Image forming apparatus

Abstract

To provide an image forming apparatus that can improve convenience, while preventing the occurrence of an image defect.SOLUTION: A control unit can execute an image forming mode for controlling an electrification voltage on the basis of the relationship between an electrification current and the surface potential of an image carrier to adjust the surface potential and performing image formation, and a correction mode for correcting the relationship between the electrification current and the surface potential. During the execution of the correction mode, the control unit calculates the surface potential of the image carrier on the basis of a developing voltage to be applied and a developing current detected by a developing current detection unit, and corrects the relationship between the electrification current and the surface potential on the basis of the calculated surface potential.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine thereof, which is equipped with an image carrier. [Background technology]

[0002] A conventional image forming apparatus includes an image forming unit, a developing voltage power supply, a charging voltage power supply, a developing current detection unit, a charging current detection unit, 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 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. The developing voltage power supply applies a developing voltage to the developer carrier. The charging voltage power supply applies a charging voltage containing at least a DC component to the charging member. The developing current detection unit detects the developing current flowing between the developer carrier and the image carrier. The charging current detection unit detects the charging current flowing between the charging member and the image carrier. The control unit controls the image forming unit, the developing voltage power supply, and the charging voltage power supply.

[0003] The image forming apparatus disclosed in Patent Document 1 can calculate the surface potential of the image carrier based on the applied developing voltage and the developing current detected by the developing current detection unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-157163 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, if the surface potential is corrected based on the calculated surface potential when the image formation mode is executed, the waiting time for the user may become longer, which may reduce convenience.

[0006] SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus that can improve convenience while suppressing the occurrence of image defects. [Means for solving the problem]

[0007] In order to achieve the above object, a first aspect of the present invention is an image forming apparatus including an image forming unit, a developing voltage power supply, a charging voltage power supply, a developing current detection unit, a charging current detection unit, 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 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. The developing voltage power supply applies a developing voltage to the developer carrier. The charging voltage power supply applies a charging voltage containing at least a DC component to the charging member. The developing current detection unit detects the developing current flowing between the developer carrier and the image carrier. The charging current detection unit detects the charging current flowing between the charging member and the image carrier. The control unit controls the image forming unit, the developing voltage power supply, and the charging voltage power supply. The control unit can execute an image formation mode in which an image is formed by controlling the charging voltage based on the relationship between the charging current and the surface potential of the image carrier to adjust the surface potential, and a correction mode in which the relationship between the charging current and the surface potential is corrected. When executing the correction mode, the control unit calculates the surface potential of the image carrier based on the applied developing voltage and the developing current detected by the developing current detection unit, and corrects the relationship between the charging current and the surface potential based on the calculated surface potential. [Effects of the Invention]

[0008] According to the first aspect of the present invention, it is possible to provide an image forming apparatus that can improve convenience while suppressing the occurrence of image defects. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a side cross-sectional view showing the internal configuration of an image forming apparatus 100 according to a first embodiment of the present invention. [Figure 2] 1 is a side cross-sectional view of a developing device 3a mounted in an image forming apparatus 100 according to a first embodiment of the present invention; [Figure 3] FIG. 1 is a partially enlarged view of the periphery of an image forming unit Pa including a control path of an image forming apparatus 100 according to a first embodiment of the present invention; [Figure 4] 1 is a flowchart showing an example of execution of an image forming mode in the image forming apparatus 100 according to the first embodiment of the present invention; [Figure 5] Graph showing the relationship between charging current and surface potential of photosensitive drum 1a [Figure 6] Graph showing the relationship between the DC voltage and the DC current [Figure 7] Graph showing the relationship between the DC voltage and the DC current [Figure 8] Graph showing the relationship between the charging current after correction and the surface potential of the photosensitive drum 1a [Figure 9] 10 is a flowchart showing an example of execution of an image forming mode in the image forming apparatus 100 according to the second embodiment of the present invention. [Figure 10] Graph showing the relationship between charging current and DC developing current [Figure 11] Table showing evaluation results for image defects DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a side cross-sectional view showing the internal structure of an image forming apparatus 100 according to a first embodiment of the present invention.

[0011] The image forming apparatus 100 includes image forming units Pa to Pd, a development voltage power supply 43, a charging voltage power supply 45, a transfer voltage power supply 47, a development current detection unit 44, a charging current detection unit 46, a main control unit (control unit) 80, an image density sensor (image density detection device) 40, and a temperature detection sensor (temperature measurement unit) 41.

[0012] Within the main body of image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in this order from the upstream side in the transport direction (left side in FIG. 1). Image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposure, development, and transfer, respectively.

[0013] The image forming units Pa to Pd each 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. Adjacent to each of the image forming units Pa to Pd is an intermediate transfer belt (transfer recipient) 8 that rotates counterclockwise in FIG. 1 by a driving means (not shown).

[0014] Primary transfer rollers (transfer members) 6a to 6d are disposed opposite 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 onto intermediate transfer belt (transfer recipient) 8. As a result, the toner images formed on the photosensitive drums 1a to 1d are sequentially primarily transferred and superimposed onto the intermediate transfer belt 8, which moves while contacting each of the photosensitive drums 1a to 1d.

[0015] The toner image that has been primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a sheet S, which is an example of a recording medium, by a secondary transfer roller 9. The sheet S onto which the toner image is secondarily transferred is stored in a paper cassette 16 that is located at the bottom of the main body of the image forming apparatus 100. The sheet S is transported to a nip portion between the secondary transfer roller 9 and a drive roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a pair of registration rollers 12b.

[0016] 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.

[0017] The photosensitive drums (image carriers) 1a to 1d have a photosensitive layer 111 formed on their surfaces (see FIG. 3). 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, which is a positively chargeable photoconductor. In other words, the photosensitive layer 111 is a positively chargeable single-layer type. It is preferable that the photosensitive layer 111 has a film thickness of approximately 20 μm when unused.

[0018] The charging devices 2a to 2d each have a charging roller (charging member) 34 that charges the photosensitive drums (image carriers) 1a to 1d. Each charging roller 34 is disposed opposite 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 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.

[0019] 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.

[0020] The developing devices 3a to 3d each have a developing roller (developer carrier) 31. The developing roller (developer carrier) 31 is disposed opposite the photosensitive drum (image carrier) 1a to 1d and carries a two-component developer containing a magnetic carrier and toner. The developing devices 3a to 3d apply a predetermined developing voltage to the developing roller (developer carrier) 31 to cause the toner to adhere to the electrostatic latent image formed on the photosensitive drum (image carrier) 1a to 1d, thereby forming a toner image.

[0021] 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.

[0022] The developing devices 3a to 3d are filled with a predetermined amount of two-component developer containing yellow, cyan, magenta, and black toner, respectively. 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.

[0023] 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 yellow, cyan, magenta, 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.

[0024] 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.

[0025] 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.

[0026] 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 is generally an optical sensor equipped with a light-emitting element such as an LED and a light-receiving element such as a photodiode. When measuring the amount of toner adhesion on the intermediate transfer belt 8, the light-emitting element irradiates each reference image formed on the intermediate transfer belt 8 with measurement light, and the measurement light is reflected by the toner and the belt surface and enters the light-receiving element.

[0027] The light reflected from the toner and belt surface includes specularly reflected light and diffusely reflected light. This specularly reflected light and diffusely reflected light are separated by a polarizing separation prism and then incident on separate light receiving elements. Each light receiving element photoelectrically converts the received specularly reflected light and diffusely reflected light and outputs an output signal to the main control unit 80 (see Figure 2). The density of the toner image is then detected from the change in the characteristics of the output signals of the specularly reflected light and diffusely reflected light.

[0028] That is, an image density sensor (density detection device) 40 detects the density of the toner image formed by the developing devices 3a to 3d and transferred onto the intermediate transfer belt (transfer receiving body) 8.

[0029] 2 is a side cross-sectional view of the developing device 3a mounted on the image forming apparatus 100. In the following description, the developing device 3a arranged in the image forming section Pa in FIG. 1 will be exemplified, but the configurations of the developing devices 3b to 3d arranged in the image forming sections Pb to Pd are basically the same, so description thereof will be omitted.

[0030] 2, the developing device 3a includes a developing container 20 that contains a two-component developer (hereinafter simply referred to as developer) containing a magnetic carrier and toner, and the developing container 20 is partitioned by a partition wall 20a into an agitation conveying chamber 21 and a supply conveying chamber 22. The agitation conveying chamber 21 and the supply conveying chamber 22 are rotatably provided with an agitation conveying screw 25a and a supply conveying screw 25b, respectively, for mixing and agitating the toner supplied from the toner container 4a (see FIG. 1) with the magnetic carrier and charging the toner.

[0031] The developer is then transported in the axial direction (the direction perpendicular to the paper surface of FIG. 2) while being agitated by the agitation transport screw 25a and the supply transport screw 25b, and circulates between the agitation transport chamber 21 and the supply transport chamber 22 via developer passages (not shown) formed at both ends of the partition wall 20a. That is, a developer circulation path is formed in the developing container 20 by the agitation transport chamber 21, the supply transport chamber 22, and the developer passages.

[0032] The developing container 20 extends diagonally upward to the right in Figure 2, and a developing roller (developer carrier) 31 is disposed diagonally above the right of the supply / conveyor screw 25b within the developing container 20. A portion of the outer circumferential surface of the developing roller 31 is exposed from the opening 20b of the developing container 20 and faces the photosensitive drum 1a. The developing roller 31 rotates counterclockwise in Figure 2.

[0033] 2, and a magnet (not shown) with multiple magnetic poles fixed inside the developing sleeve. Note that, although a developing sleeve with a knurled surface is used here, it is also possible to use a developing sleeve with a large number of recesses (dimples) formed on the surface, a developing sleeve with a blasted surface, or a developing sleeve with a blasted surface in addition to a knurled or recessed surface, or a plated developing sleeve.

[0034] In addition, a regulating blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 31 (the direction perpendicular to the paper surface of FIG. 2). A small gap is formed between the tip of the regulating blade 27 and the surface of the developing roller 31.

[0035] 3 is a partially enlarged view of the periphery of image forming unit Pa, including the control path of developing unit 3a. In the following explanation, the configuration of image forming unit Pa and the control path of developing unit 3a will be described, but the configurations of image forming units Pb to Pd and the control paths of developing units 3b to 3d are similar, so their explanations will be omitted.

[0036] The developing voltage power supply 43 is connected to the developing roller 31. The developing voltage 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 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 the sine wave AC voltage generated from the DC voltage modulated into a pulse shape using a step-up transformer.

[0037] During image formation, the development voltage power supply 43 applies a development voltage obtained by superimposing an AC voltage Vac on a DC voltage Vdc from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b to the development roller (developer carrier) 31. By applying the development voltage to the development roller 31, the potential difference between the development roller 31 and the surface potential V0 of the photosensitive drum 1a causes toner to fly from the development roller 31 to the photosensitive drum 1a, developing the electrostatic latent image (exposed portion) on the photosensitive drum 1a. At this time, applying a development voltage obtained by superimposing an AC voltage Vac on a DC voltage Vdc to the development roller 31 makes it easier to control the developability of the toner during image formation, improving image quality. Note that, although the development voltage is obtained by superimposing an AC voltage Vac on a DC voltage Vdc in this embodiment, the DC voltage Vdc alone may be used as the development voltage.

[0038] The development current detection unit 44 detects the development current (development DC current) flowing between the development roller (developer carrier) 31 and the photosensitive drum (image carrier) 1a. Specifically, the development current detection unit 44 detects the DC component (development DC current) of the development current flowing between the development roller 31 and the photosensitive drum 1a when a development voltage is applied to the development roller (developer carrier) 31. The development current detection unit 44 also detects the DC component of the fog toner current when the development voltage applied to the development roller 31 is set to zero while the surface potential of the photosensitive drum (image carrier) 1a is zero.

[0039] In addition, in this embodiment, the developer is a two-component developer containing a magnetic carrier and a toner, and the DC component of the charging voltage applied when the surface potential of the photosensitive drum (image carrier) 1a is zero and in an uncharged state is zero is zero.

[0040] The charging voltage power supply 45 applies a charging voltage containing at least a DC component to the charging roller (charging member) 34 of the charging device 2a. In this embodiment, during image formation, the charging voltage power supply 45 applies a charging voltage obtained by superimposing an AC voltage on a DC voltage from the AC constant voltage power supply 45a and the DC constant voltage power supply 45b to the charging roller 34. By changing the charging voltage, the development potential difference V0-Vdc between the surface potential V0 of the photosensitive drum 1a and the development DC voltage Vdc (the DC component of the development voltage applied to the development roller 31) can be adjusted to a predetermined value. Note that the charging voltage applied may be a DC voltage only.

[0041] The charging current detection unit 46 detects the charging current (charging DC current) flowing between the charging roller (charging member) 34 and the photosensitive drum (image carrier) 1a. Specifically, the charging current detection unit 46 detects the DC component (charging DC current) of the charging current flowing between the charging roller (charging member) 34 and the photosensitive drum 1a when a charging voltage is applied to the charging roller (charging member) 34.

[0042] The photosensitive layer 111 of the photosensitive drum 1a is formed by vapor deposition of amorphous silicon, a positively charged photoconductor, and has a high dielectric constant. Therefore, if unevenness in the surface potential difference occurs on the photosensitive drum 1a, there is a possibility that unevenness in the image density will occur in the developed toner image. To address this issue, applying a charging voltage superimposed with an AC voltage can suppress the occurrence of uneven surface potential. Furthermore, the level of the surface potential can be controlled by the DC voltage included in the transfer voltage.

[0043] A transfer voltage 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.

[0044] 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.

[0045] 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 (such as 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, development voltage power supply 43, charging voltage power supply 45, transfer voltage power supply 47, development current detection unit 44, charging current detection unit 46, and voltage control unit 50) based on a control program and control data stored in the storage unit 70. That is, the main control unit (control unit) 80 controls the image forming units Pa-Pd, the development voltage power supply 43, and the charging voltage power supply 45.

[0046] The voltage control unit 50 controls a development voltage power supply 43 that applies a development voltage to the development roller 31, a charging voltage power supply 45 that applies a charging voltage to the charging roller 34, and a transfer voltage 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.

[0047] 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.

[0048] The temperature detection sensor 48 detects the temperatures around the photosensitive drums (image carriers) 1a to 1d.

[0049] As mentioned above, the surface potential of the photosensitive drum 1a may vary from the target value due to errors in the high-voltage board of the charging voltage power supply 45. Conventionally, it has been necessary to adjust the variation in surface potential using a dedicated jig on the production line of the image forming apparatus 100.

[0050] In this embodiment, the main control unit (control unit) 80 can execute a correction mode in addition to the normal image formation mode. By providing the correction mode in addition to the image formation mode, it is possible to reduce the waiting time for the user and improve convenience.

[0051] FIG. 4 is a flowchart showing an example of execution in image forming apparatus 100 according to this embodiment. When a user inputs an instruction to execute image formation processing, main control unit 80 executes the image formation mode (step S1). FIG. 5 is a graph showing the relationship between charging current and surface potential of photosensitive drum 1a, which is stored in advance in storage unit 70. First relational expression L1 in FIG. 5 shows the relationship between charging current and surface potential of photosensitive drum 1a. In this embodiment, first relational expression L1 is expressed as a linear function.

[0052] In the image formation mode, the charging voltage applied is controlled based on the relationship between the charging current and the surface potential of the image carrier (first relational expression L1), and the surface potential is adjusted to form an image. For example, when the surface potential V01 is set to a target value, the charging current I1 is output based on the relational expression L1.

[0053] When the job in the image formation mode is completed, it is determined whether it is time to execute the correction mode stored in the storage unit 70 (step S2). The determination of whether it is time to execute the correction mode is made, for example, based on whether the cumulative number of printed sheets since the previous execution of the correction mode is equal to or greater than a predetermined number (e.g., 50,000). By executing the correction mode after the image formation mode is completed, the user's waiting time can be reduced. The first execution of the correction mode may be performed when the power is turned on for the first time after shipment.

[0054] When the correction mode is executed, the control unit 80 calculates a plurality of different surface potentials V01, V02 and the corresponding charging currents I1, I2 based on the first relational expression L1 (see FIG. 5) used when the image formation mode is executed (step S3). Note that the first relational expression L1 is a relational expression that is set before shipping and stored in the storage unit 70, or a relational expression that is corrected when the correction mode is executed the previous time and stored in the storage unit 70.

[0055] Next, with the surface potential of the photosensitive drum (image carrier) 1a at zero, the DC component of the development voltage applied to the development roller 31 is set to zero, and the reference development DC current (reference DC current) Idcm detected by the development current detection unit 44 is measured (step S4). At this time, the reference development DC current Idcm is a fog toner current generated by the movement of toner.

[0056] Next, a charging voltage is applied to the charging roller (charging member) 34 so that the charging current detected by the charging current detection unit 46 becomes equal to the charging current I1 calculated in step S3, and then different developing voltages are applied. At this time, the developing current detection unit 44 measures the developing DC currents Idc1 and Idc2 for the DC components (developing DC voltages) Vdc1 and Vdc2 of the applied different developing voltages (step S5).

[0057] When the development DC current Idc1 corresponding to the initially applied development DC voltage Vdc1 is smaller than the reference DC current Idcm, it is preferable to apply a development DC voltage Vdc2 larger than the development DC voltage Vdc1. On the other hand, when the development DC current Idc1 corresponding to the initially applied development DC voltage Vdc1 is larger than the reference DC current Idcm, it is preferable to apply a development DC voltage Vdc2 smaller than the development DC voltage Vdc1.

[0058] Next, a second relational expression L2a is created from the applied development DC voltages Vdc1 and Vdc2 and the detected development DC currents Idc1 and Idc2 (step S6). Fig. 6 is a graph showing the relationship between the development DC voltage and the development DC current, and in this embodiment, the second relational expression L2a is expressed by a linear function.

[0059] Next, a developing DC voltage Vdcm1 that flows a developing DC current (developing current) Idcm having the same current value as the reference developing DC current Idcm measured in step S4 is calculated from the second relational expression L2a. At this time, the developing DC voltage Vdcm1 becomes the surface potential Vdcm1 of the photosensitive drum 1a corresponding to the charging current I1 (step S7).

[0060] Next, a charging voltage is applied to the charging roller (charging member) 34 so that the charging current detected by the charging current detection unit 46 becomes equal to the charging current I2 calculated in step S3, and then different developing voltages are applied. At this time, the developing current detection unit 44 measures the developing DC currents Idc3 and Idc4 for the DC components (developing DC voltages) Vdc3 and Vdc4 of the applied different developing voltages (step S8). The developing DC voltages Vdc3 and Vdc4 are applied in the same manner as in step S5.

[0061] Next, a second relational expression L2b is created from the applied development DC voltages Vdc3 and Vdc4 and the detected development DC currents Idc3 and Idc4 (step S9). Fig. 7 is a graph showing the relationship between the development DC voltage and the development DC current, and in this embodiment, the second relational expression L2b is expressed as a linear function.

[0062] Next, a developing DC voltage Vdcm2 that flows a developing DC current (developing current) Idcm having the same current value as the reference developing DC current Idcm measured in step S4 is calculated from the second relational expression L2b. At this time, the developing DC voltage Vdcm2 becomes the surface potential Vdcm2 of the photosensitive drum 1a corresponding to the charging current I2 (step S10).

[0063] Next, a corrected first relational expression L1' is created from the charging current I1 and developing voltage Vdcm1 calculated in step S7 and the charging current I2 and developing voltage Vdcm2 calculated in step S10 (step S11). FIG. 8 is a graph showing the relationship between the corrected charging current and the surface potential of the photosensitive drum 1a. The corrected first relational expression L1' is stored in the memory unit 70, and the memory mode is terminated. The next time the image formation mode is executed, the charging voltage applied is controlled based on the first relational expression L1' to adjust the surface potential, and image formation is performed.

[0064] According to this embodiment, when the correction mode is executed, the main control unit (control unit) 80 calculates the surface potential of the photosensitive drum (image carrier) 1a based on the applied development voltage and the development current detected by the development current detection unit 44 (steps S3 to S10), and corrects the relationship between the charging current and the surface potential (first relational expression L1) based on the calculated surface potential to create a new relationship between the charging current and the surface potential (first relational expression L1') (step S11).

[0065] By executing the next image formation mode based on the first relational expression L1' corrected by executing the correction mode, the surface potential of the photosensitive drum 1a is prevented from varying from the target value, carrier development and toner fogging are suppressed, and image defects are prevented. Furthermore, by observing changes in the charging current over a long period of time, performance degradation of the drum unit including the photosensitive drum 1a can be accurately detected. Therefore, the time to replace the drum unit can also be predicted.

[0066] Furthermore, when the correction mode is executed, the main control unit (control unit) 80 applies different development voltages (development DC voltages) Vdc1, Vdc2, Vdc3, and Vdc4 to the same charging current I1 or I2, and calculates the surface potentials Vdcm1 and Vdcm2 from the relationship (second relational expressions L2a and L2b) between the development currents (development DC currents) Idc1, Idc2, Idc3, and Idc4 detected by the development current detection unit 44 and the development voltages (development DC voltages) Vdc1, Vdc2, Vdc3, and Vdc4 (steps S4 to S10). This allows the surface potential to be calculated accurately based on the development voltages and development currents.

[0067] Furthermore, when the correction mode is executed, the main control unit (control unit) 80 calculates, from the relationship between the development current and the development voltage (second relational expressions L2a and L2b), development voltages Vdcm1 and Vdcm2 that cause a development current of the same current value as the reference development current Idcm detected by the development current detection unit 44 when the surface potential of the photosensitive drum (image carrier) 1a is zero and in an uncharged state, and calculates the calculated development voltages Vdcm1 and Vdcm2 as the surface potentials Vdcm1 and Vdcm2 (steps S7 and S11). This allows the surface potential to be calculated more accurately.

[0068] In this embodiment, when the image formation mode is executed, the charging voltage applied is controlled based on the relationship between the charging current and the surface potential of the image carrier, and the surface potential is adjusted to form an image, but the relationship between the charging current and the surface potential of the image carrier changes with changes in the ambient temperature of the photosensitive drum 1a. For example, if the ambient temperature of the photosensitive drum 1a rises, the fluctuation in the surface potential can be suppressed by increasing the charging current.

[0069] For this reason, when the correction mode is executed, it is preferable to correct the relationship between the charging current and the surface potential of the image carrier based on the temperature change around the photosensitive drum 1a. That is, when the correction mode is executed, it is preferable that the control unit (control unit) 80 corrects the relationship between the charging current and the surface potential based on the predicted temperature change around the photosensitive drum 1a and the calculated surface potential. This makes it possible to prevent deviations in the surface potential due to temperature changes around the photosensitive drum 1a when the image formation mode is executed.

[0070] Second Embodiment Next, a second embodiment of the present invention will be described. Fig. 9 is a flowchart showing an example of execution in the image forming apparatus 100 according to the second embodiment. For ease of explanation, the same parts as those in the first embodiment shown in Figs. 1 to 8 are denoted by the same reference numerals. In the second embodiment, the procedure of the correction mode differs from that in the first embodiment.

[0071] FIG. 9 is a flowchart showing an example of execution in the image forming apparatus 100 according to this embodiment, and steps S1 and S2 are the same as those in the first embodiment.

[0072] When the correction mode is executed, the control unit 80 calculates, for example, the charging current I1 corresponding to the target surface potential V01 based on the first relational expression L1 (see FIG. 5) used when the image formation mode is executed (step S13).

[0073] Next, with the surface potential of the photosensitive drum (image carrier) 1a at zero, the DC component of the development voltage applied to the development roller 31 is set to zero, and the reference development DC current Idcm detected by the development current detection unit 44 is measured (step S14). At this time, the reference development DC current Idcm is a fogging toner current generated by the movement of toner.

[0074] Next, a charging voltage is applied to the charging roller (charging member) 34 so that the charging current detected by the charging current detection unit 46 becomes equal to the charging current I1 calculated in step S13, and then a developing voltage E is applied. At this time, the developing DC current Idc5 detected by the developing current detection unit 44 is measured (step S15).

[0075] Next, a charging voltage is applied to the charging roller (charging member) 34 so that a charging current I2 different from the charging current I1 is detected, and then a developing voltage E is applied. At this time, the developing DC current Idc6 detected by the developing current detection unit 44 is measured (step S16).

[0076] When the development DC current Idc5 is smaller than the reference development DC current Idcm, it is preferable to allow a charging current I2 larger than the charging current I1 to flow. On the other hand, when the development DC current Idc5 is larger than the reference development DC current Idcm, it is preferable to allow a charging current I2 smaller than the charging current I1 to flow.

[0077] Next, a third relational expression L3 is created from the charging currents I1 and I2 and the development DC currents Idc5 and Idc6 (step S17). Fig. 10 is a graph showing the relationship between the charging current and the development DC current, and in this embodiment, the third relational expression L3 is expressed as a linear function.

[0078] Next, the charging current Im when a developing current of the same current value as the reference developing DC current Idcm flows is calculated from the third relational expression L3, and the developing voltage E corresponding to the calculated charging current Im is calculated as the surface potential (step S18). The relationship between the corrected charging current Im and the developing voltage E is stored in the memory unit 70, and the memory mode is terminated. As a result, when the next image formation mode is executed, the charging voltage is applied and controlled based on the relationship between the charging current Im and the developing voltage E to form an image.

[0079] According to this embodiment, when the correction mode is executed, the main control unit (control unit) 80 applies the same development voltage E to the different charging currents I1 and I2, and calculates the surface potential from the relationship (relational formula L3) between the development current and the charging current detected by the development current detection unit 44 (steps S15 to S18). This makes it possible to accurately calculate the surface potential based on the development voltage and the development current.

[0080] More specifically, when the correction mode is executed, the main control unit (control unit) 80 calculates, from the relationship between the development current and the charging current (relational formula L3), a charging current Im that causes the DC component of the development voltage applied to the development roller 31 to be zero when the surface potential of the photosensitive drum (image carrier) 1a is zero, to flow a current value equal to the reference development DC current Idcm detected by the development current detection unit 44, and calculates the development voltage E corresponding to the calculated charging current Im as the surface potential (step S18). This makes it possible to calculate the surface potential more accurately.

[0081] Next, an evaluation was conducted to see whether the occurrence of image defects could be suppressed by executing the correction mode. The test machine conditions were as shown in FIG. 1, in an image forming apparatus 100 (manufactured by Kyocera Document Solutions Inc.), and photosensitive drums 1a to 1d (outer diameter 30 mm) having an amorphous silicon (a-Si) photosensitive layer 111. The charging roller 34 is composed of epichlorohydrin rubber (outer diameter 12 mm, manufactured by Synztec Co., Ltd.) and a shaft (outer diameter 8 mm). The charging roller 34 has an inner resistance value of 10 across the transfer paper width. 5 Over 10 6 The hardness is 60 degrees in Ω or less. The pressing force of the charging roller 34 against the photosensitive drums 1a to 1d was 10 (N), and the charging voltage was a DC voltage superimposed with an AC voltage. The printing speed was 70 sheets / min.

[0082] In addition, the developing devices 3a to 3d used a developing roller 31 with an outer diameter of 20 mm and knurled to form 80 rows of V-shaped grooves, each 50 μm deep, in the circumferential direction, and a magnetic blade (thickness 1.5 mm) made of stainless steel (SUS430) as the regulating blade 35.

[0083] The outer diameter of the developing roller 31 is set to 20 mm, and the developer transport amount by the developing roller 31 is set to 350 g / m 2 The peripheral speed ratio between the developing roller 31 and the photosensitive drums 1a to 1d was 1.8 (trail rotation at opposing positions), and the distance between the developing roller 31 and the photosensitive drums 1a to 1d was 0.375 mm. A developing voltage was applied to the developing roller 31 with a rectangular wave of 10 kHz, duty = 50%, and a voltage superimposed with an AC voltage Vpp of 1100 V.

[0084] A two-component developer consisting of a positively charged toner with an average particle diameter of 6.8 μm and a ferrite-resin coated carrier with an average particle diameter of 40 μm was used, and the toner concentration was set to 6%.

[0085] The evaluation method was to evaluate whether or not image defects due to fogging occurred as the number of printed sheets increased.

[0086] In the examples and comparative examples, the target value of the development potential difference V0-Vdc during execution of the image formation mode was set to 50 V. The print rate was set to 5%, and continuous printing in black was performed. In addition, evaluation was performed by changing the ambient temperature of the image forming apparatus 100.

[0087] In the comparative example, the charging roller 34 was controlled by the charging DC current, and the correction mode was not performed. In the example, the correction mode was performed every 50 K. In the correction mode, the relationship between the charging current and the surface potential was corrected based on the temperature change around the photosensitive drum 1 a.

[0088] The surface potential of the examples and comparative examples was calculated using the development voltage by the method described above.

[0089] Fog was measured using a reflection densitometer (product number: TC-6DS, manufactured by Tokyo Denshoku Co., Ltd.) by measuring the image density of the paper before printing and the image density of the white background after printing. From the measurement results, fog density = "image density of the white background after printing" - "image density of the paper before printing" was calculated, and the measurement results are shown in the table in Figure 11. When the fog density was 0.01 or less, it was evaluated as good (◯). When the fog density was greater than 0.01, it was evaluated as poor (×).

[0090] From these evaluations, it was found that the occurrence of image defects during image formation can be prevented by executing the correction mode and correcting the relationship between the charging current and the surface potential based on the temperature change around the photosensitive drum 1a.

[0091] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the toner charge amount may be calculated by a method other than the above-described method. For example, in this embodiment, the configuration of the image forming units Pb to Pd and the control paths of the developing devices 3b to 3d are not described, but the AC constant voltage power supplies 43a and 45a of the developing voltage power supply 43 and charging voltage power supply 45 provided for each photosensitive drum 1a to 1d may be common (see FIG. 3). This reduces the cost of the image forming apparatus 100.

[0092] In addition, 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 machines, facsimiles, etc. [Industrial Applicability]

[0093] The present invention can be used in an image forming apparatus equipped with a charging roller. [Explanation of symbols]

[0094] 1a to 1d Photosensitive drum 2a~2d Charging device 3a~3d developing device 5 Exposure equipment 6a~6d Primary transfer rollers 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 32 Cleaning blade 33 Rubbing roller 34 Charging roller 35 Conveying spiral 40 Image density sensor (image density detection device) 41 Temperature detection sensor 43 Development voltage power supply 43a, 45b AC constant voltage power supply 43b, 45b DC constant voltage power supply 45 Charge voltage power supply 46 Charging current detection unit 47 Transfer voltage power supply 50 Voltage control section 70 Storage 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 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 causing the toner to adhere to the electrostatic latent image formed on the image carrier; an image forming unit including: a developing voltage power source that applies a developing voltage to the developer carrier; a charging voltage power source that applies a charging voltage including at least a DC component to the charging member; a development current detection unit that detects a development current flowing between the developer carrier and the image carrier; a charging current detection unit that detects a charging current flowing between the charging member and the image carrier; a control unit that controls the image forming unit, the developing voltage power supply, and the charging voltage power supply; In an image forming apparatus comprising: The control unit an image forming mode in which the charging voltage to be applied is controlled based on the relationship between the charging current and the surface potential of the image carrier, thereby adjusting the surface potential and forming an image; a correction mode for correcting the relationship between the charging current and the surface potential; When the correction mode is executed, the control unit calculates the surface potential of the image carrier based on the applied developing voltage and the developing current detected by the developing current detection unit, and corrects the relationship between the charging current and the surface potential based on the calculated surface potential.

2. 2. The image forming apparatus according to claim 1, wherein, when the correction mode is executed, the control unit applies different developing voltages to the same charging current, and calculates the surface potential from the relationship between the developing current detected by the developing current detection unit and the developing voltage.

3. 3. The image forming apparatus according to claim 2, wherein, when the correction mode is executed, the control unit calculates the development voltage that causes the development current to flow with the same current value as the reference development current detected by the development current detection unit when the surface potential of the image carrier is zero and the image carrier is in an uncharged state, from the relationship between the development current and the development voltage, and calculates the calculated development voltage as the surface potential.

4. 2. The image forming apparatus according to claim 1, wherein, when the correction mode is executed, the control unit applies the same developing voltage to different charging currents, and calculates the surface potential from the relationship between the developing current detected by the developing current detection unit and the charging current.

5. 5. The image forming apparatus according to claim 4, wherein, when the correction mode is executed, the control unit calculates the charging current that causes the developing current to flow with the same current value as the reference developing current detected by the developing current detection unit when the surface potential of the image carrier is zero and the developing voltage is calculated as the surface potential, from the relationship between the developing current and the charging current.

6. the developer is a two-component developer containing a magnetic carrier and a toner, 6. The image forming apparatus according to claim 3, wherein, when the correction mode is executed, the DC component of the charging voltage applied by the control unit when the surface potential of the image carrier is zero and the image carrier is in an uncharged state is zero.

7. a temperature measuring unit for measuring the temperature around the image carrier; 2. The image forming apparatus according to claim 1, wherein the control unit corrects the relationship between the charging current and the surface potential based on a predicted temperature change around the image carrier and the calculated surface potential when the correction mode is executed.

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