JP2008096715A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can form an excellent image by reducing a rotational load generated in an image carrier. <P>SOLUTION: The image forming apparatus is provided with: an intermediate transfer belt 2 which carries a toner image and is rotated; an opposing roller 6 and a transfer roller 7 which transfer the toner image carried by the intermediate transfer belt 2 on a sheet 8; and a transfer section gap forming member supporting member 11 and a transfer section gap forming member 12 which form a gap between the intermediate transfer belt 2 and the transfer roller 7 at a predetermined timing. The image forming apparatus is further provided with: an opposing roller side cylindrical member 41 and a transfer roller side cylindrical member 42 which hold the transfer section gap forming member 12 and the transfer section gap forming member 12 which are arranged at both ends of the opposing roller 6 and the transfer roller 7; and a transfer section torque limiter 13 which drives the transfer section gap forming member supporting member 11 and the transfer section gap forming member 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that employs an image forming method such as an electrophotographic method, an electrostatic recording method, an ionography method, and a magnetic recording method for recording on a single-sheet recording medium. More specifically, the present invention relates to an image forming apparatus that suppresses speed fluctuations of an image carrier and an intermediate transfer member.

  Conventionally, in this type of image forming apparatus, when an image is not formed on the image carrier, at least one of the image carrier and the pressure roll is moved by a driving force from a driving unit that rotationally drives the image carrier. Using the urging force of the urging means that presses the image carrier and the pressure roll in synchronization with the timing at which the recording medium enters between the pressure contact portions of the image carrier and the pressure roll. A device that releases the separation of the press contact portion is known (for example, see Patent Document 1).

  In addition, the recording member enters the pressure contact portion between the image carrier and the transfer member by pushing down the transfer member with a push-down amount corresponding to the thickness of the recording medium to provide a gap between the image carrier and the transfer member. An image carrier that suppresses the speed fluctuation of the image carrier that is sometimes generated is known (for example, see Patent Document 2).

Also, an image carrier that is formed when the recording medium enters the pressure contact portion between the image carrier and the transfer member by forming a concave groove in the image carrier or the transfer member to form a gap that is narrower than the thickness of the recording medium. Is known in which the speed fluctuation is suppressed (for example, see Patent Document 3).
JP-A-6-274051 JP-A-4-242276 Japanese Utility Model Publication No. 56-47639

  However, since the press contact portion is separated until the recording medium enters, the one described in Patent Document 1 can be expected to suppress the rotational load of the image carrier when the recording medium enters, but the press contact portion When the separation is released, the image carrier, the recording medium, and the transfer roller collide with each other with a certain urging force, which causes a problem that a rotational load is generated on the image carrier and causes image deterioration.

  Further, the one disclosed in Japanese Patent Application Laid-Open No. H10-228707 depresses the transfer member by a depressing amount corresponding to the thickness of the recording medium so that a gap is provided between the image carrier and the transfer member, so that the speed when the recording medium enters is increased. The effect of reducing fluctuations is considered to be obtained regardless of the thickness of the recording medium, but it must be equipped with a device that detects the thickness of the recording medium, or it must be driven by determining the adjustment amount according to the thickness of the recording medium. As a result, there is a problem that the apparatus is expensive and complicated.

  In addition, the one described in Patent Document 3 forms a gap using a concave groove, and it can be expected that the rotational load of the image carrier when the recording medium enters is suppressed. Since the image carrier or the transfer member is in contact with only the provided part, there is a problem that stress concentration locally occurs only in that part, and plastic deformation may occur during long-term use. .

  In general, in a conventional image forming apparatus employing an electrophotographic method, the leading end of the recording paper enters the nip area of the transfer method in which the transfer roller presses and transfers the recording paper to the image carrier side. In this case, there is a problem that the conveyance speed of the image carrier is temporarily reduced, and the phenomenon becomes more prominent as the recording paper is thicker. In particular, in recent years, the distance from the registration roller to the pressure contact portion of the transfer roller has become shorter due to a demand for downsizing of the apparatus, and thus the speed fluctuation of the image carrier has become more problematic than before.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reducing the rotational load generated on an image carrier and performing good image formation.

  An image forming apparatus according to the present invention includes an image carrier that carries and rotates a toner image, a roller-shaped transfer member that transfers a toner image carried by the image carrier to a recording medium, and the image carrier at a predetermined timing. A gap forming means for forming a gap between the transfer member and the transfer member, the gap forming means being arranged at both ends of the transfer member, a clamping means for clamping the gap forming member, and the gap It has a gap forming member driving means for driving the forming member.

  With this configuration, it is possible to form a gap between the image carrier and the transfer member by holding the gap forming member with the holding means, and further, the shape and material of the gap forming member and the holding means are appropriately set. As a result, the amount of the gap can be adjusted freely and accurately.

  In the image forming apparatus according to the aspect of the invention, the transfer member may include a transfer roller that rotates in contact with the image carrier, and a counter roller that is disposed to face the transfer roller. The transfer roller-side cylindrical member disposed coaxially with the transfer roller, and the opposed-roller side cylindrical member disposed coaxially with the opposed roller.

  With this configuration, the transfer roller side cylindrical member and the counter roller side cylindrical member are rotated by obtaining a driving force from the counter roller shaft or the transfer roller shaft. During this, the gap forming member can be smoothly wound.

  In the image forming apparatus of the present invention, the opposed roller side cylindrical member rotates independently of the opposed roller, and the transfer roller side cylindrical member rotates integrally with the transfer roller.

  With this configuration, by rotating the cylindrical member on the transfer roller side integrally with the transfer roller shaft, it is possible to obtain power for winding the gap forming member between the opposed roller side cylindrical member and the transfer roller side cylindrical member. . Also, by rotating the counter roller side cylindrical member independently with respect to the counter roller shaft, this occurs in the counter roller side cylindrical member when the gap forming member is wound between the counter roller side cylindrical member and the transfer roller side cylindrical member. Can be prevented from propagating to the opposing roller shaft and the image carrier. Furthermore, even if there is a linear velocity difference between the surfaces of the opposed roller side cylindrical member and the transfer roller side cylindrical member, the effect of the linear velocity difference is absorbed because the opposed roller side cylindrical member and the opposed roller shaft rotate independently. .

  In the image forming apparatus of the present invention, the counter roller side cylindrical member rotates independently of the counter roller, and the transfer roller side cylindrical member rotates via a damper member between the transfer roller shaft. It is characterized by doing.

  With this configuration, the cylindrical member on the transfer roller side is rotated about the transfer roller shaft via the damper member, so that power for entraining the gap forming member between the opposing roller side cylindrical member and the transfer roller side cylindrical member is obtained. And the load torque generated in the transfer roller side cylindrical member when the gap forming member is wound between the counter roller side cylindrical member and the transfer roller side cylindrical member is prevented from propagating to the transfer roller shaft. it can. Further, since the opposed roller side cylindrical member is rotated independently with respect to the opposed roller shaft, it is generated in the opposed roller side cylindrical member when the gap forming member is wound between the opposed roller side cylindrical member and the transfer roller side cylindrical member. It is possible to prevent the load torque from propagating to the opposed roller shaft and the image carrier.

  In the image forming apparatus of the present invention, the diameter of the transfer roller side cylindrical member is smaller than the diameter of the counter roller side cylindrical member.

  With this configuration, the diameter of the cylindrical member on the transfer roller side is made smaller than the diameter of the cylindrical member on the counter roller side, so that the gap forming member is wound between the counter roller side cylindrical member and the transfer roller side cylindrical member. It is possible to prevent the load torque generated in the opposed roller side cylindrical member from being propagated to the opposed roller shaft and the image carrier.

  In the image forming apparatus of the present invention, the surface friction coefficient of the transfer roller side cylindrical member is larger than the surface friction coefficient of the counter roller side cylindrical member.

  With this configuration, it is possible to increase the winding force when the transfer portion gap forming member 12 is wound between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42, and the transfer portion gap forming member 12 can be reliably prevented from slipping. It is possible to entrain between the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42.

  The image forming apparatus of the present invention further includes an image forming unit that primarily transfers an image onto the surface of the image carrier, and the transfer member uses the image that is primarily transferred onto the surface of the image carrier as the recording medium. It is characterized by secondary transfer.

  With this configuration, a so-called intermediate transfer tandem configuration in which the toner image formed by the image forming unit is primarily transferred to the image carrier and then secondarily transferred from the image carrier to the recording medium is used in the image forming apparatus. It is possible to prevent the load torque generated in the opposed roller side cylindrical member from being propagated to the opposed roller shaft and the image carrier when the gap forming member is wound between the transfer roller side cylindrical member.

  The present invention can provide an image forming apparatus capable of reducing the rotational load generated on the image carrier and performing good image formation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIGS. 1 to 11 are diagrams showing a first embodiment of an image forming apparatus according to the present invention, and show an embodiment in which the image forming apparatus according to the present invention is applied to a color laser copying machine. Yes.

  FIG. 1 is a schematic configuration diagram of the image forming apparatus 50. In the figure, an image forming apparatus 50 includes a printer unit 100, a paper feeding unit 200, a scanner unit 300 fixed to the upper part of the printer unit 100, an automatic document feeder (hereinafter referred to as ADF) 400, and the like. Control means (not shown) for controlling the operation of the apparatus is provided.

  The scanner unit 300 reads image information of a document placed on the contact glass 301. The printer unit 100 includes an intermediate transfer unit 101 and an exposure device, an image forming unit, a fixing unit, a toner supply device, and the like, and the paper feeding unit 200 includes a plurality of paper feeding cassettes, a paper conveyance path, and the like.

  FIG. 2 is a cross-sectional view of the intermediate transfer unit 101. In the figure, an intermediate transfer belt 2 as an image carrier is stretched by a driving roller 3, a driven roller 4, a tension roller 5, and a counter roller 6, and is driven clockwise by the driving roller 3 in the figure. It has become. A transfer roller 7 is provided below the counter roller 6 so as to be movable in the vertical direction. The transfer roller 7 is pressed against the counter roller 6 by the urging force of the compression spring 9.

  A paper thickness detection sensor 20 and a registration part paper passage detection sensor 25 are provided in the path between the paper supply unit 200 and the registration roller 23 and the registration pressure roller 24. During the transfer operation, the paper supply unit The sheet 8 is fed from 200 and temporarily stands by the registration roller 23 and the registration pressure roller 24. When the toner images formed by the plurality of photosensitive drums 1 are primarily transferred to the intermediate transfer belt 2, the registration roller 23 is driven by a drive motor (not shown) to synchronize with the leading end of the toner image on the intermediate transfer belt 2. The sheet 8 is conveyed to the pressure contact portion between the opposing roller 6 and the transfer roller 7, and the toner image carried by the intermediate transfer belt 2 is secondarily transferred to the sheet 8 by the pressure applied by the compression spring 9 and a transfer bias (not shown). . That is, the image forming apparatus 50 of the present embodiment has an intermediate transfer tandem configuration. The opposing roller 6 and the transfer roller 7 constitute a transfer unit 112, and the registration roller 23 and the registration pressure roller 24 constitute a registration unit 113. Further, the transfer bias may be applied by either the counter roller 6 or the transfer roller 7.

  3 and 4 are a perspective view and a cross-sectional view of the transfer portion 112, respectively. As shown in the figure, the transfer unit 112 is disposed at both ends of the transfer roller 7 and a transfer unit gap forming member 12 that forms a gap between the opposing roller 6 and the transfer roller 7 at a predetermined timing. And a transfer part gap forming member support member 11 that supports the forming member 12.

  A transfer portion torque limiter 13 is press-fitted into the transfer portion gap forming member 12, and a transfer roller shaft 10 is inserted into the transfer portion torque limiter 13. The rotational torque of the transfer roller shaft 10 is limited by the torque limiter 13. Thus, it is transmitted to the transfer part gap forming member 12. For this reason, the transfer portion gap forming member support member 11 is subjected to a rotational torque that rotates about the transfer roller shaft 10 as a rotation center. The torque limiting characteristic of the transfer unit torque limiter 13 is controlled so that the transfer unit gap forming member support member 11 does not rotate by a transfer unit solenoid 15 and a transfer unit ratchet 14 driven by the transfer unit solenoid 15 described later. Even so, the rotation of the transfer roller shaft 10 is set so as not to be affected.

  Opposite roller side cylindrical members 41 for sandwiching the transfer portion gap forming member 12 are arranged at both ends of the opposing roller 6, and the opposing roller side cylindrical member 41 is interposed via a bearing 43 with respect to the opposing roller shaft 17. Is provided. As the bearing 43, for example, a sliding bearing made of resin having a low friction coefficient is suitable. On the other hand, a transfer roller side cylindrical member 42 for sandwiching the transfer portion gap forming member 12 is disposed at both ends of the transfer roller 7, and the transfer roller side cylindrical member 42 is press-fitted into the transfer roller shaft 10. It is in the state. Thus, the opposed roller side cylindrical member 41 is configured to rotate independently of the opposed roller shaft 17 via the bearing 43, and the transfer roller side cylindrical member 42 is integrated with the transfer roller shaft 10. It is configured to rotate at. This is because even if the diameters of the transfer roller 7 and the counter roller 6 are the same, the rotational speeds of the transfer roller shaft 10 and the counter roller shaft 17 are different due to the elastic deformation of the transfer roller 7. When both the cylindrical member 41 and the transfer roller side cylindrical member 42 are press-fitted into the opposed roller shaft 17 and the transfer roller shaft 10, respectively, a linear velocity difference is generated between the surfaces of the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. This is because of this.

  In the present embodiment, the transfer portion gap forming member 12 is wound and sandwiched between the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42, and the transfer roller 7 resists the pressure applied by the compression spring 9. Since a constant driving force is required for at least one of the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42 to push down the roller, the driving force is obtained from the transfer roller shaft 10. Therefore, the transfer roller side cylindrical member 42 is the driving side, and the opposing roller side cylindrical member 41 is the driven side.

  The counter roller side cylindrical member 41 is the driven side because the load torque when the transfer portion gap forming member 12 is inserted between the counter roller side cylindrical member 41 and the transfer roller side cylindrical member 42 is the counter roller shaft. This is to prevent the load torque that has propagated to 17 and propagated to the opposed roller shaft 17 from being transmitted to the photosensitive drum 1 via the intermediate transfer belt 2. That is, in the present embodiment, when the opposed roller side cylindrical member 41 is the driven side, when the transfer portion gap forming member 12 is inserted between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. The toner image is first transferred from the photosensitive drum 1 to the intermediate transfer belt 2 by preventing a load torque from being applied to the opposing roller 6 that stretches the intermediate transfer belt 2 and causing a running load of the intermediate transfer belt 2. Will not be adversely affected.

  Further, as the material of the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42, there is no occurrence of eccentricity or shake that may cause the eccentricity or shake to adversely affect the rotation of the opposed roller 6 and the transfer roller 7. As such, a light material such as a resin is desirable.

  Further, in order to allow the transfer portion gap forming member 12 to be caught between the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42 without slipping, the surface friction of the transfer roller side cylindrical member 42 which is the drive side. The coefficient needs to be higher than the surface friction coefficient of the opposed roller side cylindrical member 41 which is the driven side. In the present embodiment, the surface layer of the transfer roller side cylindrical member 42 is generally used for a sheet conveying roller or the like. The ethylene propylene rubber used is used.

  The material constituting the transfer portion gap forming member 12 is preferably a flexible sheet material. When the transfer portion gap forming member 12 is sandwiched between the opposing roller 6 and the transfer roller 7, it is necessary to be in close contact with both rollers, and thus sufficient flexibility is required. This is because the flatness of the film needs to be ensured. As the flexible sheet material, for example, a polymer material such as polyethylene terephthalate (PET), polycarbonate (PC), polyamide (nylon), polyimide (PI) is suitable, and polyimide (PI) is particularly a mechanical property. And is preferable. In addition, there are phosphor bronze strips, beryllium copper strips, etc. that are supplied to the market as metal thin plates if they are sheet materials made of metal materials, but stainless steel strips are excellent in mechanical properties and are convenient for precipitation. There is a hardening type SUS631-CSP, but austenite type SUS631-CSP and SUS304-CSP are most excellent in consideration of repeated fatigue. Moreover, as a manufacturing method which is easy to process into a desired thickness, it can also be manufactured with nickel foil by an electroforming method.

  Further, as shown in FIG. 6, the resist part gap forming member 27 and the resist part gap forming member support member 26 in the resist part 113 are transferred to the transfer part gap forming member 12 and the transfer part gap forming member support member 11 in the transfer part 112. Therefore, the resist unit 113 may have the same configuration as the transfer unit 112 shown in FIGS.

  FIG. 5 shows a control unit 114 that controls the transfer unit 112 and the resist unit 113. The control unit 114 includes a transfer unit paper passage detection sensor 19, a registration unit paper passage detection sensor 25, a microprocessor 21, a transfer unit solenoid drive circuit 22, a transfer unit solenoid 15, a registration unit solenoid drive circuit 32, And a resist unit solenoid 29. In the control unit 114 configured as described above, the microprocessor 21 detects the rush of the paper 8 into the transfer unit 112 by the transfer unit paper passage detection sensor 19 and the rear end of the paper 8 from the transfer unit 112. When it is detected that the transfer has been lost, the transfer portion solenoid drive circuit 22 drives the transfer portion solenoid 15. Further, the microprocessor 21 drives the registration unit solenoid 29 by the registration unit solenoid drive circuit 32 when the registration unit sheet passage detection sensor 25 detects the trailing end of the sheet 8 from the registration unit 113. That is, in the three cases, when the leading edge of the paper 8 enters the transfer section 112, when the trailing edge of the paper 8 comes out of the transfer section 112, and when the trailing edge of the paper 8 comes out of the registration section 113, the transfer section 112 is used. Alternatively, a gap is formed in the resist portion 113 to suppress the speed fluctuation of the intermediate transfer belt 2. Here, the detection of the entry of the sheet 8 into the transfer unit 112 is not limited to the configuration performed by the transfer unit sheet passage detection sensor 19. For example, the distance between the transfer unit 112 and the registration unit 113 is as follows. Since it is constant, the registration part paper passage detection sensor 25 detects the leading or trailing edge of the paper 8 from the registration part 113 and the amount of paper 8 sent out by the registration resist roller 23 and the resist pressure roller 24. The timing of the entry of the paper 8 into the transfer unit 112 can be acquired. Therefore, the transfer section paper passage detection sensor 19 is not an essential component.

  Next, the operation of the image forming apparatus 50 configured as described above will be described. 6 to 10 show a control state of the rotational movement of the transfer part gap forming member support member 11, and show side views of the transfer part 112 and the resist part 113. FIG. FIG. 11 is a flowchart for explaining the operation of the control unit 114 shown in FIG.

  At the time of printing standby, as shown in FIG. 6, the transfer unit solenoid drive circuit 22 and the registration unit solenoid drive circuit 32 are turned off, and the transfer unit ratchet 14 and the registration unit ratchet 28 include the transfer unit compression spring 16 and the registration unit. Since it is pushed up by the compression spring 30, the movement of the transfer part gap forming member support member 11 and the resist part gap forming member support member 26 is stopped. At the start of printing, the intermediate transfer belt 2 is driven, and the transfer roller shaft 10 rotates accordingly. However, since the transfer portion ratchet 14 is pushed up by the transfer portion compression spring 16, the transfer portion gap forming member support member 11 is driven. The movement is stopped. At this time, the transfer portion torque limiter 13 shown in FIG. 4 does not affect the transfer roller shaft 10 due to the suppression of the rotational movement of the support member. Even when the registration roller 23 is driven and the conveyance of the paper 8 is started, the registration portion ratchet 28 is pushed up by the registration portion compression spring 30, so that the movement of the registration portion gap forming member support member 26 is stopped. . Similarly, in the registration portion, the rotational movement of the registration roller 23 is not affected by a torque limiter (not shown).

  That is, at the time of printing standby, the control unit 114 determines whether or not the thick paper mode is selected (step S1), and if it is the thick paper mode, determines whether or not there is a print request (step S2). Further, when there is a print request, the control unit 114 starts driving the intermediate transfer belt 2 (step S3).

  As shown in FIG. 7, when the thick paper mode is selected by the user, when the transfer section paper passage detection sensor 19 detects the passage of the leading edge of the paper 8, as shown in FIG. The transfer portion solenoid 15 is driven by the circuit 22 and the transfer portion ratchet 14 is pulled. As a result, the suppression of the rotational movement of the transfer part gap forming member support member 11 is released, and the driving force of the opposing roller shaft 10 is transmitted to the transfer part gap forming member support member 11 via the transfer part torque limiter 13. The axis 10 moves around the center of rotation. Thereafter, before the sheet 8 enters the pressure contact portion of the transfer portion 112 due to the rotation of the transfer portion gap forming member support member 11, a gap is formed at the pressure contact portion of the transfer portion 112 by the transfer portion gap forming member 12, and the intermediate transfer The speed fluctuation of the belt 2 is suppressed. When the transfer portion solenoid drive circuit 22 is turned off, the transfer portion ratchet 14 is again pushed up by the urging force of the transfer portion compression spring 16, and the transfer portion gap forming member support member 11 is rotated once and returned to its original position. The movement of the transfer part gap forming member support member 11 is suppressed. When the thick paper mode is not selected, the transfer unit solenoid drive circuit 22 is kept off and stands by, and printing is performed in an image forming cycle of plain paper in which the transfer unit gap forming member 12 is not inserted.

  That is, at the time of entry of the sheet transfer pressure contact portion, the control unit 114 determines whether or not it is detected that the leading edge of the sheet 8 has entered the transfer unit 112 (step S4). The transfer unit solenoid 15 is turned on (step S5). When the transfer unit solenoid 15 is turned on, the transfer unit ratchet 14 is pulled down and the transfer unit gap forming member support member 11 rotates once. Next, the control unit 114 turns off the transfer unit solenoid 15 (step S6). When the transfer unit solenoid 15 is turned off, the transfer unit ratchet 14 is pushed up, and when the transfer unit gap forming member support member 11 that has completed one rotation returns to the original position, the transfer unit ratchet 14 is moved to the transfer unit gap forming member. The rotation of the support member 11 is prevented.

  As shown in FIG. 8, when the registration part paper passage detection sensor 25 detects the passage of the rear end of the paper 8 when the paper registration roller pressure contact part comes off, the registration part solenoid drive circuit 32 drives the registration part solenoid 29. The resist portion ratchet 28 is pulled. As a result, the same operation as described above is performed in the registration section, and the registration section gap forming member 27 is inserted into the registration section 113 before the trailing edge of the paper 8 completely comes out of the registration section 113. The acceleration of the pressure roller 24 and the trailing edge of the paper 8 is reduced. When the resist unit solenoid drive circuit 32 is turned off, the same operation as described above is performed. When the resist unit gap forming member support member 26 is rotated once and returned to the original position, the resist unit gap forming member support member 26 It will suppress the movement.

  That is, when the sheet registration roller pressure contact part is removed, the control unit 114 determines whether or not it has been detected that the rear end of the sheet 8 has been removed from the registration unit 113 (step S7). If detected, the registration unit solenoid 29 is turned on (step S8). When the registration unit solenoid 29 is turned on, the registration unit ratchet 28 is pulled down and the registration unit gap forming member support member 26 rotates once. Next, the control unit 114 turns off the registration unit solenoid 29 (step S9). When the registration part solenoid 29 is turned off, the registration part ratchet 28 is pushed up, and when the registration part gap forming member support member 26 that has completed one rotation returns to the original position, the registration part ratchet 28 is moved to the registration part gap forming member. The rotation of the support member 26 is prevented.

  As shown in FIG. 9, when the passage of the rear end of the paper 8 is detected by the transfer portion paper passage detection sensor 19, the transfer portion 112 performs the same operation as described above when the paper transfer pressure contact portion comes off. The transfer portion gap forming member 12 is inserted into the transfer portion 112 before the rear end of the transfer portion 112 comes out of the transfer portion 112, and the acceleration of the intermediate transfer belt 2 is alleviated. When the transfer unit solenoid drive circuit 22 is turned off, the same operation as described above is performed, and when the transfer unit gap forming member support member 11 rotates once and returns to the original position, the transfer unit gap forming member support member 11 It will suppress the movement.

  That is, when the sheet transfer pressure contact part is missing, the control unit 114 determines whether or not it has been detected that the trailing edge of the sheet 8 has been removed from the transfer part 112 (step S10), and detects the trailing edge of the sheet 8 being lost. If so, the transfer unit solenoid 15 is turned on (step S11). When the transfer unit solenoid 15 is turned on, the transfer unit ratchet 14 is pulled down and the transfer unit gap forming member support member 11 rotates once. Next, the control unit 114 turns off the transfer unit solenoid 15 (step S12). When the transfer unit solenoid 15 is turned off, the transfer unit ratchet 14 is pushed up, and when the transfer unit gap forming member support member 11 that has completed one rotation returns to the original position, the transfer unit ratchet 14 is moved to the transfer unit gap forming member. The rotation of the support member 11 is prevented.

  Further, when waiting for the next print, as shown in FIG. 10, the transfer unit solenoid drive circuit 22 and the registration unit solenoid drive circuit 32 are off and wait for the next print.

  As described above, in this embodiment, since the gap is formed in the pressure contact portion of the transfer portion 112 where the intermediate transfer belt 2 and the opposing roller 6 and the transfer roller 7 are in contact, the sheet 8 is in the position where the contact is made. The rotational load generated on the intermediate transfer belt 2 when the toner enters the intermediate transfer belt 2 can be reduced. If the gap is always formed, the intermediate transfer belt 2, the opposing roller 6 and the transfer roller 7 may be deformed due to wear or the like, but in this embodiment, the gap is formed only at a predetermined timing. Therefore, the intermediate transfer belt 2, the opposing roller 6 and the transfer roller 7 can be prevented from being deformed. Further, in the present embodiment, the transfer part gap forming member 12 is not directly sandwiched between the counter roller 6 and the transfer roller 7, but the counter roller side disposed at both ends of the counter roller 6 and the transfer roller 7, respectively. Since the transfer portion gap forming member 12 is sandwiched between the cylindrical member 41 and the transfer roller side cylindrical member 42, the shapes of the transfer portion gap forming member 12, the opposing roller side cylindrical member 41, and the transfer roller side cylindrical member 42 are configured. By appropriately setting the material and the material, the amount of the gap between the facing roller 6 and the transfer roller 7 can be adjusted freely and accurately.

  In the present embodiment, the opposing roller side cylindrical member 41 is provided on the opposing roller shaft 17 and the transfer roller side cylindrical member 42 is provided on the transfer roller shaft 10, and the driving force is applied from the opposing roller shaft 17 or the transfer roller shaft 10. Since the transfer roller side cylindrical member 42 and the counter roller side cylindrical member 41 are configured to rotate, the transfer portion gap forming member 12 is interposed between the counter roller side cylindrical member 41 and the transfer roller side cylindrical member 42. Can be smoothly involved.

  In the present embodiment, the opposed roller side cylindrical member 41 is configured to rotate independently of the opposed roller shaft 17 via the bearing 43, and the transfer roller side cylindrical member 42 is press-fitted into the transfer roller shaft 10. Therefore, it is possible to obtain power for entraining the transfer portion gap forming member 12 between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. Further, it is possible to prevent the load torque generated in the opposed roller side cylindrical member 41 from being propagated to the opposed roller shaft 17 and the intermediate transfer belt 2 when the transfer portion gap forming member 12 is wound. Further, even if there is a difference in linear velocity on the surfaces of the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42 based on the difference in diameter between the two cylindrical members, it can be absorbed by the bearing 43.

  In the present embodiment, the surface layer of the transfer roller side cylindrical member 42 is made of ethylene propylene rubber, which is generally used for a paper conveying roller, and the transfer roller side cylindrical member 42 on the drive side. Since the surface friction coefficient is larger than the surface friction coefficient of the opposed roller side cylindrical member 41 on the driven side, the transfer portion gap forming member 12 is wound between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. The winding force at the time can be increased, and the transfer portion gap forming member 12 can be reliably wound between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42 without slipping.

(Second Embodiment)
An image forming apparatus 50 according to the second embodiment will be described with reference to FIGS. The image forming apparatus 50 according to the second embodiment has a configuration in which a rubber bush 44 is provided between the transfer roller side cylindrical member 42 and the transfer roller shaft 10. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted.

  12 and 13 are a perspective view and a cross-sectional view of the transfer portion 122, respectively.

  In the first embodiment, when the transfer portion gap forming member 12 is inserted between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42, the transfer roller 7 is substantially in contact with the intermediate transfer belt 2. In the case of complete separation, the speed fluctuation in the transfer roller shaft 10 does not affect the running of the intermediate transfer belt 2. Otherwise, the running of the intermediate transfer belt 2 may be affected. There is a possibility that the load torque generated in the roller side cylindrical member 42 propagates to the transfer roller shaft 10 and the speed of the transfer roller 7 fluctuates.

  Therefore, in the present embodiment, unlike the first embodiment in which the transfer roller side cylindrical member 42 is press-fitted and fixed to the transfer roller shaft 10, the transfer roller side cylindrical member 42 is an elastic body that functions as a damper member. The transfer roller shaft 10 is provided via a rubber bush 44.

  Thus, in the present embodiment, the transfer roller side cylindrical member 42 is provided on the transfer roller shaft 10 via the rubber bush 44. By providing the rubber bush 44, the transfer roller side cylindrical member 42 obtains a driving force from the transfer roller shaft 10, and the load torque when the transfer portion gap forming member 12 is inserted propagates to the transfer roller shaft 10. Can be suppressed. Also in the present embodiment, the opposed roller side cylindrical member 41 rotates independently via the bearing 43 with respect to the opposed roller shaft 17, and therefore, between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. Therefore, it is possible to prevent the load torque generated in the opposed roller side cylindrical member 41 from being propagated to the opposed roller shaft 17 and the intermediate transfer belt 2 when the transfer portion gap forming member 12 is wound around the transfer portion gap forming member 12.

(Third embodiment)
An image forming apparatus 50 according to the third embodiment will be described with reference to FIGS. The image forming apparatus 50 according to the third embodiment is configured such that the diameter of the transfer roller side cylindrical member 42 is smaller than the diameter of the counter roller side cylindrical member 41. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted.

  14 and 15 are a perspective view and a cross-sectional view of the transfer unit 132, respectively.

  In the present embodiment, in order to reduce the load torque of the transfer roller side cylindrical member 42 generated when the transfer portion gap forming member 12 is inserted between the transfer roller side cylindrical member 42 and the opposing roller side cylindrical member 41. The diameter of the transfer roller side cylindrical member 42 is smaller than the diameter of the counter roller side cylindrical member 41.

  FIG. 16 shows the relationship of the mechanical force at the moment when the transfer portion gap forming member 12 enters the pressure contact portion between the opposed roller side cylindrical member 41 and the transfer roller side cylindrical member 42. Since the opposed roller side cylindrical member 41 is fixed in both the horizontal direction and the vertical direction, it can move only in the rotational direction. On the other hand, the transfer roller side cylindrical member 42 is fixed in the horizontal direction, but can move in the vertical direction, which is the pressing direction of the compression spring 9, and can also move in the rotational direction. In addition, the transfer part gap forming member 12 can move in the horizontal direction and the vertical direction on the assumption that the movement in the rotational direction is not considered.

  Considering the balance of force in the transfer unit 122 shown in FIG. 3, the following relational expression is established with respect to the balance in the rotation direction of the transfer roller side cylindrical member 42.

  Further, the following relational expression is established regarding the balance in the rotation direction of the opposed roller side cylindrical member 41.

  Further, the following relational expression holds for the balance of the paper 8 in the horizontal direction.

  Further, the following relational expression holds for the balance of the paper 8 in the vertical direction.

  Further, the following relational expression holds for the vertical balance of the transfer roller side cylindrical member 42.

  Here, a torque ΔT necessary for the transfer roller side cylindrical member 42 to be pushed down and the transfer portion gap forming member 12 to advance in the traveling direction is obtained. At this time, since the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42 are separated from each other, N3 = 0 and R3 = 0 are satisfied, and the following relational expressions are established from the expressions shown in Equations 1 to 5.

  From the above, the torque ΔT necessary for the transfer roller gap forming member 12 to move forward by pushing down the transfer roller side cylindrical member 42 becomes the load torque of the transfer roller side cylindrical member 42. Therefore, as shown in FIGS. 14 and 15, the radius r2 of the transfer roller side cylindrical member 42 is set to be equal to that of the opposed roller side cylindrical member 41 in order to reduce the load torque ΔT of the transfer roller side cylindrical member 42 as shown in FIGS. It can be seen that it is better to make it smaller than the radius r1.

  Thus, in the present embodiment, the radius of the transfer roller side cylindrical member 42 is smaller than the radius of the counter roller side cylindrical member 41, so that the gap between the transfer roller side cylindrical member 42 and the counter roller side cylindrical member 41 is between. The force for entraining the transfer section gap forming member 12 can be increased, the transfer section gap forming member 12 can be more reliably wound, and transfer between the opposing roller side cylindrical member 41 and the transfer roller side cylindrical member 42 can be performed. It is possible to prevent the load torque generated in the opposed roller side cylindrical member 41 from being propagated to the opposed roller shaft 17 and the intermediate transfer belt 2 when the part gap forming member 12 is wound.

  As described above, the image forming apparatus according to the present invention has the effect of reducing the rotational load generated on the image carrier and performing good image formation, and performs recording on a single-sheet recording medium. It is useful as an image forming apparatus such as a copying machine, a printer, or a facsimile machine that employs an image forming system such as an electrophotographic system, an electrostatic recording system, an ionography system, or a magnetic recording system.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. Sectional drawing of the intermediate transfer part of the image forming apparatus which concerns on the 1st Embodiment of this invention 1 is a perspective view of a transfer unit of an image forming apparatus according to a first embodiment of the present invention. Sectional drawing of the transfer part of the image forming apparatus which concerns on the 1st Embodiment of this invention 1 is a block diagram showing a control unit of a transfer unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a side view of a transfer portion and a resist portion of an image forming apparatus according to a first embodiment of the present invention. 1 is a side view of a transfer portion and a resist portion of an image forming apparatus according to a first embodiment of the present invention. 1 is a side view of a transfer portion and a resist portion of an image forming apparatus according to a first embodiment of the present invention. 1 is a side view of a transfer portion and a resist portion of an image forming apparatus according to a first embodiment of the present invention. 1 is a side view of a transfer portion and a resist portion of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a flowchart for explaining the operation of the control unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 7 is a perspective view of a transfer unit of an image forming apparatus according to a second embodiment of the present invention. Sectional drawing of the transfer part of the image forming apparatus which concerns on the 2nd Embodiment of this invention FIG. 9 is a perspective view of a transfer unit of an image forming apparatus according to a third embodiment of the present invention. Sectional drawing of the transfer part of the image forming apparatus which concerns on the 3rd Embodiment of this invention Sectional drawing which shows the mechanical relationship of the transfer part of the image forming apparatus which concerns on the 3rd Embodiment of this invention

Explanation of symbols

1 Photosensitive drum (image forming means)
2 Intermediate transfer belt (image carrier)
3 Driving roller 4 Driven roller 5 Tension roller 6 Opposite roller (transfer member)
7 Transfer roller (transfer member)
8 Paper 9 Compression spring 10 Transfer roller shaft 11 Transfer part gap forming member support member (gap forming means)
12 Transfer part gap forming member (gap forming means, gap forming member)
13 Transfer part torque limiter (gap forming member driving means)
DESCRIPTION OF SYMBOLS 14 Transfer part ratchet 15 Transfer part solenoid 16 Transfer part compression spring 17 Opposed roller shaft 19 Transfer part paper passage detection sensor 20 Paper thickness detection sensor 21 Microprocessor 22 Transfer part solenoid drive circuit 23 Registration roller 24 Registration pressure roller 25 Registration part Paper Passing Detection Sensor 26 Registration Section Gap Forming Member Support Member 27 Registration Section Gap Formation Member 28 Registration Section Ratchet 29 Registration Section Solenoid 30 Registration Section Compression Spring 32 Registration Section Solenoid Drive Circuit 41 Opposite Roller Side Cylindrical Member (Nipping Unit)
42 Transfer roller side cylindrical member (clamping means)
43 Bearing 44 Rubber bush (damper member)
50 Image forming apparatus 101 Intermediate transfer unit 112, 122, 132 Transfer unit 113 Registration unit 114 Control unit

Claims (7)

An image carrier that carries and rotates a toner image;
A roller-shaped transfer member for transferring a toner image carried by the image carrier to a recording medium;
A gap forming means for forming a gap between the image carrier and the transfer member at a predetermined timing;
The gap forming means includes a gap forming member disposed at both ends of the transfer member, a clamping means for clamping the gap forming member, and a gap forming member driving means for driving the gap forming member. Forming equipment. The transfer member has a transfer roller that rotates in contact with the image carrier, and an opposing roller disposed to face the transfer roller,
2. The image according to claim 1, wherein the clamping unit includes a transfer roller side cylindrical member disposed coaxially with the transfer roller, and an opposed roller side cylindrical member disposed coaxially with the opposed roller. Forming equipment. The counter roller side cylindrical member rotates independently of the counter roller,
The image forming apparatus according to claim 2, wherein the transfer roller side cylindrical member rotates integrally with the transfer roller. The counter roller side cylindrical member rotates independently of the counter roller,
The image forming apparatus according to claim 2, wherein the transfer roller side cylindrical member rotates via a damper member between the transfer roller shaft and the transfer roller shaft.   The image forming apparatus according to claim 3, wherein a diameter of the transfer roller side cylindrical member is smaller than a diameter of the counter roller side cylindrical member.   6. The image forming apparatus according to claim 2, wherein a surface friction coefficient of the transfer roller side cylindrical member is larger than a surface friction coefficient of the counter roller side cylindrical member. Comprising image forming means for primarily transferring an image to the surface of the image carrier;
The image forming apparatus according to claim 1, wherein the transfer member secondarily transfers an image primarily transferred onto the surface of the image carrier onto the recording medium.

Images