Image forming apparatus

Abstract

After detecting the density of the adjustment toner image formed on the image carrier, toner scattering caused by static electricity removal from the image carrier is suppressed. [Solution] A primary transfer section is formed, and by applying a transfer voltage... Formed on the image carrier Toner image To the intermediate transfer A transferable transfer member, Downstream from the development position and The system includes a detection unit that detects the density of a correction toner image formed on the image carrier upstream of the primary transfer unit, a static elimination unit that removes static electricity from the surface of the image carrier downstream of the primary transfer unit, a cleaning unit that removes toner from the intermediate transfer unit, and a control unit that can perform a first mode in which the toner image formed on the image carrier is transferred to the intermediate transfer unit and then transferred from the intermediate transfer unit to the recording material, and a second mode in which a correction toner image is formed on the image carrier and the correction toner image is detected by the detection unit, wherein when the second mode is performed, the control unit transfers the correction toner image to the intermediate transfer unit and rotates the intermediate transfer unit so that the transferred correction toner image passes through the cleaning unit.

Description

[Technical Field]

[0001] This invention relates to an image forming apparatus using electrophotographic technology, such as a printer, copier, facsimile, or multifunction device. [Background technology]

[0002] In an image forming apparatus, adjustment toner images (called patches) are formed, the density of the formed patches is detected, and the image forming conditions are changed according to the density of the patches to adjust the density of the toner images formed on the recording material. In Patent Document 1, in full-color mode, the patches formed on the photosensitive drum are transferred to an intermediate transfer belt, and the density of the patches transferred to the intermediate transfer belt is detected by a patch sensor on the belt. The patches formed on the intermediate transfer belt are removed by a belt cleaning device. In black monochrome mode, the patches are not transferred from the photosensitive drum to the intermediate transfer belt, and the density of the patches formed on the photosensitive drum is detected by a patch sensor on the drum. The patches formed on the photosensitive drum are removed by a drum cleaning device. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-222406 [Overview of the project] [Problems that the invention aims to solve]

[0004] Image forming apparatuses may be equipped with a pre-exposure device that discharges the surface of the photosensitive drum before uniformly charging its surface. The pre-exposure device discharges the photosensitive drum upstream of the drum cleaning device in the direction of rotation of the photosensitive drum (this is called pre-exposure). However, conventionally, when a pre-exposure device is equipped, the discharge of the patched photosensitive drum can cause toner to scatter from the patch on the photosensitive drum, and the scattered toner can adhere to and contaminate the photosensitive drum and the pre-exposure device.

[0005] The present invention has been made in view of the above problems, and aims to provide an image forming apparatus capable of suppressing toner scattering caused by electrostatic discharge of the photosensitive drum after detecting the density of a patch formed on the photosensitive drum. [Means for solving the problem]

[0006] An image forming apparatus according to one embodiment of the present invention is an image forming apparatus for forming an image on a recording material, comprising: a rotating image carrier; a charging unit for charging the image carrier; an exposure unit for exposing the charged image carrier to form an electrostatic latent image; a developing unit for developing the electrostatic latent image formed on the image carrier into a toner image; an intermediate transfer unit for transferring the toner image from the image carrier and transferring the transferred toner image to a recording material; a primary transfer unit for transferring the toner image formed on the image carrier to the intermediate transfer unit, and a transfer member capable of transferring the toner image by applying a transfer voltage; a detection unit for detecting the density of an adjustment toner image formed on the image carrier downstream of the developing unit and upstream of the primary transfer unit in the rotation direction of the image carrier; and a destaticizing unit for destaticizing the surface of the image carrier by irradiating it with light downstream of the primary transfer unit and upstream of the charging unit in the rotation direction. The device comprises an electrical unit, a cleaning unit that removes toner from the intermediate transfer body upstream of the primary transfer unit and downstream of the secondary transfer unit that transfers a toner image from the intermediate transfer body to a recording material with respect to the rotation direction of the intermediate transfer body, a first mode in which a toner image formed on the image carrier is transferred to the intermediate transfer body and transferred from the intermediate transfer body to a recording material, and a second mode in which an adjustment toner image is formed on the image carrier and the adjustment toner image is detected by the detection unit, wherein, when executing the second mode, the control unit applies a transfer voltage to the transfer member that is opposite to the normal charging polarity of the toner, at least while the adjustment toner image is passing through the primary transfer unit, transfers the adjustment toner image to the intermediate transfer body, and rotates the intermediate transfer body so that the transferred adjustment toner image passes through the cleaning unit. [Effects of the Invention]

[0007] According to the present invention, toner scattering caused by electrostatic discharge of the image carrier after detecting the density of the adjustment toner image formed on the image carrier can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram showing the image forming apparatus of this embodiment. [Figure 2] Schematic diagram showing the image forming apparatus in the black monochrome mode. [Figure 3] Schematic diagram showing the patch sensor. [Figure 4] Schematic diagram showing the pre-exposure device. [Figure 5] Cross-sectional view showing an example of the layer configuration of the intermediate transfer belt. [Figure 6] Schematic diagram showing the belt cleaning device. [Figure 7] Graph for explaining the signal value of the patch sensor. [Figure 8] (a) Schematic diagram showing an example of a patch used in the adjustment mode, (b) Schematic diagram showing an example of an ATR patch used in ATR control. [Figure 9] Block diagram showing the control system of the image forming apparatus. [Figure 10] Schematic diagram for explaining toner scattering of a patch, where (a) is the state of the patch before pre-exposure, and (b) is the state of the patch during pre-exposure. [Figure 11] Flowchart showing the density adjustment processing of the present embodiment. [Figure 12] (a) Diagram showing the sequence of Embodiment 1 (Comparative Example 2), (b) Diagram showing the sequence of Comparative Example 1, (c) Diagram showing the sequence of Embodiment 2. [Figure 13] Diagram for explaining the effects of the present embodiment. [Mode for Carrying Out the Invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] <Image Forming Apparatus> First, the image forming apparatus of the present embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing the image forming apparatus of the present embodiment. Figure 2 is a schematic diagram showing the image forming apparatus in the black monochrome mode. The image forming apparatus 100 of the present embodiment is a tandem type laser beam printer that adopts an intermediate transfer method, and is capable of forming a full-color image on a recording material using an electrophotographic system.

[0011] As shown in Figure 1, the image forming apparatus 100 includes first, second, third, and fourth image forming units SY, SM, SC, and SK. The respective image forming units SY, SM, SC, and SK form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the present embodiment, the configurations and operations of the respective image forming units SY, SM, SC, and SK have many common portions except that the colors of the toners used are different. Therefore, in the following description, when no particular distinction is required, the suffixes Y, M, C, and K at the end of the reference numerals indicating elements provided for any one of the colors are omitted, and the elements will be described collectively.

[0012] The image forming unit S includes a photosensitive drum 1 which is a drum-shaped (cylindrical) electrophotographic photosensitive member (photosensitive member) disposed to be rotatable. The photosensitive drum 1 serving as an image bearing member is rotationally driven in the direction of an arrow R1 by a drive motor (not shown). Around the photosensitive drum 1, the process devices described below are arranged along the rotational direction of the photosensitive drum 1. First, a charging roller 2 is arranged. Then, starting from the charging roller 2, the exposure device 3, the developing device 4, the on-drum patch sensor 160, the pre-exposure device 140, the drum cleaning device 6, and the post-cleaning exposure device 130 are arranged in this order from the upstream side in the rotational direction. These will be described later.

[0013] An endless intermediate transfer belt 7 is positioned opposite each photosensitive drum 1 of each image forming unit S. The intermediate transfer belt 7, acting as an intermediate transfer body, is stretched over tension rollers such as a drive roller 71, a tension roller 72, a secondary transfer opposing roller 73, and push-up rollers 74 and 75. The drive roller 71 transmits drive to the intermediate transfer belt 7. The tension roller 72 applies a predetermined tension to the intermediate transfer belt 7. The secondary transfer opposing roller 73 becomes the opposing member (opposing electrode) of the secondary transfer roller 8, which will be described later. The push-up rollers 74 and 75 form a primary transfer plane 70 for transferring the toner image onto the intermediate transfer belt 7. Four image forming units SY, SM, SC, and SK are arranged in series along the horizontal portion of this primary transfer plane 70. The drive roller 71 is driven to rotate at a peripheral speed of "400 mm / sec" by a drive motor (not shown), such as a pulse motor. As a result, the intermediate transfer belt 7 rotates (moves in a circular motion) in the direction indicated by arrow R2 (hereinafter also referred to as the "rotation direction" or "conveying direction"). The tension rollers other than the drive roller 71 rotate in accordance with the rotation of the intermediate transfer belt 7.

[0014] On the inner circumferential surface (back side) of the intermediate transfer belt 7, a roller-shaped primary transfer roller 5 is positioned opposite each photosensitive drum 1 of each image forming unit S, serving as a transfer member. The primary transfer roller 5 is biased (pressed) toward the photosensitive drum 1 via the intermediate transfer belt 7, forming a primary transfer section (primary transfer nip section) T1 where the intermediate transfer belt 7 and the photosensitive drum 1 come into contact. On the outer circumferential surface (front side) of the intermediate transfer belt 7, a roller-shaped secondary transfer roller 8 is positioned opposite the secondary transfer opposing roller 73. The secondary transfer roller 8 is biased (pressed) toward the secondary transfer opposing roller 73 via the intermediate transfer belt 7, forming a secondary transfer section (secondary transfer nip section) T2 where the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact. Furthermore, a belt cleaning device 9 is positioned opposite the drive roller 71 on the outer circumferential surface of the intermediate transfer belt 7.

[0015] The rotating photosensitive drum 1 is uniformly charged by the charging roller 2. The charged photosensitive drum 1 is exposed by the exposure device 3 according to the image information, and an electrostatic latent image corresponding to the image information is formed on it. The electrostatic latent image formed on the photosensitive drum 1 is developed as a toner image by supplying toner of the color corresponding to each image forming unit S from the developing device 4. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) to the rotating intermediate transfer belt 7 in the primary transfer unit T1 by the action of the primary transfer roller 5. At this time, a primary transfer bias (primary transfer voltage), which is a DC voltage with the opposite polarity to the charging polarity of the toner during development (normal charging polarity), is applied to the primary transfer roller 5 from the primary transfer power supply 51, and a primary transfer electric field is formed in the primary transfer unit T1. In this embodiment, primary transfer power supplies 51Y, 51M, 51C, and 51K are connected to each of the primary transfer rollers 5Y, 5M, 5C, and 5K of each image forming unit SY, SM, SC, and SK, respectively. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed in each image forming unit S are sequentially transferred to the intermediate transfer belt 7 in each primary transfer unit T1 by overlapping them.

[0016] The toner image transferred to the intermediate transfer belt 7 can be transferred to the recording material P in the secondary transfer section T2 by the action of the secondary transfer roller 8, which acts as a secondary transfer member (secondary transfer). At this time, a secondary transfer bias (secondary transfer voltage), which is a DC voltage with the opposite polarity to the normal charging polarity of the toner, is applied to the secondary transfer roller 8 from the secondary transfer power supply 81, and a secondary transfer electric field is formed in the secondary transfer section T2. ​​By this time, the recording material P has been fed out from the paper feed cassette 10, stopped briefly by the registration roller 12, and then transported to the secondary transfer section T2 at a predetermined timing. The recording material P on which the toner image has been transferred is transported to the fixing device 11. In the fixing device 11, the toner image is fixed (fixed) to the recording material P by heat and pressure. After that, the recording material P is discharged (output) to the outside of the main body of the image forming apparatus 100.

[0017] In the primary transfer process, any remaining toner on the photosensitive drum 1 (image carrier) that was not transferred to the intermediate transfer belt 7 is removed from the photosensitive drum 1 by the drum cleaning device 6. In the secondary transfer process, any remaining toner on the intermediate transfer belt 7 (intermediate transfer body) that was not transferred to the recording material P is removed from the intermediate transfer belt 7 by the belt cleaning device 9.

[0018] <Image Formation Mode> The image forming apparatus 100 of this embodiment can perform a full-color mode and a black monochrome mode as multiple image forming modes with different numbers of image forming units S used for toner image formation. In the full-color mode, a full-color image can be formed by forming a toner image with image forming units SY, SM, SC, and SK. In the black monochrome mode, a black image can be formed by forming a toner image with only the image forming unit SK among the image forming units SY, SM, SC, and SK. Furthermore, the image forming apparatus 100 has a belt contact / separation mechanism 170 (see Figure 9) that enables non-contact between the photosensitive drums 1Y, 1M, and 1C of the image forming units SY, SM, and SC that are not used in the black monochrome mode and the intermediate transfer belt 7.

[0019] The belt contact / separation mechanism 170 can move the push-up rollers 74, 75 and the primary transfer rollers 5Y, 5M, 5C shown in Figure 2, thereby moving the primary transfer plane 70. In full-color mode, the primary transfer plane 70 is formed by the push-up rollers 74, 75 and the tension roller 72. In black monochrome mode, the primary transfer plane 70 is formed by the push-up roller 75 and the tension roller 72 on the downstream side in the transport direction of the intermediate transfer belt 7. As a result, in full-color mode, the photosensitive drums 1Y, 1M, 1C, 1K are in contact with the intermediate transfer belt 7. On the other hand, in black monochrome mode, the photosensitive drums 1Y, 1M, 1C are separated from the intermediate transfer belt 7. By making it possible to separate the photosensitive drums 1Y, 1M, 1C of the image forming units SY, SM, and SC, which are not used in black monochrome mode, from the intermediate transfer belt 7, the lifespan of these photosensitive drums 1Y, 1M, 1C is extended.

[0020] <Photosensitive drum> The photosensitive drum 1 is constructed by coating the outer surface of an aluminum cylinder with an organic photoconductor layer (OPC). The photosensitive drum 1 is rotatably supported at both ends in its longitudinal direction (direction of the rotation axis) by flanges, and is rotationally driven by a drive motor (not shown) that transmits driving force to one end. In this embodiment, the charge polarity of the photosensitive drum 1 is negative. For example, the outer diameter of the photosensitive drum 1 is 80 mm.

[0021] <Electrifying roller> The charging roller 2, acting as the charging unit, is a contact charging member that contacts the surface of the photosensitive drum 1 and uniformly charges the circumferential surface of the photosensitive drum 1. The charging roller 2 is a conductive roller in which an elastic layer is formed around a core metal (core material). The charging roller 2 is rotatably held at both ends in its longitudinal direction (direction of rotation axis) by bearing members and is biased toward the photosensitive drum 1 by a compression spring. As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force and rotates in accordance with the rotation of the photosensitive drum 1. A charging bias (charging voltage) is applied to the core metal of the charging roller 2 from a charging power supply 21 (see Figure 9). As a result, the circumferential surface of the rotating photosensitive drum 1 is charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment). The charging bias is an oscillating voltage obtained by superimposing an alternating current voltage (Vac) on a direct current voltage (Vdc). More specifically, it is an oscillating voltage obtained by superimposing a sinusoidal AC voltage (AC component) with a frequency f of 1 kHz and a peak-to-peak voltage Vpp of 1.5 kV onto a DC voltage (DC component) of -600 V. As a result, the surface of the photosensitive drum 1 is uniformly charged to -600 V (dark area potential Vd).

[0022] <Exploration equipment> The exposure unit, exposure apparatus 3, is a laser scanner device equipped with a laser light source, polygon mirrors, etc., and its lighting is controlled by a drive circuit according to image information. The exposure apparatus 3 projects a laser beam corresponding to the image information of the component colors of the original document corresponding to each image forming unit S onto the photosensitive drum 1 via the polygon mirrors, etc.

[0023] <Developing equipment> The developing unit, the developing apparatus 4, uses a two-component developer containing a non-magnetic toner and a magnetic carrier as the developer. In this embodiment, the toner is a negatively charged toner. The developing apparatus 4 has a developing container that houses the developer. Each developing apparatus 4 contains a two-component developer containing a non-magnetic toner and a magnetic carrier for each color: yellow, magenta, cyan, and black. The developing apparatus 4 also has a developing sleeve that is partially exposed from an opening in the developing container facing the photosensitive drum 1. The developing sleeve is positioned adjacent to the surface of the photosensitive drum 1 and is rotationally driven by a drive motor (not shown), and a developing bias (developing voltage) is applied by a developing power supply 41 (see Figure 9). As a result, the toner of the developer, which is carried on the developing sleeve and transported to the position facing the photosensitive drum 1, is supplied, and the electrostatic latent image on the photosensitive drum 1 is developed as a toner image. In this embodiment, the developing apparatus 4 forms a toner image by reverse development, which involves depositing toner with the same polarity as the charge polarity of the photosensitive drum 1 onto the exposed area on the photosensitive drum 1, which has been uniformly charged and then had its absolute potential reduced. An external additive is added to the toner to improve its release properties.

[0024] <Drum-top patch sensor> In the image forming apparatus 100 of this embodiment, an adjustment mode can be executed to adjust the density of the toner image formed on the recording material P by changing the image forming conditions according to the density of the adjustment toner image (called a patch) formed on the photosensitive drum 1. The image forming apparatus 100 has a drum-top patch sensor 160 for detecting the density of the patch formed on the photosensitive drum 1. The drum-top patch sensor 160 is positioned to detect the density of the patch on the photosensitive drum 1 downstream of the position where the developing sleeve and the photosensitive drum 1 face each other in the rotational direction of the photosensitive drum 1, and upstream of the primary transfer unit T1. With this arrangement, the drum-top patch sensor 160 can detect the patch without disturbing it in the primary transfer unit T1.

[0025] Figure 3 is a schematic diagram showing the general configuration of the drum-top patch sensor 160. The drum-top patch sensor 160, as a detection unit, irradiates light from an LED light source 161 and detects the amount of reflected light from the surface of the photosensitive drum 1. The specular reflection component is detected by the first photosensor 162, and the diffuse reflection component is detected by the second photosensor 163. In this embodiment, an LED with a wavelength of "880 nm" is used as the LED light source 161 of the drum-top patch sensor 160. Since the photosensitive drum 1 is exposed by the LED light source only when reading the patch, it is preferable that the wavelength range is in the near-infrared range, which is the wavelength range in which the sensitivity of the photosensitive drum 1 is low when exposed to light.

[0026] <Primary Transfer Roller> The primary transfer roller 5 is a conductive roller in which an elastic layer is formed around a core metal (core material). The core metal is a cylindrical member with a diameter of "8 mm" made of conductive metal. The elastic layer has a resistance value of "1.0 × 10 4 ~1.0×10 8 It is a conductive foam with a thickness of 5 mm in the Ω range, and it surrounds the core metal. In this embodiment, the outer diameter of the primary transfer roller 5 is the same in all image forming sections S.

[0027] The primary transfer roller 5 is supported by a pressing mechanism so as to contact the photosensitive drum 1 from the back surface of the intermediate transfer belt 7, in order to transfer the toner image from the photosensitive drum 1 to the intermediate transfer belt 7 by electrical action and pressing force. In this embodiment, both ends of the primary transfer roller 5 in its longitudinal direction (direction of the rotation axis) are pressed vertically upward by pressing springs.

[0028] <Pre-exposure device> The pre-exposure device 140 is positioned downstream of the primary transfer unit T1 and upstream of the drum cleaning device 6 in the rotational direction of the photosensitive drum 1. As a static elimination unit, the pre-exposure device 140 exposes the surface of the photosensitive drum 1 that has passed through the primary transfer unit T1 to eliminate static electricity from the photosensitive drum 1. An LED array or a light guide that transmits the light emission of the LEDs can be used as the pre-exposure device 140. Figure 4 is a schematic diagram showing the pre-exposure device 140. In this embodiment, an LED array is used as the pre-exposure device 140. As shown in Figure 4, a plurality of light-emitting elements 141 are arranged in the LED array (pre-exposure device 140). The amount of light emitted by the light-emitting elements 141 can be changed by a control current from the pre-exposure control unit 142 (see Figure 9). By increasing the control current from the pre-exposure control unit 142, the amount of light emitted by the light-emitting elements 141 can be increased.

[0029] <Exposure equipment after cleaning> The post-cleaning exposure device 130 is positioned downstream of the drum cleaning device 6 and upstream of the charging roller 2 in the rotational direction of the photosensitive drum 1. As a post-static removal unit, the post-cleaning exposure device 130 exposes the surface of the photosensitive drum 1 that has passed through the drum cleaning device 6 to re-staticize the photosensitive drum 1. The post-cleaning exposure device 130 can be configured in the same way as the pre-exposure device 140. The amount of light emitted by the post-cleaning exposure device 130 can be changed by a control current from the post-cleaning exposure control unit 132 (see Figure 9).

[0030] <Drum cleaning device> The drum cleaning device 6 is positioned downstream of the pre-exposure device 140 and upstream of the post-cleaning exposure device 130 in the rotational direction of the photosensitive drum 1. The drum cleaning device 6 consists of a cleaning blade made of a plate-shaped member of rubber such as urethane rubber. The drum cleaning device 6 is positioned so that the cleaning blade contacts the photosensitive drum 1 while maintaining, for example, an penetration amount of "1.0 mm". The cleaning blade is in contact with the surface of the photosensitive drum 1 such that the free end is upstream of the rotational direction of the photosensitive drum 1 than the fixed end (counter-contact).

[0031] <Intermediate Transfer Belt> In the present embodiment, as the intermediate transfer belt 7, an endless belt having a plurality of layers and including an elastic layer is used. FIG. 5 is a cross-sectional view showing an example of the layer configuration of the intermediate transfer belt 7. In the present embodiment, the intermediate transfer belt 7 has a three-layer structure consisting of a base layer (resin layer) 7a, an elastic layer 7b, and a surface layer 7c. In order to maintain image quality, the three-layer surface resistivity of the intermediate transfer belt 7 is set to 1×10 10 ~1×10 13 Ω / □", and the volume resistivity is set to 1×10 8 ~5×10 12 Ω·cm, which is preferable. In the present embodiment, the surface resistivity is set to 1×10 12 Ω / □", and the volume resistivity is set to 1×10 11 Ω·cm. The resistivity measurement was performed using a high resistivity meter Hiresta-UPM, CP-HT450, and UR probe manufactured by Mitsubishi Chemical Corporation, under the measurement conditions of an applied voltage of 1000V and an application time of 10 seconds. Further, as for the film thickness of each layer of the intermediate transfer belt 7, it is preferable that the base layer 7a is approximately 50 to 100 μm, the elastic layer 7b is approximately 200 to 300 μm, and the surface layer 7c is approximately 2 to 20 μm. In the present embodiment, the base layer 7a is set to 85 μm, the elastic layer 7b is set to 260 μm, and the surface layer 7c is set to 2 μm. In addition, regarding the surface hardness of the three layers of the intermediate transfer belt 7, an IRHD hardness of approximately 40 to 90 degrees is preferable, and it is set to 73±3 degrees in the present embodiment.

[0032] The base layer 7a and the elastic layer 7b may be made of any material that satisfies the above-described characteristics, and representative examples thereof include the following. As the resin material constituting the base layer (resin layer) 7a, for example, a material having a Young's modulus (conforming to JIS K7127) of 5.0×10 2 ~5.0×10 3 MPa, such as polycarbonate, fluororesin (ETFE, PVDF), polyamide resin, and polyimide resin, can be used. Further, as the elastic material (elastic rubber, elastomer) constituting the elastic layer 7b, a material having a Young's modulus of 0.1~1.0×10 2Butyl rubber, fluororubber, CR rubber, EPDM, urethane rubber, etc., with a Young's modulus of "MPa" can be used. Furthermore, while there are no particular restrictions on the material of the surface layer 7c, it is desirable to use a material that reduces the adhesion of toner to the surface of the intermediate transfer belt 7 and improves secondary transferability. For example, a Young's modulus of "1.0 × 10" is desirable. 2 ~5.0×10 3 Examples include resin materials such as fluororesins and fluorine compounds with a hardness of MPa, urethane-based resins in which fluororesin fine particles are dispersed, and elastic materials. However, the materials are not limited to the above for any of the base layer 7a, elastic layer 7b, and surface layer 7c. Thus, in this embodiment, the intermediate transfer body is composed of at least multiple layers, and the layer on the side that carries the toner image has lower hardness than the bottom layer on the side that does not carry the toner image.

[0033] In this embodiment, an elastic intermediate transfer belt as described above was used as the intermediate transfer belt 7, but a single-layer belt such as a resin belt may also be used.

[0034] <Secondary Transfer Roller> The secondary transfer roller 8 is a conductive roller in which an elastic layer of ion-conductive foamed rubber (such as NBR rubber, EPDM rubber, or hydrin rubber) is formed around a core metal (core material). This secondary transfer roller 8 has an outer diameter of "24 mm" and a surface roughness Rz of "6.0 to 12.0 μm". Furthermore, the resistance value of this secondary transfer roller 8 was measured N / N (23°C, 50% RH) with "2 kV" applied and was "1.0 × 10⁻¹⁰". 5 ~1.0×10 8 It is "Ω".

[0035] In this embodiment, the image forming apparatus 100 has a secondary transfer roller contact / separation mechanism 180 (see Figure 9) that brings the secondary transfer roller 8 into contact with or away from the intermediate transfer belt 7. This configuration allows the secondary transfer roller 8 to be selectively switched between an operating state in contact with the intermediate transfer belt 7 and rotating in conjunction with the rotation of the intermediate transfer belt 7, and a non-operating state separated from the intermediate transfer belt 7. The secondary transfer roller contact / separation mechanism 180 consists of a support member for the secondary transfer roller 8, a switching unit for moving the secondary transfer roller via the support member, and the like. In this embodiment, a solenoid is used as the switching unit. The secondary transfer roller contact / separation mechanism 180, as the moving unit, moves the secondary transfer roller 8 up and down by the switching unit, allowing the secondary transfer roller 8 to move between a contact position in contact with the intermediate transfer belt 7 where the secondary transfer section T2 is formed, and a separated position separated from the intermediate transfer belt 7.

[0036] <Belt cleaning device> In this embodiment, an electrostatic cleaning type belt cleaning device 9 is used primarily to remove residual toner from the intermediate transfer belt 7. Figure 6 is a schematic diagram showing the belt cleaning device 9. The belt cleaning device 9 is positioned upstream of the primary transfer section T1 (more specifically, the uppermost primary transfer section T1Y) and downstream of the secondary transfer section T2 in the transport direction of the intermediate transfer belt 7.

[0037] The belt cleaning device 9 has a housing 98 positioned near the intermediate transfer belt 7. Inside the housing 98, the belt cleaning device 9 has an upstream fur brush 91a positioned upstream in the transport direction of the intermediate transfer belt 7, and a downstream fur brush 91b positioned downstream. The upstream fur brush 91a and the downstream fur brush 91b contact the intermediate transfer belt 7 at a position opposite the drive roller 71 via the intermediate transfer belt 7, forming first and second electrostatic cleaning sections CL1 and CL2 that recover toner from the intermediate transfer belt 7. The belt cleaning device 9 also has an upstream bias roller 92a that contacts the upstream fur brush 91a and a downstream bias roller 92b that contacts the downstream fur brush 91b inside the housing 98. Furthermore, the belt cleaning device 9 has an upstream blade 93a that abuts the upstream bias roller 92a and a downstream blade 93b that abuts the downstream bias roller 92b inside the housing 98.

[0038] The upstream and downstream fur brushes (91a, 91b) have a thread resistance value of "1 × 10 10 The fibers are carbon-dispersed nylon fibers with a density of Ω / cm and a fiber thickness of 2 denier, and the flocking density is 240,000 strands / inch. 2 This conductive fur brush is constructed by implanting bristles onto a metal roller (core material) in a specific ratio. In this embodiment, the diameters of the upstream and downstream fur brushes (91a, 91b) are 21 mm. The upstream and downstream bias rollers (92a, 92b) are made of aluminum metal rollers. In this embodiment, the diameters of the upstream and downstream bias rollers (92a, 92b) are 20 mm. The upstream and downstream blades (93a, 93b) are made of plate-shaped members formed of urethane rubber. Thus, in this embodiment, the upstream cleaning member 96a is composed of the upstream fur brush 91a, the upstream bias roller 92a, and the upstream blade 93a. The downstream cleaning member 96b is composed of the downstream fur brush 91b, the downstream bias roller 92b, and the downstream blade 93b. These upstream and downstream cleaning members (96a, 96b) are arranged in parallel along the conveying direction of the intermediate transfer belt 7.

[0039] The upstream and downstream fur brushes (91a, 91b) are positioned to slide against the intermediate transfer belt 7, maintaining an insertion depth of approximately 1.5 mm. The upstream and downstream fur brushes (91a, 91b) are rotated in the direction of arrow R3 at a speed (circumferential speed) of 150 mm / second by a drive motor (not shown). This direction of movement indicated by arrow R3 is opposite to the direction of movement of the intermediate transfer belt 7 in the first and second electrostatic cleaning sections CL1 and CL2. The upstream and downstream bias rollers (92a, 92b) are positioned to maintain an insertion depth of approximately 2.0 mm relative to the upstream and downstream fur brushes (91a, 91b). The upstream and downstream bias rollers (92a, 92b) are rotated in the direction of arrow R4 at the same speed (circumferential speed) as the upstream and downstream fur brushes (91a, 91b) by a drive motor (not shown). The direction of movement indicated by arrow R4 is the same as the direction of movement of the upstream and downstream fur brushes (91a, 91b) at the contact point with the upstream and downstream fur brushes (91a, 91b). The upstream and downstream blades (93a, 93b) are positioned to maintain a penetration amount of "1.0 mm" into the upstream and downstream bias rollers (92a, 92b). The upstream and downstream blades (93a, 93b) are in contact with the upstream and downstream bias rollers (92a, 92b) such that the free ends are on the upstream side of the rotation direction of the upstream and downstream bias rollers (92a, 92b) than the fixed ends (counter-contact).

[0040] A negative DC voltage is applied to the upstream bias roller 92a as a cleaning bias from the first cleaning power supply 94a. A positive DC voltage is applied to the downstream bias roller 92b as a cleaning bias from the second cleaning power supply 94b. The first and second cleaning power supplies (94a and 94b) apply the cleaning bias using constant current control to accommodate the potentials of the intermediate transfer belt 7 and the upstream and downstream fur brushes (91a and 91b) under various conditions. The current value of the cleaning bias is pre-stored in memory 111 (see Figure 9, described later) or the like, to be suitable for cleaning the residual toner on the intermediate transfer belt 7.

[0041] The operation for cleaning residual toner on the intermediate transfer belt 7 will now be described. By applying a negative polarity (-) cleaning bias to the upstream bias roller 92a, a potential difference is created between the intermediate transfer belt 7 and the upstream fur brush 91a. This causes the positively charged (+) toner in the residual toner on the intermediate transfer belt 7 to be attracted to and transferred to the upstream fur brush 91a. The toner attracted to and transferred to the upstream fur brush 91a is then transferred from the upstream fur brush 91a to the upstream bias roller 92a due to the potential difference between the upstream fur brush 91a and the upstream bias roller 92a. The toner transferred to the upstream bias roller 92a is then scraped off by the upstream blade 93a and collected in the recovered toner storage section formed in the housing 98.

[0042] Even after cleaning the residual toner on the intermediate transfer belt 7 with the upstream cleaning member 96a, toner without polarity and toner charged with a negative polarity (-) remain on the intermediate transfer belt 7. These toners become negatively charged (-) due to the negative polarity (-) cleaning bias applied to the upstream fur brush 91a. This is thought to be due to charge injection or discharge.

[0043] Then, by applying a positive (+) cleaning bias to the downstream bias roller 92b, a potential difference is created between the intermediate transfer belt 7 and the downstream fur brush 91b, causing the toner to be attracted to and transferred to the downstream fur brush 91b. The toner attracted to and transferred to the downstream fur brush 91b is then transferred from the downstream fur brush 91b to the downstream bias roller 92b due to the potential difference between the downstream fur brush 91b and the downstream bias roller 92b. The toner transferred to the downstream bias roller 92b is then scraped off from the downstream bias roller 92b by the downstream blade 93b. In this way, the remaining toner on the intermediate transfer belt 7 can be removed.

[0044] <About the patch> Next, the patches formed during the execution of the adjustment mode will be described. During the execution of the adjustment mode, the patches formed on the photosensitive drum 1 are detected by the drum-top patch sensor 160 before reaching the primary transfer section T1. For yellow, magenta, and cyan patches, the density is detected by the amount of diffusely reflected light component using the drum-top patch sensors 160Y, 160M, and 160C. For black patches, the density is detected by the amount of specularly reflected light component using the drum-top patch sensor 160K (see Figure 1). Based on these detection results, the exposure amount by each exposure device 3Y, 3M, 3C, and 3K is changed, thereby adjusting the density of the toner image formed on the recording material P.

[0045] Figure 7 is a graph showing the behavior of the signal value of the specular reflected light component of the drum-mounted patch sensor 160 with respect to the patch density. When optically detecting the patch density, the amount of specular reflected light decreases as the patch density increases. Therefore, in Figure 7, the vertical axis shows the difference between the amount of specular reflected light on the surface of the photosensitive drum 1 and the amount of specular reflected light at the time of patch detection as the signal value.

[0046] As shown in Figure 7, in the high density range beyond a certain density, saturation behavior is observed where the signal value does not increase linearly even when the patch density is increased. This can be attributed to the following reasons: In order to form a toner image, toner particles are stacked on the photosensitive drum 1 in accordance with the electrostatic latent image to form the image. However, when more toner is stacked to increase the density, and multiple layers or more are stacked, the amount of reflected light does not fluctuate significantly. Furthermore, even in very low density patches, the linearity of the signal value with respect to the patch density is low. This can be attributed to the following reasons: In order to form a very low density patch image, when toner corresponding to the electrostatic latent image is stacked, the toner particles are only sparsely arranged. In contrast, the drum-mounted patch sensor 160 detects the amount of reflected light within a detection range of several millimeters, and is therefore affected by the surface of the photosensitive drum 1. For the reasons described above, in this embodiment, five gradations with input signal values ​​of "20, 64, 128, 192, 255" in 8 bits are used as targets for the density of the patch image in order to broadly cover the density of the patch image.

[0047] <Patch shape> Figure 8(a) is a schematic diagram showing an example of a patch used in adjustment mode. The side of the image forming apparatus 100 corresponding to the front of the paper in Figure 1 is referred to as the front side, and the opposite side as the back side. The depth direction connecting this front side and the back side corresponds to the longitudinal direction (main scanning direction) of the photosensitive drum 1.

[0048] In adjustment mode (second mode), as shown in Figure 8(a), patches consisting of patch images for black, magenta, cyan, and yellow are used for each of the photosensitive drums 1K, 1M, 1C, and 1Y. Each color patch image consists of five patch images formed consecutively in the rotation direction of the photosensitive drum 1, each having five gradations with input signal values ​​of "32, 96, 128, 192, and 255" using 8 bits, as described above. In addition, when adjusting the image density for different screens, two types of the above five patch images may be formed consecutively for each color, resulting in a total of 10 patch images. The size of one patch image is, for example, "25 mm" in the rotation direction of the photosensitive drum 1 and "12 mm" in the main scanning direction (direction intersecting the rotation direction). The size of the patch image should be such that the drum-mounted patch sensor 160 can detect the density. For example, a patch consisting of 10 patch images may be formed, in which case the length of the patch in the rotational direction of the photosensitive drum 1 is "250 mm (25 × 10)".

[0049] The above describes the patch used in adjustment mode, but an ATR (Automatic Toner Replenishment) patch may also be formed to detect the developability of the toner in ATR control.

[0050] In this embodiment, a two-component developer mainly composed of non-magnetic toner and a magnetic carrier is used as the developer. As is well known, the T / D ratio (the ratio of toner weight to the total weight of carrier and toner) and toner charge amount of this two-component developer are important factors in stabilizing image quality. The toner in the developer is consumed during development, which decreases the T / D ratio of the developer and simultaneously increases the toner charge amount, thus lowering the image density. Therefore, ATR control is performed to maintain image quality by detecting the developer concentration or image density in a timely manner and replenishing toner from the toner bottle according to the changes, thereby controlling the T / D ratio or image density to be as constant as possible.

[0051] Figure 8(b) is a schematic diagram showing an example of an ATR patch for ATR control. There is only one patch image for the ATR patch formed in one ATR control, and the size of the patch image may be the same as in the adjustment mode described above, "25 mm × 12 mm". This ATR patch is preferably a patch pattern of midtone density, for example, a patch with an input signal value of "96" for an 8-bit density signal is used.

[0052] <Control System> Next, the control system of the image forming apparatus 100 will be explained using Figure 9. Although various other devices are connected to the CPU 110 besides those shown, their illustration and explanation are omitted here as they are not relevant to the essence of the invention.

[0053] As shown in Figure 9, the image forming apparatus 100 is equipped with a CPU (Central Processing Unit) 110 as a control unit that comprehensively controls the image forming apparatus 100, as well as memory 111 including ROM (Read Only Memory) and RAM (Random Access Memory). The RAM stores sensor detection results, calculation results, etc., and the ROM stores control programs, pre-determined data tables, etc. The CPU 110 is connected to an image forming control unit 31, a charge bias control unit 22, a primary transfer bias control unit 52, a secondary transfer bias control unit 82, a cleaning bias control unit 95, a pre-exposure control unit 142, and a post-cleaning exposure control unit 132, all of which operate under the control of the CPU 110. Although not shown in the figure, the CPU 110 receives image information from a document reader that reads images from the original document and from external devices (e.g., a personal computer) to control the above-mentioned devices. The CPU 110 is also connected to a drum patch sensor 160, a belt contact / separation mechanism 170, a secondary transfer roller contact / separation mechanism 180, a temperature and humidity sensor 190, a potential sensor 195, etc.

[0054] The image formation control unit 31 controls the exposure timing of the exposure device 3. The photosensitive drum 1 rotates at a predetermined rotational speed during image formation. Therefore, the time from when the photosensitive drum 1 is exposed by the exposure device 3 and an electrostatic latent image is formed until the toner image is first transferred to the intermediate transfer belt 7 is constant. The image formation control unit 31 controls the exposure timing of the photosensitive drum 1 by the exposure device 3 to adjust the image formation timing or patch formation timing. In this embodiment, the patch formation timing on the photosensitive drum 1 is controlled so that a patch is formed on the photosensitive drum 1 every predetermined number of sheets (for example, every 200 sheets). The image formation control unit 31 also controls the timing of the next image formation on the photosensitive drum 1 at an appropriate timing when cleaning of the patches on the photosensitive drum 1 is completed.

[0055] The charge bias control unit 22 can output a voltage from the charge power supply 21 to the charge roller 2 that is a DC voltage superimposed with an AC voltage. The develop bias control unit 42 can output a voltage from the develop power supply 41 to the develop device 4 that is a DC voltage superimposed with an AC voltage. Furthermore, the primary transfer bias control unit 52 can output a constant current controlled voltage or a constant voltage controlled voltage from the primary transfer power supply 51 to the primary transfer roller 5. In other words, the primary transfer bias control unit 52 has a current detection unit that detects the current value flowing when voltage is applied to the primary transfer roller 5, and a voltage detection unit that detects the output voltage value. By feeding the detection results back to the CPU 110, the bias applied to the primary transfer roller 5 can be controlled by constant current control or constant voltage control. The secondary transfer bias control unit 82 is similar to the primary transfer bias control unit 52.

[0056] In this embodiment, during normal image formation, the primary transfer bias applied to the primary transfer roller 5 of the image forming unit S is set to a "positive bias" with the opposite polarity to the normal charging polarity of the toner, thereby transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 7. Furthermore, during normal image formation, the secondary transfer bias applied to the secondary transfer roller 8 is set to a "secondary positive bias" with the opposite polarity to the normal charging polarity of the toner, thereby transferring the toner image from the intermediate transfer belt 7 to the recording material P. In this specification, "normal image formation" (first mode) refers to the formation of a toner image on the recording material P, not a patch image.

[0057] The cleaning bias control unit 95 can output a constant-current controlled voltage from the cleaning power supply 94 to the bias roller 92. In other words, the cleaning bias control unit 95 has a current detection unit that detects the current value flowing when voltage is applied to the bias roller 92. By feeding the detection result back to the CPU 110, the bias applied to the bias roller 92 can be controlled by a constant current.

[0058] The pre-exposure control unit 142 controls the amount of light emitted by controlling the current applied to the pre-exposure device 140. The post-cleaning exposure control unit 132 controls the amount of light emitted by controlling the current applied to the post-cleaning exposure device 130. The CPU 110 sets the charging bias and primary transfer bias to predetermined values ​​according to the absolute moisture content calculated from the temperature and humidity detected by the temperature and humidity sensor 190. The potential sensor 195 detects the surface potential (dark area potential) of the photosensitive drum 1.

[0059] Incidentally, conventionally, in adjustment mode, patches formed on the photosensitive drum 1 are not transferred to the intermediate transfer belt 7 after density detection by the drum-top patch sensor 160, but instead pass through the pre-exposure device 140 and are removed by the drum cleaning device 6. However, if the patches are pre-exposed by the pre-exposure device 140, there was a risk of toner scattering from the patches.

[0060] Here, the phenomenon of toner scattering from the patch due to pre-exposure will be explained using Figures 10(a) and 10(b). Figure 10(a) shows the state of the patch before pre-exposure, and Figure 10(b) shows the state of the patch during pre-exposure.

[0061] As shown in Figure 10(a), the toner in the patch formed on the photosensitive drum 1 is electrostatically constrained by electric field lines generated between the dark area potential Vd (-600V) and the electrostatic latent image (-200V). Before pre-exposure, the electric field lines are directed from the electrostatic latent image (-200V) to the dark area potential Vd (-600V). When the patch is pre-exposed by the pre-exposure device 140, as shown in Figure 10(b), the dark area potential Vd is discharged to "0V", and the direction of the electric field lines is reversed compared to before pre-exposure. As a result, the toner is released from electrostatic constraint, and some of the toner from the patch is scattered from the photosensitive drum 1 to the pre-exposure device 140 according to the potential difference between the pre-exposure device 140 and the photosensitive drum 1.

[0062] <Concentration adjustment process> In view of the above, in this embodiment, during the adjustment mode, the patch detected by the drum-top patch sensor 160 is transferred from the photosensitive drum 1 to the intermediate transfer belt 7. By transferring the patch to the intermediate transfer belt 7, the patch does not pass through the pre-exposure device 140, thus suppressing toner scattering from the patch caused by pre-exposure. The patch transferred to the intermediate transfer belt 7 is removed by the belt cleaning device 9, which acts as a cleaning unit. The adjustment mode of this embodiment will be described below with reference to Figures 11 to 13, with reference to Figures 1 and 9. Figure 11 is a flowchart of the density adjustment process of this embodiment. The adjustment mode is performed during non-image formation times, other than when an image is formed on the recording material P.

[0063] Here, the image forming apparatus 100 performs an "image forming job," which is a series of image output operations that are started by a start instruction and involve forming and outputting an image on one or more recording materials P. An image forming job generally includes an image forming process, a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials P, and a post-rotation process. The image forming process is the period during which the electrostatic latent image of the image to be actually formed and output on the recording material P is formed, the toner image is formed, and the toner image is transferred; this period is referred to as the image forming time. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when a start instruction is input until the image is actually formed. The paper-to-paper process is the period corresponding to the space between recording materials P when performing continuous image forming, where images are formed on multiple recording materials P in succession. The post-rotation process is the period during which tidying operations (preparatory operations) are performed after the image forming process. Non-image forming periods refer to periods other than image forming, and include the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is the preparation operation when the image forming apparatus 100 is powered on or when it returns from sleep mode. Here, to make the explanation easier to understand, we will explain using the case where adjustment mode is performed during the inter-paper process as an example.

[0064] As shown in Figure 11, the CPU 110 performs an image formation process to form an image on the recording material P (S1). The CPU 110 counts the number of recording materials P on which images have been formed and determines whether a predetermined number (e.g., 200) of recording materials P have been formed since the end of the previous density adjustment process (S2). If the predetermined number of recording materials P have not been formed (No in S2), the CPU 110 jumps to the process in step S7. On the other hand, if the predetermined number of recording materials P have been formed (Yes in S2), the CPU 110 forms a patch on the photosensitive drum 1, for example, as shown in Figure 8(a) (S3). The CPU 110 obtains the density of the patch formed on the photosensitive drum 1 and detected by the drum-top patch sensor 160 (S4).

[0065] The CPU 110 then applies a "positive bias" to the primary transfer roller 5, at least while the patch is passing through the primary transfer section T1, to transfer the patch from the photosensitive drum 1 to the intermediate transfer belt 7 (S5). The CPU 110 also performs a "patch passing process" (S6) to ensure that the patch transferred to the intermediate transfer belt 7 passes through the secondary transfer section T2 and reaches the belt cleaning device 9. As an example of the "patch passing process," the CPU 110 applies a "reverse bias" with the same polarity as the normal charging polarity of the toner to the secondary transfer roller 8, at least while the patch is passing through the secondary transfer section T2.

[0066] The CPU 110 determines whether or not to terminate image formation (S7). If image formation is terminated (Yes in S7), the CPU 110 terminates the density adjustment process. On the other hand, if image formation is not terminated (No in S7), the CPU 110 returns to the process in step S1 and resumes image formation on the recording material P, and repeats the processes in steps S1 to S7.

[0067] Next, the effects obtained in this embodiment will be briefly described with reference to comparative examples. Figures 12(a) to 12(c) show the sequences (operation order) of Embodiment 1 (Comparative Example 2), Comparative Example 1, and Embodiment 2, with time on the horizontal axis. Figure 13 shows the effects obtained in Embodiment 1 (Comparative Example 2), Comparative Example 1, and Embodiment 2, respectively. As can be seen from Figure 13, the control conditions in adjustment mode differ in Embodiment 1 (Comparative Example 2), Comparative Example 1, and Embodiment 2. In Figure 13, the control conditions during normal image formation are also shown to illustrate the difference from the control conditions in adjustment mode. The pre-exposure control conditions are indicated by the control current value from the pre-exposure control unit 142 (see Figure 9). The pre-exposure control conditions are the same in adjustment mode and during normal image formation in all cases of Embodiment 1 (Comparative Example 2), Comparative Example 1, and Embodiment 2.

[0068] As shown in Figures 13 and 12(a), in Embodiment 1, as described above, the primary transfer bias is set to "positive bias" during adjustment mode. By setting the primary transfer bias to "positive bias," the patch is transferred to the intermediate transfer belt 7 and does not undergo pre-exposure by the pre-exposure device 140, thus suppressing toner scattering from the patch caused by pre-exposure. Therefore, as shown in "Embodiment 1" of Figure 13, no contamination occurs in the pre-exposure device 140.

[0069] As shown in Figures 13 and 12(b), in Comparative Example 1, the primary transfer bias is "positive bias" during image formation and "reverse bias" during adjustment mode. In this case, the patches are not transferred to the intermediate transfer belt 7 but are pre-exposed by the pre-exposure device 140. As shown in "Comparative Example 1" in Figure 13, after image formation on "20k sheets" of recording material P, the pre-exposure device 140 becomes contaminated.

[0070] As shown in Figure 13, the control conditions in adjustment mode for Comparative Example 2 are the same as those in Embodiment 1. Therefore, as shown in Figure 12(a), the sequence for Comparative Example 2 is the same as that for Embodiment 1. As a result, the patch is transferred to the intermediate transfer belt 7, and as shown in "Comparative Example 2" in Figure 13, no contamination occurs in the pre-exposure apparatus 140. However, Comparative Example 2 is the case when a blade-type belt cleaning device is used. A blade-type belt cleaning device removes toner from the intermediate transfer belt 7 by bringing a plate-shaped cleaning blade into contact with the surface of the intermediate transfer belt 7. In the case of Comparative Example 2, the lifespan of the belt cleaning device is "600k" sheets, which is half that of Embodiment 1 (1200k sheets) when using an electrostatic belt cleaning device 9. This is because the cleaning blade comes into contact with the surface of the intermediate transfer belt 7 to remove toner, and generally has a short lifespan. As the rotation speed of the intermediate transfer belt 7 increases with normal image formation, the blade may break after about "600k" sheets.

[0071] As shown in Figures 13 and 12(c), Embodiment 2 differs from Embodiment 1 in that the patch cleaning time during adjustment mode is longer. That is, in Embodiment 2, in order to have the electrostatic belt cleaning device 9 remove patches formed with a large amount of toner, the patches are passed through the belt cleaning device 9 multiple times (in this case, twice). In this case, as shown in "Embodiment 2" of Figure 13, the patches are transferred to the intermediate transfer belt 7, so no contamination occurs in the pre-exposure device 140. And since the patches are removed in two stages by the belt cleaning device 9, the amount of toner removed per stage is limited, and cleaning defects do not occur in the belt cleaning device 9. However, because the patches are passed through the belt cleaning device 9 multiple times, the time required for adjustment mode is longer, and the productivity of the image forming apparatus 100 is reduced compared to Embodiment 1. The productivity of the image forming apparatus 100 is the number of images formed on the recording material P per unit time.

[0072] As described above, in this embodiment, during adjustment mode, the primary transfer bias is set to "positive bias," and the patch, after density detection by the drum-top patch sensor 160, is transferred from the photosensitive drum 1 to the intermediate transfer belt 7. By transferring the patch to the intermediate transfer belt 7, the patch does not pass through the pre-exposure device 140, and the patch is not pre-exposed by the pre-exposure device 140. Since the patch is not pre-exposed, toner scattering from the patch caused by pre-exposure is suppressed, and there is no risk of it adhering to or contaminating the photosensitive drum 1 or the pre-exposure device 140.

[0073] <Other Embodiments> In the "patch passing process" described above (see S6 in Figure 11), a "reverse bias" is applied to the secondary transfer roller 8 so that the patch transferred to the intermediate transfer belt 7 can pass through the secondary transfer section T2, but this is not the only option. For example, when executing the adjustment mode, the secondary transfer roller 8 may be moved from a contact position to a separated position away from the intermediate transfer belt 7 before the patch transferred to the intermediate transfer belt 7 passes through the secondary transfer section T2. ​​In this case, the time for which the secondary transfer roller 8 is kept in the separated position may be determined, for example, based on the density of the patch (a predetermined condition).

[0074] In other words, information regarding the density of the patch formed on the photosensitive drum 1 is obtained, and the retraction time of the secondary transfer roller 8 is determined based on whether or not the patch density is below a predetermined value. In this embodiment, the information regarding the patch density may be obtained from the patch density detected by the drum-top patch sensor 160, or it may be a value predicted according to the usage environment and durability.

[0075] If the patch density is below a predetermined value, the amount of toner transferred to the intermediate transfer belt 7 is small. Therefore, passing the patch through the belt cleaning device 9 once (the first number of times) is sufficient to remove the patch from the intermediate transfer belt 7. In this case, the secondary transfer roller 8 should be retracted to a separated position until the patch passes through the belt cleaning device 9 once.

[0076] Conversely, if the patch density is greater than a predetermined value, the amount of toner transferred to the intermediate transfer belt 7 will be greater. In this case, even if the patch is passed through the belt cleaning device 9 once, there is a risk that the patch may not be sufficiently removed from the intermediate transfer belt 7. Therefore, if the patch density is greater than a predetermined value, the patch is passed through the belt cleaning device 9 twice (a second time). This ensures that the patch is sufficiently removed from the intermediate transfer belt 7. Thus, when the amount of toner in the patch is large, the secondary transfer roller 8 is retracted to a separated position until the patch has passed through the belt cleaning device 9 twice. In other words, when the amount of toner in the patch is large, the retraction time of the secondary transfer roller 8 is longer than when the amount of toner is small.

[0077] In the embodiments described above, an example was given in which the adjustment mode described above is applied in full-color mode. However, the adjustment mode described above may also be applied in black monochrome mode to suppress toner scattering from patches caused by pre-exposure. Furthermore, although a full-color printer equipped with multiple image forming units SY~SK was described as an example, the printer is not limited to this, and the adjustment mode described above may also be applied to a monochrome printer equipped with, for example, only a black monochrome image forming unit SK. [Explanation of symbols]

[0078] 1…Image carrier (photosensitive drum), 2…Charging unit (charging roller), 3…Exposure unit (exposure device), 4…Developing unit (developing device), 5…Transfer member (primary transfer roller), 7…Intermediate transfer body (intermediate transfer belt), 8…Secondary transfer member (secondary transfer roller), 9…Cleaning unit (belt cleaning device), 100…Image forming apparatus, 110…Control unit (CPU), 130…Post-static elimination unit (post-cleaning exposure device), 140…Static elimination unit (pre-exposure device), 160Y (160M, 160C, 160K)…Detection unit (patch sensor on drum), 180…Movement unit (secondary transfer roller contact / separation mechanism), T1…Primary transfer unit, T2…Secondary transfer unit

Claims

1. An image forming apparatus for forming an image on a recording material, A rotating image carrier, The charging part that charges the image carrier, An exposure unit that exposes the charged image carrier to form an electrostatic latent image, A developing unit that develops the electrostatic latent image formed on the image carrier into a toner image, An intermediate transfer body transfers a toner image from the image carrier and the transferred toner image to a recording material, A primary transfer section is formed to transfer the toner image formed on the image carrier to the intermediate transfer body, and a transfer member is provided that can transfer the toner image by applying a transfer voltage. A detection unit for detecting the density of the adjustment toner image formed on the image carrier, located downstream of the developing unit and upstream of the primary transfer unit, with respect to the rotation direction of the image carrier, A static elimination unit is provided downstream of the primary transfer unit in the rotational direction and upstream of the charging unit in the rotational direction, which removes static electricity from the surface of the image carrier by irradiating it with light. With respect to the rotation direction of the intermediate transfer body, upstream of the primary transfer unit and downstream of the secondary transfer unit that transfers the toner image from the intermediate transfer body to the recording material, there is a cleaning unit that removes toner from the intermediate transfer body, The system includes a control unit capable of performing a first mode in which a toner image formed on the image carrier is transferred to an intermediate transfer body and then transferred from the intermediate transfer body to a recording material, and a second mode in which an adjustment toner image is formed on the image carrier and the adjustment toner image is detected by the detection unit. During execution of the second mode, the control unit applies a transfer voltage to the transfer member that is opposite to the normal charging polarity of the toner, at least while the adjustment toner image is passing through the primary transfer unit, transfers the adjustment toner image to the intermediate transfer body, and rotates the intermediate transfer body so that the transferred adjustment toner image passes through the cleaning unit. An image forming apparatus characterized by the following features.

2. The secondary transfer section is formed for transferring the toner image on the intermediate transfer body to a recording material, and a secondary transfer member is provided that can transfer the toner image by applying a secondary transfer voltage. During execution of the second mode, the control unit applies a transfer voltage to the secondary transfer member that has the same polarity as the normal charging polarity of the toner, at least while the adjustment toner image is passing through the secondary transfer unit. The image forming apparatus according to feature 1.

3. A secondary transfer member is formed which transfers the toner image on the intermediate transfer body to a recording material, and which is capable of transferring the toner image by applying a secondary transfer voltage. The system includes a movable part that allows the secondary transfer member to move between a contact position in contact with the intermediate transfer body on which the secondary transfer portion is formed and a separated position separated from the intermediate transfer body, During execution of the second mode, the control unit moves the secondary transfer member from the contact position to the separated position, at least while the adjustment toner image is passing through the secondary transfer unit. The image forming apparatus according to feature 1.

4. The control unit, when executing the second mode, If the predetermined conditions are met, the secondary transfer member is moved to the separated position from the time the adjustment toner image is transferred to the intermediate transfer body until the transferred adjustment toner image passes through the cleaning section for a first number of times. If the predetermined conditions are not met, the secondary transfer member is moved to the separated position from the time the adjustment toner image is transferred to the intermediate transfer body until the transferred adjustment toner image passes through the cleaning section a second time, which is more than the first time. The image forming apparatus according to feature 3.

5. The control unit acquires information regarding the density of the adjustment toner image formed on the image carrier, If the above predetermined conditions are met, the density of the acquired adjustment toner image is less than or equal to a predetermined value. The image forming apparatus according to feature 4.

Images