JP2012037591A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the positional deviation of an image generated when a recording body tip end enters a transfer nip and transfer tip end transfer failure without damaging an image carrier, and to obtain good transfer performance, in an image forming device which transfers a tonner image on the image carrier to a recording body by a transfer electric field formed on a transfer nip portion.SOLUTION: Immediately before transfer paper enters the transfer nip portion, a clearance is formed between an intermediate transfer belt 10 and a secondary transfer roller 23 by a conductive portion of a position regulating cam 72 and a conductive butting roller 78. During the formation of the clearance, through the position regulating cam and the butting roller, a current induced by transfer voltage is made to pass. When forming the transfer nip, an insulation sheet 81 pasted on a part in a circumferential direction of the position regulating cam and the butting roller 78 are oppositely separated.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more specifically, a transfer formed by an image carrier that carries a toner image and moves on the surface, and a contact member that abuts the surface of the image carrier. 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. A device including a gap forming means for forming a gap by separating the member from the member is described. 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 an apparatus that performs transfer by the transfer electric field formed in the transfer nip portion, generally, the transfer voltage is applied to either the image carrier or the contact member by the transfer voltage applying means before the leading end of the recording body enters the transfer nip. Is started to form a transfer electric field. 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.

  In order to solve such a problem, the present inventor disclosed in Japanese Patent Application No. 2009-030032 (hereinafter referred to as a prior application) “Transfer that starts applying a transfer voltage before the recording body enters the transfer nip portion”. In an image forming apparatus comprising a voltage applying unit and a gap forming unit that forms a gap by separating the image carrier and the abutting member immediately before the recording member enters the transfer nip portion, the image carrier is formed by the gap forming unit. Only when the gap is formed by separating the contact member and the contact member, the current induced by the transfer voltage applied by the transfer voltage applying means is made to flow between the image carrier and the contact member. An image forming apparatus characterized in that a conducting means is provided is proposed. In this image forming apparatus, even if a transfer voltage is applied while the gap is formed by separating the image carrier and the abutting member, a current induced by the transfer voltage via the conducting means is applied to the image carrier. Between the image bearing member and the contact member, 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.

  Furthermore, the above-mentioned prior application proposes a simple configuration in which the gap forming means also serves as the conduction means. Specifically, “the gap forming means is a conductive abutment provided on one of a rotation center axis for moving the surface of the image carrier and a rotation center axis for moving the surface of the contact member in the transfer nip. A member, a conductive position restricting member provided on the other side, and a position restricting member control means for controlling the position of the position restricting member. The position restricting member control means controls the position of the position restricting member to restrict the position. By abutting the member against the abutting member, the abutting member is moved in a direction to separate the image carrier and the abutting member to form a gap between the image carrier and the abutting member, and the abutting member In this proposal, the rotation center axis of the image carrier and the rotation center axis of the contact member are electrically connected via the member and the position regulating member. With such a configuration, it is possible to easily realize a gap forming unit that also serves as a conducting unit.

  In the image forming apparatus of the prior application, during the transfer of the toner image on the image carrier onto the recording medium, the eccentric cam as the position regulating member is rotated by the position regulating member control means so as to be separated from the abutting member. . As a result, the abutting member is moved in the direction in which the image carrier and the contact member come into contact with each other, and the image carrier and the contact member are brought into contact with each other to form a transfer nip. A current induced by the transfer voltage applied from the transfer voltage applying means flows through the transfer nip formed in this manner, whereby the toner image on the image carrier is transferred onto the recording medium.

  However, when the transfer nip is formed by bringing the image carrier into contact with the contact member, if the gap between the spaced apart conductive contact member and the conductive eccentric cam is small, the contact is caused by the applied transfer voltage. It was found that a leak was likely to occur between the member and the eccentric cam. When such a leak occurs, the current flowing through the transfer nip becomes unstable and good transfer characteristics may not be obtained. To prevent leakage between the abutting member and the eccentric cam, it is conceivable to increase the gap between the abutting member and the eccentric cam, but if the gap is increased, the amount of change in the radius per rotation angle of the eccentric cam Will increase and increase the rotational torque.

  On the other hand, in the configuration of the prior application, the eccentric cam is rotated in accordance with the entry / extraction of the recording medium to / from the transfer nip to control the contact / separation between the image carrier and the contact member. If this increases, the response speed of the eccentric cam becomes slow. For this reason, it becomes difficult to form a gap between the image carrier and the contact member that quickly responds to the entry / exit of the recording body into the transfer nip, and the above-described damage to the image carrier, image displacement, There is a possibility that the effect of preventing both of the leading edge transfer defects cannot be sufficiently obtained.

  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 that can satisfactorily prevent both image misregistration and image transfer failure at the time of entering a transfer nip and obtain good transfer performance.

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, and the image carrier and the corresponding contact member immediately before the recording body enters the transfer nip. In the image forming apparatus having a gap forming means for forming a gap by separating the image carrier, the gap forming means moves the surface of the abutting member and the rotation center axis for moving the surface of the image carrier in the transfer nip. Any one of the rotation center axis A conductive abutting member provided on the other side, a conductive position-regulating eccentric cam having an insulating portion on the peripheral surface provided on the other, and rotating the position-regulating eccentric cam at least at two or more locations. An eccentric cam control means for controlling the position, and the position of the eccentric cam for position regulation is controlled by the eccentric cam control means to abut the conductive portion of the eccentric cam for position regulation against the abutting member. Accordingly, the abutting member is moved in a direction in which the image carrier and the contact member are separated from each other to form a gap between the image carrier and the contact member, and the abutting member and the position A current induced by a transfer voltage applied by the transfer voltage applying means via a regulating eccentric cam is made to flow between the image carrier and the corresponding contact member, and the eccentric cam control means The position regulating eccentric cam position By controlling and separating the insulating portion of the position regulating eccentric cam in a state of facing the abutting member, the abutting member is released in a direction to release the separation between the image carrier and the corresponding contact member. A transfer nip is formed by moving the image carrier and the corresponding contact member into contact with each other.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the insulating portion of the position regulating eccentric cam is formed by an insulating sheet member.
According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the insulating portion of the position restricting eccentric cam is disposed coaxially with the position restricting eccentric cam, and the position restricting eccentric cam rotates. It is formed of an insulating member that rotates in conjunction with the motor.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first, second, and third aspects, the image carrier is belt-shaped, and the image carrier and the contact member define the transfer nip. A backup roller for supporting the belt is formed, 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.
According to a fifth aspect of the present invention, the conducting portion of the gap forming means has a volume electric resistance substantially equal to a total value of the volume electric resistances of the contact member, the image carrier, and the backup roller. It is what.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, or fifth aspect, the transfer voltage applying unit performs constant current control.
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 gap forming means immediately before the recording body is detached from the transfer nip. A gap is formed by separating the carrier and the contact member.
The invention according to claim 8 is the image forming apparatus according to any one of claims 1, 2, 3, 4, 5, 6 or 7, wherein the toner image on the image carrier is transferred onto the recording body. In the meantime, 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. It is.
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 recording body feeding unit feeds the recording nip toward the transfer nip. A recording medium information acquisition means for acquiring thickness information of the recording medium, and changing the size of the gap formed by the gap formation means according to the thickness of the recording body acquired by the recording body information acquisition means; It is a feature.

In the present invention, a conductive position regulating eccentric cam having an insulating portion on the peripheral surface and a conductive butting member are used as members constituting the gap forming means. This prevents damage between the position regulating eccentric cam and the abutting member when the position regulating eccentric cam and the abutting member are separated to form a transfer nip, and prevents damage to the image carrier. Thus, it is possible to satisfactorily prevent image positional deviation and image leading edge transfer failure.
Specifically, immediately before the recording body enters the transfer nip portion, the conductive portion of the eccentric cam for position regulation is abutted against the abutting member, and the abutting member is separated from the image bearing member and the abutting member. To form a gap between the image carrier and the contact member, thereby preventing image displacement. 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. Even if the transfer voltage is applied while the gap is formed by separating the image carrier and the abutting member in this way, the conductive portion of the eccentric cam for position regulation and the conductive abutting member are A current induced by the transfer voltage flows between the image carrier and the contact member. For this reason, leak discharge in the gap between the image carrier and the contact member can be prevented, and damage to the image carrier can be prevented.
Further, when forming the transfer nip, the insulating member of the position regulating eccentric cam is separated from the abutting member, and the abutting member is released from the abutment member. The image carrier and the contact member are brought into contact with each other by moving in the direction. Since the insulating part of the eccentric cam for position regulation and the conductive abutting member are opposed to each other, the position of the conductive part of the eccentric cam for position regulation and the conductive abutting member is opposed to each other. Leakage between the regulating eccentric cam and the abutting member can be made difficult to occur. Therefore, it is not necessary to prevent leakage by increasing the gap between the abutting member and the position regulating eccentric cam. If this gap is small, the rotational torque of the position restricting eccentric cam can be suppressed, so that a satisfactory response speed of the position restricting eccentric cam can be obtained. Therefore, it is possible to form a gap between the image carrier and the abutting member that quickly responds to the entry / exit of the recording body into the transfer nip by the gap forming means, damage to the image carrier, image displacement, Both image leading edge transfer defects can be prevented well.

  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, without causing damage to the image carrier, an image displacement that occurs when the leading edge of the recording body enters the transfer nip, and There is an excellent effect of preventing both image leading edge transfer failure and obtaining good transfer performance.

1 is a configuration diagram showing an example of an image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view in the depth direction of the image forming apparatus at a secondary transfer unit of the image forming apparatus. 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. Sectional drawing to the image forming apparatus depth direction in the secondary transfer part which concerns on a modification. Sectional drawing of the secondary transfer part during transfer nip formation concerning a modification. Sectional drawing of the eccentric cam for position control used for a modification.

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 40C, 40M, 40Y and 40K corresponding to toners of cyan, magenta, yellow and black 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 the alternating electric field, the developer is activated, the charge amount distribution of the toner 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, the toner images formed on the surface of the intermediate transfer belt 10 are collectively transferred onto a transfer sheet as a recording medium conveyed from the paper feed tray 44 of the paper feed table 200 2. A next transfer device 19 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 to visualize the electrostatic latent image, and cyan, magenta, yellow, and black single-color images are respectively formed on the photosensitive drums 40. Form. The monochromatic image is sequentially primary transferred by the primary transfer device 62 so as to be superimposed on the intermediate transfer belt 10, and a composite color image is formed 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 a conductive butting roller 78 as a butting member. The shaft end 71a, which is both ends of the shaft 71 of the backup roller 16, is provided with a conductive position regulating eccentric cam 72 that is a position regulating member. Both the abutment roller 78 and the position regulating eccentric cam 72 are disposed at both ends on the outer side in the width direction of the intermediate transfer belt 10. On the inner peripheral side of the intermediate transfer belt 10, there are an eccentric cam detecting means 79 for detecting the rotational position of the position restricting eccentric cam 72 provided at the shaft end 71 a of the backup roller 16, and a position restricting eccentric cam 72. An eccentric cam control means 80 for controlling the rotational position is provided. The eccentric cam control means 80 includes a driving force transmission means for rotating a position regulating eccentric 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.

  An insulating tape 81 is affixed to the position regulating eccentric cam 72 of the gap forming means so as to form an insulating portion in a part in the circumferential direction. The insulating tape 81 is affixed to a portion other than the portion used to contact the abutting roller 78 and form a gap between the secondary transfer roller 23 and the intermediate transfer belt 10 in the circumferential direction of the position regulating eccentric cam 72. In addition, in a state where the position regulating eccentric cam 72 and the abutting roller 78 are separated to form a transfer nip, an insulating tape 81 is disposed between them.

  The eccentric cam control means 80 rotates the position regulating eccentric cam 72 provided at the shaft end portion 71 a of the backup roller 16, and the conductive portion of the position regulating eccentric cam 72 is the shaft end portion of the secondary transfer roller 23. It abuts against the abutment roller 78 provided at 70a and presses the abutment roller 78 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 71a of the backup roller 16 rotates together with the position regulating eccentric cam 72 by the driving force transmitted by the driving force transmitting means (not shown) of the eccentric 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 eccentric cam 72 and the abutting roller 78 are separated from each other, and the secondary transfer roller 23 is pressed against the backup roller 16 via the intermediate transfer belt 10 by the pressing force of the pressure spring. . Further, the insulating sheet 81 attached to the position regulating eccentric cam 72 is controlled to a position facing the abutment roller 78.

  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 conveyed to a position immediately before the secondary transfer nip, the eccentric cam 72 for position regulation is rotated by the driving force transmission means of the eccentric cam control means 80 and abuts on the conductive portion. It strikes against the roller 78 and presses the butting roller 78 downward. The secondary transfer roller 23 is moved away from the intermediate transfer belt 10 to a position having a gap by the rotation of the position regulating eccentric 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. The transfer current induced at this time is transferred from the shaft end portion 71a of the backup roller 16 to the secondary transfer roller 23 via the conductive portion of the abutting position regulating eccentric cam 72 and the abutting roller 78. It flows to the shaft end part 70a. 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 operation explanatory diagram of the secondary transfer unit when the transfer paper P is transferred with the toner image in the secondary transfer nip. By the driving force transmission means of the eccentric cam control means 80 after the leading edge of the transfer paper P enters the secondary transfer nip until the leading edge of the image on the intermediate transfer belt 10 reaches the secondary transfer nip. The position regulating eccentric cam 72 rotates. As the position restricting eccentric cam 72 rotates, the position restricting eccentric cam 72 and the abutting roller 78 are separated from each other, and the secondary transfer roller 23 is intermediate between the transfer paper P and the pressing force of a pressure spring (not shown). It is pressed against the backup roller 16 via the transfer belt 10. 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, the eccentric sheet control means 80 controls the insulating sheet 81 attached to the position-regulating eccentric cam 72 and the abutting roller 78 to face each other in a separated state, and the insulating sheet 81 controls the conductive position. The insulation between the eccentric cam 72 and the conductive abutting roller 78 is maintained. As a result, the transfer current flows from the secondary transfer roller 23 to the backup roller 16 via the transfer paper P and the intermediate transfer belt 10. For this reason, a sufficient transfer electric field is obtained at the secondary transfer nip portion, and good transfer is possible.

  FIG. 6 is an operation explanatory diagram of the secondary transfer unit immediately before the transfer paper P is detached from the secondary transfer nip. After the transfer of the rear end portion of the image, until the rear end portion of the transfer paper P is detached from the secondary transfer nip portion, the eccentric cam for position regulation is driven by a driving force transmitting means (not shown) of the eccentric cam control means 80. 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 eccentric 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.

  Driving force transmitting means (not shown) of the eccentric cam control means 80 after the trailing edge of the transfer paper P is detached from the secondary transfer nip portion and before the next transfer paper P is conveyed to the secondary transfer nip portion. As a result, the position regulating eccentric cam 72 rotates. The position regulating eccentric cam 72 and the abutment roller 78 are separated from each other by the rotation of the position regulating eccentric cam 72, and the secondary transfer roller 23 and the transfer sheet P are intermediately transferred by the pressing force of a pressure spring (not shown). The state returns to the state of being pressed against the backup roller 16 via the belt 10.

  In this way, in order to reduce the impact when the leading edge of the transfer paper P enters the secondary transfer nip portion, the position regulating eccentric cam 72 is rotated so that the conductive portion abuts against the abutment roller 78. Thus, the secondary transfer roller 23 is separated from the intermediate transfer belt 10 to have a gap. While such a gap is formed, the transfer current induced by the voltage applying means 75 is applied to the backup roller 16 via the abutting position regulating eccentric cam 72 and the abutting roller 78. The shaft portion 71 flows from 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 being transferred onto the transfer paper P, the position regulating eccentric cam 72 is separated from the abutment roller 78, so that a sufficient transfer pressure can be obtained and good transfer can be achieved. Is possible. Further, since the insulating sheet 81 attached to the position restricting eccentric cam 72 and the abutting roller 78 face each other in a separated state, the insulation between the position restricting eccentric cam 72 and the abutting roller 78 is maintained. , Can prevent leakage.

  As a comparative example, the position regulating eccentric cam 72 does not have an insulating portion such as the insulating sheet 81 and the conductive portion of the position regulating eccentric cam 72 and the conductive abutting roller 78 are opposed to each other. If an attempt is made to ensure insulation only, the required gap amount increases as the transfer voltage increases. For example, when 5 kV is applied as a transfer voltage, a gap of about 5 mm is required. In the configuration of the present embodiment, when the position regulating eccentric cam 72, the insulating sheet 81, and the abutting roller 78 are opposed to each other to prevent leakage, it is not necessary to increase the gap to prevent leakage. . If the gap amount at the time of separating the position restricting cam 72 and the abutting roller 78 can be reduced, the amount of change in the radius around the rotation angle of the position restricting cam 72 is reduced, and the rotational speed is suppressed and the cam response speed is reduced. It is possible to increase. Therefore, it is possible to form an interval that responds quickly to the transfer paper P entering and leaving the transfer nip, and the above-described effects are sufficiently obtained.

  The insulating sheet 81 attached to the position regulating eccentric cam 72 will be described. As shown in FIG. 2, the insulating sheet 81 is affixed to the inside of the position regulating eccentric cam 72 so as to be shorter than the position regulating cam 72 in the axial direction, in order to prevent the sheet from floating or peeling off. Good to have been. In order to ensure insulation, the length of the insulating sheet 81 in the axial direction is preferably longer than the butting roller 78. As a material of the insulating sheet 81, for example, PET, silicone rubber, EPDM, Teflon (registered trademark), or the like can be considered.

  Further, the total volume resistance value of the abutting roller 78 and the conductive portion of the position regulating eccentric cam 72 is 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 be formed of a material that is substantially equivalent to the above. This is because if the electrical resistance is too high, the transfer current becomes difficult to flow through the gap forming means.

  Next, a modified example of the configuration in which the insulating portion is formed in a part in the circumferential direction of the position regulating eccentric cam 72 which is the gap forming means will be described. FIG. 7 is a cross-sectional view in the depth direction of the image forming apparatus in the secondary transfer unit according to the modification. FIG. 7 is the same as FIG. 2 except for the configuration in which the insulating portion is formed in a part of the position regulating eccentric cam 72 in the circumferential direction, and the description thereof is omitted. In the modified example, the insulating portion formed in a part of the circumferential direction of the position restricting eccentric cam 72 is coaxial with the position restricting eccentric cam 72 and rotates in conjunction with the rotation of the position restricting eccentric cam 72. The insulating member 82 is formed. FIG. 8 is a cross-sectional view of the secondary transfer portion when forming a transfer nip according to a modification. FIG. 9 is a cross-sectional view of the position regulating eccentric cam 72 used in the modification. As shown in FIG. 9, the position restricting eccentric cam 72 used in the modification is a part of the circumferential direction and abuts against the abutting roller 78 so that a gap is formed between the secondary transfer roller 23 and the intermediate transfer belt 10. A groove 72a is provided in a region other than the portion used for forming. The insulating member 82 has a shape that engages with the groove 72 a of the position regulating eccentric cam 72. As a result, when the position restricting cam 72 is rotated, the position restricting cam 72 is rotated coaxially with the rotation shaft of the position restricting cam, and the position restricting eccentric cam 72 and the abutting roller 78 are separated to form a transfer nip. In this case, an insulating member 82 is disposed between the two. With such an insulating member 82, the same effect as when the insulating sheet 81 is attached can be expected.

  The configuration of the modified example is advantageous in terms of attachment accuracy as compared with the configuration of attaching the insulating sheet 81 in FIG. It can be configured to cover wider than 72. Therefore, it is possible to improve insulation.

  As described above, the image forming apparatus according to the present embodiment has been described using the configuration in which the insulating portion is formed at one place in the circumferential direction of the position regulating eccentric cam 72, but a plurality of insulating portions may be provided.

  Further, in the image forming apparatus of the present embodiment, the intermediate transfer belt 10 is supported by the backup roller 16 as an image carrier, and a secondary transfer nip is formed by contacting with the secondary transfer roller 23 as a contact member. In the above description, the transfer voltage is applied to the shaft end 71a of the backup roller 16 by the transfer voltage applying means 75 to form the transfer electric field. The present invention is not limited to this, and in order to form a transfer electric field, the transfer voltage applying means 75 applies a transfer voltage to the shaft end portion 70a of the secondary transfer roller to form a transfer electric field. It 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, according to the image forming apparatus of the present embodiment, at least 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 in advance, image deterioration such as defective transfer at the tip is prevented. Further, by the eccentric cam control means 80 of the gap forming means, the transfer paper P is transferred by bringing the abutting roller 78 as the conductive abutting member into contact with the conductive portion of the position regulating eccentric cam 72 as the position regulating member. Immediately before entering the nip portion, the intermediate transfer belt 10 and the secondary transfer roller 23 are separated to form a gap, thereby reducing the impact when the leading end portion of the transfer paper P enters the secondary transfer nip portion. Further, image quality deterioration due to fluctuations in the surface moving speed of the intermediate transfer belt 10 is prevented. While the gap is formed in this way, the current induced by the transfer voltage flows through the conductive portion of the contacting position regulating eccentric cam 72 and the conductive abutting roller 78, so that the intermediate transfer is performed. There is no leakage discharge between the belt 10 and the secondary transfer roller 23. Therefore, there is no possibility of damaging the intermediate transfer belt 10 due to leak discharge. Further, when forming the transfer nip, the eccentric cam control means 80 separates the insulating portion of the position regulating eccentric cam 72 in a state of facing the abutting roller 78, so that it is separated from the intermediate transfer belt 10. The transfer roller 23 is brought into contact. Since the insulating portion of the position restricting eccentric cam 72 and the conductive abutting roller 78 are opposed to each other, a leak between the position restricting eccentric cam 72 and the abutting member 78 can be made difficult to occur. Therefore, it is not necessary to prevent leakage by increasing the gap between the abutting roller and the position regulating eccentric cam 72. If this gap is small, the rotational torque of the position restricting eccentric cam 72 can be suppressed, so that a good response speed of the position restricting eccentric cam 72 can be obtained. Therefore, the gap forming means can form a gap between the intermediate transfer belt 10 and the secondary transfer roller 23 that quickly responded to the transfer paper P entering and leaving the transfer nip, and damage to the intermediate transfer belt 10 and image Both the image misalignment and the image leading edge transfer failure can be prevented well.
Further, according to the image forming apparatus of the present embodiment, the insulating portion of the position restricting eccentric cam 72 is formed by the insulating sheet member 81, whereby a simple configuration can be achieved.
Further, according to the image forming apparatus of the present embodiment, the insulating portion of the position restricting eccentric cam 72 is arranged coaxially with the position restricting eccentric cam 72 and rotates in conjunction with the rotation of the position restricting eccentric cam 72. It is formed by a moving insulating member 82. Thereby, in addition to being advantageous in terms of attachment accuracy as compared with the configuration in which the insulating sheet 81 is pasted, there is no fear of peeling, and therefore the configuration covering the axial direction wider than the eccentric cam 72 for position regulation. it can. Therefore, it is possible to improve insulation.
According to the present embodiment, the image carrier is the belt-like intermediate transfer belt 10 supported by the backup roller 16, and applies a transfer voltage to the shaft portion 71 of the backup roller 16 or the secondary transfer roller 23. When such a belt-shaped image carrier is used, shock jitter is likely to occur when the transfer paper P enters the secondary transfer nip portion, so that the effect of preventing image deterioration such as defective transfer at the front end is great. .
In addition, according to the present embodiment, the conductive portion of the gap forming unit preferably has a volume electrical resistance substantially equal to the total volume electrical resistance of the backup roller 16, the intermediate transfer belt 10, and the secondary transfer roller 23. . As a result, an appropriate amount of current can flow.
Further, according to the present embodiment, it is preferable that the transfer voltage applying means 75 performs constant current control, which makes it easy to obtain good transfer performance.
Further, according to the present embodiment, 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 P is detached from the transfer nip, so that the post-transfer paper It is possible to prevent image deterioration when the end portion is detached.
Further, according to the present embodiment, while the toner image on the intermediate transfer belt 10 is transferred to the transfer paper P, the gap forming member releases the separation between the intermediate transfer belt 10 and the secondary transfer roller 23. The secondary transfer roller 23 is configured to press the intermediate transfer belt 10 through the transfer paper P. As a result, a sufficient transfer pressure can be obtained and good transfer is possible. Further, since the position regulating eccentric cam 72 and the abutting roller 78 are separated from each other and leakage is prevented, the transfer current is transferred from the backup roller 16 to the secondary transfer roller 23 via the transfer paper P and the intermediate transfer belt 10. To flow. Therefore, a sufficient transfer electric field is obtained at the secondary transfer nip 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 Eccentric cam for position regulation 74 Ball bearing 75 Application of transfer voltage Means 76 First support plate 77 Second support plate 78 Abutting roller 79 Eccentric cam detecting means 80 Eccentric cam control means 81 Insulating sheet 82 Insulating member 100 Copier body P Transfer paper

JP 2007-334292 A

Claims (9)

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. 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 image forming apparatus,
The gap forming means includes a conductive abutting member provided on one of a rotation center axis for moving the surface of the image carrier at the transfer nip and a rotation center axis for moving the surface of the contact member. A conductive position-regulating eccentric cam provided on the other surface having an insulating portion on the peripheral surface, and an eccentric cam control means for rotating the position-regulating eccentric cam to control at least two positions. And controlling the position of the eccentric cam for position regulation by the eccentric cam control means and abutting the conductive portion of the eccentric cam for position regulation against the abutting member, whereby the abutting member is The carrier and the contact member are moved away from each other to form a gap between the image carrier and the contact member, and the transfer is performed via the abutting member and the position-regulating eccentric cam. Transfer applied by voltage application means Conduction is performed so that a current induced by pressure flows between the image carrier and the corresponding contact member, and the position regulating eccentric cam is controlled by the eccentric cam control means. By separating the insulating portion of the cam in a state of facing the abutting member, the abutting member is moved in a direction to release the separation between the image carrier and the corresponding contact member, and the image carrier An image forming apparatus characterized in that a transfer nip is formed by contacting the contact member.   2. The image forming apparatus according to claim 1, wherein the insulating portion of the position regulating eccentric cam is formed of an insulating sheet member.   2. The image forming apparatus according to claim 1, wherein the insulating portion of the position restricting eccentric cam is disposed coaxially with the position restricting eccentric cam and rotates in conjunction with rotation of the position restricting eccentric cam. An image forming apparatus formed by the method described above.   4. The image forming apparatus according to claim 1, wherein the image carrier has a belt shape, and the image carrier and the contact member support the belt so as to form the transfer nip. An image forming apparatus comprising: a roller, wherein a transfer voltage is applied from the transfer voltage applying unit to a rotation center axis of the backup up roller or a corresponding contact member.   5. The image forming apparatus according to claim 1, wherein the conductive portion of the gap forming unit is 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 having a volumetric electrical resistance of   6. An image forming apparatus according to claim 1, wherein said transfer voltage applying means performs constant current control.   7. The image forming apparatus according to claim 1, wherein the gap forming unit connects the image carrier and the abutting member immediately before the recording body is detached from the transfer nip. An image forming apparatus characterized in that a gap is formed at a distance.   8. The image forming apparatus according to claim 1, wherein the gap forming member is in a state where the toner image on the image carrier is transferred onto the recording body. An image forming apparatus, wherein the image carrier is released from the contact member and the contact member presses the image carrier through the recording member.   9. The image forming apparatus according to claim 1, wherein recording material thickness information of a recording body fed toward the transfer nip is acquired by the recording body feeding unit. An image forming apparatus comprising: a body information acquiring unit, wherein a size of a gap formed by the gap forming unit is changed according to a thickness of the recording body acquired by the recording body information acquiring unit.

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