Image forming apparatus

Abstract

To improve secondary transfer properties while maintaining primary transfer properties in a configuration that applies a bias having the same polarity as an electrification polarity of a photoreceptor to an electrode member arranged downstream of a primary transfer unit.SOLUTION: In executing a setting operation to set a transfer bias during image formation, a control unit acquires a first result of detection performed by a detection unit when a test bias is not applied to a primary transfer member while an output current from an application unit applying a bias to an electrode member is maintained substantially constant, acquires a second result of detection performed by the detection unit when the test bias is applied to the primary transfer member while the output current from the application unit applying the bias to the electrode member is maintained substantially constant, and sets the transfer bias on the basis of the first detection result and the second detection result.SELECTED DRAWING: Figure 9

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 multifunction machine having a plurality of functions of these machines, which uses an electrophotographic or electrostatic recording system. [Background technology]

[0002] As an image forming apparatus using an electrophotographic method, such as a color copier, a color printer, or a color multifunction machine, an image forming apparatus using an intermediate transfer method is mainstream because of the advantages of being compact in size and being relatively easy to handle various recording materials. An image forming apparatus using the intermediate transfer method generally has a configuration including a plurality of photosensitive drums and an intermediate transfer belt. In such an image forming apparatus, toner images formed on the plurality of photosensitive drums are electrostatically primarily transferred onto the intermediate transfer belt in sequence at a primary transfer section. In addition, the toner images primarily transferred onto the intermediate transfer belt are electrostatically secondarily transferred onto a recording material such as paper at a secondary transfer section. In addition, with regard to the arrangement of members around the primary transfer section, the terms upstream and downstream refer to the upstream and downstream in the conveying direction of the intermediate transfer belt unless otherwise specified.

[0003] In the image forming apparatus as described above, the toner on the intermediate transfer belt tends to increase in charge due to discharge between the intermediate transfer belt and the photosensitive drum downstream of the primary transfer section. The inventors have further studied this issue and found that the increase in the charge of the toner on the intermediate transfer belt makes it difficult to transfer the toner to the recording material in the secondary transfer section. For example, the secondary transfer electric field required to transfer the toner to the recording material in the secondary transfer section becomes large, which deteriorates the graininess of the image and makes it difficult to transfer the toner uniformly to embossed paper with an uneven surface.

[0004] Here, Patent Document 1 discloses a configuration in which a conductive contact plate is provided downstream of the primary transfer section and on the inner surface of the intermediate transfer belt, and a bias of the same polarity as the charging polarity of the photosensitive drum is applied to this contact plate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-57963 A Summary of the Invention [Problem to be solved by the invention]

[0006] In order to suppress the increase in the amount of charge of the toner downstream of the primary transfer portion as described above, it is effective to suppress discharge downstream of the primary transfer portion.

[0007] Patent document 1 is silent about suppressing discharge downstream of the primary transfer unit. However, the inventors' further investigation revealed that in order to suppress discharge downstream of the primary transfer unit, it is effective to place a potential regulating member, which is a conductive electrode member, downstream of the primary transfer unit and on the inner surface of the intermediate transfer belt, and to apply a bias of the same polarity as the charging polarity of the photosensitive drum to this potential regulating member.

[0008] However, it was found that when the above-mentioned potential regulating member is used, leakage current occurs from the primary transfer portion to the potential regulating member, which may reduce the primary transfer current required in the direction of the photosensitive drum at the primary transfer portion, thereby impairing the primary transfer properties.

[0009] Therefore, it is necessary to suppress the discharge and improve the secondary transferability while maintaining the primary transferability. Patent Document 1 does not disclose correction of the primary transfer bias taking into account the current flowing from the primary transfer portion to the conductive contact plate.

[0010] Therefore, an object of the present invention is to improve secondary transfer performance while maintaining primary transfer performance in a configuration in which a bias of the same polarity as the charging polarity of a photosensitive body is applied to an electrode member arranged downstream of a primary transfer section. [Means for solving the problem]

[0011] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including a photoconductor capable of being charged to a predetermined polarity and carrying a toner image, an intermediate transfer belt capable of circulating and transporting the toner image, which has been primarily transferred from the photoconductor in a primary transfer section, to a recording material in a secondary transfer section, a primary transfer member that contacts the inner peripheral surface of the intermediate transfer belt to form the primary transfer section where the photoconductor and the intermediate transfer belt are in contact with each other and to which a bias is applied to transfer the toner image from the photoconductor to the intermediate transfer belt, a first application unit that applies a bias of a polarity opposite to the predetermined polarity to the primary transfer member, an electrode member that contacts the inner peripheral surface of the intermediate transfer belt downstream of the primary transfer section in the moving direction of the intermediate transfer belt, a second application unit that applies a bias of the same polarity as the predetermined polarity to the electrode member under constant current control, and a first application unit that applies a bias of a polarity opposite to the predetermined polarity to the electrode member under constant current control. The image forming apparatus has a detection unit that detects the voltage applied to the electrode member, and a control unit that controls execution of a setting operation to apply a test bias from the first application unit to the primary transfer member during image formation, and set the transfer bias to be applied from the first application unit to the primary transfer member during image formation, wherein, when executing the setting operation, the control unit acquires a first detection result by the detection unit when the test bias is not applied to the primary transfer member while maintaining the output current of the second application unit approximately constant, and acquires a second detection result by the detection unit when the test bias is applied to the primary transfer member while maintaining the output current of the second application unit approximately constant, and sets the transfer bias based on the first detection result and the second detection result. Effect of the Invention

[0012] According to the present invention, in a configuration in which a bias of the same polarity as the charging polarity of a photosensitive body is applied to an electrode member arranged downstream of a primary transfer section, it is possible to improve secondary transfer performance while maintaining primary transfer performance. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic block diagram of a control system of the image forming apparatus. [Diagram 3] 3A and 3B are a cross-sectional view and a perspective view of a potential restricting member; [Figure 4] FIG. 11 is a cross-sectional view of another example of a potential restricting member. [Diagram 5] FIG. 11 is a cross-sectional view of another example of a potential restricting member. [Figure 6] 4 is a cross-sectional view for explaining the arrangement of a potential restricting member. FIG. [Figure 7] 11 is a schematic graph for explaining ATVC control and correction of a primary transfer bias. FIG. [Figure 8] 5 is a schematic diagram for explaining a current path around a primary transfer portion. FIG. [Figure 9] FIG. 4 is a timing chart for explaining the control of the first embodiment. [Figure 10] FIG. 4 is a flowchart for explaining the control of the first embodiment. [Figure 11] FIG. 11 is a timing chart for explaining the control of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0015] [Example 1] 1. Overall configuration and operation of the image forming apparatus First, the overall configuration and operation of the image forming apparatus of this embodiment will be described. Fig. 1 is a schematic cross-sectional view of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 of this embodiment is a tandem type full-color printer that employs an intermediate transfer method and is capable of forming a full-color image on a sheet-shaped recording material S using an electrophotographic method.

[0016] The image forming apparatus 1 has an image forming section 2, a control section 3, a feeding section 4 for a recording material S, and a discharge section 5 for the recording material S. In addition, a temperature sensor 71 (FIG. 2) capable of detecting the temperature inside the apparatus and a humidity sensor 72 (FIG. 2) capable of detecting the humidity inside the apparatus are provided inside the image forming apparatus 1. The image forming apparatus 1 can form an image on the recording material S based on image information (image signal) acquired by a document reading device (not shown) provided in the image forming apparatus 1 or connected to the image forming apparatus 1. In addition, the image forming apparatus 1 can form an image on the recording material S based on image information (image signal) from an external device (not shown) such as a personal computer (host device), a digital camera, or a smartphone connected to the image forming apparatus 1. Incidentally, the recording material (transfer material, recording medium, sheet) S is a material on which an image is formed using toner, and specific examples include plain paper, thick paper, gloss coated paper, matte coated paper, embossed paper, or a synthetic resin sheet (synthetic paper) or overhead projector sheet (resin film) that is a substitute for plain paper, etc. Here, the recording material S may be referred to as "paper" (such as "paper," "embossed paper," or "high resistance paper"), but even in such cases, the recording material S includes materials other than paper or materials that contain materials other than paper.

[0017] The image forming section 2 forms an image on the recording material S fed from the feeding section 4 based on image information. The image forming section 2 includes image forming units 10y, 10m, 10c, and 10k, toner bottles 18y, 18m, 18c, and 18k, exposure devices 13y, 13m, 13c, and 13k, an intermediate transfer unit 20, a secondary transfer device 26, and a fixing device 27. The image forming units 10y, 10m, 10c, and 10k form toner images of yellow (y), magenta (m), cyan (c), and black (k), respectively. Note that elements having the same or corresponding functions or configurations provided for each color may be generally described by omitting the suffixes y, m, c, and k of the reference numerals indicating that the elements are for any one of the colors. The image forming apparatus 1 can also form a monochrome image, such as a black monochrome image, or a multi-color image, using the image forming units 10 for a desired single color or for some of the four colors.

[0018] The image forming unit 10 has a photosensitive drum 11 which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as an image carrier. The image forming unit 10 also has a charging roller 12 which is a roller-type charging member serving as a charging means. The image forming unit 10 also has a developing device 14 serving as a developing means. The image forming unit 10 also has a pre-exposure device 16 serving as a discharging means. The image forming unit 10 also has a drum cleaning device 17 serving as a photosensitive member cleaning means. The image forming unit 10 forms a toner image on an intermediate transfer belt 6 which will be described later.

[0019] The photosensitive drum 11 is movable (rotatable) while carrying an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 11 is a negatively charged organic photoconductor (OPC) having an outer diameter of 30 mm. The photosensitive drum 11 has an aluminum cylinder as a base and a surface layer formed on the surface of the cylinder. In this embodiment, the surface layer has three layers, an undercoat layer, a photocharge generation layer, and a charge transport layer, which are applied and laminated on the base in the following order. When an image forming operation is started, the photosensitive drum 11 is rotated in the direction of the arrow R1 in the figure (counterclockwise direction) at a predetermined peripheral speed (process speed) by a drive motor (not shown) as a drive means.

[0020] The surface of the rotating photosensitive drum 11 is uniformly charged by the charging roller 12. In this embodiment, the charging roller 12 is a rubber roller that comes into contact with the surface of the photosensitive drum 11 and rotates in accordance with the rotation of the photosensitive drum 11. A charging power source 73 (FIG. 2) serving as a charging bias application means (charging bias application section) is connected to the charging roller 12. During charging, the charging power source 73 applies a predetermined charging bias (charging voltage) to the charging roller 12.

[0021] The surface of the charged photosensitive drum 11 is scanned and exposed by the exposure device 13 based on image information, and an electrostatic image is formed on the photosensitive drum 11. In this embodiment, the exposure device 13 is a laser scanner. The exposure device 13 emits laser light according to image information of separated colors output from the control unit 3, and scans and exposes the surface (outer circumferential surface) of the photosensitive drum 11.

[0022] The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by supplying toner by the developing device 14, and a toner image (toner image, developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 is a two-component developing device that uses a two-component developer including toner (non-magnetic toner particles) and carrier (magnetic carrier particles) as a developer. A two-component developer is contained in a developing container (developing container body) 14b of the developing device 14, and an amount of toner corresponding to the consumed toner is replenished from a toner bottle 18. The developing device 14 has a developing sleeve 14a as a developing member (developer carrier). The developing sleeve 14a is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (aluminum in this embodiment). Inside the developing sleeve 14, a roller-shaped magnet (not shown) serving as a magnetic field generating means (magnetic field generating member) is fixed and arranged so as not to rotate relative to the developing container 14b. The developing sleeve 14a carries a two-component developer and transports it to a developing area facing the photosensitive drum 11. In the developing area, toner moves from the two-component developer on the developing sleeve 14a to the image area of ​​the electrostatic image on the photosensitive drum 11 and adheres to it. A developing power source 74 (FIG. 2) is connected to the developing sleeve 14 as a developing bias application means (developing bias application unit). During development, the developing power source 74 applies a predetermined developing bias (developing voltage) to the developing sleeve 14. In this embodiment, toner charged to the same polarity as the charging polarity of the photosensitive drum 11 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 11, the absolute value of the potential of which has been reduced by exposure after being uniformly charged (reversal development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0023] An intermediate transfer unit 20 is disposed so as to face the four photosensitive drums 11y, 11m, 11c, and 11k. The intermediate transfer unit 20 has an intermediate transfer belt 6, which is an endless belt serving as an intermediate transfer body. The intermediate transfer belt 6 is wound around and tensioned by a drive roller 21, a tension roller 22, and a secondary transfer inner roller 23 serving as a plurality of tension rollers. The intermediate transfer belt 6 is movable (rotatable) while carrying a toner image. The intermediate transfer belt 6 is rotated (moves orbitally) in the direction of arrow R2 in the figure (clockwise direction) at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drum 11 by a driving force transmitted by the drive roller 21 being driven to rotate by a drive motor (not shown) serving as a driving means. The tension roller 22 controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 applies a force to push the intermediate transfer belt 6 from the inner peripheral surface (back surface) side to the outer peripheral surface (front surface) side by the biasing force of a tension spring (not shown) composed of a compression coil spring, which is a biasing member as a biasing means. This force applies a tension of about 2 to 5 kg to the intermediate transfer belt 6 in its conveying direction (process progress direction, movement direction). The secondary transfer inner roller 23, together with the secondary transfer outer roller 25 described later, constitutes a secondary transfer device 26. On the inner peripheral surface side of the intermediate transfer belt 6, primary transfer rollers 15y, 15m, 15c, and 15k, which are roller-type primary transfer members as primary transfer means, are arranged corresponding to the photosensitive drums 11y, 11m, 11c, and 11k, respectively. In this embodiment, the primary transfer roller 15 is arranged opposite the photosensitive drum 11 and holds the intermediate transfer belt 6 between the photosensitive drum 11 and the primary transfer roller 15. The primary transfer roller 15 is pressed against the photosensitive drum 11 and comes into contact with the photosensitive drum 11 via the intermediate transfer belt 6, forming a primary transfer portion (primary transfer nip portion) N1, which is the contact portion between the photosensitive drum 11 and the intermediate transfer belt 6.

[0024] The toner image formed on the photosensitive drum 11 is transferred (primary transfer) onto the rotating intermediate transfer belt 6 by the action of the primary transfer roller 15 in the primary transfer portion N1. For example, when a full-color image is formed, the toner images of the respective colors of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are superimposed on the intermediate transfer belt 6 in order, and are multi-transferred. A primary transfer power supply 75 (FIG. 2) serving as a primary transfer bias application means (primary transfer bias application section) is connected to the primary transfer roller 15. During the primary transfer, the primary transfer power supply 75 applies to the primary transfer roller 15 a primary transfer bias (primary transfer voltage) which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner. As a result, the negative polarity toner image on the photosensitive drum 11 is primarily transferred onto the intermediate transfer belt 6. The primary transfer power supply 75 is connected to a voltage detection sensor 75a (FIG. 2) as a voltage detection means (voltage detection unit) for detecting the output voltage, and a current detection sensor 75b (FIG. 2) as a current detection means (current detection unit) for detecting the output current. In this embodiment, a primary transfer bias of, for example, about 1 to 2 kV is applied to the primary transfer roller 15 ("~" indicates a range including the numerical values ​​before and after it. The same applies below). In this embodiment, the primary transfer bias is controlled to a constant voltage. In this embodiment, the primary transfer power supplies 75y, 75m, 75c, and 75k are provided independently for each of the primary transfer rollers 15y, 15m, 15c, and 15k. In this embodiment, the primary transfer bias applied to each of the primary transfer rollers 15y, 15m, 15c, and 15k can be controlled individually.

[0025] In this embodiment, the primary transfer roller 15 has a core metal and an elastic layer of ion conductive foamed rubber (NBR rubber) formed around the core metal. The outer diameter of the primary transfer roller 15 is, for example, 15 to 20 mm. The primary transfer roller 15 has an electrical resistance of 1×10 5 ~1×10 8 A roller with a resistance of [Ω] (measured at N / N (23° C., 50% RH), applied voltage of 2 kV) can be suitably used.

[0026] In this embodiment, the intermediate transfer belt 6 is an endless belt having a two-layer structure in which a base layer and a surface layer are laminated in this order from the inner peripheral surface side to the outer peripheral surface side. The material constituting the base layer is a resin such as polyimide or polycarbonate, and a material containing an appropriate amount of carbon black as an antistatic agent can be suitably used. The thickness of the base layer is, for example, 0.05 to 0.15 [mm]. The material constituting the surface layer is suitably CR rubber provided with electrical conductivity by carbon black. The thickness of the surface layer is, for example, 0.200 to 0.300 [mm]. In this embodiment, the volume resistivity of the intermediate transfer belt 6 is 5×10 8 ~1×10 14 [Ω·cm] (23° C., 50% RH). Although the intermediate transfer belt 6 has a two-layer structure in this embodiment, it may have a single layer structure of a material equivalent to the above-mentioned base layer. The surface layer may be a resin coat layer containing a resin such as a fluororesin and having a thickness of about 0.002 to 0.01 [mm]. The intermediate transfer belt 6 may have a multi-layer structure of three or more layers.

[0027] On the outer peripheral surface side of the intermediate transfer belt 6, a secondary transfer outer roller 25, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed. The secondary transfer outer roller 25 as a secondary transfer member constitutes a secondary transfer device 26 together with the secondary transfer inner roller 23 as an opposing member (opposing electrode). The secondary transfer outer roller 25 is pressed toward the secondary transfer inner roller 23 and abuts against the secondary transfer inner roller 23 via the intermediate transfer belt 6 to form a secondary transfer portion (secondary transfer nip portion) N2, which is an abutment portion between the intermediate transfer belt 6 and the secondary transfer outer roller 25. The toner image formed on the intermediate transfer belt 6 is transferred (secondary transfer) onto the recording material S, which is being conveyed while being sandwiched between the intermediate transfer belt 6 and the secondary transfer outer roller 25, by the action of the secondary transfer device 26 at the secondary transfer portion N2. A secondary transfer power source 76 (FIG. 2) serving as a secondary transfer bias application means (secondary transfer bias application portion) is connected to the secondary transfer outer roller 25. During the secondary transfer, the secondary transfer power source 76 applies a secondary transfer bias (secondary transfer voltage), which is a DC voltage of the polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), to the secondary transfer outer roller 25. As a result, the negative polarity toner image on the intermediate transfer belt 6 is secondarily transferred onto the recording material S. The secondary transfer power source 76 is connected to a voltage detection sensor 76a (FIG. 2) as a voltage detection means (voltage detection unit) that detects the output voltage, and a current detection sensor 76b (FIG. 2) as a current detection means (current detection unit) that detects the output current. In addition, the core metal of the secondary transfer inner roller 23 is connected to a ground potential. In this embodiment, for example, a secondary transfer bias of about 1 to 6.5 [kV] is applied to the secondary transfer outer roller 25, and a secondary transfer current of about 15 to 100 [μA] is passed through the secondary transfer section N2, so that the toner image on the intermediate transfer belt 6 is secondarily transferred onto the recording material S. In this embodiment, the secondary transfer bias is controlled to a constant voltage. Alternatively, a secondary transfer bias, which is a DC voltage having the same polarity as the normal charging polarity of the toner, may be applied from a secondary transfer power source 76 to the secondary transfer inner roller 23 as the secondary transfer member, and the secondary transfer outer roller 25 as the opposing member may be connected to the ground potential.

[0028] The recording material S is conveyed from the feeding section 4 to the secondary transfer section N2 in parallel with the formation of the toner image on the intermediate transfer belt 6. The recording material S is accommodated in a cassette 41 as a recording material accommodation section of the feeding section 4. The recording material S accommodated in the cassette 41 is separated one by one by a feeding roller 42 as a feeding member of the feeding section 4 and sent out from the cassette 41. The recording material S is conveyed to a registration roller (a pair of registration rollers) 19 as a conveying member provided on a conveying path 44 of the recording material S by a conveying roller 43 as a conveying member of the feeding section 4. Then, the recording material S is conveyed to the secondary transfer section N2 by the registration roller 19 in synchronization with the toner image on the intermediate transfer belt 6. Although only one cassette 41 is illustrated in FIG. 1, the image forming apparatus 1 may have a plurality of cassettes 41. The feeding section 4 may also be capable of feeding the recording material S from a recording material storage section (recording material placement section) other than the cassette 41, such as a manual feed tray.

[0029] In this embodiment, the secondary transfer outer roller 25 has a core metal and an elastic layer of ion conductive foamed rubber (NBR rubber) formed around the core metal. The outer diameter of the secondary transfer outer roller 25 is, for example, 20 to 25 mm. The secondary transfer outer roller 25 has an electrical resistance of 1×10 5 ~1×10 8 A roller with a resistance of [Ω] (measured at N / N (23° C., 50% RH), applied voltage of 2 kV) can be suitably used.

[0030] The recording material S onto which the toner image has been transferred is conveyed to a fixing device 27 as a fixing means. The fixing device 27 has a fixing roller 27a and a pressure roller 27b. The fixing roller 27a incorporates a heater as a heating means. The pressure roller 27b presses against the fixing roller 27a to form a fixing section (fixing nip section). The fixing device 27 conveys the recording material S carrying an unfixed toner image by pinching it between the fixing roller 27a and the pressure roller 27b, thereby applying heat and pressure to fix (melt, fix) the toner image onto the recording material S. The temperature (fixing temperature) of the fixing roller 27a is detected by a fixing temperature sensor 77 (FIG. 2). The recording material S onto which the toner image has been fixed is conveyed by a discharge roller 51 and the like in the discharge section 5, and is discharged (output) from a discharge port (not shown) onto a discharge tray 52 provided outside the device body 1a of the image forming apparatus 1.

[0031] The surface of the photosensitive drum 11 after the primary transfer is neutralized by a pre-exposure device 16. In addition, toner (primary transfer residual toner) remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 6 during the primary transfer is removed from the photosensitive drum 11 and collected by a drum cleaning device 17. In this embodiment, the drum cleaning device 17 scrapes off the primary transfer residual toner from the surface of the rotating photosensitive drum 11 by a cleaning blade as a cleaning member and collects it in a collection container (not shown). The cleaning blade is a plate-shaped member that abuts against the photosensitive drum 11 with a predetermined pressing force. The cleaning blade abuts against the surface of the photosensitive drum 11 in a counter direction to the rotation direction of the photosensitive drum 11 so that the tip of the free end side faces the upstream side of the rotation direction of the photosensitive drum 11. In addition, deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 6 without being transferred to the recording material S during the secondary transfer are removed from the intermediate transfer belt 6 and collected by a belt cleaning device 24 as an intermediate transfer body cleaning means.

[0032] The image forming unit 10 may be configured as a cartridge (process cartridge) that is detachable from the main body 1a of the image forming apparatus 1. In this embodiment, the intermediate transfer belt 6, the tension roller of the intermediate transfer belt 6, the primary transfer rollers 15, the belt cleaning device 24, and the potential regulating members 8 described below form an intermediate transfer unit 20. The intermediate transfer unit 20 may be configured as a cartridge that is detachable from the main body 1a of the image forming apparatus 1.

[0033] 2. Control configuration FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a control unit 3 (control circuit) as a control means. The control unit 3 is configured to have a CPU 31 as an arithmetic processing means, a ROM 32 and a RAM 33 as storage means, an input / output circuit (I / F) (not shown) for inputting and outputting signals between the control unit 3 and an external device, and the like. The ROM 32 stores programs for controlling each part of the image forming apparatus 1, and the RAM 33 temporarily stores data related to control, and the like. The CPU 31 is a microprocessor that controls the entire control of the image forming apparatus 1, and is the main body of the system controller. The CPU 31 is connected to each part such as the feeding unit 4, the image forming unit 2, and the discharge unit 5, and exchanges signals with each of these parts and controls the operation of each of these parts. The ROM 32 stores an image formation control sequence for forming an image on the recording material S, and the like.

[0034] To the control unit 3, for example, a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, a secondary transfer power supply 76, a potential regulating power supply 80 described later, and the like are connected, and each of these is controlled by a signal from the control unit 3. Although not shown in the figure, in this embodiment, the charging power supply 73, the developing power supply 74, the primary transfer power supply 75, and the potential regulating power supply 80 are provided independently for each image forming unit 10. To the control unit 3, a temperature sensor 71, a humidity sensor 72, a voltage detection sensor 75a and a current detection sensor 75b of the primary transfer power supply 75, a voltage detection sensor 76a and a current detection sensor 76b of the secondary transfer power supply 76, a voltage detection sensor 80a and a current detection sensor 80b of the potential regulating power supply 80 described later, a fixing temperature sensor 77, and the like are connected. Signals (information) indicating the detection results of each sensor are input to the control unit 3.

[0035] Further, the control unit 3 is connected to an operation unit 70. The operation unit 70 has an input unit configured with operation buttons (keys) as input means, and a display unit 70a configured with a liquid crystal panel (display) as display means. In this embodiment, the display unit 70a is configured as a touch panel and also functions as an input means. An operator such as a user or a service person can operate the operation unit 70 to cause the image forming apparatus 1 to execute a job (described later). The control unit 3 receives a signal from the operation unit 70 and operates various devices of the image forming apparatus 1. Moreover, the image forming apparatus 1 can also execute a job in response to a signal not from the operation unit 70 but from an external device such as a personal computer.

[0036] Here, the image forming apparatus 1 executes a job (print job) which is a series of operations for forming and outputting an image on one or more recording materials S, which is started by one start instruction. The job generally includes an image forming process, a pre-rotation process, a paper-to-paper process in the case of forming images on multiple recording materials S, and a post-rotation process. The image forming process is a period during which electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer of the toner image are performed for the image to be actually formed on the recording material S and output, and the image formation time (image formation period) refers to this period. More specifically, the timing of the image formation time differs depending on the position where each of the processes of electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer is performed. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process, from when a start instruction is input until the image actually starts to be formed. The paper-to-paper process (recording material-to-recording material process, image-to-image process) is a period corresponding to the period between recording materials S when image formation is performed continuously on multiple recording materials S (continuous printing, continuous image formation). The post-rotation process is a period in which a tidying operation (preparatory operation) is performed after the image forming process. The non-image forming time (non-image forming period) is a period other than the image forming time, and includes the above-mentioned pre-rotation process, the sheet interval process, the post-rotation process, and further the pre-multiple rotation process which is a preparatory operation when the image forming apparatus 1 is turned on or when it returns from a sleep state.

[0037] 3. Issues with secondary transferability Next, the problem of secondary transferability will be further explained. For convenience, the magnitude (high / low) of voltage or potential refers to the magnitude (high / low) when compared in absolute value unless otherwise specified. Furthermore, with respect to the arrangement of the primary transfer section N1, the photosensitive drum 11, the primary transfer roller 15, and the potential regulating member 8 described later, the upstream and downstream refer to the upstream and downstream in the transport direction (process progress direction, movement direction) of the intermediate transfer belt 6 unless otherwise specified.

[0038] As described above, the toner on the intermediate transfer belt 6 tends to increase in charge due to discharge between the intermediate transfer belt 6 and the photosensitive drum 11 downstream of the primary transfer portion N1. As a result of the inventors' investigation, it was found that the mirror force between the intermediate transfer belt 6 and the toner increases as the charge of the toner on the intermediate transfer belt 6 increases, making it difficult to transfer the toner to the recording material S at the secondary transfer portion N2. For example, when the charge of the toner on the intermediate transfer belt 6 increases, the secondary transfer electric field required to transfer the toner to the recording material at the secondary transfer portion N2 becomes large, which may deteriorate the graininess of the image. In addition, it is difficult to uniformly transfer the toner to embossed paper or the like having an uneven surface, for example, because a gap occurs between the intermediate transfer belt 6 and the paper at the secondary transfer portion N2, and a relatively large secondary transfer electric field is required. Therefore, when the charge of the toner on the intermediate transfer belt 6 increases, it becomes even more difficult to transfer the toner to embossed paper or the like having an uneven surface. The embossed paper is a paper (fancy paper) on which a pattern is formed by embossing or embossing the surface of the paper. In addition, for recording materials (high resistance paper) that have relatively high electrical resistance, such as synthetic paper and resin film that are primarily made of synthetic resin, as with the embossed paper described above, it becomes even more difficult to transfer the toner as the charge amount of the toner on the intermediate transfer belt 6 increases.

[0039] In order to suppress the increase in the charge amount of the toner downstream of the primary transfer portion N1 as described above, it is effective to suppress discharge downstream of the primary transfer portion N1. As a result of the inventors' investigation, it was found that in order to suppress discharge downstream of the primary transfer portion N1, it is effective to dispose a potential regulating member, which is a conductive electrode member, on the inner circumferential surface of the intermediate transfer belt 6 downstream of the primary transfer portion N1 and to apply a bias of the same polarity as the charge polarity of the photosensitive drum 11 to the potential regulating member.

[0040] 4. Potential control material Next, the configuration of the potential regulating member 8 in this embodiment will be described. As shown in Fig. 1, in the image forming apparatus 1 of this embodiment, potential regulating members 8y, 8m, 8c, and 8k, which are electrode members, are disposed downstream of the primary transfer portions N1y, N1m, N1c, and N1k in contact with the inner circumferential surface of the intermediate transfer belt 6. In this embodiment, the potential regulating members 8y, 8m, 8c, and 8k provided for the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same configuration.

[0041] The shape of the potential regulating member 8 in this embodiment will be described. Fig. 3(a) is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) of the potential regulating member 8 in this embodiment. Fig. 3(b) is a perspective view of the potential regulating member 8 in this embodiment.

[0042] In this embodiment, the potential regulating member 8 has a planar first portion 81 arranged along the width direction of the intermediate transfer belt 6 (a direction substantially perpendicular to the transport direction, and a direction substantially parallel to the rotation axis direction of the photosensitive drum 11). In addition, in this embodiment, the potential regulating member 8 has a planar second portion 82 arranged along the width direction of the intermediate transfer belt 6 and extending in a direction substantially perpendicular to the plane of the first portion 81. In this embodiment, the contact surface 83, which is a contact portion of the first portion 81 of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6, is planar. That is, in this embodiment, the first portion 81 constituting the contact surface 83 of the potential regulating member 8 is a flat plate.

[0043] Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, the upstream end of the contact surface 83 is defined as "A (or upstream end A)" ​​and the downstream end of the contact surface 83 is defined as "B (or downstream end B)". In this embodiment, the upstream end A of the contact surface 83 corresponds to the upstream end of the potential regulating member 8, and the downstream end B of the contact surface 83 corresponds to the downstream end of the potential regulating member B. In order to more effectively suppress discharge between the intermediate transfer belt 6 and the photosensitive drum 11, it is preferable to bring the potential regulating member 8 into surface contact with the intermediate transfer belt 6. From this viewpoint, the length between the line segment AB, that is, the "contact width" which is the length of the contact surface 83 in the conveying direction of the intermediate transfer belt 6, is preferably 5 [mm] or more. The longer the length between the line segment AB, the greater the effect of suppressing the above-mentioned discharge, but if it is too long, it is considered that it becomes difficult to stably bring the potential regulating member 8 into contact with the intermediate transfer belt 6 due to the influence of the component precision and the like. The length between the line segments AB is often sufficient if it is 50 [mm] or less, typically 30 [mm] or less. That is, the length between the line segments AB is preferably about 5 to 50 [mm], typically about 5 to 30 [mm]. From another perspective, the length between the line segments AB is often sufficient if it is less than half the distance between the axes of the adjacent photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11. In this embodiment, the potential regulating member 8 with a length between the line segments AB of 25 [mm] is used. In this embodiment, the distance between the axes of the photosensitive drums 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drums 11 is about 100 [mm].

[0044] A potential regulating power supply 80 is connected to the potential regulating member 8 as a potential regulating bias applying means (potential regulating bias applying section). A voltage detection sensor 80a (FIG. 2) as a voltage detecting means (voltage detecting section) for detecting the output voltage of the potential regulating power supply 80 and a current detection sensor 80b (FIG. 2) as a current detecting means (current detecting section) for detecting the output current of the potential regulating power supply 80 are connected to the potential regulating member 8. In this embodiment, the potential regulating power supply 80 is connected to the second portion 82 of the potential regulating member 8. At least during the primary transfer during the image forming operation, the potential regulating member 8 is applied with a potential regulating bias (potential regulating current) which is a direct current having the same polarity as the charging polarity of the photosensitive drum 11 by the potential regulating power supply 80. During the primary transfer, more specifically, the period during which the primary transfer bias is applied, and more specifically, the period during which the image area (area to which the toner image can be transferred) on the intermediate transfer belt 6 passes through the primary transfer section N1. This makes it possible to suppress discharge between the intermediate transfer belt 6 and the photosensitive drum 11 downstream of the primary transfer section N1. In this embodiment, the potential regulating bias is a negative DC current. In this embodiment, the potential regulating bias is controlled to a constant current. In the configuration of this embodiment, the potential regulating bias (negative constant current) is preferably about -5 to -20 [μA]. The reason for adopting the constant current control is to manage the current value so that the negative charge moving from the surface of the photosensitive drum 11 downstream of the primary transfer portion N1 to the intermediate transfer belt 6 can effectively flow into the potential regulating member 8 via the inside of the intermediate transfer belt 6 in order to reduce the amount of discharge current downstream of the primary transfer portion N1. In this embodiment, a constant current is supplied to the potential regulating member 8 by the potential regulating power supply 80, but a certain effect can be expected even if the potential regulating member 8 is grounded.

[0045] The potential regulating member 8 is a member that is long in the width direction of the intermediate transfer belt 6. The length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction (the direction along the width direction of the intermediate transfer belt 6) is preferably longer than the maximum image width in the width direction of the intermediate transfer belt 6. The maximum image width is the length of the image area of ​​the largest image that can be formed by the image forming apparatus 1 in the width direction of the intermediate transfer belt 6. In this embodiment, the length of the contact surface 83 of the potential regulating member 8 in the longitudinal direction is longer than the maximum image width, and is longer than the width of the primary transfer roller 15 in the width direction of the intermediate transfer belt 6 that contacts the intermediate transfer belt 6. That is, in this embodiment, the range of the maximum image width and the range of the width of the primary transfer roller 15 in the width direction of the intermediate transfer belt 6 that contacts the intermediate transfer belt 6 are both within the range of the longitudinal length of the contact surface 83 of the potential regulating member 8. As a result, regardless of the length of the toner image transferred to the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6, the effect of suppressing the increase in the charge amount of the toner on the intermediate transfer belt 6 by suppressing the above-mentioned discharge can be obtained. On the other hand, in this embodiment, the length of the potential regulating member 8 in the longitudinal direction is shorter than the width of the intermediate transfer belt 6. That is, in this embodiment, the range of the length of the potential regulating member 8 in the longitudinal direction falls within the range of the width of the intermediate transfer belt 6. This reduces the possibility that, when the longitudinal end of the potential regulating member 8 protrudes beyond the width end of the intermediate transfer belt 6, discharge occurs between the potential regulating member 8 and the members surrounding the intermediate transfer belt 6, reducing the effect of suppressing the above-mentioned discharge.

[0046] The potential regulating member 8 can be made of, for example, only one material having electrical conductivity. In this embodiment, the potential regulating member 8 is substantially made of only a metal having electrical conductivity, such as SUS (stainless steel). More specifically, in this embodiment, the potential regulating member 8 is made by bending a metal plate (sheet metal) such as SUS to form a first portion 81 and a second portion 82. In this embodiment, neither the first portion 81 nor the second portion 82 of the potential regulating member 8 is substantially deformed when the image forming apparatus 1 is in use. By performing bending in this manner, the strength of the potential regulating member 8 can be increased. However, the present invention is not limited to such an embodiment, and the potential regulating member 8 may be made of two or more materials.

[0047] FIG. 4 is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) of another example of the potential regulating member 8. For example, as shown in FIG. 4, the potential regulating member 8 may have a base 84 having a shape similar to that of the potential regulating member 8 shown in FIG. 3, and a surface layer 85 provided on the surface of the base 84. The contact surface 83 that contacts the intermediate transfer belt 6 and the surface layer 85 that constitutes the connection portion with the potential regulating power source 80 are made of a conductive material, for example, metal or conductive resin. The base 84 may be made of a conductive material, but may also be made of a non-conductive material, for example, non-conductive resin. The base 84 and the surface layer 85 can be fixed by any fixing means, such as an adhesive or welding.

[0048] FIG. 5 is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) of still another example of the potential regulating member 8. For example, as shown in FIG. 5, the contact surface 83 of the potential regulating member 8 that contacts the intermediate transfer belt 6 may be made of a conductive nonwoven fabric 86. In FIG. 5, the conductive nonwoven fabric 86 is provided on the contact surface 83 of the potential regulating member 8 configured as shown in FIG. 4, but the conductive nonwoven fabric 86 may be provided on the contact surface 83 of the potential regulating member 8 configured as shown in FIG. 3. The conductive nonwoven fabric 86 can be fixed by any fixing means such as a conductive adhesive. Instead of the nonwoven fabric 86, a felt or pile fabric (cut pile fabric (velvet, brush) or loop pile fabric (terry cloth)) made of conductive fibers, or a sponge (foamed elastic body) made of a conductive rubber material or the like may be used. In this way, by constructing the contact surface 83 of the potential regulating member 8 that comes into contact with the intermediate transfer belt 6 from a flexible or elastic material, the possibility of scratches occurring on the inner surface of the intermediate transfer belt 6 due to friction between the inner surface of the intermediate transfer belt 6 and the potential regulating member 8 can be reduced.

[0049] Next, the arrangement of the potential regulating member 8 in this embodiment will be described. Fig. 6 is a cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 11) for explaining the arrangement of the potential regulating member 8 provided between two adjacent primary transfer portions N1 in the transport direction of the intermediate transfer belt 6. Fig. 6 shows, as an example, a potential regulating member 8c provided between the cyan and black primary transfer portions N1c and N1k.

[0050] In this embodiment, the outer diameter of the photosensitive drum 11 is 30 [mm], the outer diameter of the primary transfer roller 15 is 18 [mm], and the thickness of the intermediate transfer belt 6 is 0.350 [mm]. In this embodiment, the primary transfer roller 15 is offset downstream from the photosensitive drum 11. In this embodiment, the offset amount X1 is 3 [mm]. The offset amount X1 is the distance between the rotation center of the photosensitive drum 11 and the rotation center of the primary transfer roller 15 in the direction along the common tangent of the sides of the multiple photosensitive drums 11 that contact the intermediate transfer belt 6 in a cross section that is substantially perpendicular to the rotation axis direction of the photosensitive drum 11.

[0051] Here, in order to explain the arrangement of the potential regulating member 8, it is assumed that the potential regulating member 8 is removed. In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line passing through the tension surface on the inner peripheral side of the intermediate transfer belt 6 downstream of the primary transfer portion N1 in the absence of the potential regulating member 8 is defined as a straight line L. More specifically, this straight line L corresponds to the tension surface in a state in which only the potential regulating member 8 is substantially removed from the configuration of the image forming apparatus 1 in the image forming operation state (however, the photosensitive drum 11 and the intermediate transfer belt 6 are stopped). In addition, on the straight line L, a point where the inner peripheral surface of the intermediate transfer belt 6 separates from the tension member immediately adjacent to the upstream side of the potential regulating member 8 is defined as "C (or upstream tension portion C)", and a point where the inner peripheral surface of the intermediate transfer belt 6 separates from the tension member immediately adjacent to the downstream side of the potential regulating member 8 is defined as "D (or downstream tension portion D)". In addition, although the straight line L is shown generally horizontally in FIG. 6, if the surface of the primary transfer roller 15 is lifted toward the photosensitive drum 11 due to deformation of the elastic layer of the primary transfer roller 15 or the like, the straight line L may be inclined so as to descend downward in the figure as it approaches the downstream side.

[0052] In this embodiment, the tension member immediately upstream of the potential regulating member 8 is the primary transfer roller 15, and the position on the inner circumferential surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the primary transfer roller 15 is the upstream tension portion C. However, the tension member immediately upstream of the potential regulating member 8 is not limited to the primary transfer roller 15. For example, in the case where the primary transfer roller 15 is disposed offset upstream with respect to the photosensitive drum 11, the position on the inner circumferential surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the photosensitive drum 11 is the upstream tension portion C.

[0053] In this embodiment, the tension members immediately downstream of the potential regulating member 8 are the photosensitive drums 11m, 11c, and 11k arranged adjacent to the yellow, magenta, and cyan primary transfer portions N1y, N1m, and N1c, respectively. The downstream tension portion D is a position on the inner circumferential surface of the intermediate transfer belt 6 corresponding to a position where the intermediate transfer belt 6 separates from the photosensitive drums 11m, 11c, and 11k. However, the tension member immediately downstream of the potential regulating member 8 is not limited to the photosensitive drum 11. For example, when the primary transfer roller 15 is arranged offset upstream with respect to the photosensitive drum 11, the downstream tension portion D is a position on the inner circumferential surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the primary transfer roller 15. In this embodiment, the downstream tension member immediately downstream of the black primary transfer portion N1k is a tension roller (tension roller in this embodiment) 22. The position on the inner circumferential surface of the intermediate transfer belt 6 where the intermediate transfer belt 6 separates from the tension roller 22 is the downstream tension portion D.

[0054] Furthermore, for any primary transfer portion N1, if there is another tension roller that regulates the posture of the intermediate transfer belt 6 during image formation operation as the nearest tension member downstream of the potential regulating member 8, the straight line L and the downstream tension portion D are defined based on the tension roller. Also, even if a scraper or brush, rather than a tension roller, is in contact with the inner peripheral surface of the intermediate transfer belt 6 for the purpose of cleaning the inner peripheral surface of the intermediate transfer belt 6, it can be considered as the nearest downstream tension member as long as it regulates the posture of the intermediate transfer belt 6 during image formation. A scraper is generally made of a sheet-like or film-like member.

[0055] As shown in FIG. 6, the potential regulating member 8 is disposed downstream of the primary transfer portion N1 so as not to contact the primary transfer roller 15 and not to contact the photosensitive drum 11 via the intermediate transfer belt 6. At this time, the closer the upstream end A is to the primary transfer portion N1, the greater the effect of suppressing the above-mentioned discharge. In this embodiment (FIG. 6), the potential regulating member 8 is disposed at a position downstream of the primary transfer portion N1 so that the distance X2 from the primary transfer roller 15 to the upstream end A is about 8 [mm]. Here, the distance X2 is the distance between the rotation center of the primary transfer roller 15 and the upstream end A in the direction along the common tangent line of the side of the multiple photosensitive drums 11 that contact the intermediate transfer belt 6 in a cross section that is substantially perpendicular to the rotation axis direction of the photosensitive drum 11. That is, in this embodiment, in the direction along the common tangent line, the distance from the rotation center of the primary transfer roller 15 to the upstream end A is smaller than the distance (radius) from the rotation center of the primary transfer roller 15 to the outer periphery of the primary transfer roller 15. Although not limited thereto, the distance X2 is preferably about 1 to 20 mm, and typically about 1 to 10 mm.

[0056] In this embodiment, the potential regulating member 8 is pressed against the inner peripheral surface of the intermediate transfer belt 6 at both ends in the longitudinal direction by a pressing spring 87 (FIG. 3(b)) constituted by a compression coil spring, which is a pressing member serving as a pressing means. At this time, the contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is made to intrude toward the photosensitive drum 11 side from the straight line L. This allows the potential regulating member 8 to contact the intermediate transfer belt 6 more stably even if the intermediate transfer belt 6 is wavy or vibrated during the image forming operation (while the intermediate transfer belt 6 is running). In this embodiment, the pressing force of the pressing spring 87 is set (adjusted) so that the upstream end A and downstream end B of the contact surface 83, which is the contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6, intrude toward the photosensitive drum 11 side by about 0.5 [mm] from the straight line L. By thus causing the contact surface 83 of the potential regulating member 8 to intrude into the photosensitive drum 11 side with respect to the straight line L, the potential regulating member 8 can be brought into surface contact with the intermediate transfer belt 6 more stably even if the intermediate transfer belt 6 is wavy or vibrated during the image forming operation (while the intermediate transfer belt 6 is running). Although not limited thereto, the intrusion amount of the contact surface 83 of the potential regulating member 8 into the straight line L is preferably about 0.3 to 5 mm, and typically about 0.5 to 3 mm. If this intrusion amount is too small, it may be difficult to bring the potential regulating member 8 into stable contact with the intermediate transfer belt 6, and if it is too large, it may be difficult to transport the intermediate transfer belt 6 stably.

[0057] Here, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11, a straight line passing through the upstream end A and the downstream end B of the contact surface 83 is defined as a straight line M. In this case, it is preferable that the straight line M does not intersect with the line segment CD of the straight line L. This allows the intermediate transfer belt 6 and the potential regulating member 8 to be in surface contact with each other more reliably when the contact surface 83 of the potential regulating member 8 is flat. When the straight line M intersects with the line segment CD of the straight line L, there is a possibility that only the end of the potential regulating member 8 on the upstream end A side or the end of the potential regulating member 8 on the downstream end B side can be in contact with the inner circumferential surface of the intermediate transfer belt 6. In this case, it may be difficult to enhance the discharge suppression effect by the surface contact.

[0058] 6, the potential regulating member 8 is disposed so that the straight line M and the straight line L are substantially parallel, but the potential regulating member 8 may be disposed so that the straight line M is inclined with respect to the straight line L as long as the straight line M does not intersect with the line segment CD of the straight line L. For example, by inclining the straight line M with respect to the straight line L so that the upstream end A side is closer to the straight line L than the downstream end B side, it is possible to reduce the curvature generated in the intermediate transfer belt 6 due to the intermediate transfer belt 6 running around in the vicinity of the upstream end A. This is therefore advantageous in reducing the possibility that scratches will occur on the inner peripheral surface of the intermediate transfer belt 6 due to friction with the potential regulating member 8.

[0059] The contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 is not limited to being flat. For example, the potential regulating member 8 may be formed of a bent plate or the like in which the cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11 is curved in a convex shape toward the photosensitive drum 11, and the contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 may be a curved surface that is convex toward the photosensitive drum 11. By making the contact portion (contact surface) of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 a curved surface in this manner, it is possible to reduce stress when the potential regulating member 8 rubs against the intermediate transfer belt 6. By using a roller-shaped potential regulating member 8, the contact portion of the potential regulating member 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 may be a curved surface.

[0060] 5. Primary transfer bias correction control Next, the correction control of the primary transfer bias in this embodiment will be described. In this embodiment, the correction control of the primary transfer bias is the same for each of the primary transfer parts N1y, N1m, N1c, and N1k, and is performed synchronously and individually for each of the primary transfer parts N1y, N1m, N1c, and N1k. Here, the description will be focused on one primary transfer part N1.

[0061] In this embodiment, the image forming apparatus 1 performs ATVC (Active-Transfer-Voltage-Control) control of the primary transfer unit N1 in order to pass a primary transfer current required for primary transfer of the toner image on the photosensitive drum 11 to the intermediate transfer belt 6 during image formation. In the ATVC control, a voltage-current characteristic is obtained using a test bias (test voltage, test current) in order to determine a primary transfer bias during image formation according to the total resistance value of the primary transfer unit N1 composed of the photosensitive drum 11, the intermediate transfer belt 6, and the primary transfer roller 15. The ATVC control is executed under the control of the control unit 3.

[0062] Specifically, during non-image formation when there is no toner image on the primary transfer portion N1, a predetermined voltage or a predetermined current is supplied to the primary transfer roller 15 from the primary transfer power source 75 as a test bias. The set value of the predetermined voltage or the predetermined current of the test bias is one level or multiple levels. In this embodiment, three levels of test bias are supplied to the primary transfer roller 15 while changing the set value. Then, the current detection sensor 75a or the voltage detection sensor 75b detects the current flowing through the primary transfer roller 15 (primary transfer power source 75) when the test bias of the predetermined voltage is supplied to the primary transfer roller 15, or the voltage (output voltage of the primary transfer power source 75) applied to the primary transfer roller 15 when the test bias of the predetermined current is supplied to the primary transfer roller 15. This makes it possible to obtain the voltage-current characteristic according to the impedance (total resistance value) of the primary transfer portion N1. Also, based on this voltage-current characteristic, the voltage required to flow a primary transfer current suitable for the primary transfer of toner according to the impedance (total resistance value) of the primary transfer portion N1 is calculated. During image formation, a primary transfer bias (herein also referred to as an "effective bias") is applied to the primary transfer roller 15 under constant voltage control with the calculated voltage as a target voltage.

[0063] In this embodiment, the target current required for the primary transfer of toner is determined in advance based on an experiment or the like and stored in the ROM 32 as an appropriate value according to, for example, the environment (temperature, humidity). In the ATVC control, for example, as the first test bias, a current (for example, 50 [μA]) corresponding to the target current according to the environment at that time is first supplied to the primary transfer roller 15 under constant current control ((1) in FIG. 7(a)). Then, the voltage value (for example, 1200 [V]) applied to the primary transfer roller 15 when the first test bias is supplied to the primary transfer roller 15 is detected. Furthermore, in the ATVC control, the second and third test biases, which are two levels of test biases obtained by increasing or decreasing the voltage value detected when the first test bias is supplied, by ±200 V, are supplied to the primary transfer roller 15 under constant voltage control ((2) and (3) in FIG. 7(a)). Then, the current values ​​flowing through the primary transfer roller 15 when the second and third test biases are supplied are detected. From the above three points, the voltage-current characteristics are obtained. Further, based on the obtained voltage-current characteristics, a voltage value required to pass a target current is calculated, for example, by linear approximation. Note that the voltage value required to pass a target current may be calculated by curve approximation depending on the configuration of the image forming apparatus 1. Then, the calculated voltage value is determined as a target voltage for the effective bias Vtr to be applied during image formation. During image formation, the effective bias Vtr is applied to the primary transfer roller 15 under constant voltage control with the calculated voltage value as the target voltage.

[0064] The constant current control is a control for adjusting the output of a power supply so that the current supplied to the target is substantially constant at a target current, whereas the constant voltage control is a control for adjusting the output of a power supply so that the voltage applied to the target is substantially constant at a target voltage.

[0065] In this embodiment, the ATVC control is performed during the pre-rotation process (or pre-multiple rotation process) of a job as a non-image formation time. However, the present invention is not limited to this, and the ATVC control can be performed during the non-image formation time, such as during the inter-sheet process at a predetermined frequency (for each predetermined number of images formed) during continuous image formation.

[0066] Here, in this embodiment, the potential regulating bias applied to the potential regulating member 8 is constant current controlled. In this embodiment, the target current of the potential regulating bias is determined in advance based on experiments or the like, and an appropriate value corresponding to, for example, the environment (temperature, humidity) is stored in the ROM 32. During image formation (or during ATVC control, which will be described later), the potential regulating bias is constant current controlled with a target current corresponding to the environment. Specifically, the potential regulating bias is set so as to sufficiently suppress the increase in the charge amount of the toner on the intermediate transfer belt 6, which changes due to discharge downstream of the primary transfer portion N1. In addition, the potential regulating bias is set so as to maintain sufficient primary transferability so that the primary transfer efficiency does not fall below a target value due to the current flowing from the primary transfer portion N1 to the potential regulating member 8 or the potential difference between the primary transfer bias and the potential regulating bias. In other words, the set value of the potential regulating bias that satisfies such conditions is determined in advance by experiments or the like.

[0067] However, the resistance values ​​of the intermediate transfer belt 6, the primary transfer roller 15, etc. fluctuate due to the temperature and humidity environment in which the image forming apparatus 1 is installed, the effect of the temperature rise inside the apparatus due to the continuous operation of the image forming apparatus 1, etc. As a result, the primary transfer bias and the potential regulating bias may deviate from the current or voltage relationship set as a target, and the primary transferability may be impaired. Due to the effect of individual differences in the resistance values ​​of the intermediate transfer belt 6, the primary transfer roller 15, and the potential regulating member 8, the degree of deviation of the current or voltage as described above may vary for each individual image forming apparatus 1 and for each usage situation of the image forming apparatus 1. FIG. 8 is a schematic diagram showing the current around the primary transfer portion N1. For example, when a target current Ia is supplied from the primary transfer power source 75 to the primary transfer roller 15, if there is no potential regulating member 8, the target current Ia and the transfer effective current I1 flowing toward the photosensitive drum 11 are approximately equal. However, by disposing the potential regulating member 8 downstream of the primary transfer portion N1, the current path from the primary transfer roller 15 branches into a transfer effective current I1 and an advection current I2 flowing toward the potential regulating member 8. As described above, in the ATVC control, a target voltage of the effective bias Vtr for flowing a target current according to the total resistance value of the primary transfer portion N1 is determined. At this time, the advection current I2 to the potential regulating member 8 is affected by the resistance fluctuations described above. Therefore, if the ATVC control is performed without considering the advection current I2 to the potential regulating member 8 or the voltage Vb detected by the voltage detection sensor 80a of the potential regulating power supply 80, the actual transfer effective current I1 may decrease, and the primary transferability may be impaired.

[0068] To explain further, as described above, in order to suppress discharge downstream of the primary transfer portion N1, it is effective to dispose the potential regulating member 8, which is a conductive electrode member, on the inner peripheral surface of the intermediate transfer belt 6 downstream of the primary transfer portion N1 and to apply a bias of the same polarity as the charging polarity of the photosensitive drum 11 to the potential regulating member 8. In order to effectively suppress discharge downstream of the primary transfer portion N1 and improve secondary transferability, it is desirable to move the potential regulating member 8 closer to the primary transfer portion N1 and to set a higher bias of the same polarity as the photosensitive drum 11 to be applied to the potential regulating member 8. However, the closer the potential regulating member 8 is to the primary transfer portion N1 and the higher the bias applied to the potential regulating member 8, the more a potential difference is generated between the primary transfer portion N1 and the potential regulating member 8, and the larger the leakage current from the primary transfer portion N1 to the potential regulating member 8 becomes. As a result, the primary transfer current flowing toward the photosensitive drum 11 at the primary transfer portion N1 decreases, and the primary transferability is impaired. Conversely, the further the potential regulating member 8 is moved from the primary transfer portion N1 in order to maintain the primary transfer performance, and the lower the bias applied to the potential regulating member 8, the less effective it becomes in suppressing discharge downstream of the primary transfer portion N1, making it more difficult to suppress an increase in the charge amount of the toner, and the secondary transfer performance may be impaired. Therefore, in order to improve the secondary transfer performance while maintaining the primary transfer performance, it is desirable to correct the primary transfer bias taking into account the current flowing from the primary transfer portion N1 to the potential regulating member 8 and maintain the primary transfer current flowing in the direction of the photosensitive drum 11.

[0069] Correction control of the primary transfer bias in this embodiment will be described with reference to Fig. 9. Fig. 9 is a timing chart showing transitions of the voltage value and current value of the primary transfer bias and the potential regulating bias during execution of a job in this embodiment.

[0070] In this embodiment, the control unit 3 corrects the primary transfer bias when executing ATVC control of the primary transfer unit N1 in the pre-rotation process of the job. In this embodiment, the control unit 3 detects the voltage value applied to the potential regulating member 8 (potential regulating power source 80) in a state in which a potential regulating bias is applied to the potential regulating member 8 in the pre-rotation process of the job, when a test bias is not applied to the primary transfer roller 15 and when a test bias is applied to the primary transfer roller 15. Then, the control unit 3 corrects the primary transfer bias based on these detected voltage values.

[0071] When a job is started, the intermediate transfer belt 6 starts to be driven, and a pre-rotation process starts (T1). After that, the potential regulating power supply 80 starts to apply a potential regulating bias to the potential regulating member 8 under constant current control (T2). In this embodiment, the target current Ib of the potential regulating bias at this time is set to a predetermined current (e.g., Ib=-10 [μA]) according to the same environment as during image formation. Then, before the test bias is applied to the primary transfer roller 15, the voltage Vb1 applied to the potential regulating member 8 is detected by the voltage detection sensor 80a (e.g., Vb1=-1000 [V]).

[0072] After that, the ATVC control is started, and the test bias (the first test bias described above) is applied from the primary transfer power supply 75 to the primary transfer roller 15 under constant current control, aiming at a target current I1 (for example, I1=50 [μA]) (T3). The target current I1 at this time corresponds to the target current of the primary transfer bias during image formation according to the environment. Then, the effective bias Vtr (for example, Vtr=1200V) is determined as described above. As described above, in this embodiment, three levels of test bias are applied to the primary transfer roller 15 under the ATVC control, but for simplicity, FIG. 9 illustrates only the test bias under constant current control aiming at the target current during image formation. The effective bias Vtr is determined by the application of the test bias, but the effective bias Vtr determined here is affected by the fluctuation of the voltage Vb1 applied to the potential regulating member 8 due to the resistance fluctuation of the intermediate transfer belt 6, as described above. This may cause a deviation between the target current Ia and the actual effective transfer current I1.

[0073] Therefore, in this embodiment, when the test bias (the above-mentioned first test bias) is applied to the primary transfer roller 15, the voltage value Vb2 applied to the potential regulating member 8 is detected by the voltage detection sensor 80a (for example, Vb2=-700[V]). In addition, a difference ΔV (=|Vb1-Vb2|) (for example, ΔV=300[V]) between the voltage value Vb1 detected when the test bias is not applied to the primary transfer roller 15 and the voltage value Vb2 detected when the test bias is applied to the primary transfer roller 15 is obtained. Then, in this embodiment, this difference ΔV is regarded as the voltage of the above-mentioned advection current I2 flowing into the potential regulating member 8, and the difference ΔV is added to the above-mentioned effective bias Vtr to determine a corrected effective bias Vtr' (for example, Vtr'=1500[V]). That is, it is possible to determine the effective bias Vtr' according to the voltage-current characteristics in the case where the potential regulating member 8 is not present, as shown by the dashed line in Fig. 7(b), compared with the voltage-current characteristics in the case where the potential regulating member 8 is present, as shown by the solid line in Fig. 7(b). During image formation, the determined corrected effective bias Vtr' is applied to the primary transfer roller 15 under constant voltage control (T4 to T5).

[0074] In this embodiment, the primary transfer bias is subjected to constant voltage control, so the effective bias Vtr is corrected by the voltage difference ΔV to determine the voltage value of the corrected effective bias Vtr', but the present invention is not limited to this. For example, when the primary transfer bias is subjected to constant current control, the current difference ΔI corresponding to the voltage difference ΔV is obtained based on the voltage-current characteristic obtained by the ATVC control as described above. Then, the target current Ia is determined by adding this difference ΔI to the target current I1 of the test bias, and the primary transfer bias is subjected to constant current control with the determined target current Ia during image formation. This also makes it possible to correct the primary transfer bias in consideration of the fluctuation of the current flowing through the potential regulating member 8. When the primary transfer bias is subjected to constant current control, for example, the initial voltage value of the primary transfer bias during image formation can be determined by the ATVC control. In addition, both the constant voltage control and the constant current control of the primary transfer bias may be performed.

[0075] In this embodiment, the voltage applied to the potential control member 8 when the test bias is applied is detected as the voltage when the first test bias is applied, but the present invention is not limited to this. For example, an effective bias Vtr corresponding to a target current determined based on voltage-current characteristics obtained by applying multiple levels of test bias may be applied again as a test bias, and the voltage applied to the potential control member 8 at this time may be detected.

[0076] Next, the procedure of the correction control of the primary transfer bias in this embodiment will be described with reference to Fig. 10. Fig. 10 is a flow chart showing an outline of the job procedure in this embodiment.

[0077] When the control unit 3 starts a job (S1), it starts supplying a predetermined current from the potential regulating power source 80 to the potential regulating member 8 under constant current control, and detects the voltage Vb1 applied to the potential regulating member 8 by the voltage detection sensor 80a (S2). Next, the control unit 3 applies a test bias from the primary transfer power source 75 to the primary transfer roller 15 (S3), and determines the effective bias Vtr based on the acquired voltage-current characteristics of the primary transfer unit N1 (S4). Also, in S4, the voltage detection sensor 80a detects the voltage Vb2 applied to the potential regulating member 8 when the test bias (test bias constant current controlled at the target current I1) is applied. Next, the control unit 3 obtains the difference (potential change) ΔV (=|Vb1-Vb2|) between the voltages Vb1 and Vb2 (S5). After that, the control unit 3 calculates the corrected effective bias Vtr' by adding ΔV to the effective bias Vtr (S6). Then, the control section 3 applies the corrected effective bias Vtr' to the primary transfer roller 15 under constant voltage control to perform a normal image forming operation (S7), and ends the job (S8).

[0078] As described above, in this embodiment, the image forming apparatus 1 includes a photoconductor (photoconductor drum) 11 that can be charged to a predetermined polarity and that carries a toner image, an intermediate transfer belt 6 that can be rotated and that transports the toner image that has been primarily transferred from the photoconductor 11 at a primary transfer portion N1 to a recording material S at a secondary transfer portion N2, a primary transfer member (primary transfer roller) 15 that contacts the inner peripheral surface of the intermediate transfer belt 6 to form the primary transfer portion N1 where the photoconductor 11 and the intermediate transfer belt 6 abut, and that is applied with a bias to transfer the toner image from the photoconductor 11 to the intermediate transfer belt 6, a first application unit (primary transfer power source) 75 that applies a bias of a polarity opposite to the predetermined polarity to the primary transfer member 15, an electrode member (potential regulating member) 8 that contacts the inner peripheral surface of the intermediate transfer belt 6 downstream of the primary transfer portion N1 in the moving direction of the intermediate transfer belt 6, and a constant current bias that is the same polarity as the predetermined polarity to the electrode member 8. The control unit 3 has a second application unit (potential regulating power supply) 80 that applies a test bias under control, a detection unit (voltage detection sensor) 80a that detects the voltage applied to the electrode member 8, and a control unit 3 that performs control to execute a setting operation (ATVC control) that applies a test bias from the first application unit 75 to the primary transfer member 15 during image formation, and sets the transfer bias to be applied from the first application unit 75 to the primary transfer member 15 during image formation.When executing the setting operation, the control unit 3 acquires a first detection result by the detection unit 80a when the test bias is not applied to the primary transfer member 15 while maintaining the output current of the second application unit 80 approximately constant, and acquires a second detection result by the detection unit 80a when the test bias is applied to the primary transfer member 15 while maintaining the output current of the second application unit 80 approximately constant, and sets the transfer bias based on the first detection result and the second detection result. In addition, maintaining the output current substantially constant includes controlling the output current to approach a predetermined target value and also including a case where the output current fluctuates within an error range. In this embodiment, when performing the setting operation, the control unit 3 obtains the first detection result while performing constant current control so that a predetermined current flows through the electrode member 8 by the second application unit 80, and obtains the second detection result while performing constant current control so that the predetermined current flows through the electrode member 8 by the second application unit 80.In this embodiment, the control unit 3 performs constant current control so that the predetermined current flows from the second application unit 80 to the electrode member 8 during image formation. In addition, in this embodiment, the control unit 3 obtains the second detection result after obtaining the first detection result. In addition, in this embodiment, the image forming apparatus 1 has another detection unit (voltage detection sensor 75a, current detection sensor 75b) that detects the current flowing through the primary transfer member 15 or the voltage applied to the primary transfer member 15, and the control unit 3 sets the target voltage of the transfer bias based on the voltage-current characteristic obtained based on the detection result by the other detection units 75a and 75b when the test bias is applied from the first application unit 75 to the primary transfer member 15 in the setting operation, the target current of the transfer bias that is set in advance, and the difference between the first detection result and the second detection result. In addition, in the setting operation, the control unit 3 may be configured to set a target current of the transfer bias based on a preset target current of the transfer bias and a difference between the first detection result and the second detection result.

[0079] As described above, according to this embodiment, it is possible to maintain primary transferability by securing the target current required for primary transfer, while improving secondary transferability by effectively suppressing discharge downstream of the primary transfer section N1 with a predetermined potential regulating bias.

[0080] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0081] In the first embodiment, the potential regulating bias is applied to the potential regulating member 8 first, and then the test bias is applied to the primary transfer roller 15, but the present invention is not limited to this embodiment. For example, it is also possible to first apply the test bias to the primary transfer roller 15, and then apply the potential regulating bias to the potential regulating member 8, and correct the primary transfer bias by determining the change in the voltage applied to the potential regulating member 8. An example will be described below.

[0082] FIG. 11 is a timing chart showing the transition of the voltage value and the current value of the primary transfer bias and the potential regulating bias during the execution of a job in this embodiment. When the job is started, the driving of the intermediate transfer belt 6 is started, and the pre-rotation process is started (T1). After that, the ATVC control is started, and the test bias is applied from the primary transfer power source 75 to the primary transfer roller 15 under constant current control aiming at the target current I1, and the execution bias Vtr is determined as described in the first embodiment (T2). At this time, constant current control is performed so that the output current of the potential regulating power source 80 becomes 0 μA, and the voltage Vb2 applied to the potential regulating member 8 corresponding to the current value induced by the application of the test bias and flowing through the potential regulating member 8 is detected by the voltage detection sensor 80a. As described in the first embodiment, three levels of the test bias are applied to the primary transfer roller 15 in the ATVC control, but for simplicity, FIG. 11 shows only the test bias under constant current control aiming at the target current during image formation. Thereafter, application of the test bias is terminated, and application of a potential regulating bias under constant current control from the potential regulating power supply 80 to the potential regulating member 8 is started (T3). The target current Ib of the potential regulating bias at this time is set to a predetermined current according to the same environment as during image formation. Then, the voltage value Vb1 applied to the potential regulating member 8 is detected by the voltage detection sensor 80a.

[0083] Thereafter, a difference ΔV (=|Vb1-Vb2|) between a voltage value Vb1 detected when the test bias is not applied to the primary transfer roller 15 and a voltage value Vb2 detected when the test bias is applied to the primary transfer roller 15 is calculated. Then, this difference ΔV is regarded as the voltage of the aforementioned advection current I2 flowing into the potential regulating member 8, and the difference ΔV is added to the effective bias Vtr to determine a corrected effective bias Vtr'. During image formation, the determined corrected effective bias Vtr' is applied to the primary transfer roller 15 under constant voltage control (T4 to T5).

[0084] Thus, in this embodiment, when performing the setting operation (ATVC control), the control unit 3 acquires a second detection result by the detection unit (voltage detection sensor) 80a when the test bias is applied to the primary transfer member 15 while maintaining the output current of the second application unit (potential regulation power source) 80 at approximately 0 μA, and also acquires a first detection result by the detection unit 80a when the test bias is not applied to the primary transfer member 15 while a predetermined bias of the same polarity as the predetermined polarity (the charging polarity of the photoconductor 11) is applied from the second application unit 80 to the electrode member 8 under constant current control. Also, in this embodiment, the control unit 3 acquires the first detection result after acquiring the second detection result.

[0085] As described above, the control of this embodiment also provides the same effects as those of the first embodiment.

[0086] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0087] In the above-described embodiment, the potential regulating member (electrode member) having a flat contact surface that comes into contact with the intermediate transfer belt is a plate-shaped member made of sheet metal or the like, but as long as a similar contact surface can be formed, it may have another shape, such as a block-shaped member having a rectangular cross section. The same applies to a potential regulating member (electrode member) having a curved contact surface that comes into contact with the intermediate transfer belt.

[0088] Furthermore, the image forming apparatus is not limited to an image forming apparatus capable of forming a full-color image, but may be an image forming apparatus capable of forming only a monochrome (black and white or monochromatic) image.

[0089] In addition, in the above embodiment, the predetermined charge polarity of the photoconductor is negative, but this is not limited thereto, and the predetermined charge polarity of the photoconductor may be positive. Similarly, in the above embodiment, the normal charge polarity of the toner is negative, but the normal charge polarity of the toner may be positive. The predetermined charge polarity of the photoconductor and the various applied voltages when the normal charge polarity of the toner is positive may be appropriately changed, such as to have the opposite polarity to that of the above embodiment, in accordance with the above embodiment.

[0090] Furthermore, the photoconductor is not limited to a drum-shaped one (photoconductor drum), but may be an endless belt-shaped one (photoconductor belt) or the like. [Explanation of symbols]

[0091] 1. Image forming device 6 Intermediate transfer belt 8. Electric potential regulation components (electrode components) 11 Photosensitive drum (photoconductor) 15 Primary transfer roller (primary transfer member) 80 Potential Regulating Power Supply

Claims

1. a photoconductor capable of being charged to a predetermined polarity and carrying a toner image; an intermediate transfer belt that is movable in a circumferential direction and that conveys the toner image that has been primarily transferred from the photoconductor at a primary transfer section to a recording material at a secondary transfer section for secondary transfer; a primary transfer member that contacts an inner circumferential surface of the intermediate transfer belt to form the primary transfer portion where the photoconductor and the intermediate transfer belt are in contact with each other, and transfers a toner image from the photoconductor to the intermediate transfer belt when a bias is applied; a first applying unit that applies a bias having a polarity opposite to the predetermined polarity to the primary transfer member; an electrode member that contacts an inner circumferential surface of the intermediate transfer belt downstream of the primary transfer portion in a moving direction of the intermediate transfer belt; a second application unit that applies a bias having the same polarity as the predetermined polarity to the electrode member under constant current control; A detection unit that detects a voltage applied to the electrode member; a control unit that performs control to execute a setting operation of applying a test bias from the first application unit to the primary transfer member to set a transfer bias to be applied from the first application unit to the primary transfer member during image formation, An image forming apparatus characterized in that, when performing the setting operation, the control unit obtains a first detection result by the detection unit when the test bias is not applied to the primary transfer member while maintaining the output current of the second application unit approximately constant, and obtains a second detection result by the detection unit when the test bias is applied to the primary transfer member while maintaining the output current of the second application unit approximately constant, and sets the transfer bias based on the first detection result and the second detection result.

2. The image forming apparatus according to claim 1, characterized in that, when executing the setting operation, the control unit acquires the first detection result while performing constant current control so that a predetermined current flows through the electrode member by the second application unit, and acquires the second detection result while performing constant current control so that the predetermined current flows through the electrode member by the second application unit.

3. 3. The image forming apparatus according to claim 2, wherein the control section performs constant current control so that the predetermined current flows from the second application section to the electrode member during image formation.

4. The image forming apparatus according to claim 2 , wherein the control unit obtains the second detection result after obtaining the first detection result.

5. 2. The image forming apparatus according to claim 1, wherein, when performing the setting operation, the control unit acquires the second detection result while maintaining the output current of the second application unit at approximately 0 μA, and acquires the first detection result while applying a predetermined bias of the same polarity as the predetermined polarity from the second application unit to the electrode member under constant current control.

6. The image forming apparatus according to claim 5 , wherein the control unit obtains the first detection result after obtaining the second detection result.

7. a detection unit for detecting a current flowing through the primary transfer member or a voltage applied to the primary transfer member; The image forming apparatus according to any one of claims 1 to 6, characterized in that, in the setting operation, the control unit sets a target voltage of the transfer bias based on a voltage-current characteristic obtained based on a detection result by the other detection unit when the test bias is applied from the first application unit to the primary transfer member, a predetermined target current of the transfer bias, and a difference between the first detection result and the second detection result.

8. The image forming apparatus according to any one of claims 1 to 6, characterized in that, in the setting operation, the control unit sets a target current of the transfer bias based on a preset target current of the transfer bias and a difference between the first detection result and the second detection result.

Images