JP5865829B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an intermediate transfer member on which a toner image formed on an image carrier is primarily transferred, and a second transfer device for secondary transfer of the toner image transferred to the intermediate transfer member to a recording medium. The present invention relates to an image forming apparatus including a next transfer member.

  Conventionally, an image carrier such as a photosensitive member on which a toner image is formed on the surface, and an intermediate transfer belt (intermediate transfer member) on which toner images formed on the image carrier by rotating in synchronization with the image carrier are primarily transferred. ) And a secondary transfer roller (secondary transfer member) for transferring the toner image transferred to the intermediate transfer belt onto the transfer paper (recording medium), and separating the transfer paper from the intermediate transfer belt to a fixing device There is known an image forming apparatus that conveys the image to the surface.

  In this image forming apparatus, a paper jam phenomenon (jam) may occur when the transfer paper after the secondary transfer is wound around the intermediate transfer belt without being separated from the intermediate transfer belt. In order to improve this, a method in which a separating member for separating the transfer paper from the intermediate transfer belt is provided downstream of the nip portion between the intermediate transfer belt and the secondary transfer roller in the transfer paper transport direction. . In this method, the transfer sheet is separated from the intermediate transfer belt by discharging the transfer sheet with a separating member.

  An image forming apparatus provided with a separation member that neutralizes the transfer paper is disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-151867. In Patent Document 1, a photo sensor for detecting the type of transfer paper is provided, and the position of the separation member is changed according to the type of transfer paper. Then, by setting the charge removal amount according to the type of transfer paper, the winding of the transfer paper around the intermediate transfer belt is suppressed.

JP 2006-251664 A

  However, the conventional image forming apparatus and the image forming apparatus disclosed in Patent Document 1 have the following problems. That is, in recent years, with the increase in the speed of the apparatus, the condition range in which the transfer paper can be stably conveyed is narrowed. For this reason, there is a problem in that the transfer paper may skew (skew) between the secondary transfer nip (nip between the intermediate transfer belt and the secondary transfer roller) and the fixing device. When the transfer paper is skewed, jamming is likely to occur. Note that the skew of the transfer paper is more likely to occur when thin paper is used or when the apparatus is in a high temperature and high humidity environment.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing skew feeding of a recording medium.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier on which a toner image is formed on a surface, an intermediate transfer member on which a toner image formed on the image carrier is primarily transferred, and an intermediate transfer A secondary transfer member that is arranged in pressure contact with the body and is secondarily transferred to the recording medium, and a recording medium transported more than the nip portion between the intermediate transfer body and the secondary transfer member. A separation member that is disposed downstream of the recording medium and separates the recording medium from the intermediate transfer member, and a power supply circuit that applies a bias to the separation member, and the separation member intermediates the recording medium by applying a bias. Two or more toners are provided along the direction perpendicular to the recording medium conveyance direction and separated from the transfer body, and the toner in the direction perpendicular to the recording medium conveyance direction of the toner image transferred to the recording medium Separation according to quantity distribution Each of the wood, the bias is applied independently of each other.

  According to the present invention, two or more separation members are provided along a direction perpendicular to the recording medium conveyance direction, and a bias is applied to each of the separation members independently of each other. Thus, the bias applied to one side and the other side in the direction perpendicular to the recording medium conveyance direction can be adjusted, so that the bias on one side and the other side in the direction perpendicular to the recording medium conveyance direction can be adjusted. The conveyance speed of the recording medium can be adjusted.

  Further, according to the amount of toner of the toner image transferred to the recording medium, the difficulty of separating the recording medium from the intermediate transfer member changes, and the conveyance speed of the recording medium also changes. Therefore, as described above, according to the toner amount distribution, it is possible to appropriately adjust the conveyance speed between the one side and the other side of the recording medium by independently applying a bias to each of the separation members. it can. As a result, it is possible to suppress the skew of the recording medium and to suppress the occurrence of jam.

1 is a cross-sectional view schematically showing the structure of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which showed the structure of the secondary transfer nip part periphery of one Embodiment of this invention. FIG. 3 is a plan view showing a structure around a secondary transfer nip portion according to an embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  The structure of the image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. In the main body of the image forming apparatus 100 (here, a color printer), four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming units Pa to Pd are provided with photosensitive drums (image carriers) 1a, 1b, 1c and 1d for carrying visible images (toner images) of the respective colors, and further, driving means (FIG. An intermediate transfer belt (intermediate transfer member) 8 that rotates clockwise in FIG. 1 is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d. Thereafter, the toner image primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a transfer sheet P as an example of a recording medium by the action of a secondary transfer roller (secondary transfer member) 9. Further, the transfer paper P onto which the toner image is secondarily transferred is discharged from the main body of the image forming apparatus 100 after the toner image is fixed in the fixing device 13. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P on which the toner image is secondarily transferred is housed in a paper cassette 16 disposed at the lower part of the main body of the image forming apparatus 100, and is transferred to the secondary transfer roller via the paper feed roller 12a and the registration roller pair 12b. 9 and the intermediate transfer belt 8 are conveyed to the nip portion. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing units 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing units 3a to 3d is filled with a predetermined amount of a two-component developer containing toners of cyan, magenta, yellow, and black. If the ratio of the toner in the two-component developer filled in each of the developing units 3a to 3d is less than a specified value due to the formation of a toner image, which will be described later, each developing from the toner containers (replenishing units) 4a to 4d. The toner is supplied to the units 3a to 3d. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing units 3a to 3d and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure device 5. A toner image is formed.

  The primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and cyan, magenta, yellow, and yellow on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, the toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning units 7a to 7d.

  The intermediate transfer belt 8 is stretched over an upstream driven roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the intermediate transfer belt 8 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. Then, the full color image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P on which the toner image is secondarily transferred is conveyed to the fixing device 13.

  The transfer paper P conveyed to the fixing device 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper P, thereby forming a predetermined full color image. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when forming images on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing device 13 is once projected from the discharge roller pair 15 to the outside of the device. Then, after the trailing edge of the transfer paper P has passed through the branch portion 14, the discharge roller pair 15 is rotated in the reverse direction and the transport direction of the branch portion 14 is switched. As a result, the transfer paper P is distributed from the rear end to the paper transport path 18 and is transported again to the secondary transfer nip portion with the image surface reversed. Then, the next toner image formed on the intermediate transfer belt 8 is secondarily transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9. The transfer paper P onto which the toner image has been secondarily transferred is conveyed to the fixing device 13 where the toner image is fixed and then discharged onto the discharge tray 17.

  Next, the detailed structure around the secondary transfer nip portion will be described with reference to FIGS. 2 shows a state viewed from the back side of FIG. 1, and the arrangement of each member is reversed from that of FIG.

  As shown in FIG. 2, the secondary transfer roller 9 is disposed in pressure contact with the drive roller 11 with the intermediate transfer belt 8 interposed therebetween. On the downstream side (upper side in FIG. 2) of the transfer paper conveyance direction (recording medium conveyance direction) from the nip portion (secondary transfer nip portion) between the intermediate transfer belt 8 and the secondary transfer roller 9, the transfer paper P is placed in the middle. A metal separating plate (separating member) 20 for separating from the transfer belt 8 is disposed.

  The separation plate 20 is disposed on the secondary transfer roller 9 side with respect to the passing position of the transfer paper P, and is disposed above the secondary transfer roller 9. When a bias is applied to the separation plate 20, an electric field is generated around the separation plate 20. Since the transfer paper P that has passed through the secondary transfer nip portion is charged to a predetermined potential, an electric field generated around the separation plate 20 generates a force that pulls the transfer paper P toward the secondary transfer roller 9, and the transfer paper P P is separated from the intermediate transfer belt 8. Note that when the bias applied to the separation plate 20 is increased, the force for pulling the transfer paper P becomes stronger.

  Further, as shown in FIG. 3, two or more separation plates 20 (two in the present embodiment) are provided along the direction perpendicular to the transfer paper conveyance direction (direction in which the secondary transfer roller 9 extends) (X direction). ) Is provided. A power supply circuit 21 is connected to the separation plate 20. The power supply circuit 21 can individually control the bias applied to the separation plate 20, and the bias is applied to each of the separation plates 20 independently of each other.

  Further, as shown in FIG. 2, the toner image transferred to the transfer paper P is located upstream of the secondary transfer nip portion in the transfer paper transport direction (lower side in FIG. 2) with respect to the transfer paper transport direction. A sensor 22 is provided for detecting the amount of toner on one side and the other side in the vertical direction (X direction). Specifically, two or more sensors 22 are arranged along the direction (X direction) perpendicular to the transfer sheet conveyance direction (two in the present embodiment) while being arranged below the intermediate transfer belt 8. Is provided. That is, one sensor 22 is provided for each separation plate 20 as shown in FIG.

  The sensor 22 detects the toner amount per predetermined area by detecting the toner density of the toner image transferred to the intermediate transfer belt 8. Specifically, the sensor 22 irradiates the toner image transferred to the intermediate transfer belt 8 with measurement light and detects the amount of reflected light from the toner image. As the sensor 22, an optical sensor generally including a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is used. When the amount of toner is large, the reflected light from the belt surface is blocked by the toner, so that the amount of light received by the light receiving element decreases. On the other hand, when the amount of toner is small, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element. The sensor 22 is a density sensor for performing density correction and color misregistration correction of the toner image transferred to the intermediate transfer belt 8, and is also mounted in a conventional image forming apparatus.

  The sensors 22 are arranged at a predetermined interval in the X direction. The sensors 22 are arranged at both ends of the passing area of the transfer paper P having a minimum size (for example, A5R size) of the standard paper used in the image forming apparatus 100. Thereby, for example, it is possible to detect the toner amounts at two locations in the X direction with respect to the transfer paper P from A3 size to A5R size.

  Each sensor 22 detects the toner density of the toner image transferred to the intermediate transfer belt 8, and outputs a detection signal corresponding to the toner amount calculated from the detection result to a control unit (not shown). As a result, the control unit controls the output of the power supply circuit 21 so that there is no difference in the transfer speed of the transfer paper P on both sides in the X direction. In this way, the bias applied to the separation plate 20 is controlled according to the output of the sensor 22.

  For example, when the amount of toner in the toner image is large on one side in the X direction, the portion on one side in the X direction of the transfer paper P is not easily separated from the intermediate transfer belt 8, so The power supply circuit 21 is controlled so as to increase the applied bias. Thereby, the bending of the transfer paper P toward the intermediate transfer belt 8 is suppressed on one side in the X direction. Further, when the toner amount of the toner image is small on one side in the X direction, a portion on one side in the X direction of the transfer paper P is easily separated from the intermediate transfer belt 8 and is easily bent toward the separation plate 20 side. The power supply circuit 21 is controlled so that the bias applied to the side separation plate 20 is reduced. Thereby, the bending of the transfer paper P toward the secondary transfer roller 9 is suppressed on one side in the X direction. The same applies to the other side in the X direction. Then, by adjusting the deflection of the transfer paper P on one side and the other side in the X direction, a difference in the conveyance speed of the transfer paper P on the one side and the other side in the X direction is suppressed.

  In the present embodiment, as described above, two or more separation plates 20 are provided along a direction (X direction) perpendicular to the transfer paper conveyance direction, and each of the separation plates 20 is independent of each other. A bias is applied. Thereby, since the bias applied to one side and the other side in the X direction can be adjusted, the conveyance speed of the transfer paper P on one side and the other side in the X direction can be adjusted.

  Further, according to the toner amount of the toner image transferred to the transfer paper P, the difficulty of separating the transfer paper P from the intermediate transfer belt 8 changes, and the transfer speed of the transfer paper P also changes. For this reason, as described above, according to the amount of toner on one side and the other side, a bias is applied to each of the separation plates 20 independently of each other, so Can be adjusted appropriately. As a result, it is possible to suppress the skew of the transfer paper P between the secondary transfer nip portion and the fixing device 13, and it is possible to suppress the occurrence of a jam.

  Further, as described above, by providing the sensor 22 for detecting the toner amount on one side and the other side in the X direction, the toner amount on one side and the other side in the X direction can be easily detected. Then, by controlling the bias applied to each separation plate 20 in accordance with the output of the sensor 22, it is possible to easily suppress the transfer paper P from being skewed and to easily suppress the occurrence of a jam. Can do.

  As described above, the sensor 22 detects the toner density of the toner image, and calculates the toner amount based on the detection result. As a result, the toner amount distribution of the toner image in the X direction can be accurately detected by the sensor 22.

  As described above, the sensor 22 is a density sensor for performing density correction and color misregistration correction of the toner image transferred to the intermediate transfer belt 8. Thus, since the toner amount can be detected by the existing density sensor (sensor 22), it is not necessary to separately provide a sensor for detecting the toner amount.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, although an example in which the present invention is applied to a tandem type color image forming apparatus as shown in FIG. 1 is shown, the present invention is not limited to this. Needless to say, the present invention can be applied to various image forming apparatuses including an intermediate transfer member and a secondary transfer member, such as a monochrome copying machine, a monochrome printer, a digital multifunction peripheral, and a facsimile machine.

  In the above embodiment, an example in which an intermediate transfer belt is used as an intermediate transfer member has been described. However, the present invention is not limited to this, and a drum-shaped intermediate transfer member may be used, for example.

  In the above-described embodiment, the example using the sensor 22 that detects the toner density of the toner image transferred to the intermediate transfer belt has been described. However, the present invention is not limited to this. The printing rate on one side and the other side of the toner image transferred to the transfer paper may be calculated from the image data used for exposure, and the toner amount distribution in the X direction may be calculated based on the printing rate. In this case, the calculated toner amount may be slightly different from the actual toner amount as compared with the method using the sensor 22, but the toner amount distribution in a wider region can be easily detected.

  In the above embodiment, an example in which two separation members are provided has been described. However, four or more separation members may be provided along a direction perpendicular to the transfer paper conveyance direction. In this case, as many sensors as the separating members may be provided. Further, when the toner amount is derived (calculated) from the image data, it is not necessary to increase the number of sensors. Therefore, when four or more separation members are provided, it is preferable to derive the toner amount from the image data. Also, for example, for a postcard size image that cannot be read by the sensor, the toner amount is calculated from the image data, and for an image size that can be read by the sensor, the toner amount is calculated from the sensor detection result. For example, the sensor and the image data can be used together.

1a to 1d Photosensitive drum (image carrier)
8 Intermediate transfer belt (intermediate transfer member)
9 Secondary transfer roller (secondary transfer member)
20 Separation plate (separation member)
21 Power supply circuit 22 Sensor (concentration sensor)
100 Image forming apparatus P Transfer paper (recording medium)

Claims (2)

An image carrier on which a toner image is formed on the surface;
An intermediate transfer member to which a toner image formed on the image carrier is primarily transferred;
A secondary transfer member that is disposed in pressure contact with the intermediate transfer member and for secondary transfer of the toner image transferred to the intermediate transfer member to a recording medium;
In order to separate the recording medium from the intermediate transfer body and to prevent skewing of the recording medium, it is arranged downstream of the nip portion between the intermediate transfer body and the secondary transfer member in the recording medium conveyance direction. a separation member,
A power supply circuit for applying a bias to the separating member;
A sensor that is disposed upstream of the nip portion in the recording medium conveyance direction and detects the amount of toner transferred to the intermediate transfer member;
With
The separation member separates the recording medium from the intermediate transfer body by applying a bias, and two or more separation members are provided along a direction perpendicular to the recording medium conveyance direction.
In accordance with the toner amount distribution in the direction perpendicular to the recording medium conveyance direction of the toner image transferred to the recording medium, a bias is applied to each of the separation members independently of each other ,
One sensor is provided for each of the separation members along a direction perpendicular to the recording medium conveyance direction, and density correction or color misregistration correction of the toner image transferred to the intermediate transfer member is performed. A density sensor for detecting the toner density of the toner image,
The toner amount is calculated based on the detection result of the sensor,
The image forming apparatus , wherein when the toner amount of the toner image is large, a larger bias is applied to the separation member than when the toner amount of the toner image is small . The separating member is disposed on the secondary transfer member side with respect to the passing position of the recording medium,
When a bias is applied to the separation member, an electric field is generated around the separation member, and the electric field acts on the recording medium charged to a predetermined potential by passing through the nip portion. The image forming apparatus according to claim 1, wherein a pulling force is generated on the next transfer member side.

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