Image forming apparatus

Abstract

To provide an image forming apparatus that can surely cancel drum ghost and ensure a setting tolerance for cancelling both drum ghost and aggregated white spots.SOLUTION: An image forming apparatus comprises an image carrier, a charging device, a charging voltage power supply, an exposure device, a developing device, a developing voltage power supply, an intermediate transfer body, a primary transfer member, a secondary transfer member, a transfer voltage power supply, and a control unit. The developing device has a developer carrier that carries developer including toner, and supplies the toner in the developer carried on the developer carrier to the image carrier to develop an electrostatic latent image into a toner image. The developing voltage power supply applies, to the developer carrier, a developing voltage in which an AC voltage is superimposed on a DC voltage. The transfer voltage power supply applies a transfer voltage to the primary transfer member and the secondary transfer member. The control unit executes a first image quality improving mode for simultaneously changing a frequency of the AC voltage in the developing voltage and a primary transfer current flowing between the image carrier and the primary transfer member.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or combination machine equipped with an image carrier, and more particularly to an image forming apparatus of an intermediate transfer type in which a toner image formed on an image carrier such as a photosensitive drum is transferred onto an intermediate transfer belt. [Background technology]

[0002] Conventionally, there has been known an intermediate transfer type image forming device that includes an endless intermediate transfer belt that rotates in a predetermined direction and a plurality of image forming units arranged along the intermediate transfer belt, in which each image forming unit sequentially superimposes a toner image of each color onto the intermediate transfer belt to perform primary transfer, and then a secondary transfer roller secondarily transfers the toner image onto a recording medium such as paper.

[0003] In an intermediate transfer type image forming device, the surface potential of the photosensitive drum changes due to the flow of a primary transfer current into the photosensitive drum. Specifically, the amount of primary transfer current flowing into the part with toner (image part) decreases, and the amount of primary transfer current flowing into the part without toner (white part) increases. In other words, the surface potential changes depending on the presence or absence of toner, causing uneven density, which is called drum ghosting (history development), and this has become a problem.

[0004] In order to eliminate the above-mentioned problems, for example, Patent Document 1 proposes a means for setting image formation conditions for at least one of the charging means, exposure means, developing means, and transfer means based on the detection results of a ghost detection means so that a visible image is not formed in a non-drawing area. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-99260 A Summary of the Invention [Problem to be solved by the invention]

[0006] It is also known that the causes of drum ghosts include the inflow of the primary transfer current, absolute humidity, and the cumulative driving distance of the photosensitive drum. In the method of Patent Document 1, when drum ghosts occur due to a combination of multiple factors, it is difficult to reliably improve the drum ghosts by simply setting the image formation conditions of one of the charging means, the exposure means, the developing means, and the transfer means. In addition, there is also a problem of agglomerated white spots, which can be improved by the same means as the drum ghosts. Therefore, there is a problem that the OW (operation window) for improving both the drum ghosts and the agglomerated white spots cannot be sufficiently secured.

[0007] In view of the above problems, the present invention has an object to provide an image forming apparatus that can reliably improve drum ghosts that occur due to a combination of various conditions, while also ensuring a setting tolerance for improving both the drum ghosts and the aggregated white spots. [Means for solving the problem]

[0008] In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image carrier, a charging device, a charging voltage power supply, an exposure device, a developing device, a developing voltage power supply, an intermediate transfer body, a primary transfer member, a secondary transfer member, a transfer voltage power supply, and a control unit. The image carrier has a photosensitive layer formed on its surface. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image in which the charge is attenuated. The developing device has a developer carrier that carries a developer containing toner, and supplies the toner in the developer carried on the developer carrier to the image carrier to develop the electrostatic latent image into a toner image. The toner image formed on the image carrier is primarily transferred to the intermediate transfer body. The primary transfer member is pressed against the image carrier via the intermediate transfer body. The secondary transfer member secondarily transfers the toner image primarily transferred to the intermediate transfer body onto a recording medium. The charging voltage power supply applies a charging voltage to the charging device. The developing voltage power supply applies a developing voltage, which is a DC voltage superimposed on an AC voltage, to the developer carrier. The transfer voltage power supply applies a transfer voltage of an opposite polarity to that of the toner image to the primary transfer member and the secondary transfer member. The control unit controls the charging voltage power supply, the developing voltage power supply, and the transfer voltage power supply. The control unit executes a first image quality improvement mode that simultaneously changes the frequency of the AC voltage in the developing voltage and the primary transfer current flowing between the image carrier and the primary transfer member. Effect of the Invention

[0009] According to the first configuration of the present invention, by executing the first image quality improvement mode in which the settings of the frequencies of the primary transfer current and the developing voltage are changed simultaneously, drum ghosts and agglomerated white spots can be improved more reliably than in the conventional method in which the settings of the frequencies of the primary transfer current and the developing voltage are changed separately. In addition, the OW (operation window) when simultaneously improving drum ghosts and agglomerated white spots that can be improved by changing the settings of the frequencies of the primary transfer current and the developing voltage can be sufficiently secured. Therefore, both drum ghosts and agglomerated white spots can be effectively improved. [Brief description of the drawings]

[0010] [Figure 1]1 is a schematic diagram of a color printer 100 according to an embodiment of the present invention; [Diagram 2] An enlarged view of the image forming section Pa in FIG. [Diagram 3] A block diagram showing an example of a control path used in a color printer 100. [Figure 4] 1 is a flowchart showing an example of control for eliminating drum ghosts in the GS mode in the color printer 100 according to the first embodiment of the present invention. [Diagram 5] FIG. 1 is a plan view of a liquid crystal display unit 71 of a color printer 100 according to a first embodiment, showing a state in which the GS mode is selected. [Figure 6] FIG. 1 is a plan view of a liquid crystal display unit 71 of a color printer 100 according to a first embodiment, showing a state in which menu setting values ​​for the GS mode are displayed. [Figure 7] FIG. 1 is a plan view of a liquid crystal display unit 71 of a color printer 100 according to a first embodiment, showing a state in which menu setting values ​​for an MC mode are displayed. [Figure 8] 1 is a flowchart showing an example of control for eliminating aggregated white dots in the GS mode in the color printer 100 according to the first embodiment. [Figure 9] FIG. 11 is a diagram showing an example of a detection image used in a ghost detection mode executed in a color printer 100 according to a second embodiment of the invention. [Figure 10] A graph showing the detection results of a half-frame image when there is no drum ghost and when there is a drum ghost in ghost detection mode. [Figure 11] 11 is a flowchart showing a control example when a ghost detection mode is executed to automatically eliminate a drum ghost in the color printer 100 according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view of a color printer 100 according to one embodiment of the present invention. Fig. 2 is an enlarged view of the vicinity of image forming unit Pa in Fig. 1. Note that image forming units Pb to Pd have a basically similar configuration, so their description will be omitted.

[0012] Four image forming units Pa, Pb, Pc, and Pd are arranged in this order from the upstream side in the transport direction (the left side in FIG. 1) inside the main body of color printer 100. These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, magenta, cyan, and black), and sequentially form images of yellow, magenta, cyan, and black through the processes of charging, exposing, developing, and transferring, respectively.

[0013] Each of the image forming stations Pa to Pd is provided with a photoconductor drum 1a, 1b, 1c, and 1d that carries a visible image (toner image) of each color. An intermediate transfer belt 8 that rotates counterclockwise in Fig. 1 is provided adjacent to each of the image forming stations Pa to Pd. The intermediate transfer belt 8 is wound around a driving roller 10 on the downstream side and a tension roller 11 on the upstream side, and a belt cleaning device 30 is provided upstream of the image forming station Pa with respect to the rotation direction of the intermediate transfer belt 8, facing the tension roller 11 with the intermediate transfer belt 8 sandwiched therebetween.

[0014] As shown in FIG. 2, a charging device 2a, a developing device 3a, a cleaning device 7a, and a discharging device 20 are arranged around the photosensitive drum 1a in the drum rotation direction (clockwise in FIG. 2), and a primary transfer roller 6a is disposed with an intermediate transfer belt 8 sandwiched therebetween.

[0015] The photosensitive drums 1a to 1d are each composed of a conductive substrate 19a and a photosensitive layer 19b formed on the surface of the conductive substrate 19a. In this embodiment, a single organic photosensitive layer is laminated as the photosensitive layer 19b on the surface of the cylindrical conductive substrate 19a made of aluminum.

[0016] The charging devices 2a to 2d each have a charging roller 21 that contacts the photoconductor drums 1a to 1d and applies a charging voltage (DC voltage+AC voltage) to the drum surface, and a charging cleaning roller 24 for cleaning the charging roller 21.

[0017] The developing devices 3a to 3d are of a two-component development type having two stirring and conveying screws 25 and a developing roller 29, and are filled with a predetermined amount of two-component developer containing toner of each color, yellow, magenta, cyan, and black, and a magnetic carrier. A magnetic brush is formed on the surface of the developing roller 29 using the two-component developer, and the magnetic brush is brought into contact with the surface of the photosensitive drum 1a while a developing voltage of the same polarity as the toner (positive polarity in this case) is applied to the developing roller 29, thereby adhering the toner and forming a toner image. When the ratio of toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of the toner image, toner is replenished from the toner containers 4a to 4d to each developing device 3a to 3d.

[0018] The cleaning devices 7a to 7d each have a cleaning blade 31 and a recovery screw 33. The cleaning blade 31 removes toner and other substances remaining on the surfaces of the photoconductor drums 1a to 1d. The recovery screw 33 discharges the toner and other substances removed by the cleaning blade 31 to the outside of the cleaning devices 7a to 7d and recovers them in a waste toner recovery container (not shown). The static eliminator 20 irradiates the surfaces of the photoconductor drums 1a to 1d with static elimination light to remove residual charges.

[0019] When image data is input from a host device such as a personal computer, first, the main motor 40 (see FIG. 3) starts rotating the photoconductor drums 1a-1d. In addition, the belt drive motor 41 (see FIG. 3) starts rotating the intermediate transfer belt 8. Next, the charging devices 2a-2d uniformly charge the surfaces of the photoconductor drums 1a-1d with the same polarity as the toner (positive polarity in this case). Next, the exposure device 5 irradiates light according to the image data, and electrostatic latent images with the charge attenuated according to the image data are formed on the photoconductor drums 1a-1d.

[0020] The developing devices 3a to 3d are filled with a predetermined amount of two-component developer (hereinafter, simply referred to as developer) containing toner of each color of yellow, magenta, cyan, and black by toner containers 4a to 4d, and the toner in the developer is supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the photoconductor drums 1a to 1d. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

[0021] Then, an electric field is applied between the primary transfer rollers 6a-6d and the photoconductor drums 1a-1d by the primary transfer rollers 6a-6d at a predetermined transfer voltage, and the yellow, magenta, cyan and black toner images on the photoconductor drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. Toner and the like remaining on the surfaces of the photoconductor drums 1a-1d after the primary transfer are removed by the cleaning devices 7a-7d. Residual charges remaining on the surfaces of the photoconductor drums 1a-1d after the primary transfer are removed by the charge removing device 20.

[0022] The transfer paper P onto which the toner image is transferred is stored in a paper cassette 16 located at the bottom inside the color printer 100, and is transported at a predetermined timing via a paper feed roller 12a and a pair of registration rollers 12b to a nip portion (secondary transfer nip portion) between the intermediate transfer belt 8 and a secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8. The transfer paper P onto which the toner image has been secondarily transferred is transported to a fixing unit 13.

[0023] The transfer paper P transported to the fixing section 13 is heated and pressurized by the fixing roller pair 13a, so that the toner image is fixed onto the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full-color image has been formed is discharged onto the discharge tray 17 by the discharge roller pair 15 as is (or after being diverted to the reversing conveyance path 18 by the branching section 14 and images are formed on both sides).

[0024] An image density sensor 27 is disposed downstream of the image forming unit Pd at a position facing the intermediate transfer belt 8. An optical sensor equipped with a light-emitting element such as an LED and a light-receiving element such as a photodiode is generally used as the image density sensor 27. When measuring the amount of toner adhesion on the intermediate transfer belt 8, when the light-emitting element irradiates each patch image (reference image) formed on the intermediate transfer belt 8 with measurement light, the measurement light is reflected by the toner and the belt surface and enters the light-receiving element.

[0025] The light reflected from the toner and the belt surface includes specular and diffuse reflections. The specular and diffuse reflections are separated by a polarizing separation prism and then enter separate light receiving elements. Each light receiving element photoelectrically converts the received specular and diffuse reflections and outputs an output signal to the control unit 90 (see FIG. 3).

[0026] Then, the image density (toner amount) and image position of the patch image are detected from the characteristic changes of the output signals of the specularly reflected light and the diffusely reflected light, and by comparing them with a predetermined reference density and reference position, the characteristic value of the development voltage, the exposure start position and timing of the exposure device 5, etc. are adjusted, thereby performing density correction and color shift correction (calibration) for each color.

[0027] 3 is a block diagram showing an example of a control path used in color printer 100. Note that, because various controls are performed on each part of color printer 100 when color printer 100 is used, the control paths for color printer 100 as a whole are complex. Therefore, the following description will focus on the parts of the control paths that are necessary for implementing the present invention.

[0028] The charging voltage power supply 52 applies a charging voltage to the charging roller 21 in the charging devices 2a to 2d. The developing voltage power supply 53 applies a developing voltage, which is a DC voltage Vdc superimposed with an AC voltage Vac, to the developing roller 29 in the developing devices 3a to 3d. The transfer voltage power supply 54 applies a predetermined primary transfer voltage and secondary transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively. The voltage control circuit 55 is connected to the charging voltage power supply 52, the developing voltage power supply 53, and the transfer voltage power supply 54, and operates each of these power supplies according to an output signal from the control unit 90.

[0029] The image input unit 60 is a receiving unit that receives image data sent from a personal computer or the like to the color printer 100. The image signal input by the image input unit 60 is converted into a digital signal and then sent to the temporary storage unit 94.

[0030] The operation unit 70 is provided with a liquid crystal display unit 71 and an LED 72. The liquid crystal display unit 71 displays the operating status of the color printer 100, the image formation status, the number of copies to be printed, etc. The liquid crystal display unit 71 also functions as a touch panel when changing settings in a ghost / aggregated white spot improvement mode and a fog improvement mode, which will be described later. The LED 72 displays various statuses and errors of the color printer 100. Various settings of the color printer 100 can also be made from a printer driver on a personal computer.

[0031] In addition, the operation unit 70 is provided with a start button that the user uses to instruct the start of image formation, a stop / clear button that is used when canceling image formation, and a reset button that is used to reset various settings of the color printer 100 to their default states.

[0032] The internal temperature and humidity sensor 80 detects the temperature and humidity inside the color printer 100, particularly the temperature and humidity around the image forming units Pa to Pd, and is disposed near the image forming units Pa to Pd.

[0033] The control unit 90 at least comprises a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 which is a read-only memory unit, a RAM (Random Access Memory) 93 which is a readable and writable memory unit, a temporary memory unit 94 which temporarily stores image data and the like, a counter 95, and multiple (two in this case) I / Fs (interfaces) 96 which send control signals to each device within the color printer 100 and receive input signals from the operation unit 50. The control unit 90 can be placed anywhere inside the color printer 100 main body.

[0034] The ROM 92 stores data such as the control program for the color printer 100, numerical values ​​necessary for control, and data that will not be changed while the color printer 100 is in use. The RAM 93 stores necessary data generated during the control of the color printer 100, and data temporarily required for the control of the color printer 100. The RAM 93 (or the ROM 92) also stores the relationship between the absolute humidity and the accumulated driving distance and the frequency when the frequency of the AC voltage Vac of the developing voltage applied to the developing rollers 29 of the developing devices 3a-3d is changed based on the absolute humidity and the accumulated driving distance of the photoconductor drums 1a-1d, as described below. The temporary storage unit 94 temporarily stores the image signal input from the image input unit 60 and converted into a digital signal. The counter 95 accumulates and counts the number of printed sheets.

[0035] Furthermore, the control unit 90 transmits control signals from the CPU 91 through the I / F 96 to each part and device in the color printer 100. Furthermore, signals indicating the state of each part and device and input signals are transmitted to the CPU 91 through the I / F 96 from each part and device. Examples of parts and devices controlled by the control unit 90 include image forming units Pa to Pd, exposure unit 5, intermediate transfer belt 8, secondary transfer roller 9, fixing unit 13, voltage control circuit 55, image input unit 60, operation unit 70, and in-machine temperature and humidity sensor 80.

[0036] In the color printer 100, when a toner image is primarily transferred from the photoconductor drums 1a-1d to the intermediate transfer belt 8, a primary transfer current flows from the primary transfer rollers 6a-6d to the photoconductor drums 1a-1d, causing a drop in the surface potential of the photoconductor drums 1a-1d. More specifically, the amount of primary transfer current flowing into the portion where toner is present (image area) decreases, and the amount of primary transfer current flowing into the portion where there is no toner (non-image area) increases, causing the surface potential of the photoconductor drums 1a-1d to change depending on the presence or absence of toner. As a result, there is a problem of drum ghosts occurring, which can cause uneven density.

[0037] The occurrence of drum ghosts is closely related to the primary transfer current and the frequency of the AC voltage Vac of the developing voltage (hereinafter simply referred to as the developing frequency). Specifically, the larger the primary transfer current, the greater the change in the surface potential of the photosensitive drums 1a-1d, and the higher the developing frequency, the more likely it is that unevenness in the surface potential will occur, so that in both cases drum ghosts are more likely to occur. Therefore, it is difficult to effectively suppress drum ghosts by simply changing the setting of either the primary transfer current or the developing frequency.

[0038] On the other hand, the toner aggregates in the developing devices 3a to 3d may be developed on the photoconductor drums 1a to 1d and then primarily transferred onto the intermediate transfer belt 8. At this time, the toner aggregates may be present between the photoconductor drums 1a to 1d and the intermediate transfer belt 8, causing gaps, which may result in the toner around the toner aggregates not being transferred and resulting in white spots, known as aggregate white spots. The aggregate white spots can be effectively suppressed by increasing the primary transfer current and the development frequency.

[0039] In other words, there is a trade-off between the settings of the primary transfer current and the development frequency for suppressing drum ghosts and the settings of the primary transfer current and the development frequency for suppressing aggregated white spots. Therefore, if the primary transfer current and the development frequency are changed to improve the drum ghosts, there is a risk that the aggregated white spots will worsen.

[0040] Therefore, the color printer 100 of the first embodiment of the present invention is provided with a ghost / agglomerated white spot improvement mode (first image quality improvement mode) that improves drum ghosts and agglomerated white spots by changing the settings of the primary transfer current and the development frequency at the same time. Tables 1 and 2 show examples of the development frequency and primary transfer current settings in the ghost / agglomerated white spot improvement mode. In the example shown in Table 1, menu setting values ​​1 to 7 are provided, which have different settings for the development frequency and primary transfer current, with menu setting value 4 being the default (standard).

[0041] [Table 1] *Set based on Table 2

[0042] [Table 2]

[0043] The developing frequency is set to be lower as the menu setting value increases. More specifically, menu setting values ​​1 to 4 are determined based on the absolute humidity and the cumulative driving distance (drum driving distance) of the photoconductor drums 1a to 1d, as shown in Table 2. For menu setting values ​​5 to 7, the developing frequency is fixed regardless of the absolute humidity and the drum driving distance.

[0044] When the absolute humidity is low, the surface potential of the photosensitive drums 1a to 1d becomes unstable, and drum ghosts are likely to occur. Also, when the drum driving distance is short, the photosensitive layers 19b (see FIG. 2) of the photosensitive drums 1a to 1d are thick, and drum ghosts are likely to worsen. Therefore, if the development frequency is suddenly increased when the absolute humidity is low, drum ghosts occur significantly. Therefore, in Table 2, when the drum driving distance is short, the change range (increase range) of the development frequency with respect to the change in absolute humidity is made smaller than when the drum driving distance is long, thereby suppressing the occurrence of drum ghosts.

[0045] Specifically, the control unit 90 calculates the drum driving distance from, for example, the outer diameter and cumulative rotation number of the photosensitive drums 1a to 1d. The drum driving distance may be calculated from the rotation speed (linear speed) and cumulative driving time of the photosensitive drums 1a to 1d. Then, based on the calculated drum driving distance and the absolute humidity detected by the internal temperature and humidity sensor 80, the development frequency of the menu setting values ​​1 to 4 is determined.

[0046] If the drum travel distance is less than 62,500 m, the absolute humidity is 4 [g / m 3 ], the development frequency is 4000 [Hz], and the absolute humidity is 1 [g / m 3 The frequency is increased by 200[Hz] each time the absolute humidity increases. 3 In the range above this, the development frequency is maintained at 5000 [Hz].

[0047] On the other hand, when the drum travel distance is 62,500 m or more, the absolute humidity is 4 [g / m 3 ], the development frequency is 4000 [Hz], and the absolute humidity is 1 [g / m 3 The frequency is increased by 400[Hz] each time the absolute humidity increases. 3 In the range above this, the development frequency is maintained at 6000 [Hz].

[0048] In this way, by changing the variation width of the development frequency based on the drum driving distance, it is possible to set an appropriate frequency according to the deterioration state of the photosensitive drums 1a to 1d. Specifically, when the cumulative driving distance of the photosensitive drums 1a to 1d is equal to or greater than a predetermined distance, drum ghosts are unlikely to occur, so the variation width of the development frequency with respect to changes in absolute humidity is increased. This makes it possible to suppress the occurrence of fogging, which will be described later, while maintaining the development characteristics when the absolute humidity is low.

[0049] The primary transfer current is determined by multiplying the reference current value (here, 9 [μA]) by the primary transfer coefficient set in menu setting values ​​1 to 7. Since the primary transfer coefficient is greater than 1.0 in menu setting values ​​1 to 3, the primary transfer current is greater than the reference current value. Since the primary transfer coefficient is less than 1.0 in menu setting values ​​5 to 7, the primary transfer current is less than the reference current value.

[0050] The user can change the primary transfer current and the developing frequency at the same time by changing the menu setting value of the ghost / aggregated white spot improvement mode in the settings of the liquid crystal display unit 71 of the operation unit 70 according to the occurrence status of drum ghosts and aggregated white spots in the image output by the printing process.

[0051] For example, if drum ghosts are occurring, you can change the menu setting value from 4 to 5 to 7 and reduce the development frequency and primary transfer current to suppress the occurrence of drum ghosts. Also, if aggregated white spots are occurring, you can change the menu setting value from 4 to 1 to 3 and increase the development frequency and primary transfer current to suppress the occurrence of aggregated white spots.

[0052] Table 3 shows the occurrence of drum ghosts, clumped white spots, and image fog when the ghost / clumped white spot improvement mode was executed with the settings shown in Table 1. Also, as a comparative example, Table 4 shows the occurrence of drum ghosts, clumped white spots, and image fog when only the development frequency was fixed to 4000 [Hz] with the settings in Table 1. In Tables 3 and 4, cases where there were no problems with the image were marked with an ◯, cases where image defects occurred depending on error conditions such as absolute humidity and drum driving distance were marked with a △, and cases where image defects occurred were marked with an ×.

[0053] [Table 3]

[0054] [Table 4]

[0055] As shown in Table 3, when the development frequency was changed according to the menu setting value as shown in Table 1, it was confirmed that the occurrence of drum ghosts could be suppressed by changing the menu setting value from 5 to 7, and the occurrence of clumped white spots could be suppressed by changing the menu setting value from 1 to 3. In contrast, as shown in Table 4, when the development frequency was fixed at 4000 [Hz], neither the drum ghosts nor the clumped white spots could be sufficiently improved.

[0056] From the above results, it was confirmed that by changing the menu setting value of the ghost / aggregated white spot improvement mode to change the development frequency and primary transfer current simultaneously, the occurrence of drum ghosts and aggregated white spots can be more effectively suppressed than when only the primary transfer current is changed.

[0057] However, if the development frequency is set low to suppress drum ghosts, toner adheres to white areas, which is called image fogging (hereinafter simply referred to as fogging), and this embodiment is therefore provided with a fogging improvement mode (second image quality improvement mode) that improves fogging by increasing the charging voltage applied to the charging devices 2a to 2d. The fogging improvement mode is executed as necessary after the ghost / aggregated white spot improvement mode is executed.

[0058] An example of the charging voltage settings in the fogging improvement mode is shown in Table 5. In the example shown in Table 5, menu setting values ​​1 to 7 having different charging voltage settings are provided, with menu setting value 4 being the default (standard).

[0059] [Table 5]

[0060] The charge voltage is determined by adding the charge correction value set in menu setting values ​​1 to 7 to the reference voltage (450 [V] in this case). Because the charge correction value is negative for menu setting values ​​1 to 3, the charge voltage is smaller than the reference voltage. Because the charge correction value is positive for menu setting values ​​5 to 7, the charge voltage is larger than the reference voltage.

[0061] Depending on the occurrence of fog in the image output after execution of the ghost / aggregated white spot improvement mode, the user changes the menu setting value of the fog improvement mode in the settings of the liquid crystal display unit 71 of the operation unit 70. For example, if fog is occurring, the occurrence of fog can be suppressed by changing the menu setting value from 4 to 5 to 7 to increase the charging voltage.

[0062] Note that the menu setting values ​​1 to 3 in Table 5 are not used in the fog reduction mode because they make the charging voltage lower than the reference voltage. The menu setting values ​​1 to 3 are used when adjusting the surface potentials of the photoconductor drums 1a to 1d.

[0063] Fig. 4 is a flow chart showing an example of control when eliminating drum ghosts in the ghost / aggregated white spot improving mode (GS mode) in the color printer 100 of the first embodiment. The procedure for eliminating drum ghosts in the "ghost / aggregated white spot improving mode" will be described following the steps in Fig. 4, with reference to Figs. 1 to 3 and Figs. 5 to 7 described below as necessary.

[0064] When the user visually checks the output image and confirms the occurrence of drum ghosts (step S1), he or she selects the ghost / aggregated white spot improvement mode (GS mode) on the liquid crystal display unit 71 (step S2), and then increases the menu setting value of the GS mode by one level (step S3).

[0065] Fig. 5 is a plan view of the liquid crystal display unit 71, showing the state in which the GS mode is selected. As shown in Fig. 5, a plurality of mode setting keys 71a are displayed on the left side of the screen of the liquid crystal display unit 71. When an "adjustment / maintenance key" (shown hatched in Fig. 5) among the mode setting keys 71a is pressed, function keys 71b related to "adjustment / maintenance" are displayed on the right side of the screen. The "GS key" for selecting the GS mode among the function keys 71b shows the current menu setting value "4".

[0066] Fig. 6 is a diagram showing the state in which the menu setting values ​​of the GS mode are displayed. When the "GS key" of the function keys 71b is pressed in the state of Fig. 5, menu setting value selection keys 71c from "1" to "7" are displayed on the liquid crystal display unit 71 as shown in Fig. 6. A decision key 71d for deciding the change to the selected menu setting value is displayed on the upper right of the screen of the liquid crystal display unit 71. A cancel key 71e for canceling the display of the menu setting value and returning to the previous screen (the state of Fig. 5) is displayed on the upper left of the screen of the liquid crystal display unit 71.

[0067] The user presses the menu setting value "5" (shown by hatching in FIG. 6) which is one level higher than the current menu setting value "4" among the menu setting value selection keys 71c, and then presses the decision key 71d. This changes the menu setting value of the GS mode from "4" to "5."

[0068] Next, the user outputs an image with the changed menu setting value "5" (step S4). Then, it is determined whether the drum ghost has been eliminated in the output image (step S5). If the drum ghost has not been eliminated (No in step S5), the process returns to step S3, and the menu setting value of the GS mode is increased by one step and an image is output (steps S3 to S4).

[0069] If the drum ghost has been eliminated (Yes in step S5), the user determines whether or not fog has occurred in the output image (step S6). If fog has occurred (Yes in step S6), the user selects the fog reduction mode (MC mode) from the liquid crystal display 71 (step S7). Then, the menu setting value of the MC mode is increased by one level (step S8).

[0070] Fig. 7 is a diagram showing a state in which the menu setting values ​​of the MC mode are displayed. From the state of Fig. 5. When the "MC key" for selecting the MC mode among the function keys 71b is pressed, as shown in Fig. 7, menu setting value selection keys 71c from "1" to "7" are displayed on the liquid crystal display unit 71. A decision key 71d for deciding the change to the selected menu setting value is displayed on the upper right of the screen of the liquid crystal display unit 71. A cancel key 71e for canceling the display of the menu setting value and returning to the previous screen (the state of Fig. 5) is displayed on the upper left of the screen of the liquid crystal display unit 71.

[0071] The user presses the menu setting value "5" (shown by hatching in FIG. 7) one level higher than the current menu setting value "4" among the menu setting value selection keys 71c, and then presses the decision key 71d. This changes the menu setting value of the MC mode from "4" to "5."

[0072] Next, the user outputs an image with the changed menu setting value "5" (step S9). Then, it is determined whether the fog has been eliminated in the output image (step S10). If the fog has not been eliminated (No in step S10), the process returns to step S8, and the MC mode menu setting value is increased by one step and the image is output (steps S8 to S9).

[0073] If the fog has been eliminated (Yes in step S10), the process ends. However, if the fog has not occurred in step S6 (No in step S6), the process ends without executing the MC mode.

[0074] Fig. 8 is a flowchart showing an example of control for eliminating aggregated white points using the ghost / aggregated white point improving mode (GS mode) in the color printer 100 of the first embodiment. The procedure for eliminating aggregated white points using the "ghost / aggregated white point improving mode" will be described following the steps of Fig. 8, with reference to Figs. 1 to 3, 5, and 6 as necessary.

[0075] When the user visually checks the output image and confirms the occurrence of aggregated white dots (step S1), he or she selects the ghost / aggregated white dot improvement mode (GS mode) on the liquid crystal display unit 71 (step S2). Then, the menu setting value of the GS mode is lowered by one step (step S3). For example, if the menu setting value is the default "4", the menu setting value is changed from "4" to "3". The procedure for changing the menu setting value is the same as the procedure shown in Figs. 5 and 6.

[0076] Next, the user outputs an image with the changed menu setting value "3" (step S4). Then, it is determined whether or not the clumped white dots have been eliminated in the output image (step S5). If the clumped white dots have not been eliminated (No in step S5), the process returns to step S3, and the GS mode menu setting value is further lowered by one step and the image is output (steps S3 to S4). If the clumped white dots have been eliminated (Yes in step S5), the process ends.

[0077] In addition, when eliminating aggregated white spots, the setting is changed to increase the development frequency (decrease the menu setting value), so there is a low possibility of fog occurring after the change. Therefore, in the control example of Fig. 8, the MC mode (steps S6 to S10 in Fig. 4) is not executed, but it is possible to check for fog occurrence after eliminating aggregated white spots as in Fig. 4, and to switch to the MC mode if fog is confirmed.

[0078] According to the control examples shown in Figures 4 and 8, by providing a ghost / aggregated white spot improvement mode (GS mode) that simultaneously changes the settings of the primary transfer current and the development frequency, drum ghosts and aggregated white spots can be improved more reliably than in the conventional method of separately changing the settings of the primary transfer current and the development frequency. In addition, it is possible to sufficiently secure the OW (operation window) when simultaneously improving drum ghosts and aggregated white spots that can be improved by changing the settings of the primary transfer current and the development frequency. Therefore, it is possible to effectively improve both drum ghosts and aggregated white spots.

[0079] In addition, the control unit 90 determines the development frequency based on the absolute humidity and the drum driving distance, thereby making it possible to set appropriate conditions according to the error in the absolute humidity and the drum driving distance. This makes it possible to improve the effect of reducing drum ghosts and aggregated white spots and ensure sufficient OW even when the environment changes or the durability error is large.

[0080] In addition, if fog occurs after improving drum ghosts using the ghost / aggregated white spot improvement mode (GS mode), the fog improvement mode (MC mode) is executed. This makes it possible to simultaneously improve fog, which tends to occur as a side effect when the development frequency is changed to a lower value.

[0081] Furthermore, by making it possible to set the above-mentioned GS mode and MC mode from the liquid crystal display unit 71, the user can change the settings of the development frequency, primary transfer current, and charging voltage all at once, making it possible to improve drum ghosts and agglomerated white spots in a simple manner.

[0082] Next, another control example of the ghost: agglomerated white dot improvement mode in the color printer 100 of the first embodiment will be described. In the control example shown in Fig. 4, after changing the primary transfer current and development frequency in the ghost: agglomerated white dot improvement mode (GS mode), if fog occurs in the output image, the mode transitions to the fog improvement mode (MC mode) and changes the charging voltage. In this control example, however, the ghost: agglomerated white dot improvement mode (GS mode) and the fog improvement mode (MC mode) are combined in advance, and a ghost / agglomerated white dot / fog improvement mode is provided in which the settings of the primary transfer current, development frequency, and charging voltage are changed simultaneously. Table 6 shows examples of settings of the development frequency, primary transfer current, and charging voltage in the ghost / agglomerated white dot / fog improvement mode.

[0083] [Table 6] *Set based on Table 2

[0084] In the example shown in Table 6, menu setting values ​​1 to 7 are provided which have different setting values ​​for the development frequency, primary transfer current, and charging voltage, with menu setting value 4 being the default (reference). The setting values ​​for the development frequency, primary transfer current, and charging voltage are a combination of the setting values ​​in Tables 1 and 5 described above. However, since menu setting values ​​1 to 3 which set the charging voltage lower than the reference voltage in Table 5 are not used, the charging correction value for menu setting values ​​1 to 3 in Table 6 is also 0 [V].

[0085] By providing a ghost / aggregated white dot / fog improvement mode that can simultaneously change the three settings of primary transfer current, development frequency, and charging voltage, the charging voltage can be increased in advance to prevent fog from occurring in conditions where the development frequency is low and fog is likely to occur (menu setting values ​​5 to 7). This means that the task of outputting an image and checking for fog occurrence after changing the settings of the primary transfer current and development frequency can be omitted, further improving user convenience.

[0086] Next, a color printer 100 according to a second embodiment of the present invention will be described. In the first embodiment described above, it was unclear whether a drum ghost (history development) was occurring unless the user output an image. In addition, even if a drum ghost was occurring, there was a problem in that unless the user recognized the occurrence of the drum ghost, the user might not operate the liquid crystal display unit 71 to execute the ghost / aggregated white spot improvement mode (GS mode).

[0087] Therefore, in the color printer 100 of the second embodiment, even if the user does not output an image, a ghost detection mode is executed to detect the occurrence of drum ghosts on the intermediate transfer belt 8. Then, if the occurrence of drum ghosts is detected, a ghost / aggregated white spot improvement mode (GS mode) is automatically executed.

[0088] When solid images are primarily transferred from the photoconductor drums 1a to 1d to the intermediate transfer belt 8, the drop in surface potential of the photoconductor drums 1a to 1d caused by the inflow of the primary transfer current is smaller only in the areas where the solid images are formed than in other areas. As a result, after one revolution of the photoconductor drums 1a to 1d, the surface potential of the areas where the solid images were formed becomes higher, and the potential difference (development potential difference) between the areas where the solid images were formed and the developing roller 29 becomes smaller.

[0089] Therefore, when a halftone image is formed in an area that includes a portion where a solid image was formed, a drum ghost occurs, in which the image density decreases only in the portion where the solid image was formed. In ghost detection mode, the presence or absence of a drum ghost is detected by measuring the density difference between the portion where the solid image was formed and its surroundings.

[0090] Fig. 9 is a diagram showing an example of a detection image used in the ghost detection mode executed in color printer 100 of the second embodiment. As shown in Fig. 9, the detection image is composed of halftone images Yh-Kh of each color. More specifically, the halftone images Yh-Kh are formed after the solid images Ys-Ks are formed on intermediate transfer belt 8 and then after one rotation of photoconductor drums 1a-1d (after movement by drum circumference L).

[0091] The halftone images Yh-Kh include the area (dashed line in FIG. 9) that was the formation area of ​​the solid images Ys-Ks after one rotation of the photosensitive drums 1a-1d, and are formed to extend upstream and downstream in the transport direction of the intermediate transfer belt 8 (left and right direction in FIG. 9). The image density sensor 27 measures the image density of the halftone images Yh-Kh over the entire area in the transport direction. This measures the density difference ΔID between the area that was the formation area of ​​the solid images Ys-Ks and the areas upstream and downstream of it.

[0092] The half images Yh-Kh may include the areas where the solid images Ys-Ks were formed after one rotation of the photosensitive drums 1a-1d. For example, the half images Yh-Kh may be formed so as to extend in the width direction of the intermediate transfer belt 8 (the vertical direction in FIG. 9). However, if the half images Yh-Kh are formed so as to extend in the width direction, a mechanism for moving the image density sensor 27 in the width direction is required. By forming the half images Yh-Kh so as to extend to the upstream and downstream sides of the transport direction of the intermediate transfer belt 8 as in this embodiment, it is possible to detect the density of the entire area of ​​the half images Yh-Kh without moving the image density sensor 27.

[0093] Fig. 10 is a graph showing the detection results of a halftone image in ghost detection mode when a drum ghost occurs and when a drum ghost occurs. As shown in Fig. 10, when a drum ghost does not occur (left side of Fig. 10), the density difference ΔID with respect to the part R that was the formation area of ​​the solid image is small or zero. On the other hand, when a drum ghost occurs (right side of Fig. 10), the density difference ΔID becomes large.

[0094] Therefore, when the drum ghost is significant (the density difference ΔID is equal to or greater than a predetermined value), the ghost / aggregated white spot improvement mode is executed to change the development frequency and primary transfer current, thereby reducing the drum ghost. Table 7 shows an example of the development frequency and primary transfer current settings in the ghost / aggregated white spot improvement mode.

[0095] [Table 7]

[0096] As mentioned above, the larger the primary transfer current, the larger the change in surface potential of the photoconductor drums 1a to 1d, and the higher the development frequency, the more likely it is that unevenness in surface potential will occur, so in both cases drum ghosts are more likely to occur. Therefore, as shown in Table 7, the drum ghost can be improved by reducing the development frequency and primary transfer current as the density difference ΔID increases.

[0097] Fig. 11 is a flowchart showing an example of control when the ghost detection mode is executed to automatically eliminate the drum ghost in the color printer 100 of the second embodiment. The procedure for automatically eliminating the drum ghost by executing the ghost detection mode will be described according to the steps in Fig. 11, with reference to Figs. 1 to 10 as necessary.

[0098] First, the control unit 90 determines whether it is time to detect a drum ghost (step S1). Examples of timing for detecting a drum ghost include when a predetermined number of printed sheets (e.g., 250 sheets) has been printed since the previous ghost detection mode was executed, when the color printer 100 is turned on, etc.

[0099] If it is time to detect a drum ghost (Yes in step S1), the ghost detection mode is executed (step S2). Specifically, solid images Ys-Ks and halftone images Yh-Kh as shown in Fig. 9 are formed on the intermediate transfer belt 8. Then, the image density sensor 27 (see Fig. 1) is used to detect the density of the halftone images Yh-Kh.

[0100] Next, the control unit 90 measures the density difference ΔID between the portion of the halftone images Yh-Kh where the solid images Ys-Ks were formed and its upstream and downstream sides based on the detection result of the image density sensor 27 (step S3).

[0101] The control unit 90 adjusts the developing frequency and the primary transfer current based on the density difference ΔID (step S4). Specifically, the developing frequency and the primary transfer current are set using the relationship between the density difference ΔID and the developing frequency and the primary transfer current as shown in Table 7.

[0102] 11, the ghost detection mode is executed, and the primary transfer current and the development frequency are determined based on the density difference ΔID between the measured halftone images Yh to Kh. Therefore, even if the user does not output an image or does not recognize the occurrence of a drum ghost, the occurrence of a drum ghost can be detected, and if a drum ghost occurs, the development frequency and the primary transfer current that do not cause a drum ghost are automatically set.

[0103] This makes it possible to automatically improve the drum ghost without operating the liquid crystal display unit 71, thereby further improving user convenience. If fog occurs after the drum ghost is improved, the fog improvement mode (MC mode) is executed by operating the liquid crystal display unit 71, as in the first embodiment. If aggregated white spots occur, the ghost / aggregated white spot improvement mode (GS mode) is executed by operating the liquid crystal display unit 71.

[0104] In addition, the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the present invention. For example, in the above-mentioned embodiments, the developing devices 3a to 3d equipped with the developing roller 29 carrying the two-component developer as shown in Fig. 2 are described, but the present invention is not limited to this, and can be applied to image forming apparatuses equipped with various developing devices using a two-component developer, such as a developing device equipped with a toner supply roller that supplies only the toner in the two-component developer to the developing roller 29.

[0105] Furthermore, in each of the above embodiments, a tandem type color printer 100 has been described as an example of an image forming apparatus, but the present invention can of course also be applied to other image forming apparatuses that use an intermediate transfer method, such as color copiers and color multifunction machines. [Industrial Applicability]

[0106] The present invention can be used in an intermediate transfer type image forming apparatus. By using the present invention, it is possible to provide an image forming apparatus that can reliably improve drum ghosts that occur due to a combination of various conditions, and can ensure a setting margin for improving both drum ghosts and aggregated white spots. [Explanation of symbols]

[0107] Pa~Pd Image forming section 1a to 1d Photoconductor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5 Exposure equipment 6 Primary transfer roller (primary transfer member) 7a~7d Cleaning device 8 Intermediate transfer belt (intermediate transfer body) 9 Secondary transfer roller (secondary transfer member) 27 Image density sensor (image density detection section) 29 Developing roller (developer carrier) 52 Charge voltage power supply 53 Development voltage power supply 54 Transfer voltage power supply 70 Operation section 71 Liquid crystal display unit (input unit) 80 In-flight temperature and humidity sensor (humidity detection device) 90 Control section 100 Color printers (image forming devices)

Claims

1. an image carrier having a photosensitive layer formed on its surface; a charging device for charging the surface of the image carrier; an exposure device that exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image in which the charge is attenuated; a developing device having a developer carrier that carries a developer containing a toner, and supplying the toner in the developer carried on the developer carrier to the image carrier, thereby developing the electrostatic latent image into a toner image; an intermediate transfer member onto which the toner images formed on the image carrier are sequentially primarily transferred; 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 that has been primarily transferred to the intermediate transfer body onto a recording medium; a charging voltage power source that applies a charging voltage to the charging device; a developing voltage power source that applies a developing voltage, which is a DC voltage superimposed on an AC voltage, to the developer carrying member; a transfer voltage power source that applies a transfer voltage having a polarity opposite to that of the toner image to the primary transfer member and the secondary transfer member; a control unit for controlling the charging voltage power supply, the developing voltage power supply, and the transfer voltage power supply; In an image forming apparatus comprising: The image forming apparatus is characterized in that the control unit executes a first image quality improvement mode in which the frequency of the AC voltage among the developing voltages and the primary transfer current flowing between the image carrier and the primary transfer member are simultaneously changed.

2. a humidity detection device that detects the absolute humidity around the developing device, 2. The image forming apparatus according to claim 1, wherein the control unit determines a frequency of the AC voltage to be used in the first image quality improvement mode based on the absolute humidity detected by the humidity detection device and the accumulated driving distance of the image carrier.

3. 3. The image forming apparatus according to claim 2, wherein the control unit increases the frequency of the AC voltage in a stepwise manner as the absolute humidity increases.

4. 3. The image forming apparatus according to claim 2, wherein the control unit reduces a change range of the frequency in response to a change in the absolute humidity when the cumulative driving distance of the image carrier is less than a predetermined distance, compared to when the cumulative driving distance is equal to or greater than the predetermined distance.

5. an input unit for selecting and setting one of a plurality of modes including the first image quality improvement mode, 2 . The image forming apparatus according to claim 1 , wherein the control unit executes the first image quality improvement mode when the first image quality improvement mode is set by the input unit.

6. the input unit is capable of selecting and inputting one of a plurality of different setting values ​​for the frequency of the AC voltage and the primary transfer current in the first image quality improvement mode, 6. The image forming apparatus according to claim 5, wherein the control unit changes the frequency of the AC voltage and the primary transfer current simultaneously based on the set value input from the input unit.

7. 2 . The image forming apparatus according to claim 1 , wherein the control unit is capable of executing a second image quality improvement mode in which the charging voltage is changed after the first image quality improvement mode is executed.

8. an input unit for selecting and setting one of a plurality of modes including the first image quality improvement mode and the second image quality improvement mode, 8. The image forming apparatus according to claim 7, wherein the control unit executes the second image quality improvement mode when the second image quality improvement mode is set by the input unit.

9. the input unit is capable of selecting and inputting one of a plurality of different setting values ​​for the charging voltage in the second image quality improvement mode, 9. The image forming apparatus according to claim 8, wherein the control unit changes the charging voltage based on the set value input from the input unit.

10. 2 . The image forming apparatus according to claim 1 , wherein the control unit simultaneously changes the charging voltage in the first image quality improvement mode.

11. an input unit for selecting and setting one of a plurality of modes including the first image quality improvement mode, 11. The image forming apparatus according to claim 10, wherein the control unit executes the first image quality improvement mode when the first image quality improvement mode is set by the input unit.

12. the input unit is capable of selecting and inputting one of a plurality of different setting values ​​for a frequency of the AC voltage, a setting of the primary transfer current, and a setting of the charging voltage in the first image quality improvement mode, 12. The image forming apparatus according to claim 11, wherein the control unit simultaneously changes the frequency of the AC voltage, the primary transfer current, and the charging voltage based on the set value input from the input unit.

13. an image density detection unit that detects the density of a toner image formed on the intermediate transfer body; the control unit is capable of executing a ghost detection mode in which the image density detection unit detects an image density of a detection image formed on the intermediate transfer body, thereby detecting the presence or absence of a drum ghost, The image forming apparatus according to claim 1 , wherein the control unit executes the first image quality improvement mode based on a result of the ghost detection mode.

14. the detection image is a half image formed one revolution of the image carrier after the formation of the solid image, and including a portion that was a formation range of the solid image; 14. The image forming apparatus according to claim 13, wherein the control unit determines the frequency of the AC voltage and the primary transfer current based on a density difference ΔID between a portion of the half image that was the formation range of the solid image and its surrounding portion.

15. 15. The image forming apparatus according to claim 14, wherein the half image includes a portion that was a forming range of the solid image, and is formed so as to extend to the upstream side and downstream side in a transport direction of the intermediate transfer body.

Images