Image forming apparatus and method for acquiring electrical resistance value

Abstract

To provide an image forming apparatus and an electric resistance value acquisition method that can acquire an electric resistance value of an electrifying member without providing a power supply having a special function.SOLUTION: An image forming apparatus comprises: a first acquisition processing unit that acquires a potential value of an electrified area of a photoreceptor drum 31 electrified by an electrifying roller 32; a second acquisition processing unit that acquires a state value related to the state of a surface layer 3A based on the potential value of the electrified area and a current value of an electrifying current flowing through the electrifying roller 32 during formation of the electrified area; and a third acquisition processing unit that acquires an electric resistance value of the electrifying roller 32 based on the state value, the current value of the electrifying current, and a voltage value of an electrifying voltage applied to the electrifying roller 32 during the formation of the electrified area.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic image forming apparatus and a method for obtaining an electrical resistance value. [Background technology]

[0002] An electrophotographic image forming apparatus includes a charging member, such as a charging roller, that charges an image carrier, such as a photosensitive drum. The charging member deteriorates as the number of prints made by the image forming apparatus increases, resulting in an increase in electrical resistance. When the electrical resistance of the charging member increases, the charging performance of the charging member on the image carrier decreases, resulting in a decrease in the quality of printed images.

[0003] In response to this, a related technology is known in which an image forming apparatus acquires the electrical resistance value of the charging member and determines whether or not it is time to replace the charging member based on the acquired electrical resistance value of the charging member (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-202446 Summary of the Invention [Problem to be solved by the invention]

[0005] In the image forming apparatus according to the related art described above, two pulse voltages with different frequencies are applied to the charging member to obtain the electrical resistance value of the charging member. In other words, to obtain the electrical resistance value of the charging member using the related art described above, it is necessary to provide a power source capable of applying two pulse voltages with different frequencies to the charging member.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an electric resistance value acquisition method that can acquire the electric resistance value of a charging member without providing a power source with a special function. [Means for solving the problem]

[0007] According to one aspect of the present invention, an image forming apparatus includes an image carrier, a charging member, a first acquisition processing unit, a second acquisition processing unit, and a third acquisition processing unit. The image carrier has a surface layer. The charging member charges the image carrier. The first acquisition processing unit acquires a potential value of a charged area of ​​the image carrier charged by the charging member. The second acquisition processing unit acquires a state value relating to the state of the surface layer based on the potential value of the charged area acquired by the first acquisition processing unit and the current value of a charging current flowing through the charging member when the charged area is formed. The third acquisition processing unit acquires an electrical resistance value of the charging member based on the state value acquired by the second acquisition processing unit, the current value of the charging current, and the voltage value of a charging voltage applied to the charging member when the charged area is formed.

[0008] According to another aspect of the present invention, an electrical resistance value acquisition method is performed in an image forming apparatus including an image carrier having a surface layer and a charging member that charges the image carrier, and includes a first acquisition step, a second acquisition step, and a third acquisition step. In the first acquisition step, a potential value of a charged area of ​​the image carrier that has been charged by the charging member is acquired. In the second acquisition step, a status value relating to the status of the surface layer is acquired based on the potential value of the charged area acquired in the first acquisition step and the current value of a charging current that flows through the charging member when the charged area is formed. In the third acquisition step, an electrical resistance value of the charging member is acquired based on the status value acquired in the second acquisition step, the current value of the charging current, and the voltage value of a charging voltage applied to the charging member when the charged area is formed. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain the electrical resistance value of the charging member without providing a power source with a special function. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the system configuration of the image forming apparatus according to the embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing the configuration of an image forming unit of the image forming apparatus according to the embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. [Figure 5] FIG. 5 is a diagram showing the first development current detected in the image forming apparatus according to the embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing the relationship between the first developing current detected in the image forming apparatus according to the embodiment of the present invention and the DC component of the developing bias voltage. [Figure 7] FIG. 7 is an equivalent circuit diagram of a current path passing through a charging roller and a photosensitive drum in an image forming apparatus according to an embodiment of the present invention. [Figure 8] FIG. 8 is an equivalent circuit diagram of a current path passing through the primary transfer roller and the photosensitive drum in the image forming apparatus according to the embodiment of the present invention. [Figure 9] FIG. 9 is a flowchart showing an example of a replacement timing determination process executed in the image forming apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of a specific embodiment of the present invention and does not limit the technical scope of the present invention.

[0012] [Configuration of image forming apparatus 100] First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS.

[0013] For ease of explanation, the vertical direction in the installation state where image forming apparatus 100 is usable (the state shown in FIG. 1) is defined as the up-down direction D1. Also, the front-to-back direction D2 is defined with the left side of image forming apparatus 100 on the paper surface shown in FIG. 1 as the front (front face). Also, the left-to-right direction D3 is defined with the front face of image forming apparatus 100 in the installation state as the reference point.

[0014] Image forming apparatus 100 is a multifunction peripheral that has multiple functions, such as a scanning function for reading an image from an original document, a printing function for forming an image based on image data, a fax function, and a copy function. Note that the present invention may also be applied to image forming apparatuses such as printers, fax machines, and copy machines that are capable of forming images using an electrophotographic method.

[0015] As shown in FIGS. 1 and 2, the image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7.

[0016] The ADF 1 transports a document whose image is to be read by the image reading unit 2. The ADF 1 includes a document setting unit, a plurality of transport rollers, a document presser, and a paper discharge unit.

[0017] The image reading unit 2 realizes the scanning function and includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

[0018] The image forming unit 3 realizes the printing function. Specifically, the image forming unit 3 forms a color or monochrome image on a sheet fed from the paper feed unit 4 according to an electrophotographic method.

[0019] The paper feed unit 4 supplies sheets to the image forming unit 3. The paper feed unit 4 includes a paper feed cassette, a manual feed tray, and a plurality of transport rollers.

[0020] The operation display unit 5 is a user interface of the image forming apparatus 100. The operation display unit 5 includes a display unit and an operation unit. The display unit displays various information in accordance with control instructions from the control unit 7. For example, the display unit is a liquid crystal display. The operation unit is used by the user to input various information to the control unit 7. For example, the operation unit includes operation keys and a touch panel.

[0021] The storage unit 6 is a non-volatile storage device, such as a flash memory.

[0022] The control unit 7 performs overall control of the image forming apparatus 100. As shown in FIG. 2, the control unit 7 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various types of arithmetic processing. The ROM 12 is a non-volatile storage device that stores in advance information such as control programs for causing the CPU 11 to execute various types of processing. The RAM 13 is a volatile or non-volatile storage device that is used as a temporary storage memory (work area) for the various types of processing executed by the CPU 11. The CPU 11 performs overall control of the image forming apparatus 100 by executing the various control programs that are stored in advance in the ROM 12.

[0023] The control unit 7 may be a control unit provided separately from a main control unit that performs overall control of the image forming apparatus 100. The control unit 7 may also be configured with an electronic circuit such as an integrated circuit (ASIC).

[0024] [Configuration of image forming unit 3] Next, the configuration of the image forming section 3 will be described with reference to Figures 1 to 3. Here, Figure 3 is a cross-sectional view showing the configuration of the image forming unit 24. In Figure 3, the current path passing through the charging roller 32 and the first power source 61, the current path passing through the developing roller 44 and the second power source 63, and the current path passing through the primary transfer roller 34 and the third power source 65 are each indicated by dashed dotted lines.

[0025] As shown in FIG. 1, the image forming section 3 includes a plurality of image forming units 21 to 24, an optical scanning device 25, an intermediate transfer belt 26, a secondary transfer roller 27, a fixing device 28, and a paper discharge tray 29.

[0026] Image forming unit 21 forms a Y (yellow) toner image. Image forming unit 22 forms a C (cyan) toner image. Image forming unit 23 forms an M (magenta) toner image. Image forming unit 24 forms a K (black) toner image. As shown in FIG. 1, image forming units 21 to 24 are arranged side by side in the order of yellow, cyan, magenta, and black from the front side of image forming apparatus 100 along the front-rear direction D2 of image forming apparatus 100.

[0027] 3, the image forming unit 24 includes a photosensitive drum 31, a charging roller 32, a developing device 33, a primary transfer roller 34, and a drum cleaning unit 35. Each of the image forming units 21 to 23 has the same configuration as the image forming unit 24.

[0028] An electrostatic latent image is formed on the surface of the photosensitive drum 31. The photosensitive drum 31 has a surface layer 31A. The photosensitive drum 31 is an example of the image carrier of the present invention.

[0029] For example, the surface layer 31A is formed using an organic photosensitive material. Note that the surface layer 31A may be formed using a photosensitive material different from the organic photosensitive material.

[0030] Photoconductor drum 31 receives a rotational driving force supplied from a motor (not shown) and rotates in a rotation direction D4 shown in Fig. 3. As a result, photoconductor drum 31 conveys an electrostatic latent image formed on the surface.

[0031] The charging roller 32 charges the surface layer 31A of the photosensitive drum 31. The charging roller 32 is an example of the charging member of the present invention.

[0032] The charging roller 32 is provided in contact with the surface layer 31A of the photosensitive drum 31. The charging roller 32 is rotated by the rotation of the photosensitive drum 31. A preset charging bias voltage is applied to the charging roller 32, which charges the surface layer 31A of the photosensitive drum 31. For example, the charging roller 32 charges the surface layer 31A of the photosensitive drum 31 to a positive polarity.

[0033] The surface layer 31A of the photosensitive drum 31, which has been charged by the charging roller 32, is irradiated with light based on image data emitted from the optical scanning device 25. As a result, an electrostatic latent image is formed on the surface layer 31A of the photosensitive drum 31.

[0034] The developing device 33 uses a developer containing toner and a carrier to develop the electrostatic latent image formed on the surface layer 31A of the photosensitive drum 31. As a result, a toner image is formed on the surface layer 31A of the photosensitive drum 31.

[0035] The primary transfer roller 34 transfers the toner image formed on the surface layer 31A of the photosensitive drum 31 by the developing device 33 onto the intermediate transfer belt 26.

[0036] The primary transfer roller 34 is provided in contact with the inner circumferential surface of the intermediate transfer belt 26. The primary transfer roller 34 is also provided facing the surface layer 31A of the photosensitive drum 31 with the intermediate transfer belt 26 sandwiched therebetween. The primary transfer roller 34 is rotated by the rotation of the intermediate transfer belt 26. A preset primary transfer bias voltage is applied to the primary transfer roller 34, and the primary transfer roller 34 transfers the toner image formed on the surface layer 31A of the photosensitive drum 31 onto the outer circumferential surface of the intermediate transfer belt 26.

[0037] The drum cleaning unit 35 removes the toner remaining on the surface of the photosensitive drum 31 after the toner image has been transferred by the primary transfer roller 34 .

[0038] The image forming section 3 includes a toner container 36 (see FIG. 1) corresponding to each of the image forming units 21 to 24. The image forming section 3 also includes a first power source 61 (see FIG. 2), a first detection section 62 (see FIG. 2), a second power source 63 (see FIG. 2), a second detection section 64 (see FIG. 2), a third power source 65 (see FIG. 2), and a third detection section 66 (see FIG. 2) corresponding to each of the image forming units 21 to 24.

[0039] Here, the toner container 36, the first power source 61, the first detection unit 62, the second power source 63, the second detection unit 64, the third power source 65, and the third detection unit 66 corresponding to the image forming unit 24 will be described.

[0040] The toner container 36 contains K (black) toner and supplies K (black) toner to the developing device 33 of the image forming unit 24.

[0041] The first power source 61 (see FIG. 3) applies the charging bias voltage to the charging roller 32. Specifically, the charging bias voltage is a voltage that includes a DC component. For example, the charging bias voltage is a voltage that includes a DC component of positive polarity.

[0042] The first detector 62 (see FIG. 3) detects the current flowing through the charging roller 32. As shown in FIG. 3, the first detector 62 is provided on a current path that passes through the charging roller 32 and the first power source 61. The first detector 62 inputs an electrical signal indicating the current value of the detected current to the control unit 7.

[0043] The second power source 63 (see FIG. 3) applies a predetermined developing bias voltage to the developing roller 44 (see FIG. 3) of the developing device 33. Specifically, the developing bias voltage is a voltage including a DC component and an AC component. For example, the developing bias voltage is a voltage including a positive DC component and a square-wave AC component.

[0044] The second power source 63 can output the DC component and the AC component contained in the developing bias voltage separately, and can adjust the voltage value of the DC component contained in the developing bias voltage within a predetermined range.

[0045] The second detector 64 (see FIG. 3) detects the current flowing through the developing roller 44. As shown in FIG. 3, the second detector 64 is provided on a current path passing through the developing roller 44 and the second power source 63. The second detector 64 inputs an electrical signal indicating the current value of the detected current to the controller 7.

[0046] A third power source 65 (see FIG. 3) applies the primary transfer bias voltage to the primary transfer roller 34. Specifically, the primary transfer bias voltage is a voltage that includes a DC component. For example, the primary transfer bias voltage is a voltage that includes a negative DC component.

[0047] The third detector 66 (see FIG. 3) detects the current flowing through the primary transfer roller 34. As shown in FIG. 3, the third detector 66 is provided on a current path that passes through the primary transfer roller 34 and the third power source 65. The third detector 66 inputs an electrical signal indicating the current value of the detected current to the controller 7.

[0048] The optical scanning device 25 emits light that illuminates the charged area on the surface layer 31A of the photosensitive drum 31 that has been charged by the charging roller 32. The optical scanning device 25 is an example of the light emitting section of the present invention.

[0049] Specifically, the optical scanning device 25 emits light based on image data toward the surface 31A of the photosensitive drum 31 of each of the image forming units 21-24.

[0050] The intermediate transfer belt 26 is an endless belt member onto which the toner images formed on the surfaces of the photosensitive drums 31 of the image forming units 21 to 24 are transferred. The intermediate transfer belt 26 is stretched with a predetermined tension by a drive roller and a tension roller. The intermediate transfer belt 26 rotates in a rotation direction D5 shown in FIG. 3 as the drive roller rotates upon receiving a rotational driving force supplied from a motor (not shown).

[0051] The secondary transfer roller 27 transfers the toner image transferred onto the surface of the intermediate transfer belt 26 onto a sheet supplied from the paper feed unit 4 .

[0052] The fixing device 28 fixes the toner image transferred onto the sheet by the secondary transfer roller 27 onto the sheet.

[0053] The sheet on which the toner image has been fixed by the fixing device 28 is discharged onto the paper discharge tray 29.

[0054] [Configuration of developing device 33] 3 and 4, the configuration of the developing device 33 of the image forming unit 24 will be described. The developing device 33 of each of the image forming units 21 to 23 also has the same configuration as the developing device 33 described below.

[0055] As shown in FIGS. 3 and 4, the developing device 33 includes a housing 41, a first transport member 42, a second transport member 43, a developing roller 44, a regulating member 45, and a toner sensor 46.

[0056] The housing 41 accommodates a first transport member 42, a second transport member 43, a developing roller 44, and a regulating member 45. The housing 41 also accommodates the developer. The housing 41 is formed to be elongated in the left-right direction D3.

[0057] 3 and 4, the housing 41 has a first transport path 52 and a second transport path 53 extending in the left-right direction D3. Specifically, a partition wall 54 (see FIG. 4) is provided on the bottom surface 51 of the housing 41 to divide the lower part of the housing 41 into the first transport path 52 and the second transport path 53.

[0058] The first transport member 42 transports the developer accommodated in the first transport path 52 in a transport direction D6 (see FIG. 4) along the first transport path 52. The first transport member 42 also agitates the developer, causing frictional charging of the toner and carrier contained in the developer. For example, the first transport member 42 is a screw-shaped member that is rotatable about a rotation axis along the first transport path 52 in the first transport path 52. The first transport member 42 rotates upon receiving a rotational driving force supplied from a motor (not shown), thereby transporting and agitating the developer. For example, the toner contained in the developer agitated by the first transport member 42 is positively charged due to frictional charging with the carrier contained in the developer.

[0059] The second transport member 43 transports the developer accommodated in the second transport path 53 in a transport direction D7 (see FIG. 4) along the second transport path 53. The second transport member 43 also agitates the developer to frictionally charge the toner and carrier contained in the developer. For example, the second transport member 43 is a screw-shaped member that is rotatable about a rotation axis along the second transport path 53 in the second transport path 53. The second transport member 43 rotates by receiving a rotational driving force supplied from a motor (not shown), thereby transporting and agitating the developer.

[0060] A first passage 55 (see FIG. 4) leading to the second conveying path 53 is provided at the downstream end of the first conveying path 52 in the conveying direction D6. A second passage 56 (see FIG. 4) leading to the first conveying path 52 is provided at the downstream end of the second conveying path 53 in the conveying direction D7. The first conveying path 52, the first passage 55, the second conveying path 53, and the second passage 56 form a circulating conveying path along which the developer is circulated and conveyed in one direction.

[0061] The developing roller 44 is provided facing the photosensitive drum 31. The developing roller 44 transports the developer to an opposing portion R1 (see FIG. 3) between the developing roller 44 and the photosensitive drum 31. The developing roller 44 is an example of the developing member of the present invention.

[0062] 3, the developing roller 44 is provided facing the second transport path 53 and the photosensitive drum 31. The developing roller 44 draws up the developer from the second transport path 53. The developer drawn up by the developing roller 44 forms a magnetic brush on the outer circumferential surface of the developing roller 44 due to the magnetic force of the magnetic poles provided inside the developing roller 44.

[0063] The developing roller 44 is rotatably supported by the housing 41. The developing roller 44 receives a rotational driving force supplied from a motor (not shown) and rotates in a rotation direction D8 shown in Fig. 3. As a result, the developing roller 44 transports the magnetic brush formed on the outer circumferential surface to the opposing portion R1.

[0064] An electrostatic latent image formed on the surface layer 31A of the photosensitive drum 31 is transported to the opposing portion R1 by the rotation of the photosensitive drum 31. Here, the electrostatic latent image includes an exposed area and a non-exposed area. The exposed area is a region of the charged area on the surface layer 31A of the photosensitive drum 31 that is charged by the charging roller 32 and that is irradiated with light emitted by the optical scanning device 25. The non-exposed area is a region of the charged area that is not irradiated with light emitted by the optical scanning device 25.

[0065] When the developing bias voltage is applied to the developing roller 44, a first electric field is formed between the developing roller 44 and the exposed area at the opposing portion R1, which moves the toner contained in the magnetic brush toward the exposed area. Furthermore, when the developing bias voltage is applied to the developing roller 44, a second electric field is formed between the developing roller 44 and the non-exposed area at the opposing portion R1, which moves the toner contained in the magnetic brush toward the developing roller 44. The toner contained in the magnetic brush is selectively moved to the exposed area formed on the surface layer 31A of the photosensitive drum 31 by the action of the first electric field and the second electric field formed at the opposing portion R1. This develops the electrostatic latent image formed on the surface layer 31A of the photosensitive drum 31.

[0066] The regulating member 45 regulates the layer thickness of the magnetic brush formed on the outer peripheral surface of the developing roller 44. As shown in Fig. 3, the regulating member 45 is provided downstream in the rotation direction D8 of the opposing position between the second transport member 43 and the developing roller 44, and upstream in the rotation direction D8 of the opposing portion R1. The regulating member 45 is provided opposite the outer peripheral surface of the developing roller 44 so that a predetermined gap is formed between the regulating member 45 and the outer peripheral surface of the developing roller 44.

[0067] An opening 57 is provided above the first transport path 52. As shown in FIG. 3, the opening 57 is provided in an outer wall of the housing 41 that covers the upper side of the first transport path 52. The opening 57 opens toward the upstream end of the first transport path 52 in the transport direction D6. Toner supplied from the toner container 36 passes through the opening 57 and is transported to a transport position P1 (see FIG. 4) in the first transport path 52 that faces the opening 57.

[0068] The toner sensor 46 detects toner at a detection position P2 (see FIG. 4) downstream of the carry-in position P1 in the first transport path 52 in the transport direction D6. For example, the toner sensor 46 is provided on the bottom of the housing 41 as shown in FIG. 3. For example, the toner sensor 46 is a magnetic permeability sensor including an LC oscillation circuit that outputs an electric signal according to the magnetic permeability of the developer contained in the housing 41. The toner sensor 46 is used by the control unit 7 to control the supply of toner from the toner container 36 to the developing device 33.

[0069] [Configuration of control unit 7] Next, the configuration of the control unit 7 will be described with reference to FIG.

[0070] As shown in FIG. 2, the control unit 7 includes a second detection processing unit 71, a first detection processing unit 72, a potential value acquisition unit 73, a state value acquisition unit 74, a first resistance value acquisition unit 75, a second resistance value acquisition unit 76, a first timing judgment unit 77, a second timing judgment unit 78, and a third timing judgment unit 79.

[0071] Specifically, a replacement timing determination program for causing the CPU 11 to function as each of the above-mentioned units is stored in advance in the ROM 12 of the control unit 7. The CPU 11 then executes the replacement timing determination program stored in the ROM 12 to function as each of the above-mentioned units.

[0072] The replacement timing determination program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the memory unit 6. Some or all of the second detection processing unit 71, first detection processing unit 72, potential value acquisition unit 73, state value acquisition unit 74, first resistance value acquisition unit 75, second resistance value acquisition unit 76, first timing determination unit 77, second timing determination unit 78, and third timing determination unit 79 may be configured as electronic circuits such as integrated circuits (ASICs).

[0073] In the following, of the image forming units 21 to 24, the description will be given taking as an example the various parts included in the image forming unit 24 and the various parts provided corresponding to the image forming unit 24. The following description also applies to each of the image forming units 21 to 23.

[0074] The second detection processing unit 71 detects the second development current that flows through the opposing portion R1 (see Figure 3), which includes the developer and an uncharged area on the photosensitive drum 31 that is not charged by the charging roller 32 when no DC voltage is applied to the development roller 44.

[0075] For example, the second detection processing unit 71 detects the second development current when a predetermined determination timing arrives. For example, the determination timing is when the number of printed sheets by the image forming apparatus 100 exceeds a multiple of a predetermined specific number. The determination timing may also be when the image forming apparatus 100 is turned on.

[0076] For example, the second detection processing unit 71 detects the second developing current in the following procedure.

[0077] First, the second detection processing unit 71 transports the uncharged area of ​​the photosensitive drum 31 to the opposing portion R1, and also transports the developer to the opposing portion R1. Specifically, the second detection processing unit 71 rotates the photosensitive drum 31 while the outputs of the first power source 61 and the optical scanning device 25 are stopped. The second detection processing unit 71 also drives the developing device 33. Note that the second detection processing unit 71 may neutralize the uncharged area transported to the opposing portion R1 using the optical scanning device 25 or a neutralization unit (not shown) that neutralizes the surface layer 31A of the photosensitive drum 31.

[0078] Next, the second detection processing unit 71 applies an AC voltage to the second power source 63 at the timing when the non-charged area and the developer are present in the opposing portion R1. Specifically, the second detection processing unit 71 outputs an AC component included in the development bias voltage.

[0079] Then, the second detection processing unit 71 detects the second development current flowing in the current path passing through the second power source 63 and the development roller 44 in response to the application of AC voltage, using the second detection unit 64. Note that the second detection processing unit 71 may also detect the second development current flowing in the current path passing through the second power source 63 and the development roller 44 in a state where AC voltage is not applied to the development roller 44.

[0080] The first detection processing unit 72 detects, for each of a plurality of specific voltages having different DC voltage values ​​applied to the developing roller 44, a first development current that flows through the developer and the opposing portion R1 (see Figure 3) including the non-exposed area of ​​the photosensitive drum 31 in response to the application of the specific voltage.

[0081] For example, the specific voltage is a voltage including a DC component and an AC component. Note that, when the second developing current is a current that flows through a current path that passes through the second power source 63 and the developing roller 44 when no AC voltage is applied to the developing roller 44, the specific voltage may be a voltage that includes only a DC component.

[0082] For example, when the second detection processing section 71 detects the second development current, the first detection processing section 72 detects the first development current.

[0083] For example, the first detection processing unit 72 detects the first developing current in the following procedure.

[0084] First, the first detection processing unit 72 transports the non-exposed area of ​​the photosensitive drum 31 to the opposing portion R1, and also transports the developer to the opposing portion R1. Specifically, the first detection processing unit 72 applies the charging bias voltage to the first power source 61 and rotates the photosensitive drum 31 while the output of the optical scanning device 25 is stopped. The first detection processing unit 72 also drives the developing device 33.

[0085] Next, the first detection processing unit 72 causes the second power source 63 to output one of the specific voltages when the non-exposed area and the developer are present in the opposing portion R1. Specifically, the first detection processing unit 72 causes the second power source 63 to output the developing bias voltage with the voltage value of the DC component adjusted.

[0086] Then, the first detection processing section 72 uses the second detection section 64 to detect the first development current that flows through the current path that passes through the second power source 63 and the development roller 44 in response to the application of the specific voltage.

[0087] FIG. 5 shows an example of the first developing current for each of the plurality of specific voltages having different DC voltage values ​​detected by the first detection processing unit 72.

[0088] The potential value acquiring unit 73 acquires the potential value of the charged area of ​​the photosensitive drum 31 that has been charged by the charging roller 32. The potential value acquiring unit 73 is an example of a first acquisition processing unit of the present invention.

[0089] Specifically, the potential value acquisition unit 73 acquires the potential value of the non-exposed area based on the DC voltage value of each of the specific voltages and the current value of the first development current detected by the first detection processing unit 72 corresponding to each of the specific voltages.

[0090] Here, the relationship between the potential difference between the developing roller 44 and the non-exposed area and the first developing current will be described with reference to Fig. 6. Fig. 6 is a diagram showing an approximate straight line showing the relationship between the DC voltage value of the specific voltage and the current value of the first developing current, based on the data shown in Fig. 5. In Fig. 6, the approximate straight line is shown by a dashed line.

[0091] When the potential difference between the developing roller 44 and the non-exposed area is small, the first developing current, which includes the following first toner current and first carrier current, flows. The first toner current is a current that flows when toner present in the opposing portion R1 mechanically adheres to the non-exposed area. The first carrier current is a current that flows via carriers present in the opposing portion R1. When the potential of the developing roller 44 is higher than the potential of the non-exposed area, the first carrier current flows in the direction from the developing roller 44 to the non-exposed area. When the potential of the developing roller 44 is lower than the potential of the non-exposed area, the first carrier current flows in the direction from the non-exposed area to the developing roller 44.

[0092] Also, when the potential difference between the developing roller 44 and the non-exposed area is zero, the first developing current containing only the first toner current flows.

[0093] Here, the second development current flowing between the development roller 44 to which no DC voltage is applied and the non-charged area on the photosensitive drum 31 can be considered to be the same as the first development current when the potential difference between the development roller 44 and the non-exposed area is zero.

[0094] Therefore, it is possible to estimate that the DC voltage value of the specific voltage when the current value of the first developing current becomes the current value of the second developing current detected by the second detection processing unit 71 on the approximate straight line shown in Figure 6 is the potential value of the non-exposed area on the photosensitive drum 31.

[0095] For example, the potential value acquiring unit 73 acquires, as the potential value of the non-exposed region, the DC voltage value of the specific voltage corresponding to the current value of the first developing current, which is estimated based on the DC voltage value of each of the specific voltages and the current value of the first developing current detected by the first detection processing unit 72 corresponding to each of the specific voltages, such that the difference between the current value of the second developing current detected by the second detection processing unit 71 and the DC voltage value of the specific voltage is equal to or smaller than a predetermined tolerance. The tolerance may be any value including zero.

[0096] In addition, when the potential difference between the developing roller 44 and the non-exposed area is large, the following second toner current or the first developing current including a second carrier current flows. The second toner current is a current that flows when toner present in the opposing portion R1 electrostatically adheres to the non-exposed area. The second carrier current is a current that flows when carriers present in the opposing portion R1 electrostatically adhere to the non-exposed area. When the first developing current detected by the first detection processing unit 72 includes the second toner current or the second carrier current, the accuracy of acquiring the potential value of the non-exposed area by the potential value acquiring unit 73 decreases.

[0097] Therefore, it is desirable that the DC voltage value of each of the specific voltages be determined within a predetermined specific range so that the first development current detected by the first detection processing unit 72 does not include the second toner current or the second carrier current. For example, the specific range is a range based on the potential value of the non-exposed area last acquired by the potential value acquisition unit 73. For example, the specific range is a range of ±25 V (volts) centered on the potential value of the charged area last acquired by the potential value acquisition unit 73.

[0098] Since the first toner current is minute, it may be ignored. That is, the potential value acquiring unit 73 may acquire, as the potential value of the non-exposed region, the DC voltage value of the specific voltage when the current value of the first developing current is zero, which is estimated based on the DC voltage value of each specific voltage and the current value of the first developing current detected by the first detection processing unit 72 corresponding to each specific voltage. In this case, the control unit 7 does not need to include the second detection processing unit 71.

[0099] The potential value acquiring unit 73 may also acquire the potential value of the charged area using a surface potential sensor capable of detecting the surface potential of the photosensitive drum 31 .

[0100] The state value acquisition unit 74 acquires a state value relating to the state of the surface layer 31A based on the potential value of the charged region acquired by the potential value acquisition unit 73 and the current value of the charging current flowing through the charging roller 32 when the charged region is formed. The state value acquisition unit 74 is an example of a second acquisition processing unit of the present invention.

[0101] For example, the state value is the capacitance value of the surface layer 31A. Alternatively, the state value may be the thickness value of the surface layer 31A. For example, the thickness value of the surface layer 31A can be obtained based on the capacitance value of the surface layer 31A and a predetermined dielectric constant of the surface layer 31A.

[0102] For example, the state value acquisition unit 74 acquires the state value using the following equation (1). Here, Cp is the electrostatic capacitance of the surface layer 31A. Idc is the charging current detected by the first detection unit 62. Vo is the potential of the charged area acquired by the potential value acquisition unit 73. ΔV1 is the amount of potential decrease due to dark attenuation while the charged area is transported from the position facing the charging roller 32 to the opposing portion R1. v is the linear speed of the photosensitive drum 31. L is the width of the charged area.

[0103] Cp=Idc / ((Vo+ΔV1)·v·L)···(1)

[0104] It is sufficient that ΔV1 is determined in advance based on the linear velocity of the photosensitive drum 31. ΔV1 may also be calculated based on the number of prints made by the image forming apparatus 100, the temperature inside the apparatus, and the like.

[0105] Incidentally, the charging roller 32 deteriorates more and the electrical resistance value increases as the number of printed sheets by the image forming apparatus 100 increases. When the electrical resistance value of the charging roller 32 increases, the charging performance of the charging roller 32 for the photosensitive drum 31 decreases, and the quality of the printed image decreases.

[0106] In response to this, an image forming apparatus is known as a related technology that acquires the electrical resistance value of the charging roller 32 and determines whether or not it is time to replace the charging roller 32 based on the acquired electrical resistance value of the charging roller 32.

[0107] Here, in the image forming apparatus according to the related art described above, two pulse voltages with different frequencies are applied to the charging roller 32 in order to obtain the electrical resistance value of the charging roller 32. In other words, in order to obtain the electrical resistance value of the charging roller 32 using the related art described above, it is necessary to provide a power source capable of applying two pulse voltages with different frequencies to the charging roller 32.

[0108] In contrast to this, in the image forming apparatus 100, as will be described below, it is possible to obtain the electrical resistance value of the charging roller 32 without providing a power source with special functions.

[0109] The first resistance value acquisition unit 75 acquires the electrical resistance value of the charging roller 32 based on the state value acquired by the state value acquisition unit 74, the current value of the charging current, and the voltage value of the charging bias voltage applied to the charging roller 32 when forming the charged region. The first resistance value acquisition unit 75 is an example of a third acquisition processing unit of the present invention. The charging bias voltage is an example of a charging voltage of the present invention.

[0110] For example, the current path passing through the charging roller 32 and the photosensitive drum 31 can be expressed by the equivalent circuit shown in FIG. 7. From the equivalent circuit shown in FIG. 7, the following equation (2) can be derived. Here, Vdc is the DC component of the charging bias voltage. R1 is the electrical resistance of the charging roller 32. Vth1 is the potential difference between the charging roller 32 and the photosensitive drum 31. Vp1 is the potential of the charging region at the position facing the charging roller 32. Vth1 can be calculated based on Cp and the dielectric constant of a vacuum.

[0111] Vdc=Idc·R1+Vth1+Vp1···(2)

[0112] Moreover, by modifying the above equation (2), the following equation (3) can be derived: In the following equation (3), Vp1 is replaced with (Vo+ΔV1).

[0113] R1=(Vdc-(Vth1+(Vo+ΔV1))) / Idc...(3)

[0114] The first resistance value acquiring unit 75 acquires the electrical resistance value of the charging roller 32 using the above formula (3).

[0115] Incidentally, the primary transfer roller 34 deteriorates and its electrical resistance increases as the number of printed sheets by the image forming apparatus 100 increases. When the electrical resistance of the primary transfer roller 34 increases, the transfer performance of the toner image by the primary transfer roller 34 decreases, and the quality of the printed image decreases.

[0116] In response to this, a related art image forming apparatus is known that acquires the electrical resistance value of the primary transfer roller 34 and sets the primary transfer bias voltage to be applied to the primary transfer roller 34 based on the acquired electrical resistance value of the primary transfer roller 34. In this related art image forming apparatus, the electrical resistance value of the primary transfer roller 34 is calculated based on the primary transfer bias voltage applied to the primary transfer roller 34 and the current that flows in response to the application of the primary transfer bias voltage to the primary transfer roller 34.

[0117] Here, the current that flows in response to the application of the primary transfer bias voltage to the primary transfer roller 34 varies not only with the electrical resistance value of the primary transfer roller 34 but also with the capacitance of the photosensitive drum 31. However, in the image forming apparatus according to the related art described above, the capacitance of the photosensitive drum 31 is not taken into consideration when calculating the electrical resistance value of the primary transfer roller 34, and therefore the electrical resistance value cannot be obtained with high accuracy.

[0118] In contrast to this, in the image forming apparatus 100, as will be described below, it is possible to obtain the electrical resistance value of the primary transfer roller 34 with high accuracy.

[0119] The second resistance value acquisition unit 76 acquires the electrical resistance value of the primary transfer roller 34 based on the state value acquired by the state value acquisition unit 74, the voltage value of the primary transfer bias voltage applied to the primary transfer roller 34, and the current value of the transfer current flowing through the charged area in response to the application of the primary transfer bias voltage.

[0120] For example, the current path passing through the primary transfer roller 34 and the photosensitive drum 31 can be expressed by the equivalent circuit shown in FIG. 8. From the equivalent circuit shown in FIG. 8, the following equation (4) can be derived. Here, Vt is the DC component of the primary transfer bias voltage. Furthermore, It is the transfer current detected by the third detection unit 66. Furthermore, R2 is the electrical resistance of the primary transfer roller 34. Furthermore, Vth2 is the potential difference between the primary transfer roller 34 and the photosensitive drum 31. Furthermore, Vp2 is the potential of the charged area at the transfer position of the toner image by the primary transfer roller 34.

[0121] Vt=It·R2+Vth2+Vp2···(4)

[0122] Furthermore, by modifying the above equation (4), the following equation (5) can be derived. In the following equation (5), Vp2 is replaced with (Vo-ΔV2). ΔV2 is the amount of potential decrease due to dark attenuation while the charged area is transported from the opposing portion R1 to the transfer position of the toner image by the primary transfer roller 34.

[0123] R2=(Vt-(Vth2+(Vo-ΔV2))) / It...(5)

[0124] The second resistance value acquisition unit 76 acquires the electrical resistance value of the primary transfer roller 34 using the above formula (5).

[0125] The first timing determination unit 77 determines whether or not it is time to replace the photosensitive drum 31, based on the state value acquired by the state value acquisition unit 74. The first timing determination unit 77 is an example of a first determination processing unit of the present invention.

[0126] For example, when the state value acquired by the state value acquisition unit 74 exceeds a predetermined first threshold value, the first timing determination unit 77 determines that the time to replace the photosensitive drum 31 has arrived.

[0127] The second timing determination unit 78 determines whether or not it is time to replace the charging roller 32, based on the electrical resistance value of the charging roller 32 acquired by the first resistance value acquisition unit 75. The second timing determination unit 78 is an example of the second determination processing unit of the present invention.

[0128] For example, the second timing determination unit 78 determines that the time to replace the charging roller 32 has arrived when the electrical resistance value of the charging roller 32 acquired by the first resistance value acquisition unit 75 exceeds a predetermined second threshold value.

[0129] The third timing determination unit 79 determines, based on the electrical resistance value of the primary transfer roller 34 acquired by the second resistance value acquisition unit 76, whether or not it is time to replace the primary transfer roller 34.

[0130] For example, the third timing determination unit 79 determines that the time to replace the primary transfer roller 34 has arrived when the electrical resistance value of the primary transfer roller 34 acquired by the second resistance value acquisition unit 76 exceeds a predetermined third threshold value.

[0131] [Replacement timing determination process] 9, an example of the procedure for determining the timing of replacement executed by the control unit 7 in the image forming apparatus 100 and the method for acquiring the electrical resistance value of the present invention will be described. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) executed by the control unit 7.

[0132] The replacement timing determination process is executed when the determination timing arrives.

[0133] <Step S11> First, in step S11, the control unit 7 detects the second development current. The process of step S11 is executed by the second detection processing unit 71 of the control unit 7.

[0134] Specifically, the control unit 7 detects the second developing current in the following procedure.

[0135] First, the control unit 7 causes the non-charged area of ​​the photosensitive drum 31 to be transported to the opposing portion R1, and also causes the developer to be transported to the opposing portion R1. Specifically, the control unit 7 causes the photosensitive drum 31 to rotate while the outputs of the first power source 61 and the optical scanning device 25 are stopped. The control unit 7 also drives the developing device 33.

[0136] Next, when the non-charged area and the developer are present in the opposing portion R1, the control portion 7 causes the second power source 63 to apply an AC voltage. Specifically, the control portion 7 causes the second power source 63 to output an AC component included in the development bias voltage.

[0137] Then, the control unit 7 uses the second detection unit 64 to detect the second development current that flows through the current path that passes through the second power source 63 and the development roller 44 in response to the application of the AC voltage.

[0138] <Step S12> In step S12, the control unit 7 detects the charging current.

[0139] Specifically, the control unit 7 applies the charging bias voltage to the first power source 61. Then, the control unit 7 uses the first detection unit 62 to detect the charging current that flows through the current path that passes through the first power source 61 and the charging roller 32 in response to the application of the charging bias voltage.

[0140] <Step S13> In step S13, the control unit 7 detects the first developing current for each of the plurality of specific voltages. The process of step S13 is executed by the first detection processing unit 72 of the control unit 7.

[0141] Specifically, the control unit 7 detects the first developing current in the following procedure.

[0142] First, the control unit 7 causes the non-exposed area of ​​the photosensitive drum 31 to be transported to the opposing portion R1, and also causes the developer to be transported to the opposing portion R1. Specifically, the control unit 7 causes the first power source 61 to apply the charging bias voltage and rotates the photosensitive drum 31 while the output of the optical scanning device 25 is stopped. The control unit 7 also drives the developing device 33.

[0143] Next, when the non-exposed area and the developer are present in the opposing portion R1, the control portion 7 causes the second power source 63 to output one of the specific voltages. Specifically, the control portion 7 causes the second power source 63 to output the developing bias voltage whose DC component voltage value has been adjusted.

[0144] Then, the control unit 7 uses the second detection unit 64 to detect the first development current that flows through the current path that passes through the second power source 63 and the development roller 44 in response to the application of the specific voltage.

[0145] <Step S14> In step S14, the control unit 7 detects the transfer current.

[0146] Specifically, the control unit 7 causes the third power source 65 to apply the primary transfer bias voltage at the timing when the non-exposed region is transported to a position where the toner image is transferred by the primary transfer roller 34. Then, the control unit 7 uses the third detection unit 66 to detect the transfer current that flows in the current path that passes through the third power source 65 and the primary transfer roller 34 in response to the application of the primary transfer bias voltage.

[0147] <Step S15> In step S15, the control unit 7 acquires the potential value of the charged area on the photosensitive drum 31. The process of step S15 is an example of a first acquisition step of the present invention, and is executed by the potential value acquisition unit 73 of the control unit 7.

[0148] Specifically, the control unit 7 obtains the potential value of the non-exposure area based on the DC voltage value of each of the specific voltages and the current value of the first development current detected in step S13 corresponding to each of the specific voltages.

[0149] For example, the control unit 7 acquires a linear equation corresponding to an approximate straight line (see FIG. 6) showing the relationship between the DC voltage value of the specific voltage and the current value of the first developing current, based on the DC voltage value of each of the specific voltages and the current value of the first developing current detected in step S13 corresponding to each of the specific voltages. Then, the control unit 7 acquires, as the potential value of the non-exposed region, the DC voltage value of the specific voltage corresponding to the current value of the first developing current, the difference of which from the current value of the second developing current detected in step S11 is estimated based on the acquired linear equation and is equal to or smaller than the allowable value.

[0150] <Step S16> In step S16, the control unit 7 acquires the state value based on the potential value of the charged region acquired in step S15 and the current value of the charging current detected in step S12. The process of step S16 is an example of a second acquisition step of the present invention, and is executed by the state value acquisition unit 74 of the control unit 7.

[0151] Specifically, the control unit 7 obtains the state value using the above-mentioned equation (1).

[0152] <Step S17> In step S17, the control unit 7 acquires the electrical resistance value of the charging roller 32 based on the state value acquired in step S16 and the current value of the charging current and the voltage value of the charging bias voltage detected in step S12. The process of step S17 is an example of a third acquisition step of the present invention, and is executed by the first resistance value acquisition unit 75 of the control unit 7.

[0153] Specifically, the control unit 7 obtains the electrical resistance value of the charging roller 32 using the above-mentioned formula (3).

[0154] <Step S18> In step S18, the control unit 7 acquires the electrical resistance value of the primary transfer roller 34 based on the state value acquired in step S16, the voltage value of the primary transfer bias voltage, and the current value of the transfer current detected in step S14. Here, the process of step S18 is executed by the second resistance value acquisition unit 76 of the control unit 7.

[0155] Specifically, the control unit 7 obtains the electrical resistance value of the primary transfer roller 34 using the above-mentioned formula (5).

[0156] <Step S19> In step S19, the control unit 7 executes a first determination process to determine, based on the state value acquired in step S16, whether or not it is time to replace the photosensitive drum 31. Here, the process of step S19 is executed by the first timing determination unit 77 of the control unit 7.

[0157] Specifically, when the state value acquired in step S16 exceeds the first threshold value, the control unit 7 determines that the time to replace the photosensitive drum 31 has come.

[0158] <Step S20> In step S20, the control unit 7 executes a second determination process to determine whether or not it is time to replace the charging roller 32, based on the electrical resistance value of the charging roller 32 acquired in step S17. Here, the process of step S20 is executed by the second timing determination unit 78 of the control unit 7.

[0159] Specifically, the control unit 7 determines that it is time to replace the charging roller 32 when the electrical resistance value of the charging roller 32 acquired in step S17 exceeds the second threshold value.

[0160] <Step S21> In step S21, the control unit 7 executes a third determination process to determine whether or not it is time to replace the primary transfer roller 34, based on the electrical resistance value of the primary transfer roller 34 acquired in step S18. Here, the process of step S21 is executed by the third timing determination unit 79 of the control unit 7.

[0161] Specifically, when the electrical resistance value of the primary transfer roller 34 acquired in step S18 exceeds the third threshold value, the control unit 7 determines that it is time to replace the primary transfer roller 34.

[0162] <Step S22> In step S22, the control unit 7 branches the processing depending on the results of the first judgment processing executed in step S19, the second judgment processing executed in step S20, and the third judgment processing executed in step S21.

[0163] Specifically, if it is determined in one or more of the determination processes that the replacement time has arrived (Yes in S22), the control unit 7 shifts the process to step S23. On the other hand, if it is not determined in any of the determination processes that the replacement time has arrived (No in S22), the control unit 7 ends the replacement time determination process.

[0164] <Step S23> In step S23, the control unit 7 executes a notification process to notify the user that the replacement time has come for the member determined to be due for replacement in the processes from step S19 to step S21.

[0165] Specifically, the control unit 7 causes the operation display unit 5 to display the name of the component determined to be due for replacement and a message informing the user that the replacement time has come for the component.

[0166] In this way, in image forming apparatus 100, the potential value of the charged area on photosensitive drum 31 is acquired. Furthermore, the state value is acquired based on the acquired potential value of the charged area and the current value of the charging current. Then, the electrical resistance value of charging roller 32 is acquired based on the acquired state value, the current value of the charging current, and the charging bias voltage. This makes it possible to acquire the electrical resistance value of charging roller 32 without providing a power supply with special functions, compared to a configuration in which two pulsed voltages with different frequencies are applied to charging roller 32 to acquire the electrical resistance value of charging roller 32.

[0167] In the image forming apparatus 100, the potential value of the charged region on the photosensitive drum 31 is acquired. The state value is acquired based on the acquired potential value of the charged region and the current value of the charging current. The electrical resistance value of the primary transfer roller 34 is then acquired based on the acquired state value, the current value of the transfer current, and the primary transfer bias voltage. This makes it possible to acquire the electrical resistance value with higher accuracy than in a configuration in which the electrical resistance value of the primary transfer roller 34 is calculated based on the primary transfer bias voltage and the transfer current without taking the state value into consideration.

[0168] Furthermore, in the image forming apparatus 100, the first developing current is detected for each of the plurality of specific voltages, and the potential value of the non-exposed area is obtained based on the DC voltage value of each of the specific voltages and the current value of the first developing current corresponding to each of the specific voltages. This makes it possible to obtain the potential value of the charged area without using a surface potential sensor capable of detecting the surface potential of the photosensitive drum 31.

[0169] The present invention may be applied to an image forming apparatus that forms an image using a one-component developer that does not contain a carrier. [Explanation of symbols]

[0170] 1 ADF 2 Image reading unit 3 Image forming unit 4 Paper feed section 5 Operation display section 6 Memory section 7 Control Unit 24 Image forming unit 25 Optical scanning device 26 Intermediate transfer belt 31 Photosensitive drum 31A Surface layer 32 Charging roller 33 Developing device 34 Primary transfer roller 44 Developing roller 61 1st power supply 62 First detection unit 63 2nd power supply 64 Second detection unit 65 Third power supply 66 Third detection unit 71 Second detection processing section 72 First detection processing section 73 Potential value acquisition unit 74 Status value acquisition unit 75 First resistance value acquisition unit 76 Second resistance value acquisition unit 77 First timing decision unit 78 Second timing judgment unit 79 Third timing judgment unit 100 Image forming device

Claims

1. an image carrier having a surface layer; a charging member for charging the image carrier; a first acquisition processing unit that acquires a potential value of a charged area of ​​the image carrier that has been charged by the charging member; a second acquisition processing unit that acquires a state value relating to the state of the surface layer based on the potential value of the charged region acquired by the first acquisition processing unit and the current value of a charging current that flows through the charging member when the charged region is formed; a third acquisition processing unit that acquires an electrical resistance value of the charging member based on the state value acquired by the second acquisition processing unit, the current value of the charging current, and the voltage value of the charging voltage applied to the charging member when the charging region is formed; An image forming apparatus comprising:

2. a light emitting unit that emits light to illuminate the charged area of ​​the image carrier; a developing member provided opposite the image carrier and configured to transport a developer to a facing portion between the developing member and the image carrier; a first detection processing unit that detects, for each of a plurality of specific voltages having different DC voltage values ​​applied to the developing member, a first development current that flows through the developer and the facing portion including the non-exposed area of ​​the charged area of ​​the image carrier that is not irradiated with light in response to the application of the specific voltage; Equipped with the first acquisition processing unit acquires a potential value of the non-exposure area based on a DC voltage value of each of the specific voltages and a current value of the first development current detected by the first detection processing unit corresponding to each of the specific voltages; The image forming apparatus according to claim 1 .

3. a second detection processing unit that detects a second development current that flows through the developer and the opposing portion including a non-charged region of the image carrier that is not charged by the charging member when a DC voltage is not applied to the development member, the first acquisition processing unit acquires, as the potential value of the non-exposed region, a DC voltage value of the specific voltage corresponding to a current value of the first developing current, the difference of which between the DC voltage value of each of the specific voltages and the current value of the first developing current detected by the first detection processing unit corresponding to each of the specific voltages and the current value of the second developing current detected by the second detection processing unit being equal to or less than a predetermined allowable value; The image forming apparatus according to claim 2 .

4. a first determination processing unit that determines whether or not the timing for replacing the image carrier has arrived based on the state value acquired by the second acquisition processing unit; 4. The image forming apparatus according to claim 1.

5. a second determination processing unit that determines whether or not the timing for replacing the charging member has arrived based on the electrical resistance value of the charging member acquired by the third acquisition processing unit; 5. The image forming apparatus according to claim 1.

6. the surface layer is formed using an organic photosensitive material; 6. The image forming apparatus according to claim 1.

7. 1. A method for acquiring an electrical resistance value, which is carried out in an image forming apparatus including an image carrier having a surface layer and a charging member that charges the image carrier, a first acquiring step of acquiring a potential value of a charged area of ​​the image carrier that has been charged by the charging member; a second acquisition step of acquiring a state value relating to the state of the surface layer based on the potential value of the charged region acquired in the first acquisition step and the current value of a charging current flowing through the charging member when the charged region is formed; a third acquisition step of acquiring an electrical resistance value of the charging member based on the state value acquired in the second acquisition step, the current value of the charging current, and the voltage value of the charging voltage applied to the charging member when forming the charging region; A method for obtaining electrical resistance values, including:

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