Image forming apparatus

Abstract

An image forming apparatus includes an image carrier, a charging device, a charging voltage power source, an exposure device, a developing device, a developing voltage power source, an intermediate transfer body, a primary transfer member, a secondary transfer member, a transfer voltage power source, and a control unit. The developing device includes a developer carrier that carries a developer containing a toner, and the developing device develops an electrostatic latent image into a toner image by supplying the toner in the developer carried on the developer carrier to an image carrier. The developing voltage power supply applies, to the developer carrier, a developing voltage obtained by superimposing an AC voltage 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 improvement mode in which 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 are simultaneously changed.

Description

Technical Field

[0001] The present invention relates to an image forming device, which is an image forming device such as a copier, printer, fax machine and multi-function machine equipped with an image carrier, and in particular to an image forming device using an intermediate transfer method, which transfers a colorant image formed on an image carrier such as a photosensitive drum to an intermediate transfer belt. Background Art

[0002] An image forming device using an intermediate transfer method is known, which comprises: an endless intermediate transfer belt rotating in a specified direction, and a plurality of image forming units arranged along the intermediate transfer belt, wherein colorant images of different colors are sequentially overlapped and transferred to the intermediate transfer belt once by each image forming unit, and then the colorant images are secondarily transferred to a recording medium such as paper by a secondary transfer roller.

[0003] In an image forming apparatus using an intermediate transfer method, 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 portion with toner (image portion) decreases, and the amount of primary transfer current flowing into the portion without toner (blank portion) increases. That is, there is a problem that the surface potential changes depending on the presence or absence of toner, resulting in uneven density, which is the so-called drum ghosting (delayed development). Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] An object of the present invention is to provide an image forming apparatus that reliably improves drum ghosting caused by a combination of various conditions and can ensure a setting margin required for improving both drum ghosting and concentrated white spots.

[0006] (II) Technical solution

[0007] The image forming device of the first structure of the present invention is characterized in that it comprises: an image carrier having a photosensitive layer formed on the surface; a charging device for charging the surface of the image carrier; an exposure device for exposing the surface of the image carrier charged by the charging device to form an electrostatic latent image with charge decay; a developing device having a developer carrier carrying a developer containing a toner, supplying the toner in the developer carried on the developer carrier to the image carrier to develop the electrostatic latent image into a toner image; an intermediate transfer body for sequentially transferring the toner image formed on the image carrier; a primary transfer member for pressing against the image carrier via the intermediate transfer body; and a secondary transfer member for transferring the primary transfer image to the image carrier. The colorant image printed on the intermediate transfer body is secondarily transferred to a recording medium; a charging voltage power supply, which applies a charging voltage to the charging device; a developing voltage power supply, which applies to the developer carrier: a developing voltage in which an AC voltage is superimposed on a DC voltage; a transfer voltage power supply, which applies to the primary transfer component and the secondary transfer component: a transfer voltage with a polarity opposite to that of the colorant image; and a control unit, which controls the charging voltage power supply, the developing voltage power supply, and the transfer voltage power supply, and the control unit executes a first image quality improvement mode, in which: the frequency of the AC voltage in the developing voltage, and the primary transfer current flowing between the image carrier and the primary transfer component are simultaneously changed.

[0008] (III) Beneficial effects

[0009] According to the first configuration of the present invention, by executing the first image quality improvement mode of simultaneously changing the settings of the primary transfer current and the frequency of the developing voltage, it is possible to reliably improve the drum ghosting and the aggregated white spots, compared with the conventional method of changing the settings of the primary transfer current and the frequency of the developing voltage individually. In addition, it is also possible to fully ensure the OW (operation window) when simultaneously improving the drum ghosting and the aggregated white spots that can be improved by changing the settings of the primary transfer current and the frequency of the developing voltage. Therefore, it is possible to effectively improve both the drum ghosting and the aggregated white spots. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic structural diagram of a color printer 100 according to an embodiment of the present invention.

[0011] Figure 2 yes Figure 1 An enlarged view of the vicinity of the image forming portion Pa in FIG.

[0012] Figure 3 1 is a block diagram showing an example of a control path for the color printer 100 .

[0013] Figure 4This is a flowchart showing a control example when eliminating drum ghost in the GS mode in the color printer 100 according to the first embodiment of the present invention.

[0014] Figure 5 It is a plan view of the liquid crystal display unit 71 of the color printer 100 according to the first embodiment, and shows a state in which the GS mode is selected.

[0015] Figure 6 It is a plan view of the liquid crystal display unit 71 of the color printer 100 according to the first embodiment, and shows a state where menu setting values ​​of the GS mode are displayed.

[0016] Figure 7 It is a plan view of the liquid crystal display unit 71 of the color printer 100 according to the first embodiment, and shows a state where menu setting values ​​of the MC mode are displayed.

[0017] Figure 8 This is a flowchart showing a control example when eliminating aggregated white spots in the GS mode in the color printer 100 according to the first embodiment.

[0018] Fig. 9 This is a diagram showing an example of a detection image used in the ghost detection mode executed in the color printer 100 according to the second embodiment of the present invention.

[0019] Fig.10 Graphs showing detection results of half images when no drum ghost occurs and when a drum ghost occurs in the ghost detection mode.

[0020] Fig.11 This is a flowchart showing a control example when the ghost detection mode is executed and the drum ghost is automatically eliminated in the color printer 100 according to the second embodiment. DETAILED DESCRIPTION

[0021] Embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 It is a schematic cross-sectional view of a color printer 100 according to an embodiment of the present invention. Figure 2 yes Figure 1 1 is an enlarged view of the vicinity of the image forming section Pa in FIG. The image forming sections Pb to Pd also have basically the same configuration, and thus their description is omitted.

[0022] In the main body of the color printer 100, from the upstream side in the conveying direction (in Figure 1 The image forming units Pa, Pb, Pc, and Pd are arranged in sequence. These image forming units Pa to Pd are arranged corresponding to images of different four colors (yellow, magenta, cyan, and black), and form yellow, magenta, cyan, and black images in sequence through charging, exposure, development, and transfer processes.

[0023] The image forming sections Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d for carrying visible images (toner images) of respective colors. Figure 1 The intermediate transfer belt 8 rotates counterclockwise as shown. 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. With respect to the rotation direction of the intermediate transfer belt 8, a belt cleaning device 30 is arranged on the upstream side of the image forming section Pa so as to face the tension roller 11 with the intermediate transfer belt 8 interposed therebetween.

[0024] like Figure 2 As shown, around the photosensitive drum 1a, along the drum rotation direction ( Figure 2 In the clockwise direction of the image processing apparatus, a charging device 2a, a developing device 3a, a cleaning device 7a, and a neutralizing device 20 are provided, and a primary transfer roller 6a is provided across the intermediate transfer belt 8.

[0025] The photosensitive drums 1a to 1d are 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 on the surface of a cylindrical conductive substrate 19a made of aluminum as the photosensitive layer 19b.

[0026] The charging devices 2 a to 2 d include a charging roller 21 that contacts the photosensitive drums 1 a to 1 d and applies a charging voltage (DC voltage+AC voltage) to the drum surfaces, and a charging cleaning roller 24 for cleaning the charging roller 21 .

[0027] The developing devices 3a to 3d are two-component developing devices having two stirring and conveying screws 25 and a developing roller 29, and are respectively filled with a predetermined amount of two-component developer containing toners of 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 a developing voltage having the same polarity as the toner (positive polarity in this case) is applied to the developing roller 29. In this state, the magnetic brush is brought into contact with the surface of the photosensitive drum 1a to 1d, so that the toner adheres and a toner image is formed. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d becomes lower than a predetermined value due to the formation of the toner image, the toner is replenished from the toner container 4a to 4d to each developing device 3a to 3d.

[0028] The cleaning devices 7a to 7d include a cleaning blade 31 and a recovery screw 33. The cleaning blade 31 removes the toner and the like remaining on the surface of the photosensitive drums 1a to 1d. The recovery screw 33 discharges the toner and the like 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 elimination device 20 irradiates the surface of the photosensitive drums 1a to 1d with static elimination light to eliminate the residual charge.

[0029] When image data is input from a host device such as a personal computer, first, the main motor 40 (see Figure 3 ) starts the rotation of the photosensitive drums 1a to 1d. In addition, the belt drive motor 41 (see Figure 3 ) The intermediate transfer belt 8 is started to be rotated. Then, the surfaces of the photosensitive drums 1a to 1d are uniformly charged to the same polarity as the toner (positive polarity in this case) by the charging devices 2a to 2d. Then, the exposure device 5 irradiates light according to the image data, and forms an electrostatic latent image on each photosensitive drum 1a to 1d, the charging of which is attenuated according to the image data.

[0030] The developing devices 3a to 3d are filled with a predetermined amount of two-component developer (hereinafter referred to as developer) containing yellow, magenta, cyan, and black toners by toner containers 4a to 4d, and the toners in the developer are supplied to the photosensitive drums 1a to 1d by the developing devices 3a to 3d for electrostatic adhesion, thereby forming a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5.

[0031] Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and the yellow, magenta, cyan, and black toner images on the photosensitive drums 1a to 1d are primarily transferred to the intermediate transfer belt 8. After the primary transfer, the toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d are removed by the cleaning devices 7a to 7d. After the primary transfer, the residual charge remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the charge removing device 20.

[0032] The transfer paper P to which the toner image is transferred is stored in a paper cassette 16 disposed at the lower part of the color printer 100, and the transfer paper P is conveyed to a nip portion (secondary transfer nip portion) between a secondary transfer roller 9 disposed adjacent to the intermediate transfer belt 8 and the intermediate transfer belt 8 via a paper feed roller 12a and a registration roller pair 12b at a predetermined timing. The transfer paper P to which the toner image is secondarily transferred is conveyed to the fixing unit 13.

[0033] The transfer paper P conveyed to the fixing section 13 is heated and pressed by the fixing roller pair 13a, so that the toner image is fixed on the surface of the transfer paper P, thereby forming a predetermined full-color image. The transfer paper P with the full-color image formed thereon is discharged to the discharge tray 17 by the discharge roller pair 15 directly (or after being distributed to the reverse conveying path 18 by the branch section 14 and having images formed on both sides).

[0034] An image density sensor 27 is disposed at a position facing the intermediate transfer belt 8 on the downstream side of the image forming section Pd. As the image density sensor 27, an optical sensor is generally used, and the optical sensor includes a light emitting element composed of an LED or the like, and a light receiving element composed of a photodiode or the like. When measuring the amount of toner attached to the intermediate transfer belt 8, if the measurement light is irradiated from the light emitting element to each patch image (reference image) formed on the intermediate transfer belt 8, the measurement light is incident on the light receiving element as light reflected by the toner and light reflected by the belt surface.

[0035] The reflected light from the toner and the belt surface includes regular reflected light and diffuse reflected light. The regular reflected light and diffuse reflected light are separated by the polarization separation prism and then incident on different light receiving elements. Each light receiving element performs photoelectric conversion on the received regular reflected light and diffuse reflected light and transmits the received light to the control unit 90 (see Figure 3 ) outputs the output signal.

[0036] Furthermore, the image density (amount of colorant) and image position of the small image are detected based on the characteristic changes of the output signals of the regular reflected light and the diffuse reflected light, and compared with the predetermined reference density and reference position, and the characteristic value of the developing voltage, the exposure start position and timing of the exposure device 5, etc. are adjusted, thereby performing concentration correction and color shift correction (calibration) on each color.

[0037] Figure 3 1 is a block diagram showing an example of a control path for the color printer 100. In addition, since various controls are performed on each part of the color printer 100 when the color printer 100 is used, the control path of the color printer 100 as a whole is complicated. Therefore, the part of the control path necessary for implementing the present invention will be described here in detail.

[0038] The charging voltage power supply 52 applies a charging voltage to the charging roller 21 in the charging device 2a to 2d. The developing voltage power supply 53 applies a developing voltage obtained by superimposing an AC voltage Vac on a DC voltage Vdc to the developing roller 29 in the developing device 3a to 3d. The transfer voltage power supply 54 applies a predetermined primary transfer voltage and a 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 the above-mentioned power supplies according to the output signal from the control unit 90.

[0039] The image input unit 60 is a receiving unit that receives image data transmitted from a personal computer or the like to the color printer 100 . The image signal input from the image input unit 60 is converted into a digital signal and then output to the temporary storage unit 94 .

[0040] 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 state of the color printer 100, the image forming status, the number of copies, etc. In addition, the liquid crystal display unit 71 also has a function as a touch panel for changing the settings in the ghosting / aggregated white spot improvement mode and the blur improvement mode described later. The LED 72 displays various states and errors of the color printer 100. Various settings of the color printer 100 can also be performed by the printer driver of the personal computer.

[0041] The operation unit 70 also includes a start button for the user to instruct the start of image formation, a stop / clear button for suspending image formation, and a reset button for returning various settings of the color printer 100 to default.

[0042] The internal temperature and humidity sensor 80 detects the temperature and humidity inside the color printer 100 , especially the temperature and humidity around the image forming units Pa to Pd. The internal temperature and humidity sensor 80 is disposed near the image forming units Pa to Pd.

[0043] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 which is a storage unit dedicated to reading, a RAM (Random Access Memory) 93 which is a storage unit that can read and write, a temporary storage unit 94 which temporarily stores image data, etc., a counter 95, and a plurality of (here, two) I / Fs (interfaces) 96 which send control signals to various devices in the color printer 100 or receive input signals from the operation unit 70. The control unit 90 can be arranged at any position inside the main body of the color printer 100.

[0044] The ROM 92 stores data such as a control program for the color printer 100 and numerical values ​​required for control, which data will not change during the use of the color printer 100. The RAM 93 stores data required during the control process of the color printer 100 and data temporarily required during the control of the color printer 100. In addition, the RAM 93 (or the ROM 92) also stores the relationship between the absolute humidity and the cumulative driving distance and the frequency of the AC voltage Vac of the developing voltage applied to the developing roller 29 of the developing device 3a to 3d when the frequency is changed based on the absolute humidity and the cumulative driving distance of the photosensitive drums 1a to 1d as described later. 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 the number of printed sheets for counting.

[0045] In addition, the control unit 90 sends control signals from the CPU 91 to each part and device in the color printer 100 through the I / F 96. In addition, signals indicating the status and input signals are sent from each part and device to the CPU 91 through the I / F 96. As the parts and devices controlled by the control unit 90, for example, there can be mentioned: image forming units Pa to Pd, exposure device 5, intermediate transfer belt 8, secondary transfer roller 9, fixing unit 13, voltage control circuit 55, image input unit 60, operation unit 70, in-machine temperature and humidity sensor 80, etc.

[0046] In the color printer 100, when the toner image is primarily transferred from the photosensitive drums 1a to 1d to the intermediate transfer belt 8, the primary transfer current flows from the primary transfer rollers 6a to 6d to the photosensitive drums 1a to 1d, and the surface potential of the photosensitive drums 1a to 1d decreases. More specifically, the amount of the primary transfer current flowing into the portion with toner (image area) decreases, and the amount of the primary transfer current flowing into the portion without toner (non-image area) increases, and the surface potential of the photosensitive drums 1a to 1d changes depending on the presence or absence of toner. As a result, there is a problem of drum ghosting due to uneven density.

[0047] The occurrence of drum ghosting is closely related to the frequency of the primary transfer current and the AC voltage Vac of the developing voltage (hereinafter 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 to 1d, and the larger the developing frequency, the more likely it is that the surface potential will be uneven, so drum ghosting is likely to occur. Therefore, it is difficult to effectively suppress drum ghosting by only changing the setting of either the primary transfer current or the developing frequency.

[0048] On the other hand, the toner aggregates in the developing devices 3a to 3d may be developed on the photosensitive drums 1a to 1d and then transferred to the intermediate transfer belt 8. In this case, there is also a problem that the toner aggregates are interposed between the photosensitive drums 1a to 1d and the intermediate transfer belt 8 to form a gap, and the toner around the toner aggregates is not transferred, resulting in blanks, so-called aggregated white spots. By increasing the primary transfer current and the development frequency, the aggregated white spots can be effectively suppressed.

[0049] That is, the setting of the primary transfer current and the developing frequency for suppressing drum ghosting and the setting of the primary transfer current and the developing frequency for suppressing aggregated white spots are in a trade-off relationship. Therefore, when the primary transfer current and the developing frequency are changed to improve drum ghosting, the aggregated white spots may be aggravated.

[0050] Therefore, in the color printer 100 of the first embodiment of the present invention, a ghosting / aggregated white spot improvement mode (first image quality improvement mode) is set, in which the settings of the primary transfer current and the development frequency are changed at the same time to improve drum ghosting and aggregated white spots. Tables 1 and 2 show examples of the development frequency and primary transfer current settings in the ghosting / aggregated white spot improvement mode. In the example shown in Table 1, menu setting values ​​1 to 7 with different setting values ​​for the development frequency and the primary transfer current are set, and menu setting value 4 is the default (reference).

[0051] [Table 1]

[0052]

[0053] ※Set based on Table 2

[0054] [Table 2]

[0055]

[0056] The development frequency is set so that the larger the menu setting value is, the lower the development frequency is. More specifically, menu setting values ​​1 to 4 are determined based on the absolute humidity and the cumulative drive distance (drum drive distance) of the photosensitive drums 1a to 1d as shown in Table 2. For menu setting values ​​5 to 7, the development frequency is fixed and has nothing to do with the absolute humidity and the drum drive distance.

[0057] When the absolute humidity is low, the surface potential of the photosensitive drums 1a to 1d is unstable, and it is easy to produce drum ghosting. In addition, when the drum driving distance is short, the photosensitive layer 19b (refer to Figure 2 ) is thicker, and drum ghosting is more likely to worsen. Therefore, if the development frequency is increased sharply when the absolute humidity is low, drum ghosting will occur significantly. Therefore, in Table 2, when the drum driving distance is short, the change range (increase range) of the development frequency relative to the change in absolute humidity is reduced compared to the case where the drum driving distance is long, thereby suppressing the occurrence of drum ghosting.

[0058] Specifically, the control unit 90 calculates the drum drive distance based on the outer diameter of the photosensitive drums 1a to 1d and the cumulative number of rotations. The drum drive distance can also be calculated based on the rotation speed (linear speed) of the photosensitive drums 1a to 1d and the cumulative drive time. And, based on the calculated drum drive distance and the absolute humidity detected by the internal temperature and humidity detection sensor 80, the developing frequency of the menu setting values ​​1 to 4 is determined.

[0059] When the drum drive distance is less than 62500m, when the absolute humidity is less than 4 [g / m 3 ], the developing frequency is set to 4000[Hz], and the absolute humidity increases by 1[g / m3 ], increasing the frequency by 200 [Hz]. Also, at an absolute humidity of 8 [g / m 3 ]or above the range, keeping the developing frequency at 5000[Hz].

[0060] On the other hand, when the drum driving distance is 62500m or more, when the absolute humidity is less than 4 [g / m 3 ], the developing frequency is set to 4000[Hz], and the absolute humidity increases by 1[g / m 3 ], increasing the frequency by 400 [Hz]. Also, at an absolute humidity of 8 [g / m 3 ]or above the range, keeping the developing frequency at 6000[Hz].

[0061] In this way, the variation range of the development frequency is changed based on the drum driving distance, so that it can be set to an appropriate frequency corresponding to the degradation state of the photosensitive drums 1a to 1d. Specifically, when the cumulative driving distance of the photosensitive drums 1a to 1d is greater than a predetermined distance, it is difficult to generate drum ghosting, so the variation range of the development frequency relative to the absolute humidity change is increased. In this way, the development characteristics when the absolute humidity is low can be maintained, and the occurrence of blurring described later can be suppressed.

[0062] The primary transfer current is determined by multiplying the primary transfer coefficient set by the menu setting values ​​1 to 7 by the reference current value (here, 9 [μA]). For menu setting values ​​1 to 3, the primary transfer coefficient is greater than 1.0, so the primary transfer current is greater than the reference current value. For menu setting values ​​5 to 7, the primary transfer coefficient is less than 1.0, so the primary transfer current is less than the reference current value.

[0063] The user can change the menu setting value of the ghost / aggregate white spot improvement mode by setting the liquid crystal display unit 71 of the operation unit 70 according to the situation of drum ghosting and aggregated white spots in the image output by the printing process, thereby changing the primary transfer current and the development frequency at the same time.

[0064] For example, when drum ghosting occurs, the menu setting value is changed from 4 to 5 to 7, the development frequency and the primary transfer current are reduced, and thus the generation of drum ghosting can be suppressed. In addition, when aggregated white spots occur, the menu setting value is changed from 4 to 1 to 3, the development frequency and the primary transfer current are increased, and thus the generation of aggregated white spots can be suppressed.

[0065] Table 3 shows the conditions of drum ghosting, white spot accumulation, and image blurring when the ghosting / white spot accumulation improvement mode is executed by the settings shown in Table 1. In addition, Table 4 shows, as a comparative example, the conditions of drum ghosting, white spot accumulation, and image blurring when the development frequency is fixed to 4000 [Hz] in the settings of Table 1. In Tables 3 and 4, 0 is marked for the case where there is no problem in the image, △ is marked for the case where the image is poor due to error conditions such as absolute humidity and drum drive distance, and × is marked for the case where the image is poor.

[0066] [Table 3]

[0067]

[0068] [Table 4]

[0069]

[0070] As shown in Table 3, it was confirmed that when the development frequency was changed according to the menu setting value as shown in Table 1, the generation of drum ghosting could be suppressed by changing the menu setting value to 5 to 7, and the generation of aggregated white spots could be suppressed by changing the menu setting value to 1 to 3. In contrast, as shown in Table 4, when the development frequency was fixed at 4000 [Hz], neither the drum ghosting nor the aggregated white spots could be sufficiently improved.

[0071] The above results confirm that by changing the menu setting value of the ghost / aggregated white spot improvement mode and simultaneously changing the development frequency and the primary transfer current, the occurrence of drum ghost and aggregated white spots can be effectively suppressed compared to the case of changing only the primary transfer current.

[0072] However, if the developing frequency is set to a low level in order to suppress drum ghosting, so-called image blurring (hereinafter referred to as blurring) in which toner adheres to the blank area is likely to occur. Therefore, in this embodiment, a blurring improvement mode (second image quality improvement mode) is set, in which the charging voltage applied to the charging devices 2a to 2d is increased to improve blurring. The blurring improvement mode is executed as needed after the ghosting / aggregated white spot improvement mode is executed.

[0073] Table 5 shows an example of setting the charging voltage in the fuzzy improvement mode. In the example shown in Table 5, menu setting values ​​1 to 7 with different setting values ​​for the charging voltage are set, and menu setting value 4 is a default (standard).

[0074] [Table 5]

[0075]

[0076] The charging voltage is determined by adding the charging correction value set by the menu setting values ​​1 to 7 to the reference voltage (here, 450 [V]). For menu setting values ​​1 to 3, the charging correction value is negative, so the charging voltage is smaller than the reference voltage. For menu setting values ​​5 to 7, the charging correction value is positive, so the charging voltage is larger than the reference voltage.

[0077] The user changes the menu setting value of the blur improvement mode according to the blur generated in the image output after the ghost / stuck white spot improvement mode is executed, by setting the liquid crystal display unit 71 of the operation unit 70. For example, when blur is generated, the menu setting value is changed from 4 to 5 to 7 to increase the charging voltage, thereby suppressing the blur.

[0078] In addition, regarding the menu setting values ​​1 to 3 in Table 5, since the charging voltage is lower than the reference voltage, they are not used in the blur improvement mode. The menu setting values ​​1 to 3 are used when adjusting the surface potentials of the photosensitive drums 1 a to 1 d.

[0079] Figure 4 This is a flowchart showing a control example when eliminating drum ghosts in the ghost / aggregated white spot improvement mode (GS mode) in the color printer 100 of the first embodiment. Figure 1 to Figure 3 and the following Figure 5 to Figure 7 , and follow Figure 4 The following steps describe the process of eliminating drum ghosting using the "Ghosting / Clustered White Spot Improvement Mode".

[0080] When the user observes the output image and confirms that a drum ghost occurs (step S1), the user selects a ghost / spot improvement mode (GS mode) from the liquid crystal display unit 71 (step S2), and then increases the menu setting value of the GS mode by one level (step S3).

[0081] Figure 5 FIG. 2 is a top view of the liquid crystal display unit 71, showing the state where the GS mode is selected. Figure 5 As shown in FIG. 1 , a plurality of mode setting keys 71a are displayed on the left side of the screen of the liquid crystal display unit 71. When the "adjustment / maintenance key" (in Figure 5 When the function key 71b associated with "Adjustment / Maintenance" is displayed on the right side of the screen (indicated by gray shadow in the figure), the function key 71b associated with "Adjustment / Maintenance" is displayed on the right side of the screen. The current menu setting value "4" is displayed on the "GS key" for selecting the GS mode in the function key 71b.

[0082] Figure 6 is a diagram showing the state where the menu setting values ​​of the GS mode are displayed. Figure 5 If the "GS key" in the function key 71b is pressed from the state of Figure 6As shown, a menu setting value selection key 71c of "1" to "7" is displayed on the liquid crystal display unit 71. A confirmation key 71d is displayed on the upper right of the screen of the liquid crystal display unit 71. The confirmation key 71d is used to confirm the change to the selected menu setting value. A cancel key 71e is displayed on the upper left of the screen of the liquid crystal display unit 71. The cancel key 71e is used to cancel the display of the menu setting value and return to the previous screen ( Figure 5 status).

[0083] The user presses the menu setting value "5" (in the menu setting value selection key 71c) which is one level higher than the current menu setting value "4". Figure 6 The menu setting value of the GS mode is thereby changed from "4" to "5".

[0084] Next, the user performs image output with the changed menu setting value "5" (step S4). Then, it is determined whether the drum ghost is eliminated in the output image (step S5). If the drum ghost is not eliminated (No in step S5), the process returns to step S3, and the menu setting value of the GS mode is further increased by one step to perform image output (steps S3-S4).

[0085] When the drum ghost is eliminated (Yes in step S5), the user determines whether blur occurs in the output image (step S6). When blur occurs (Yes in step S6), the blur improvement mode (MC mode) is selected from the liquid crystal display unit 71 (step S7). Then, the menu setting value of the MC mode is increased by one level (step S8).

[0086] Figure 7 is a diagram showing the state where the menu setting values ​​of the MC mode are displayed. Figure 5 In the state of Figure 7 As shown, a menu setting value selection key 71c of "1" to "7" is displayed on the liquid crystal display unit 71. A confirmation key 71d is displayed on the upper right of the screen of the liquid crystal display unit 71. The confirmation key 71d is used to confirm the change to the selected menu setting value. A cancel key 71e is displayed on the upper left of the screen of the liquid crystal display unit 71. The cancel key 71e is used to cancel the display of the menu setting value and return to the previous screen ( Figure 5 status).

[0087] The user presses the menu setting value "5" (in the menu setting value selection key 71c) which is one level higher than the current menu setting value "4". Figure 7 The menu setting value of the MC mode is changed from "4" to "5".

[0088] Next, the user outputs the image with the changed menu setting value "5" (step S9). Then, it is determined whether blur is eliminated in the output image (step S10). If blur is not eliminated (No in step S10), the process returns to step S8, and the menu setting value of the MC mode is further increased by one step to output the image (steps S8 to S9).

[0089] If blur is eliminated (YES in step S10 ), the process is terminated directly. If blur is not generated in step S6 (NO in step S6 ), the MC mode is not executed and the process is terminated.

[0090] Figure 8 This is a flowchart showing a control example when eliminating aggregated white spots in the color printer 100 according to the first embodiment by the ghost / aggregated white spot improvement mode (GS mode). Figure 1 to Figure 3 and Figure 5 , Figure 6 , and follow Figure 8 The following steps explain the process of eliminating clustered white spots using the "Ghosting / Clustered White Spot Improvement Mode".

[0091] When the user observes the output image and confirms that a white spot is generated (step S1), the user selects the ghosting / white spot improvement mode (GS mode) from the liquid crystal display unit 71 (step S2). Then, the menu setting value of the GS mode is lowered by one level (step S3). For example, when the menu setting value is the default "4", the menu setting value is changed from "4" to "3". The process of changing the menu setting value is the same as Figure 5 and Figure 6 The process shown is the same.

[0092] Next, the user outputs the image with the changed menu setting value "3" (step S4). Then, it is determined whether the aggregated white spots are eliminated in the output image (step S5). If the aggregated white spots are not eliminated (No in step S5), the process returns to step S3, and the menu setting value of the GS mode is further reduced by one step to output the image (steps S3 to S4). If the aggregated white spots are eliminated (Yes in step S5), the process ends directly.

[0093] In addition, when eliminating aggregated white spots, since the setting is changed in the direction of increasing the development frequency (lowering the menu setting value), the possibility of blurring after the change is low. Figure 8 In the control example, the MC mode is not executed ( Figure 4 Steps S6 to S10), but can also be Figure 4 Similarly, after eliminating the concentrated white spots, check whether blur has occurred, and if blur has been confirmed, switch to the MC mode.

[0094] according to Figure 4 and Figure 8 In the control example shown, since the ghosting / aggregated white spot improvement mode (GS mode) is set to change the settings of the primary transfer current and the development frequency at the same time, it is possible to reliably improve the drum ghosting and aggregated white spots compared to the conventional method of changing the settings of the primary transfer current and the development frequency individually. In addition, it is possible to fully ensure the OW (operation window) when the drum ghosting and aggregated white spots that can be improved by changing the settings of the primary transfer current and the development frequency are improved at the same time. Therefore, both the drum ghosting and aggregated white spots can be effectively improved.

[0095] In addition, the control unit 90 determines the development frequency based on the absolute humidity and the drum drive distance, so that appropriate conditions can be set according to the errors of the absolute humidity and the drum drive distance. Thus, even in the case of environmental changes and large durability errors, the improvement effect of drum ghosting and aggregated white spots can be improved, and sufficient OW can be ensured.

[0096] Furthermore, if blurring occurs after drum ghosting is improved in the ghosting / aggregated white spot improvement mode (GS mode), the blurring improvement mode (MC mode) is executed. This can simultaneously improve blurring that is likely to occur as a side effect when the development frequency is reduced.

[0097] Furthermore, since the GS mode and MC mode can be set from the liquid crystal display unit 71, the user can simultaneously change the developing frequency, primary transfer current, and charging voltage settings, thereby improving drum ghosting and aggregated white spots in a simple manner.

[0098] Next, another control example of the ghost / aggregated white spot improvement mode in the color printer 100 of the first embodiment will be described. Figure 4 In the control example shown, when blurring occurs in the output image after the primary transfer current and the development frequency are changed in the ghost / aggregated white spot improvement mode (GS mode), the blurring improvement mode (MC mode) is entered and the charging voltage is changed. However, in this control example, the ghost / aggregated white spot improvement mode (GS mode) and the blurring improvement mode (MC mode) are combined in advance to set the ghost / aggregated white spot / blurring improvement mode, in which the settings of the primary transfer current, the development frequency, and the charging voltage are changed at the same time. Table 6 shows an example of the setting of the development frequency, the primary transfer current, and the charging voltage in the ghost / aggregated white spot / blurring improvement mode.

[0099] [Table 6]

[0100]

[0101] ※Set based on Table 2

[0102] In the example shown in Table 6, menu setting values ​​1 to 7 are set to different values ​​for the setting of the development frequency, the primary transfer current, and the charging voltage, and menu setting value 4 is the default (reference). The setting values ​​of the development frequency, the primary transfer current, and the charging voltage are a combination of the setting values ​​of Table 1 and Table 5 described above. However, since menu setting values ​​1 to 3 that make the charging voltage lower than the reference voltage are not used in Table 5, the charging correction values ​​of menu setting values ​​1 to 3 in Table 6 are also 0 [V].

[0103] Since the ghosting / aggregated white spot / blur improvement mode is set to change the settings of the primary transfer current, development frequency, and charging voltage at the same time, the charging voltage can be increased in advance to prevent blurring in the condition setting (menu setting values ​​5 to 7) where the development frequency is low and blurring is likely to occur. Therefore, the work of outputting the image to confirm whether blurring has occurred after changing the settings of the primary transfer current and development frequency can be omitted, which can further improve user convenience.

[0104] Next, a color printer 100 according to a second embodiment of the present invention will be described. In the first embodiment described above, the user does not know whether drum ghosting (delayed development) has occurred unless an image is output. In addition, there is a problem that even if drum ghosting has occurred, if the user does not recognize the occurrence of drum ghosting, there is a possibility that the liquid crystal display unit 71 will not be operated to execute the ghosting / aggregated white spot improvement mode (GS mode).

[0105] Therefore, in the color printer 100 of the second embodiment, even if the user does not output an image, the ghost detection mode is executed to detect whether a drum ghost is generated on the intermediate transfer belt 8. And when a drum ghost is detected, the ghost / aggregate white spot improvement mode (GS mode) is automatically executed.

[0106] When the real image is primarily transferred from the photosensitive drums 1a to 1d to the intermediate transfer belt 8, the decrease in the surface potential of the photosensitive drums 1a to 1d caused by the flow of the primary transfer current is smaller only in the area where the real image is formed than in other parts. As a result, after the photosensitive drums 1a to 1d rotate one circle, the surface potential of the part that was the range of the real image formation increases, so the potential difference (development potential difference) between the part that was the range of the real image formation and the developing roller 29 becomes smaller.

[0107] Therefore, if a half image is formed in an area including a portion of the formation range that was once a solid image, a drum ghost will be generated in which the image density of only the portion of the formation range that was once a solid image is reduced. In the ghost detection mode, whether a drum ghost has occurred is detected by measuring the density difference between the portion of the formation range that was once a solid image and its surroundings.

[0108] Fig. 9FIG. 2 is a diagram showing an example of a detection image used in the ghost detection mode executed in the color printer 100 according to the second embodiment. Fig. 9 More specifically, the half images Yh to Kh are formed after the solid images Ys to Ks are formed on the intermediate transfer belt 8 and the photosensitive drums 1a to 1d rotate once (travel by the drum circumference L).

[0109] The half images Yh to Kh include the portion of the formation range of the solid images Ys to Ks after the photosensitive drums 1a to 1d rotate one circle ( Fig. 9 dotted line), and is formed to extend toward the upstream and downstream sides of the conveying direction of the intermediate transfer belt 8 ( Fig. 9 The image density sensor 27 is used to measure the image density of the half images Yh to Kh in the entire area in the conveying direction. Thus, the density difference ΔID between the portion that was the formation range of the solid images Ys to Ks and the portions on the upstream and downstream sides thereof is measured.

[0110] The half images Yh to Kh may include the portion of the formation range of the solid images Ys to Ks after the photosensitive drums 1a to 1d rotate one circle. For example, the half images Yh to Kh may be formed along the width direction ( Fig. 9 However, when the half images Yh to Kh are formed to extend in the width direction, a mechanism for moving the image density sensor 27 in the width direction is required. As in the present embodiment, the half images Yh to Kh are formed to extend toward the upstream and downstream sides of the conveying direction of the intermediate transfer belt 8, so that the density of the entire area of ​​the half images Yh to Kh can be detected without moving the image density sensor 27.

[0111] Fig.10 Graph showing the detection results of the half images when the drum ghost is not generated and when the drum ghost is generated in the ghost detection mode. Fig.10 As shown, when no drum ghosting occurs ( Fig.10 ), the density difference ΔID with the portion R which was the formation range of the solid image is small or zero. On the other hand, when the drum ghost is generated ( Fig.10 on the right side of the image), the concentration difference ΔID is larger.

[0112] Therefore, when drum ghost is significant (density difference ΔID is greater than a predetermined value), the ghost / aggregate white spot improvement mode is executed to change the development frequency and primary transfer current to reduce drum ghost. Table 7 shows an example of the setting of the development frequency and primary transfer current in the ghost / aggregate white spot improvement mode.

[0113] [Table 7]

[0114]

[0115] As described above, the larger the primary transfer current, the greater the change in the surface potential of the photosensitive drums 1a to 1d, and the larger the development frequency, the more likely it is that the surface potential will be uneven, so that drum ghosting will be easily generated. Therefore, as shown in Table 7, the larger the density difference ΔID, the smaller the development frequency and the primary transfer current, so that drum ghosting can be improved.

[0116] Fig.11 This is a flowchart showing a control example when the ghost detection mode is executed in the color printer 100 of the second embodiment and the drum ghost is automatically eliminated. Figures 1 to 10 , and follow Fig.11 The steps in the following section describe the process of executing the ghost detection mode to automatically eliminate drum ghosting.

[0117] First, the control unit 90 determines whether it is time to detect drum ghost (step S1). Examples of the detection timing of drum ghost include when a predetermined number of prints (e.g., 250 prints) have been printed since the ghost detection mode was last executed, or when the color printer 100 is powered on.

[0118] When it is the detection timing of the drum ghost (Yes in step S1), the ghost detection mode is executed (step S2). Specifically, the following image is formed on the intermediate transfer belt 8: Fig. 9 The real images Ys to Ks and the half images Yh to Kh shown in FIG. Figure 1 ) is used to detect the concentration of half images Yh~Kh.

[0119] Next, the control unit 90 measures the density difference ΔID between the portion of the half images Yh to Kh that was the formation range of the solid images Ys to Ks and the upstream and downstream sides thereof based on the detection result of the image density sensor 27 (step S3 ).

[0120] The control unit 90 adjusts the development frequency and the primary transfer current based on the density difference ΔID (step S4 ). Specifically, the development frequency and the primary transfer current are set using the relationship between the density difference ΔID, the development frequency, and the primary transfer current as shown in Table 7.

[0121] according to Fig.11 The control example shown executes the ghost detection mode and determines the primary transfer current and the development frequency based on the measured density difference ΔID of the half images Yh to Kh. Therefore, even when the user does not output an image or does not recognize the occurrence of drum ghost, the occurrence of drum ghost can be detected, and when drum ghost occurs, the development frequency and the primary transfer current are automatically set so that drum ghost does not occur.

[0122] Thus, the drum ghosting can be automatically improved without operating the liquid crystal display unit 71, so that the convenience of the user can be further improved. In addition, when blurring occurs after the drum ghosting is improved, the blurring improvement mode (MC mode) is executed by operating the liquid crystal display unit 71 as in the first embodiment. In addition, when a concentrated white spot occurs, the ghosting / concentrated white spot improvement mode (GS mode) is executed by operating the liquid crystal display unit 71.

[0123] In addition, the present invention is not limited to the above-mentioned embodiments, and various changes can be made without departing from the scope of the present invention. Figure 2 The developing devices 3a to 3d of the developing roller 29 carrying the two-component developer as shown are described, but are not limited to this. The present invention can be applied to an image forming device having various developing devices using a two-component developer, and the developing device may be, for example, a developing device having a colorant supplying roller that only supplies the colorant in the two-component developer to the developing roller 29.

[0124] In the above-mentioned embodiments, the tandem color printer 100 is described as an example of the image forming apparatus, but the present invention is of course also applicable to other intermediate transfer image forming apparatuses such as color copiers and color multifunction machines.

[0125] The present invention can be used in an image forming apparatus of an intermediate transfer method. By using the present invention, it is possible to provide an image forming apparatus that reliably improves drum ghosting caused by a combination of various conditions and can ensure a setting margin required for improving both drum ghosting and aggregated white spots.

Claims

1. An image forming device comprising: Like a carrier, it has a photosensitive layer formed on the surface; a charging device for charging the surface of the image carrier; an exposure device for exposing the surface of the image carrier charged by the charging device to form an electrostatic latent image whose charge is attenuated; A developing device having a developer carrier carrying a developer including a toner, and supplying the toner in the developer carried on the developer carrier to the image carrier to develop the electrostatic latent image into a toner image; an intermediate transfer body for sequentially transferring the toner images formed on the image carrier; a primary transfer member, which is pressed against the image carrier via the intermediate transfer body; a secondary transfer member for secondarily transferring the toner image primarily transferred to the intermediate transfer body onto a recording medium; a charging voltage power supply that applies a charging voltage to the charging device; A developing voltage power source, which applies to the developer carrier: a developing voltage in which an alternating current voltage is superimposed on a direct current voltage; a transfer voltage power supply for applying to the primary transfer member and the secondary transfer member: a transfer voltage having a polarity opposite to that of the toner image; and a control unit that controls the charging voltage power supply, the developing voltage power supply, and the transfer voltage power supply, The image forming apparatus is characterized in that The control section executes a first image quality improvement mode in which a frequency of the AC voltage in the development voltage and a primary transfer current flowing between the image carrier and the primary transfer member are simultaneously changed.

2. The image forming apparatus according to claim 1, wherein: A humidity detection device is provided for detecting the absolute humidity around the developing device. The control unit determines a frequency of the AC voltage used in the first image quality improvement mode based on the absolute humidity detected by the humidity detection device and a cumulative drive distance of the image carrier.

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

4. The image forming apparatus according to claim 2, wherein: When the cumulative drive distance of the image carrier is less than a predetermined distance, the control unit reduces the change width of the frequency with respect to the change in the absolute humidity compared to when the cumulative drive distance is greater than or equal to the predetermined distance.

5. The image forming apparatus according to claim 1, wherein: An input unit is provided, wherein the input unit selects and sets: any one of a plurality of modes including the first image quality improvement mode; When the first image quality improvement mode is set through the input unit, the control unit executes the first image quality improvement mode.

6. The image forming apparatus according to claim 5, wherein: In the first image quality improvement mode, the input unit can select and input any one of a plurality of different setting values ​​of the frequency of the AC voltage and the primary transfer current, The control unit simultaneously changes: the frequency of the AC voltage and the primary transfer current based on the set value input from the input unit.

7. The image forming apparatus according to claim 1, wherein: The control unit may execute a second image quality improvement mode of changing the charging voltage after executing the first image quality improvement mode.

8. The image forming apparatus according to claim 7, wherein: An input unit is provided, wherein the input unit selects and sets: any one of a plurality of modes including the first image quality improvement mode and the second image quality improvement mode; When the second image quality improvement mode is set through the input unit, the control unit executes the second image quality improvement mode.

9. The image forming apparatus according to claim 8, wherein: In the second image quality improvement mode, the input unit can select and input: any one of a plurality of different setting values ​​for setting the charging voltage; The control unit changes the charging voltage based on the set value input from the input unit.

10. 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. The image forming apparatus according to claim 10, wherein: An input unit is provided, wherein the input unit selects and sets: any one of a plurality of modes including the first image quality improvement mode; When the first image quality improvement mode is set through the input unit, the control unit executes the first image quality improvement mode.

12. The image forming apparatus according to claim 11, wherein: In the first image quality improvement mode, the input unit can select and input any one of a plurality of different setting values ​​of the frequency of the AC voltage, the primary transfer current, and the charging voltage. 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. The image forming apparatus according to claim 1, wherein: An image density detection unit is provided for detecting the density of the 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 the image density of the detection image formed on the intermediate transfer body to detect whether a drum ghost occurs. The control unit executes the first image quality improvement mode based on a result of the ghost detection mode.

14. The image forming apparatus according to claim 13, wherein: The detection image is a half image, which is formed after the image carrier rotates one circle from the formation of the real image, and includes a portion that was once the formation range of the real image. The control section 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 a formation range of the solid image and a peripheral portion thereof.

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

Images