Image forming apparatus
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- CANON KK
- Filing Date
- 2023-06-15
- Publication Date
- 2026-06-11
Smart Images
Figure 00000000_0000_ABST
Abstract
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 in 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). Also, conventionally, 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 screening processing or FM screening processing is performed, image defects due to burrs on the sheet are 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 one embodiment of the present invention is an image forming apparatus capable of forming an image on a perforated sheet, and comprises an image carrier that carries a toner image, an image forming unit that forms a toner image to be carried on the image carrier, a transfer unit that transfers the toner image carried on the image carrier to a sheet, an image processing unit that performs at least one of screening and error diffusion processing on acquired image data, and 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, wherein when the image processing unit is set to perform the screening processing on the acquired image data, if the sheet on which the toner image is formed is a perforated sheet, the image processing unit is capable of executing a mode that performs the error diffusion processing on the acquired image data without performing the screening processing.
[0007] An image forming apparatus according to one embodiment of the present invention is an image forming apparatus capable of forming an image on a perforated sheet, and comprises an image carrier that carries a toner image, an image forming unit that forms a toner image to be carried on the image carrier, a transfer unit that transfers the toner image carried on the image carrier to a sheet, an image processing unit that performs at least one of screen processing and error diffusion processing on acquired image data, and 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, wherein when the image processing unit is set to perform the screen processing on the acquired image data, if the sheet on which the toner image is formed is a perforated sheet, the image processing unit is capable of executing a mode in which the error diffusion processing is performed on image data located in a specified area where a perforation burr is formed, and the screen processing is performed on image data located in an area other than the specified area. 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 change / non-change selection screen. [Figure 7] FIG. [Figure 8] FIG. 13 is a schematic diagram showing an image obtained by performing AM screen processing. [Figure 9] FIG. 11 is a schematic diagram showing an image when error diffusion processing is performed. [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 change range setting screen. [Figure 13] 11A and 11B are schematic diagrams showing an image obtained when error diffusion processing is performed on a perforation area and an image obtained when AM screen processing is performed on an area other than the perforation area. 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 apparatus 100 forms a toner image on a sheet S based on image data sent from, for example, a document reading device 130 connected to the image forming apparatus 100 or an external device 1000 such as 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 (second transfer section) 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 as a developing section, a charging device 2d as a charging section, a photosensitive drum 3d as a photosensitive member, a photosensitive drum cleaner 4d, an exposure device 5d as an exposure section, 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 a primary transfer roller 6d (first transfer section) 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 (intermediate transfer body) as an image carrier is stretched by the secondary transfer inner 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 halftone processing (also called halftone processing) on the image data acquired by the control unit 101. Here, the user can set AM screen processing or 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 "change / no change 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, the "sheet selection screen" displays a dialog box 1201 that allows the user to select the type of sheet S on which an image can be formed by the image forming apparatus 100, which is pre-stored in the ROM 103 (see FIG. 2). Here, "plain paper," "cardboard," and "perforated paper" (perforated sheet) are displayed, but the user can scroll the screen displayed in the dialog box 1201 to display other types on which an image can be formed. The user can select the type of sheet S from the multiple types displayed in the dialog box 1201. The selected type of sheet S is confirmed by operating a confirm 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 the following description will be given taking as an example a case where the user has already set AM screen processing as halftone processing from the operation unit 110 before starting an 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 sheet S is not a perforated sheet S (No in S1), 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 (S2). The output image data is used when exposing the photosensitive drums 3a to 3d using the exposure devices 5a to 5d. After the control unit 101 exposes the photosensitive drums 3a to 3d using the exposure devices 5a to 5d based on the output image data, the control unit 101 develops the electrostatic latent images into toner images using the developing devices 1a to 1d. Thereafter, the toner images formed on the photosensitive drums 3a to 3d are 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 (S5). 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 S5), 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 S5), 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 S.
[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 or not the function for changing the halftone processing is enabled (S3). The determination of whether or not the function for changing the halftone processing is enabled is based on the user's selection using a "change yes / no selection screen" (see FIG. 6) described later.
[0036] If the function for changing the halftone processing is enabled (Yes in S3), the control unit 101 changes the halftone processing from the AM screen processing preset by the user to the error diffusion processing (S4). The control unit 101 performs error diffusion processing on the input image data by the image processing unit 105, and causes the image forming units Pa to Pd to form an image based on the output image data (S2).
[0037] If the function for changing the halftone processing is not enabled (No in S3), the control unit 101 does not change the AM screening processing to the error diffusion processing, but performs the AM screening processing preset by the user on the input image data using the image forming units Pa to Pd, and causes the image forming units Pa to Pd to form an image based on the output image data (S2).
[0038] <Change / No Change Selection Screen> Next, the above-mentioned "change or non-change 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 "change or non-change 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 "change or non-change selection screen".
[0039] In the selection button display area 1202, an "enable" button for enabling the halftone processing change function and an "invalid" button for deactivating the halftone processing change function are displayed so that the user can select whether or not to execute the halftone processing change function (mode). The user can select whether or not to enable the halftone processing change 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 halftone processing change function is confirmed as either "enable (executed)" or "invalid (not executed)". The confirmed type of sheet S and whether or not to execute the halftone processing change function are stored in the RAM 104 (see FIG. 2). When executing an image forming job, the control unit 101 refers to the type of sheet S and whether or not to execute the halftone processing change function stored in the RAM 104.
[0040] <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 image defects such as disorganized shapes and arrangements of dots forming the image and changes in the color of the toner image. In particular, when AM screen processing is performed, image defects caused by 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 caused by burrs on the perforated sheet S by changing the halftone processing for the image formed on the perforated sheet S from AM screen processing to error diffusion processing (see S4 in FIG. 5). Table 1 shows the results of an evaluation of the occurrence of image defects caused by burrs on the perforated sheet S when AM screen processing and error diffusion processing are performed as halftone processing. [Table 1]
[0041] The occurrence of image defects in Table 1 was evaluated as follows. An image was formed on perforated sheet S with a print rate of 30% using K toner alone by performing the "AM screen" process and "error diffusion" process described in the "halftone process" column in Table 1. The print rate referred to here is the ratio of the area where toner exists in the micro area 201 based on a print rate of "100%" defined as the case where toner exists over the entire surface of the micro area 201 in the image formation area 200 as shown in Figure 7.
[0042] The user visually checked the toner images formed when AM screening processing was performed and when error diffusion processing was performed, and judged whether or not image defects occurred. As shown in Table 1, when AM screening processing was performed, image defects caused by burrs on the sheet S occurred. In contrast, when error diffusion processing was performed, no image defects caused by burrs on the sheet S occurred. Here, FIG. 8 shows an image when AM screening processing was performed, and FIG. 9 shows an image when error diffusion processing was performed.
[0043] As shown in FIG. 8, when the AM screen process is performed, the image is formed by arranging K toner dots in a straight line. However, in the perforation area including the perforation 260, the shape of some dots changes. Or, the dots are not arranged in a straight line and are disordered (see the minute area 211). In this case, the phenomenon that occurs in the image formed in the image forming area 200 is as follows. The perforation area where the burrs occur is an area 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 perforation area. This unintended discharge causes the toner to be transferred to an unintended location, and the shape and arrangement of the dots become disordered. Therefore, the toner image formed in the perforation area looks different in color compared to the toner image formed in the other areas, which becomes apparent as an image defect.
[0044] On the other hand, as shown in Fig. 9, when error diffusion processing is performed, the image is formed with random dot arrangement and size (see minute area 222). With a random dot arrangement pattern, even if the shape and arrangement of the dots become disordered due to unintended local discharge as described above, the difference from the surroundings is less noticeable. Therefore, when comparing the toner image formed in the perforated area with the toner image formed in the area other than the perforated area, there is no difference in color.
[0045] As described above, in the image forming apparatus 100 of this embodiment, when the type of sheet S is a perforated sheet S, the halftone processing can be changed from the AM screen processing preset by the user to the error diffusion processing. In this way, when forming an image on a perforated sheet S, the image forming apparatus 100 of this embodiment can reduce the appearance of localized dot shapes and random arrangements, thereby suppressing the occurrence of image defects caused by sheet curling.
[0046] In addition, the image forming apparatus 100 of the present embodiment allows the user to arbitrarily select whether or not to change the halftone processing on the "change / non-change selection screen" (see FIG. 6). This is because it is possible that the output image data resulting from the changed halftone processing may not be 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 change the halftone processing individually for each condition. In the case where the user determines that the halftone processing change function is not operating normally under unexpected circumstances, including a malfunction of the image forming apparatus 100, it is desirable to be able to set the change function to "inactive." Therefore, by allowing each user to select whether or not to enable the change function depending on the usage situation and the deliverable, a deliverable of higher quality can be provided.
[0047] [Second embodiment] In the first embodiment described above, the halftone processing can be changed from AM screen processing to error diffusion processing over 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 the above. For example, the halftone processing can be changed from AM screen processing to error diffusion processing only for the toner image formed in the perforated area. The image forming process of the second embodiment that can achieve 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.
[0048] In this example, a case will be described in which the user has set AM screen processing as halftone processing from the operation unit 110 before starting an image formation job. In addition, in the image formation process shown in Fig. 10, the description of the same processes as those in the image formation process shown in Fig. 5 will be simplified or omitted.
[0049] 10, 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 (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 S1), the control unit 101 performs AM screen processing preset by the user on the input image data by 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).
[0050] 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.
[0051] On the other hand, if the type of sheet S is a perforated sheet S (Yes in S11), the control unit 101 sets the position information of the perforated area (S13). The position information of the perforated area is set based on the coordinates set by the user using the "Perforation Position Setting Screen" (see FIG. 11) described later. After the position information of the perforated area is set, the control unit 101 determines whether there is an image to be formed in the perforated area based on the input image data and the set position information (S14). If there is no image to be formed in the perforated area (No in S14), the control unit 101 performs AM screen processing, which is preset by the user, on the input image data by the image processing unit 105 for the entire area of the perforated sheet S, regardless of whether it is a perforated area or an area other than the perforated area, and causes the image forming units Pa to Pd to form an image based on the output image data (S12).
[0052] If there is an image to be formed in the perforated area (Yes in S14), the control unit 101 determines whether the range in which the halftone processing is to be changed is limited to the perforated area (S15). The control unit 101 determines whether the range in which the halftone processing is to be changed is limited to the perforated area based on the change range set by the user using the "change range setting screen" (see FIG. 12) described later.
[0053] If the range in which the halftone processing is to be changed is not limited to the perforated area but is the entire area of the perforated sheet S (No in S15), the control unit 101 determines whether or not the function for changing the halftone processing is enabled (S16). The determination of whether or not the function for changing the halftone processing is enabled is based on the user's selection using a selection button display unit 1202 (see FIG. 12) displayed on a "change range setting screen" described later.
[0054] If the function for changing the halftone processing is enabled (Yes in S16), the control unit 101 changes the halftone processing for the entire area of the perforated sheet S from the AM screen processing preset by the user to the error diffusion processing (S17). The control unit 101 performs error diffusion processing on the input image data by 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). If the function for changing the halftone processing is not enabled (No in S16), the control unit 101 does not change the halftone processing for the entire area of the perforated sheet S from the error diffusion processing, but instead performs AM screen processing for the input image data preset by the user by 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).
[0055] On the other hand, if the range in which the halftone processing is changed 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 "change range setting screen" described later. After that, the control unit 101 determines whether the function for changing the halftone processing is enabled (S19).
[0056] If the function for changing the halftone processing is enabled (Yes in S19), the control unit 101 changes the halftone processing for the perforated area from the AM screening processing preset by the user to error diffusion processing (S20). The control unit 101 performs error diffusion processing on the input image data for the perforated area using the image processing unit 105, performs AM screening processing on the input image data for the area other than the perforated area, and causes the image forming units Pa to Pd to form images based on the output image data (S12). The control unit 101 can identify the input image data for the perforated area and the input image data for the area other than the perforated area based on the position of the perforations.
[0057] If the function to change the halftone processing is not enabled (No in S19), the control unit 101 performs AM screening processing on the input image data for the entire area of the sheet S by the image processing unit 105, regardless of whether the area is a perforated area or not, without changing the halftone processing to error diffusion processing, and causes the image forming units Pa to Pd to form an image based on the output image data (S12).
[0058] <Perforation position setting screen> A "perforation position setting screen" is displayed on display unit 111 (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.
[0059] 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).
[0060] 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.
[0061] "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.
[0062] <Change range setting screen> Next, the "change range setting screen" (S15 in Fig. 10) will be described with reference to Fig. 12. The "change range setting screen" is displayed on display unit 111, for example, when the user operates a change range setting button for halftone processing on a "menu screen" (not shown) displayed on display unit 111.
[0063] 12, the "change range setting screen" displays a dialog box 1208 that allows the user to select the change range for changing the halftone processing. Here, "Full" is displayed, which sets the change range to the entire area of the perforated sheet S, and "Perforated area" is displayed, which sets the change range to the perforated area of the perforated sheet S. The user can set the change range for the halftone processing by touching any of the items displayed in the dialog box 1208.
[0064] The "change range setting screen" also displays an area width setting box 1209. The user can set the width (mm) of the perforation 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 perforation area is set to "10 mm." As described above, the toner that constitutes the sheet changes in shape due to the perforation process may be transferred to unintended locations, causing the dot shapes and arrangement to become disordered. For this reason, it is desirable to set the width of the area where the screen processing is changed to error diffusion, i.e., the width of the perforation area, larger than the area where the dot shapes and arrangement become disordered.
[0065] Furthermore, the "change 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 change 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).
[0066] <Whether or not image defects occur> As already mentioned, when a toner image is transferred to the perforated sheet S, unintended discharge may occur in the perforated area where burrs have occurred, causing the toner to be transferred to unintended locations, resulting in image defects such as disorganized shapes and arrangements of dots forming the image and changes in the color of the toner image. Therefore, in this embodiment, the halftone processing for the image formed in the perforated area where burrs have occurred is changed from AM screen processing to error diffusion processing (see S20 in FIG. 10), thereby making it possible to suppress image defects caused by burrs on the sheet.
[0067] Table 2 shows the results of an evaluation of whether or not image defects occurred due to burrs on sheet S when AM screening was performed regardless of whether the area was perforated or not, and when error diffusion processing was performed on the perforated area and then AM screening was performed on the non-perforated area. [Table 2]
[0068] The occurrence of image defects in Table 2 was evaluated as follows. First, a toner image was formed on a perforated sheet S based on predetermined image information. The predetermined image information here is image information using each process listed in the halftone process column in Table 2 so that the printing rate is 30% with K toner alone. Note that the printing rate here refers to the ratio of the area where toner exists in the micro area 201 based on a printing rate of "100%" when toner exists over the entire surface of the micro area 201 in the image formation area 200 as shown in FIG. 7 (area rate).
[0069] The user visually checked the toner images formed based on the output image data outputted after each halftone process to determine whether an image defect occurred. As shown in Table 2, when the AM screen process was performed regardless of whether it was the perforation area or the area other than the perforation area, an image defect caused by the burr of the sheet S occurred. In contrast, when the error diffusion process was performed on the perforation area and the AM screen process was performed on the area other than the perforation area, the image defect caused by the burr of the sheet S was suppressed. FIG. 13 shows an image formed based on the output image data outputted after the error diffusion process was performed on the perforation area and the AM screen process was performed on the area other than the perforation area. The width of the perforation area 265 set based on the perforation 260 is, for example, "10 mm".
[0070] 13, in the area other than the perforated area 265 where the AM screen processing has been performed, the K toner dots are arranged in a straight line to form an image (see the minute area 250). In the area other than the perforated area 265, unintended discharge does not occur, so the 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.
[0071] On the other hand, in the perforated region 265 where the error diffusion process has been performed, the image is formed by randomly arranging dots of K toner (see the minute region 251). As described above, unintended localized discharge occurs in the perforated region 265. However, since the image forming apparatus 100 changes the halftone process for the image formed in the perforated region 265 from the AM screen process to the error diffusion process, even if the shape and arrangement of the dots become random due to the unintended localized discharge, it becomes difficult to know whether randomization has occurred or not.
[0072] In this way, when the type of sheet S is a perforated sheet S, the halftone processing for the perforated area can be changed from the screen processing preset by the user to the error diffusion processing, and an image is formed based on the output image data that has been subjected to the error diffusion processing. This makes it possible to reduce the appearance of localized dot shapes and random arrangements when forming an image on the perforated sheet S, thereby suppressing image defects caused by sheet curling.
[0073] In the second embodiment described above, when the function for changing the halftone processing is enabled (Yes in S19), the control unit 101 performs error diffusion processing on the input image data for the perforated area 265 using the image processing unit 105, and performs AM screening processing on the input image data for the area other than the perforated area, but this is not limited to the above. For example, the control unit 101 may change the processing from AM screening processing to error diffusion processing not only on the input image data for the perforated area 265, but also on the input image data for an entire image formed in a range including the perforated area 265.
[0074] <Other embodiments> 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 to this. 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 able to transmit and receive data, and the information processing device 101A may have an image processing unit 105A that performs AM screen processing and error diffusion processing. In this configuration, the external device 1000A is connected to the information processing device 101A so as to be able to transmit and receive 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 halftone processing on the input image data by the image processing unit 105A, and transmits the input image data to the image forming device 100 as output image data. The control unit 101 of the image forming device 100 causes the image forming units Pa to Pd to form an image based on the output image data received from the information processing device 101A, without performing halftone processing on the output image data received from the information processing device 101A. 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 halftone processing change function, the range of change in halftone processing, the width of the perforation area, the position of the perforations, etc. Based on this information as described above, the information processing device 101A can switch from AM screen processing to error diffusion processing for the perforated sheet S, and perform halftone processing on the input image data by the image processing unit 105A.
[0075] In the above-described first and second embodiments, a case has been described in which the user has set AM screening processing as the halftone processing from the operation unit 110 before starting an image forming job, but this is not limiting. It may also be the case in which FM screening processing has been set as the halftone processing. In this case, when the function for changing the halftone processing is enabled, the halftone processing is changed from FM screening processing to error diffusion processing.
[0076] 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 conveyed by the conveyor belt having a nip formed between the photosensitive drums and the conveyor belt by applying a voltage to transfer rollers disposed opposite the photosensitive drums and conveyor belt. The image forming apparatus may also be an image forming apparatus capable of forming a single black toner image (monochrome machine). [Explanation of symbols]
[0077] 1a to 1d...developing section (developing device), 2a to 2d...charging section (charging device), 3a to 3d...photosensitive member (photosensitive drum), 5a to 5d...exposure section (exposure device), 6a to 6d...first transfer section (primary transfer roller), 11...transfer section (second transfer section, secondary transfer outer roller), 80...image carrier (intermediate transfer belt), 100...image forming device, 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 to Pd...image forming section, S...sheet
Claims
1. An image forming apparatus capable of forming an image on a perforated sheet, An image forming unit that forms a toner image on a sheet, An image processing unit performs at least one of the following image processing operations on acquired image data: screen processing and error diffusion processing. 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 performs the error diffusion process on the acquired image data when the sheet on which the toner image is formed is a perforated sheet. An image forming apparatus characterized by the following features.
2. The system includes a selection unit that allows selection of 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.
3. 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 2.
4. The image processing unit performs the error diffusion process on image data corresponding to a predetermined area in the perforated sheet where perforations are formed, and performs the screen processing on image data corresponding to an area other than the predetermined area. The image forming apparatus according to feature 1.
5. 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 4.
6. The device comprises an illumination unit that irradiates light onto a sheet, a light receiving unit that receives reflected light from the sheet, and a document reading unit 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 5.
7. 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 5.
8. The screen processing is AM screen processing. The image forming apparatus according to feature 1.
9. An image forming apparatus capable of forming an image on a perforated sheet, A reception desk that accepts information regarding the type of seat, If the sheet type is a perforated sheet, the system includes a display unit that shows at least screen processing and error diffusion processing as options on a screen for selecting the type of image processing to be performed on the image data. An image forming apparatus characterized by the following features.
10. 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 9.
11. The display unit displays a screen for inputting the area in which perforations are formed. The image forming apparatus according to feature 9.