Image forming apparatus

Abstract

To appropriately improve an image defect occurring in an image forming apparatus with a simple operation.SOLUTION: An image forming apparatus comprises a printing unit, an image reading unit, and a control unit. The control unit causes the image reading unit to read a sheet with a mark in which the mark is applied to an image defect area, acquires image data with the mark generated through the reading of the sheet with the mark, acquires reference image data that is the basis of an image printed on the sheet with the mark, compares the reference image data with the image data with the mark to detect a marking area in the image data with the mark, and determines the type and degree of an image defect occurring in the image defect area. The control unit changes setting values of predetermined setting items related to printing performed by the printing unit on the basis of the type and degree of the image defect occurring in the image defect area.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] A conventional image forming apparatus prints a test image on a sheet and outputs it as a diagnostic sheet. The conventional image forming apparatus reads the diagnostic sheet and identifies the content of the image defect based on the image data of the read diagnostic sheet. The conventional image forming apparatus then corrects settings related to the image defect. Such an image forming apparatus is disclosed in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-141898 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, a user obtains a desired output image (herein, for convenience, referred to as a user output image) by performing printing using an image forming device. Then, when there is an image defect in the user output image, the user performs a panel operation to print a diagnostic sheet, and after the diagnostic sheet is printed, the diagnostic sheet is scanned using the same image forming device as when it was printed.

[0005] Here, since the test image of the diagnostic sheet is different from the user output image, there are cases where an image defect appears in the user output image but the image defect does not appear in the test image of the diagnostic sheet. In this case, even if the settings related to the image defect are corrected, the image defect may not be improved. In addition, from the user's perspective, it is troublesome to perform panel operations to print the diagnostic sheet.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide an image forming apparatus that is capable of appropriately improving image defects occurring in the image forming apparatus with simple operations. [Means for solving the problem]

[0007] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention includes a printing unit that prints an image based on image data for printing on a sheet, an image reading unit that reads an object to be read and generates read image data, and a control unit. When performing an image quality improvement process for improving the print quality by the printing unit, the control unit causes the image reading unit to read a marked sheet that has been printed by the printing unit and has marks applied to image defect areas, obtains marked image data that is read image data generated by reading the marked sheet, obtains reference image data that is image data for printing on which the image printed on the marked sheet is based, and compares the reference image data with the marked image data to detect a marking area in the marked image data that corresponds to an area indicated by the mark on the marked sheet and to determine the type and degree of image defect occurring in the image defect area. As the image quality improvement process, the control unit performs a process for changing the setting values ​​of predetermined setting items related to printing by the printing unit based on the type and degree of image defect occurring in the image defect area. Effect of the Invention

[0008] According to the present invention, image defects occurring in an image forming apparatus can be appropriately improved by a simple operation. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram of an image forming unit according to an embodiment. [Diagram 3] FIG. 2 is a schematic diagram of an image reading unit according to an embodiment. [Figure 4] 1 is a block diagram of an image forming apparatus according to an embodiment. [Diagram 5] 5 is a conceptual diagram of mode information stored in a storage unit according to the embodiment. FIG. [Figure 6] 10A and 10B are diagrams illustrating an example of a marked sheet (a marked sheet when a drum ghost occurs) to be read by an image reading unit according to an embodiment. [Figure 7] 1 is a diagram showing an example of a marked sheet (a marked sheet in which aggregated white dots have occurred) to be read by an image reading unit according to an embodiment; [Figure 8] 5 is a flowchart showing a flow of processing performed by a control unit according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Configuration of Image Forming Apparatus> 1, an image forming apparatus 100 of this embodiment is placed on a substantially flat floor surface FL. The up-down direction of the image forming apparatus 100 is a direction perpendicular to the floor surface FL.

[0011] The image forming apparatus 100 includes a main transport path MP. The image forming apparatus 100 also includes a sheet cassette CA. The sheet cassette CA is detachable from the main body of the image forming apparatus 100. The sheet cassette CA accommodates sheets S to be used in a print job. The main transport path MP runs from a supply position P0 for the sheet S from the sheet cassette CA, through a transfer position P1 and a fixing position P2, to an output tray ET.

[0012] In a print job, a sheet S in a sheet cassette CA is supplied from a supply position P0 to a main transport path MP. The sheet S is transported along the main transport path MP. An image is formed using toner. The image is then printed on the sheet S during transport. In other words, a transfer process of the image onto the sheet S during transport is performed at a transfer position P1. A fixing process of the image onto the sheet S is performed at a fixing position P2.

[0013] The image forming apparatus 100 includes a printing unit 1. The printing unit 1 includes an image forming unit 10. There are four image forming units 10. The four image forming units 10 correspond to the colors cyan, magenta, yellow, and black, respectively. The four image forming units 10 form images (i.e., toner images) using toner of the corresponding color. The following description focuses on one image forming unit 10 and describes its configuration, but the four image forming units 10 have the same configuration as each other. Therefore, the description of the configurations of the other image forming units 10 will be omitted, as the following description will be used as an example.

[0014] As shown in FIG. 2, the image forming unit 10 includes a photoconductor drum 11, a charging device 12, an exposure device 13, and a developing device 14. When the image forming unit 10 forms an image, the photoconductor drum 11 rotates. The charging device 12 charges the surface of the photoconductor drum 11. The exposure device 13 forms an electrostatic latent image on the surface of the photoconductor drum 11. The developing device 14 develops the electrostatic latent image into a toner image. The image forming unit 10 also includes a cleaning device (reference number omitted). The cleaning device cleans the surface of the photoconductor drum 11.

[0015] The photoconductor drum 11 has a photosensitive layer 110 on its surface. The photoconductor drum 11 has a cylindrical conductive substrate (reference number omitted). The photosensitive layer 110 is formed on the surface of the conductive substrate. The photoconductor drum 11 corresponds to an "image carrier."

[0016] The charging device 12 has a charging roller 120. The charging roller 120 contacts the surface of the photoconductor drum 11. The charging roller 120 applies a charging voltage to the surface of the photoconductor drum 11.

[0017] The exposure device 13 exposes the surface of the photoconductor drum 11 to light and attenuates the charge. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 11. For example, the exposure device 13 is a separate unit from the photoconductor drum 11, the charging device 12, and the developing device 14.

[0018] The developing device 14 contains a developer containing toner. The developer is a two-component developer containing toner and a magnetic carrier. The developing device 14 also has a developing roller 140. The developing roller 140 carries the developer on its surface. A magnetic brush is formed on the surface of the developing roller 140. The developing roller 140 corresponds to a "developer carrier."

[0019] A developing voltage of the same polarity as the toner is applied to the developing roller 140. While receiving the developing voltage, the developing roller 140 brings a magnetic brush into contact with the surface of the photoconductor drum 11. This causes the toner to adhere to the surface of the photoconductor drum 11, and a toner image is formed on the surface of the photoconductor drum 11. In other words, the toner is supplied to the surface of the photoconductor drum 11, and the electrostatic latent image is developed into a toner image.

[0020] Returning to FIG. 1, the printing unit 1 includes an intermediate transfer belt 15. The intermediate transfer belt 15 corresponds to an "intermediate transfer body." The intermediate transfer belt 15 is an endless belt. The intermediate transfer belt 15 is rotatably supported by a plurality of tension rollers 150. The plurality of tension rollers 150 tension the intermediate transfer belt 15.

[0021] One of the multiple tension rollers 150 is connected to a belt motor (not shown). In the following description, the tension roller 150 connected to the belt motor is referred to as a drive roller, and the drive roller is denoted by the reference symbol 151. The drive roller 151 rotates by power transmitted from the belt motor. The intermediate transfer belt 15 rotates in response to the rotation of the drive roller 151. The other tension rollers 150 rotate in response to the intermediate transfer belt 15.

[0022] The image forming apparatus 100 includes primary transfer rollers 16. The primary transfer rollers 16 correspond to the "primary transfer member." There are four primary transfer rollers 16. One primary transfer roller 16 is assigned to each of the colors cyan, magenta, yellow, and black. Each primary transfer roller 16 is pressed against the photoconductor drum 11 carrying a toner image of the corresponding color via the intermediate transfer belt 15.

[0023] The image forming apparatus 100 also includes a secondary transfer roller 17. The secondary transfer roller 17 corresponds to a "secondary transfer member." The secondary transfer roller 17 is in pressure contact with the intermediate transfer belt 15 at a transfer position P1. The secondary transfer roller 17 sandwiches the intermediate transfer belt 15 between itself and a drive roller 151, forming a transfer nip between itself and the intermediate transfer belt 15. This forms the transfer nip at the transfer position P1. The main transport path MP passes through the transfer nip.

[0024] In a print job, the sheet S is transported toward the transfer position P1 (i.e., the transfer nip). The sheet S passes through the transfer nip during the transport. That is, the intermediate transfer belt 15 contacts the sheet S during the transport downstream of the contact position with each photoconductor drum 11 in the belt rotation direction.

[0025] Each image forming unit 10 forms an image using toner of a corresponding color. Each primary transfer roller 16 primarily transfers a toner image onto the intermediate transfer belt 15. In other words, the intermediate transfer belt 15 sequentially receives the primary transfers of the toner images from each photoconductor drum 11. The intermediate transfer belt 15 rotates while carrying the toner image. While the sheet S is passing through the transfer nip, the sheet S comes into contact with the intermediate transfer belt 15. The secondary transfer roller 17 secondary transfers the toner image onto the sheet S passing through the transfer nip.

[0026] The image forming apparatus 100 includes a fixing unit FX. The fixing unit FX includes a heating roller and a pressure roller. The fixing unit FX is disposed at a fixing position P2. The heating roller has a built-in heater. The pressure roller is in pressure contact with the heating roller. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position P2.

[0027] In a print job, the sheet S passes through the fixing position P2. That is, the sheet S is sandwiched in the fixing nip. The fixing unit FX heats the sheet S as it passes through the fixing position P2. Pressure is applied to the sheet S at the fixing position P2. The fixing unit FX applies heat and pressure to the sheet S to fix the toner image to the sheet S. The sheet S after the fixing process is discharged to an output tray ET.

[0028] The image forming apparatus 100 includes a transport unit, the reference numerals of which are omitted. The transport unit includes a transport roller pair. The transport roller pair includes a pair of rollers. The pair of rollers has a transport nip between the rollers. The transport roller pair rotates to transport the sheet S that has entered the transport nip. The transport unit transports the sheet S along a main transport path MP. The transport unit also transports the sheet S along a double-sided printing transport path DP, which will be described later.

[0029] The image forming apparatus 100 is capable of executing a double-sided print job in which an image is printed on both sides of a sheet S, in addition to a single-sided print job in which an image is printed on only one side of the sheet S. In order to execute a double-sided print job, the image forming apparatus 100 is provided with a double-sided print transport path DP.

[0030] The double-sided printing transport path DP branches off from the main transport path MP at a branching position P3 downstream of the fixing position P2 in the sheet transport direction of the main transport path MP, and merges with the main transport path MP at a merging position P4 upstream of the transfer position P1 in the sheet transport direction of the main transport path MP.

[0031] When the job to be executed is a single-sided print job, the sheet S passes through the transfer nip only once, and a single transfer process is performed on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is discharged directly onto the discharge tray ET.

[0032] When the job to be executed is a double-sided printing job, the sheet S passes through the transfer nip twice in order to perform the transfer process once on each of the front and back sides of the sheet S. Specifically, when the sheet S passes through the transfer nip for the first time, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after the rear end of the sheet S passes through the branch position P3 and before the sheet S is completely discharged onto the discharge tray ET. As a result, the rear end of the sheet S is drawn into the double-sided printing transport path DP.

[0033] Thereafter, the sheet S is transported along the double-sided printing transport path DP. Then, the sheet S on the double-sided printing transport path DP is returned to the main transport path MP from the junction position P4. The sheet S returned to the main transport path MP is transported along the main transport path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is reversed to the orientation when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, a transfer process is performed on the other side of the sheet S that is opposite to the one side.

[0034] As shown in Fig. 3, the image forming apparatus 100 includes an image reading unit 2. The image reading unit 2 is disposed on top of a main body (indicated by a two-dot chain line in Fig. 3) of the image forming apparatus 100 that includes the printing unit 1. The image reading unit 2 reads a reading object T and generates read image data. The reading object T may be a sheet S that has been printed by the printing unit 1.

[0035] The image reading unit 2 includes contact glasses C1 and C2. The contact glasses C1 and C2 are disposed in a housing RH of the image reading unit 2. The housing RH has an opening on the top surface. The contact glasses C1 and C2 are attached to the openings on the top surface of the housing RH.

[0036] The image reading unit 2 includes a document transport device 20. The document transport device 20 is attached to the housing RH. When viewed from the front of the image forming apparatus 100, the document transport device 20 rotates so as to swing the front portion up and down, with the rear portion as a fulcrum. The document transport device 20 opens and closes with respect to the top surface of the housing RH.

[0037] The document transport device 20 has a set tray ST on which a target object T to be read is set. The document transport device 20 transports the target object T set on the set tray ST onto a contact glass C1.

[0038] In the transport reading mode, the object T to be read is set on the set tray ST. Then, the object T to be read is automatically transported onto the contact glass C1 by the document transport device 20 and read. In the placement reading mode, the object T to be read is set on the contact glass C2 and the object T to be read on the contact glass C2 is read.

[0039] The image reading unit 2 includes a light source 21, an image sensor 22, a mirror 23, and a lens 24. The light source 21, the image sensor 22, the mirror 23, and the lens 24 are disposed inside the housing RH. The image reading unit 2 performs a scanning operation in which light is irradiated from the light source 21 toward the contact glass C1 or C2, and the image sensor 22 performs photoelectric conversion.

[0040] The light source 21 has a plurality of LED elements. The plurality of LED elements are arranged in a line in the main scanning direction (a direction perpendicular to the paper surface of FIG. 3). The image sensor 22 has a plurality of photoelectric conversion elements arranged in the main scanning direction. The mirror 23 reflects light toward the lens 24. The lens 24 collects the light reflected by the mirror 23 and guides it to the image sensor 22.

[0041] The light source 21 and the mirror 23 are mounted on a carriage 25 that is movable in a sub-scanning direction (left and right direction in FIG. 3) perpendicular to the main scanning direction. When the carriage 25 moves in the sub-scanning direction, the reading line of the image reading unit 2 moves in the sub-scanning direction.

[0042] 4, the image forming apparatus 100 includes a control unit 3. The control unit 3 includes processing circuits such as a CPU and an ASIC. The control unit 3 also includes storage devices such as a ROM and a RAM. The control unit 3 controls the printing unit 1. The control unit 3 controls the image reading unit 2.

[0043] The image forming apparatus 100 includes a communication unit 301. The communication unit 301 includes a communication circuit, a communication memory, a communication connector, and the like. The communication unit 301 is communicably connected to an external device via a network such as a LAN. An example of the external device is a user terminal. A personal computer (PC), a smartphone, a tablet computer, and the like can serve as the user terminal.

[0044] The control unit 3 communicates with an external device using the communication unit 301. For example, print data of a print job is transmitted from an external device (user terminal) to the image forming apparatus 100. The print data includes image data to be printed in the print job.

[0045] In a print job based on print data sent from an external device, the printing unit 1 prints an image based on image data included in the print data onto a sheet S. In a copy job as a print job, the printing unit 1 prints an image based on read image data obtained by reading by the image reading unit 2 (i.e., an image of the reading target T) onto a sheet S. Note that the image data included in the print data corresponds to "image data to be printed." In the following description, the image data included in the print data will be referred to as image data to be printed in order to distinguish it from read image data.

[0046] Image forming apparatus 100 includes an operation unit 302. Operation unit 302 is an operation panel and includes a touch screen. Operation unit 302 receives settings, instructions, and the like from a user. Operation unit 302 is connected to control unit 3. Control unit 3 detects the settings, instructions, and the like received by operation unit 302 from the user.

[0047] The image forming apparatus 100 includes a storage unit 4. A non-volatile storage device such as an HDD or SSD is used as the storage unit 4. The storage unit 4 is connected to the control unit 3. The control unit 3 writes data to the storage unit 4 and reads data from the storage unit 4.

[0048] The printing unit 1 also includes a charging voltage power supply 101, a developing voltage power supply 102, and a transfer voltage power supply 103. The charging voltage power supply 101 applies a charging voltage to the charging roller 120. The developing voltage power supply 102 applies a developing voltage to the developing roller 140. The developing voltage is a voltage in which an AC voltage is superimposed on a DC voltage. The transfer voltage power supply 103 applies a transfer voltage to each of the primary transfer roller 16 and the secondary transfer roller 17. The transfer voltage is a voltage of a polarity opposite to that of the toner.

[0049] The control unit 3 is connected to a voltage control circuit 30. The voltage control circuit 30 controls the charging voltage power supply 101, the developing voltage power supply 102, and the transfer voltage power supply 103 based on an output signal from the control unit 3. That is, the control unit 3 controls the charging voltage power supply 101, the developing voltage power supply 102, and the transfer voltage power supply 103.

[0050] <Change print settings> In the image forming apparatus 100, an image defect called drum ghost may occur. When drum ghost occurs, a part of the image transferred previously is transferred faintly in the next or subsequent transfers, and appears on the printed matter as a ghost image. In other words, an afterimage appears. The afterimage causes uneven density.

[0051] During the primary transfer of the toner image from the photoconductor drum 11 to the intermediate transfer belt 15, a primary transfer current flows from the primary transfer roller 16 to the photoconductor drum 11, lowering the surface potential of the photoconductor drum 11. Since the amount of primary transfer current flowing into areas where there is toner (i.e., image areas) is small and the amount of primary transfer current flowing into areas where there is no toner (i.e., non-image areas) is large, the surface potential of the photoconductor drum 11 changes depending on whether or not there is toner. As a result, drum ghosts that cause uneven density can occur.

[0052] The occurrence of drum ghosts is closely related not only to the primary transfer current but also to the frequency of the AC voltage in the development voltage (hereinafter, this frequency is referred to as the development frequency). The larger the primary transfer current, the greater the change in the surface potential of the photoconductor drum 11, and the higher the development frequency, the more likely it is that unevenness in the surface potential will occur. For this reason, there are cases where the occurrence of drum ghosts cannot be effectively suppressed by simply changing either the primary transfer current or the development frequency.

[0053] On the other hand, there are cases where toner aggregates are developed on the photoconductor drum 11 and primarily transferred to the intermediate transfer belt 15. In this case, the presence of toner aggregates between the photoconductor drum 11 and the intermediate transfer belt 15 can cause image defects known as aggregated white spots, in which the toner around the toner aggregates is not transferred and becomes blank. When aggregated white spots occur, white spots that are visible to the user appear on the printed matter. In order to suppress the occurrence of aggregated white spots, it is effective to increase the primary transfer current and the development frequency, respectively.

[0054] Therefore, the control unit 3 performs an image quality improvement process to improve the print image quality by the printing unit 1. By performing the image quality improvement process, the control unit 3 changes settings related to printing by the printing unit 1. Note that there are multiple setting items related to printing by the printing unit 1. In the image quality improvement process, the setting values ​​of predetermined setting items among the multiple setting items related to printing by the printing unit 1 are changed.

[0055] The predetermined setting items are two, a setting item related to the development frequency and a setting item related to the primary transfer current. However, the predetermined setting items listed here are only examples. Other setting items may be added as the predetermined setting items. In other words, there may be two or more predetermined setting items.

[0056] When performing the image quality improvement process, the control unit 3 refers to mode information 40 (see FIG. 4) stored in the storage unit 4. The control unit 3 changes the setting values ​​of one or more predetermined setting items based on the mode information 40. When a setting item related to the development frequency and a setting item related to the primary transfer current exist as predetermined setting items, the setting values ​​of one or both of the setting item related to the development frequency and the setting item related to the primary transfer current are changed.

[0057] A conceptual diagram of the mode information 40 is shown in FIG. 5. The mode information 40 is information indicating the setting contents of a plurality of modes in which the setting contents related to printing by the printing unit 1 are different from each other. In other words, in the mode information 40, the setting values ​​of a plurality of predetermined setting items are defined for each mode so that the combinations of the setting values ​​of the plurality of predetermined setting items are different from each other between the modes. In the case where the setting items related to the development frequency and the setting items related to the primary transfer current are present as the respective predetermined setting items, the setting values ​​of the setting items related to the development frequency and the setting items related to the primary transfer current are defined for each mode. That is, in the mode information 40, the modes related to the development frequency and the primary transfer current are defined. Here, seven modes (modes 1 to 7) are defined, of which mode 4 is the default mode. In the following description, the number indicating the mode is referred to as the mode number.

[0058] The development frequency setting for modes 1 to 3 is 4000Hz. The development frequency setting for modes 4 and 5 is 3500Hz. The development frequency setting for modes 6 and 7 is 3000Hz. In other words, the higher the mode number, the lower the development frequency.

[0059] The primary transfer coefficients of modes 1 to 7 are "1.3", "1.2", "1.1", "1.0", "0.9", "0.8" and "0.7", respectively. The set value of the primary transfer current of each of modes 1 to 7 is a value obtained by multiplying the corresponding primary transfer coefficient and the default value of the primary transfer current. For example, in mode 1, the set value of the primary transfer current is a value obtained by multiplying the default value by 1.3, and in mode 2, the set value of the primary transfer current is a value obtained by multiplying the default value by 1.2. The same is true for modes 3 to 7. As a result, the primary transfer current decreases as the mode number increases.

[0060] At the initial time of use of the image forming apparatus 100 (in other words, at the time of delivery of the image forming apparatus 100), the modes related to the development frequency and the primary transfer current are set to the default mode (i.e., mode 4). At this time, the control unit 3 sets the development frequency to 3500 Hz. The control unit 3 also sets the primary transfer current to a default value (i.e., 1.0 times the default value). The control unit 3 controls the transfer voltage so that the primary transfer current becomes a target value.

[0061] Suppose that an image defect, either a drum ghost or a coagulated white spot, occurs thereafter. In this case, the control unit 3 changes the mode related to the developing frequency and the primary transfer current from the current mode. In other words, the control unit 3 changes the setting values ​​of one or more predetermined setting items. In further other words, the control unit 3 changes the setting value of at least one of the setting items related to the developing frequency and the setting items related to the primary transfer current. When the mode is switched, at least the setting value of the primary transfer current is changed. The setting value of the developing frequency may not be changed even when the mode is switched.

[0062] When drum ghosts occur in the default mode, it is preferable to perform at least one of a process of lowering the development frequency and a process of reducing the primary transfer current. Therefore, the control unit 3 performs a process of changing the mode related to the development frequency and the primary transfer current to a mode with a larger mode number than the default mode (mode 4) as an image quality improvement process. By performing this image quality improvement process, the mode related to the development frequency and the primary transfer current is changed from the default mode (mode 4) to any one of modes 5 to 7.

[0063] For example, when the mode is changed from the default mode (mode 4) to mode 5, the development frequency is not changed from 3500 Hz, but the primary transfer current is changed to 0.9 times the default value. When the mode is changed from the default mode (mode 4) to mode 6, the development frequency is changed to 3000 Hz, and the primary transfer current is changed to 0.8 times the default value. In either case, at least one of the process of lowering the development frequency and the process of reducing the primary transfer current is performed.

[0064] Furthermore, when aggregated white dots occur in the default mode, it is preferable to perform at least one of a process of increasing the development frequency and a process of increasing the primary transfer current. Therefore, the control unit 3 performs a process of changing the mode related to the development frequency and the primary transfer current to a mode having a smaller mode number than the default mode (mode 4) as the image quality improvement process. By performing this image quality improvement process, the mode related to the development frequency and the primary transfer current is changed from the default mode (mode 4) to any one of modes 1 to 3.

[0065] For example, when the mode is changed from the default mode (mode 4) to mode 3, the development frequency is changed to 4000 Hz, and the primary transfer current is changed to 1.1 times the default value. When the mode is changed from the default mode (mode 4) to mode 2, the development frequency is changed to 4000 Hz, the same as mode 3, and the primary transfer current is changed to 1.2 times the default value. In either case, at least one of the process of increasing the development frequency and the process of increasing the primary transfer current is performed.

[0066] <Select mode> As one process of the image quality improvement process, the control unit 3 performs a mode selection process to select one of a plurality of modes related to the development frequency and the primary transfer current. Then, the control unit 3 changes the setting contents related to printing by the printing unit 1 to the setting contents of the mode selected in the mode selection process. In other words, the control unit 3 causes the printing unit 1 to print in the mode selected in the mode selection process.

[0067] The control unit 3 performs image quality improvement processing in response to a user's instruction. For example, when the image quality of a printout output from the image forming apparatus 100 is checked and an image defect is found, the user instructs the execution of image quality improvement processing. The instruction to execute the image quality improvement processing is received by the operation unit 302.

[0068] Before issuing an instruction to execute the image quality improvement process, the user performs an operation of applying a mark MK (see FIGS. 6 and 7) to the image defect area, which is an area where an image defect exists, on the sheet S on which a defective image has been printed. In the marking operation, either an area where an afterimage (ghost image) exists or an area where a blank space (white dot) exists is marked on the sheet S on which printing has been performed by the printing unit 1. In the following explanation, the sheet S on which printing has been performed by the printing unit 1 and to which a mark MK has been applied is referred to as a marked sheet Sm.

[0069] For example, as shown in Fig. 6, when a drum ghost occurs as an image defect, a ghost image G0 that should not be printed is printed faintly in addition to a normal image G1. In this case, a mark MK is added to a part of the ghost image G0.

[0070] 7, when aggregated white dots occur as an image defect, the white dots WP appear in the area of ​​the normal image G1. In this case, a mark MK is added to the white dots WP.

[0071] The mark MK is applied so as to surround at least a part of the image defect area. That is, the mark MK is annular. However, the mark MK does not have to be a continuous ring without any breaks, and may be an annular shape with one or more breaks.

[0072] After the marking operation, the user operates the operation unit 302 to enable the image quality improvement function. At this time, for example, the control unit 3 causes the operation unit 302 to display a message urging the user to scan the marked sheet Sm. When this message is displayed, the user places the marked sheet Sm in the image reading unit 2. Then, the user operates the operation unit 302 to start scanning.

[0073] Thereafter, the control unit 3 performs processing according to the flow shown in Fig. 8. When a scan start operation is detected with the image improvement function enabled, the control unit 3 starts processing according to the flow shown in Fig. 8.

[0074] In step #1, the control unit 3 causes the image reading unit 2 to read the marked sheet Sm. The image reading unit 2 reads the marked sheet Sm and generates read image data of the marked sheet Sm. The control unit 3 acquires the read image data of the marked sheet Sm. In the following description, the read image data of the marked sheet Sm is referred to as marked image data.

[0075] In step #2, the control unit 3 compares the print image data stored in the storage unit 4 with the marked image data. The storage unit 4 stores print data (including print image data) of a predetermined number of print jobs previously executed by the image forming apparatus 100. For example, the print data of the most recent several tens of print jobs (e.g., 20 print jobs) may be stored in the storage unit 4.

[0076] The control unit 3 compares the marked image data with the past print image data stored in the memory unit 4. In this way, the control unit 3 identifies the print image data that is the basis of the image printed on the marked sheet Sm read in step #1, and obtains it as reference image data to be compared with the marked image data.

[0077] In step #3, the control unit 3 compares the reference image data with the marked image data, thereby detecting the marking area in the marked image data that corresponds to the area indicated by the mark MK on the marked sheet Sm.

[0078] In the marked image data, an image corresponding to the mark MK exists. On the other hand, in the reference image data, an image corresponding to the mark MK does not exist. Therefore, by comparing the marked image data with the reference image data, the marking area can be detected from the marked image data. Note that the marking area is an area surrounded by the image that constitutes the mark MK, and is not the image that constitutes the mark MK itself.

[0079] In step #4, the control unit 3 determines the type and degree of the image defect occurring in the image defect area of ​​the marked sheet Sm based on the image data of the marking area (i.e., the area surrounded by the image forming the mark MK) in the marked image data. The mark MK is applied to the image defect area in the image printed on the marked sheet Sm. In other words, the marking area is an area corresponding to the image defect area of ​​the marked sheet Sm. Therefore, the image defect occurring in the image defect area is reflected in the marking area. This makes it possible to determine the type and degree of the image defect occurring in the image defect area of ​​the marked sheet Sm based on the image data of the marking area.

[0080] Therefore, when determining the type of image defect occurring in the image defect area of ​​the marked sheet Sm, the control unit 3 compares the marked image data with the reference image data, and based on the comparison result, the control unit 3 determines the type of image defect occurring in the image defect area of ​​the marked sheet Sm.

[0081] For example, if there are no white dots in the marking area of ​​the marked image data and the color information (such as brightness, hue, and saturation) between the marking area of ​​the marked image data and the area corresponding to the marking area of ​​the reference image data is different, it can be determined that the type of image defect occurring in the image defect area of ​​the marked sheet Sm is a drum ghost.

[0082] On the other hand, if there are white dots in the marking area of ​​the marked image data and there are no white dots in the area corresponding to the marking area of ​​the reference image data, it can be determined that the type of image defect occurring in the image defect area of ​​the marked sheet Sm is agglomerated white dots.

[0083] Furthermore, the control unit 3 compares the marked image data with the reference image data to determine the degree of the image defect occurring in the image defect area of ​​the marked sheet Sm.

[0084] When the image defect occurring in the image defect area of ​​the marked sheet Sm is a drum ghost, the control unit 3 obtains an average value of color information of the image portion of the marking area of ​​the marked image data as a target value. Furthermore, the control unit 3 obtains an average value of color information of a portion of the reference image data corresponding to the image portion as a reference value. Then, the control unit 3 sets the difference value between the target value and the reference value as a value indicating the degree of the image defect occurring in the image defect area of ​​the marked sheet Sm. The greater the difference value between the target value and the reference value, the greater the degree of the image defect. As the color information, lightness, hue, saturation, Lab color space values, etc. can be used.

[0085] When the image defect occurring in the image defect area of ​​the marked sheet Sm is agglomerated white dots, the control unit 3 counts the number of white dots present in the marked image data. When counting the number of white dots, if there are white dots in areas other than the marking area, the white dots in the areas other than the marking area may also be counted. If it is specified that one mark MK is applied to one white dot, the number of marks MK may be counted as the number of white dots. Then, the control unit 3 regards the number of white dots as a value indicating the degree of the image defect occurring in the image defect area of ​​the marked sheet Sm. The greater the number of white dots, the greater the degree of the image defect.

[0086] In step #5, the control unit 3 performs an image quality improvement process to improve the print quality of the printing unit 1. As the image quality improvement process, the control unit 3 performs a process to change one or both of the setting values ​​of the setting item related to the development frequency and the setting item related to the primary transfer current based on the type and degree of the image defect occurring in the image defect area of ​​the marked sheet Sm (i.e., the information obtained in step #4). In other words, as the image quality improvement process, the control unit 3 switches the mode related to the development frequency and the primary transfer current. By switching the mode, the setting values ​​of one or both of the setting items related to the development frequency and the primary transfer current are changed.

[0087] When the image defect occurring in the image defect area of ​​the marked sheet Sm is a drum ghost, the control unit 3 obtains a difference value between the color information of the marking area of ​​the marked image data and the color information of the area corresponding to the marking area of ​​the reference image data. That is, the control unit 3 obtains a difference value between the target value and the reference value (hereinafter referred to as a difference value of color information).

[0088] Then, the control unit 3 compares the difference value of the color information with a predetermined first threshold. The control unit 3 also compares the difference value of the color information with a predetermined second threshold. The second threshold is a value greater than the first threshold. When Lab color space values ​​are used as the color information, the first threshold may be set to "2" and the second threshold may be set to "3."

[0089] The control unit 3 determines whether the difference value of the color information is less than the first threshold value. If the difference value of the color information is less than the first threshold value, it means that the degree of image defects occurring on the marked sheet Sm is extremely small. Therefore, it is not necessary to change the setting values ​​of both the setting items related to the development frequency and the setting items related to the primary transfer current. Therefore, if the difference value of the color information is less than the first threshold value, the control unit 3 does not switch the modes related to the development frequency and the primary transfer current.

[0090] The control unit 3 determines whether the difference value of the color information is equal to or greater than the first threshold value and less than the second threshold value. If the difference value of the color information is equal to or greater than the first threshold value and less than the second threshold value, the control unit 3 switches the mode related to the development frequency and the primary transfer current to a mode having a mode number 1 greater than the current mode. That is, the control unit 3 performs at least one of a process of lowering the development frequency and a process of reducing the primary transfer current. For example, at least a process of reducing the primary transfer current is performed. This can improve image defects caused by drum ghosts.

[0091] If the current mode is mode 4 (default mode), it switches to mode 5 (mode number = 4 + 1). In this case, the development frequency is not changed, and the primary transfer current is changed to 0.9 times the default value. If the current mode is mode 5, it switches to mode 6 (mode number = 5 + 1). In this case, the development frequency is changed from 3500 Hz to 3000 Hz, and the primary transfer current is changed to 0.8 times the default value.

[0092] The control unit 3 judges whether the difference value of the color information is equal to or greater than the second threshold. The fact that the difference value of the color information is equal to or greater than the second threshold means that the degree of image defects caused by the drum ghost is large. Therefore, when the difference value of the color information is equal to or greater than the second threshold, the control unit 3 switches the mode related to the development frequency and the primary transfer current to a mode having a mode number two higher than the current mode. That is, similar to the case where the difference value of the color information is equal to or greater than the first threshold and less than the second threshold, the control unit 3 performs at least one of the process of lowering the development frequency and the process of reducing the primary transfer current. For example, at least the process of reducing the primary transfer current is performed. However, the change width of the primary transfer current is larger. This can improve the image defects caused by the drum ghost.

[0093] If the current mode is mode 4 (default mode), it is switched to mode 6 (mode number = 4 + 2). In this case, the development frequency is changed from 3500 Hz to 3000 Hz, and the primary transfer current is changed to 0.8 times the default value. The mode number ends with "7." Therefore, if the current mode is mode 6, it is switched to mode 7. If the current mode is mode 7, a message prompting maintenance (service call) of the image forming apparatus 100 may be displayed on the operation unit 302.

[0094] Furthermore, when the image defect occurring in the image defect area of ​​the marked sheet Sm is agglomerated white dots, the control unit 3 counts the number of white dots. Then, the control unit 3 compares the number of white dots with a predetermined third threshold value. Furthermore, the control unit 3 compares the number of white dots with a predetermined fourth threshold value. The fourth threshold value is a value larger than the third threshold value. For example, the third threshold value is set to "1" and the fourth threshold value is set to "20".

[0095] The third threshold and the fourth threshold are changeable and may be changed according to the size of the marked sheet Sm. For example, the larger the size of the marked sheet Sm, the more likely it is that the number of white dots will increase. Therefore, the larger the size of the marked sheet Sm, the larger the third threshold and the fourth threshold may be. The third threshold may be fixed to "1" regardless of the size of the marked sheet Sm.

[0096] The control unit 3 judges whether the number of white dots is less than the third threshold. If the number of white dots is less than the third threshold, it means that the degree of image defect occurring on the marked sheet Sm is extremely small. If the third threshold is "1", it means that there are no white dots as image defects. Therefore, it is not necessary to change the setting values ​​of both the setting items related to the development frequency and the setting items related to the primary transfer current. Therefore, if the number of white dots is less than the third threshold, the control unit 3 does not switch the modes related to the development frequency and the primary transfer current.

[0097] The control unit 3 determines whether the number of white dots is equal to or greater than a third threshold and less than a fourth threshold. If the number of white dots is equal to or greater than the third threshold and less than the fourth threshold, the control unit 3 switches the mode related to the development frequency and the primary transfer current to a mode having a mode number that is one less than the current mode. That is, the control unit 3 performs at least one of a process of increasing the development frequency and a process of increasing the primary transfer current. For example, at least a process of increasing the primary transfer current is performed. This can improve image defects caused by aggregated white dots.

[0098] If the current mode is mode 4 (default mode), it switches to mode 3 (mode number = 4-1). In this case, the development frequency is changed from 3500 Hz to 4000 Hz, and the primary transfer current is changed to 1.1 times the default value. If the current mode is mode 3, it switches to mode 2 (mode number = 3-1). In this case, the development frequency is not changed, and the development frequency is changed to 1.2 times the default value.

[0099] The control unit 3 judges whether the number of white dots is equal to or greater than a fourth threshold. The fact that the number of white dots is equal to or greater than the fourth threshold means that the degree of image defects caused by aggregated white dots is large. Therefore, when the number of white dots is equal to or greater than the fourth threshold, the control unit 3 switches the mode related to the development frequency and the primary transfer current to a mode having a mode number two smaller than the current mode. That is, similar to the case where the number of white dots is equal to or greater than the third threshold and less than the fourth threshold, the control unit 3 performs at least one of a process of increasing the development frequency and a process of increasing the primary transfer current. For example, at least a process of increasing the primary transfer current is performed. However, the change range of the primary transfer current is larger. This can improve the image defects caused by aggregated white dots.

[0100] If the current mode is mode 4 (default mode), it is switched to mode 2 (mode number = 4-2). In this case, the development frequency is changed from 3500 Hz to 4000 Hz, and the primary transfer current is changed to 1.2 times the default value. The smallest mode number is "1." Therefore, if the current mode is mode 2, it is switched to mode 1. If the current mode is mode 1, a message prompting maintenance (service call) of the image forming apparatus 100 may be displayed on the operation unit 302.

[0101] In step #6, the control unit 3 causes the printing unit 1 to print an image based on the reference image data onto the sheet S. The printing by the printing unit 1 at this time is performed according to the settings changed in the process of step #5 (i.e., the image quality improvement process).

[0102] After the process of step #6, the user checks the printout that is output based on the reference image data. In the user's check, it is determined whether the improvement in image quality is insufficient. If the result is that the improvement in image quality is insufficient, the user marks the defective image area of ​​the printout obtained in the process of step #5 with a mark MK and instructs the execution of image quality improvement processing for that printout. In this case, the flow shown in FIG. 8 is repeated.

[0103] In this embodiment, image quality improvement processing is performed based on the read image data obtained by reading the sheet S on which the defective image is printed. That is, correction is performed according to the image quality defect that actually occurs (specifically, changing the setting value of the predetermined setting item). This allows the image quality defect to be appropriately improved.

[0104] In this embodiment, when an image defect occurs during printing with the image forming apparatus 100, a mark MK is added to the image defect area on the printed sheet S, and the image quality improvement process is performed simply by scanning the marked sheet Sm with the same image forming apparatus 100 as used for printing. In other words, no complicated panel operations are required, and it is sufficient to simply write the mark MK directly on the printed sheet S. From the user's perspective, this is convenient because the image defect occurring in the image forming apparatus 100 can be appropriately improved with a simple operation.

[0105] Furthermore, in this embodiment, the setting values ​​of one or more predetermined setting items are changed in one image quality improvement process. The setting values ​​of the predetermined setting items for which the setting values ​​are changed vary depending on the type and degree of the image defect. Note that the setting values ​​of one or more predetermined setting items are changed by switching the mode. This makes it possible to easily and appropriately improve the image quality defect.

[0106] Furthermore, in this embodiment, the development frequency and the primary transfer current are set to predetermined settings, so that drum ghosts and aggregated white spots can be effectively improved.

[0107] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0108] 1 Printing section 2 Image reading section 3. Control Unit 4 Storage section 11 Photoconductor drum (image carrier) 12 Charging device 13 Exposure equipment 14 Developing device 15 Intermediate transfer belt (intermediate transfer body) 16 Primary transfer roller (primary transfer member) 17 Secondary transfer roller (secondary transfer member) 40 Mode Information 100 Image forming device 101 Charge voltage power supply 102 Development voltage power supply 103 Transfer voltage power supply 110 Photosensitive layer 140 Developing roller (developer carrier) MK Mark S Seat Sm marked sheet T Reading target

Claims

1. a printing unit that prints an image based on the print image data on a sheet; an image reading unit that reads an object to be read and generates read image data; A control unit, When performing an image quality improvement process for improving the print image quality by the printing unit, the control unit a mark-added sheet on which a mark has been added to an image defective area, the mark-added sheet being printed by the printing unit, is read by the image reading unit, and mark-added image data, which is the read image data generated by reading the mark-added sheet, is obtained; acquiring reference image data, which is the print image data on which the image printed on the marked sheet is based; By comparing the reference image data with the marked image data, a marking area in the marked image data corresponding to an area indicated by the mark on the marked sheet is detected, and a type and a degree of an image defect occurring in the image defect area are determined; The control unit performs, as the image quality improvement process, a process of changing setting values ​​of predetermined setting items related to printing by the printing unit based on the type and degree of image defects occurring in the image defect area.

2. There are a plurality of the predetermined setting items, The image forming apparatus according to claim 1 , wherein the control unit changes the setting values ​​of one or more of the predetermined setting items in one execution of the image quality improvement process.

3. a storage unit for storing mode information indicating each setting content of a plurality of modes having different setting contents related to printing by the printing unit; The control unit selects one of the modes and causes the printing unit to perform printing according to settings of the selected mode. In the mode information, setting values ​​of the plurality of predetermined setting items are defined for each of the modes such that combinations of setting values ​​of the plurality of predetermined setting items are different between the modes; The image forming apparatus according to claim 2 , wherein the control unit selects the mode based on the type and degree of the image defect occurring in the image defect area.

4. The printing unit includes: an image carrier having a photosensitive layer on its surface; a charging device for charging a surface of the image carrier; an exposure device for exposing a surface of the image carrier to light to form an electrostatic latent image; a developing device having a developer carrier that carries a developer containing toner, and supplying the toner from the developer carrier to the image carrier to develop the electrostatic latent image into a toner image; an intermediate transfer member onto which the toner image is primarily transferred from the image carrier; a primary transfer member that is pressed against the image carrier via the intermediate transfer member; a secondary transfer member that secondarily transfers the toner image from the intermediate transfer body to the sheet; a charging voltage power source that applies a charging voltage to the charging device; a developing voltage power source that applies a developing voltage in the form of a DC voltage superimposed on an AC voltage to the developer carrier; a transfer voltage power source that applies a transfer voltage having a polarity opposite to that of the toner to the primary transfer member and the secondary transfer member; As the predetermined setting items, A setting item related to a development frequency, which is a frequency of the AC voltage among the development voltages; 4. The image forming apparatus according to claim 3, further comprising a setting item relating to a primary transfer current flowing between said image carrier and said primary transfer member.

5. When the type of the image defect occurring in the image defect area is a drum ghost, the control unit performs a process of reducing at least one of the set values ​​of the developing frequency and the primary transfer current as the image quality improvement process, 5. The image forming apparatus according to claim 4, wherein when the image defect occurring in the image defect area is agglomerated white dots, the control unit performs a process of increasing at least one of the set values ​​of the development frequency and the primary transfer current as the image quality improvement process.

Images