Image forming device

Abstract

To make it possible to suppress an image defect such as scattering that could occur depending on the type of recording material in a structure capable of suppressing a rise of charge amount of a toner on an intermediate transfer body by applying a bias to the electrode member located downstream from a primary transfer unit.SOLUTION: An image forming device 1 is constituted to comprise: a photoreceptor 11 capable of being charged to prescribed polarity; an intermediate transfer belt 6; a primary transfer member 15; a first application unit 75 for applying a first bias to the primary transfer member 15; an electrode member 8 that contacts the inner circumferential face of the intermediate transfer belt 6 downstream from a primary transfer unit N1; a second application unit 80 for applying a second bias of the same polarity as the prescribed polarity to the electrode member 8; a storage unit 35 in which the set value of the second bias is stored in association with the type of recording material S; and a control unit 3 that controls the second application unit 80 on the basis of the set value of the second bias stored in the storage unit 35 in association with the type of the prescribed recording material S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, printer, facsimile machine, or multifunction machine having a plurality of functions of these machines, which uses an electrophotographic system or an electrostatic recording system. [Background technology]

[0002] Among electrophotographic image forming apparatuses, such as color copiers, color printers, and color multifunction devices, intermediate transfer image forming apparatuses have become mainstream due to their advantages of compact size and relatively easy compatibility with various recording materials. Intermediate transfer image forming apparatuses typically include multiple photosensitive drums and an intermediate transfer belt. Toner images formed on the multiple photosensitive drums are electrostatically transferred sequentially onto the intermediate transfer belt at a primary transfer unit. The toner images transferred onto the intermediate transfer belt are then electrostatically transferred onto a recording material, such as paper, at a secondary transfer unit. Regarding the arrangement of components around the primary transfer unit, the terms "upstream" and "downstream" refer to upstream and downstream in the direction of transport of the intermediate transfer belt, unless otherwise specified.

[0003] In such image forming apparatuses, 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' further investigations revealed that an increase in the charge of the toner on the intermediate transfer belt increases the reflective force between the intermediate transfer belt and the belt, making it difficult to transfer the toner to the recording material at the secondary transfer section. For example, uniformly transferring toner to embossed paper with an uneven surface is difficult because a gap occurs between the intermediate transfer belt and the recording material at the secondary transfer section, requiring a relatively large secondary transfer electric field. Therefore, an increase in the charge of the toner on the intermediate transfer belt makes it even more difficult to transfer to embossed paper with an uneven surface. Furthermore, with secondary-color toner images, the toner image transferred to the intermediate transfer belt at the upstream primary transfer section is further subject to discharge when it passes through the downstream primary transfer section. Therefore, due to differences in the charge of the toner on the intermediate transfer belt between the secondary color and the single color, it can be difficult to set a secondary transfer bias appropriate for the secondary transfer (i.e., the secondary transfer latitude becomes narrow).

[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 side 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] Japanese Patent Application Laid-Open No. 2003-57963 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to suppress the increase in the amount of charge on 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 does not mention suppressing discharge downstream of the primary transfer unit. However, the inventors of the present invention have conducted further research and found 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 peripheral surface side of the intermediate transfer belt, and to apply a bias (potential regulating bias) of the same polarity as the charging polarity of the photosensitive drum to this potential regulating member.

[0008] By suppressing discharge between the intermediate transfer belt and the photosensitive drum downstream of the primary transfer unit, it is possible to suppress an increase in the charge amount of the toner on the intermediate transfer belt, making it easier to transfer the toner uniformly to, for example, embossed paper with an uneven surface. In addition, by reducing the difference in charge amount of the toner between the secondary color and the single color, it becomes easier to ensure the secondary transfer latitude.

[0009] However, the types of recording materials have become increasingly diverse in recent years. In addition to plain paper, the commercial printing industry, in particular, is increasingly using coated paper with a low surface roughness due to the application of a coating agent and synthetic paper with a resin-based base material. Such coated paper and synthetic paper generally have higher electrical resistance (volume resistivity) than plain paper due to the influence of the materials used for the surface treatment and the base material. When such recording materials are used, the secondary transfer bias tends to be set high (with a large absolute value) to ensure good secondary transfer performance. Therefore, if the application of a potential regulating bias to the potential regulating member reduces the charge amount of the toner on the intermediate transfer belt, and the toner's retention force on the intermediate transfer belt decreases, the toner may easily scatter due to an electric field at the secondary transfer section (or its upstream vicinity) (also referred to as "scattering"). Furthermore, if the recording material has a high smoothness, the toner image may become distorted due to friction between the intermediate transfer belt and the recording material when the toner's retention force on the intermediate transfer belt decreases (also referred to as "image distortion").

[0010] Therefore, the object of the present invention is to suppress image defects such as scattering that can occur depending on the type of recording material, in a configuration that can suppress an increase in the charge amount of toner on an intermediate transfer body by applying a bias to an electrode member arranged downstream of the primary transfer unit. [Means for solving the problem]

[0011] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention comprises a photosensitive member that can be charged to a predetermined polarity and that carries a toner image, a circumferentially movable intermediate transfer belt that contacts the photosensitive member to form a primary transfer section and transports the toner image that has been primarily transferred from the photosensitive member at the primary transfer section to a recording material at a secondary transfer section, a primary transfer member that contacts the inner peripheral surface of the intermediate transfer belt and is applied with a first bias to perform primary transfer of the toner image from the photosensitive member to the intermediate transfer belt, a first application section that applies the first bias of a polarity opposite to the predetermined polarity to the primary transfer member, and a movement direction of the intermediate transfer belt. The image forming apparatus is characterized by having an electrode member that contacts the inner surface of the intermediate transfer belt downstream of the primary transfer unit in the direction of rotation; a second application unit that applies a second bias of the same polarity as the predetermined polarity to the electrode member; a memory unit that stores a set value of the second bias associated with the type of recording material; and a control unit that controls the second application unit to apply the second bias to the electrode member when forming an image on the predetermined type of recording material, based on the set value of the second bias stored in the memory unit associated with the predetermined type of recording material. [Effects of the Invention]

[0012] According to the present invention, in a configuration in which a bias is applied to an electrode member arranged downstream of the primary transfer unit to suppress an increase in the charge amount of toner on the intermediate transfer body, it is possible to suppress image defects such as scattering that can occur depending on the type of recording material, etc. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic block diagram of a control system of the image forming apparatus. [Figure 3] 3A and 3B are a cross-sectional view and a perspective view of a potential regulation member; [Figure 4] FIG. 10 is a cross-sectional view of another example of a potential restricting member. [Figure 5] FIG. 10 is a cross-sectional view of another example of a potential restricting member. [Figure 6] FIG. 10 is a cross-sectional view illustrating the arrangement of a potential regulation member. [Figure 7] FIG. 10 is a flowchart of the primary transfer ATVC. [Figure 8] FIG. 10 is a schematic graph of voltage-current characteristics obtained in the primary transfer ATVC. [Figure 9] 10A and 10B are schematic diagrams for explaining scattering and image disturbance. [Figure 10] FIG. 10 is a flowchart illustrating an example of a procedure for adjusting a potential regulating bias. [Figure 11] 5A and 5B are schematic diagrams illustrating an example of a recording material selection screen and a recording material setting screen. [Figure 12] 10A and 10B are schematic diagrams illustrating an example and another example of a secondary transfer bias adjustment screen. [Figure 13] FIG. 10 is a schematic diagram of an example of an image for adjusting a secondary transfer bias. [Figure 14] FIG. 10 is a schematic diagram of an example of a potential regulating bias adjustment screen. [Figure 15] FIG. 10 is a schematic diagram of an example of an image for adjusting a potential regulating bias. [Figure 16] FIG. 10 is a schematic diagram of another example of the potential regulating bias adjustment screen. [Figure 17] FIG. 10 is a schematic diagram of yet another example of the potential regulating bias adjustment screen. [Figure 18] 10 is a graph illustrating a change in the relationship between the output voltage of the primary transfer power supply and the current flowing through the primary transfer power supply due to a potential regulating bias. FIG. [Figure 19] FIG. 10 is a flowchart of another example of the procedure for adjusting the potential regulating bias. [Figure 20]FIG. 4 is a schematic diagram for explaining a current path around a primary transfer portion. [Figure 21] FIG. 10 is a schematic block diagram of another example of a control system of the image forming apparatus. [Figure 22] FIG. 10 is a timing chart illustrating correction control of the primary transfer bias. DETAILED DESCRIPTION OF THE INVENTION

[0014] The image forming apparatus according to the present invention will be described in more detail below 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. Figure 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 full-color printer that employs an intermediate transfer system and is capable of forming a full-color image on a sheet-shaped recording material S using an electrophotographic system.

[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 an ejection section 5 for the recording material S. Also provided inside the image forming apparatus 1 are 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. The image forming apparatus 1 can form an image on the recording material S based on image information (image signals) acquired by a document reading device (not shown) provided in the image forming apparatus 1 or connected to the image forming apparatus 1. Also, the image forming apparatus 1 can form an image on the recording material S based on image information (image signals) from an external device (not shown) connected to the image forming apparatus 1, such as a personal computer (host device), a digital camera, or a smartphone. 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, cardboard, gloss coated paper, matte coated paper, embossed paper, and synthetic resin sheets (synthetic paper) and overhead projector sheets (resin films) that are substitutes for plain paper. Here, the recording material S is sometimes referred to as "paper" (such as "paper," "embossed paper," and "high resistance paper"), but even in this case, the recording material S includes materials other than paper or materials containing materials other than paper.

[0017] The image forming section 2 forms an image based on image information on the recording material S fed from the feeding section 4. 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 and provided for each color may be generally described by omitting the suffixes y, m, c, and k, which indicate that the element is for one of the colors. The image forming apparatus 1 can also form a monochrome image, such as a black monochrome image, or a multicolor image using image forming units 10 for a desired monochrome 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 charging means. The image forming unit 10 also has a developing device 14 serving as developing means. The image forming unit 10 also has a pre-exposure device 16 serving as discharging means. The image forming unit 10 also has a drum cleaning device 17 serving as 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) and carries an electrostatic image (electrostatic latent image) or a toner image. In this embodiment, the photosensitive drum 11 is a negatively charged organic photoconductor (OPC) with an outer diameter of 30 mm. The photosensitive drum 11 has an aluminum cylinder as a base and a surface layer formed on its surface. In this embodiment, the surface layer has three layers: an undercoat layer, a photocharge generation layer, and a charge transport layer, which are coated and stacked on the base in the following order. When an image formation operation starts, the photosensitive drum 11 is rotated in the direction of arrow R1 (counterclockwise) in the figure by a drive motor (not shown) as a driving means at a predetermined peripheral speed (process speed).

[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 supply 73 (FIG. 2) serving as a charging bias application means (charging bias application unit) is connected to the charging roller 12. During charging, the charging power supply 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 in accordance with image information of separated colors output from the control unit 3, and scans and exposes the surface (outer peripheral surface) of the photosensitive drum 11.

[0022] The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by the developing device 14 by supplying toner, 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 containing toner (non-magnetic toner particles) and carrier (magnetic carrier particles) as the developer. A developer container (developer container body) 14b of the developing device 14 contains the two-component developer, 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 and adheres to the image portion of the electrostatic image on the photosensitive drum 11. A developing power supply 74 (FIG. 2) serving as a developing bias application means (developing bias application unit) is connected to the developing sleeve 14. During development, the developing power supply 74 applies a predetermined developing bias (developing voltage) to the developing sleeve 14. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 11 (negative in this embodiment) adheres to the exposed portion (image portion) of the photosensitive drum 11, which has been uniformly charged and then exposed to light, thereby reducing the absolute value of the potential (reverse 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.

[0023] An intermediate transfer unit 20 is disposed facing 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 plurality of tension rollers: a drive roller 21, a tension roller 22, and a secondary transfer inner roller 23. The intermediate transfer belt 6 is movable (rotatable) while carrying a toner image. The drive roller 21 is driven to rotate by a drive motor (not shown) serving as a driving means, transmitting a driving force to the intermediate transfer belt 6, causing it to rotate (circumferentially move) in the direction of arrow R2 (clockwise) in the figure at a predetermined peripheral speed corresponding to the peripheral speed of the photosensitive drums 11. A tension roller 22 controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 applies a force to the intermediate transfer belt 6 from its inner peripheral surface (back surface) to its outer peripheral surface (front surface) by the biasing force of a tension spring (not shown) composed of a compression coil spring, which serves as a biasing member. This force applies a tension of approximately 2 to 5 kgf to the intermediate transfer belt 6 in its conveyance direction (process progress direction, movement direction). The inner secondary transfer roller 23, together with the outer secondary transfer roller 25 described below, constitutes a secondary transfer device 26. Primary transfer rollers 15y, 15m, 15c, and 15k, which are roller-type primary transfer members serving as primary transfer means, are disposed on the inner peripheral surface of the intermediate transfer belt 6, corresponding to the photosensitive drums 11y, 11m, 11c, and 11k, respectively. In this embodiment, the primary transfer roller 15 is disposed opposite the photosensitive drum 11 and sandwiches the intermediate transfer belt 6 between itself and the photosensitive drum 11. 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. The tension rollers other than the drive roller 21 and each primary transfer roller 15 are rotated in accordance with the rotation of the intermediate transfer belt 6.

[0024] The toner images formed on the photosensitive drums 11 are transferred (primary transfer) onto the rotating intermediate transfer belt 6 by the action of the primary transfer rollers 15 at the primary transfer portion N1. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 11 are superimposed one on top of the other and transferred onto the intermediate transfer belt 6. A primary transfer power supply 75 (FIG. 2) serving as a primary transfer bias application means (primary transfer bias application unit) is connected to the primary transfer rollers 15. During primary transfer, the primary transfer power supply 75 applies 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, to the primary transfer roller 15. 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) that detects the output voltage, and a current detection sensor 75b (FIG. 2) as a current detection means (current detection unit) that detects the output current. In this embodiment, a primary transfer bias of approximately 1 to 2 kV is applied to the primary transfer roller 15 (the symbol "to" indicates a range including the values ​​before and after it, and the same applies below). In this embodiment, the primary transfer bias is controlled to a constant voltage. In this embodiment, 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 individually controlled.

[0025] In this embodiment, the primary transfer roller 15 has a core and an elastic layer of ion-conductive foam rubber (NBR rubber) formed around the core. 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) and 2 kV applied) 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 base layer can be made of 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 surface layer can be made of a material such as CR rubber provided with 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). In this embodiment, the intermediate transfer belt 6 has a two-layer structure, but it may also have a single-layer structure made of a material equivalent to the above-mentioned base layer. The surface layer may also be a resin coating layer containing a resin such as a fluororesin and having a thickness of approximately 0.002 to 0.01 [mm]. The intermediate transfer belt 6 may also have a multi-layer structure of three or more layers.

[0027] An outer secondary transfer roller 25, a roller-type secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 6. The outer secondary transfer roller 25 as a secondary transfer member, together with the inner secondary transfer roller 23 as an opposing member (opposing electrode), constitutes a secondary transfer device 26. The outer secondary transfer roller 25 is pressed toward the inner secondary transfer roller 23 and contacts the inner secondary transfer roller 23 via the intermediate transfer belt 6, forming a secondary transfer portion (secondary transfer nip portion) N2, which is the contact portion between the intermediate transfer belt 6 and the outer secondary transfer roller 25. At the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 6 is transferred (secondarily transferred) onto the recording material S, which is being conveyed while being sandwiched between the intermediate transfer belt 6 and the outer secondary transfer roller 25, by the action of the secondary transfer device 26. A secondary transfer power supply 76 (FIG. 2) serving as a secondary transfer bias application means (secondary transfer bias application portion) is connected to the outer secondary transfer roller 25. During secondary transfer, the secondary transfer power supply 76 applies a secondary transfer bias (secondary transfer voltage), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, to the outer secondary transfer 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 supply 76 is connected to a voltage detection sensor 76a (FIG. 2) as a voltage detection means (voltage detection unit) that detects the output voltage of the secondary transfer power supply 76 and a current detection sensor 76b (FIG. 2) as a current detection means (current detection unit) that detects the output current of the secondary transfer power supply 76. The core of the inner secondary transfer roller 23 is connected to ground potential. In this embodiment, a secondary transfer bias of, for example, approximately 1 to 6.5 kV is applied to the outer secondary transfer roller 25, and a secondary transfer current of approximately 15 to 100 μA is passed through the secondary transfer section N2, thereby secondarily transferring the toner image on the intermediate transfer belt 6 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 inner secondary transfer roller 23 as the secondary transfer member, and the outer secondary transfer roller 25 as the opposing member may be connected to ground potential. The outer secondary transfer roller 25 may be configured to rotate following the rotation of the intermediate transfer belt 6, or may be configured to be rotationally driven by a driving means.

[0028] The recording material S is transported from the feeding unit 4 toward the secondary transfer unit N2 in parallel with the formation of a toner image on the intermediate transfer belt 6. The recording material S is stored in a cassette 41 serving as a recording material storage unit of the feeding unit 4. The recording materials S stored in the cassette 41 are separated one by one by a feeding roller 42 or the like serving as a feeding member of the feeding unit 4 and sent out from the cassette 41. The recording material S is transported to a registration roller (pair of registration rollers) 19 serving as a transport member provided on a transport path (transport path) 44 for the recording material S by a transport roller 43 or the like serving as a transport member of the feeding unit 4. The recording material S is then transported by the registration roller 19 to the secondary transfer unit N2 in synchronization with the toner image on the intermediate transfer belt 6. Note that although only one cassette 41 is shown in FIG. 1, the image forming apparatus 1 may have a plurality of cassettes 41. The feeding section 4 may also be configured to be able to feed the recording material S from a recording material storage section (recording material loading section) other than the cassette 41, such as a manual feed tray.

[0029] In this embodiment, the outer secondary transfer roller 25 has a core metal and an elastic layer of ion-conductive foam rubber (NBR rubber) formed around the core metal. The outer diameter of the outer secondary transfer roller 25 is, for example, 20 to 25 mm. The outer secondary transfer 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) and 2 kV applied) can be suitably used.

[0030] The recording material S onto which the toner image has been transferred is transported to a fixing device 27 serving as a fixing unit. The fixing device 27 includes a fixing roller 27a and a pressure roller 27b. The fixing roller 27a incorporates a heater serving as a heating unit. The pressure roller 27b presses against the fixing roller 27a to form a fixing portion (fixing nip portion). The fixing device 27 heats and presses the recording material S bearing the unfixed toner image by sandwiching it between the fixing roller 27a and the pressure roller 27b and transporting it, thereby fixing (melting and adhering) 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 transported in the discharge unit 5 by discharge rollers 51 and the like and discharged (output) from a discharge port (not shown) onto a discharge tray 52 provided outside the main body 1a of the image forming apparatus 1 (hereinafter simply referred to as the "main body") of the image forming apparatus 1.

[0031] In the case of single-sided printing, in which an image is formed on one side of the recording material S, the recording material S with the toner image fixed on one side is discharged to the discharge tray 52 through the discharge section 5 as described above. The image forming apparatus 1 of this embodiment also has a double-sided mechanism 60 that enables double-sided printing (automatic double-sided printing), in which an image is formed on both sides of the recording material S. In the case of double-sided printing, the recording material S with the toner image fixed on its first side as described above is guided to the reverse conveying path 62 by the reverse conveying rollers 61 and the like. The recording material S conveyed to the reverse conveying path 62 has its conveying direction reversed and is guided to the double-sided conveying path 63, where it is conveyed to the registration rollers 19 by the double-sided conveying rollers 64 and the like as double-sided conveying members, and then supplied again to the secondary transfer section N2. A toner image is then transferred to the second side of the recording material S, fixed thereon, and the recording material S is discharged to the discharge tray 52 through the discharge section 5. The double-sided mechanism 60 is composed of the reverse conveying rollers 61, the reverse conveying path 62, the double-sided conveying path 63, the double-sided conveying rollers 64, and the like.

[0032] After the primary transfer, the surface of the photosensitive drum 11 is neutralized by a pre-exposure device 16. Toner remaining on the photosensitive drum 11 (primary transfer residual toner) that was not 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 uses a cleaning blade as a cleaning member to scrape the primary transfer residual toner from the surface of the rotating photosensitive drum 11 and collect it in a collection container (not shown). The cleaning blade is a plate-shaped member that contacts the photosensitive drum 11 with a predetermined pressure. The cleaning blade contacts the surface of the photosensitive drum 11 in a counter-direction relative to the rotational direction of the photosensitive drum 11, with the tip of its free end facing upstream in the rotational direction of the photosensitive drum 11. Furthermore, deposits such as toner remaining on the intermediate transfer belt 6 (secondary transfer residual toner) that was not 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.

[0033] The image forming unit 10 may be configured as a cartridge (process cartridge) that is detachable from the apparatus main body 1a as a whole. 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 later) form an intermediate transfer unit 20. The intermediate transfer unit 20 may be detachable from the apparatus main body 1a as a whole.

[0034] 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 (control circuit) 3 as a control means. The control unit 3 is configured with a CPU 31 as a processing unit, a memory unit 35 as a storage unit, and an input / output circuit (I / F) (not shown) for inputting and outputting signals between the control unit 3 and external devices. The memory unit 35 is configured with a ROM (including rewritable) 32, a RAM 33, a non-volatile memory 34, and the like. The ROM 32 stores programs for controlling each unit of the image forming apparatus 1. The RAM 33 temporarily stores control-related data. The non-volatile memory 34 stores various setting information, usage history information, and the like. The CPU 31 is a microprocessor that controls the overall control of the image forming apparatus 1 and is the main system controller. The CPU 31 is connected to each unit, such as the feeding unit 4, the image forming unit 2, and the ejection unit 5, and exchanges signals with these units and controls their operation. The ROM 32 stores an image formation control sequence for forming an image on the recording material S, etc.

[0035] The control unit 3 is connected to, for example, a charging power supply 73, a developing power supply 74, a primary transfer power supply 75, a secondary transfer power supply 76, and a potential regulating power supply 80 (described later), each of which 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 independently provided for each image forming unit 10. The control unit 3 is also connected to 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 fixing temperature sensor 77, and the like. Signals (information) indicating the detection results of each sensor are input to the control unit 3.

[0036] An operation unit 70 is also connected to the control unit 3. The operation unit 70 has an input unit including operation buttons (keys) as input means and a display unit 70a including 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 input means. The operation unit 70 (display unit 70a) can display various setting screens under the control of the control unit 3. Furthermore, an operator such as a user or a service representative can input various settings to the control unit 3 and input instructions to start a job (described later) by operating the operation unit 70. The control unit 3 can register various settings in the storage unit 35 and control the operation of various devices in the image forming apparatus 1 in response to signals from the operation unit 70, rather than from an external device such as a personal computer.

[0037] Here, the image forming apparatus 1 executes a job (print job, image forming operation) that is a series of operations that starts with a single start command and forms and outputs an image on one or more recording materials S. The job generally includes an image forming process, a pre-rotation process, an inter-sheet process when 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 that is actually formed and output on the recording materials S, and this period is referred to as the image formation time (image formation period). More specifically, the timing of the image formation process differs depending on the positions where the electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer are performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. The inter-sheet process (inter-recording material process, inter-image process) is a period corresponding to the interval 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 rearrangement operation (preparatory operation) is performed after the image forming process. The non-image formation time (non-image formation period) is a period other than the image formation time, and includes the 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.

[0038] The type of recording material S includes classifications of recording materials S based on information about any recording material S, such as attributes (so-called paper type categories) based on general characteristics (basis weight, thickness, surface properties, light reflectivity, light transmittance, etc.) such as plain paper, high-quality paper, glossy paper (glossy paper), coated paper, embossed paper, thick paper, thin paper, rough paper, etc., numerical values ​​or numerical ranges for basis weight, thickness, stiffness, etc., brand (including manufacturer, product name, product number, etc.), or combinations thereof. In other words, each recording material S classified by information about the recording material S can be considered to constitute a type of recording material S. In the image forming apparatus 1, for example, image formation conditions (transfer conditions, fixing conditions, process speed, etc.) corresponding to each type of recording material S classified by paper type category and basis weight are set.

[0039] 3. Secondary transferability issues Next, the issue of secondary transferability will be further explained. For convenience, unless otherwise specified, the magnitude (high / low) of voltage or potential refers to the magnitude (high / low) when compared in absolute value. Furthermore, with regard to the arrangement of the primary transfer section N1, photosensitive drum 11, primary transfer roller 15, and potential regulating member 8 (described later), unless otherwise specified, upstream and downstream refer to the upstream and downstream in the transport direction (process progress direction, movement direction) of the intermediate transfer belt 6.

[0040] As mentioned 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. Through further investigation, the inventors have found that an increase in the charge of the toner on the intermediate transfer belt 6 increases the reflective force between the intermediate transfer belt 6 and the photosensitive drum 11, making it difficult to transfer the toner to the recording material S at the secondary transfer portion N2. For example, as mentioned above, it becomes difficult to uniformly transfer toner onto embossed paper with an uneven surface. Embossed paper is paper (fancy paper) with an uneven pattern created by embossing or embossing the surface. Furthermore, for example, differences in the charge of the toner on the intermediate transfer belt 6 between secondary colors and single colors can make it difficult to set a secondary transfer bias appropriate for the secondary transfer (i.e., the secondary transfer latitude becomes narrow).

[0041] In order to suppress the increase in the amount of charge 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 further investigations, the inventors of the present invention have 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, downstream of the primary transfer portion N1 and on the inner circumferential surface side of the intermediate transfer belt 6, and to apply a bias of the same polarity as the charge polarity of the photosensitive drum 11 to this potential regulating member.

[0042] 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 arranged downstream of each 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 each of the primary transfer portions N1y, N1m, N1c, and N1k have substantially the same configuration.

[0043] 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.

[0044] In this embodiment, the potential regulating member 8 has a planar first portion 81 that is arranged along the width direction of the intermediate transfer belt 6 (a direction substantially perpendicular to the conveyance 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 that is arranged along the width direction of the intermediate transfer belt 6 and extends in a direction substantially perpendicular to the plane of the first portion 81. In this embodiment, the contact surface 83, which is the contact portion of the first portion 81 of the potential regulating member 8 that comes into contact with the inner circumferential surface of the intermediate transfer belt 6, is planar. In other words, in this embodiment, the first portion 81 that constitutes the contact surface 83 of the potential regulating member 8 is a flat plate.

[0045] Here, in a cross section substantially perpendicular to the rotational axis 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. To more effectively suppress discharge between the intermediate transfer belt 6 and the photosensitive drum 11 by the action of the electric field formed in the space between the photosensitive drum 11 and the potential regulating member 8, it is preferable that the potential regulating member 8 be in surface contact with the intermediate transfer belt 6. From this perspective, the length between the line segment AB, i.e., the “contact width,” which is the length of the contact surface 83 in the transport 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 discharge. However, if the length is too long, it may be difficult to stably bring the potential regulating member 8 into contact with the intermediate transfer belt 6 due to factors such as component precision. The length between the line segment AB is often sufficient if it is 50 mm or less, typically 30 mm or less. That is, the length between the line segment AB is preferably about 5 to 50 mm, typically about 5 to 30 mm. From another perspective, it can be said that the length between the line segment AB is often sufficient if it is less than half the distance between the axes of adjacent photosensitive drums 11 in a cross section substantially perpendicular to the rotational axis direction of the photosensitive drums 11. In this embodiment, a potential regulating member 8 with a length between the line segment 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 rotational axis direction of the photosensitive drums 11 is about 100 mm.

[0046] A potential regulating power supply 80 serving as a potential regulating bias application means (potential regulating bias application unit) is connected to the potential regulating member 8. In this embodiment, the potential regulating power supply 80 is connected to a second portion 82 of the potential regulating member 8. During at least the primary transfer during the image forming operation, the potential regulating member 8 is applied with a potential regulating bias (potential regulating voltage), which is a DC voltage having the same polarity as the charging polarity of the photosensitive drum 11. The primary transfer is, more specifically, the period during which the primary transfer bias is applied, and more specifically, the period during which the image area (the area to which the toner image can be transferred) on the intermediate transfer belt 6 passes through the primary transfer portion N1. This suppresses discharge between the intermediate transfer belt 6 and the photosensitive drum 11 downstream of the primary transfer portion N1. In this embodiment, the potential regulating bias is a negative DC voltage. In this embodiment, the potential regulating bias is controlled to a constant voltage. In the configuration of this embodiment, the potential regulating bias (positive constant voltage) is preferably approximately −500 to −3000 V.

[0047] 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 also longer than the width of the area where the primary transfer roller 15 contacts the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6. That is, in this embodiment, the range of the maximum image width and the range of the area where the primary transfer roller 15 contacts the intermediate transfer belt 6 in the width direction of 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. This makes it possible to obtain the effect of suppressing an increase in the charge amount of the toner on the intermediate transfer belt 6 due to the suppression of the discharge, 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. 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. In other words, in this embodiment, the range of the length of the potential regulating member 8 in the longitudinal direction is within the range of the width of the intermediate transfer belt 6. This reduces the possibility that, when the longitudinal ends of the potential regulating member 8 protrude beyond the width ends of the intermediate transfer belt 6, discharge will occur between the potential regulating member 8 and the components around the intermediate transfer belt 6, reducing the effect of suppressing the discharge described above.

[0048] The potential regulation member 8 can be made of, for example, only one conductive material. In this embodiment, the potential regulation member 8 is made essentially of only a conductive metal, such as SUS (stainless steel). More specifically, in this embodiment, the potential regulation member 8 is made by bending a metal plate (sheet metal) made of SUS or other metal 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 regulation member 8 is substantially deformed when the image forming apparatus 1 is in use. By performing the bending process in this manner, the strength of the potential regulation member 8 can be increased. However, the present invention is not limited to this embodiment, and the potential regulation member 8 may be made of two or more materials.

[0049] 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 surface layer 85, which forms a contact surface 83 that contacts the intermediate transfer belt 6 and a connection portion with the potential regulating power source 80, is made of a conductive material, such as metal or conductive resin. The base 84 may be made of a conductive material, but may also be made of a non-conductive material, such as non-conductive resin. The base 84 and the surface layer 85 can be fixed to each other by any fixing means, such as adhesive or welding.

[0050] 5 is a cross-sectional view (a cross-section substantially perpendicular to the rotational axis direction of the photosensitive drum 11) of yet another example of the potential regulation member 8. For example, as shown in FIG. 5, the contact surface 83 of the potential regulation member 8 that comes into contact with the intermediate transfer belt 6 may be made of a conductive nonwoven fabric 86. Note that in FIG. 5, the conductive nonwoven fabric 86 is provided on the contact surface 83 of the potential regulation member 8 configured as shown in FIG. 4, but the conductive nonwoven fabric 86 may also be provided on the contact surface 83 of the potential regulation 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. Furthermore, instead of the nonwoven fabric 86, felt or pile fabric (cut pile fabric (velvet, brush) or loop pile fabric (terry cloth)) made of conductive fibers, or a sponge (elastic foam) made of a conductive rubber material, etc. 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.

[0051] 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.

[0052] 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 disposed 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 a direction along a common tangent line of the multiple photosensitive drums 11 on the side that contacts the intermediate transfer belt 6, in a cross section that is approximately perpendicular to the rotation axis direction of the photosensitive drum 11.

[0053] To explain the arrangement of the potential regulation member 8, let us assume that the potential regulation member 8 is removed. In a cross section substantially perpendicular to the rotational axis of the photosensitive drum 11, the line passing through the tensioned surface on the inner circumferential side of the intermediate transfer belt 6 downstream of the primary transfer unit N1 in the absence of the potential regulation member 8 is defined as line L. More specifically, line L corresponds to the tensioned surface in a state in which only the potential regulation member 8 is substantially removed from the configuration of the image forming apparatus 1 during image formation operation. Also, on line L, the point where the inner circumferential surface of the intermediate transfer belt 6 separates from the tension member immediately upstream of the potential regulation member 8 is defined as "C (or upstream tensioning portion C)," and the point where the inner circumferential surface of the intermediate transfer belt 6 separates from the tension member immediately downstream of the potential regulation member 8 is defined as "D (or downstream tensioning portion D)." Although the straight line L is shown schematically as being approximately horizontal 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 downward in the figure as it goes downstream.

[0054] In this embodiment, the tension member closest to the upstream side 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 closest to the upstream side of the potential regulating member 8 is not limited to the primary transfer roller 15. For example, if the primary transfer roller 15 is disposed offset upstream from 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.

[0055] In this embodiment, the tension members closest to the downstream side of the potential regulating member 8 are the photosensitive drums 11m, 11c, and 11k disposed adjacently downstream of the yellow, magenta, and cyan primary transfer units N1y, N1m, and N1c, respectively. The downstream tension members D are the positions on the inner circumferential surface of the intermediate transfer belt 6 corresponding to the positions where the intermediate transfer belt 6 separates from the photosensitive drums 11m, 11c, and 11k, respectively. However, the tension member closest to the downstream side of the potential regulating member 8 is not limited to the photosensitive drum 11. For example, if the primary transfer roller 15 is disposed offset upstream from the photosensitive drum 11, the downstream tension member D is 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. In this embodiment, the tension member closest to the downstream side of the black primary transfer unit N1k, which is the most downstream, is a tension roller 22 (tension roller in this embodiment). 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.

[0056] 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 as the nearest tension member downstream of the potential regulation member 8, the line L and the downstream tension portion D are defined based on that tension roller. Also, even if a scraper or brush, rather than a tension roller, is in contact with the inner circumferential surface of the intermediate transfer belt 6 for purposes such as cleaning the inner circumferential surface of the intermediate transfer belt 6, it can be considered to be the nearest downstream tension member as long as it regulates the posture of the intermediate transfer belt 6 during image formation. Scrapers are generally made of sheet-like or film-like members.

[0057] As shown in FIG. 6, the potential regulating member 8 is disposed downstream of and adjacent to 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. In this case, the closer the upstream end A is to the primary transfer portion N1, the greater the effect of suppressing the discharge. In this embodiment (FIG. 6), the potential regulating member 8 is disposed downstream of the primary transfer portion N1 so that the distance X2 from the primary transfer roller 15 to the upstream end A is approximately 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 a direction along a common tangent line on the side of the multiple photosensitive drums 11 that contact the intermediate transfer belt 6, in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 11. In other words, in this embodiment, the distance from the rotation center of the primary transfer roller 15 to the upstream end A is shorter than the distance (radius) from the rotation center of the primary transfer roller 15 to the outer periphery of the primary transfer roller 15 in the direction along the common tangent line. Although not limited to this, the distance X2 is preferably about 1 to 20 mm, and typically about 1 to 10 mm.

[0058] In this embodiment, the potential regulating member 8 is pressed against the inner circumferential surface of the intermediate transfer belt 6 at both longitudinal ends thereof by pressure springs 87 (FIG. 3B) composed of compression coil springs, which serve as biasing members serving as biasing means. At this time, the contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6 is set to be closer to the photosensitive drum 11 than the line L. This allows the potential regulating member 8 to be more stably brought into contact with the intermediate transfer belt 6 even if undulations or vibrations occur in the intermediate transfer belt 6 during image formation (while the intermediate transfer belt 6 is running). In this embodiment, the pressure of the pressure springs 87 is set (adjusted) so that the upstream end A and the downstream end B of the contact surface 83, which is the contact portion of the potential regulating member 8 that contacts the inner circumferential surface of the intermediate transfer belt 6, are pushed toward the photosensitive drum 11 by approximately 0.5 mm relative to the line L. By thus causing the contact surface 83 of the potential regulating member 8 to intrude toward the photosensitive drum 11 with respect to the line L, the potential regulating member 8 can be brought into more stable surface contact with the intermediate transfer belt 6 even if undulations or vibrations occur in the intermediate transfer belt 6 during image formation (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 with respect to the line L is preferably about 0.3 to 5 mm, and is 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.

[0059] Here, a line M is defined as a line passing through the upstream end A and the downstream end B of the contact surface 83 in a cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 11. It is preferable that line M does not intersect with the line segment CD of line L. This ensures more reliable surface contact between the intermediate transfer belt 6 and the potential regulating member 8 when the contact surface 83 of the potential regulating member 8 is flat. If line M intersects with the line segment CD of line L, it is possible 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 may be able to contact the inner circumferential surface of the intermediate transfer belt 6. In this case, it may be difficult to enhance the discharge suppression effect due to surface contact.

[0060] 6, the potential regulation member 8 is disposed so that the lines M and L are substantially parallel to each other. However, the line M may be disposed so that it is inclined with respect to the line L, as long as the line M does not intersect with the line segment CD of the line L. For example, by inclining the line M with respect to the line L so that the upstream end A is closer to the line L than the downstream end B, the curvature of the intermediate transfer belt 6 caused by the routing of the intermediate transfer belt 6 near the upstream end A can be reduced. This is therefore advantageous in reducing the possibility of scratches occurring on the inner circumferential surface of the intermediate transfer belt 6 due to friction with the potential regulation member 8.

[0061] The contact portion of the potential regulating member 8 that comes into contact with the inner circumferential 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, the cross section of which is approximately perpendicular to the rotation axis direction of the photosensitive drum 11 being curved in a convex shape toward the photosensitive drum 11, and the contact portion of the potential regulating member 8 that comes into contact with the inner circumferential 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 comes into contact with the inner circumferential surface of the intermediate transfer belt 6 curved in this way, stress when the potential regulating member 8 rubs against the intermediate transfer belt 6 can be reduced. By using a roller-shaped potential regulating member 8, the contact portion of the potential regulating member 8 that comes into contact with the inner circumferential surface of the intermediate transfer belt 6 may be a curved surface.

[0062] In this embodiment, a default value of the potential regulating bias is set in advance according to the type of recording material S. In this embodiment, a default value of the potential regulating bias is set for each type of recording material S according to the environment (temperature, humidity), and is stored in the storage unit 35 (ROM 32 or nonvolatile memory 34). In this embodiment, for example, in a predetermined environment (for example, a normal temperature and humidity environment: 23°C, 50% RH), a default value of the potential regulating bias is set for general plain paper (for example, paper with a basis weight of 64 to 75 g / m 2 ), the default value of the potential regulating bias is set to -1500V. Also, for example, in the above-mentioned specified environment, the default value of the potential regulating bias is set to -3000V for embossed paper. Similarly, in the above-mentioned specified environment, for double-sided coated paper (for example, with a basis weight of 106 to 128 g / m 2 ) and synthetic paper, the default value of the potential regulation bias is set to -3000V.

[0063] 5. Primary Transcription ATVC Next, the control of the primary transfer bias in this embodiment will be described. Note that in this embodiment, the control of the primary transfer bias is the same for each of the primary transfer portions N1y, N1m, N1c, and N1k, and is performed synchronously and individually at each of the primary transfer portions N1y, N1m, N1c, and N1k. Here, the description will focus on one primary transfer portion N1.

[0064] In this embodiment, the image forming apparatus 1 applies a constant voltage to the primary transfer unit N1 (primary transfer roller 15) to transfer a toner image from the photosensitive drum 11 to the intermediate transfer belt 6. In this embodiment, the image forming apparatus 1 uses active transfer voltage control (ATVC) to set the voltage conditions of the primary transfer bias applied to the primary transfer unit N1 (primary transfer roller 15) during image formation (primary transfer). The ATVC of the primary transfer unit N1 (also referred to as the "primary transfer ATVC" here) acquires voltage-current characteristics using a test bias (test voltage, test current) to determine the primary transfer bias during image formation (primary transfer) that corresponds to the total resistance value of the primary transfer unit N1, which is composed of the photosensitive drum 11, the intermediate transfer belt 6, and the primary transfer roller 15. The primary transfer ATVC is controlled and executed by the control unit 3.

[0065] In the primary transfer ATVC, when no toner image is present at the primary transfer unit N1 and no image is being formed, a predetermined voltage or current is supplied to the primary transfer unit N1 (primary transfer roller 15) as a test bias from the primary transfer power supply 75. The predetermined voltage or current setting for the test bias may be one or more levels. The current detection sensor 75a detects the current flowing through the primary transfer roller 15 (primary transfer power supply 75) when the predetermined voltage test bias is supplied. Alternatively, the voltage detection sensor 75b detects the voltage (output voltage of the primary transfer power supply 75) applied to the primary transfer roller 15 when the predetermined current test bias is supplied. This allows for the determination of voltage-current characteristics according to the impedance (total resistance) of the primary transfer unit N1. Furthermore, based on this voltage-current characteristic, the voltage required to supply a primary transfer current appropriate for the primary transfer of toner according to the impedance (total resistance) of the primary transfer unit N1 is calculated. During image formation (primary transfer), a primary transfer bias is applied to the primary transfer roller 15 under constant voltage control with the calculated voltage as the target voltage.

[0066] FIG. 7 is a flowchart of the primary transfer ATVC in this embodiment. FIG. 8 is a graph diagram schematically illustrating the voltage-current characteristics acquired in the primary transfer ATVC. When the primary transfer ATVC is started, the control unit 3 applies the target voltage (set voltage) V1 [V] of the primary transfer bias determined in the previous primary transfer ATVC to the primary transfer roller 15 while applying the same charging bias as during normal image formation to the charging roller 12. The control unit 3 then acquires the detected current I1 from the current detection sensor 75a (S101). If there is no target voltage determined in the previous primary transfer ATVC, a predetermined target voltage V1 may be used. Next, the control unit 3 compares the detected current I1 [μA] with the target current I0 [μA] and determines whether I1 is equal to or greater than I0 (I0≦I1) (S102). The target current I0 is determined in advance based on experiments or other factors, for example, depending on the environment (temperature, humidity), and is stored in the storage unit 35 (ROM 32). If I1 is not equal to or greater than I0, i.e., if I1 is less than I0 (I0>I1), the control unit 3 applies V2 (=V1+α) [V], which is obtained by adding a predetermined voltage value α [V] to V1, to the primary transfer roller 15. The control unit 3 then obtains the detected current I2 from the current detection sensor 75a (S103). On the other hand, if I1 is equal to or greater than I0 (I0≦I1), the control unit 3 applies V2 (=V1−α) [V], which is obtained by subtracting the predetermined voltage value α [V] from V1, to the primary transfer roller 15. The control unit 3 then obtains the detected current I2 from the current detection sensor 75a (S104). FIG. 8 shows an example where I0>I1, in which V2=V1+α [V]. Next, the control unit 3 determines a target voltage V0 corresponding to the target current I0 by linearly interpolating the detected currents I2 and I1 (S105). Then, during image formation (primary transfer), the primary transfer bias applied to the primary transfer unit N1 (primary transfer roller 15) is controlled to a constant voltage of the determined target voltage V0.

[0067] The primary transfer ATVC may use a test bias that is constant at a predetermined current (e.g., a target current I0), or may use both a test bias that is constant-current controlled at a predetermined current and a test bias that is constant-voltage controlled at a predetermined voltage. Here, constant current control refers to control that adjusts the output of a power supply so that the current supplied to the target is substantially constant at a target current. Constant voltage control refers to control that adjusts the output of a power supply so that the voltage applied to the target is substantially constant at a target voltage. The test bias may have one level (e.g., a test bias corresponding to the target current I0) or three or more levels. The voltage-current characteristic is not limited to being calculated by linear approximation, but may also be calculated by curve approximation. In this embodiment, the primary transfer ATVC is performed during a pre-rotation process (or pre-multiple rotation process) of a job as a non-image formation period. However, the present invention is not limited to this. The primary transfer ATVC may be performed during a non-image formation period, such as during a sheet-to-sheet process at a predetermined frequency (e.g., after every predetermined number of images formed) during continuous image formation. In this embodiment, when the primary transfer ATVC is performed, a potential regulating bias is applied to the potential regulating member 8 under constant voltage control, as in the case of image formation.

[0068] When an ion-conductive foam rubber is used for the primary transfer member, as in this embodiment, the electrical resistance of the primary transfer member changes depending on the environment and usage conditions. A change in the electrical resistance of the primary transfer member changes the current required for toner transfer, so the primary transfer ATVC must be performed appropriately. In this embodiment, if the environmental temperature has changed by 3°C or more (a 3°C increase or decrease) from the temperature at the time of the previous primary transfer ATVC, the primary transfer ATVC is performed again at the timing of the next pre-rotation. Furthermore, in this embodiment, if 500 sheets have been printed since the previous primary transfer ATVC, the primary transfer ATVC is performed again at the timing of the next pre-rotation. While it is possible to perform the primary transfer ATVC before each image formation, this is not desirable because it increases the First Copy Output Time (FCOT).

[0069] Regarding the secondary transfer portion N2, an ATVC (also referred to herein as the "secondary transfer ATVC") similar to the primary transfer ATVC is performed during non-image formation when there is no toner image or recording material S at the secondary transfer portion N2. In the secondary transfer ATVC, a base voltage (secondary transfer partial voltage) of the secondary transfer bias during image formation (secondary transfer) is calculated according to the electrical resistance of the secondary transfer portion N2 (mainly the outer secondary transfer roller 25). A target voltage of the secondary transfer bias during image formation (secondary transfer) is determined based on this base voltage and a recording material partial voltage according to the type of recording material S. Then, during image formation (secondary transfer), the secondary transfer bias applied to the secondary transfer portion N2 (outer secondary transfer roller 25) is subjected to constant voltage control at the determined target voltage. In this embodiment, the secondary transfer ATVC is performed during non-image formation during the pre-rotation process (or pre-multiple rotation process) of the job. However, this is not limited to this, and the secondary transfer ATVC can be performed during non-image formation, such as during the inter-sheet process at a predetermined frequency (e.g., after every predetermined number of images formed) during continuous image formation.

[0070] 6. Adjustment of Potential Regulatory Bias Next, the adjustment (correction) of the potential regulating bias in this embodiment will be described. Note that, unless otherwise specified, the leading edge and trailing edge of the recording material S refer to the leading edge and trailing edge in the conveying direction of the recording material S when passing through the secondary transfer portion N2.

[0071] As described above, in order to suppress discharge downstream of the primary transfer portion N1 and thereby suppress an increase in the charge amount of the toner on the intermediate transfer belt 6, it is effective to apply a potential regulating bias of the same polarity as the charge polarity of the photosensitive drum 11 to the potential regulating member 8. This makes it easier to transfer the toner uniformly to, for example, embossed paper with an uneven surface. In addition, by reducing the difference in the charge amount of the toner between the secondary color and the single color, it becomes easier to ensure the secondary transfer latitude.

[0072] However, as mentioned above, when a recording material S with a relatively high electrical resistance, such as coated paper or synthetic paper (herein also referred to as "high resistance paper"), is used, the amount of charge on the toner on the intermediate transfer belt 6 decreases when a potential regulating bias is applied to the potential regulating member 8, and if the toner's holding force on the intermediate transfer belt 6 decreases, "scattering" and "image distortion" may become more likely to occur.

[0073] That is, as described above, in this embodiment, a default value for the potential regulating bias is preset for each type of recording material S, for example, by selecting a representative one. However, it is expected that some recording materials S available on the market may have characteristics different from those of the representative ones. Therefore, with the default value of the potential regulating bias, the charge amount of the toner on the intermediate transfer belt 6 may be too low, which may result in a too low electrostatic holding force between the intermediate transfer belt 6 and the toner. When the recording material S used by users is high-resistivity paper such as coated paper or synthetic paper, the secondary transfer bias tends to be set high (with a large absolute value) to ensure secondary transfer performance. When high-resistivity paper is transported to the secondary transfer unit N2 in this state, "scattering" may occur at areas where the recording material S exhibits unstable behavior, such as the leading or trailing edge of the recording material S. This is because the gap between the recording material S and the intermediate transfer belt 6 changes at areas where the recording material S exhibits unstable behavior, changing the magnitude of the electric field applied to the toner. Furthermore, "image distortion" may occur not only at the leading or trailing edge of the recording material S. This is because the intermediate transfer belt 6 and the recording material S rub against each other in a state where the toner holding force on the intermediate transfer belt 6 is reduced.

[0074] FIG. 9(a) is a schematic diagram showing scattering that occurs at the leading and trailing edges of a recording material S when a halftone image (for example, a halftone image with an image area ratio of 50%) is formed over the entire surface of the recording material S. Scattering tends to be more noticeable in halftone images, and typically, areas where scattering occurs appear darker than areas where it does not occur. This is because toner that has scattered ends up in positions in the halftone image where toner should not actually be deposited. In FIG. 9(a), the shapes of the areas where scattering has occurred at the leading and trailing edges are different due to differences in the attitude and shape (waviness) of the recording material S during transport. FIG. 9(b) is a schematic diagram showing image disturbance that occurs in a portion of the leading edge of the recording material S when a halftone image (for example, a halftone image with an image area ratio of 50%) is formed over the entire surface of the recording material S. Image disturbances tend to be more noticeable in halftone images, and for the same reason as with scattering described above, areas where image disturbances occur typically appear darker than areas where they do not occur. In Figure 9(b), image disturbances occur from the leading edge of the recording material S to a certain position on the trailing edge side, but no image disturbances occur from that position to the trailing edge because the trailing edge of the recording material S passes through the registration rollers 19, improving the tracking of the recording material S with respect to the intermediate transfer belt 6, among other things.

[0075] "Scattering" and "image distortion" are influenced by the amount of charge of the toner on the intermediate transfer belt 6, as well as the type of recording material S and image duty (image ratio, print rate). For this reason, it is preferable that the user be able to freely adjust the value of the potential regulating bias so that the desired results can be obtained depending on the type of recording material S, the pattern of the image to be output, etc.

[0076] Therefore, in this embodiment, the image forming apparatus 1 is configured so that the user can adjust the value of the potential regulating bias. In particular, in this embodiment, a default value of the potential regulating bias is preset in the image forming apparatus 1 according to the type of recording material S. Then, in this embodiment, the image forming apparatus 1 is configured so that the user can adjust the value of the potential regulating bias from this default value to a desired value.

[0077] 10 is a flowchart showing an example of a procedure for a user to adjust the potential regulating bias for the recording material S used in image formation. Here, an example will be described in which a user performs an operation related to adjustment, such as inputting an adjustment value, on the operation unit 70 of the image forming apparatus 1.

[0078] First, the user outputs an image onto a prepared recording material S (S201), and checks whether the value of the secondary transfer bias preset for that recording material S is appropriate (S202).

[0079] At this time, before outputting an image, the user specifies the type of recording material S corresponding to the type of recording material S prepared on a recording material selection screen 200 as shown in FIG. 11(a) displayed on the operation unit 70 (display unit 70a). As a result, the image is output under image formation conditions (voltage conditions for the secondary transfer bias, voltage conditions for the potential regulating bias, fixing conditions, process speed, etc.) that are preset for that type of recording material S. The recording material selection screen 200 in FIG. 11(a) displays information 201 about the recording material S (paper type category, basis weight, size, etc.) that is associated with the paper feed unit 4 (cassette 41, etc.) and stored in the memory unit 35 in advance, and a selection button 202 for selecting the type of recording material S to be used.

[0080] If the preset secondary transfer bias value is not optimal, the user adjusts the secondary transfer bias (S203 to S205).

[0081] At this time, the user specifies the type of recording material S for which the secondary transfer bias is to be adjusted on a recording material setting screen 300 as shown in FIG. 11(b) displayed on the operation unit 70 (display unit 70a) and proceeds to adjust the secondary transfer bias. The recording material setting screen 300 in FIG. 11(b) displays an adjustment button 301 associated with a paper type category 303 of the recording material S pre-registered in the storage unit 35. The user can proceed to the secondary transfer bias adjustment screen by operating the adjustment button 301 corresponding to the paper type category of the recording material S for which the image formation conditions are to be adjusted. Operating the adjustment button 301 on the recording material setting screen 300 in FIG. 11(b) also allows the user to proceed to adjustment screens for other image formation conditions, such as an adjustment screen for the potential regulating bias (described later), in addition to the secondary transfer bias adjustment screen. The recording material setting screen 300 in FIG. 11(b) also includes a copy button 302 so that the user can register a desired setting while retaining the default settings. For example, the copied paper type category 303 is registered in the storage unit 35 under a different name, and the default settings are maintained except for the image forming conditions whose settings have been changed.

[0082] When the user operates the adjustment button 301 on the recording material setting screen 300, a secondary transfer bias adjustment screen 400 such as that shown in FIG. 12A is displayed on the operation unit 70 (display unit 70a). The secondary transfer bias adjustment screen 400 in FIG. 12A displays an adjustment value display section 401 that displays the adjustment value (offset value) of the secondary transfer bias, and an adjustment value input section (+ button, − button) 402 for inputting (changing) the adjustment value. In this embodiment, the adjustment value display section 401 and the adjustment value input section 402 are provided for the front side (image side in a single-sided print, the first side in a double-sided print) and the back side (second side in a double-sided print) of the recording material S, respectively. The secondary transfer bias adjustment screen 400 also displays a confirmation (OK) button 403 for confirming the setting change and storing it in the memory unit 35, and a cancel button 404 for canceling the setting change. By operating the adjustment value input unit 402, the user can change the secondary transfer bias (more specifically, the recording material distribution voltage) in a predetermined change range (for example, +50 to +500 V (or -50 to -500 V)) in increments of +1 (or -1) from the default value corresponding to an adjustment value of 0. The adjustment value changed by the adjustment value input unit 402 is displayed on the adjustment value display unit 401. The user can then confirm the change in setting by operating the confirm button 403 to store it in the storage unit 35, or can cancel the change in setting by operating the cancel button 404. The user can set an optimal value for the secondary transfer bias (S205) by repeatedly inputting the adjustment value (S203) and checking the output image (S204). At this time, it is preferable to check whether the secondary color has been properly transferred.

[0083] The image output for adjusting (checking) the secondary transfer bias may be an image the user actually wants to obtain as a final product, or a predetermined adjustment image. When adjusting the secondary transfer bias for image formation on both sides of the recording material S, an image for adjusting the secondary transfer bias can be output by double-sided printing using the duplexer 60 described above. When using the image the user actually wants to obtain as a final product, the user can set the optimal secondary transfer bias value by repeatedly inputting the adjustment value and outputting the image as described above. If the voltage value of the secondary transfer bias is insufficient, the toner cannot be sufficiently transferred to the recording material S, resulting in reduced image density. If the voltage value of the secondary transfer bias is excessive, image defects such as partial toner transfer due to abnormal discharge may occur. Furthermore, when using a predetermined adjustment image, the user can output an adjustment chart in which multiple patches (test images, test toner images) of representative colors are transferred by changing the voltage value of the secondary transfer bias for each patch. In this case, the user can have the image forming apparatus 1 output the adjustment chart by operating the chart output button 405 displayed on the secondary transfer bias adjustment screen 400, as shown in FIG. 12(b). Fig. 13 is a schematic diagram showing an example of an adjustment chart. In the adjustment chart of Fig. 13, multiple solid images of secondary colors (e.g., blue) and multiple solid images of black are transferred by switching the voltage value of the secondary transfer bias. For example, a user can set an optimal value for the secondary transfer bias by inputting an adjustment value printed in association with a patch that has obtained optimal transferability (density) into the adjustment value display section 401 on the secondary transfer bias adjustment screen 400.

[0084] Next, the user checks whether the value of the potential regulating bias preset for the recording material S is appropriate, and adjusts it (S206 to S208).

[0085] At this time, the user may first check whether the value of the potential regulating bias is appropriate by checking the image last output in the adjustment of the secondary transfer bias, or may check whether the value of the potential regulating bias is appropriate by checking a newly output image. As described above, when the user operates the adjustment button 301 on the recording material setting screen 300 (FIG. 11(b)), a potential regulating bias adjustment screen 500 such as that shown in FIG. 14 is displayed on the operation unit 70 (display unit 70a). The potential regulating bias adjustment screen 500 of FIG. 14 displays an adjustment value display section 501 that displays the adjustment value (offset value) of the potential regulating bias, and an adjustment value input section (+ button, − button) 502 for inputting (changing) the adjustment value. In this embodiment, the adjustment value display section 501 and the adjustment value input section 502 are provided for the front side (image side of a single-sided print, the first side of a double-sided print) and the back side (the second side of a double-sided print) of the recording material S for each of the image forming units 10 for yellow, magenta, cyan, and black, respectively. The potential regulating bias adjustment screen 500 also displays a confirm (OK) button 503 for confirming the change in setting and storing it in the storage unit 35, and a cancel button 504 for canceling the change in setting. The user can change the potential regulating bias by operating the adjustment value input unit 502, from the default value corresponding to an adjustment value of 0, in a predetermined change amount (for example, +50 to +500 V (or −50 to −500 V) in increments of +1 (or −1). The adjustment value changed by the adjustment value input unit 502 is displayed in the adjustment value display unit 501. The user can confirm the change in setting and store it in the storage unit 35 by operating the confirm button 503, or can cancel the change in setting by operating the cancel button 504. The user can set an optimal value for the potential regulating bias (S208) by repeatedly inputting an adjustment value (offset value) (S206) and checking the output image (S207).

[0086] The image output for adjusting (checking) the potential regulating bias may be an image the user actually desires to obtain as a final product, or a predetermined adjustment image. To adjust the potential regulating bias for image formation on both sides of the recording material S, an image for adjusting the potential regulating bias can be output by double-sided printing using the double-sided printing mechanism 60. For example, halftone images (e.g., halftone images with an image area ratio of 50%) in monochrome (yellow, magenta, cyan, and black) are output on the entire surface of the recording material S (including margins). If scattering occurs at the leading or trailing edge as shown in FIG. 9(a) or if image distortion occurs overall (or in part near the leading edge) as shown in FIG. 9(b), the potential regulating bias is adjusted. In other words, if such scattering or image distortion occurs, the absolute value of the potential regulating bias is decreased. If no scattering or image distortion occurs, the absolute value of the potential regulating bias is increased, which further improves secondary transfer performance in addition to the aforementioned adjustment of the secondary transfer bias. The user can then input the adjustment values ​​and output the image again as described above, and when the user confirms that the image has been improved, the user can end the adjustment of the potential regulating bias. FIG. 15 is a schematic diagram showing another example of an adjustment image that can be used to adjust the potential regulating bias. In the adjustment image of FIG. 15, strip-shaped halftone images (e.g., halftone images with an image area ratio of 50%) of yellow, magenta, cyan, and black are formed over substantially the entire area (margins may be present) from the leading edge to the trailing edge of the recording material S. Using such an adjustment image, it is possible to check for scattering and image distortion for multiple colors (all colors in the example of FIG. 15) on a single sheet of recording material S, thereby reducing the number of recording materials S required to adjust the potential regulating bias and the effort required for adjustment.

[0087] Furthermore, for example, when adjusting the potential regulating bias using the image a user actually wants to obtain as a final product, it may be difficult to achieve the desired results by adjusting the potential regulating bias for each color, such as yellow, magenta, cyan, and black. Therefore, for example, it may be possible to adjust the potential regulating bias for all colors simultaneously: yellow, magenta, cyan, and black. In this case, the change amount of the potential regulating bias for each color per predetermined adjustment value may be the same or different. For example, the more upstream the primary transfer unit N1 is, the more primary transfer units N1 the toner transferred onto the intermediate transfer belt 6 passes through before reaching the secondary transfer unit N2, and the more discharged the toner is, and the more likely it is to increase its charge amount. Therefore, when decreasing the absolute value of the potential regulating bias, the change amount of the potential regulating bias per predetermined adjustment value can be made smaller for the image forming unit 10 located further upstream. When increasing the absolute value of the potential regulating bias, the change amount of the potential regulating bias per predetermined adjustment value can be made larger for the image forming unit 10 located further upstream. The change amount of the potential regulating bias per predetermined adjustment value can be set in advance through experiments or the like based on the degree of increase in the charge amount of toner of each color. FIG. 16 shows an example of a potential regulating bias adjustment screen 500 in this case. The potential regulating bias adjustment screen 500 in FIG. 16 differs from the potential regulating bias adjustment screen 500 in FIG. 14 in that an adjustment value display section 501 and an adjustment value input section 502 are provided, one for the front side and one for the back side of the recording material S. By operating the adjustment value input section 502, the user can collectively change the potential regulating bias for all colors (yellow, magenta, cyan, and black) from the default value corresponding to the adjustment value 0. In this case, as described above, the change amount of the potential regulating bias per adjustment value +1 (or -1) may be the same or different for each color (yellow, magenta, cyan, and black). Furthermore, the change amount may be the same for at least two colors, for example, by making the change amount different between yellow and magenta and between cyan and black, or the change amount for at least one color may be different from the change amount for the other colors.

[0088] 17, a chart output button 505 may be provided on the potential regulating bias adjustment screen 500, which allows the image forming apparatus 1 to output an image for adjusting the potential regulating bias (adjustment chart) as shown in Fig. 15. This eliminates the need for the user to prepare an adjustment image as shown in Fig. 15, and allows the potential regulating bias to be adjusted more easily.

[0089] One way to suppress scattering and image distortion is to reduce the absolute value of the secondary transfer bias. However, doing so makes it difficult to ensure the secondary transfer latitude between the single color and the secondary color, making it difficult for users to find settings that will produce the results they desire. Therefore, adjusting the potential control bias is an effective way to suppress scattering and image distortion. Adjusting the potential control bias makes it possible to suppress scattering and image distortion while ensuring the secondary transfer latitude.

[0090] As described above, in this embodiment, the image forming apparatus 1 includes a photoconductor 11 that can be charged to a predetermined polarity and that carries a toner image, a circumferentially movable intermediate transfer belt 6 that contacts the photoconductor 11 to form a primary transfer portion N1 and transports the toner image that has been primarily transferred from the photoconductor 11 at the primary transfer portion N1 to a recording material S for secondary transfer at a secondary transfer portion N2, a primary transfer member 15 that contacts the inner peripheral surface of the intermediate transfer belt 6 and to which a first bias (primary transfer bias) is applied to perform primary transfer of the toner image from the photoconductor 11 to the intermediate transfer belt 6, and a first application portion 75 that applies a first bias of a polarity opposite to the predetermined polarity to the primary transfer member 15. The image forming apparatus 1 includes 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 movement direction of the intermediate transfer belt 6, a second applying unit 80 that applies a second bias (potential regulating bias) of the same polarity as the predetermined polarity to the electrode member 8, a memory unit 35 that stores a set value of the second bias associated with the type of recording material S, and a control unit 3 that controls the second applying unit 80 to apply the second bias to the electrode member 8 during image formation on the predetermined type of recording material S based on the set value of the second bias stored in the memory unit 35 in association with the type of recording material S. In this embodiment, the image forming apparatus 1 includes changing means (operation unit 70, potential regulating bias adjustment screen 500, CPU 31) that can change the set value of the second bias associated with the type of recording material S and stored in the memory unit 35. Furthermore, in this embodiment, the image forming apparatus 1 has at least two photoconductors 11, at least two primary transfer members 15 provided corresponding to the at least two photoconductors 11, and at least two electrode members 8 provided corresponding to the at least two photoconductors 11, and the changing unit is capable of independently changing the set values ​​of the second bias applied to each of the at least two electrode members 8, which are associated with the type of the predetermined recording material S and stored in the memory unit 35, by separate change instructions. Alternatively, the changing unit may be capable of collectively changing the set values ​​of the second bias applied to each of the at least two electrode members 8, which are associated with the type of the predetermined recording material S and stored in the memory unit 35, by a single change instruction.In this embodiment, the change unit includes an adjustment value input unit 502 on the potential regulating bias adjustment screen 500 as an input unit that receives an instruction to change the set value of the second bias through an operation by an operator. Note that the image forming apparatus 1 may be configured so that an operator issues an instruction to change the set value of the second bias in an external device, and in this case, the change unit may include an input / output circuit (input / output unit) that serves as an input unit that receives an instruction to change from the external device.

[0091] As described above, according to this embodiment, in a configuration in which a bias is applied to an electrode member arranged downstream of the primary transfer unit to suppress an increase in the charge amount of toner on the intermediate transfer body, it is possible to suppress image defects such as scattering that can occur depending on the type of recording material, etc.

[0092] [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 assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0093] 1. Overview of this Example This embodiment differs from the first embodiment in that when the value of the potential regulating bias is changed, the primary transfer ATVC is always executed before the next image formation.

[0094] The potential regulating member 8 is provided adjacent to the downstream side of the primary transfer portion N1 and in contact with the rear surface of the intermediate transfer belt 6. Therefore, if the value of the potential regulating bias applied to the potential regulating member 8 changes, it may affect the value of the primary transfer bias.

[0095] 18 is a graph showing an example of the relationship between the voltage value of the primary transfer bias (the output voltage value of the primary transfer power supply 75) and the current value (the value of the current flowing through the primary transfer power supply 75). In FIG. 18, the dotted line indicates the case where a potential regulating bias of −1500 V is applied to the potential regulating member 8, the dashed-dotted line indicates the case where a potential regulating bias of −3000 V is applied to the potential regulating member 8, and the solid line indicates the case where no potential regulating bias is applied to the potential regulating member 8 (the potential regulating member 8 is in an electrically floating state). FIG. 18 also shows the current value when a primary transfer bias (DC voltage) is applied to the primary transfer roller 15 in a state where a charging bias (DC voltage) of −600 V is applied.

[0096] As shown in FIG. 18 , when a potential regulating bias is applied to the potential regulating member 8, the current flowing to the primary transfer power supply 75 may be larger than when the potential regulating bias is not applied, even if the voltage value of the primary transfer bias applied to the primary transfer roller 15 is the same. This is for the following reason. When the primary transfer bias is applied to the primary transfer roller 15, in addition to current flowing to the photosensitive drum 11 (primary transfer current), current also flows to the potential regulating member 8. The current flowing to the potential regulating member 8 changes depending on whether or not the potential regulating bias is applied to the potential regulating member 8, or whether the value of the potential regulating bias applied to the potential regulating member 8 is changed. When the primary transfer bias is controlled at a constant voltage, the output voltage of the primary transfer power supply 75 is controlled to be approximately constant. Therefore, if the current flowing to the potential regulating member 8 increases, the current flowing to the primary transfer power supply 75 increases. In other words, if the primary transfer bias is controlled so that the same target current flows to the primary transfer power supply 75, the current actually flowing to the photosensitive drum 11 (primary transfer current) decreases. Therefore, if image formation is performed without performing primary transfer ATVC after adjusting the value of the potential regulating bias, an excess or deficiency of the primary transfer current may cause image defects due to primary transfer defects. For example, if the absolute value of the potential regulating bias applied to the potential regulating member 8 is large or the impedance of the primary transfer section N1 is low, and the amount of current flowing into the potential regulating member 8 increases, the primary transfer efficiency may decrease.

[0097] FIG. 19 is a flowchart showing an example of the procedure for adjusting the potential regulating bias in this embodiment. The details of the procedures S301 to S307 and S309 in FIG. 19 are the same as the details of the procedures S201 to S207 and S208 in FIG. 10. In this embodiment, as shown in S307, when the user changes the adjustment value (offset value) of the potential regulating bias, the primary transfer ATVC is executed before the next image formation. Specifically, when the adjustment value of the potential regulating bias is changed, the control unit 3 controls so that the primary transfer ATVC is executed before the next image (the image the user actually wants to obtain as a deliverable or an adjustment image) is formed.

[0098] 2. Primary transfer bias correction control Next, a method for adjusting the value of the primary transfer bias with greater precision when the value of the potential regulating bias is changed will be described. As described above, in this embodiment, a default value for the target voltage of the potential regulating bias is preset for each type of recording material S according to the environment (temperature, humidity). Then, during image formation or primary transfer ATVC, the potential regulating bias is controlled to a constant voltage at the target voltage. Due to the influence of individual differences in the resistance values ​​of the intermediate transfer belt 6, the primary transfer roller 15, or the potential regulating member 8, the value of the current flowing into the potential regulating member 8 as described above due to changes in the environment (such as a rise in temperature inside the image forming apparatus 1) or changes in the potential regulating bias may vary for each individual image forming apparatus 1 and for each usage situation of the image forming apparatus 1.

[0099] FIG. 20 is a schematic diagram showing the current flowing around the primary transfer portion N1. For example, when a target current Ia is supplied from the primary transfer power supply 75 to the primary transfer roller 15, the target current Ia and the effective transfer current I1 flowing toward the photosensitive drum 11 would be approximately equal if the potential regulating member 8 were not present. However, by placing the potential regulating member 8 downstream of the primary transfer portion N1, the current path from the primary transfer roller 15 branches into the effective transfer current I1 and the advection current I2 flowing toward the potential regulating member 8. The primary transfer ATVC determines the target voltage of the effective bias Vtr to supply a target current corresponding to the total resistance value of the primary transfer portion N1. At this time, the advection current I2 to the potential regulating member 8 fluctuates due to factors such as the resistance fluctuations described above. Therefore, if primary transfer ATVC control is performed without considering the advection current I2 to the potential regulating member 8, the actual effective transfer current I1 may decrease, potentially impairing primary transfer performance. Therefore, by correcting the primary transfer bias taking into account the current flowing from the primary transfer portion N1 to the potential regulating member 8, the primary transfer current flowing toward the photosensitive drum 11 can be maintained at an appropriate value with higher accuracy.

[0100] Figure 21 is a block diagram showing a schematic configuration of the control system of image forming apparatus 1 in this case. The configuration shown in Figure 21 is generally similar to the configuration shown in Figure 2. However, in the configuration shown in Figure 21, potential regulating power supply 80 is connected to voltage detection sensor 80a as voltage detection means (voltage detection unit) that detects its output voltage, and current detection sensor 80b as current detection means (current detection unit) that detects its output current.

[0101] 22 is a timing chart illustrating the transition of the voltage and current values ​​of the primary transfer bias and potential regulating bias to explain the correction control of the primary transfer bias in this case. The control unit 3 corrects the primary transfer bias when performing the primary transfer ATVC. With the potential regulating bias applied to the potential regulating member 8, the control unit 3 detects the value of the current flowing through the potential regulating member 8 (potential regulating power supply 80) when no test bias is applied to the primary transfer roller 15 and when a test bias is applied to the primary transfer roller 15. The control unit 3 then corrects the primary transfer bias based on these detected current values.

[0102] That is, the intermediate transfer belt 6 starts to be driven, and the pre-rotation process begins (T1). Then, the potential regulating power supply 80 starts to apply a potential regulating bias to the potential regulating member 8 under constant voltage control (T2). Then, before the test bias is applied to the primary transfer roller 15, the current detection sensor 80b detects the current value Ib1 flowing through the potential regulating member 8. Then, the primary transfer ATVC starts, and the primary transfer power supply 75 applies a test bias to the primary transfer roller 15 under constant current control, aiming for a target current I1 (T3). The target current I1 corresponds to the target current of the primary transfer bias during image formation according to the environment. Then, the effective bias Vtr is determined as described above. As described above, the primary transfer ATVC applies three levels of test bias to the primary transfer roller 15. However, for simplicity, FIG. 22 illustrates only the test bias under constant current control, aiming for the target current during image formation. The effective bias Vtr determined here is affected by fluctuations in the current Ib1 flowing through the potential regulating member 8, as described above. This may result in a deviation between the target current Ia and the actual effective transfer current I1.

[0103] Therefore, when the test bias is applied to the primary transfer roller 15, the current detection sensor 80b detects the current value Ib2 flowing through the potential regulating member 8. The difference ΔI (=|Ib1-Ib2|) between the current value Ib1 detected when the test bias is not applied to the primary transfer roller 15 and the current value Ib2 detected when the test bias is applied to the primary transfer roller 15 is calculated. This difference ΔI is then regarded as the advection current I2, and the target current Ia is determined by adding this difference ΔI to the target current I1 of the test bias. Furthermore, based on the voltage-current characteristics acquired by ATVC control, the effective bias Vtr' corrected to correspond to the target current Ia is determined. During image formation, the corrected effective bias Vtr' is applied to the primary transfer roller 15 under constant voltage control (T4-T5).

[0104] Although the voltage value corresponding to the target current Ia is determined because the primary transfer bias is subjected to constant voltage control, this is not limiting. For example, if the primary transfer bias is subjected to constant current control, the target current Ia is determined as described above, and the primary transfer bias is subjected to constant current control at the determined target current Ia during image formation. Furthermore, while the current flowing through the potential control member 8 when a test bias is applied is detected by applying a predetermined test bias corresponding to the target current, this is not limiting. For example, multiple levels of test bias may be applied to determine a test bias corresponding to the target current, and the current flowing through the potential control member 8 may be detected by applying the test bias again. Furthermore, although the potential control bias applied to the potential control member 8 during image formation is subjected to constant voltage control, the potential control bias may also be subjected to constant current control. In this case, the primary transfer bias may be determined based on the voltage detected when the test bias is applied to the primary transfer roller 15 in the primary transfer ATVC and when it is not.

[0105] As described above, in this embodiment, when a predetermined condition is satisfied, the control unit 3 can control the first application unit 75 to apply a test bias to the primary transfer member 15 during non-image formation to perform a setting operation (primary transfer ATVC) to set a first bias to be applied by the first application unit 75 to the primary transfer member 15 during image formation. In this embodiment, when the setting value of the second bias (potential regulating bias) is not changed by the changing unit after the first image formation and before the second image formation that follows the first image formation, even if the setting operation is not performed during non-image formation before the second image formation, when the setting value of the second bias is changed by the changing unit after the first image formation and before the second image formation, the control unit 3 controls to perform the setting operation during non-image formation before the second image formation.

[0106] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and also, the change in the primary transfer property due to the adjustment of the potential regulating bias can be suppressed.

[0107] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0108] In the above-described 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-described 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 polarities opposite to those of the above-described embodiment, in accordance with the above-described embodiment.

[0109] Furthermore, the photosensitive member is not limited to a drum-shaped member (photosensitive drum), but may be an endless belt-shaped member (photosensitive belt) or the like.

[0110] 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 monocolor) image.

[0111] Furthermore, the displays and operations described in the above embodiment as being performed on the operation unit of the image forming apparatus may be performed on an external device.

[0112] Furthermore, in the above embodiment, the secondary transfer bias is also adjusted when the potential regulating bias is adjusted, but it is also possible to adjust only the potential regulating bias.

[0113] In addition, in the above embodiment, the adjustment of the secondary transfer bias and the potential regulating bias was described as an example of adjustment from the default value, but if the adjustment has already been made from the default value, it is also possible to make adjustments from the current settings.

[0114] In the above embodiment, the primary transfer bias and the secondary transfer bias are each controlled to a constant voltage, but at least one of them may be controlled to a constant current.

[0115] In addition, in the above-described embodiment, a halftone image having an image area ratio of 50% was used as an example of a halftone image, but the halftone image may be any halftone image having an image area ratio (ratio of toner amount to solid image) of, for example, approximately 30 to 80%.

[0116] Furthermore, in the above-described embodiment, the voltage applied to the potential regulating member (electrode member) during image formation is controlled to be a constant voltage, but the voltage applied to the potential regulating member (electrode member) may be controlled to be a constant current.

[0117] Furthermore, information on the environment (the installation environment of the image forming apparatus) used for various controls in the image forming apparatus may be information on at least one of the temperature and humidity inside or outside the image forming apparatus. [Explanation of symbols]

[0118] 1. Image forming device 6 Intermediate transfer belt 8. Potential regulation member (electrode member) 11 Photosensitive drum (photoconductor) 15 Primary transfer roller (primary transfer member) 80 Potential Regulated 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 in contact with the photoconductor to form a primary transfer section and that conveys the toner image that has been primarily transferred from the photoconductor at the primary transfer section to a recording material at a secondary transfer section; a primary transfer member that contacts an inner circumferential surface of the intermediate transfer belt and that is applied with a first bias to perform primary transfer of a toner image from the photoconductor to the intermediate transfer belt; a first applying section that applies the first 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 applying unit that applies a second bias having the same polarity as the predetermined polarity to the electrode member; a storage section in which a set value of the second bias is stored in association with a type of recording material; a control unit that controls the second application unit so as to apply the second bias to the electrode member during image formation on a predetermined type of recording material, based on a set value of the second bias stored in the storage unit in association with the predetermined type of recording material; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, further comprising a change unit capable of changing a set value of the second bias stored in the storage unit in association with the type of the predetermined recording material.

3. at least two of the photoconductors, at least two of the primary transfer members provided corresponding to the at least two of the photoconductors, respectively, and at least two of the electrode members provided corresponding to the at least two of the photoconductors, The image forming apparatus according to claim 2, characterized in that the change means is capable of independently changing the set values ​​of the second bias applied to each of the at least two electrode members, which are stored in the memory unit in association with the type of the specified recording material, by separate change instructions.

4. at least two of the photoconductors, at least two of the primary transfer members provided corresponding to the at least two of the photoconductors, respectively, and at least two of the electrode members provided corresponding to the at least two of the photoconductors, The image forming apparatus according to claim 2, characterized in that the change means is capable of changing the setting values ​​of the second bias applied to each of at least two of the electrode members, which are stored in the memory unit in association with the type of the specified recording material, all at once by a single change instruction.

5. 5. The image forming apparatus according to claim 2, wherein the change unit has an input unit that receives an instruction to change the set value of the second bias through an operation by an operator.

6. the control unit is capable of performing control to execute a setting operation for applying a test bias to the primary transfer member by the first application unit during non-image formation when a predetermined condition is satisfied, and setting the first bias to be applied to the primary transfer member by the first application unit during image formation; The image forming apparatus according to any one of claims 2 to 4, characterized in that the control unit controls the setting operation to be performed during non-image formation before the second image formation when the setting value of the second bias is changed by the changing means after a first image formation and before a second image formation following the first image formation, even if the setting operation is not performed during non-image formation before the second image formation, when the setting value of the second bias is changed by the changing means after the first image formation and before the second image formation.

Images