be described. First, the image forming units Pa, Pb, Pc, and Pd for each color are configured almost the same except that the toners used in the developing devices 1a, 1b, 1c, and 1d are yellow (Y), magenta (M), cyan (C), and black (K). Therefore, the following description will be given of the black image forming unit Pd as a representative, and the description of the other image forming units Pa, Pb, and Pc will be omitted.

[0015] The image forming section Pd is mainly composed of a developing device 1d, a charging device 2d, a photosensitive drum 3d, a photosensitive drum cleaner 4d, an exposure device 5d, a primary transfer roller 6d, and the like. The surface of the rotating photosensitive drum 3d is uniformly charged in advance by the charging device 2d, and then an electrostatic latent image is formed on the surface of the photosensitive drum 3d by the exposure device 5d, which is driven based on a signal of image information. Next, the electrostatic latent image formed on the photosensitive drum 3d is developed into a toner image by the developing device 1d using a developer. Then, the toner image formed on the photosensitive drum 3d is primarily transferred onto the intermediate transfer belt 80 in response to the application of a primary transfer voltage to the primary transfer roller 6d, which is disposed with the photosensitive drum 3d and the intermediate transfer belt 80 sandwiched therebetween. A small amount of primary transfer residual toner remaining on the photosensitive drum 3d is collected by the photosensitive drum cleaner 4d.

[0016] The intermediate transfer belt 80 as an image carrier is stretched by the inner secondary transfer roller 14 and tension rollers 15 and 16, and is driven in the direction of the arrow R2 while contacting the photosensitive drums 3a to 3d. The tension roller 16 also serves as a drive roller for driving the intermediate transfer belt 80. The image forming processes of each color, which are processed in parallel by the image forming units Pa to Pd, are performed at a timing when the image is sequentially superimposed on the toner image of the upstream color that has been primarily transferred onto the intermediate transfer belt 80. As a result, a full-color toner image is finally formed on the intermediate transfer belt 80, and is carried by the intermediate transfer belt 80 and conveyed to the secondary transfer nip T2. The secondary transfer residual toner after passing through the secondary transfer nip T2 is removed from the intermediate transfer belt 80 by the belt cleaner 22.

[0017] Through the above-described conveying process and image forming process, the timing of the sheet S and the full-color toner image coincides at the secondary transfer nip T2, and secondary transfer is performed. Thereafter, the sheet S is conveyed to the fixing device 50, where heat and pressure are applied to fix the toner image on the sheet. The fixing device 50 clamps and conveys the sheet S on which the toner image has been formed, and applies heat and pressure to the sheet S, thereby fixing the toner image to the sheet S. That is, the toner of the toner image formed on the sheet S is melted and mixed by the heat and pressure, and is fixed to the sheet S as a full-color image. The sheet S on which the toner image has been fixed is discharged to a discharge tray 95 provided outside the main body of the image forming apparatus 100. Alternatively, if a post-processing device (not shown), such as a finisher, is connected to the main body of the image forming apparatus 100, the sheet S on which the toner image has been fixed is conveyed to the post-processing device. The finisher performs, for example, a punching process for making holes in the sheet S, or a stapling process for bundling and staple multiple sheets S.

[0018] <Developer> In the image forming apparatus 100 of this embodiment, a two-component developer containing a toner and a carrier is used as the developer. The toner contains a binder resin, a colorant, and a release agent. The binder resin may be a known one. For example, a vinyl copolymer such as a styrene-(meth)acrylic copolymer, a polyester resin, a hybrid resin in which a vinyl copolymer and a polyester are chemically bonded, an epoxy resin, a styrene-butadiene copolymer, or other resin may be used. Known colorants may be used for yellow (Y), magenta (M), cyan (C), and black (K).

[0019] Examples of the release agent include aliphatic hydrocarbon waxes such as low molecular weight polyethylene wax, low molecular weight olefin copolymer wax, microcrystalline wax, Fischer-Tropsch wax, and paraffin wax, oxides of aliphatic hydrocarbon waxes such as oxidized polyethylene wax, and block copolymers thereof; waxes containing fatty acid esters as the main component such as carnauba wax and montan acid ester wax, ester waxes which are synthetic reaction products of higher fatty acids and higher alcohols such as behenyl behenate and behenyl stearate, and partially or completely deoxidized fatty acid esters such as deoxidized carnauba wax.

[0020] <Control Unit> As shown in Fig. 1, image forming apparatus 100 includes a control unit 101. The control configuration of image forming apparatus 100 by control unit 101 will be described using Fig. 2 with reference to Fig. 1. In addition to those shown in Fig. 2, various devices such as each unit constituting image forming apparatus 100 and drive sources (motors, power sources, etc.) for operating each unit are connected to control unit 101. However, since this is not the main point of the invention, illustration and description of those will be omitted here.

[0021] The control unit 101 has a central processing unit (CPU) 102, a read only memory (ROM) 103, and a random access memory (RAM) 104, and controls the entire image forming apparatus 100. Various programs such as image forming jobs are stored in the ROM 103. The control unit 101 can acquire, for example, various data input from the operation unit 110, image data transmitted from an external device 1000 (see FIG. 1), or image data of an image read by the document reading device 130 (referred to as input image data). The data acquired by the control unit 101 is stored in the RAM 104. The RAM 104 can also temporarily store the results of calculations associated with the execution of the various programs.

[0022] The image forming apparatus 100 includes an operation unit 110 having a display unit 111 (see FIG. 1), and the operation unit 110 is connected to the control unit 101. The control unit 101 can display various screens on the display unit 111 presenting various programs and various data, and also accepts inputs for starting various programs and inputting various data in response to user operations from the operation unit 110. As will be described later, the operation unit 110 as an input unit allows the user to input the position of the burrs to be formed on the perforated sheet S and the range of the perforation area.

[0023] When the control unit 101 receives a command to start an image forming job, it executes an image forming process (program) stored in the ROM 103 and controls the image forming units Pa to Pd to form an image on the sheet S. The image processing unit 105 performs color conversion processing and halftone processing (also called halftone processing) on ​​the image data acquired by the control unit 101. Here, the user can set AM screen processing and error diffusion processing as the type of halftone processing. The image processing unit 105 performs halftone processing on the input image data and outputs image data for image output (called output image data). The control unit 101 causes the image forming units Pa to Pd to form a toner image based on the output image data.

[0024] AM screening is a process that expresses halftones with a periodic dot (halftone dot) arrangement, and examples include dot screening and line screening. Dot screening expresses shades by changing the area of ​​evenly spaced halftone dots. In dot screening, the halftone dots are circular and arranged at equal intervals, so a periodic dot pattern is generated. Line screening also generates a periodic dot pattern, but instead of expressing shades by changing the size of the halftone dot area as in dot screening, line screening expresses shades by changing the thickness of evenly spaced lines. Here, the direction in which the dots are arranged in AM screening (screen angle) is predetermined for each color. For example, yellow (Y) is set to 0 degrees, and a different screen angle is set for each CMYK color, with cyan (C) at 15 degrees, black (K) at 45 degrees, and magenta (M) at 75 degrees, clockwise from yellow.

[0025] Error diffusion processing is processing for generating a dot pattern without periodicity. In error diffusion processing, first, the density of one pixel is binarized (called a pixel of interest) based on density information of pixels constituting an image of input image data, and the error (difference) between the density after binarization and the density before binarization is obtained. Then, a value (called a diffusion value) is obtained by multiplying the error by a weighting coefficient, and the diffusion value is added to the density of each of the other pixels within a predetermined range from the pixel of interest. Next, one of the other pixels within a predetermined range from the pixel of interest is binarized (next pixel of interest), and the density before binarization at this time is the density to which the diffusion value has been added. After that, the error between the density after binarization and the density before binarization is obtained for the next pixel of interest, and the diffusion value is added to the density of each of the other pixels within a predetermined range from the next pixel of interest. In this way, the error of the pixel of interest is diffused so as to be added to the surrounding pixels, and since there is no periodicity in the degree of distribution of the error, a dot pattern without periodicity is generated in error diffusion processing.

[0026] <Operation section> Next, the operation unit 110 as a selection unit (input unit) will be described with reference to Fig. 3. As shown in Fig. 3, the operation unit 110 has a display unit 111, such as a liquid crystal monitor, and hardware keys. The display unit 111 may be a touch panel that can be operated by the user by touch, and can display a screen including various buttons, switches, etc. as software keys that can be operated by touch. The display unit 111 displays a "sheet selection screen" (see Fig. 4) and a "replacement selection screen" (see Fig. 6), which will be described later, and the like.

[0027] The hardware keys include, for example, a setting key 1102, a power saving key 1103, a group of hard keys 1104, a reset key 1105, a stop key 1106, and a start key 1107. The start key 1107 has a function of instructing the start of, for example, reading and printing (copying) an image of an original document, and other operations. The start key 1107 has a built-in two-color LED, green and red (not shown), which indicates that an operation can be started when lit green and that an operation cannot be started when lit red. The stop key 1106 has a function of temporarily pausing an operation such as image formation that is in progress. The group of hard keys 1104 includes, for example, a numeric keypad, a clear key, and an authentication key.

[0028] The power saving key 1103 has a function of switching the image forming apparatus 100 from the normal mode to a sleep mode in which the image forming apparatus 100 waits in a power-saving state, or of returning the image forming apparatus 100 from the sleep mode to the normal mode. That is, when the power saving key 1103 is pressed by the user in the normal mode, the image forming apparatus 100 switches to the sleep mode, and when the power saving key 1103 is pressed by the user in the sleep mode, the image forming apparatus 100 switches to the normal mode. The setting key 1102 is used, for example, when setting the type of sheet S, etc. The reset key 1105 is used, for example, when canceling the type of sheet S that has been set.

[0029] <Sheet selection screen> A "sheet selection screen" is displayed on display unit 111 of operation unit 110. The "sheet selection screen" is displayed on display unit 111, for example, when the user operates a sheet type selection button from a "menu screen" (not shown) displayed on display unit 111, or when the user opens cassette 10 or manual feed tray 17. The "sheet selection screen" will be described with reference to FIG. 4.

[0030] As shown in FIG. 4, on the "sheet selection screen", types of sheets S on which images can be formed by image forming apparatus 100, which are pre-stored in ROM 103 (see FIG. 2), are displayed in a selectable dialog box 1201. Here, "plain paper", "cardboard", and "perforated paper" (perforated sheet) are displayed, but the user can scroll the screen displayed in dialog box 1201 to display other types on which images can be formed. The user can select the type of sheet S from the multiple types displayed in dialog box 1201. The selected type of sheet S is confirmed by operating confirmation button 1203.

[0031] <Image formation process> Next, the image forming process of the image forming apparatus 100 will be described with reference to Fig. 2 and Fig. 5 to Fig. 9. The image forming process is started when the control unit 101 receives a start command for an image forming job. Note that, in the following description, the user has already set AM screen processing as halftone processing from the operation unit 110 before starting the image forming job.

[0032] As shown in Fig. 5, when the control unit 101 receives a command to start an image formation job, it determines whether the type of sheet S is a perforated sheet S (S1). The control unit 101 determines whether the type of sheet S is a perforated sheet S based on whether the type of sheet S selected by the user from the above-mentioned "sheet selection screen" (see Fig. 4) is a perforated sheet S. Note that if the image formation job is configured to have paper information related to the sheet, the control unit 101 may determine whether the type of sheet S is a perforated sheet S based on the paper information of the image formation job.

[0033] If the type of the sheet S is not a perforated sheet S (No in S1), the control unit 101 forms an image using CMYK toner (S2). That is, if the type of the sheet S is not a perforated sheet S, the control unit 101 performs AM screen processing preset by the user on the input image data using the image processing unit 105, and causes the image forming units Pa to Pd to form an image based on the output image data. The output image data is used when exposing the photosensitive drums 3a to 3d using the exposure devices 5a to 5d. The control unit 101 exposes the photosensitive drums 3a to 3d using the exposure devices 5a to 5d based on the output image data, and then controls the developing devices 1a to 1d to develop the electrostatic latent image into a toner image using CMYK toner based on color information previously stored in the input image data. Thereafter, the toner image formed on the photosensitive drums 3a to 3d is transferred to the sheet S via the intermediate transfer belt 80.

[0034] After forming an image on the sheet S, the control unit 101 determines whether or not to end the image formation job (S6). When the control unit 101 has formed images on the number of sheets S specified by the user, it determines that the image formation job is to be ended (Yes in S6), and the control unit 101 ends this image formation process. When the control unit 101 does not want to end the image formation job (No in S6), it returns to the process of step S1 to form an image on the next sheet S, and repeats the image formation process until images are formed on the specified number of sheets.

[0035] On the other hand, if the type of sheet S is a perforated sheet S (Yes in S1), the control unit 101 determines whether the image to be formed in the perforated area is a K toner monochromatic image (S3). Information about the perforated area is stored in the input image data, and the control unit 101 identifies the perforated area according to that information.

[0036] If the image to be formed in the perforated area is not a K toner monochromatic image (No in S3), the control unit 101 forms an image in all areas including the perforated area using CMYK toner (S2). After forming the image on the perforated sheet S, the control unit 101 proceeds to the process of step S6 described above.

[0037] If the image to be formed in the perforation area is a K toner monochromatic image (Yes in S3), the control unit 101 determines whether a monochromatic replacement function that replaces the monochromatic image data with multi-color image data that reproduces pseudo colors is enabled (S4). The determination of whether the monochromatic replacement function is enabled is based on the user's selection using the "Replacement Selection Screen" (see FIG. 6) described later.

[0038] If the single-color replacement function is enabled (Yes in S4), the control unit 101 replaces all black single-color areas in one page with a combination of CMY toners that reproduces black in a pseudo manner from the K toner single-color of black (S5). Here, the black reproduced in a pseudo manner using CMY toners without using K toner is called process black. If the single-color replacement function is not enabled, the image processing unit 105 performs a color conversion process to generate image data of four color components, cyan, magenta, yellow, and black, from the input image data. On the other hand, if the single-color replacement function is enabled, the image processing unit 105 performs a color conversion process to generate image data of three color components, cyan, magenta, and yellow, from the input image data. Then, the control unit 101 performs an image formation process by the image forming units Pa to Pc based on the image data of the three color components, cyan, magenta, and yellow, so that the black single-color areas are replaced with process black reproduced using CMY toners (S2). In this way, the K toner single-color toner image can be replaced with a replacement toner image formed using the three colors of CMY toner. In step S5, the mixed color area including the K toner is not replaced with the CMY toner.

[0039] If the single color replacement function is not enabled (No in S4), the control unit 101 forms an image using CMYK toners without replacing the black K toner single color with a combination of CMY toners (S2).

[0040] The control unit 101 performs the above-mentioned replacement of the K toner monochromatic color with the CMY toner by referring to the monochromatic replacement table stored in the ROM 103. The monochromatic replacement table specifies that the print amounts of the C toner, M toner, and Y toner after replacement are substantially the same for the K toner monochromatic color. The print amount of each color is discretized into 256 levels of "0 to 255" (tone value), and the print amount of each color is determined by specifying this tone value. For example, when replacing the K toner monochromatic color with the maximum density (tone value 255) with the CMY toner, the monochromatic replacement table specifies values ​​that can reproduce pseudo colors by specifying the tone, such as C toner "150", M toner "150", and Y toner "150".

[0041] <Replacement selection screen> Next, the "Replacement On / Off Selection Screen" will be described with reference to Fig. 6. When "perforated paper" is selected as the type of sheet S on the "sheet selection screen" (see Fig. 4), the "replacement on / off selection screen" is displayed on the display unit 111 of the operation unit 110 as shown in Fig. 6. In Fig. 6, a selection button display unit 1202 is displayed as a pop-up as the "replacement on / off selection screen".

[0042] In the selection button display area 1202, an "enable" button for enabling the monochromatic replacement function and an "invalid" button for deactivating the monochromatic replacement function are displayed so that the user can select whether or not to execute the monochromatic replacement function (mode). The user can select whether or not to enable the monochromatic replacement function by operating either the "enable" button or the "invalid" button in the selection button display area 1202. Thereafter, in response to the user operating the confirm button 1203, the monochromatic replacement function is confirmed as either "enable (executed)" or "invalid (not executed)". The confirmed type of sheet S and the presence or absence of the monochromatic replacement function are stored in the RAM 104 (see FIG. 2) of the control unit 101. When an image forming job is executed, the control unit 101 refers to the type of sheet S and the presence or absence of the monochromatic replacement function stored in the RAM 104.

[0043] <Whether or not image defects occur> As already mentioned, when a toner image is transferred to the perforated sheet S, unintended discharge occurs in the perforated area where burrs have occurred, causing the toner to be transferred to unintended locations, resulting in a disordered shape and arrangement of dots forming the image, and image defects such as changes in the color of the toner image. In particular, when a monochrome image is formed by performing AM screen processing, image defects due to burrs on the sheet are likely to occur in the perforated area. In response to this, the image forming apparatus 100 can suppress image defects due to burrs on the sheet by replacing the color information of the image to be formed in the perforated area where burrs have occurred from the black K toner to a combination of CMY toners that can reproduce black in a pseudo manner (see S5 in FIG. 5). Table 1 shows the results of an evaluation of the occurrence of image defects in the perforated area due to burrs on the sheet S when the AM screen processing is performed as halftone processing, using CMY toners and using monochrome K toner. [Table 1]

[0044] The occurrence of image defects in Table 1 was evaluated as follows. First, a toner image was formed on the perforated sheet S based on predetermined color information. The predetermined color information was determined by using the toners listed in the "Toner Used" column in Table 1, so that the print rate was 30% when K toner alone was used, and the print rate was determined based on a known technique that can simulate the black of an image formed using K toner alone when CMY toners were used. The print rate referred to here is the ratio of the area where toner exists in the minute area 201 based on the print rate of "100%" when toner exists over the entire surface of the minute area 201 in the image forming area 200 as shown in FIG. 7.

[0045] In the image forming apparatus 100, the color information when using a single color K toner corresponds to the color information before replacement, and the color information when using CMY toner corresponds to the color information after replacement. The user visually checked the toner image formed based on each color information to determine whether an image defect occurred. As shown in Table 1, when using a single color K toner before replacement, an image defect occurred due to burrs on the sheet S. In contrast, when using CMY toner after replacement, no image defect occurred due to burrs on the sheet S. Here, FIG. 8 shows an image formed in the perforated area using a single color K toner before replacement, and FIG. 9 shows an image formed in the perforated area using CMY toner after replacement.

[0046] As shown in FIG. 8, an image is formed by arranging K toner dots in a straight line (screen angle 45°). However, in the perforated area, some dots are disorganized, such as changing in shape or not being arranged in a straight line (see minute area 211). At this time, the phenomenon that occurs in the image formed in the image forming area 200 is as follows. The perforated area where burrs occur is a place where the thickness of the sheet S changes locally or a hole is formed in the sheet S. Then, when the toner image is transferred to the perforated sheet S in the secondary transfer nip T2 (see FIG. 1), an unintended local discharge may occur in the perforated area. This unintended discharge causes the toner to be transferred to an unintended place, causing the shape and arrangement of the dots to become disorganized. Therefore, the toner image formed in the perforated area looks different in color compared to the toner image formed in other areas, which becomes apparent as an image defect.

[0047] On the other hand, when an image is formed using CMY toners, the arrangement directions (screen angles) of the dots of each color are different, resulting in a state known as a rosette pattern (see minute area 222). The rosette pattern is a random dot arrangement pattern that is caused by complex interference, and even if unintended local discharge occurs in the perforated area described above and the shape and arrangement of the dots become random, the color does not change compared to the toner image formed in other areas.

[0048] As described above, in the image forming apparatus 100, when the type of the sheet S is a perforated sheet S, it is possible to form an image by replacing a monochromatic K toner image with a pseudo-color image (replacement toner image) using CMY toner. At that time, the user can select whether to enable or disable the monochromatic replacement function for replacing the monochromatic K toner with CMY toner by using the "change / non-change selection screen" (see FIG. 6). In this way, when forming an image on the perforated sheet S, it is possible to provide a higher quality product by allowing the user to select whether to enable or disable the monochromatic replacement function according to the usage situation and the product. That is, when the enablement of the monochromatic replacement function is selected, the monochromatic K toner is replaced with CMY toner as described above, and a pseudo-color image in which dots of each of the CMY toners are arranged at different screen angles is formed in accordance with the AM screen processing. Compared to a monochromatic K toner image in which the dots are arranged in one direction, the pseudo-color image has a different dot arrangement for each color, so that even if unintended discharge occurs in the perforation area, the shape and arrangement of the dots are less likely to become disordered. Therefore, when comparing the toner image formed in the perforated area with the toner image formed in the area other than the perforated area, the color does not change. In this way, when forming an image on the perforated sheet S, the image forming apparatus 100 can reduce the appearance of local dot shape and arrangement disorder, thereby suppressing image defects caused by sheet curl.

[0049] The image forming apparatus 100 allows the user to arbitrarily select whether or not to perform monochromatic replacement on the "Replacement Selection Screen" (see FIG. 6). This is because it is possible that the color information after replacement is not optimized depending on the user's usage environment, color design preferences, and the like. In this case, it is desirable to be able to select whether or not to replace color information individually for each condition. In the case where the user determines that the monochromatic replacement function is not working properly under unexpected circumstances, including a malfunction of the image forming apparatus 100, it is desirable to be able to set the monochromatic replacement function to "inactive." Thus, by allowing each user to select whether or not to enable the monochromatic replacement function depending on the usage situation and the deliverable, it is possible to provide a deliverable of higher quality.

[0050] [Second embodiment] In the first embodiment described above, the toner can be changed from K toner monochromatic to CMY toner in the entire area of ​​the perforated sheet S, regardless of whether it is a perforated area or a non-perforated area, but this is not limited to this. For example, the toner can be changed from K toner monochromatic to CMY toner only for the toner image formed in the perforated area. The image forming process of the second embodiment that can realize this will be described using Figs. 10 to 13 with reference to Fig. 2. The image forming process is started when the control unit 101 receives a start command for an image forming job. Note that in the image forming process shown in Fig. 10, the description of the same process as the image forming process shown in Fig. 5 will be simplified or omitted.

[0051] 10, when the control unit 101 receives a command to start an image forming job, it determines whether the type of sheet S is a perforated sheet S (S11). The control unit 101 determines whether the type of sheet S is a perforated sheet S based on whether the type of sheet S selected by the user from the above-mentioned "sheet selection screen" (see FIG. 4) is a perforated sheet S. If the type of sheet S is not a perforated sheet S (No in S11), the control unit 101 performs AM screen processing preset by the user on the input image data using the image processing unit 105, and causes the image forming units Pa to Pd to form an image based on the output image data (S12).

[0052] After forming an image on the sheet S, the control unit 101 determines whether or not to end the image formation job (S21). When the control unit 101 has formed images on the number of sheets S specified by the user, it determines that the image formation job is to be ended (Yes in S21), and the control unit 101 ends this image formation process. When the control unit 101 does not want to end the image formation job (No in S21), it returns to the process of step S11 to form an image on the next sheet S, and repeats the process until images are formed on the specified number of sheets S.

[0053] On the other hand, if the type of sheet S is a perforated sheet S (Yes in S11), the control unit 101 sets position information of the perforated area (S13). The position information of the perforated area is set based on coordinates set by the user using a "perforation position setting screen" (see FIG. 11) described later. After setting the position information of the perforated area, the control unit 101 determines whether the image to be formed in the perforated area is a K toner monochromatic image based on the input image data and the set position information (S14). If the image to be formed in the perforated area is not a K toner monochromatic image (No in S14), the control unit 101 forms an image with CMYK toner in all areas including the perforated area (the entire area of ​​the perforated sheet S) (S12). After forming the image on the perforated sheet S, the control unit 101 proceeds to the process of step S21 described above.

[0054] If the image to be formed in the perforated area is a K toner monochromatic image (Yes in S14), the control unit 101 determines whether the range in which the monochromatic replacement function is to be performed is only the perforated area or the entire area including the perforated area (the entire area of ​​the perforated sheet S) (S15). The control unit 101 determines whether the range in which the monochromatic replacement function is to be performed is only the perforated area or the entire area of ​​the perforated sheet S, based on the replacement range set by the user using the "replacement range setting screen" (see FIG. 12) described later.

[0055] When the range of the single-color replacement function is not limited to the perforated area but is the entire area of ​​the perforated sheet S (No in S15), the control unit 101 judges whether the single-color replacement function is enabled (S16). The judgment of whether the single-color replacement function is enabled or not is made based on the user's selection using a selection button display unit 1202 (see FIG. 12) displayed on a "replacement range setting screen" described later. When the single-color replacement function is not enabled (No in S16), the control unit 101 forms an image with CMYK toners based on the color information set in the input image data in the entire area of ​​the perforated sheet S (S21). On the other hand, when the single-color replacement function is enabled (Yes in S16), the control unit 101 replaces the black K toner single color with a combination of CMY toners that reproduces black in a pseudo manner for all black single-color areas formed in the input image data in the entire area of ​​the perforated sheet S (S17). Thereafter, the control unit 101 executes the processes of steps S12 and S21.

[0056] On the other hand, if the range in which the single-color replacement function is to be performed is limited to the perforated area (Yes in S15), the control unit 101 sets the range of the perforated area (S18). The range of the perforated area is set by the user using an area width setting box 1209 (see FIG. 12) displayed on a "replacement range setting screen" to be described later. Thereafter, the control unit 101 determines whether the single-color replacement function is enabled (S19).

[0057] If the single color replacement function is enabled (Yes in S19), the control unit 101 replaces the black K toner with a combination of CMY toners that can reproduce a pseudo black for all black single color areas formed in the perforated area (S20). The control unit 101 then executes the processes of steps S12 and S21. In this case, the control unit 101 replaces the K toner single color with a combination of CMY toners for the input image data for the perforated area, and performs image formation without replacing the K toner single color with a combination of CMY toners for the input image data for the areas other than the perforated area (S12). The control unit 101 can identify the input image data for the perforated area and the input image data for the areas other than the perforated area based on the position of the perforations.

[0058] If the single color replacement function is not enabled (No in S19), the control unit 101 forms an image using CMYK toners based on the color information set in the input image data, regardless of whether the area is a perforated area or not (S12). After forming an image on the perforated sheet S, the control unit 101 proceeds to the process of step S21 described above.

[0059] <Perforation position setting screen> A "perforation position setting screen" is displayed on display unit 111 (see S13 in FIG. 10). The "perforation position setting screen" is displayed on display unit 111, for example, when a user operates a predetermined setting start button on a "menu screen" (not shown) displayed on display unit 111. The "perforation position setting screen" will be described with reference to FIG. 11.

[0060] As shown in Fig. 11, the "perforation position setting screen" displays a dialog box 1204 that allows the user to select a perforation position acquisition method for acquiring the coordinate positions of the perforations on the perforated sheet S. Here, an example is shown in which "scan" and "input" are displayed as perforation position acquisition methods that are pre-stored in the ROM 103. "Scan" is a method for reading the positions of the perforations on the perforated sheet S with the document reading device 130 (see Fig. 1).

[0061] When the user selects "scan" as the perforation position acquisition method, the user places the perforated sheet S on which no image is formed on the document reading device 130 (see FIG. 1) and presses the scan start button 1205. Then, the document reading device 130 reads the positions of the perforations (burrs) on the perforated sheet S, and the read positions of the perforations (start point coordinates and end point coordinates) are displayed in the position coordinate setting box 1206. In the example shown in FIG. 11, as shown in the preview screen, the perforated sheet S has two perforations, so the start point coordinates and end point coordinates are displayed for each of "perforation 1" and "perforation 2". When the user presses the confirm button 1207, the start point coordinates and end point coordinates of the perforations are stored in the RAM 104 (see FIG. 2). Note that the user may change the start point coordinates and end point coordinates of the perforations displayed in the position coordinate setting box 1206 by operating the numeric keys of the hard key group 1104 as necessary.

[0062] "Input" is a method in which the user directly inputs the start and end coordinates of the perforations of the perforated sheet S without reading the perforated sheet S with the document reading device 130. After selecting "input" in the dialog box 1204, the user can input the start and end coordinates of the perforations of the perforated sheet S by specifying any input field in the position coordinate setting box 1206 and operating the numeric keys of the hard key group 1104. Then, when the user presses the confirm button 1207, the start and end coordinates of the perforations input by the user are stored in the RAM 104 (see FIG. 2). Note that the above-mentioned method of acquiring perforation positions is just one example, and the above-mentioned method does not necessarily have to be used.

[0063] <Replacement range setting screen> Next, the "replacement range setting screen" (see S15 and S18 in Fig. 10) will be described with reference to Fig. 12. The "replacement range setting screen" is displayed on the display unit 111, for example, when the user operates a predetermined replacement range setting button on a "menu screen" (not shown) displayed on the display unit 111.

[0064] 12, the "replacement range setting screen" displays a dialog box 1208 that allows the selection of the range for single-color replacement. Here, "Full surface," which specifies the replacement range for the entire area of ​​the perforated sheet S, and "Perforated area," which specifies the replacement range for the perforated area of ​​the perforated sheet S, are displayed. The user can set the replacement range for the single-color replacement function by specifying one of the items displayed in the dialog box 1208.

[0065] Furthermore, when the replacement range is the perforated area of ​​the perforated sheet S, an area width setting box 1209 is displayed on the "replacement range setting screen." The user can set the width (mm) of the perforated area in the area width setting box 1209 by operating the numeric keys of the hard key group 1104. For example, the width of the perforated area is set to "10 mm." As described above, the toner constituting the sheet changes in shape due to the perforation process, and the shape and arrangement of the dots become disordered. For this reason, it is desirable to set the width of the area to which the single-color replacement function is applied, i.e., the width of the perforated area, larger than the area where the dot shapes and arrangement become disordered.

[0066] Furthermore, the "replacement range setting screen" displays the above-mentioned selection button display portion 1202. The user can select whether to enable or disable the halftone processing change function by operating either the "enable" button or the "disable" button of the selection button display portion 1202. Then, when the user presses the confirm button 1210, the replacement range of the halftone processing, the width of the perforation area, and the presence or absence of the halftone processing change function are stored in the RAM 104 (see FIG. 2).

[0067] 13 shows an image formed based on output image data that has been subjected to AM screen processing when single-color replacement has been performed in the perforated area and single-color replacement has not been performed in the area other than the perforated area. The width of the perforated area 265, which is set based on the perforation 260, is, for example, 10 mm.

[0068] 13, in areas other than the perforated area 265 where single-color replacement has not been performed, an image is formed by arranging K toner dots in a straight line (see the minute area 250). In areas other than the perforated area 265, unintended discharge does not occur, so toner is not transferred to unintended locations. In other words, the shape and arrangement of the dots that form the image are not disordered, so no image defects such as changes in the color of the toner image occur.

[0069] On the other hand, in the perforated region 265 where the single color replacement has been performed, an image is formed by arranging the dots of CMY toner at different screen angles. As described above, unintended local discharge occurs in the perforated region 265. However, in the image forming apparatus 100, the K toner single color image formed in the perforated region 265 is changed to a pseudo-color image using CMY toner, so even if the shape and arrangement of the dots become disordered due to unintended local discharge, it is difficult to know whether or not the disorder has occurred.

[0070] In this way, when the type of sheet S is a perforated sheet S, the user can change the K toner monochrome image in the perforated area to a pseudo-color image using CMY toner and form an image. This reduces the appearance of local dot shapes and random arrangements when forming an image on the perforated sheet S by performing AM screen processing, thereby suppressing image defects caused by sheet curling.

[0071] In the second embodiment described above, the control unit 101 performs monochromatic replacement on the input image data related to the perforated area, and does not perform monochromatic replacement on the input image data related to areas other than the perforated area, but this is not limited to the above. For example, when performing monochromatic replacement, the control unit 101 may perform monochromatic replacement on the input image data related to one image formed in a range including the perforated area, not limited to only the input image data related to the perforated area.

[0072] <Other embodiments> In the above-described first and second embodiments, an example is shown in which the single color K toner is replaced with CMY toner when the type of sheet S is a perforated sheet S, but the present invention is not limited to this. For example, the single color K toner may be replaced with CMYK toner. When replacing the single color K toner with CMYK toner, the control unit 101 replaces the color information of the image to be formed in the perforated area in the input image data from the black K toner to a combination of CMYK toners that can reproduce black in a pseudo manner. The control unit 101 performs the above-described color information replacement by referring to a single color replacement table stored in the ROM 103.

[0073] In this case, the single color replacement table specifies that the print amounts of the C toner, M toner, and Y toner are substantially the same for a single color K toner, and that the print amount of the K toner is greater than them. For example, when replacing the K toner of maximum density (tone value 255) with the CMYK toner, the table specifies that the gradation is specified so that the pseudo color can be reproduced, such as C toner "150", M toner "150", Y toner "150", and K toner "200". After replacing the color information, the control unit 101 performs image formation processing using the CMYK toner based on the replaced color information for the perforated area, and performs image formation using the CMYK toner based on the color information set in the input image data for the area other than the perforated area. As a result, the K toner single color toner image is replaced with a replacement toner image formed using the four colors of the CMYK toner.

[0074] Table 2 shows the results of evaluating the occurrence of image defects in the perforation area caused by burrs on the sheet S when CMYK toners and K toner alone are used. [Table 2]

[0075] The occurrence of image defects in Table 2 was evaluated as follows. First, a toner image was formed on the perforated sheet S based on predetermined color information. The predetermined color information is color information determined by using the toner listed in the "Toner Used" column in Table 2 so that the print rate is 30% when K toner alone is used, and the print rate is determined based on a known technology that can pseudo-reproduce the black of an image formed using K toner alone when CMYK toner is used. The print rate referred to here is the ratio of the area where toner exists in the minute area 201 based on the print rate of "100%" when toner exists over the entire surface of the minute area 201 in the image forming area 200 as shown in FIG. 7.

[0076] In the image forming apparatus 100, the color information when using a single color K toner corresponds to the color information before replacement, and the color information when using CMYK toner corresponds to the color information after replacement. The user visually checked the toner image formed based on each color information and judged whether an image defect occurred. As shown in Table 2, when a single color K toner was used, an image defect caused by burrs on the sheet S occurred. In contrast, when CMYK toner was used, no image defect caused by burrs on the sheet S occurred. FIG. 14 shows an image formed in the perforation area using CMYK toner after replacement.

[0077] As shown in Fig. 14, when an image is formed using CMYK toner, the arrangement direction (screen angle) of the dots of each color is different, resulting in a state called a rosette pattern (see minute area 233). The rosette pattern is a random dot arrangement pattern consisting of complex interference, and even if unintended local discharge occurs in the perforation area described above and the shape and arrangement of the dots become random, the color does not change compared to the toner image formed in other areas.

[0078] In the above-mentioned first and second embodiments, the control unit 101 has the image processing unit 105, but the present invention is not limited thereto. For example, as shown in FIG. 1, an information processing device 101A having a CPU or the like may be connected to the image forming device 100 so as to be capable of transmitting and receiving data, and the information processing device 101A may have an image processing unit 105A that performs color conversion processing on input image data. In this configuration, the external device 1000A is connected to the information processing device 101A so as to be capable of transmitting and receiving data, so that the information processing device 101A receives image data (input image data) transmitted from the external device 1000A. The information processing device 101A performs color conversion processing on the input image data using the image processing unit 105A, generates image data in which the K toner single color is replaced with CMY or CMYK, and transmits the image data to the image forming device 100. The control unit 101 of the image forming device 100 performs halftone processing on the image data received from the information processing device 101A, and then causes the image forming units Pa to Pd to form an image based on the output image data. At that time, the control unit 101 transmits to the information processing device 101A as needed information input by the user operating the operation unit 110, such as the type of sheet S, whether or not to execute the monochromatic replacement function, the range in which the monochromatic replacement function is executed, the width of the perforation area, the position of the perforations, etc. The information processing device 101A can perform monochromatic replacement on the perforated sheet S based on this information as described above.

[0079] In the above-mentioned first and second embodiments, when the type of sheet S is a perforated sheet S, the case where the single color K toner is replaced with CMY toner or CMYK toner has been described as an example, but the present invention is not limited to this. Even when the single color toner other than black is used, the occurrence of image defects caused by the above-mentioned sheet burrs can be suppressed by replacing the "single color toner other than black" with CMY toner or CMYK toner. For example, the single color Y toner is replaced with CM toner, the single color M toner with YC toner, and the single color C toner with YM toner. That is, each single color toner image is replaced with a replacement toner image formed of two or more of the other colors.

[0080] In the above-mentioned first and second embodiments, an image forming apparatus configured to perform primary transfer of the toner images of each color from the photosensitive drums 3a to 3d of each color onto the intermediate transfer belt 80, and then secondary transfer of the composite toner images of each color collectively onto the sheet S has been described, but the present invention is not limited to this. For example, the image forming apparatus may be of a direct transfer type in which the toner images on the photosensitive drums are directly transferred onto the sheet by applying a voltage to transfer rollers disposed opposite the photosensitive drums and the conveying belt, with respect to the sheet conveyed by the conveying belt having a nip formed between the photosensitive drums and the sheet. [Explanation of symbols]

[0081] 11...transfer section (secondary transfer outer roller), 80...image carrier (intermediate transfer belt), 100...image forming apparatus, 101...control section, 105...image processing section, 110...selection section (input section, operation section), 111...display section, 130...original reading section (original reading device), 131a...irradiation section, 131b...light receiving section, Pa, Pb, Pc, Pd...first image forming section, second image forming section, third image forming section, fourth image forming section, S...sheet

Claims

1. An image forming apparatus capable of forming an image on a perforated sheet, An image forming unit capable of forming a toner image using multiple toner colors, An image processing unit that performs image processing on acquired image data, The system comprises a control unit that causes the image forming unit to form a toner image based on the image data processed by the image processing unit, The image processing unit, when the sheet on which the toner image is formed is a perforated sheet, performs image processing on the black image data so that the image forming unit forms a process black toner image using multiple toner colors. An image forming apparatus characterized by the following features.

2. The image processing unit performs AM screen processing on the image data. The image forming apparatus according to feature 1.

3. comprising a selection unit capable of selecting the type of image processing, The image processing unit performs the type of image processing selected by the selection unit. The image forming apparatus according to feature 1.

4. The selection unit has a display unit, The display unit displays a screen for selecting the image processing when the sheet on which the toner image is formed is a perforated sheet. The image forming apparatus according to feature 3.

5. The image processing unit replaces the black image data with image data of three colors: yellow, magenta, and cyan. The image forming apparatus according to feature 1.

6. The image processing unit replaces the black image data with image data of four colors: black, yellow, magenta, and cyan. The image forming apparatus according to feature 1.

7. The image processing unit performs image processing such that the image forming unit forms a toner image of the process black on a perforated sheet, corresponding to a predetermined area on which perforations are formed. The image forming apparatus according to feature 1.

8. The control unit is capable of obtaining the position where perforations are formed on the perforated sheet, The image processing unit identifies image data corresponding to the predetermined region based on the position where the perforations are formed. The image forming apparatus according to feature 7.

9. A document reading unit having an illumination unit that irradiates light onto a sheet and a light receiving unit that receives reflected light from the sheet of the irradiated light, and capable of reading an image on the sheet, The control unit acquires the position of the perforations based on the result of reading the perforated sheet by the document reading unit. The image forming apparatus according to feature 8.

10. The input unit is capable of inputting the position of the perforation and the range of the predetermined area, The image forming apparatus according to feature 8.

11. An image forming apparatus capable of forming an image on a perforated sheet, A reception desk that accepts information regarding the type of seat, The device includes a display unit that shows a screen for selecting the type of image processing to be performed on black image data when the sheet is a perforated sheet. An image forming apparatus characterized by the following features.

12. Further comprising an image processing unit that performs image processing on acquired image data, The image processing unit performs image processing according to the selected type of image processing. The image forming apparatus according to feature 11.

13. Further comprising an image forming unit capable of forming a toner image using multiple toner colors, The type of image processing includes a process of replacing black image data with image data formed by the image forming unit as a process black toner image using multiple toner colors. The image forming apparatus according to feature 11.

14. The display unit displays a screen for inputting the area in which perforations are formed. The image forming apparatus according to feature 11.

Images