Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the occurrence of density unevenness while reducing manufacturing cost.SOLUTION: A control unit can execute an image forming operation to form an image, an aging operation, and a determination operation. The aging operation is to apply a transfer bias to a transfer member and supply a transfer current to an image carrier, with the image forming operation being stopped. The determination operation is executed before the execution of the aging operation, and to determine the electrification ability of the image carrier. The control unit sets a condition for the aging operation on the basis of a determination result of the determination operation.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A conventional image forming apparatus includes an image forming unit, a developing bias power supply, a charging bias power supply, and a control unit. The image forming unit includes an image carrier, a charging device, an exposure device, and a developing device. The image carrier has a photosensitive layer formed on its surface. The charging device is disposed opposite the image carrier and has a charging member that charges the image carrier. The exposure device forms an electrostatic latent image by exposing the image carrier charged by the charging device. The developing device is disposed opposite the image carrier and has a developer carrier that carries developer, and forms a toner image by attaching toner to the electrostatic latent image formed on the image carrier.

[0003] The developing bias power supply applies a developing bias to the developer carrier. The charging bias power supply applies a voltage to the charging member. The control unit controls the image forming unit, the developing bias power supply, and the charging bias power supply.

[0004] In the image forming apparatus of Patent Document 1, the casing that houses the charging member is covered with a metallic shielding member and is in close contact with the shielding member. In the image forming apparatus of Patent Document 2, the developing bias power supply is concealed by covering it with a conductive member with respect to the charging member.

[0005] This reduces the influence of the electric field of the developing bias applied by the developing bias power supply on the charging bias applied by the charging bias power supply, thereby reducing unevenness in the surface potential of the image carrier and suppressing the occurrence of density unevenness (stained images). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-164866

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the configurations of Patent Document 1 and Patent Document 2, there was a problem that the number of components increased and the manufacturing cost rose.

[0008] In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of density unevenness while suppressing the manufacturing cost.

Means for Solving the Problems

[0009] To achieve the above object, a first aspect of the present invention is an image forming apparatus including an image forming unit, a transfer member, a development bias power supply, a charging bias power supply, a transfer bias power supply, and a control unit. The image forming unit includes an image carrier, a charging device, an exposure device, and a development device. The image carrier has a photosensitive layer formed on its surface. The charging device is disposed opposite the image carrier and has a charging member that charges the image carrier. The exposure device forms an electrostatic latent image by exposing the image carrier charged by the charging device. The development device is disposed opposite the image carrier and has a developer carrier that carries developer, and forms a toner image by attaching toner to the electrostatic latent image formed on the image carrier. The transfer member is disposed opposite the image carrier and is applied with a predetermined transfer voltage to transfer the toner image formed on the image carrier to a transfer target. The development bias power supply applies a development bias, which is a DC voltage superimposed on an AC voltage, to the developer carrier. The charging bias power supply applies a charging bias including a DC voltage to the charging member. The transfer bias power supply applies a transfer bias including a DC voltage to the transfer member. The control unit controls the image forming unit, the development bias power supply, the charging bias power supply, and the transfer bias power supply. The control unit is capable of executing an image forming operation for forming an image, an aging operation, and a determination operation. The aging operation applies a transfer bias to the transfer member while the image forming operation is stopped, thereby supplying a transfer current to the image carrier. The determination operation is executed before the aging operation is executed, and determines the charging ability of the image carrier. The control unit sets the conditions for the aging operation based on the determination results of the determination operation. [Effects of the Invention]

[0010] According to the first aspect of the present invention, it is possible to provide an image forming apparatus that can suppress the occurrence of density unevenness while suppressing manufacturing costs. [Brief explanation of the drawings]

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to a first embodiment of the present invention, and Fig. 2 is a partially enlarged view of the periphery of image forming unit Pa, including the control path of image forming apparatus 100. Note that the configuration of image forming units Pb-Pd and the control path of charging devices 2a-2d are similar to the configuration of image forming unit Pa and the control path of charging device 2a, and therefore description thereof will be omitted.

[0013] The image forming apparatus 100 includes image forming units Pa to Pd, primary transfer rollers (transfer members) 6a to 6d, a development bias power supply 43, a charging bias power supply 45, a transfer bias power supply 47, current detection units 43 and 46, a main control unit (control unit) 80, and a detection sensor 48.

[0014] Inside the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the conveyance direction (the left side in FIG. 1). The image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, yellow, and black images are sequentially formed through the steps of charging, exposure, development, and transfer, respectively.

[0015] The image forming units Pa to Pd include primary transfer rollers (transfer members) 6a to 6d, photosensitive drums (image carriers) 1a to 1d that carry visible images (toner images) of each color, charging devices 2a to 2d, an exposure device 5, and developing devices 3a to 3d. Further, adjacent to each of the image forming units Pa to Pd, an intermediate transfer belt (transfer body) 8 that rotates in the counterclockwise direction in FIG. 1 by a driving means (not shown) is provided.

[0016] The primary transfer rollers (transfer members) 6a to 6d are arranged to face the photosensitive drums (image carriers) 1a to 1d, and a predetermined transfer voltage is applied to transfer the visible images (toner images) of each color formed on the photosensitive drums (image carriers) 1a to 1d to the intermediate transfer belt (transfer body) 8. As a result, the toner images formed on the photosensitive drums 1a to 1d are sequentially primary transferred and superimposed onto the intermediate transfer belt 8 that moves while contacting each of the photosensitive drums 1a to 1d.

[0017] The toner image primary transferred onto the intermediate transfer belt 8 is secondary transferred onto a sheet S as an example of a recording medium by a secondary transfer roller 9. The sheet S on which the toner image is secondary transferred is housed in a paper cassette 16 arranged at the lower part of the main body of the image forming apparatus 100. The sheet S is conveyed to the nip portion between the secondary transfer roller 9 and the driving roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a registration roller pair 12b.

[0018] A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a seamless belt is usually used. In addition, a blade-shaped belt cleaner 19 is disposed downstream of the secondary transfer roller 9 to remove toner and other particles remaining on the surface of the intermediate transfer belt 8.

[0019] The photosensitive drums (image carriers) 1a to 1d have a photosensitive layer 111 formed on their surfaces (see FIG. 2). In this embodiment, the photosensitive drums (image carriers) 1a to 1d have the photosensitive layer 111 formed on the surface of an aluminum cylinder, and the photosensitive layer 111 is formed by vapor deposition of amorphous silicon, a positively chargeable photoconductor. In other words, the photosensitive layer 111 is an electrostatically charged single layer type. It is preferable that the photosensitive layer 111 has a film thickness of 37 μm or more in an unused state. Increasing the film thickness improves the durability of the photosensitive drums 1a to 1d against wear.

[0020] Each of the charging devices 2a to 2d has a charging roller (charging member) 34. The charging roller 34 is disposed opposite the corresponding photosensitive drum (image carrier) 1a to 1d and charges the corresponding photosensitive drum (image carrier) 1a to 1d. The charging roller 34 is formed, for example, by coating a core metal with an epichlorohydrin rubber layer, which is a conductive elastic material. In this embodiment, the charging roller 34 is in contact with each of the photosensitive drums 1a to 1d. However, the charging roller 34 may not be in contact with each of the photosensitive drums 1a to 1d.

[0021] The exposure device 5 exposes the photosensitive drums (image carriers) 1a to 1d charged by the charging devices 2a to 2d, thereby forming electrostatic latent images.

[0022] Developing devices 3a to 3d are disposed opposite photosensitive drums (image carriers) 1a to 1d and each have a developing roller (developer carrier) 31. Developing devices 3a to 3d apply a predetermined developing bias to developing roller (developer carrier) 31 to cause toner to adhere to the electrostatic latent images formed on the photosensitive drums (image carriers) 1a to 1d, thereby forming a toner image. Developing roller (developer carrier) 31 is disposed opposite photosensitive drums (image carriers) 1a to 1d and carries a two-component developer containing a magnetic carrier and toner.

[0023] When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then the exposure device 5 irradiates the photosensitive drums 1a to 1d with light according to the image data, forming electrostatic latent images on the photosensitive drums 1a to 1d according to the image data.

[0024] The developing devices 3a to 3d are filled with a predetermined amount of two-component developer containing toner of each color, cyan, magenta, yellow, and black. The toner in the developer is supplied to the photosensitive drums 1a to 1d by the developing devices 3a to 3d, respectively, and electrostatically adheres to the photosensitive drums 1a to 1d, forming a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5.

[0025] Then, primary transfer rollers 6a-6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a-6d and the photosensitive drums 1a-1d, and the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed in a predetermined positional relationship for forming a predetermined full-color image. After that, toner and the like remaining on the surfaces of the photosensitive drums 1a-1d after the primary transfer are removed by cleaning devices 7a-7d in preparation for the subsequent formation of a new electrostatic latent image.

[0026] The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a drive roller 11 on the downstream side, and when the intermediate transfer belt 8 starts to rotate counterclockwise as the drive roller 11 is rotated by a drive motor (not shown), the sheet S is transported from the registration roller pair 12b to a nip portion (secondary transfer nip portion) between the drive roller 11 and a secondary transfer roller 9 provided adjacent thereto at a predetermined timing, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the sheet S. The sheet S onto which the toner image has been secondarily transferred is transported to a fixing unit 13.

[0027] The sheet S conveyed to the fixing unit 13 is heated and pressurized by the fixing roller pair 13a, and the toner image is fixed to the surface of the sheet S, forming a predetermined full-color image. The sheet S on which the full-color image has been formed is then directed to a branching unit 14, which branches into multiple directions, and is then discharged directly (or after being sent to the double-sided conveying path 18 and having images formed on both sides) onto a discharge tray 17 by the discharge roller pair 15.

[0028] Furthermore, an image density sensor 40 is disposed at a position facing the drive roller 11 across the intermediate transfer belt 8. The image density sensor 40 measures the amount of toner adhesion on the intermediate transfer belt 8. A detection sensor 48 detects the temperature and humidity around the charging roller 34.

[0029] The developing bias power supply 43 is connected to the developing roller 31 (see FIG. 2). The developing bias power supply 43 includes an AC constant voltage power supply 43a and a DC constant voltage power supply 43b. The AC constant voltage power supply 43a outputs a sine wave AC voltage generated from a low voltage DC voltage modulated into a pulse shape using a step-up transformer (not shown). The DC constant voltage power supply 43b outputs a DC voltage obtained by rectifying a sine wave AC voltage generated from a low voltage DC voltage modulated into a pulse shape using a step-up transformer.

[0030] During image formation, the development bias power supply 43 applies a development bias, which is a DC voltage superimposed on an AC voltage, from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b to the development roller 31. The current detection unit 44 detects the value of the DC current flowing between the development roller 31 and the photosensitive drum 1a. By applying the development bias, which is a DC voltage superimposed on an AC voltage, to the development rotor 31, it becomes easier to control the developability of the toner during image formation, improving image quality.

[0031] The charging roller 34 is connected to a charging bias power supply 45 (see FIG. 2). The charging bias power supply 45 includes a DC constant voltage power supply 45b. The DC constant voltage power supply 45b outputs a DC voltage obtained by rectifying a sinusoidal AC voltage generated from a low DC voltage modulated into a pulse using a step-up transformer.

[0032] In this embodiment, during image formation, the charging bias power supply 45 applies a charging bias consisting of only a DC voltage from the DC constant voltage power supply 45b to the charging roller (charging member) 34. By configuring the charging bias to consist of only a DC voltage, it is possible to reduce wear of the photosensitive layer 111, reduce the amount of ozone generated, and reduce charging noise.

[0033] The transfer bias power supply 47 applies a primary transfer voltage (transfer voltage) and a secondary transfer voltage to the primary transfer rollers (transfer members) 6a to 6d and the secondary transfer roller 9 (see FIG. 1), respectively. The charging bias power supply 47 includes a DC constant voltage power supply 47b. The DC constant voltage power supply 47b outputs a DC voltage obtained by rectifying a sinusoidal AC voltage generated from a low-voltage DC voltage modulated into a pulse using a step-up transformer.

[0034] In this embodiment, during image formation, transfer bias power supply 47 applies a transfer bias consisting of only a DC voltage from DC constant voltage power supply 47b to primary transfer rollers (transfer members) 6a to 6d and secondary transfer roller 9 (see FIG. 1).

[0035] The cleaning device 7a includes a cleaning blade 32 that removes residual toner from the surface of the photosensitive drum 1a, a rubbing roller 33 that removes residual toner from the surface of the photosensitive drum 1a and also rubs against the surface of the photosensitive drum 1a to polish it, and a conveying spiral 35 that discharges the residual toner removed from the photosensitive drum 1a by the cleaning blade 32 and the rubbing roller 33 to the outside of the cleaning device 7a.

[0036] The image forming apparatus 100 is provided with a main control unit 80 that is configured with a CPU and the like. The main control unit 80 is connected to a storage unit 70 that is configured with a ROM, RAM and the like. The main control unit 80 controls each unit of the image forming apparatus 100 (charging devices 2a-2d, developing devices 3a-3d, exposure device 5, primary transfer rollers 6a-6d, cleaning devices 7a-7d, secondary transfer roller 9, fixing unit 13, developing bias power supply 43, current detection unit 46, charging bias power supply 45, transfer bias power supply 47, voltage control unit 50, etc.) based on the control program and control data stored in the storage unit 70.

[0037] The voltage control unit 50 controls a development bias power supply 43 that applies a development bias to the development roller 31, a charging bias power supply 45 that applies a charging bias to the charging roller 34, and a transfer bias power supply 47 that applies a transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9. The voltage control unit 50 may be configured by a control program stored in the storage unit 70.

[0038] The main control unit 80 is connected to a liquid crystal display unit 90 and a transmission / reception unit 91. The liquid crystal display unit 90 functions as a touch panel for the user to make various settings for the image forming apparatus 100, and also displays the status of the image forming apparatus 100, the image formation status, the number of printed sheets, etc. The transmission / reception unit 91 communicates with the outside world using a telephone line or an internet line.

[0039] As described above, the charging bias applied by the charging bias power supply 45 during image formation is affected by the AC component of the developing bias. As a result, unevenness may occur in the surface potential of the photosensitive drums (image carriers) 1a to 1d, and density unevenness (foggy images) may occur in the toner images of each color formed on the photosensitive drums (image carriers) 1a to 1d.

[0040] In addition, as the charging ability of the photosensitive drums (image carriers) 1a to 1d increases, they are more easily affected by the AC component of the developing bias. As a result, density unevenness is more likely to occur.

[0041] In addition, the photosensitive layers 111 of the photosensitive drums (image carriers) 1a to 1d are worn (film collapse) and the film thickness becomes thinner as the cumulative number of rotations increases compared to when not in use. On the other hand, the electrostatic capacitance of the photosensitive drums 1a to 1d in the initial state with a thick film thickness of the photosensitive layer 111 decreases compared to the state with a thin film thickness. As a result, the photosensitive drums 1a to 1d in the initial state have a higher charging ability than the photosensitive drums 1a to 1d with a thin film thickness of the photosensitive layer 111 and are more easily affected by the AC component of the developing bias. As a result, unevenness in the surface potential is likely to occur in the photosensitive drums (image carriers) 1a to 1d in the initial state.

[0042] In addition, the resistance value of the charging roller (charging member) 34 increases as the ambient temperature and humidity decrease. Therefore, when the applied charging bias is increased, the discharge from the charging roller 34 to the photosensitive drums 1a to 1d is likely to become uneven. As a result, unevenness is likely to occur in the surface potential of the photosensitive drums (image carriers) 1a to 1d.

[0043] In addition, as the ambient humidity around the charging roller (charging member) 34 increases, the charging roller 34 contains water and the resistance value decreases. At this time, the discharge from the charging roller 34 to the photosensitive drums 1a to 1d is likely to become uneven.

[0044] In this embodiment, the main control unit (control unit) 80 can execute an image forming operation for forming an image, an aging operation, and a determination operation. The aging operation applies a transfer bias to the primary transfer rollers (transfer members) 6a to 6d in a state where the image forming operation is stopped, and supplies a transfer current to the photosensitive drums (image carriers) 1a to 1d. The determination operation is executed before the execution of the aging operation, and determines the charging ability of the photosensitive drums (image carriers) 1a to 1d.

[0045] For example, the main control unit (control unit) 80 recognizes the cumulative rotation numbers of the photosensitive drums (image carriers) 1a to 1d, and determines the charging ability of the photosensitive drums (image carriers) 1a to 1d based on the cumulative rotation numbers of the photosensitive drums (image carriers) 1a to 1d when executing the determination operation. As the cumulative rotation numbers of the photosensitive drums (image carriers) 1a to 1d increase, the photosensitive drums (image carriers) 1a to 1d wear (film collapse), the film thickness becomes thinner, and the charging ability decreases. Thereby, the charging ability of the photosensitive drums (image carriers) 1a to 1d can be accurately determined. Note that the cumulative rotation numbers of the photosensitive drums 1a to 1d can be calculated based on, for example, the cumulative number of image formations by the image forming units Pa to Pd.

[0046] Also, the determination of the charging ability may be performed by a method other than being determined based on the cumulative rotation numbers of the photosensitive drums (image carriers) 1a to 1d. For example, when executing the determination operation, a charging device may be applied to the photosensitive drums (image carriers) 1a to 1d, and the charging ability of the photosensitive drums (image carriers) 1a to 1d may be determined based on the relationship between the supplied charging current and the surface potential. At this time, as the rising rate of the surface potential increases with the increase in the charging current, the charging ability also increases (see FIG. 3).

[0047] By executing the aging operation and supplying a transfer current to the photosensitive drums (image carriers) 1a to 1d, the charging ability of the photosensitive drums (image carriers) 1a to 1d can be reduced. Therefore, the photosensitive drums 1a to 1d are less likely to be affected by the AC component of the developing bias, and the occurrence of density unevenness (stain image) can be suppressed. Thereby, the occurrence of density unevenness can be suppressed by executing the aging operation without increasing the number of parts.

[0048] At this time, the conditions for the aging operation are set based on the determination results of the determination operation. For example, the application time of the transfer bias in the aging operation is set longer as the charging ability of the photosensitive drums (image carriers) 1a to 1d determined in the determination operation increases. If the application time of the transfer bias is too long, image defects due to fogging and the like occur. On the other hand, if the application time of the transfer bias is too short, image defects due to image unevenness occur. Therefore, the occurrence of image defects can be suppressed by setting the optimal application time of the transfer bias based on the determination results of the determination operation.

[0049] The transfer bias in the aging operation may be set to a larger value as the charging ability of the photosensitive drums (image carriers) 1a to 1d determined in the determination operation increases. By setting the transfer bias to a larger value, the charging ability can be reduced in a short period of time. This allows the application time of the transfer bias in the aging operation to be shortened.

[0050] Furthermore, during the aging operation, a charging bias is applied to the charging roller (charging member) 34 to charge the photosensitive drums (image carriers) 1a to 1d. At this time, the charging transfer bias in the aging operation may be set to be smaller as the charging ability of the photosensitive drums (image carriers) 1a to 1d determined in the determining operation becomes higher.

[0051] By setting the surface potential of the photosensitive drums (image carriers) 1a to 1d low, the charging ability can be reduced in a short time, which further shortens the application time of the transfer bias during the aging operation.

[0052] Furthermore, when the aging operation is performed, it is not necessary to apply a charging bias to the charging roller (charging member) 34. When the surface potential of the photosensitive drums (image carriers) 1a to 1d is set to zero, the charging ability can be reduced in a shorter time.

[0053] As described above, image defects are particularly likely to occur when the charging roller 34 is in a low-temperature, low-humidity environment or a high-humidity environment.

[0054] Therefore, the main control unit (control unit) 80 may execute the aging operation only when it is determined based on the detection result of the detection sensor 48 that the charging roller 34 is in a low-temperature and low-humidity environment or a high-humidity environment. Thereby, unnecessary determination operations and execution of the aging operation can be omitted, and the start of the image forming operation can be accelerated. Note that the low-temperature and low-humidity environment is, for example, an environment where the temperature is 8°C or higher and 23°C or lower and the relative humidity is 5% or higher and 15% or lower. Also, the high-humidity environment is, for example, an environment where the relative humidity is 70% or higher.

[0055] FIG. 3 is a flowchart showing an example of an image forming operation in the image forming apparatus 100. In step S1, the main control unit (control unit) 80 determines whether the periphery of the charging roller 34 is in a low-temperature and low-humidity environment or a high-humidity environment based on the detection result of the detection sensor 48. If it is determined that it is not in a low-temperature and low-humidity environment or a high-humidity environment, the process proceeds to step S5 and a normal image forming operation is executed. On the other hand, if it is determined that it is in a low-temperature and low-humidity environment or a high-humidity environment, the process proceeds to step S2.

[0056] In step S2, the main control unit (control unit) 80 determines whether an aging operation has been executed on the photosensitive drums 1a to 1d in the past. If the aging operation has been executed in the past, the process proceeds to step S5 and a normal image forming operation is executed. Also, if the aging operation has not been executed in the past, the process proceeds to step S3. Note that even if any of the photosensitive drums 1a to 1d has been replaced and the aging operation has not been executed, the process proceeds to step S3.

[0057] In step S3, a determination operation is executed to determine the charging ability of the photosensitive drums 1a to 1d. The charging ability of the photosensitive drums 1a to 1d is determined based on, for example, the cumulative rotation number of the photosensitive drums (image carriers) 1a to 1d. When the determination of the charging ability is completed, the process proceeds to step S4.

[0058] In step S4, an aging operation is executed, and a transfer bias is applied to the primary transfer rollers (transfer members) 6a to 6d. As a result, a transfer current is supplied to the photoreceptor drums (image carriers) 1a to 1d, and the charging ability can be reduced. At this time, a charging bias may be applied to charge the photoreceptor drums (image carriers) 1a to 1d. Further, the application time of the transfer device and the application voltage of the transfer device are set based on the charging ability of the photoreceptor drums (image carriers) 1a to 1d determined in step S3.

[0059] When the aging operation ends, the process proceeds to step S5, and a normal image forming operation is executed. In the normal image forming operation, the photoreceptor drums 1a to 1d are less affected by the AC component of the developing bias, and the occurrence of density unevenness (stain image) is suppressed.

[0060] Next, the effects of the present invention will be specifically described using a plurality of embodiments. In the following evaluation, the relationship between the surface potential V0 of the photoreceptor drum (image carrier) 1a and the occurrence of image defects was evaluated. In the following evaluation, the ambient temperature around the charging roller 34 was 28°C, and the relative humidity (RH) was 80%.

[0061] FIG. 4 is a graph showing the charging ability (V / μA) from the relationship between the charging current Ia (μA) and the surface potential V0 (V).

[0062] As shown in FIG. 4, the rate of increase in the surface potential with respect to the charging current Ia supplied to the photoreceptor drum 1a is higher for the photoreceptor drum 1a according to Example 1 than for the photoreceptor drum 1a according to Example 2. Thus, it was found that the charging ability (V / μA), which indicates the ease of charging, is higher for the photoreceptor drum according to Example 1 than for the photoreceptor drum according to the example. Therefore, by calculating the rate of increase in the surface potential with respect to the charging current Ia supplied to the photoreceptor drum 1a, the charging ability (V / μA) of the photoreceptor drum 1a can be accurately determined.

[0063] FIG. 5 is a graph showing the relationship between the charging ability (V / μA) of the photoreceptor drum 1a after the aging operation and the operation time (sec) of the aging operation. The density unevenness (ΔE) is calculated from the density difference between the half-image and the fog image formed in the image adjustment pattern by measuring the density of the image adjustment pattern (toner image with half density) printed on the sheet S with a fluorescence spectroscopic densitometer (FD-5 manufactured by Konica Minolta).

[0064] In the aging operation according to Example 3, a transfer current Ia of -10 (μA) was supplied to the photoreceptor drum 1a. In the aging operations according to Example 4 and Example 5, a transfer current Ia of -25 (μA) was supplied to the photoreceptor drum 1a.

[0065] Also, in the aging operations according to Example 3 and Example 4, the surface potential V0 of the photoreceptor drum 1a was set to 470 (V). Also, in the aging operation according to Example 5, the surface potential V0 of the photoreceptor drum 1a was set to 0 (V).

[0066] As shown in FIG. 5, it was found that the charging ability (V / μA) decreases as the application time (aging time) of the transfer bias in the aging operation is lengthened. Also, when comparing Example 3 and Example 4, it was found that the charging ability (V / μA) decreases by increasing the absolute value of the transfer current Ia. Also, when comparing Example 4 and Example 5, it was found that the charging ability (V / μA) decreases by lowering the surface potential V0.

[0067] FIG. 6 is a table summarizing the charging ability of the photoreceptor drum 1a, the conditions of the aging operation, and the presence or absence of image defects. The photoreceptor drum 1a according to Examples 6 to 8 had a film thickness of the light-emitting layer 111 of 40 (μm) and a charging ability (V / μA) of 12.5. The photoreceptor drum 1a according to Examples 9 to 11 had a film thickness of the light-emitting layer 111 of 38 (μm) and a charging ability (V / μA) of 11.5.

[0068] In the aging operations according to Examples 6 and 9, a transfer current Ia of -10 (μA) was supplied to the photosensitive drum 1a. In the aging operations according to Examples 7, 8, 10, and 11, a transfer current Ia of -25 (μA) was supplied to the photosensitive drum 1a.

[0069] In the aging operations according to Examples 6, 7, 9, and 10, the surface potential V0 of the photosensitive drum 1a was set to 470 (V). In the aging operations according to Examples 8 and 11, the surface potential V0 of the photosensitive drum 1a was set to 0 (V).

[0070] As shown in Figure 6, if the application time of the transfer bias in the aging operation (aging time) is too short, image defects due to stains will occur, and if it is too long, image defects due to fogging will occur. Therefore, by setting the conditions for the aging operation based on the charging capacity (V / μA) of the photosensitive drum 1a, it is possible to prevent image defects from occurring.

[0071] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the invention. For example, in the above embodiment, a color printer as shown in Fig. 1 was used as an example of image forming apparatus 100, but the image forming apparatus is not limited to a color printer, and may be other image forming apparatuses such as monochrome and color copiers, digital multifunction peripherals, facsimiles, etc. [Industrial Applicability]

[0072] The present invention can be used in an image forming apparatus equipped with a charging roller. [Explanation of symbols]

[0073] 1a to 1d: photosensitive drum (image bearing member) 2a~2d Charging device 3a~3d developing device 5 Exposure equipment 6a to 6d Primary transfer roller (transfer member) 7a~7d Cleaning device 8 Intermediate transfer belt 9 Secondary transfer roller 10 driven roller 11 Drive roller 12a Paper feed roller 12b Registration Roller Pair 13 Fixing section 13a Fuser roller pair 14 Branch 15 Discharge Roller Pair 16 Paper cassette 17 Output tray 18-sided conveyor 19 Belt cleaner 31 Developing roller (developer carrier) 32 Cleaning blade 33 Rubbing roller 34 Charging roller (charging member) 35 Conveying spiral 40 Image density sensor 43 Development bias power supply 43a AC constant voltage power supply 43b, 45b DC constant voltage power supply 45 Charging bias power supply 46 Current detection section 47 Transfer bias power supply 50 Voltage control section 70 Memory section 80 Main control unit 90 LCD display section 91 Transmitter / Receiver 100 Image forming device 111 Photosensitive layer

Claims

1. An image carrier having a photosensitive layer formed on its surface, A charging device having a charging member disposed opposite to the image carrier for charging the image carrier, An exposure device for forming an electrostatic latent image by exposing the image carrier charged by the charging device, A developing device having a developer carrier disposed opposite to the image carrier for carrying a developer, and for forming a toner image by attaching toner to the electrostatic latent image formed on the image carrier, An image forming unit including the above, A transfer member disposed opposite to the image carrier, to which a predetermined transfer voltage is applied to transfer the toner image formed on the image carrier to a transfer medium, A developing bias power source for applying a developing bias obtained by superimposing an AC voltage on a DC voltage to the developer carrier, A charging bias power source for applying a charging bias including a DC voltage to the charging member, A transfer bias power source for applying a transfer bias including a DC voltage to the transfer member, In an image forming apparatus including the image forming unit, the developing bias power source, the charging bias power source, and the transfer bias power source, and a control unit for controlling them, The control unit, An image forming operation for forming an image, An aging operation for applying the transfer bias to the transfer member in a state where the image forming operation is stopped to supply a transfer current to the image carrier, A determination operation that is executed before the execution of the aging operation to determine the charging ability of the image carrier, and is executable, The control unit, An image forming apparatus that sets conditions of the aging operation based on a determination result of the determination operation.

2. The control unit, An image forming apparatus that sets a longer application time of the transfer bias in the aging operation as the charging ability of the image carrier determined in the determination operation increases.

3. The control unit, The image forming apparatus according to claim 1 or claim 2, wherein the transfer bias in the aging operation is set larger as the charging ability of the image carrier determined in the determination operation increases.

4. During the execution of the aging operation, the charging bias is applied to the charging member to charge the image carrier, The control unit, The image forming apparatus according to claim 1 or claim 2, wherein the charging bias is set smaller as the charging ability of the image carrier determined in the determination operation increases.

5. The control unit, The image forming apparatus according to claim 1 or claim 2, wherein when the charging ability of the image carrier determined in the determination operation is higher than a predetermined threshold value, the charging bias is not applied to the charging member.

6. further comprising a detection sensor for detecting the temperature and humidity around the charging member, The control unit executes the aging operation when it determines that the environment is a low temperature and low humidity environment or a high humidity environment based on the detection result of the detection sensor. The image forming apparatus according to claim 1 or claim 2.

7. The control unit recognizes the cumulative rotation number of the image carrier, The image forming apparatus according to claim 1 or claim 2, wherein the charging ability of the image carrier is determined based on the cumulative rotation number of the image carrier when the determination operation is executed.

8. The charging bias consists only of a DC voltage. The image forming apparatus according to claim 1 or claim 2.

9. The photosensitive layer is a positive charging single layer type, and has a film thickness of 37 μm or more in an unused state. The image forming apparatus according to claim 1 or claim 2.

Images