JP2024028062A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain good pre-electrification performance for a long period to maintain good cleaning performance even if impurities gradually accumulate on a pre-electrifying member, while simplifying an apparatus configuration and reducing cost.

SOLUTION: An image forming apparatus 100 has: image carriers 1; an intermediate transfer belt 7; a rotary brush 22 that recovers toner on the intermediate transfer belt 7; a first power supply 28 that applies voltage to the rotary brush 22; a stationary brush 21 that electrifies the toner on the intermediate transfer belt 7 on the upstream side of a contact part of the rotary brush 22 and the intermediate transfer belt 7; a second power supply 27 that applies voltage to the stationary brush 21; and a control unit 15 that controls the first power supply 28 and the second power supply 27. During image formation, the control unit 15 performs control to apply, to the rotary brush 22, a DC voltage having a polarity opposite to the normal electrification polarity of the toner, and apply, to the stationary brush 21, a DC voltage having the same polarity as the normal electrification polarity of the toner in constant current control.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine using an electrophotographic method or an electrostatic recording method, or a multifunction device having a plurality of these functions.

In an image forming apparatus using electrophotography or the like, a toner image formed on an image bearing member such as a photoreceptor or an intermediate transfer member is transferred onto a recording material. After the toner image is transferred, toner and other deposits remaining on the image carrier are cleaned by a cleaning device.

As a cleaning device for cleaning an image carrier, there is an electrostatic cleaning device that uses a brush member such as a rotating brush (brush roller). Such an electrostatic cleaning device is particularly effective for cleaning an intermediate transfer body (intermediate transfer belt) made up of an elastic belt having an elastic layer.

Patent Document 1 discloses a cleaning device that includes a collection member made of a brush member and a pre-charging member made of a brush member disposed upstream of the collection member in the moving direction of the intermediate transfer body. There is. In this cleaning device, the collection member forms an electric field with a polarity opposite to the normal charging polarity of the toner on the intermediate transfer member, and the pre-charging member forms an electric field with the same polarity as the normal charging polarity of the toner on the intermediate transfer member. An electric field is formed. Then, the pre-charging member pre-charges the toner on the intermediate transfer body to a normal charging polarity, and the collecting member collects the pre-charged toner.

In this type of cleaning device, when cleaning the toner on the intermediate transfer body, the toner on the intermediate transfer body is aligned with normal charge polarity by charge injection from a pre-charging member (pre-charging). The toner pre-charged by the pre-charging member (pre-charged toner) is repelled by the polarity of the pre-charging member, so it moves onto the intermediate transfer body and is conveyed to the collection member without accumulating on the pre-charging member. . Then, this pre-charged toner is collected by the collection member by a cleaning electric field having a polarity opposite to the normal charging polarity of the toner, which is formed by the collection member.

Brush members used in the cleaning device include a rotatable rotating brush (brush roller) and a fixed brush (deck brush-like member) that is fixedly arranged. The rotating brush has a high ability to scatter and scrape off toner on the intermediate transfer member. However, since the rotating brush requires a mechanism for rotating the rotating brush, a mechanism for scraping toner from the rotating brush, etc., it is disadvantageous for simplifying the device configuration and reducing costs. On the other hand, fixed brushes are advantageous in simplifying the device configuration and reducing costs compared to rotating brushes. Therefore, it is preferable to use a fixed brush as the pre-charging member, which is advantageous for simplifying the structure and reducing costs, and to use a rotating brush, which has a high cleaning ability, as the collecting member.

Japanese Patent Application Publication No. 2006-208761

However, when a fixed brush, which is advantageous for simplifying the structure and reducing costs, is used as the pre-charging member, the following problems arise. In other words, when the pre-charging member is a fixed brush, toner present on the intermediate transfer body that is difficult to be charged normally (toner charged to the opposite polarity to the normal charging polarity), external additives for toner (toner fluidizing agent, etc.) ), recording material powder (paper dust, etc. if it is paper), recording material filler (talc, etc. if it is paper), etc., other than the regular charged toner, gradually collect and accumulate on the pre-charging member. easy to be Therefore, in image formation over a long period of time, the pre-charging performance of the pre-charging member gradually deteriorates, and it may become difficult to charge the toner on the intermediate transfer member to the normal charging polarity. Then, the toner collection performance of the collection member decreases, and as a result, the amount of uncollected toner on the intermediate transfer body increases, resulting in poor cleaning in which the toner slips through the cleaning device, that is, a defective image occurs. Sometimes.

Patent Document 1 proposes executing a pre-charging member cleaning mode during non-image formation. In this pre-charging member cleaning mode, the following operations are performed. In other words, during normal image formation, the collection member has the same polarity as the normal charging polarity of the toner on the intermediate transfer member, and the pre-charging member has the opposite polarity to the normal charging polarity of the toner on the intermediate transfer member. The cleaning electric field is the formation of an opposite electric field. Alternatively, the application of an alternating electric field to the pre-charging member. In this pre-charging member cleaning mode, at least one of forming a reverse electric field and applying an alternating electric field is performed.

However, although the pre-charging member is cleaned in the pre-charging cleaning mode during non-image formation, it is difficult to remove all impurities from the pre-charging member. Therefore, the impurities remaining in the pre-charging member gradually deteriorate the pre-charging performance of the pre-charging member.

Therefore, an object of the present invention is to maintain good pre-charging performance over a long period of time even when impurities gradually accumulate in the pre-charging member, and to achieve good cleaning performance while simplifying the device configuration and reducing costs. It is to maintain.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, and a circular movement that transports the toner image transferred from the image carrier in a primary transfer section to a recording material in a secondary transfer section. an intermediate transfer belt that rotates in contact with the surface of the intermediate transfer belt downstream of the secondary transfer section and upstream of the primary transfer section in the moving direction of the surface of the intermediate transfer belt; a rotating brush that collects toner on the intermediate transfer belt; a first power source that applies voltage to the rotating brush; and a contact portion between the rotating brush and the intermediate transfer belt in the direction of movement of the surface of the intermediate transfer belt. a fixed brush that is fixedly arranged in contact with the surface of the intermediate transfer belt at an upstream side of the secondary transfer section and a downstream side of the secondary transfer section, and that charges the toner on the intermediate transfer belt; and a voltage is applied to the fixed brush. a second power source for controlling the first power source and a control section for controlling the first power source and the second power source; , a DC voltage with a polarity opposite to the normal charging polarity of the toner is applied to the rotating brush, and the normal charging polarity of the toner is determined by constant current control so that the current supplied to the fixed brush becomes a target current value. The image forming apparatus is characterized in that the image forming apparatus is controlled to apply a DC voltage of the same polarity to the fixed brush.

According to the present invention, it is possible to maintain good pre-charging performance over a long period of time and maintain good cleaning performance even when impurities gradually accumulate in the pre-charging member, while simplifying the device configuration and reducing costs. be able to.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 1 is a block diagram schematically showing the electrical configuration of an image forming apparatus. FIG. 1 is a schematic diagram for explaining the basic configuration of a belt cleaning device. FIG. 1 is a schematic diagram for explaining the configuration of a belt cleaning device according to an embodiment. 3 is a graph diagram showing the relationship between constant current value and voltage value of the pre-charging brush of Example 1. FIG. 7 is a graph diagram showing the relationship between constant current value and voltage value of the pre-charging brush of Example 2. FIG. FIG. 7 is a graph diagram showing the relationship between absolute humidity and voltage value of a pre-charging brush of a comparative example. 7 is a graph diagram showing the relationship between absolute humidity and voltage value of the pre-charging brush of Example 3. FIG. FIG. 7 is a graph diagram showing the relationship between absolute humidity and voltage value of the pre-charging brush of Example 4.

Hereinafter, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

[Example 1]
1. Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem-type full-color multifunction device. However, the present invention is not limited to tandem-type image forming apparatuses, but can also be applied to image forming apparatuses of other types.

As shown in FIG. 1, the image forming apparatus 100 includes an apparatus main body 96 including an image forming section, a discharge section 97, a control section 15, an image reading section 98, and an operation section 99 as a UI (user interface). It is equipped with.

The image forming apparatus 100 can form a four-color full-color image on the recording material P in response to an image signal from the image reading section 98 or a host device such as a personal computer or an external device such as a digital camera or smartphone. can. The recording material (recording medium, transfer material, sheet, paper) P is one on which a toner image is formed, and specific examples include plain paper, cardboard, colored paper, recycled paper, and synthetic paper that is a substitute for plain paper. There is a wide variety of recording materials with metal layers, such as resin sheets, transparent resin sheets for overhead projectors, envelopes, postcards, coated paper, embossed paper, waterproof paper (resin sheets, resin-coated paper), vapor-deposited paper, etc. . Here, the recording material P is sometimes referred to as "paper" or "paper," but it is a recording material made of a material other than paper, or a recording material made of a material containing a material other than paper. This includes:

The image forming apparatus 100 of this embodiment is capable of full-color image formation, and has separate sections for each of four colors: a yellow image forming section 50Y, a magenta image forming section 50M, a cyan image forming section 50C, and a black image forming section 50K. An image forming member having a similar configuration is provided. In addition, regarding elements that have the same or corresponding functions or configurations provided for each color, the suffix Y, M, C, or K of the code indicating that the element is for one of the colors will be omitted to refer to them generically. I have something to explain. Note that the image forming apparatus 100 can produce, for example, a black monochrome image, a monochrome image using one of the four colors, a monochrome image using some of the four colors, or a multicolor image. It is also possible to form

The image forming sections 50Y, 50M, 50C, and 50K for each color include a photosensitive drum 1, a charging roller 2, a developing device 4, and a photosensitive member cleaning device 6. The photosensitive drum 1 is a drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as a rotatable first image carrier that carries an electrostatic latent image or a toner image. The image forming sections 50Y, 50M, 50C, and 50K may have, for example, a structure in which each part is made into a unit for each color and can be attached to and detached from the apparatus main body 96 as a cartridge. By replacing the cartridge with a new one depending on the lifespan of each part, it is possible to form a four-color toner image on the intermediate transfer belt 7 as if it were new.

The photosensitive drum 1 is rotatable and carries an electrostatic latent image or a toner image. In this embodiment, the photosensitive drum 1 is a negatively charged organic photoconductor (OPC) with an outer diameter of 30 [mm], and is rotated in the direction of the arrow (clockwise) at a predetermined process speed (peripheral speed) (not shown). Rotationally driven by a drive motor. The photosensitive drum 1 has an aluminum cylinder as a base, and has three layers on its surface, which are coated and laminated in order: an undercoat layer, a photocharge generation layer, and a charge transport layer.

The charging roller 2, which is a roller-type charging member serving as a charging means, is a conductive rubber roller that comes into contact with the surface of the photosensitive drum 1 and rotates as a result of rotation, and uniformly charges the surface of the photosensitive drum 1. Depending on the voltage applied to the charging roller 2, it is classified into an AC charging method using AC voltage + DC voltage (a voltage obtained by superimposing an AC voltage on a DC voltage), and a DC charging method using only a DC voltage (DC voltage). In the example, an AC charging method with less uneven charging was adopted.

An exposure device 3 serving as an exposure means applies a photosensitive drum for each color onto the photosensitive drums 1Y, 1M, 1C, and 1K that have been uniformly (uniformly) charged, according to image information of the separated colors output from the control section 15. It emits laser beams 3Y, 3M, 3C, and 3K. Thereby, the exposure device 3 forms electrostatic latent images (electrostatic images) on the photosensitive drums 1Y, 1M, 1C, and 1K of each color.

A developing device 4 serving as a developing means accommodates toner, which in this embodiment has a negatively charged polarity, supplied from a replenishment toner bottle 14 and develops an electrostatic latent image on the photosensitive drum 1 . In this embodiment, the developing device 4 employs a two-component developing method using a two-component developer (developer) comprising a non-magnetic toner (toner) and a magnetic carrier (carrier). A developer is supplied to a development area facing the. A developing bias (a voltage obtained by superimposing an alternating current voltage on a direct current voltage) is applied to the developing sleeve carrying the developer of the developing device 4, and the electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) with toner. be done. In this embodiment, the exposed area (image area) on the photosensitive drum 1 whose absolute value of charge has decreased by being exposed according to image information after being uniformly charged is charged with the same polarity as the charging polarity of the photosensitive drum 1. Toner charged with polarity (negative polarity in this embodiment) is attached (reversal development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

The toner image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 7 by a primary transfer roller 5, which is a roller-type primary transfer member serving as a primary transfer means. The photosensitive drum 1 after the primary transfer is cleaned by a photosensitive member cleaning device 6 serving as a photosensitive member cleaning means. The photoconductor cleaning device 6 removes transfer residual toner remaining on the photoconductor drum 1 without being transferred to the intermediate transfer belt 7, for example, with a photoconductor cleaning blade that contacts the photoconductor drum 1 with a predetermined pressing force. Remove. Thereafter, the surface of the photosensitive drum 1 is neutralized by a pre-exposure device (not shown) in preparation for the next image forming process.

The intermediate transfer belt 7, which is a rotatable intermediate transfer body composed of an endless belt and serves as a second image carrier carrying a toner image, is connected to a driving roller 8 and a driven roller 9 as a plurality of tension rollers. It is wrapped and strung up. The intermediate transfer belt 7 includes primary transfer rollers 5Y, 5M, 5C, and 5K. Further, a belt cleaning device 20 is provided on the outer peripheral surface side of the intermediate transfer belt 7. In this embodiment, these are integrated as an intermediate transfer belt unit that can be detached from the apparatus main body 96 and replaced, and in the event of component lifespan or failure, this intermediate transfer belt unit can be replaced with a new one. The driven roller 9 is a tension roller that controls the tension of the intermediate transfer belt 7 to be constant. A force is applied to the driven roller 9 to push the intermediate transfer belt 7 from the inner circumferential surface (back side) side to the outer circumferential surface (front side) side by the biasing force of a biasing spring (not shown), and this force causes the intermediate transfer belt 7 to A tension of about 20 to 50 [N] is applied to the belt 7 in the conveying direction. Further, in this embodiment, the intermediate transfer belt 7 is supported by two axes, but it may be supported by, for example, three axes, and one of the axes controls the deviation of the intermediate transfer belt 7.

The primary transfer rollers 5Y, 5M, 5C, and 5K are arranged facing the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The primary transfer roller 5 is pressed toward the photosensitive drum 1 with the intermediate transfer belt 7 interposed therebetween. As a result, a primary transfer portion (primary transfer nip) N1 where each photosensitive drum 1 and intermediate transfer belt 7 come into contact is formed. The primary transfer roller 5 transfers the toner image formed on the photosensitive drum 1 by applying a primary transfer voltage (primary transfer bias), which is a DC voltage with a polarity opposite to the normal charging polarity of the toner. , primary transfer is performed onto the intermediate transfer belt 7. The primary transfer voltages applied to the primary transfer rollers 5Y, 5M, 5C, and 5K can be individually controlled by the control unit 15. In this embodiment, the primary transfer roller 5 has an outer diameter of 15 to 20 [mm], for example, and includes an elastic layer of ion conductive foam rubber (NBR rubber) and a core metal. Further, in this embodiment, the primary transfer roller 5 has a resistance value of, for example, 1×10 ⁵ to 1×10 ⁷ [Ω] (measurement conditions: 23° C., 50% RH environment, φ30 mm aluminum drum, nip width of approx. A roller of 7 mm and 2 KV applied is used.

The intermediate transfer belt 7 of this embodiment is an endless belt with an elastic layer, which has a three-layer structure from the back side (inner peripheral side) to the front side (outer peripheral side): a base layer, an elastic layer, and a surface layer. be. The resin material constituting the base layer is made of resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent, and the thickness of the base layer is 0.05 to 0. .15 [mm]. The elastic material constituting the elastic layer is made of various rubbers such as urethane rubber and silicone rubber containing an appropriate amount of ion conductive material, and the thickness of the elastic layer is 0.1 to 0.5[ mm]. The surface layer is made of a resin such as fluororesin, and is a coating material that reduces the adhesion of the toner to the surface of the intermediate transfer belt 7 and makes it easier to transfer the toner onto the recording material P at the secondary transfer portion N2. The thickness is 0.002 to 0.03 [mm]. In this example, the base layer is made of polyimide resin (thickness: 70 [μm]) in which a conductive material is dispersed, the elastic layer is made of conductive CR rubber (chloroprene rubber) (thickness: 300 [μm]), and the surface layer is made of PTFE (thickness: 5 μm). An intermediate transfer belt 7 having a total thickness of 375 [μm] was used. The intermediate transfer belt 7 of this embodiment has a volume resistivity of 1×10 ⁷ to 1×10 ⁹ [Ω·cm] (measurement conditions: 23° C., 50% RH environment, resistivity meter, 100 V applied), and a surface The hardness is 65° (measurement conditions: 23° C., 50% RH environmental measurement, Wallace hardness meter).

A secondary transfer roller 10, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed opposite to a drive roller 8 with an intermediate transfer belt 7 interposed therebetween. The secondary transfer roller 10 is pressed toward the drive roller 8 with the intermediate transfer belt 7 sandwiched therebetween. As a result, a secondary transfer portion (secondary transfer nip) N2 is formed where the intermediate transfer belt 7 and the secondary transfer roller 10 are in contact with each other. A secondary transfer voltage (secondary transfer bias), which is a DC voltage with a polarity opposite to the normal charging polarity of the toner, is applied to the secondary transfer roller 10 . As a result, the secondary transfer roller 10 transfers the four-color superimposed toner image that has been primarily transferred onto the intermediate transfer belt 7, for example, to the nip portion (secondary transfer portion) between the drive roller 8 and the secondary transfer roller 10. Secondary transfer is performed all at once onto the recording material P supplied to N2. Drive roller 8 is connected to ground potential. In this embodiment, for example, by applying a secondary transfer voltage of +2 to +5 [KV] to the secondary transfer roller 10, a current of about +50 [μA] is applied to record the toner image on the intermediate transfer belt 7. Secondary transfer is performed onto material P.

Further, the primary transfer voltage or the primary transfer current is an arbitrary value determined according to the following conditions. For example, the material of the photosensitive drum 1, the charge amount of the toner, the image forming speed, that is, the rotational speed of the photosensitive drum 1 and the intermediate transfer belt 7, the resistance value of the primary transfer roller 5, the resistance value of the intermediate transfer belt 7, the environment ( temperature, humidity), etc. Furthermore, the secondary transfer voltage or secondary transfer current is an arbitrary value determined according to the following conditions. For example, the material, surface roughness and resistance value of the recording material P, the resistance value of the secondary transfer roller 10, the environment (temperature, humidity), etc. However, the resistance value is generally in the relationship "intermediate transfer belt<paper", and the resistance value is higher for paper than for intermediate transfer belt 7. Therefore, the transfer voltage usually has a relationship of "|Primary transfer voltage|<|Secondary transfer voltage|", and compared to the primary transfer voltage, the secondary transfer voltage is higher by the resistance value of the paper. , requiring high voltage.

The secondary transfer roller 10 has an outer diameter of 20 to 25 [mm], for example, and includes an elastic layer of ion conductive foam rubber (NBR rubber) and a core metal. The secondary transfer roller 10 has a resistance value of 1×10 ⁵ to 1×10 ⁷ [Ω], which is almost the same as that of the primary transfer roller 5 (measurement conditions: 23°C, 50% RH environment, Φ30mm aluminum drum, nip width of approx. A roller of 7 mm and 2 KV applied is used.

Furthermore, a belt cleaning device 20 is provided on the outer peripheral surface side of the intermediate transfer belt 7 as intermediate transfer body cleaning means. The belt cleaning device 20 removes adhered substances such as toner and paper dust remaining on the intermediate transfer belt 7 after the secondary transfer process. Details of the belt cleaning device 20 will be described later.

The recording material P is taken out from the cassette 12 by the paper feed roller 11, and is transported to the secondary transfer portion N2 at a predetermined timing by a transport means (not shown) according to the arrow in the figure. The recording material P carrying the secondarily transferred toner image is conveyed to the fixing device 13.

The fixing device 13 as a fixing means includes a fixing roller 13a and a pressure roller 13b that presses against the fixing roller 13a. The recording material P is conveyed while being sandwiched between the heated fixing roller 13a and the pressure roller 13b. As a result, the toner image secondarily transferred onto the recording material P is heated and pressurized, melts, and is fixed onto the recording material P. The recording material P on which the toner image has been fixed is conveyed (ejected) to the discharge section 97, and image formation on the recording material P is completed.

Here, FIG. 2 is a schematic block diagram showing the electrical configuration (control mode) of the image forming apparatus 100 shown in FIG. 1. As shown in FIG.

The image forming apparatus 100 includes a control section 15 that controls the operation of the entire apparatus. The control unit 15 includes, for example, a CPU that executes predetermined arithmetic processing, a ROM that stores a predetermined control program, a RAM that temporarily stores data, and their peripheral circuits (input/output circuits, etc.). It is configured with the following. The control section 15 functions as an image forming control section 150, an image forming speed control section 151, and a cleaning control section 152, for example, by executing a control program stored in a ROM.

Further, the control unit 15 is connected to, for example, an operation unit 99, an environment sensor 155, a communication I/F 156, an image reading unit 98, a fixing device 13, and image forming units 50Y, 50M, 50C, and 50K. Further, the control unit 15 is connected to a drive motor 153, a paper transport mechanism 153, a constant current control device 30, a limit voltage control device 31, and the like.

The drive motor 153 is controlled by the image forming control unit 150, and, for example, drives and rotates the drive roller 8 to move (rotate) the intermediate transfer belt 7 in the above-mentioned circumferential direction. Further, the drive motor 153 is controlled by the image forming control section 150, and fixes the toner image on the recording material P by driving and rotating the fixing roller 13a of the fixing device 13, for example. Further, for example, if a failure or abnormality occurs in the fixing device 13 or the like, the image forming control unit 150 stops driving the entire image forming apparatus and notifies the operation unit 99 of the occurrence of the failure or abnormality. Display information. In this way, each device connected to the control unit 15 communicates with the control unit 15 bidirectionally and is controlled.

Here, the image forming apparatus 100 executes a print job (print operation), which is a series of operations for forming and outputting an image on a single or multiple recording materials P, which is started by one start instruction. A print job generally includes an image forming process, a pre-rotation process, a paper spacing process when images are formed on a plurality of recording materials P, and a post-rotation process. The image forming process is a period in which an electrostatic latent image of an image to be actually formed and output on the recording material P is formed, a toner image is formed, a primary transfer of the toner image, and a secondary transfer of the toner image are performed. Formation refers to this period. More specifically, the timing at the time of image formation differs depending on the position where each process of forming the electrostatic latent image, forming the toner image, primary transfer of the toner image, and secondary transfer of the toner image is performed. This corresponds to the period during which the image forming area on the intermediate transfer belt 7 passes through each of the above positions. Furthermore, the timing during image formation corresponds to a period during which the image forming area on the intermediate transfer belt 7 passes through a contact position with a pre-charging brush 21 and a rotating brush 22 of a belt cleaning device 20, which will be described later. The pre-rotation process is a period from when a start instruction is input until actually starting to form an image, during which preparatory operations are performed before the image forming process. The inter-paper process (inter-image process, inter-recording material process) is the correspondence between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation, continuous printing). This is the period during which The post-rotation process is a period in which organizing operations (preparatory operations) are performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the pre-rotation process, inter-sheet process, post-rotation process, and preparatory operations when the image forming apparatus 100 is turned on or returned from a sleep state. This includes a pre-multi-rotation process. More specifically, the timing during non-image formation is such that the non-image forming area on the photosensitive drum 1 or the intermediate transfer belt 7 is formed during the formation of the electrostatic latent image, the formation of a toner image, the primary transfer of a toner image, This corresponds to the period during which the toner image passes through each position where each step of secondary transfer is performed. Furthermore, the timing during non-image formation corresponds to a period during which the non-image forming area on the intermediate transfer belt 7 passes through a contact position with a pre-charging brush 21 and a rotating brush 22 of a belt cleaning device 20, which will be described later. . Note that the image forming area on the photosensitive drum 1 or on the intermediate transfer belt 7 refers to a toner image that is transferred to the recording material P and output from the image forming apparatus 100, which is set in advance according to the size of the recording material P, etc. The non-image forming area is an area other than the image forming area.

2. Outline of Belt Cleaning Device In each image forming unit 50 , primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer is cleaned by the photoconductor cleaning device 6 . Furthermore, the secondary transfer residual toner remaining on the intermediate transfer belt 7 after the secondary transfer is cleaned by the belt cleaning device 20 . Here, the belt cleaning device 20 is controlled by the cleaning control section 152 of the control section 15 in FIG.

Most of the toner remaining or attached to the photosensitive drum 1 after the primary transfer is primary transfer residual toner. On the other hand, since the intermediate transfer belt 7 comes into contact with the recording material P during the secondary transfer, what remains or adheres to the intermediate transfer belt 7 after the secondary transfer is not only the secondary transfer residual toner but also the recording material P. There are also paper powder and fillers derived from paper. Furthermore, if the developing device 4 in the image forming section 50 uses a two-component developer, carriers (magnetic particles) contained in the two-component developer may adhere to the intermediate transfer belt 7 .

The intermediate transfer belt 7 may have a one-layer structure with only a base layer, or a two-layer structure with a base layer and a surface layer, but in this embodiment, as described above, an elastic three-layer structure consisting of a base layer, an elastic layer, and a surface layer from the back side is used. It is an endless belt with layers. The intermediate transfer belt 7 having an elastic layer can follow the uneven portions of the paper even when uneven paper such as embossed paper is used as the recording material P. Therefore, the intermediate transfer belt 7 and the paper can come into contact with each other without any gaps, so that it is possible to obtain a good image with suppressed secondary transfer unevenness.

The single-layer intermediate transfer belt without an elastic layer has low releasability with toner, so secondary transfer unevenness occurs even on plain paper with a slightly rough surface, resulting in minute image density problems. Unevenness may occur. Furthermore, in the intermediate transfer belt having a two-layer structure without an elastic layer, the surface layer is coated with a fluororesin or the like having good releasability from toner. Therefore, even on plain paper with a slightly rough surface, secondary transfer unevenness is suppressed, and a good image with suppressed minute image density unevenness can be obtained. However, since there is no elastic layer, it is difficult for the surface of the intermediate transfer belt to follow the uneven portions of paper such as embossed paper with large unevenness. As a result, gaps occur between the intermediate transfer belt and the paper at the edges of concave and convex areas, reducing the transferability of toner to the paper, causing the density to become thinner in those areas, and causing density unevenness. There are cases where

On the other hand, when using an intermediate transfer belt having an elastic layer, it is difficult to use a cleaning blade in a belt cleaning device. That is, when a cleaning blade is used as a cleaning device for an elastic belt having an elastic layer, the cleaning blade may bite into the elastic layer of the elastic belt, causing the cleaning blade to be rolled up. Alternatively, since the angle formed between the cleaning blade and the elastic belt is not stable, toner may slip through. Furthermore, if there are cracks in the releasable coating on the surface of the elastic belt, toner may enter the cracks and slip through. For this reason, it is difficult to stably clean toner and the like on the intermediate transfer belt made of an elastic belt with a cleaning blade. Therefore, as a cleaning device for an intermediate transfer belt constituted by an elastic belt having an elastic layer, it is effective to use electrostatic cleaning using a brush member such as a rotating brush (brush roller) as a toner collecting member.

As shown in FIG. 1, the belt cleaning device 20 cleans the intermediate transfer belt 7 from the secondary transfer section N2 to the primary transfer section N1Y of the most upstream image forming section 50Y in the moving direction of the surface of the intermediate transfer belt 7. Just set it up. In this embodiment, the belt cleaning device 20 is provided facing the driven roller 9 around which the intermediate transfer belt 7 is wound.

First, the basic configuration of the belt cleaning device 20 will be explained. FIG. 3 is a schematic cross-sectional view showing the basic configuration of the belt cleaning device 20 (a cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1 and the tension roller of the intermediate transfer belt 7). The characteristic configuration of this embodiment will be described in detail later.

The belt cleaning device 20 includes a rotating brush (brush roller) 22 as a collection member that collects secondary transfer residual toner and the like on the intermediate transfer belt 7 . The belt cleaning device 20 also includes a collection roller 23 that collects toner and the like attached to the rotating brush 22. The belt cleaning device 20 also includes a cleaning blade 24 that mechanically scrapes off toner and the like on the collection roller 23. Further, the belt cleaning device 20 includes a conveyance screw 25 that carries out toner and the like scraped off by the cleaning blade 24. The belt cleaning device 20 also includes a seal member 26 disposed close to the collection roller 23. The sealing member 26 is used to prevent toner from flying up in the form of powder smoke and re-adhering to the intermediate transfer belt 7 on the airflow generated by the rotation of the rotating brush 22 when the cleaning blade 24 scrapes off the toner. belongs to. The belt cleaning device 20 further includes a pre-charging brush 21 which is a fixed brush (deck brush-like member) as a pre-charging member and is located upstream of the rotating brush 22 in the direction of movement of the surface of the intermediate transfer belt 7 . have.

The pre-charging member may be any member as long as it can contact the toner or the like on the intermediate transfer belt 7 and inject an electric charge, and it is also possible to use a conductive resin sheet or metal sheet. However, in this embodiment, a pre-charging brush 21 in which a conductive brush is held by a conductive holding member is used as a brush that can contact the toner and the like on the intermediate transfer belt 7 as uniformly as possible or under low pressure. The pre-charging brush 21 is fixedly placed in contact with the intermediate transfer belt 7 with light pressure.

Each rotating member in the belt cleaning device 20 is rotationally driven by a drive motor (not shown) as a drive source that constitutes the belt cleaning device 20 under instructions from the cleaning control section 152 of the control section 15. The rotating brush 22 is driven to rotate in a counter direction so that the brush fibers move against the direction of movement of the surface of the intermediate transfer belt 7 so that the toner and the like on the intermediate transfer belt 7 can be sufficiently scraped and collected. . The direction of movement of the surface of the intermediate transfer belt 7 is the direction of the arrow of the driven roller 9 in FIG. 3 (counterclockwise direction). Further, the rotating direction of the rotating brush 22 is the direction of the arrow of the rotating brush 22 in FIG. 3 (counterclockwise direction). The collection roller 23 is rotationally driven in the forward direction of the rotating brush 22 (in the direction of the arrow (clockwise direction) of the collection roller 23 in FIG. 3).

In this embodiment, the rotating brush 22, the collecting roller 23, and the pre-charging brush 21 are all electrically conductive. The rotation axis direction (longitudinal direction) of the rotating brush 22 and the collection roller 23 and the longitudinal direction of the pre-charging brush 21 are the rotation axis direction of the tension roller of the intermediate transfer belt 7 (approximately the direction of movement of the surface of the intermediate transfer belt 7). It is substantially parallel to the perpendicular width direction).

The rotating brush 22 is configured as follows, for example. In other words, conductive brush fibers (original threads) are woven into a base fabric that is entirely conductive, or a conductive base fabric whose back surface is coated with a conductive agent, and the base fabric woven with the conductive brush fibers is then woven into a core. Wrap it around. Then, the base fabric and the core metal are bonded together so that they are electrically conductive (for example, bonded using a conductive adhesive). The core metal may be formed of a bar, pipe, or the like made of conductive metal.

Examples of the material of the conductive brush fibers include polyamide (such as nylon) in which conductive carbon is dispersed, polyester, acrylic, and rayon.

Regarding the thickness and resistance of the brush fibers, the thickness is 1 to 10 [decitex] in terms of yarn diameter, and the resistance is 1 x 10 ³ to 1 x 10 ¹⁵ [Ω/cm] in terms of yarn resistance. ] I can give an example of the degree. An example of the brush fiber density in the base fabric is 50 to 300 [kF/inch ² ] (k is 10 ³ and F is the number of fibers).

In this embodiment, the rotating brush 22 using such brush fibers is used, and the relationship between the moving speed (peripheral speed) of the surface of the intermediate transfer belt 7 and the circumferential speed of the rotating brush 22 is determined by the circumferential speed ratio θ( The rotational brush circumferential speed/belt surface movement speed) is approximately 1 to 5. In this way, by making the circumferential speed of the rotating brush 22 equal to or faster than the moving speed of the surface of the intermediate transfer belt 7, the efficiency of collecting toner and the like by the rotating brush 22 is improved. Further, the amount of penetration of the rotating brush 22 into the intermediate transfer belt 7 was set to be approximately 0.3 to 2.0 [mm].

The pre-charging brush 21 may also be constructed using brush fibers similar to those used to form the rotating brush 22. However, the resistance may be lower than that of the rotating brush 22 in order to facilitate charge injection. The brush fibers are woven into the base fabric at a fiber density of about 50 to 300 [kF/inch ² ] to form the pre-charged brush 21. The amount of penetration (intrusion amount) of the pre-charging brush 21 into the intermediate transfer belt 7 may be set to about 0.1 to 2 [mm].

The collection roller 23 is formed of a conductive metal pipe such as aluminum, iron, or SUS, and its surface is smoothed so as not to scratch the cleaning blade 24, which is a plate-shaped rubber material.

The rotating brush 22, the collecting roller 23, the cleaning blade 24, the pre-charging brush 21, and the sealing member 26 all have a length in the longitudinal direction that is equivalent to the width in the width direction that is substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7. It has a length of Furthermore, the rotating brush 22, collection roller 23, conveyance screw 25, seal member 26, and pre-charging brush 21 are supported by the case 20a.

During image formation (when cleaning the toner on the intermediate transfer belt 7), the belt cleaning device 20 forms a cleaning electric field for cleaning and collecting secondary transfer residual toner and the like on the intermediate transfer belt 7. The polarity (±) and output value (voltage value, etc.) of the DC voltage power supplies 27, 28, and 29 are controlled by the cleaning control unit 152 of the control unit 15.

For example, when forming a cleaning electric field during image formation, the pre-charging brush 21 is applied with a direct current voltage (DC voltage) set to the same polarity (-) as the normal charging polarity (-) of the toner by the power supply 27. Ru.

Further, a direct current voltage (DC voltage) set to the opposite polarity (+) side (including 0 [V]) from the normal charging polarity (-) of the toner is applied to the rotating brush 22 by grounding or a power source 28. Ru. As a result, a cleaning electric field is formed between the rotating brush 22 and the intermediate transfer belt 7, and the toner and the like on the intermediate transfer belt 7 is collected (cleaned).

The collection roller 23 is powered by a DC voltage (DC) which is set by a power source 29 to have a polarity (+) opposite to the normal charging polarity (-) of the toner and to a positive (+) side than the rotating brush 22. voltage) is applied.

Here, basically, the electric field formed by the power supplies 27, 28, and 29 may be either constant voltage or constant current. Although it depends on the rotational speed of the intermediate transfer belt 7, in the case of constant voltage, the absolute value is, for example, about 1 to 2 [KV] or less, and in the case of constant current, the absolute value is, for example, 30 to 50 [μA]. It is best to set it to a level below. However, as will be described in detail later, in this embodiment, the DC voltage applied to the pre-charging brush 21 by the power source 27 is controlled to be a constant current. Note that constant voltage control is control that adjusts the output of the power supply so that the voltage applied to the object is substantially constant at a target voltage. Further, constant current control is control that adjusts the output of the power supply so that the current supplied to the supply target is substantially constant at a target current.

During image formation (while cleaning the toner on the intermediate transfer belt 7 ), the cleaning control section 152 of the control section 15 removes toner, paper powder, etc. on the intermediate transfer belt 7 by charge injection from the pre-charging brush 21 . Aligned to negative polarity (-). The pre-charged toner and the like repel the polarity (-) of the pre-charging brush 21 and move onto the intermediate transfer belt 7 without accumulating on the pre-charging brush 21, and due to the rotation of the intermediate transfer belt 7, It is conveyed to the rotating brush 22. Then, this toner, etc. is removed mechanically and statically from the intermediate transfer belt 7 under a cleaning electric field by a rotating brush 22 set to the opposite polarity (+) to the normal charging polarity (-) of the toner. It is electrically scraped off and collected by the rotating brush 22.

The intermediate transfer belt 7 is cleaned, and the toner and the like collected by the rotating brush 22 are further collected by a collecting roller 23 that rotates in contact with the rotating brush 22. The toner and the like on the collection roller 23 are scraped off by a cleaning blade 24 and fall, and then transported to a waste toner container (not shown) by a transport screw 25.

3. Voltage/Constant current control applied to the pre-charging brush in this embodiment Next, the characteristic configuration of the belt cleaning device 20 of this embodiment will be further described. FIG. 4 is a schematic cross-sectional view of the belt cleaning device 20 of this embodiment (a cross-section substantially perpendicular to the rotation axis direction of the photosensitive drum 1 and the tension roller of the intermediate transfer belt 7). The basic configuration of the belt cleaning device 20 of this embodiment shown in FIG. 4 is the same as the basic configuration of the belt cleaning device 20 described using FIG. 3. In the belt cleaning device 20 of this embodiment, the same reference numerals are given to elements that are the same as or correspond to the basic configuration of the belt cleaning device 20 described using FIG. 3.

As mentioned above, while the toner, etc. on the intermediate transfer belt 7 is collected by the cleaning electric field, impurities (toner that is difficult to charge properly, external additives for toner, recording material powder, The filler of the recording material gradually accumulates and accumulates on the pre-charging brush 21.

In other words, toner that is difficult to charge normally (toner that is charged to the opposite polarity to the normal charge polarity) existing on the intermediate transfer belt 7, toner external additives (toner fluidizing agent, etc.), recording material powder (paper "Impurities" other than the regularly charged toner, such as paper dust (in some cases), recording material filler (talc, etc. in the case of paper), etc., gradually accumulate in the pre-charging brush 21. Here, as described above, it is preferable to use a fixed brush as the pre-charging member, which is advantageous for simplifying the structure and reducing costs, and using a rotating brush with high cleaning ability as the collecting member. However, the impurities are likely to accumulate in the pre-charging member 21, which is composed of a fixed brush. Therefore, during image formation over a long period of time, the pre-charging performance of the pre-charging brush 21 gradually deteriorates, and it may become difficult to charge the toner on the intermediate transfer belt 7 to the normal charging polarity. Then, the toner collection performance of the rotating brush 22 decreases, and as a result, the amount of uncollected toner on the intermediate transfer belt 7 increases, resulting in poor cleaning in which toner slips through the belt cleaning device 20, that is, a defective image. It may occur.

Therefore, in this embodiment, the belt cleaning device 20 includes a constant current control device 30 between the DC power source 27 and the pre-charging brush 21, as shown in FIG. The constant current control device 30 controls the voltage value of the DC voltage output by the DC power supply 27 so that a constant current value flows to the pre-charging brush 21 under the control of the control unit 15 (cleaning control unit 152). Adjust. As a result, the toner on the intermediate transfer belt 7 can be uniformly charged to the same polarity as the normal charging polarity of the toner over a long period of time.

FIG. 5 is a graph showing the relationship between the constant current value (target current, target value) and voltage value of the voltage applied to the pre-charging brush 21 when the process speed in this embodiment is 400 [mm/sec]. be. For example, as shown in FIG. 5, when the constant current value is set to -30 [μA], if the pre-charging brush 21 is new (black dot), a voltage of about -500 [V] will be applied, which will reduce the durability. At the advanced end of life (white spot), a voltage of about -700 [V] was applied. This is because, as described above, the impurities are deposited on the pre-charging brush 21 due to durability, and the resistance value between the pre-charging brush 21 and the intermediate transfer belt 7 increases.

At this time, if the voltage applied to the pre-charging brush 21 is under constant voltage control, the resistance value will increase due to the impurities and the current value will decrease, so the intermediate transfer belt due to the pre-charging brush 21 The injection charging performance of the toner on No. 7 deteriorates.

On the other hand, in the case of constant current control as in this embodiment, even if the resistance value increases due to the impurities, the DC voltage value also increases by that amount and a constant current value is attempted to flow. The performance of injecting and charging the toner onto the intermediate transfer belt 7 by the charging brush 21 remains unchanged.

In this manner, according to the present embodiment, since it is possible to suppress the deterioration of the pre-charging performance, it is also possible to suppress the deterioration of the toner collection performance of the rotating brush 22. As a result, an increase in uncollected toner on the intermediate transfer belt 7 can be suppressed. Therefore, it is possible to suppress the occurrence of image defects due to poor cleaning over a long period of time.

In this embodiment, the voltage applied to the rotating brush 22 during image formation was controlled at a constant voltage. Constant voltage control allows a uniform electric field to be formed in the plane (in the longitudinal direction of the rotating brush 22) regardless of the presence or absence of toner depending on the position on the intermediate transfer belt 7, which is advantageous for toner collection. It is. That is, a pre-charging voltage is applied to the pre-charging brush 21 under constant current control, and a recovery voltage is applied to the rotating brush 22 under constant voltage control. However, the recovery voltage may be applied to the rotating brush 22 under constant current control.

- Limit voltage As described above, when applying a constant current controlled DC voltage to the pre-charging brush 21 during image formation, even if the impurities are deposited on the pre-charging brush 21 and the resistance value increases, A DC voltage can be applied so that a constant current flows. Therefore, the pre-charging performance is less likely to deteriorate compared to the case where a constant voltage controlled DC voltage is applied.

On the other hand, for example, even if the pre-charging brush 21 is damaged or out of order, there is a possibility that too much or too little DC voltage will be applied to the pre-charging brush 21 due to constant current control.

Therefore, in this embodiment, the belt cleaning device 20 includes a limit voltage control device 31 between the DC power supply 27 and the pre-charging brush 21, as shown in FIG. The limit voltage control device 31 determines the limit voltage (upper limit voltage, lower limit voltage) according to the constant current value of the pre-charging brush 21 under the control of the control section 15 (cleaning control section 152). Then, using a voltage within the range between the upper limit voltage and the lower limit voltage, the voltage applied to the pre-charging brush 21 is controlled at a constant current. For convenience, the magnitude (high/low) of current and voltage refers to the magnitude (high/low) when compared in absolute value.

For example, the center (initial) voltage (dotted line), lower limit voltage (thick solid line), and upper limit voltage (thin solid line) in FIG. 5 are as follows.
(1) When constant current value = -40 [μA], center = -667 [V]
Lower limit = -367 [V]
Upper limit = -967 [V]
(2) When constant current value = -30 [μA], center = -500 [V]
Lower limit = -200 [V]
Upper limit = -800 [V]
(3) When constant current value = -20 [μA], center = -333 [V]
Lower limit = -33 [V]
Upper limit = -633 [V]
(4) When constant current value = -10 [μA], center = -167 [V]
Lower limit = 0 [V]
Upper limit = -467 [V]

In this way, by making the limit voltage (upper limit voltage, lower limit voltage) variable according to the constant current value, the limit voltage is also changed when the constant current value is changed. Therefore, the DC voltage applied to the pre-charging brush 21 is adjusted within the above limit voltage range. This prevents excessive voltage and insufficient voltage from being applied to the pre-charging brush 21. Therefore, safe and stable pre-charging performance can be maintained.

For example, when normal plain paper is used as the recording material P, if the constant current value = -30 [μA], even after durability, the voltage remains within the limit voltage range = -200 to -800 [V]. .

Here, as an example of changing the constant current value of the pre-charging brush 21 at the same process speed in the image forming apparatus 100, a case will be described in which the constant current value is changed depending on the paper type. Here, the types of recording materials P (herein also referred to as "paper types") include plain paper, thick paper, colored paper, recycled paper, synthetic resin sheets, sheets for overhead projectors, envelopes, postcards, coated paper, Distinguishes recording materials P based on general characteristics such as embossed paper, waterproof paper (resin sheet, resin-coated paper), metallized paper, etc. (so-called paper type category), manufacturer, brand, product number, basis weight, thickness, etc. It includes any possible information.

For example, in the case of paper with large surface irregularities such as embossed paper, the secondary transfer efficiency may be low, resulting in a large amount of secondary transfer residual toner on the intermediate transfer belt 7. Therefore, it may be desirable to change the constant current value from -30 [μA] to -40 [μA]. In other words, by increasing the constant current value, the pre-charging performance is increased, and the secondary transfer residual toner is more uniformly charged on the negative (-) side, thereby increasing the amount of toner collected by the rotating brush 22. .

In the case of constant current value = -40 [μA], initial value = approximately -667 [V], and after durability = approximately -850 [V]. Therefore, if the limit voltage of constant current value = -30 [μA] remains at -200 [V], -800 [V], after endurance = approximately -850 [V] will exceed the upper limit voltage, and the constant current Since it is not possible to flow the value = -40 [μA], the pre-charging performance deteriorates.

On the other hand, by configuring the limit voltage (upper limit voltage, lower limit voltage) to be changed according to the constant current value as in this embodiment, when the constant current value = -40 [μA], As shown in FIG. 5, the limit voltages are -367 [V] and -967 [V]. As a result, the voltage after the endurance test of -850 [V] does not exceed the limit voltage, so constant current control can be maintained. Thereby, safe and stable pre-charging performance can be maintained, and the occurrence of cleaning failures can be suppressed.

Here, the limit voltage (upper limit voltage, lower limit voltage) is set with a margin so that the voltage applied to the pre-charging brush 21 remains within a range where constant current control is possible even after the resistance increases due to the durability of the pre-charging brush 21. It is recommended to set it as follows. Therefore, as shown in FIG. 5, it is preferable to set the limit voltage so that the voltage does not exceed the upper limit voltage even if the resistance of the pre-charging brush 21 increases due to accumulation of paper dust etc. after durability.

In this embodiment, as shown in FIG. 5, for example, if "voltage at initial constant current value = center voltage", then "limit voltage (upper limit voltage, lower limit voltage) = ±300 [V of center (initial) voltage] ]”. Thereby, an appropriate limit voltage is set so that constant current control can be performed within the limit voltage range even after durability. However, the lower limit voltage shall not exceed 0 [V] (the polarity will not be reversed).

Here, for example, as shown in FIG. 5, a case will be considered in which the image forming apparatus 100 has a print speed of 80 [ppm] (80 sheets/minute) with A4 horizontal paper passing at a process speed of 400 [mm/sec]. When the constant current value of the pre-charging brush 21 is set to -30 [μA], the limit voltage control device 31 sets the lower limit voltage to -200 [V] and the upper limit voltage to -800 [V]. At this time, the constant current control device 31 applies an initial voltage of about -500 [V] to the pre-charging brush 21 and controls the constant current to -30 [μA], thereby improving the cleaning properties of the intermediate transfer belt 7. was in good condition.

Then, after the durability test, paper dust etc. accumulate, the resistance of the pre-charging brush 21 increases, and the constant current control device 31 applies a voltage of about -700 [V] after the durability test, and the constant current = -30 [V]. Constant current is controlled to [μA]. Since the upper limit voltage is -800 [V], it is well within the set limit voltage range (-200 to -800 [V]) even after durability. Therefore, constant current control is performed, and the toner on the intermediate transfer belt 7 can be sufficiently injected and charged even after durability. Therefore, since the rotating brush 22 can collect (clean) the toner and the like on the intermediate transfer belt 7, it is possible to suppress the occurrence of cleaning defects.

For example, if due to some malfunction only one half of the area of the pre-charging brush 21 comes into contact with the intermediate transfer belt 7, the resistance value will approximately double, so the constant current value will be -30 [μA] Even in the initial case, about -1000 [V] is applied. In such a case, the upper limit voltage = -800 [V] determined by the limit voltage control device 31 is controlled so as not to exceed the upper limit voltage = -800 [V], so the upper limit voltage = -800 [V] is applied to the pre-charging brush 21. be done. Thereby, application of excessive voltage can be suppressed. However, in this case, a constant current value of -30 [μA] cannot be passed. In this case, the constant current control device 30 can send a signal indicating an error to the image forming control section 150. Then, the image formation control unit 150 stops image formation, displays error notification information on the operation unit 99, and informs the operator, such as the user or service personnel, whether there is any problem with the pre-charging brush 21. It is preferable to display a message on the operation unit 99 asking for confirmation.

As described above, in this embodiment, the voltage applied to the pre-charging brush 21 is controlled by the constant current control device 30 to cause a constant current to flow through the pre-charging brush 21. As a result, even if impurities such as paper dust accumulate on the pre-charging brush 21 due to durability and the resistance increases, the flowing current value remains the same as the initial value, so the ability to inject and charge secondary transfer residual toner etc. But it is difficult to decline.

Furthermore, in this embodiment, since the limit voltage is determined according to the constant current value, the limit voltage will not be exceeded throughout the lifespan unless something goes wrong, so it is safe and stable over a long period of time. Can control current. Further, in the constant current control, by providing a limit voltage, neither overvoltage nor undervoltage is applied, making it easy to extend the life of the pre-charging brush 21. Further, if a malfunction occurs due to some abnormal situation, such as applying a voltage exceeding a limit voltage or being unable to control a constant current, these abnormalities can be detected. Therefore, it is also possible to stop the image forming apparatus 100 or display an error. This makes it possible to prevent damage to the image forming apparatus 100, which is safer.

In this embodiment, "limit voltage (upper limit voltage, lower limit voltage) = ±300 [V] of the center (initial) voltage" is set, but ±300 [V] is just one example. For example, in other image forming apparatuses with different configurations, the limit voltage may be set within an arbitrary range depending on the initial resistance value of the pre-charging brush 21, the resistance increase value due to durability, etc. Alternatively, a configuration may be adopted in which only the upper limit voltage of the limit voltage is provided. Thereby, effects such as ensuring safety as described above can be obtained. Although the lower limit voltage can contribute to maintaining stable pre-charging performance, the applied voltage value is unlikely to become small due to a decrease in the resistance value of the pre-charging brush 21, for example. Therefore, it is often possible to omit providing a lower limit voltage. Further, depending on the device configuration, etc., if the possibility of excessive voltage being applied is sufficiently low, providing an upper limit voltage as a limit voltage may be omitted.

Furthermore, the process speed and constant current value described in this embodiment are merely examples, and may be set to arbitrary values in other image forming apparatuses having different configurations, for example.

As described above, in the present embodiment, the image forming apparatus 100 records the toner image transferred from the image carrier 1 in the primary transfer section N1 on the image carrier 1 that carries the toner image in the secondary transfer section N2. An intermediate transfer belt 7 that can be circumferentially moved to be conveyed for transferring onto a material P, and an intermediate transfer belt 7 that is downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 in the direction of movement of the surface of the intermediate transfer belt 7. A rotating brush 22 that rotates in contact with the surface of the transfer belt 7 to collect toner on the intermediate transfer belt, a first power source 28 that applies voltage to the rotating brush 22, and a direction in which the surface of the intermediate transfer belt 7 moves. is fixedly arranged in contact with the surface of the intermediate transfer belt 7 upstream of the contact portion between the rotating brush 22 and the intermediate transfer belt 7 and downstream of the secondary transfer portion N2, and charges the toner on the intermediate transfer belt. a second power source 27 that applies a voltage to the fixed brush 21, and a control section 15 that controls the first power source 28 and the second power source 27. During image formation in which a toner image is transferred from the transfer belt 7 to the recording material P, a DC voltage with a polarity opposite to the normal charging polarity of the toner is applied to the rotating brush 22, and a target current is supplied to the fixed brush 21. A DC voltage having the same polarity as the normal charging polarity of the toner is applied to the fixed brush 21 by constant current control so that the current value is the same. In this embodiment, the control unit 15 uses constant voltage control to rotate a DC voltage with a polarity opposite to the normal charging polarity of the toner so that the voltage applied to the rotating brush 22 becomes a target voltage value during image formation. The voltage is controlled to be applied to the brush 22. Furthermore, in this embodiment, the control unit 15 is capable of changing the target current value during image formation, and also changes the upper limit of the absolute value of the voltage that the second power supply 27 applies to the fixed brush 21 during image formation. The second upper limit is set according to the target current value, and the absolute value of the target current value is larger than the first value when the absolute value of the target current value is the first value. Increase the above upper limit value when the value is a value. Further, in this embodiment, the control unit 15 can change the target current value based on the type of recording material P to which the toner image is transferred. For example, the control unit 15 may set the absolute value of the target current value when the recording material P to which the toner image is transferred is embossed paper to the absolute value of the target current value when the recording material P to which the toner image is transferred is plain paper. Make it larger than the absolute value of the current value. Further, in this embodiment, the intermediate transfer belt 7 has an elastic layer.

As explained above, according to this embodiment, it is possible to simplify the device configuration and reduce costs, while maintaining good pre-charging performance over a long period of time even when impurities gradually accumulate in the pre-charging member. can be maintained to maintain good cleaning performance. Furthermore, in this embodiment, the voltage applied to the pre-charging member that is subject to constant current control is adjusted to at least the upper limit voltage or lower, thereby suppressing excessive voltage from being applied to the pre-charging member and ensuring safety. Pre-charging performance can be maintained.

[Example 2]
Next, other embodiments 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 the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as in Embodiment 1, and detailed explanations thereof will be omitted. .

In the first embodiment, by connecting the constant current control device 30 and the limit voltage control device 31 to the DC voltage power source 27 of the pre-charging brush 21, the voltage applied to the pre-charging brush 21 is controlled at a constant current. A limit voltage was set according to the constant current value. Then, the DC voltage was adjusted within the limit voltage range. Further, in Example 1, the constant current value of the pre-charging brush 21 was changed depending on the paper type of the recording material P used for image formation.

In this embodiment, in an image forming apparatus 100 having a plurality of image forming speeds (process speeds), the constant current value of the pre-charging brush 21 is changed depending on the process speed. As a result, even if the process speed changes, the secondary transfer residual toner on the intermediate transfer belt 7 can be injected and charged so that it has a constant charge, so even if the process speed changes, a constant cleaning performance can be maintained. Can be done.

FIG. 6 shows the constant current value and voltage value of the pre-charging brush 21 at PS (process speed) = 400 [mm/sec], PS = 200 [mm/sec], and PS = 100 [mm/sec] in this embodiment. It is a graph diagram showing the relationship between.

Here, the "process speed" is an image forming speed, and in the case of the image forming apparatus 100 of this embodiment, the rotation speed (peripheral speed) of the photosensitive drum 1 or the rotation speed (peripheral speed) of the intermediate transfer belt 7. speed), or the conveyance speed of the recording material P during secondary transfer.

As shown in FIG. 6, the constant current value is changed in proportion to the process speed. For example, the center (initial) voltage (dotted line), lower limit voltage (thick solid line), and upper limit voltage (thin solid line) in FIG. 6 are as follows.
(1) When PS = 400 [mm/sec] Constant current value = -30 [μA], Center = -500 [V]
Lower limit = -200 [V]
Upper limit = -800 [V]
(2) When PS = 200 [mm/sec] Constant current value = -15 [μA], center = -250 [V]
Lower limit = 0 [V]
Upper limit = -550 [V]
(3) When PS = 100 [mm/sec] Constant current value = -7.5 [μA], Center = -125 [V]
Lower limit = 0 [V]
Upper limit = -425 [V]

Here, as an example of changing the process speed of the image forming apparatus 100, a case will be described in which the process speed is changed depending on the difference in fixability depending on the paper type. Here, "fixability" refers to the adhesive force between the toner and the recording material P.

If the amount of heat applied to the recording material P and toner by the fixing device 13 is excessively small, the toner will not melt and will not be fixed to the recording material P. In other words, the fixing performance will deteriorate and the toner will not melt when touched by hand. There is a possibility that "poor fixing" may occur, which causes the film to stick to the hands. Conversely, if the amount of heat applied to the recording material P and toner by the fixing device 13 is excessively large, the toner will melt too much. As a result, the molten toner adheres to the fixing roller 13a, and the adhered toner is fixed to the recording material P after one rotation of the fixing roller 13a, potentially causing a "hot offset" that stains the recording material P. be. Therefore, it is desirable that the amount of heat given to the recording material P and toner by the fixing device 13, that is, the fixing temperature of the fixing roller 13a, be adjusted to an appropriate fixing temperature depending on the fixing device 13, the recording material P, and the toner. .

For example, plain paper (basis weight 64 to 80 [g/m ² ]) has good fixing properties even at PS=400 [mm/sec] and print speed of 80 [ppm]. However, for example, with cardboard (basis weight 200 to 300 [g/m ² ]), under the same conditions, the toner will not melt sufficiently, and when rubbed by hand, the toner will come off from the cardboard, resulting in poor fixing. There are cases.

Therefore, in order to obtain good fixing performance on thick paper (basis weight 300 [g/m ² ]), the fixing temperature of the fixing roller 13a should be adjusted when using plain paper (basis weight 64 to 80 [g/m ² ]). It is best to set the temperature higher than that. However, if it is not possible to increase the temperature of the fixing roller 13a due to the heat resistance of the parts of the fixing device 13, for example, the process speed may be reduced without increasing the temperature of the fixing roller 13a to ensure good fixing performance. You can also get it. Therefore, for example, in the case of thick paper (basis weight 200 to 300 [g/m ² ]), PS = 200 [mm/sec] and the printing speed is reduced to half of 40 [ppm], and the print speed is reduced to half speed per unit area of the cardboard. Good fixing performance can be obtained by increasing the amount of heat applied. In this way, the process speed can be changed depending on the basis weight (g/m ² ) of the recording material P in order to ensure fixing performance.

In the case of the image forming apparatus 100 that changes the process speed in this manner, the constant current value of the pre-charging brush 21 may be changed in proportion to the process speed. For example, the above (1) PS=400 [mm/sec] and constant current value=-30 [μA] are sufficient to pre-charge the toner on the intermediate transfer belt 7. At this time, when the above (2) PS = 200 [mm/sec] is set at half speed, the current amount per unit area of the intermediate transfer belt 7 is approximately the same, and the constant current value = -15 [μA]. , is sufficient to pre-charge the toner on intermediate transfer belt 7.

(2) If the conditions of (1) above, where PS = 200 [mm/sec] and constant current value = -30 [μA], remain, the amount of current per unit area of the intermediate transfer belt 7 is too large. Then, not only the toner on the intermediate transfer belt 7 but also the surface of the intermediate transfer belt 7 may be locally charged to the negative (-) side. This locally charged portion on the negative (-) side of the surface of the intermediate transfer belt 7 transfers the positive (+) charged toner on the rotating brush 22 on the downstream side in the rotational direction of the intermediate transfer belt 7 onto the intermediate transfer belt 7. You may have to move it again. Therefore, a cleaning failure in which toner remains on the intermediate transfer belt 7 may occur. Furthermore, if the locally charged portion on the negative (-) side of the surface of the intermediate transfer belt 7 has a large potential on the negative (-) side, the image forming section 50Y on the downstream side in the rotational direction of the intermediate transfer belt 7 In the primary transfer portion N1, there may be a portion where it is difficult to perform the primary transfer. Therefore, local density unevenness may occur due to this primary transfer unevenness. On the other hand, for example, if the conditions of (2) above (1) PS = 400 [mm/sec] and constant current value = -15 [μA] remain, the toner on the intermediate transfer belt 7 will not be pre-charged. There is not enough current to do so. Then, insufficient injection charging may occur, and the toner on the intermediate transfer belt 7 may not be uniformly pre-charged. Therefore, toner collection by the rotating brush 22 may become insufficient, resulting in a cleaning failure in which toner remains on the intermediate transfer belt 7.

Therefore, in order for the pre-charging brush 21 to pre-charge the toner on the intermediate transfer belt 7 so that it has a certain amount of charge on the same polarity side as the toner, it is necessary to set an appropriate constant current value according to the change in process speed. It is desirable to change this. By changing the constant current value according to the process speed, the pre-charged toner can be charged at a constant amount even if the process speed changes, so the cleaning performance of the rotating brush 22 can be made constant. . This makes it possible to suppress the occurrence of poor cleaning over a long period of time.

Even in such a case, in this embodiment, the limit voltage (upper limit voltage, lower limit voltage) is determined according to the constant current value. In this example, as in Example 1, by setting the limit voltage (upper limit voltage, lower limit voltage) = ±300 [V] of the center (initial) voltage, the voltage can be maintained within the limit voltage range even after durability. An appropriate limit voltage is set to enable constant current control. However, the lower limit voltage is not to exceed 0 [V]. Due to this limit voltage, even if the process speed is changed and the voltage increases due to an increase in the resistance of the pre-charging brush 21 due to the accumulation of paper dust etc. after durability as shown in FIG. 6, the voltage will remain within the upper limit voltage. fits in. Therefore, even if the process speed is changed, constant current control can be maintained after durability, and good pre-charging performance can be maintained over a long period of time.

In this manner, in this embodiment, the control unit 15 can change the target current value of the current supplied to the fixed brush 21 based on the moving speed of the surface of the intermediate transfer belt 7 during image formation. In the present embodiment, the control unit 15 sets a second moving speed at which the moving speed is slower than the first moving speed than the absolute value of the target current value when the moving speed is the first moving speed. The absolute value of the target current value in the case of .

As described above, according to this embodiment, the same effects as in the first embodiment can be obtained even when the target current value of the current supplied to the pre-charging member is changed depending on the process speed.

[Example 3]
Next, other embodiments 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 the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as in Embodiment 1, and detailed explanations thereof will be omitted. .

In Example 2, by changing the constant current value of the pre-charging brush 21 according to the process speed, the pre-charging performance was made constant even when the process speed changed.

In this embodiment, the image forming apparatus 100 includes an environment sensor 155 as an environment detecting means for detecting an environment of at least one of temperature and humidity inside and outside of the image forming apparatus 100. In this embodiment, the environment sensor 155 detects the temperature and humidity inside the image forming apparatus 100 as information regarding the amount of moisture in the atmosphere. In this embodiment, the image forming apparatus 100 changes the limit voltage (upper limit voltage, lower limit voltage) of the pre-charging brush 21 based on the detection result of the environment sensor 155. As a result, even if the resistance value of the pre-charging brush 21 increases due to the accumulation of paper dust etc. after durability, or even if the environment (temperature/humidity) changes, the pre-charging brush 21 can be controlled at a constant current. The voltage applied to 21 can be set within the limit voltage range. Therefore, even if the installation environment (temperature and humidity) of the image forming apparatus changes, safe and stable pre-charging performance can be maintained over a long period of time.

FIG. 7 is a graph diagram showing the relationship between the absolute humidity and the voltage value of the pre-charging brush 21 of the comparative example. The dotted line in FIG. 7 is the voltage during constant current control at a process speed of 400 [mm/sec] and an initial constant current value of the pre-charging brush 21 of -30 [μA]. It shows the transition with respect to the absolute humidity [g/m ³ ] calculated from the temperature [° C.] detected by the environmental sensor 155 and the relative humidity [%].

As shown by the dotted line in FIG. 7, in a high humidity environment where the absolute humidity is high (the amount of water is large), the resistance value of the pre-charging brush 21 decreases, and the voltage value applied under constant current control decreases. Conversely, in a low-humidity environment where the absolute humidity is low (water content is low), the resistance value of the pre-charging brush 21 increases, and the voltage value applied under constant current control increases.

Moreover, since FIG. 7 shows a comparative example, the limit voltage is constant with respect to absolute humidity. The thick solid line is the lower limit voltage, and the thin solid line is the upper limit voltage. As shown in Figure 7, when the limit voltage is constant, for example in a low-humidity environment with low absolute humidity, the voltage is initially within the limit voltage, but due to durability, paper dust etc. accumulates and pre-charging occurs. If the resistance value of the brush 21 increases, the upper limit voltage will be exceeded. Therefore, a situation occurs where the current is smaller than -30 [μA] even though the constant current value is -30 [μA]. In such a case, the amount of current that flows decreases, and the performance of pre-charging the toner and the like on the intermediate transfer belt 7 deteriorates. As a result, the cleaning performance for collecting toner by the rotating brush 22 also deteriorates, which may cause toner to slip through from the belt cleaning device 20, resulting in poor cleaning such as streaks on the image. .

Therefore, in this embodiment, as shown in FIG. 8, by changing the limit voltage according to the absolute humidity, safe and stable constant current control of the pre-charging brush 21 can be performed over a long period of time. do it like this.

FIG. 8 is a graph diagram showing the relationship between absolute humidity and voltage value of the pre-charging brush 21 of this embodiment. The dotted line in FIG. 8 is similar to the dotted line in FIG. 7, and is the voltage value during constant current control when the initial constant current value of the pre-charging brush 21 is −30 [μA]. The thick solid line is the lower limit voltage, and the thin solid line is the upper limit voltage. In this embodiment, "limit voltage=initial voltage value of the pre-charging brush 21 ±300 [V]" is set. However, since this voltage is 0 [V] or less (minus side), if it exceeds 0 [V] (becomes positive side), it is set to 0 [V]. As shown in FIG. 8, even if the resistance value of the pre-charging brush 21 increases due to accumulation of paper dust due to durability in a low-humidity environment with low absolute humidity, the voltage remains within the limit voltage range. Therefore, constant current control can be performed normally. Therefore, even if the installation environment (temperature and humidity) of the image forming apparatus 100 changes, safe and stable pre-charging performance can be maintained over a long period of time.

As described above, in this embodiment, the image forming apparatus 100 includes the environmental sensor 155 that detects information regarding the amount of moisture in the atmosphere, and the control unit 15 controls the second The upper limit of the absolute value of the voltage that the power supply 27 applies to the fixed brush 21 can be changed. In this embodiment, the control unit 15 controls the control unit 15 so that the amount of moisture indicated by the detection result by the environment sensor 155 is higher than the upper limit value when the amount of moisture indicated by the detection result by the environment sensor 155 is the first amount of moisture. When the second moisture content is larger than the moisture content, the upper limit value is reduced.

As described above, according to the present example, the same effects as in Example 1 can be obtained, and even when the environment changes, good pre-charging performance can be maintained.

[Example 4]
Next, other embodiments 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 the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as in Embodiment 1, and detailed explanations thereof will be omitted. .

In Example 3, the image forming apparatus 100 includes an environment sensor 155, and changes the limit voltage (upper limit voltage, lower limit voltage) of the pre-charging brush 21 based on the detection result of the environment sensor 155.

In this embodiment, the image forming apparatus 100 includes an environment sensor 155 and changes the constant current value of the pre-charging brush 21 based on the detection result of the environment sensor 155. As a result, even if the environment (temperature/humidity) changes, the pre-charging performance of the pre-charging brush 21 can be kept constant, so the amount of toner charge on the intermediate transfer belt 7 after passing through the pre-charging brush 21 can be kept constant. It can be done. By keeping the toner charge amount after pre-charging constant even if the environment changes, the toner recovery performance, that is, the cleaning performance of the rotating brush 22 can be kept constant. Therefore, even if the environment changes, it is possible to safely and stably suppress the occurrence of cleaning defects over a long period of time.

In each of the above examples, the constant current value of the pre-charging brush 21 was constant regardless of the environment. Therefore, the absolute value of the charge amount of the toner on the intermediate transfer belt 7 after pre-charging tends to be low in a high humidity environment and high in a low humidity environment. Therefore, the recovery (cleaning) ability of the rotating brush 22 for secondary transfer residual toner may also be dependent on the environment, such that it is low in a high humidity environment and high in a low humidity environment. In this embodiment, the influence of this environment dependence is suppressed.

FIG. 9 is a graph diagram showing the relationship between the absolute humidity [g/m ³ ] and the voltage value [V] of the pre-charging brush 21 during constant current control in this embodiment.

As shown in FIG. 9, for example, in a normal environment where the absolute humidity is intermediate (absolute humidity = 5 to 19 [g/m ³ ]), the ease with which toner is charged is moderate. The absolute value of the amount of charge of the toner on the transfer belt 7 is medium. Therefore, in a normal environment, the constant current value is set to -30 [μA].

On the other hand, in a high humidity environment with high absolute humidity (absolute humidity = over 19 [g/m ³ ]), toner is difficult to charge, so the absolute value of the charge amount of toner on intermediate transfer belt 7 after pre-charging is small. Therefore, in a high humidity environment, in order to increase the amount of pre-charging of the toner on the intermediate transfer belt 7, it is desirable to increase the absolute value of the constant current value of the pre-charging brush 21 to increase the amount of injection charging. Therefore, the constant current value is set to -35 [μA].

On the other hand, in a low-humidity environment where the absolute humidity is low (absolute humidity = less than 5 [g/m ³ ]), the toner is easily charged, so the absolute value of the amount of charge of the toner on the intermediate transfer belt 7 after pre-charging is large. . Therefore, in a low-humidity environment, in order to match the pre-charge amount of the toner on the intermediate transfer belt 7 with the normal environment, it is desirable to reduce the absolute value of the constant current value of the pre-charging brush 21 to reduce the injection charge amount. Therefore, the constant current value is set to -25 [μA].

Furthermore, as shown in FIG. 9, the limit voltage is changed according to each constant current value by setting "limit voltage (upper limit voltage, lower limit voltage) = initial constant current control voltage value ±300 [V]".

As shown in FIG. 9, by controlling the constant current value to change according to the absolute humidity, even if the environment (temperature/humidity) changes, the intermediate transfer belt 7 after pre-charging by the pre-charging brush 21 The charge amount of the toner can be kept constant and stable. Therefore, the toner collection (cleaning) ability of the rotating brush 22 can be kept constant and stable.

Furthermore, even if paper dust or the like accumulates on the pre-charging brush 21 during durability and the resistance of the pre-charging brush 21 increases, the pre-charging performance can be maintained constant by constant current control and limit voltage control, and Application of too much or too little voltage to the pre-charging brush 21 can be suppressed. Therefore, safe and stable pre-charging can be performed.

As described above, in this embodiment, the image forming apparatus 100 includes the environmental sensor 155 that detects information regarding the amount of moisture in the atmosphere, and the control unit 15 controls the amount of water supplied to the fixed brush 21 based on the detection result by the environmental sensor 155. It is possible to change the target current value of the current. In this embodiment, the control unit 15 determines that the amount of moisture indicated by the detection result by the environment sensor 155 is higher than the absolute value of the target current value when the amount of moisture indicated by the detection result by the environment sensor 155 is the first moisture amount. The absolute value of the target current value is increased when the second moisture content is larger than the first moisture content.

As described above, according to the present example, the same effects as in Example 1 can be obtained, and even when the environment changes, better pre-charging performance can be obtained.

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

In the above embodiment, since negative (-) toner was used, a negative (-) DC voltage having the same polarity as the toner was applied to the pre-charging brush. However, in the case of an image forming apparatus that uses positive (+) toner, a positive (+) DC voltage is applied to the pre-charging brush, and a rotating brush is used to collect the positive (+) toner. It is best to ground or apply a negative (-) DC voltage. In this way, in the case of an image forming apparatus that uses plus (+) toner, the polarity of the voltage applied to the member can be changed as appropriate from when using minus (-) toner to plus (+)/minus (-). ) should be applied with the polarity reversed.

Further, the pre-charging member cleaning mode may be executed during non-image formation. For example, in the pre-charging member cleaning mode, the following operations can be performed. In other words, during normal image formation, the collection member has the same polarity as the normal charging polarity of the toner on the intermediate transfer member, and the pre-charging member has the opposite polarity to the normal charging polarity of the toner on the intermediate transfer member. The cleaning electric field is the formation of an opposite electric field. Alternatively, the application of an alternating electric field to the pre-charging member. In this pre-charging member cleaning mode, at least one of forming a reverse electric field and applying an alternating electric field can be performed. Thereby, good pre-charging performance can be maintained for a longer period of time.

Further, the process speed is not limited to changing depending on the paper type as in the above embodiment. For example, when an image forming apparatus with a resolution of 600 [dpi] is set to half speed and the resolution is increased to 1200 [dpi] only in the sub-scanning direction, the process speed can be changed according to the resolution. You can also do it.

7 Intermediate transfer belt 10 Secondary transfer roller 15 Control unit 20 Belt cleaning device 21 Pre-charging brush 22 Rotating brush 27 DC voltage power supply 28 DC voltage power supply 29 DC voltage power supply 30 Constant current control device 31 Limit voltage control device 100 Image forming device 155 Environmental sensor P Recording material

Claims (12)

an image carrier that carries a toner image;
a circumferentially movable intermediate transfer belt that conveys the toner image transferred from the image carrier in a primary transfer unit to a recording material in a secondary transfer unit;
The toner on the intermediate transfer belt rotates in contact with the surface of the intermediate transfer belt downstream of the secondary transfer section and upstream of the primary transfer section in the moving direction of the surface of the intermediate transfer belt. A rotating brush that collects
a first power source that applies voltage to the rotating brush;
fixedly disposed in contact with the surface of the intermediate transfer belt upstream of the contact portion between the rotating brush and the intermediate transfer belt and downstream of the secondary transfer portion in the moving direction of the surface of the intermediate transfer belt. , a fixed brush that charges the toner on the intermediate transfer belt;
a second power source that applies voltage to the fixed brush;
a control unit that controls the first power source and the second power source;
has
The control unit applies a DC voltage having a polarity opposite to the normal charging polarity of the toner to the rotating brush and supplies it to the stationary brush during image formation in which the toner image is transferred from the intermediate transfer belt to the recording material. An image forming apparatus characterized in that a DC voltage having the same polarity as the normal charging polarity of the toner is applied to the fixed brush by constant current control so that the current applied to the fixed brush becomes a target current value. The control unit applies a DC voltage having a polarity opposite to the normal charging polarity of the toner to the rotating brush by constant voltage control so that the voltage applied to the rotating brush becomes a target voltage value during the image formation. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled so as to perform the following operations. The control unit is capable of changing the target current value during the image formation, and sets an upper limit of the absolute value of the voltage applied by the second power source to the fixed brush to the target current value during the image formation. and the absolute value of the target current value is a second value larger than the first value than the upper limit value when the absolute value of the target current value is the first value. The image forming apparatus according to claim 1, wherein the upper limit value of is increased. The image forming apparatus according to claim 3, wherein the control section is capable of changing the target current value based on the type of recording material to which the toner image is transferred. The control unit determines the absolute value of the target current value when the recording material to which the toner image is transferred is embossed paper, and the absolute value of the target current value when the recording material to which the toner image is transferred is plain paper. The image forming apparatus according to claim 4, wherein the image forming apparatus is set to be larger than the value. The image forming apparatus according to claim 3, wherein the control section is capable of changing the target current value based on a moving speed of the surface of the intermediate transfer belt during the image formation. The control unit is configured to control the absolute value of the target current value when the moving speed is a first moving speed, and the absolute value of the target current value when the moving speed is a second moving speed slower than the first moving speed. 7. The image forming apparatus according to claim 6, wherein the absolute value of the target current value is made small. It has an environmental sensor that detects information about the amount of moisture in the atmosphere.
The image forming apparatus according to claim 3, wherein the control unit is capable of changing the target current value based on a detection result by the environmental sensor. The control unit is configured such that the moisture content indicated by the detection result by the environmental sensor is greater than the absolute value of the target current value when the moisture content indicated by the detection result by the environmental sensor is the first moisture content. The image forming apparatus according to claim 8, wherein the absolute value of the target current value is increased when the second moisture content is larger than the moisture content. It has an environmental sensor that detects information about the amount of moisture in the atmosphere.
The image forming apparatus according to claim 3, wherein the control unit is capable of changing the upper limit value based on a detection result by the environmental sensor. The control unit is configured such that the amount of moisture indicated by the detection result by the environmental sensor is lower than the upper limit value when the amount of moisture indicated by the detection result by the environmental sensor is the first amount of moisture. The image forming apparatus according to claim 10, wherein the upper limit value is made small when the second moisture content is large. The image forming apparatus according to any one of claims 1 to 11, wherein the intermediate transfer belt has an elastic layer.

Images