JP5397746B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like. The present invention relates to an image forming apparatus that feeds a recording medium into a nip and transfers a toner image on the image carrier onto the recording medium by a transfer electric field formed in a transfer nip portion.

  In this type of image forming apparatus, when the front end of the recording body enters the transfer nip formed by the image carrier and the contact member, or when the rear end of the recording body leaves the transfer nip, Load fluctuation occurs, and the surface moving speed of the image carrier is disturbed. As a result, so-called shock jitter causes image quality degradation due to image displacement. Such image quality deterioration is more likely to occur in a recording medium having a larger basis weight such as cardboard.

  In Patent Document 1, the image carrier is brought into contact with the image carrier at a predetermined timing immediately before the front end of the recording body enters the transfer nip where the image carrier and the contact member contact each other or just before the rear end of the recording body leaves. There is described a device provided with a gap forming means for forming a gap by separating the member. In this apparatus, a gap is formed between the image carrier and the contact member immediately before the leading end of the recording body enters or immediately before the trailing end of the recording body separates. It is possible to reduce the load fluctuation generated in the image carrier.

  In general, in an apparatus that performs transfer by a transfer electric field formed in the transfer nip portion, a transfer voltage applying means is applied to either the image carrier or the contact member before the leading end of the recording body enters the transfer nip. A transfer electric field is formed by starting to apply a transfer voltage. This is because if the transfer voltage application means starts to apply a transfer voltage after the leading edge of the recording body has entered the transfer nip, the output of the transfer voltage application means cannot be sufficiently increased until the transfer of the image leading edge starts. There is a possibility that a sufficient transfer electric field cannot be obtained at the portion. This is because in such a case, image deterioration such as transfer failure of the tip end portion occurs.

  However, if a transfer voltage is applied before the leading end of the recording body enters the transfer nip in order to prevent a transfer failure at the leading end, the image carrier formed in the apparatus of Patent Document 1 immediately before entering the transfer nip. Leakage discharge occurs in the gap between the contact member and the contact member, causing a side effect that the image carrier is damaged.

  The present invention has been made in view of the above background, and an object thereof is to form an image carrier that carries a toner image and moves on the surface, and a contact member that abuts on the surface of the image carrier. In an image forming apparatus in which a recording body is fed into a transfer nip and a toner image on the image carrier is transferred to the recording body by a transfer electric field formed in the transfer nip portion, the front end of the recording body without damaging the image carrier It is an object of the present invention to provide an image forming apparatus capable of preventing both image misalignment and image leading edge transfer failure that occur when an image enters a transfer nip.

In order to achieve the above object, the invention according to claim 1 forms an image nip that carries a toner image and moves on the surface thereof, and abuts against the surface of the image carrier while moving itself to form a transfer nip. The recording body is formed so as to form a contact member, a recording body feeding means for feeding the recording body toward the transfer nip, and a transfer electric field for transferring a toner image on the image carrier to the recording body. A transfer voltage applying means for starting to apply a transfer voltage to the image carrier or the corresponding contact member before entering the transfer nip portion; and the image carrier and the corresponding contact member immediately before the recording member enters the transfer nip portion. In an image forming apparatus provided with a gap forming means for forming a gap by separating
The current induced by the transfer voltage applied by the transfer voltage applying means is applied to the image carrier only while the gap forming means separates the image carrier and the contact member to form a gap. Conductive means is provided for electrical conduction so as to flow between the contact members.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the gap forming means has a function of the conducting means.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the gap forming means rotates the central axis for moving the surface of the image carrier in the transfer nip and the surface for moving the contact member. A conductive abutting member provided on one of the moving center shafts, a conductive position restricting member provided on the other, and a position restricting member control means for controlling the position of the position restricting member, A direction in which the abutting member is separated from the contact member by controlling the position of the position regulating member by the position regulating member control means and abutting the position regulating member against the abutting member. To form a gap between the image carrier and the corresponding contact member, and the rotation center axis of the image carrier and the rotation of the contact member through the abutting member and the position regulating member. Configured to be connected to the dynamic center axis It is an feature.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the position regulating member is an eccentric cam that can be controlled to at least two positions.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, and fourth aspects, the image carrier is belt-shaped, and the image carrier and the contact member are in the transfer state. A backup roller for supporting the belt so as to form a nip is provided, and a transfer voltage is applied from the transfer voltage applying means to the rotation center axis of the backup up roller or a corresponding contact member .
Also, the invention of claim 6 is the image forming apparatus according to claim 1, 2, 3, 4 or 5, said conducting means, said abutment member, the volume electric resistance of the image bearing member and the backup roller It has a volume electric resistance substantially equal to the total value.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, fifth and sixth aspects, the transfer voltage applying means performs constant current control. .
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, fifth, sixth, and seventh aspects, the gap forming unit is immediately before the recording body is separated from the transfer nip. The image carrier and the contact member are separated from each other to form a gap.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, fifth, sixth, seventh, or eighth aspects, the toner image on the image carrier is transferred onto the recording medium. The gap forming member releases the separation between the image carrier and the contact member, and the contact member presses the image carrier through the recording member. To do.
The invention of claim 1 0, in any one of the image forming apparatus according to claim 5, 6, 7, 8 or 9, toward the transfer nip by the recording material infeed means The recording medium information acquisition means for acquiring the thickness information of the recording body fed in, and the size of the gap formed by the gap forming means is changed according to the thickness of the recording body acquired by the recording body information acquisition means It is characterized by doing.

  In the present invention, a positional deviation of an image is prevented by forming a gap between the image carrier and the contact member immediately before the recording body enters the transfer nip portion. Further, by starting to apply the transfer voltage from the transfer voltage applying means before the recording body enters the transfer nip portion, the transfer failure of the leading end of the image is prevented. Thus, even if the transfer voltage is applied while the gap is formed by separating the image carrier and the contact member, the current induced by the transfer voltage is contacted with the image carrier via the conduction means. Since it flows between the members, there is no risk of leakage discharge in the gap between the image carrier and the contact member. Therefore, it is possible to prevent the image carrier from being damaged by the leak discharge.

  According to the present invention, the recording medium is fed into the transfer nip formed by the image carrier that carries the toner image and moves on the surface, and the contact member that contacts the surface of the image carrier, and is formed in the transfer nip portion. In an image forming apparatus that transfers a toner image on an image carrier to a recording medium by a transfer electric field, image misregistration that occurs when the leading edge of the recording medium enters the transfer nip without damaging the image carrier. In addition, it is possible to prevent both image front end transfer defects and the like.

1 is a configuration diagram showing an example of an image forming apparatus according to the present invention. Sectional drawing which shows the principal part structure of a secondary transfer part. FIG. 6 is an operation explanatory diagram of a secondary transfer unit when transfer paper is conveyed toward a secondary transfer nip. FIG. 6 is an operation explanatory diagram of the secondary transfer unit immediately before the transfer paper leading end enters the secondary transfer nip. FIG. 5 is an operation explanatory diagram of a secondary transfer unit when a transfer sheet is transferring a toner image in a secondary transfer nip. FIG. 6 is an operation explanatory diagram of the secondary transfer portion immediately before the transfer paper rear end portion is detached from the secondary transfer nip.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a configuration diagram illustrating an example of an image forming apparatus according to the present embodiment. The image forming apparatus includes a copying machine main body 100, a paper feed table 200 on which the copying machine main body 100 is placed, a scanner 300 attached on the copying machine main body 100, and an automatic document attached on the scanner 300. It is mainly composed of a transfer device (ADF) 400.

  The scanner 300 is placed on the contact glass 32 as the first traveling body 33 equipped with a document illumination light source or mirror and the second traveling body 34 equipped with a plurality of reflecting mirrors reciprocate. Scanning of a document (not shown) is performed. The scanning light sent out from the second traveling body 34 is condensed by the imaging lens 35 on the imaging surface of the reading sensor 36 disposed behind it, and then read as an image signal by the reading sensor 36.

  The copying machine main body 100 is provided with photosensitive drums 40Y, 40C, 40M, and 40K corresponding to yellow, cyan, magenta, and black toners as latent image carriers. Each means for performing an electrophotographic process such as charging, developing, and cleaning is disposed around each photosensitive drum 40, and thereby each image forming unit 18 is formed. Four image forming units 18 are arranged in parallel to form a tandem type image forming apparatus 20.

  In the developing device 61 of each image forming unit 18, the developer containing the four color toners is used. In the developing device 61, the developer carrying member carries and conveys the developer, and an alternating electric field is applied at a position facing the photoconductor drum 40 to develop the latent image on the photoconductor drum 40. By applying an alternating electric field, the developer can be activated, the toner charge amount distribution can be narrowed, and the developability can be improved. Further, the developing device 61 can be integrally supported together with the photosensitive drum 40 and can be formed detachably with respect to the main body of the image forming apparatus to form a process cartridge. In addition to this, the process cartridge may include charging means and cleaning means.

  Above the tandem type image forming apparatus 20, there is provided an exposure device 21 that forms a latent image by exposing the photosensitive drum 40 with laser light or LED light based on image information.

  Further, an intermediate transfer belt 10 made of an endless belt member is disposed at a lower position facing the photosensitive drum 40 of the tandem type image forming apparatus 20. The intermediate transfer belt 10 is supported by support rollers 14, 15 and 16. A primary transfer device 62 that transfers the toner images of the respective colors formed on the photosensitive drum 40 to the intermediate transfer belt 10 is disposed at a position adjacent to the photosensitive drum 40 via the intermediate transfer belt 10. The intermediate transfer belt 10 is provided with a cleaning device 17 for removing toner remaining on the surface thereof. The cleaning device 17 causes a cleaning blade made of, for example, a fur brush or urethane rubber to come into contact with the intermediate transfer belt 10 and scrapes off secondary transfer residual toner adhering to the intermediate transfer belt 10.

  Below the intermediate transfer belt 10, a secondary transfer device 19 that collectively transfers a toner image formed on the surface of the intermediate transfer belt 10 to transfer paper conveyed from the paper feed tray 44 of the paper feed table 200. Is arranged. The secondary transfer device 19 includes a secondary transfer roller 23, and the secondary transfer device 19 presses the secondary transfer roller 23 against the support roller 16 through the intermediate transfer belt 10, and the toner on the intermediate transfer belt 10. The image is transferred to transfer paper (not shown). Hereinafter, the support roller 16 is referred to as a secondary transfer backup roller 16.

  A conveyance belt device 29 that conveys transfer paper is provided adjacent to the secondary transfer device 19, and a fixing device 28 is provided downstream of the conveyance belt device 29. The fixing device 28 fixes the image on the transfer paper. The fixing device 28 mainly includes a fixing belt 26 that is an endless belt and a pressure roller 27 that is pressed against the fixing belt 26. A reversing device for reversing the transfer paper is disposed below the secondary transfer device 19 and the fixing device 28. The reversing device reverses the transfer paper so as to record images on both sides of the transfer paper.

Next, the operation of the image forming apparatus having the above configuration will be described.
A document is set on the document table 30 of the automatic document feeder 400 shown in FIG. 1, or the automatic document feeder 400 is opened to set a document on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed. In this state, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. When this occurs, the scanner 300 is immediately driven to cause the first traveling body 33 and the second traveling body 34 to travel. The first traveling body 33 emits light from the light source and receives reflected light from the document surface, reflects the reflected light toward the second traveling body 34, and further reflects the reflected light by the mirror of the second traveling body 34. Then, the light enters the reading sensor 36 through the imaging lens 35, and the reading sensor 36 reads the content of the document.

  Further, by pushing a start switch of the apparatus, a drive motor (not shown) is driven to rotate one of the support rollers 14, 15, and 16 and the other two support rollers are driven to rotate, thereby performing intermediate transfer. The belt 10 is rotated. At the same time, in each image forming unit 18, the photosensitive drum 40 is uniformly charged by the charger, and then charged by irradiating the writing light L from the exposure device 21 with a laser, LED, or the like according to the reading content of the scanner 300. An electrostatic latent image is formed on each photosensitive drum 40. Toner is supplied from the developing device 61 to the photosensitive drum 40 on which the electrostatic latent image is formed, the electrostatic latent image is visualized, and a single color image of black, yellow, magenta, and cyan on each photosensitive drum 40, respectively. Form. A single color image is sequentially primary transferred by the primary transfer device 62 so as to be superimposed on the intermediate transfer belt 10, thereby forming a composite color image on the intermediate transfer belt 10. Residual toner is removed from the surface of the photoreceptor drum 40 after image transfer by a photoreceptor cleaning device (not shown), and the charge is removed by a charge removal device (not shown) to prepare for another image formation.

  By pressing the start switch, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated, and the transfer paper (sheet) is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43. The paper is separated one by one by the separation roller 45 and inserted into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, abutted against the registration roller 49, and stopped. On the other hand, when the sheet is manually fed, the sheet feeding roller 50 is rotated to feed out the sheet on the manual feed tray 51, and the sheet is separated one by one by the separation roller 52 and inserted into the manual sheet feeding path 53. It stops against the roller 49. Next, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer belt 10, the sheet is fed between the intermediate transfer belt 10 and the secondary transfer device 19, and transferred by the secondary transfer device 19. Transfer the color image onto the sheet.

  The sheet carrying the unfixed toner image that has passed through the secondary transfer roller 23 is conveyed to the fixing device 28, and heat and pressure are applied by the fixing device 28 to fix the transferred image as a permanent image. The sheet after image fixing is switched by the switching claw 55 and discharged by the discharge roller 56 and stacked on the paper discharge tray 57, or switched by the switching claw 55 and introduced into the sheet reversing device, where it is reversed and again The image is guided to the transfer position, an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56. At this time, residual toner remaining on the intermediate transfer belt 10 after image transfer is removed by the cleaning device 17 to prepare for re-image formation by the tandem image forming device 20.

  Next, a secondary transfer unit by the secondary transfer device 19 that is a characteristic part of the present embodiment will be described. FIG. 2 is a cross-sectional view in the depth direction of the image forming apparatus in the secondary transfer portion of the image forming apparatus.

  The configuration of the secondary transfer unit will be described with reference to FIG. The secondary transfer roller 23 has a cylindrical conductive shaft portion 70 made of metal, and a conductive elastic layer 23 a covered on the outer peripheral surface thereof. The secondary transfer backup roller 16 includes a cylindrical conductive shaft portion 71 made of metal, and a conductive surface elastic layer 16a configured such that the shaft portion 71 is freely rotatable by a ball bearing 74. And have. Such a secondary transfer roller 23 is pressed against the secondary transfer backup roller 16 via the intermediate transfer belt 10 by a pressing force of a pressure spring (not shown) to form a secondary transfer nip. As will be described later, a transfer electric field is formed in the secondary transfer nip, and the toner image on the intermediate transfer belt 10 is transferred to transfer paper.

  The shaft end portion 70a that is both ends of the shaft portion 70 of the secondary transfer roller 23 is provided with an abutting roller 78 as an abutting member. Further, the shaft end portion 71a that is both ends of the shaft portion 71 of the backup roller 16 is provided with a position restricting cam 72 as a position restricting member. The abutting rollers 78 and the position regulating cams 72 are both disposed at both ends on the outer side in the width direction than the intermediate transfer belt 10. Further, on the inner peripheral side of the intermediate transfer belt 10, a position restricting cam detecting means 79 for detecting the rotational position of the position restricting cam 72 provided at the shaft end portion 71 a of the backup roller 16, and a position restricting cam. Position restricting cam control means 80 for controlling the rotational position of 72 is provided. The position regulating cam control means 80 includes a driving force transmitting means for rotating a position regulating cam 72 (not shown). These function as a gap forming means for forming a gap by separating the intermediate transfer belt 10 and the backup roller 16 from each other.

  The position restricting cam control means 80 rotates the position restricting cam 72 provided at the shaft end portion 71 a of the backup roller 16, and the position restricting cam 72 is provided at the shaft end portion 70 a of the secondary transfer roller 23. The butting roller 78 is abutted against the butting roller 78 and pressed downward in FIG. As a result, the secondary transfer roller 23 moves away from the backup roller 16.

  Further, the surface elastic layer 16 a and the shaft portion 71 of the backup roller 16 can be freely rotated by the ball bearings 74, and the surface elastic layer 16 a of the backup roller 16 rotates around the intermediate transfer belt 10. The shaft end portion 71a of the backup roller 16 rotates together with the position restricting cam 72 by the driving force transmitted by the driving force transmitting means (not shown) of the position restricting cam control means 80.

  Further, the shaft end portion 71a of the backup roller 16 is rotatably supported by the first support plate 76, and the shaft end portion 70a of the secondary transfer roller 23 is rotatably supported by the second support plate 77. Yes. A transfer voltage applying means 75 for applying a secondary transfer voltage is connected to the shaft end 71a of the backup roller 16, and a shaft end 70a of the secondary transfer roller 23 is connected to the ground. A secondary transfer voltage having the same polarity as the toner (negative polarity in the illustrated example) is applied to the backup roller 16 from the transfer voltage applying means 75, and the intermediate transfer belt 10 is connected to the grounded secondary transfer roller 23. A secondary transfer electric field for transferring the upper toner image onto the transfer paper is formed.

Next, the operation of the secondary transfer unit will be described.
FIG. 3 is a diagram for explaining the operation of the secondary transfer unit when the transfer paper P is conveyed toward the secondary transfer nip. When printing information is input to the image forming apparatus, the transfer paper P is conveyed toward the secondary transfer nip portion by a registration roller 49 at a timing that matches the image position on the intermediate transfer belt 10. At this time, the position regulating cam 72 and the abutting roller 78 are separated from each other, and the secondary transfer roller 23 is moved against the backup roller 16 via the intermediate transfer belt 10 by the pressing force of a pressure spring (not shown). Pressed.

    FIG. 4 is an operation explanatory diagram of the secondary transfer portion immediately before the leading end portion of the transfer paper P enters the secondary transfer nip. When the leading edge of the transfer paper P is transported to a position just before the secondary transfer nip, the position regulating cam 72 is rotated by the driving force transmitting means of the position regulating cam control means 80 to the abutment roller 78. At the end, the abutting roller 78 is pressed downward. The secondary transfer roller 23 moves to a position having a gap away from the intermediate transfer belt 10 by the rotation of the position regulating cam 72 and the pressing force of a pressure spring (not shown). As a result, the impact when the leading edge of the transfer paper P enters the secondary transfer nip is reduced, and image quality deterioration due to fluctuations in the surface movement speed of the intermediate transfer belt 10 can be suppressed.

Here, the size of the gap between the secondary transfer roller 23 and the intermediate transfer belt 10 is changed according to the thickness of the transfer paper P acquired by the transfer paper information acquisition means provided in the image forming apparatus. Is preferred. For example, when using thick paper having a basis weight of 160 to 300 [g / m ² ] of the transfer paper P, the gap amount between the surface of the secondary transfer roller 23 and the surface of the intermediate transfer belt 10 is 0 to 0.5. Set to [mm].

  In addition, a transfer voltage for transferring the image on the intermediate transfer belt 10 onto the transfer paper P is started to be applied by the voltage applying means 75 before the transfer paper P enters the secondary transfer nip portion. As a result, the output of the transfer voltage applying means is sufficiently increased before the transfer of the leading edge of the image is started, so that a sufficient transfer electric field can be formed, and image deterioration such as a leading edge transfer failure can be prevented. Further, the transfer current induced at this time flows from the shaft end portion 71a of the backup roller 16 to the shaft end portion 70a of the secondary transfer roller 23 through the abutting position regulating cam 72 and the abutting roller 78. . For this reason, leak discharge does not occur in the gap between the surface of the secondary transfer roller 23 and the surface of the intermediate transfer belt 10, and damage to the intermediate transfer belt 10 due to discharge can be prevented.

  FIG. 5 is an explanatory diagram of the operation of the secondary transfer unit when the toner image is transferred to the transfer paper in the secondary transfer nip. Driving force transmission of the position regulating cam control means 80 after the leading edge of the transfer paper P enters the secondary transfer nip portion and before the leading edge of the image on the intermediate transfer belt 10 reaches the secondary transfer nip portion. The position regulating cam 72 is rotated by the means. The position regulating cam 72 and the abutment roller 78 are separated from each other by the rotation of the position regulating cam 72, and the secondary transfer roller 23 is moved from the transfer paper P and the intermediate transfer belt 10 by the pressing force of a pressure spring (not shown). Is pressed against the backup roller 16. Therefore, when the image on the intermediate transfer belt 10 is transferred onto the transfer paper P, a sufficient transfer pressure can be obtained and good transfer can be achieved.

  At this time, since the position regulating cam 72 and the abutting roller 78 are separated from each other, the transfer current flows from the backup roller 16 to the secondary transfer roller 23 via the transfer paper P and the intermediate transfer belt 10. For this reason, a sufficient transfer electric field is obtained in the secondary transfer nip, and good transfer is possible. When the abutment roller 78 and the position regulating cam 72 are separated from each other, the gap amount between them is set to be about 3 to 5 mm depending on the shape of the cam 72. Thereby, leakage discharge due to the secondary transfer current can be prevented between the abutment roller 78 and the position regulating cam 72 during the secondary transfer. That is, if the gap is sufficiently large, discharge is prevented.

  FIG. 6 is an explanatory diagram of the operation of the secondary transfer unit immediately before the transfer paper is detached from the secondary transfer nip. After the transfer of the rear end portion of the image, the drive force transmission means (not shown) of the position control cam control means 80 is used for position control until the rear end portion of the transfer paper P is detached from the secondary transfer nip portion. The cam 72 rotates. The secondary transfer roller 23 is moved to a position having a gap from the intermediate transfer belt 10 by the rotation of the position regulating cam 72 and the pressing force of a pressure spring (not shown). For this reason, the impact when the rear end portion of the transfer paper P separates from the secondary transfer nip portion is reduced, and image quality deterioration due to fluctuations in the surface movement speed of the intermediate transfer belt 10 can be suppressed.

  The driving force transmitting means (not shown) of the cam control means 80 for position regulation after the rear end portion of the transfer paper P is separated from the secondary transfer nip portion until the next transfer paper is conveyed to the secondary transfer nip portion. ) Rotates the position regulating cam 72. The position regulating cam 72 and the abutment roller 78 are separated from each other by the rotation of the position regulating cam 72, and the secondary transfer roller 23 is moved from the transfer paper P and the intermediate transfer belt 10 by the pressing force of a pressure spring (not shown). Then, the state returns to the state of being pressed against the backup roller 16.

  Thus, in order to reduce the impact when the leading edge of the transfer paper P enters the secondary transfer nip portion, the position restricting cam 72 is rotated and abutted against the abutting roller 78 to perform secondary transfer. The roller 23 is separated from the intermediate transfer belt 10 so as to have a gap. While such a gap is formed, the transfer current induced by the voltage applying means 75 is applied to the axis of the backup roller 16 via the abutting position regulating cam 72 and the abutting roller 78. Flow from the portion 71 to the shaft portion 70 of the secondary transfer roller 23. Therefore, it is possible to prevent damage on the surface of the intermediate transfer belt 10 without causing leak discharge in the gap.

  Further, while the image on the intermediate transfer belt 10 is transferred onto the transfer paper P, the position regulating cam 72 and the abutting roller 78 are separated from each other, so that a sufficient transfer pressure is obtained and good transfer is possible. It is. Further, since the position regulating cam 72 and the abutting roller 78 are separated from each other, the transfer current flows from the backup roller 16 to the secondary transfer roller 23 via the transfer paper P and the intermediate transfer belt 10, and therefore the secondary transfer nip. A sufficient transfer electric field is obtained at the portion, and good transfer is possible.

Furthermore, the total volume resistance value of both the abutment roller 78 as the gap forming means and the position regulating cam 72 is 1.0 × 10 ^{6 to} 1.0 × 10 ¹⁰ [Ω · cm ³ ]. . Further, the total volume resistance value of the butting roller 78 and the position regulating cam 72 is substantially equal to the total volume resistance value of the secondary transfer roller 23, the intermediate transfer belt 10, and the backup roller 16. It is preferable to form with such a material.

  Here, the volume resistance value is measured by a butt forming means when a DC voltage of 1 KV is applied between the shaft end portion 71a of the backup roller 16 and the shaft end portion 70a of the secondary transfer roller 23. A current value flowing through the roller 78 and the position regulating cam 72 is measured and calculated. At this time, the backup is sufficiently performed so that current does not flow from the shaft end 71a of the backup roller 16 to the shaft end 70a of the secondary transfer roller 23 via the backup roller 16, the intermediate transfer belt 10, and the secondary transfer roller 23. The roller 16 and the secondary transfer roller 23 are separated. Alternatively, the measurement is performed after the backup roller 16 and the secondary transfer roller 23 are insulated.

  If the electrical resistance of the gap forming means is too low, when the abutting roller 78 and the position regulating cam 72 are separated from each other, leakage discharge occurs between the gaps between them, and a sufficient transfer electric field is generated at the secondary transfer nip portion. Cannot be obtained, resulting in transfer failure. If the electrical resistance of the gap forming means is too high, the transfer current does not flow through the gap forming means and does not function as a conduction means, and is formed between the secondary transfer roller 23 and the intermediate transfer belt 10. There is a risk of leak discharge in the gap. Therefore, the electrical resistance of the gap forming means is preferably in the above range. More preferably, it is substantially equal to the total volume resistance of the secondary transfer roller 23, the intermediate transfer belt 10, and the backup roller 16.

  Further, the electrical resistance of the gap forming means may be given to the butting roller 78 or the position regulating cam 72. Further, the shaft end portion 70a provided with the abutment roller 78 may be provided, or the shaft end portion 71a provided with the position regulating cam 72 may be provided. Further, the electrical resistance may be provided in a part of the gap adjusting means, or may be provided in a plurality of locations.

  As described above, in the image forming apparatus according to this embodiment, the transfer voltage applying unit 75 applies the present invention only while the gap forming unit forms the gap by separating the intermediate transfer belt 10 and the secondary transfer roller 23. A description has been given using a device that also serves as a conduction means for conducting current so that a current induced by the transfer voltage flows between the intermediate transfer belt 10 and the secondary transfer roller 23. However, the present invention is not limited to this, and a separate conducting means may be provided, and similar effects can be obtained.

  In the image forming apparatus of the present embodiment, the intermediate transfer belt is supported by the backup roller 16 as an image carrier, and a secondary transfer nip is formed by contacting the secondary transfer roller 23 as a contact member. In the above description, the transfer voltage is applied to the shaft end portion 71a of the backup roller 16 by the transfer voltage applying means 75 to form a transfer electric field. However, the present invention is not limited to this, and in order to form a transfer electric field, a transfer voltage is applied to the shaft end portion 70a of the secondary transfer roller by the transfer voltage applying means 75 to form a transfer electric field. Can be applied, and the same effect can be obtained. Further, the image carrier is not limited to the intermediate transfer belt 10 and can be applied to a drum-shaped intermediate transfer member or a photosensitive member, and similar effects can be obtained.

As described above, in the image forming apparatus of the present embodiment, at least before the transfer paper P enters the secondary transfer nip portion so as to form a transfer electric field for transferring the toner image on the intermediate transfer belt 10 to the transfer paper P. By applying a transfer voltage by the transfer voltage applying means 75, image deterioration such as a leading edge transfer failure is prevented. Further, by forming the gap by separating the intermediate transfer belt 10 and the secondary transfer roller 23 immediately before the transfer paper P enters the transfer nip portion by the gap forming means, the leading edge of the transfer paper P is subjected to the secondary transfer. The impact at the time of entering the nip portion is reduced, and image quality deterioration due to fluctuations in the surface moving speed of the intermediate transfer belt 10 is prevented. Furthermore, a conduction unit is provided that conducts so that a current induced by the transfer voltage flows between the intermediate transfer belt 10 and the secondary transfer roller 23 only while the gap is formed by the gap forming unit. As a result, the current induced by the transfer voltage while the gap is formed flows between the intermediate transfer belt 10 and the secondary transfer roller 23 via the conduction means, so that the intermediate transfer belt 10 and the secondary transfer roller No leakage discharge occurs between the first and second terminals. Therefore, there is no possibility of damaging the intermediate transfer belt 10 due to leak discharge.
In addition, since the gap forming means has the function of the conduction means, a simple configuration can be achieved and the cost can be reduced.
Further, the gap forming means includes a conductive butting roller 78 provided on the shaft end portion 70a of the secondary transfer roller 23 and a conductive position restriction provided on the shaft end portion 71a of the backup roller 16 of the intermediate transfer belt 10. Cam 72 and position control cam control means 80. The position restricting cam control means 80 of the gap forming means controls the position of the position restricting cam 72 and abuts against the abutting roller 78, so that the abutting roller 78 is brought into contact with the intermediate transfer belt 10 and the secondary transfer roller 23. The gap is formed between the intermediate transfer belt 10 and the secondary transfer roller 23 by moving in the separating direction. By this operation, the conductive position restricting cam 78 and the conductive abutting roller 78 abut against each other, so that the shaft portion 71 of the backup roller 16 and the secondary transfer roller 23 are interposed via the position restricting cam 78 and the abutting roller 78. The shaft portion 70 conducts, and a current induced by the transfer voltage flows between the intermediate transfer belt 10 and the secondary transfer roller 23. With such a configuration, it is possible to easily realize a gap forming unit that also serves as a conducting unit.
Further, by using the position restricting cam 72 which can be controlled to at least two positions as the position restricting member, it can be easily realized.
The image carrier is a belt-like member supported by the backup roller, and applies a transfer voltage to the shaft portion 71 of the backup up roller 16 or the secondary transfer roller 23. When such a belt-shaped image carrier is used, a shock jitter is likely to occur when the transfer paper enters the secondary transfer nip portion. Therefore, the present invention can prevent image deterioration such as transfer failure at the leading edge. Is big.
The electrical resistance of the gap forming means is preferably a volume electrical resistance of 1.0 × 10 ^{6 to} 1.0 × 10 ¹⁰ [Ω · cm ³ ]. If the electrical resistance of the gap forming means is too low, when the abutting roller 78 and the position regulating cam 72 are separated from each other, leakage discharge occurs between the gaps between them, and a sufficient transfer electric field is generated at the secondary transfer nip portion. Cannot be obtained, resulting in transfer failure. If the electrical resistance of the gap forming means is too high, the transfer current does not flow through the gap forming means and does not function as a conduction means, and is formed between the secondary transfer roller 23 and the intermediate transfer belt 10. There is a risk of leak discharge in the gap. Therefore, the electrical resistance of the gap forming means is preferably in the above range.
Furthermore, the electrical resistance of the gap forming means preferably has a volume electrical resistance substantially equal to the total volume electrical resistance of the secondary transfer roller 23, the intermediate transfer belt 10 and the backup roller 16.
Further, the transfer voltage applying means performs constant current control, so that good transfer characteristics can be obtained.
Further, the gap forming means forms the gap by separating the intermediate transfer belt 10 and the secondary transfer roller 23 immediately before the transfer paper is released from the transfer nip, thereby forming an image when the rear end of the transfer paper is released. Deterioration can be prevented.
Further, while the toner image on the intermediate transfer belt 10 is transferred to the transfer paper, the gap forming member releases the separation between the intermediate transfer belt 10 and the secondary transfer roller 23, and the secondary transfer roller 23 transfers the toner image. The intermediate transfer belt 10 is configured to be pressed through paper. As a result, a sufficient transfer pressure can be obtained and good transfer is possible. Further, since the position regulating cam 72 and the abutting roller 78 are separated from each other, the transfer current flows from the backup roller 16 to the secondary transfer roller 23 via the transfer paper P and the intermediate transfer belt 10, and therefore the secondary transfer nip. A sufficient transfer electric field is obtained at the portion, and good transfer is possible.
Further, the recording medium information acquisition means for acquiring the thickness information of the transfer paper fed toward the transfer nip is provided, and the gap formed by the gap formation means according to the thickness of the recording medium acquired by the recording body information acquisition means. Change the size. Thereby, it is possible to prevent shock jitter more effectively.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 16 Secondary transfer backup roller 18 Image forming unit 19 Secondary transfer device 20 Tandem type image forming device 23 Secondary transfer roller
40 Photosensitive drum 49 Registration roller 70 Shaft portion of secondary transfer roller 70a Shaft end portion of secondary transfer roller 71 Shaft portion of backup roller 71a Shaft end portion of backup roller 72 Position restricting cam 74 Ball bearing 75 Transfer voltage applying means 76 First Support Plate 77 Second Support Plate 78 Abutting Roller 79 Position Restriction Cam Detection Means 80 Position Restriction Cam Control Means 100 Copying Machine Main Body P Transfer Paper

JP 2007-334292 A

Claims (10)

An image carrier that carries the toner image and moves on the surface, a contact member that abuts against the surface of the image carrier while moving on its surface, and forms a transfer nip, and sends the recording member toward the transfer nip Before the recording body enters the transfer nip, the image carrier or the corresponding contact is formed so as to form a transfer electric field for transferring the recording body feeding means and the toner image on the image carrier to the recording body. An image provided with transfer voltage applying means for starting to apply a transfer voltage to the member and gap forming means for forming a gap by separating the image carrier from the contact member immediately before the recording body enters the transfer nip portion. In the forming device,
While the gap forming means separates the image carrier and the contact member to form a gap, a current induced by the transfer voltage applied by the transfer voltage applying means corresponds to the image carrier. An image forming apparatus comprising: a conduction unit configured to conduct between a contact member and the contact member.   2. The image forming apparatus according to claim 1, wherein the gap forming unit functions as the conduction unit.   3. The image forming apparatus according to claim 2, wherein the gap forming means is either one of a rotation center axis that moves the surface of the image carrier in the transfer nip and a rotation center axis that moves the surface of the contact member. A conductive abutting member provided; a conductive position restricting member provided on the other; and position restricting member control means for controlling the position of the position restricting member; By controlling the position of the restricting member and abutting the position restricting member against the abutting member, the abutting member is moved in a direction in which the image bearing member and the contact member are separated from each other. A gap is formed between the contact member and the rotation center axis of the image carrier and the rotation center axis of the contact member are electrically connected via the abutting member and the position regulating member. Image forming apparatus characterized in that   4. The image forming apparatus according to claim 3, wherein the position regulating member is an eccentric cam that can be controlled to at least two positions.   5. The image forming apparatus according to claim 1, wherein the image carrier has a belt shape and supports the belt so that the image carrier and the contact member form the transfer nip. An image forming apparatus comprising: a backup roller configured to apply a transfer voltage from the transfer voltage applying unit to a rotation center axis of the backup up roller or a corresponding contact member. 6. The image forming apparatus according to claim 1, wherein the conducting means has a volume electric resistance substantially equal to a total value of volume electric resistances of the contact member, the image carrier, and the backup roller. An image forming apparatus comprising: The image forming apparatus according to claim 2, 3, 4, 5 or 6, the transfer voltage application means an image forming apparatus and performs constant current control. The image forming apparatus according to claim 3, 4, 5, 6 or 7, the said gap forming means immediately before the recording medium is detached from the transfer nip, the image carrier and the contact member An image forming apparatus characterized in that a gap is formed by separating them from each other. The image forming apparatus according to claim 7 or 8, while the toner image on the image carrier is transferred onto a recording medium, said gap forming member The image forming apparatus is configured to release the separation between the image carrier and the contact member, and the contact member presses the image carrier through the recording body. The image forming apparatus according to claim 5, 6, 7, 8 or 9, acquires thickness information of the recording medium to be fed toward the transfer nip by the recording material infeed means An image forming apparatus comprising: a recording body information acquiring unit configured to change a size of a gap formed by the gap forming unit according to a thickness of the recording body acquired by the recording body information acquiring unit.

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