JP2012098364A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reducing manufacturing cost therefor.SOLUTION: The image forming device comprises: an image forming part (16) which includes an image carrier (18), develops a latent image on the image carrier by toner by driving of the image carrier and forms a toner image; a transfer belt (50) which is stretched between rollers, runs between the image carrier and a transfer roller (31) with a recording material placed on a conveyance surface of the transfer belt, and transfers the toner image directly to the recording material by voltage application of reverse polarity to toner adhering to the latent image; cleaning means (57) for recovering residual toner adhering to the conveyance surface using electrostatic force; and bias control means (39, 92) for making the toner image transferred directly to the recording material and making the residual toner recovered, by applying voltage which has reverse polarity to the toner and makes electric potential of the whole transfer belt higher than the image carrier, to the cleaning means.

Description

  The present invention relates to an image forming apparatus that forms an image using a transfer belt.

  In this type of image forming apparatus, an electrophotographic method is used. When a charger precharges an image carrier (for example, a photosensitive drum) and the exposure unit irradiates light on the surface of the photosensitive drum, the photosensitive member is used. An electrostatic latent image is formed on the surface of the drum. Further, the developing device carries toner, and when a developing bias voltage is applied, the toner charged in advance adheres to the electrostatic latent image, and a toner image is formed.

  Then, the sheet is conveyed to the transfer nip by a pair of rollers disposed on the upstream side of the transfer nip, and the visualized toner image is transferred to the sheet on the transfer belt that is rotationally driven. In many cases, a rubber belt is used as the transfer belt. If a resin belt is used, a tension mechanism must be provided separately, and when the alignment accuracy between the drive and driven rollers is comparable, the rubber belt is less than the resin belt. This is because there is an advantage that it is difficult to meander.

  Here, when this toner image is transferred onto the paper, the toner that moves from the photosensitive drum toward the paper may also adhere to the conveyance surface of the transfer belt (for example, fog toner between papers or Toner stains at the time of jamming, etc.) and residual toner adhering to the transport surface cause the back side of the paper to become dirty. Therefore, a technique for removing the residual toner from the conveyance surface is disclosed (for example, see Patent Document 1).

  Specifically, when the rubber belt is used, it is very difficult to scrape the remaining toner with a blade. Therefore, a bias cleaning unit is installed and has a polarity opposite to that of the toner attached to the electrostatic latent image. When the cleaning bias is applied to the transfer belt, the residual toner is collected by the bias cleaning unit.

JP 2002-49248 A

However, the above-described conventional technique has a problem that the manufacturing cost of the image forming apparatus cannot be reduced.
This is because, in this technique, when transferring a toner image onto a sheet, a transfer bias having a polarity opposite to that of the toner adhering to the electrostatic latent image is applied to the transfer roller. This is because, in addition to the high-voltage substrate that generates the cleaning bias, another high-voltage substrate that generates the transfer bias is required.

In other words, the conventional technique requires independent high-voltage substrates in spite of the transfer bias and the cleaning bias having the same polarity, so that there is still a problem in terms of reducing the manufacturing cost. Yes.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of solving the above-described problems and reducing the manufacturing cost of the image forming apparatus.

  A first invention for achieving the above object has an image carrier, and develops an electrostatic latent image on the image carrier with toner to form a toner image between the roller and the image forming unit. It is a belt member that is wrapped around, and a recording material is placed on the conveying surface and travels between the image carrier and the transfer roller. By applying a voltage having a polarity opposite to that of the toner attached to the latent image, A transfer belt that directly transfers the toner image to the recording material, a cleaning unit that collects residual toner adhering to the conveyance surface using electrostatic force, and a voltage of a polarity opposite to that of the toner is applied to the cleaning unit. And a bias control means for transferring the toner image directly onto the recording material by applying a voltage that raises the potential of the entire transfer belt more than that of the image carrier, and collecting the residual toner.

The present invention focuses on the fact that the bias used for transfer to the recording material and the bias used for collecting the remaining toner have the same polarity.
According to the first aspect of the invention, the transfer belt is a belt for electrostatically conveying the recording material, and a voltage having a polarity opposite to that of the toner attached to the electrostatic latent image on the image carrier is applied to the transfer belt side. Then, the toner image is transferred to the recording material. On the other hand, the toner moving from the image carrier toward the recording material can adhere to the transfer belt as well as the recording material. However, the residual toner adhering to the conveyance surface is charged by the electrostatic force of the image carrier. When a voltage having a polarity opposite to that of the toner adhering to the latent image is applied to the transfer belt, the toner is collected by the cleaning unit.

The bias control means of the present invention does not apply a transfer bias only to the transfer roller at the time of transfer to the recording material, but transfers the entire transfer belt including the transfer roller and the transfer belt running roller. A bias for collecting residual toner that also serves as a bias is provided.
Specifically, the bias control unit applies a voltage with a polarity opposite to that of the toner adhering to the electrostatic latent image to the cleaning unit so that the potential of the entire transfer belt is higher than the potential of the image carrier. A signal to be applied is output.

As a result, the output current from the cleaning unit flows through the transfer belt to the recording material and then to the image carrier, and the voltage gradient gradually decreases toward the image carrier between the cleaning unit and the image carrier. Therefore, the residual toner can be collected by the cleaning means, and the toner image can be transferred to the recording material.
Thus, as a result of applying the bias used for transfer to the recording material from the cleaning means, a conventional high voltage substrate for applying a voltage to the transfer roller can be omitted, and the manufacturing cost of the image forming apparatus can be reduced. it can.

According to a second aspect of the present invention, in the configuration of the first aspect, the image carrier is grounded, and the transfer roller and the transfer belt running roller are both floated with respect to the ground position. .
According to the second invention, in addition to the action of the first invention, the transfer roller and the transfer belt running roller are all floated with respect to the GND. The toners are formed almost the same, and the residual toner can be collected and transferred to the recording material with certainty.

According to a third aspect of the invention, in the configuration of the first or second aspect of the invention, the bias control means is a voltage having a polarity opposite to that of the toner by constant current control with respect to the cleaning means, and the potential of the entire transfer belt is image-carrying. A voltage higher than that of the body is applied.
According to the third invention, in addition to the effects of the first and second inventions, if the resistance value of the transfer belt changes due to, for example, variations during manufacturing or deterioration during durability, in the constant voltage control, the recording material However, if the output current from the cleaning means is controlled to be constant by constant current control, the current gradually decreases toward the image carrier. Since the voltage gradient can be maintained, the remaining toner can be collected and transferred to the recording material more reliably.

According to a fourth aspect of the present invention, in the configuration of the first to third aspects, the recording material is vertically conveyed from the lower side to the upper side, and the transfer belt is provided with a driving roller disposed on the lower side and an upper side. It is characterized in that it is slanted around the arranged driven roller.
According to the fourth invention, in addition to the effects of the first to third inventions, the transfer belt is used when the recording material is conveyed longitudinally, and the recording material is held only by the image carrier and the transfer roller. Compared to the case, the recording material can move toward the next fixing step with a more stable posture, which contributes to good operation of the image forming apparatus.

  According to the present invention, since the transfer bias is applied from the cleaning unit, it is possible to omit an exclusive high-voltage substrate for generating the transfer bias, and to provide an image forming apparatus capable of reducing the manufacturing cost of the image forming apparatus. be able to.

1 is a schematic configuration diagram of a printer according to an embodiment. It is a block diagram of the printer of FIG. 1 including a controller. FIG. 2 is an explanatory diagram around a transfer unit in FIG. 1. It is explanatory drawing of the voltage application to the transfer unit of FIG. It is explanatory drawing of the voltage application to the conventional transfer unit.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 schematically shows the structure of a printer 1 for monochrome printing which is an example of an image forming apparatus. The cross section shown in FIG. 1 is seen from the left side of the printer 1. Therefore, the front surface of the printer 1 is located on the right side of FIG.

As shown in FIG. 1, a paper discharge tray 36 is provided above the apparatus main body 2 of the printer 1, and a plurality of operation keys used for various operations by the user are provided near the paper discharge tray 36. A front cover 5 on which a screen for displaying various types of information is arranged is provided.
A sheet feeding cassette 4 is disposed below the apparatus main body 2, and a sheet of paper (recording material) is stored in the storage unit 40 in a stacked state.

As shown in FIG. 1, a paper feed roller 46 is provided on the upper right side of the accommodating portion 40, and the paper is sent toward the upper right side of the paper feed cassette 4. It is vertically transported upward along the front surface of the printer 1 inside.
Further, the paper feed cassette 4 is configured to be able to be pulled out to the front side of the printer 1, that is, in the right direction in FIG. 1, and in this pulled out state, a new sheet can be replenished to the storage section 40. The paper can be replaced with another type of paper.

Inside the apparatus main body 2, a conveyance roller 10, a registration roller 14, an image forming unit 16, and a transfer unit 30 are sequentially arranged on the downstream side when viewed in the sheet conveyance direction from the sheet feeding cassette 4.
The image forming unit 16 is provided with a single photosensitive drum (image carrier) 18, which is rotatably installed and is driven counterclockwise in FIG. 1 by a drum motor. Note that the photosensitive drum 18 of this embodiment is an a-Si drum having an amorphous silicon-based layer on the surface thereof.

  As shown in FIG. 1, an exposure unit 15 is provided on the left side of the photosensitive drum 18, and laser light is emitted from the exposure unit 15 toward the photosensitive drum 18. As shown in FIG. 1, a charging device 20, a developing device 24, a transfer roller 31 of the transfer unit 30 and a cleaning unit 25 are provided at appropriate positions around the photosensitive drum 18.

The charger 20 of this embodiment is located obliquely above and to the left of the photosensitive drum 18 as shown in FIG. 1, and has a charging roller that contacts the photosensitive drum 18 and a rubbing roller that polishes and rubs the surface of the charging roller. Then, the surface of the photosensitive drum 18 is charged.
The developing device 24 is disposed obliquely below and to the left of the photosensitive drum 18 and has a developing roller that faces the photosensitive drum 18. This developing roller is driven clockwise by a developing motor in FIG.

A black toner container 23 is disposed between the exposure unit 15 and the paper feed cassette 4.
Here, the transfer unit 30 of this embodiment has a transfer belt 50 that attracts and conveys paper with electrostatic force as will be described later (FIGS. 2 and 3), and the transfer belt 50 is obliquely below the photosensitive drum 18. It is arranged and travels clockwise as viewed in FIGS.

  The transfer belt 50 is configured to be able to press against the photosensitive drum 18 from the lower right side via the transfer roller 31. The transfer belt 50 and the photosensitive drum 18 form a nip portion for transferring a toner image onto a sheet. The transfer roller 31 of the present embodiment is configured with a size of about 14 mm in diameter, in which EPDM foam rubber is formed on a metal shaft (about 8 mm in diameter), and the back surface of the transfer belt 50 faces the photosensitive drum 18. Pressing.

In addition, a fixing unit 32, a discharge branching unit 34, and a discharge roller 35 are sequentially arranged on the downstream side of the transfer unit 30 when viewed in the sheet conveyance direction (FIG. 1).
In this embodiment, the transfer unit 30 and the manual feed tray 3 are provided with a transfer unit 48 that can be pulled out with respect to the apparatus main body 2 together with the transfer unit 30, and on the front side of the apparatus main body 2 as viewed from the transfer unit 48. A double-sided printing conveyance path 38 is formed. The duplex printing conveyance path 38 branches from the discharge branching portion 34 on the front side of the apparatus main body 2 and extends downward, and is connected to the upstream side of the registration roller 14.

  As the transfer belt 50 described above, an endless belt in which both end portions of a rubber sheet material are overlapped and joined, or a seamless belt without a seam, is used, as shown in FIG. The driving roller 52 disposed on the registration roller 14 side and the driven roller 54 disposed on the upper fixing unit 32 side are placed in parallel and run clockwise in an inclined state.

For example, acrylonitrile butadiene rubber (NBR) is used for the rubber sheet material, and the surface thereof is coated with a fluorine-based coating (for example, PTFE) in order to improve the releasability of the toner.
Further, the triboelectric charging characteristic of the transfer belt 50 has a reverse polarity relationship with the triboelectric charging characteristic of the toner adhering to the electrostatic latent image on the photosensitive drum 18.

  Then, a voltage having a polarity opposite to that of the toner attached to the electrostatic latent image is applied between the transfer belt 50 and the photosensitive drum 18 as will be described later. In other words, if the toner used in this embodiment is a positively chargeable toner, when a voltage having a polarity opposite to that of the toner is applied to the transfer belt 50, the positively chargeable toner on the photosensitive drum 18 is It moves away from the photosensitive drum 18 and basically goes to the paper on the transfer belt 50.

  Here, on the conveying surface of the transfer belt 50, positively charged toner separated from the photosensitive drum 18 or negatively charged toner generated due to an increase in the surface potential of the photosensitive drum 18 as residual toner. May adhere. In addition, the positively chargeable toner may include the same positively chargeable residual toner that is gradually charged up by the rotation of the transfer belt 50.

Therefore, the bias cleaning unit (cleaning means) 57 in FIG. 3 removes the residual toner remaining on the conveyance surface of the transfer belt 50.
The bias cleaning unit 57 of this embodiment includes a cleaning roller 58, a blade 59, a cleaning roller driving unit (bias control unit) 39 of FIGS.

The cleaning roller 58 is disposed in the vicinity of the downstream side of the driven roller 54 when viewed in the traveling direction of the transfer belt 50 (FIG. 3), and collects residual toner adhering to the conveyance surface on which the paper is placed by electrostatic force to convey the conveyance surface. Remove from.
Specifically, the cleaning roller 58 is made of metal (for example, SUS430) and extends in the width direction of the transfer belt 50 so as to be rotatable. Further, the cleaning roller 58 rotates counterclockwise in FIG. 3 at a speed (linear speed ratio: for example, 1.2 to 2.0) higher than that of the transfer belt 50, and moves in the trail direction on the conveyance surface of the transfer belt 50. Abut.

The blade 59 is made of urethane, extends in the width direction of the transfer belt 50, and contacts the cleaning roller 58 in the counter direction on the side opposite to the conveyance surface.
Further, a voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image on the photosensitive drum 18 is applied between the cleaning roller 58 and the transfer belt 50 from the cleaning roller driving unit 39. An electric field is generated from the conveyance surface 50 toward the cleaning roller 58.

As a result, the positively chargeable toner adhering to the conveyance surface of the transfer belt 50 is collected from the conveyance surface and adheres to the cleaning roller 58. Residual toner adhering to the cleaning roller 58 is scraped off by a blade 59 and collected in a collection container.
On the other hand, the cleaning assisting unit 60 is disposed in the vicinity of the upstream side of the driving roller 52 in the traveling direction of the transfer belt 50 and extends in the width direction of the transfer belt 50 so as to be rotatable.

The cleaning assisting unit 60 is configured by a brush whose frictional charging characteristic has a relationship opposite to that of a regular charged toner (negative charging property in this embodiment). Then, it rotates clockwise in FIG. 3 at the same speed as the transfer belt 50 (linear speed ratio: 1.0), and abuts against the transport surface of the transfer belt 50 in the counter direction.
As a result, even if the negatively chargeable toner adhering to the transport surface passes through the cleaning roller 58, it is disturbed by the cleaning assisting unit 60 and is all adjusted to positively chargeable toner.

A sheet is placed near the registration roller 14 on the transport surface on which the prepared positively charged toner is adhered, and is directed to the photosensitive drum 18.
Next, when a voltage having a polarity opposite to that of the toner is applied to the transfer belt 50, the positively chargeable toner on the photosensitive drum 18 moves away from the photosensitive drum 18 toward the paper, but adheres to the transfer surface of the transfer belt 50. The positively charged toner that has been applied does not go to the back side of the paper but continues to adhere to the transport surface.

According to the bias cleaning unit 57, an electric field from the conveying surface to the cleaning roller 58 is generated by the cleaning roller driving unit 39, which is the high-pressure substrate. Therefore, the positively charged toner that continues to adhere to the conveying surface is removed. The toner can be collected from the conveyance surface, and residual toner is difficult to accumulate on the subsequent conveyance surface.
Note that reference numeral 55 in FIG. 3 is a support table, and a density sensor capable of detecting toner on the transfer belt 50 is installed on the support table 55.

By the way, in this embodiment, when transferring the toner image on the photosensitive drum 18 to a sheet, voltage is not applied to the transfer roller 31 but voltage is applied to the entire transfer belt 50 including the driving roller 52 and the driven roller 54. Applied.
Specifically, due to the bias applied to the cleaning roller 58 by the cleaning roller driving unit 39 described above, the output current from the cleaning roller 58 flows in the order of the transfer belt 50, the sheet, and the photosensitive drum 18. The positively chargeable toner above is not only collected from the conveying surface, but the positively chargeable toner on the photosensitive drum 18 is also directed toward the paper.

More specifically, the transfer belt 50 of this embodiment has a volume resistance value set to the sixth power to the ninth power Ω · cm, and a volume resistance value of a general electrostatic chuck belt from the tenth power to the eleventh power Ω · cm. Has been lowered slightly.
Further, as shown in FIG. 4, in addition to the transfer roller 31, the driving roller 52 and the driven roller 54 are not grounded, and are configured in a floating state with respect to the grounded photosensitive drum 18. The driving roller 52, the driven roller 54, and the transfer roller 31 are electrically connected to the transfer belt 50.

  2, when the toner image on the photosensitive drum 18 is transferred onto the sheet, the bias cleaning unit 57 causes the potential of the entire transfer belt 50 to be transferred to the photosensitive drum 18. A cleaning bias applying signal for making the potential higher than the potential is output to the cleaning roller driving unit 39.

Further, the cleaning bias controller 92 of this embodiment sets the voltage applied to the cleaning roller 58 by constant current control.
As a result, when a voltage (minus) of, for example, about 2 kV is applied to the cleaning roller 58 that collects residual toner, a voltage (minus) of, for example, about 1 kV is applied to the entire transfer belt 50. The potential is lower than the potential of the cleaning roller 58 but higher than the potential of the photosensitive drum 18 (0 kV), and the positively chargeable toner on the photosensitive drum 18 can be electrostatically transferred to the sheet.

  The cleaning bias control unit 92 outputs a cleaning bias application signal to the cleaning roller driving unit 39 so that the timing of voltage application to the cleaning roller 58 is slightly earlier than the transfer timing to the paper. On the other hand, when the sheet is sent toward the fixing unit 32 and is not electrostatically attracted, the cleaning bias control unit 92 temporarily stops voltage application to the cleaning roller 58. This is to avoid toner charge-up. Note that a bias opposite to that at the time of transfer / cleaning may be applied when the transfer belt 50 makes one turn.

  Returning to FIG. 1 again, when the printer 1 performs printing, the paper feed roller 46 separates and feeds the paper from the paper feed cassette 4 one by one. The fed paper reaches the registration roller 14 from the transport roller 10. The registration roller 14 feeds the paper to the transfer unit 30 at a predetermined paper feed timing while correcting the oblique feeding of the paper and measuring the image transfer timing with the toner image formed by the image forming unit 16. .

On the other hand, the input port 91 in FIG. 2 is configured to be able to receive image data as a printing source from the outside. This image data is data in which various images such as characters, codes, figures, symbols, diagrams, and patterns are converted into data. Based on this data, the controller 90 controls laser light irradiation and the like.
Specifically, after the surface of the photosensitive drum 18 is neutralized, the charger 20 charges the surface of the photosensitive drum 18.

Next, when the exposure unit 15 irradiates the surface of the photosensitive drum 18 with laser light, an electrostatic latent image is formed on the surface of the photosensitive drum 18, and a black toner image is formed from the electrostatic latent image. .
This toner image is transferred onto a sheet conveyed by the transfer belt 50. The toner remaining on the surface of the photosensitive drum 18 is removed by the cleaning unit 25, and the residual toner and the like adhering to the conveyance surface of the transfer belt 50 is removed by the bias cleaning unit 57.

Subsequently, the sheet is fed toward the fixing unit 32 with an unfixed toner image carried thereon, and is heated and pressed by the fixing unit 32 to fix the toner image. Thereafter, the sheet sent from the fixing unit 32 is discharged to the discharge tray 36 via the discharge roller 35 and stacked in the height direction.
When double-sided printing is performed on this single-sided printing, the conveyance direction of the paper discharged from the fixing unit 32 is switched by the discharge branching unit 34.

That is, the sheet printed on one side is pulled back into the apparatus main body 2 and conveyed to the duplex printing conveyance path 38. Subsequently, the sheet is sent toward the upstream side of the registration roller 14 and is sent again toward the transfer unit 30. As a result, the toner image is transferred to the surface of the paper that has not been printed.
As described above, according to the present exemplary embodiment, the transfer belt 50 is a belt that electrostatically conveys and conveys paper, and can easily be prevented from being wrapped around the photosensitive drum 18, so that the paper separation property is improved. In addition, since it can be conveyed while being adsorbed until the next fixing, it contributes to stabilizing the performance of a high-speed machine or the like.

  Here, when a transfer bias having a polarity opposite to that of the toner adhering to the electrostatic latent image on the photosensitive drum 18 is applied to the transfer belt 50, the toner image is transferred onto the sheet. On the other hand, the toner moving from the photosensitive drum 18 toward the sheet can adhere to the conveyance surface of the transfer belt 50 in addition to the sheet, but the remaining toner adhered to the conveyance surface is static on the photosensitive drum 18. When a cleaning bias having a polarity opposite to that of the toner attached to the electrostatic latent image is applied to the transfer belt 50 side, the toner is collected by the bias cleaning unit 57.

The cleaning bias control unit 92 according to the present embodiment does not apply a transfer bias only to the transfer roller 31 at the time of transfer onto the sheet, but includes a transfer belt 50 including the transfer roller 31, the drive roller 52, and the driven roller 54. A cleaning bias that also serves as a transfer bias is applied to the entirety.
Specifically, the cleaning bias control unit 92 is a voltage having a polarity opposite to that of the toner attached to the electrostatic latent image with respect to the bias cleaning unit 57, and the potential of the entire transfer belt 50 is the potential of the photosensitive drum 18. A signal for applying a higher voltage is output to the cleaning roller drive unit 39.

  As a result, the output current from the cleaning roller 58 flows through the transfer belt 50 to the sheet and then to the photosensitive drum 18, and between the bias cleaning unit 57 and the photosensitive drum 18, toward the photosensitive drum 18. Since a gradually decreasing voltage gradient is formed, the residual toner can be collected by the bias cleaning unit 57, so that the backside of the paper can be prevented and the toner image can also be transferred to the paper.

Further, a conventional high voltage substrate that applies a voltage only to the transfer roller 31 can be omitted.
This point will be described in detail. In order to facilitate understanding, configurations having equivalent functions are denoted by the same reference numerals, and FIG. 5 shows a conventional transfer unit 30. In this configuration, the high-pressure substrate 38 is connected to the transfer roller 31. When a voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image is applied between the photosensitive drum 18 and the photosensitive drum 18, the toner on the photosensitive drum 18 is separated from the photosensitive drum 18 and applied to the sheet on the transfer belt 50. Head.

  On the other hand, in FIG. 5, in addition to the photosensitive drum 18, the driving roller 52 and the driven roller 54 are also grounded, and the high-voltage substrate 39 is interposed between the cleaning roller 58 and the driving roller 52 and the driven roller 54. A voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image is applied, and residual toner remaining on the transfer surface of the transfer belt 50 is collected by the cleaning roller 58.

That is, according to the structure shown in FIG. 5, two high voltage substrates, ie, a high voltage substrate 38 for applying a transfer bias and a high voltage substrate 39 for applying a cleaning bias are required.
However, according to the structure of the present embodiment shown in FIG. 4 described above, transfer bias to the paper is applied from the bias cleaning unit 57 in combination with setting of the resistance value of the transfer belt 50 and the like.

As a result, if only the cleaning roller driving unit 39, which is a high-pressure substrate for applying a cleaning bias to the transfer belt 50, is provided, the high-voltage substrate 38 in FIG. 4 can be omitted, and the manufacturing cost of the printer 1 can be reduced. it can.
Further, the transfer roller 31 and the driving and driven rollers 52 and 54 are all floated with respect to the GND, so that the potential of the entire transfer belt 50 is formed substantially the same, and the remaining toner is collected and transferred to the sheet. Can be implemented reliably.

  Further, in the constant voltage control, if the resistance value of the transfer belt 50 changes due to, for example, variations during manufacturing or deterioration during durability, there is a concern that a current necessary for transferring to a sheet or collecting remaining toner cannot be obtained. There is. However, if the output current from the cleaning roller 58 is controlled to be constant by constant current control, the gradually decreasing voltage gradient toward the photosensitive drum 18 can be maintained, so that the remaining toner can be collected and transferred to the sheet more reliably. Can be implemented.

Furthermore, the transfer belt 50 is used when the paper is conveyed vertically, and the paper is more stable in posture than the case where the paper is held only by the photosensitive drum 18 and the transfer roller 31, and the next fixing unit 32. This contributes to the favorable operation of the printer 1.
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims.

For example, in the above-described embodiment, the positively charged toner is described as a regular charged toner. However, the present invention can also be applied to a case where a negatively charged toner is used as a regular charged toner.
In the above embodiment, an example in which a printer is embodied as an image forming apparatus is shown. However, the image forming apparatus according to the present invention can naturally be applied to a multifunction machine, a copier, a facsimile machine, and the like.

  In any of these cases, similar to the above, the manufacturing cost of the image forming apparatus can be reduced.

1 Printer (image forming device)
16 Image forming unit 18 Photosensitive drum (image carrier)
30 Transfer Unit 31 Transfer Roller 39 Cleaning Roller Drive Unit (Bias Control Unit)
50 Transfer Belt 52 Drive Roller 54 Driven Roller 57 Bias Cleaning Unit (Cleaning Unit)
90 controller 92 cleaning bias control section (bias control means)

Claims (4)

An image carrier having an image carrier, developing an electrostatic latent image on the image carrier with toner, and forming a toner image;
A belt member that is wound around rollers, and has a recording material placed on its conveying surface and travels between the image carrier and the transfer roller, and has a polarity opposite to that of the toner adhering to the latent image. A transfer belt that directly transfers the toner image to the recording material by applying a voltage of
Cleaning means for recovering residual toner adhering to the conveying surface using electrostatic force;
The toner image is directly transferred to the recording material by applying a voltage having a polarity opposite to that of the toner and increasing the potential of the entire transfer belt to be higher than that of the image carrier. And a bias control means for collecting the residual toner. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the image carrier is grounded, and both the transfer roller and the transfer belt running roller are in a floating state with respect to a ground position. The image forming apparatus according to claim 1, wherein
The bias control unit causes the cleaning unit to apply a voltage having a polarity opposite to that of the toner by constant current control, which increases the potential of the entire transfer belt as compared with the image carrier. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The recording material is conveyed vertically from below to above, and the transfer belt is inclined between a driving roller disposed on the lower side and a driven roller disposed on the upper side. An image forming apparatus that is rotated.

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