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 controls an image forming unit, a developing bias power supply, an electrification bias power supply, and a transfer bias power supply. The control unit can execute an image forming operation to form an image and an aging 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.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Conventional image forming apparatuses include an image forming unit, a developing bias power source, a charging bias power source, 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 to the image carrier and has a charging member for charging 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 to the image carrier and has a developer carrier for carrying a developer, and attaches toner to the electrostatic latent image formed on the image carrier to form a toner image.

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

[0004] In the image forming apparatus of Patent Document 1, the casing that houses the charging member is covered with a metal shield member and is in close contact with the shield member. Further, in the image forming apparatus of Patent Document 2, the developing bias power source is covered and hidden from the charging member by a conductive member.

[0005] Thereby, the influence of the electric field of the developing bias applied by the developing bias power source on the charging bias applied by the charging bias power source can be suppressed. Therefore, it is possible to reduce the occurrence of unevenness in the surface potential of the image carrier and suppress the occurrence of density unevenness (stained image).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

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 parts 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 configuration of the present invention is an image forming apparatus including an image forming unit, a transfer member, a developing bias power source, a charging bias power source, a transfer bias power source, 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 to the image carrier and has a charging member for charging 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 to the image carrier and has a developer carrier for carrying a 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 to the image carrier, and a predetermined transfer voltage is applied to transfer the toner image formed on the image carrier to a transfer medium. The developing bias power source applies a developing bias obtained by superimposing an AC voltage on a DC voltage to the developer carrier. The charging bias power source applies a charging bias including a DC voltage to the charging member. The transfer bias power source applies a transfer bias including a DC voltage to the transfer member. The control unit controls the image forming unit, the developing bias power source, the charging bias power source, and the transfer bias power source. The control unit is capable of executing an image forming operation for forming an image and an aging operation. The aging operation supplies a transfer current to the image carrier by applying a transfer bias to the transfer member in a state where the image forming operation is stopped.

Effects of the Invention

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

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 100 according to the first embodiment of the present invention, and FIG. 2 is a partial enlarged view around the image forming unit Pa including the control path of the image forming apparatus 100. Note that the configurations of the image forming units Pb to Pd and the control paths of the charging devices 2a to 2d are the same as those of the image forming unit Pa and the control path of the charging device 2a, and thus the 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 developing bias power source 43, a charging bias power source 45, a transfer bias power source 47, current detectors 43 and 46, a main control unit (control unit) 80, and a detection sensor 48.

[0014] In the image forming apparatus 100 (here, a color printer) main body, 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 by the respective processes of charging, exposure, development, and transfer.

[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 respective colors, charging devices 2a to 2d, an exposure device 5, and developing devices 3a to 3d. Further, an intermediate transfer belt (transfer body) 8 that rotates in the counterclockwise direction in FIG. 1 by driving means (not shown) is provided adjacent to each of the image forming units Pa to Pd.

[0016] The primary transfer rollers (transfer members) 6a to 6d are disposed 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 respective colors formed on the photosensitive drums (image carriers) 1a to 1d to the intermediate transfer belt (transfer body) 8. Thereby, the toner images formed on the photosensitive drums 1a to 1d are sequentially primary transferred and superimposed on 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 onto 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 resist roller pair 12b.

[0018] A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt having no seam is mainly used. Also, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged on the downstream side of the secondary transfer roller 9.

[0019] The photosensitive drums (image carriers) 1a to 1d have a photosensitive layer 111 formed on their surfaces (see FIG. 2). In the present 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 depositing amorphous silicon, which is a positively chargeable photoconductor. That is, the photosensitive layer 111 is of a single-layer type for static charge. The photosensitive layer 111 preferably has a film thickness of 37 μm or more in an unused state. By increasing the film thickness, the durability of the photosensitive drums 1a to 1d against wear is improved.

[0020] The charging devices 2a to 2d each have a charging roller (charging member) 34. Each charging roller 34 is arranged to face the photosensitive drums (image carriers) 1a to 1d and charges the photosensitive drums (image carriers) 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 the present embodiment, the charging roller 34 is in contact with each of the photosensitive drums 1a to 1d. Note that the charging roller 34 may be non-contact with each of the photosensitive drums 1a to 1d.

[0021] The exposure device 5 forms an electrostatic latent image by exposing the photosensitive drums (image carriers) 1a to 1d charged by the charging devices 2a to 2d.

[0022] The developing devices 3a to 3d are arranged to face the photosensitive drums (image carriers) 1a to 1d and have developing rollers (developer carriers) 31. The developing devices 3a to 3d apply a predetermined developing bias to the developing rollers (developer carriers) 31 to attach toner to the electrostatic latent images formed on the photosensitive drums (image carriers) 1a to 1d, thereby forming toner images. The developing rollers (developer carriers) 31 are arranged to face the photosensitive drums (image carriers) 1a to 1d and carry 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 charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data to form electrostatic latent images corresponding to the image data on the respective photosensitive drums 1a to 1d.

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

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

[0026] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream driving roller 11. When the intermediate transfer belt 8 starts to rotate counterclockwise as the driving roller 11 rotates by a driving motor (not shown), the sheet S is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the 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 conveyed to the fixing unit 13.

[0027] The sheet S conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the sheet S, and a predetermined full-color image is formed. The sheet S on which the full-color image has been formed has its conveyance direction sorted by the branching portion 14 branched in a plurality of directions, and is then discharged to the discharge tray 17 by the discharge roller pair 15 (either as it is or after being sent to the duplex conveyance path 18 and having images formed on both sides).

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

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

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

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

[0032] In this embodiment, during image formation, the charging bias power source 45 applies a charging bias consisting only of a DC voltage from the DC constant voltage power source 45b to the charging roller (charging member) 34. By configuring the charging bias with only a DC voltage, wear of the photosensitive layer 111 can be reduced, the amount of ozone generation can be reduced, and charging noise can be reduced.

[0033] The transfer bias power source 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 transfer bias power source 47 includes a DC constant voltage power source 47b. The DC constant voltage power source 47b outputs a DC voltage obtained by rectifying a sine wave AC voltage generated from a low-voltage DC voltage modulated in a pulse shape using a step-up transformer.

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

[0035] The cleaning device 7a includes a cleaning blade 32 that removes residual toner on the surface of the photoreceptor drum 1a, a rubbing roller 33 that removes residual toner on the surface of the photoreceptor drum 1a and rubs and polishes the surface of the photoreceptor drum 1a, and a conveying spiral 35 that discharges the residual toner removed from the photoreceptor 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 composed of a CPU or the like. The main control unit 80 is connected to a storage unit 70 composed of a ROM, a RAM, or the like. The main control unit 80 controls each part of the image forming apparatus 100 (charging devices 2a to 2d, developing devices 3a to 3d, exposure device 5, primary transfer rollers 6a to 6d, cleaning devices 7a to 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 control programs and control data stored in the storage unit 70.

[0037] The voltage control unit 50 controls a developing bias power supply 43 that applies a developing bias to the developing 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. Note that the voltage control unit 50 may be composed of a control program stored in the storage unit 70.

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

[0039] As described above, the charging bias applied by the charging bias power source 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 image) 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, the photosensitive drums are more easily affected by the AC component of the developing bias. As a result, density unevenness is more likely to occur. The charging ability of the photosensitive drums (image carriers) 1a to 1d is highest in the unused state.

[0041] Also, 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 non-uniform. As a result, unevenness is likely to occur in the surface potential of the photosensitive drums (image carriers) 1a to 1d.

[0042] In addition, as the ambient humidity around the charging roller (charging member) 34 increases, the charging roller 34 absorbs water and its resistance value decreases. At this time, the discharge from the charging roller 34 to the photosensitive drums 1a to 1d is likely to become non-uniform.

[0043] In this embodiment, the main control unit (control unit) 80 can execute an image forming operation for forming an image and an aging operation. In the aging operation, a transfer bias is applied to the primary transfer rollers (transfer members) 6a to 6d in a state where the image forming operation is stopped, and a transfer current is supplied to the photosensitive drums (image carriers) 1a to 1d.

[0044] By performing an aging operation to supply a transfer current to the photoreceptor drums (image carriers) 1a to 1d, the charging ability of the photoreceptor drums (image carriers) 1a to 1d can be reduced. Therefore, the photoreceptor 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 images) can be suppressed. As a result, the occurrence of density unevenness can be suppressed by performing the aging operation without increasing the number of components.

[0045] Also, when performing the aging operation, a charging bias is applied to the charging roller (charging member) 34 to charge the photoreceptor drums (image carriers) 1a to 1d. The charging bias applied at this time is smaller than the charging bias applied during the execution of the image forming operation.

[0046] The photoreceptor drums (image carriers) 1a to 1d can reduce their charging ability in a shorter time when the surface potential is set to be small. Thereby, the application time of the transfer bias in the aging operation can be shortened. Also, during the execution of the aging operation, it is not necessary to apply a charging bias to the charging roller (charging member) 34. When the surface potential of the photoreceptor drums (image carriers) 1a to 1d is set to zero, the charging ability can be reduced in an even shorter time.

[0047] Image defects are particularly likely to occur when the charging roller 34 is in a low-temperature and low-humidity environment or a high-humidity environment as described above.

[0048] Therefore, the main control unit (control unit) 80 may perform 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 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%. Also, the high-humidity environment is, for example, an environment where the relative humidity is 70% or higher.

[0049] 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 S4 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.

[0050] In step S2, the main control unit (control unit) 80 determines whether an aging operation has been performed on the photosensitive drums 1a to 1d in the past. If the aging operation has been performed in the past, the process proceeds to step S4 and a normal image forming operation is executed. Also, if the aging operation has not been performed in the past, the process proceeds to step S3. Note that if any of the photosensitive drums 1a to 1d has been replaced and the aging operation has not been performed, the process proceeds to step S3.

[0051] In step S3, 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 can be supplied to the photosensitive drums (image carriers) 1a to 1d to reduce the charging ability. When the aging operation is completed, the process proceeds to step S4 and a normal image forming operation is executed. In the normal image forming operation, 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 (foggy image) is suppressed.

[0052] 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 photosensitive drum (image carrier) 1a and the occurrence of image defects was evaluated. In the following evaluation, the environmental temperature around the charging roller 34 was 28°C and the relative humidity (RH) was 80%.

[0053] 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).

[0054] As shown in FIG. 4, the rate of increase in 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 ease of charging, is higher for the photoreceptor drum according to Example 1 than for the photoreceptor drum according to the Example.

[0055] 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. FIG. 6 is a graph showing the relationship between density unevenness (ΔE) 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 a half density) printed on the sheet S with a fluorescence spectroscopic densitometer (FD-5 manufactured by Konica Minolta).

[0056] 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.

[0057] 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). In a normal image forming operation, the transfer current Ia is -25 (μA), and the surface potential V0 of the photoreceptor drum 1a is set to 470 (V).

[0058] As shown in FIG. 5, it was found that the charging ability (V / μA) decreases as the time of the aging operation is lengthened. Also, when comparing Example 3 and Example 4, it was found that increasing the absolute value of the transfer current Ia causes the charging ability (V / μA) to decrease. Also, when comparing Example 4 and Example 5, it was found that decreasing the surface potential V0 causes the charging ability (V / μA) to decrease.

[0059] As shown in FIG. 6, it is a graph showing the relationship between density unevenness (ΔE) and the operation time (sec) of the aging operation. It was found that the density unevenness (ΔE) was reduced as the time of the aging operation was lengthened. Also, when comparing Example 3 and Example 4, it was found that the density unevenness (ΔE) was reduced rather than increasing the absolute value of the transfer current Ia.

[0060] Also, when comparing Example 4 and Example 5, it was found that the density unevenness (ΔE) was reduced by lowering the surface potential V0. Thereby, it was found that the density unevenness (ΔE) can be reduced by making the charging bias applied during the execution of the aging operation smaller than the charging bias applied during the execution of the image forming operation and lowering the surface potential.

[0061] Also, when the allowable value of the density unevenness (ΔE) is set to 2.00 or less, normal printing becomes possible by the 5-minute aging operation in Example 3. Also, in Example 4, normal printing becomes possible by the 2-minute aging operation. It was found that normal printing becomes possible by the 1-minute aging operation in Example 5.

[0062] Thereby, it was found that the time of the aging operation can be shortened by lowering the surface potential V0 of the charged photosensitive drum 1a and supplying a large transfer current to the photosensitive drum 1a.

[0063] 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, the color printer as shown in FIG. 1 has been described as an example of the image forming apparatus 100, but it is not limited to a color printer, and other image forming apparatuses such as monochrome and color copiers, digital multifunction machines, and facsimiles may also be used.

Industrial Applicability

[0064] The present invention can be used in an image forming apparatus including a charging roller.

Description of Symbols

[0065] 1a to 1d Photoconductor drum (image carrier member) 2a to 2d Charging device 3a to 3d Developing device 5 Exposure device 6a to 6d Primary transfer roller (transfer member) 7a to 7d Cleaning device 8 Intermediate transfer belt 9 Secondary transfer roller 10 Driven roller 11 Driving roller 12a Paper feed roller 12b Registration roller pair 13 Fixing unit 13a Fixing roller pair 14 Branching section 15 Discharge roller pair 16 Paper cassette 17 Discharge tray 18 Surface conveyance path 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 Developing 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 section 90 Liquid crystal display section 91 Transmission / reception section 100 Image forming apparatus 111 Photosensitive layer

Claims

1. an image carrier having a photosensitive layer formed on its surface; a charging device disposed opposite the image carrier and having a charging member for charging the image carrier; an exposure device that exposes the image carrier charged by the charging device to light to form an electrostatic latent image; a developing device disposed opposite the image carrier, the developing device having a developer carrier that carries a developer, and that forms a toner image by attaching toner to the electrostatic latent image formed on the image carrier; an image forming unit including: a transfer member disposed opposite the image carrier and configured to transfer the toner image formed on the image carrier to a transfer target by application of a predetermined transfer voltage; a developing bias power supply that applies a developing bias, which is a DC voltage superimposed on an AC voltage, to the developer carrier; a charging bias power supply that applies a charging bias including a DC voltage to the charging member; a transfer bias power supply that applies a transfer bias including a DC voltage to the transfer member; an image forming apparatus including the image forming unit, a control unit that controls the developing bias power supply, the charging bias power supply, and the transfer bias power supply; The control unit an image forming operation for forming an image; The image forming apparatus is capable of performing an aging operation in which the transfer bias is applied to the transfer member and a transfer current is supplied to the image carrier while the image forming operation is stopped.

2. During the aging operation, the charging bias is applied to the charging member to charge the image carrier; 2. The image forming apparatus according to claim 1, wherein the charging bias applied during the aging operation is smaller than the charging bias applied during the image forming operation.

3. 2. The image forming apparatus according to claim 1, wherein the charging bias is not applied to the charging member during the aging operation.

4. a detection sensor for detecting the temperature and humidity around the charging member; 3. The image forming apparatus according to claim 1, wherein the control unit executes the aging operation when it determines that the image forming apparatus is in a low-temperature, low-humidity environment or a high-humidity environment based on the detection result of the detection sensor.

5. 3. The image forming apparatus according to claim 1, wherein the charging bias is composed of only a DC voltage.

6. 3. The image forming apparatus according to claim 1, wherein the photosensitive layer is a positively charged single layer type and has a thickness of 37 [mu]m or more in an unused state.

Images