JP2008299247A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing satisfactory image formation by reducing rotation load on an image carrier. <P>SOLUTION: The image forming apparatus includes: an intermediate transfer belt 2 rotating holding an image thereon; a transfer roller 7 rotating in contact with the intermediate transfer belt 2 and used to transfer the image, formed on the surface of the intermediate transfer belt 2, to paper 8; a resist part 103 conveying the paper 8 to the place where the intermediate transfer belt 2 and the transfer roller come into contact with each other; and a transfer section gap forming member 12 rotating on the contact faces of the intermediate transfer belt 2 and the transfer roller 7. A transfer section gap forming member support member 11 and the transfer section gap forming member 12 are disposed to form a gap by inserting the transfer section gap forming member 12 into the place where the intermediate transfer belt 2 and the transfer roller 7 are in contact with each other immediately before the paper 8 rushes into the contact place. <P>COPYRIGHT: (C)2009,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).

  In addition, a concave groove is provided in the image carrier or transfer member, and a gap narrower than the thickness of the recording medium is formed in the pressure contact portion between the image carrier and the transfer member, and the pressure contact portion between the image carrier and the transfer member is formed. There is known one that suppresses the speed fluctuation of the image carrier that occurs when the recording medium enters (see, for example, Patent Document 3).

Further, as shown in FIGS. 19 to 22, the pressure contact portion of the transfer portion of the conventional image forming apparatus causes the paper 58 to move in synchronization with the front end of the toner image on the intermediate transfer belt 52, with the opposing roller 56 and the transfer roller 57. The toner image carried on the intermediate transfer belt 52 is transferred onto the paper 58 by the pressure applied by the compression spring 59 and a transfer bias (not shown). 19 and 20 show the state when the leading edge of the paper 58 enters the pressure contact portion of the transfer portion, and FIGS. 21 and 22 show the state when the rear end of the paper 58 comes out from the pressure contact portion of the transfer portion. It is shown. FIGS. 19A, 20A, 21A, and 22A are cross-sectional views of the transfer portion in the width direction of the paper 58, and FIGS. b), FIG. 21B, and FIG. 22B are cross-sectional views of the transfer section in the conveyance direction of the paper 58. FIG. When the leading edge of the paper 58 enters the pressure contact portion of the transfer portion, the transfer roller 57 is pressed against the intermediate transfer belt 52 by the compression spring 59 as shown in FIG. The front end of the paper 58 is engaged with the paper 58 and enters, and the transfer roller 57 is pushed down by an amount corresponding to the thickness of the paper 58 as shown in FIG. Further, when the trailing edge of the paper 58 comes out from the pressure contact portion of the transfer portion, as shown in FIG. The transfer roller 57 that has been pushed down is pushed up by the pressure applied by the compression spring 59 by an amount corresponding to the thickness of the paper 58 and the paper 58 has passed through.
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 due to the urging force of the urging means, so that a rotational load is generated on the image carrier, causing image deterioration. Specifically, as shown in FIG. 16, when the gap between the transfer roller 503 and the image carrier 501 is released, the transfer roller 503 is moved by the urging force of the spring 504 connected to the arm 502. There was a problem that a rotational load was generated by colliding with the body 501.

  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. Although it is considered that the effect of reducing fluctuations can be obtained regardless of the thickness of the recording medium, a device for detecting the thickness of the recording medium must be provided, or the adjustment amount must be determined and driven according to the thickness of the recording medium. In other words, there is a problem that the apparatus is expensive and complicated. Further, as shown in FIG. 17, since it is necessary to provide the motor 511 separately from the driving of the rollers in order to form the gap, there is a problem that the cost is increased.

  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. . Specifically, as shown in FIG. 18, since the end portion of the roller 521 is in constant pressure contact with the roller 522, local stress concentration occurs in the pressure contact portion, and the roller when used for a long period of time. There was a problem that could be deformed.

  In general, a conventional image forming apparatus adopting an electrophotographic method, which employs a transfer method in which a transfer roller is pressed against an image carrier with a recording sheet sandwiched between them, is a transfer roller. When the leading edge of the recording paper enters the pressure contact portion with the image carrier, a phenomenon that the conveying speed of the image carrier temporarily decreases occurs, and the phenomenon becomes more remarkable as the recording paper is thicker. There is. In particular, in recent years, the distance from the registration roller to the pressure contact portion between the transfer roller and the image carrier has become shorter due to a request for downsizing of the apparatus, and thus the speed fluctuation of the image carrier has become more problematic than before. Yes.

  Due to this phenomenon in which the conveyance speed of the image carrier temporarily decreases, not only the transfer process, but also the linear speed of the cleaning, exposure, and development processes performed on the photosensitive member fluctuate. There is a problem in that image defects called banding such as band-like shading unevenness in the sub-scanning direction and image displacement occur.

  In the conventional image forming apparatus shown in FIGS. 19 to 22, when the leading edge of the paper 58 enters the pressure contact portion of the transfer portion, the intermediate transfer belt is used to push down the transfer roller 57 by an amount corresponding to the thickness of the paper 58. Since the rotational torque of the opposing roller 56 is used via 52, the rotational load of the opposing roller 56 and the running load of the intermediate transfer belt 52 are generated. For this reason, there is a problem in that a position shift occurs in a primary transfer portion between a photosensitive drum (not shown) and the intermediate transfer belt 52, and an image density unevenness occurs in an image formed on the paper 58. In this case, density unevenness occurs between the leading edge of the paper 58 and the position L1 where L1 is the distance between the two transfer portions, that is, the distance from the primary transfer portion to the secondary transfer portion. On the other hand, when the trailing edge of the sheet 58 comes out from the pressure contact portion of the transfer portion, a load torque is generated in the rotation direction of the opposing roller 56 via the intermediate transfer belt 52, so that the rotation of the opposing roller 56 is accelerated and intermediate. Travel of the transfer belt 52 is accelerated. For this reason, there has been a problem that a positional shift occurs in the primary transfer portion, and an image density unevenness occurs in an image formed on the paper 58. In this case, if the distance from the trailing edge of the paper 58 to the leading edge of the next paper is L2, and the length of the paper 58 in the sub-scanning direction is L, the next paper 58 is L2 <L1 <L2 + L. It occurs between the positions of L1-L2 from the tip of the. Note that the above problem occurs not only in the pressure contact portion of the transfer portion but also in the pressure contact portion of the registration portion located upstream of the transfer portion in the sheet conveyance direction.

  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. And

  An image forming apparatus according to the present invention includes an image carrier that carries and rotates an image, and a transfer that rotates in contact with the image carrier and transfers an image formed on the surface of the image carrier to a recording medium. A member, a recording medium conveying means for conveying a recording medium to a position where the image carrier and the transfer member abut, and a contact surface where the image carrier and the transfer member abut on the same surface. A gap forming member that has a gap forming member and inserts the gap forming member at a position where the image carrier and the transfer member abut immediately before the recording medium enters; It is characterized by that.

  With this configuration, the gap is formed by inserting the gap forming member immediately before the recording medium enters the position where the image carrier and the transfer member come into contact with each other, so that the rotational load generated on the image carrier is reduced. In addition, by rotating the gap forming member on the same surface as the contact surface where the image carrier and the transfer member abut, the image carrier and the transfer member are in contact with each other. When the gap forming member passes through the contact position, the gap forming member can be prevented from being bent excessively.

  Further, in the image forming apparatus according to the present invention, the gap forming unit is located at a position where the image carrier and the transfer member come into contact with each other by the driving force of the recording medium conveyed by the recording medium conveying unit. Immediately before the recording medium enters, the gap forming member is inserted to form a gap.

  With this configuration, the gap forming member is inserted by being pushed by the tip of the recording medium at a position where the image carrier and the transfer member abut, so that the recording medium enters the position where the image carrier and the transfer member abut. The gap forming member can be inserted in a timely manner immediately before.

  The image forming apparatus according to the present invention includes a transmission unit that transmits a driving force from the same driving source as the transfer member or the image carrier to the gap forming member, and a support member that supports the gap forming member. And a control means for suppressing movement of the support member.

  With this configuration, it is not necessary to separately provide a drive source for driving the gap forming member, so that the structure can be avoided from being complicated, and the cost can be reduced and the space can be saved. Further, the gap forming member can be inserted into the position where the image carrier and the transfer member abut at an arbitrary timing by the transmission means and the control means for transmitting the driving force.

  In the image forming apparatus according to the present invention, the transmission unit may apply the driving force from the driving source to the gap so that the axial direction of the rotating shaft of the driving source differs from the axial direction of the rotating shaft of the gap forming member. An axial direction changing means for transmitting to the forming member and a driving force limiting means for limiting and transmitting the driving force from the driving source are provided.

  With this configuration, it is possible to transmit the driving force from the transfer member, which is a drive source, to the gap forming member so that the gap forming member rotates on the same surface as the contact surface on which the image carrier and the transfer member abut. . Further, since the driving force from the driving source is limited and transmitted to the gap forming member via the driving force limiting means, when the movement of the support member is suppressed by the control means, the transfer member or the image carrier The driving source is not affected. Further, the support member can be reliably rotated when the movement of the support member is not suppressed by the control means.

  Further, in the image forming apparatus according to the present invention, the axial direction changing means is configured so that the driving force from the driving source is such that the axial direction of the rotating shaft of the driving source is orthogonal to the axial direction of the rotating shaft of the gap forming member. Is transmitted to the gap forming member.

  With this configuration, since the axial direction of the rotating shaft of the driving source and the axial direction of the rotating shaft of the gap forming member are orthogonal, the driving force from the driving source is applied to the gap forming member using a simple and inexpensive gear such as a bevel gear. Can be communicated to.

  Further, in the image forming apparatus according to the present invention, the axial direction changing means drives the axial direction of the rotational axis of the driving source and the axial direction of the rotational axis of the gap forming member so as to have a twisted positional relationship. A driving force from a source is transmitted to the gap forming member.

  With this configuration, the degree of freedom regarding the installation position of the rotation shaft of the gap forming member can be improved. Further, by disposing the rotation axis of the gap forming member upstream of the rotation axis of the transfer member, the gap forming member can stand by in parallel with the width direction of the recording medium. Can be stably received from the recording medium when pressed by the recording medium.

  According to the present invention, it is possible to provide an image forming apparatus capable of reducing the rotational load generated on the image carrier and performing good image formation.

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

(First embodiment)
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

  First, the configuration will be described.

  As shown in FIG. 1, the image forming apparatus 50 includes a printer unit 100, a paper feed unit 200, a scanner unit 300, and an automatic document feeder 400. In addition, the image forming apparatus 50 includes a control unit (not shown) that controls the operations of these units.

  The printer unit 100 includes an intermediate transfer unit 101, an exposure device, an image forming unit, a fixing unit, a toner supply device, and the like, and forms an image on a sheet 8 (see FIG. 2) that is a recording medium. The paper feed unit 200 includes a plurality of paper feed cassettes, a paper transport path, and the like, and stores and transports the paper 8. The scanner unit 300 includes a contact glass 301 and reads image information of a document placed on the contact glass 301. The automatic document feeder 400 includes a document tray 401 and conveys a document placed on the document tray 401 onto the contact glass 301. That is, the image forming apparatus 50 shows an example in which the image forming apparatus according to the present invention is applied to a color laser copying machine.

  FIG. 2 is a cross-sectional view of the intermediate transfer portion of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 2, the intermediate transfer unit 101 includes an intermediate transfer belt 2 as an image carrier, a driving roller 3, a driven roller 4, a tension roller 5, and a counter roller 6. The 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 by the driving roller 3 in the clockwise direction in the figure. The intermediate transfer belt 2 carries toner images primarily transferred from the four photosensitive drums 1 corresponding to cyan, magenta, yellow, and black colors, and presses the toner images against the opposing roller 6 and the opposing roller 6. It moves to the transfer roller 7 provided in this way.

  The transfer roller 7 is supported by a transfer roller shaft 10 and rotates in contact with the intermediate transfer belt 2 below the opposing roller 6. Further, both end portions of the transfer roller shaft 10 are urged upward by the compression spring 9, and the transfer roller 7 is pressed against the opposing roller 6 by the urging force of the compression spring 9. Further, the opposing roller 6 and the transfer roller 7 are configured to secondarily transfer the toner image carried by the intermediate transfer belt 2 onto the paper 8. On the right side of the opposing roller 6 and the transfer roller 7, there are provided a registration roller 26 and a registration pressure roller 27 that convey the paper 8 to a pressure contact portion where the opposing roller 6 and the transfer roller 7 are in pressure contact with the intermediate transfer belt 2. The registration roller 26 is driven by a motor (not shown), and the registration pressure roller 27 is driven in contact with the registration roller 26.

  Further, the entry of the leading edge of the sheet 8 into the transfer unit 102 is detected in the path downstream of the registration roller 26 and the registration pressure roller 27 in the sheet conveyance direction, and the trailing end of the sheet 8 is removed from the transfer unit 102. A transfer section paper passage detection sensor 19 for detecting the above is provided.

  During the transfer operation, the paper 8 supplied from the paper supply unit 200 stands by at the installation position of the registration roller 26 and the registration pressure roller 27, and when the toner image is transferred to the intermediate transfer belt 2, the registration roller 26 and By the registration pressure roller 27, the opposing roller 6 and the transfer roller 7 are conveyed to a pressure contact portion in pressure contact with the intermediate transfer belt 2 in synchronization with the leading edge of the toner image on the intermediate transfer belt 2. The toner image carried on the intermediate transfer belt 2 is transferred to the sheet 8 sandwiched between the intermediate transfer belt 2 and the transfer roller 7 by the pressure applied by the compression spring 9 and a transfer bias (not shown). As described above, the image forming apparatus 50 conveys the intermediate transfer belt 2 onto which the toner image has been transferred by the primary transfer while being sandwiched by the registration rollers 26, and the toner image is secondarily transferred onto the paper 8 by the transfer roller 7. A transfer method is adopted. The counter roller 6 and the transfer roller 7 constitute a transfer unit 102, and the registration roller 26 and the registration pressure roller 27 constitute a registration unit 103. The image carrier is not limited to the intermediate transfer belt 2 and may be the photosensitive drum 1. That is, FIG. 2 shows an intermediate transfer type configuration in which the intermediate transfer belt 2 and the transfer roller 7 are in contact with each other to perform secondary transfer on the paper 8, but the photosensitive drum 1 and the transfer roller 7 are in contact with each other. Thus, the present invention can be applied even to a direct transfer type configuration in which direct transfer is performed on the paper 8.

  FIG. 3A is a plan view of the pressure contact portion of the transfer portion of the image forming apparatus according to the first embodiment of the present invention. FIG. 3B is a side view of the transfer unit of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 3A and FIG. 3B, the transfer unit 102 is formed between the intermediate transfer belt 2 and the transfer roller 7 at a pressure contact portion where the opposing roller 6 and the transfer roller 7 are pressed against the intermediate transfer belt 2. A transfer portion gap forming member 12 that forms a gap therebetween, and a pressure contact surface of the transfer portion 102 that supports the transfer portion gap forming member 12, that is, a contact surface on which the intermediate transfer belt 2 and the transfer roller 7 abut. A transfer part gap forming member support member 11 that rotates on the same plane is provided. The transfer part gap forming member 12 is set to be thinner than the paper 8.

  The transfer portion gap forming member 12 is required to have sufficient flexibility to be in close contact with both rollers when sandwiched between the opposing roller 6 and the transfer roller 7, and is sandwiched between the opposing roller 6 and the transfer roller 7. In a standby state where there is no, a certain degree of flatness must be maintained by the restoring force. Therefore, a flexible sheet material is used for the transfer portion gap forming member 12. 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, when a sheet material made of a metal material is used as a flexible sheet material, phosphor bronze strips, beryllium copper strips, etc. that are supplied to the market as metal thin plates are suitable, but stainless steel strips have mechanical properties. It is more suitable because it is excellent in. SUS304-CSP is the most excellent stainless steel strip. Further, as the stainless steel strip, there is precipitation hardening SUS631-CSP, but it is preferable to use austenitic SUS631-CSP in consideration of repeated fatigue. Moreover, the transfer part gap forming member 12 can also be made of nickel foil by an electroforming method that can be easily processed into a desired thickness.

  FIG. 4A is a plan view of the pressure contact portion of the transfer portion of the image forming apparatus according to the first embodiment of the present invention. FIG. 4B is a cross-sectional view of the transfer portion of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIGS. 4A and 4B, the transfer unit 102 has a bevel gear 23 that is press-fitted into the transfer roller shaft 10 and a bevel gear 23 that meshes with the bevel gear 23 and is press-fitted into the rotary shaft 24 a. And a gear 24. The reduction ratio of the bevel gear 23 and the bevel gear 24 is 1.

  The transfer unit 102 includes a transfer unit torque limiter 13 that constitutes a transmission unit that transmits the rotational driving force of the rotation shaft 24 a to the transfer unit gap forming member support member 11. That is, the drive source of the transfer portion gap forming member 12 is directly the transfer roller shaft 10 and indirectly, the drive roller 3 that drives the intermediate transfer belt 2 that contacts the transfer roller 10. ing. A transfer portion torque limiter 13 is press-fitted into the transfer portion gap forming member support member 11, and a rotation shaft 24 a is inserted into the transfer portion torque limiter 13. The rotational driving force of the transfer roller shaft 10 is transmitted to the transfer part gap forming member support member 11 by the transfer part torque limiter 13. If the load torque applied to the transfer unit torque limiter 13 is equal to or less than the set torque, the transfer unit gap forming member support member 11 causes the rotation shaft 24a to be driven by the driving force of the transfer roller shaft 10 transmitted through the bevel gears 23 and 24. It can rotate as the center of rotation. The set torque of the transfer portion torque limiter 13 is set so that the rotation of the transfer roller shaft 10 is not affected even if the rotational movement of the transfer portion gap forming member support member 11 is suppressed. Further, the axis of the rotation axis of the transfer roller shaft 10 and the axis of the rotation axis of the transfer part gap forming member support member 11 are orthogonal to each other.

  In addition, the transfer unit 102 includes a transfer unit solenoid 15 attached to the bracket 25 a of the side plate 25. The transfer part solenoid 15 is for suppressing rotation of the transfer part gap forming member support member 11 by bringing a plunger 15a into contact with a protrusion 11a provided on the upper surface of the transfer part gap forming member support member 11. . The plunger 15a of the transfer part solenoid 15 is in a lowered position that restricts rotation of the transfer part gap forming member support member 11, that is, a position that suppresses rotation, and an elevated position that allows rotation of the transfer part gap forming member support member 11. That is, it can move between positions where the suppression of rotation is released.

  FIG. 5 is a block diagram of a control unit that controls the transfer unit of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 5, the control unit 104 includes a microprocessor 21 to which a detection signal from the transfer unit paper passage detection sensor 19 is input, and a transfer unit solenoid drive circuit 22 that drives the transfer unit solenoid 15. . When the transfer unit paper passage detection sensor 19 detects the entry of the paper 8 into the transfer unit 102 and when the microprocessor 21 detects that the rear end of the paper 8 has been removed from the transfer unit 102, the microprocessor 21 The transfer unit solenoid 15 is driven by a solenoid drive circuit 22. That is, in the present embodiment, when the leading end of the sheet 8 enters the transfer unit 102 and when the trailing end of the sheet 8 comes out of the transfer unit 102, a gap is formed in the transfer unit 102 to speed the intermediate transfer belt 2. It is designed to suppress fluctuations.

  At the pressure contact portion of the transfer portion 102, the distance L between the transfer roller 7 and the rotating shaft 24a is set equal to the radius of the transfer roller 7, so that the linear velocity at the base portion of the transfer portion gap forming member 12 is transferred. Since it is made equal to the roller 7, the linear velocity at the tip of the transfer part gap forming member 12 is faster than that of the transfer roller 7. Therefore, the transfer portion torque limiter 13 limits the driving force in both the forward and reverse rotation directions so that the transfer portion gap forming member 12 does not receive excessive shearing force at the press contact portion of the transfer portion 102. It has become. Further, a Teflon (registered trademark) tape or the like having a low friction coefficient is attached to the transfer portion gap forming member 12 so that the transfer portion gap forming member 12 does not receive excessive shearing force at the press contact portion of the transfer portion 102. Also good.

  Next, the operation of the image forming apparatus 50 configured as described above will be described.

  FIG. 6 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. FIGS. 7A to 7C and FIGS. 8A to 8C show the transfer portion in the pressure contact portion of the transfer portion of the image forming apparatus according to the first embodiment of the present invention. It is a top view which shows the rotational motion of a gap | interval formation member in a time series.

  As shown in FIG. 6, the control unit 104 determines whether or not the setting mode is the cardboard mode during printing standby (step S1), and determines whether or not there is a print request in the cardboard mode. It discriminate | determines (step S2). In addition, when there is a print request, the control unit 104 starts driving the intermediate transfer belt 2 (step S3).

  Next, the control unit 104 determines whether or not it is detected that the leading edge of the sheet 8 has entered the transfer unit 102 (step S4). If the entry of the sheet 8 is detected, the transfer unit solenoid 15 is turned on. (Step S5). When the transfer part solenoid 15 is turned on, the plunger 15a is raised, and the transfer part gap forming member support member 11 starts to rotate. Next, the control unit 104 turns off the transfer unit solenoid 15 (step S6). When the transfer unit solenoid 15 is turned off, the plunger 15a is lowered to restrict the rotation of the transfer unit gap forming member support member 11 that has finished one rotation and has returned to the original state.

  In this way, in the standby state shown in FIG. 7A, when the user has selected the thick paper mode, if the transfer section sheet passage detection sensor 19 detects the passage of the leading edge of the sheet 8, the transfer section solenoid. The transfer unit solenoid 15 is driven by the drive circuit 22, and the plunger 15a is raised. As a result, the transfer portion gap forming member support member 11 and the transfer portion gap forming member 12 are allowed to rotate and are transmitted to the transfer portion gap forming member support member 11 via the bevel gears 23 and 24 and the transfer portion torque limiter 13. Due to the driving force of the transfer roller shaft 10, the rotary shaft 24a moves around the rotation center. Thereafter, as shown in FIG. 7B, immediately before the sheet 8 enters the pressure contact portion of the transfer portion 102 by the rotation of the transfer portion gap forming member support member 11, the transfer portion gap forming member 12 A gap is formed in the pressure contact portion, and the speed fluctuation of the intermediate transfer belt 2 is suppressed. At this time, the transfer portion gap forming member 12 is inserted into the transfer portion 102 while rotating on the same surface as the contact surface on which the intermediate transfer belt 2 and the transfer roller 7 are in contact with each other. When the transfer unit solenoid 15 is turned off by the transfer unit solenoid drive circuit 22, the plunger 15a is lowered as shown in FIG. 7C, and then, as shown in FIG. The movement of the transfer part gap forming member support member 11 that has returned to the above is suppressed.

  Next, the control unit 104 determines whether or not it has been detected that the rear end of the paper 8 has been removed from the transfer unit 102 (step S7). 15 is turned on (step S8). When the transfer part solenoid 15 is turned on, the plunger 15a is raised, and the transfer part gap forming member support member 11 starts to rotate. Next, the control unit 104 turns off the transfer unit solenoid 15 (step S9). When the transfer unit solenoid 15 is turned off, the plunger 15a is lowered, and the rotation of the transfer unit gap forming member support member 11 that has finished one rotation and returned to the original state is restricted.

  In this way, when the transfer portion paper passage detection sensor 19 detects the passage of the rear end of the paper 8, the transfer portion 102 performs the same operation as described above, and as shown in FIG. Before the rear end of the transfer portion 102 is completely removed, the transfer portion gap forming member 12 is inserted into the pressure contact portion of the transfer portion 102 to alleviate the acceleration of the intermediate transfer belt 2. Further, as shown in FIG. 8C, when the transfer portion solenoid 15 is turned off by the transfer portion solenoid drive circuit 22, the plunger 15a is lowered, and as shown in FIG. The movement of the transfer part gap forming member support member 11 that has returned to the above is suppressed.

  If the thick paper mode is not selected, the plunger 15a is in a lowered state while the transfer unit solenoid 15 is off, so that the image forming cycle of plain paper, that is, the paper 8 having a normal thickness thinner than the thick paper is targeted. The transfer portion gap forming member 12 is not inserted into the press contact portion of the transfer portion 102. The other end side of the transfer unit 102 is configured in the same manner.

  As described above, the image forming apparatus according to the present embodiment includes the transfer portion gap forming member 12 that rotates on the same surface as the contact surface on which the intermediate transfer belt 2 and the transfer roller 7 contact, Immediately before the sheet 8 enters the pressure contact portion 102, the transfer portion gap forming member 12 is inserted to form a gap, so that the rotational load generated on the intermediate transfer belt 2 can be reduced and good image formation can be performed. In addition, it is possible to prevent the transfer portion gap forming member 12 from being excessively bent when the transfer portion gap forming member 12 passes through the pressure contact portion of the transfer portion 102.

  In addition, the image forming apparatus according to the present embodiment is configured such that the transfer portion gap forming member includes the bevel gears 23 and 24 that transmit driving force from the same drive source as the transfer roller 7 and the transfer portion gap forming member support member 11. 12, and the transfer unit solenoid 15 controlled by the control unit 104 suppresses the movement of the transfer unit gap forming member support member 11. Therefore, it is necessary to provide a separate drive source for driving the transfer unit gap forming member 12. Therefore, the complexity of the structure can be avoided, the cost can be reduced and the space can be saved, and the transfer portion solenoid 15 can be moved up and down to move the transfer portion gap forming member 12 to an arbitrary position. It can be inserted into the pressure contact portion of the transfer portion 102 at the timing.

  Further, in the image forming apparatus according to this embodiment, the transfer roller 7 and the bevel gears 23 and 24 are configured such that the axial direction of the rotation shaft of the transfer roller 7 and the axial direction of the rotation shaft of the transfer portion gap forming member 12 are different. Is transferred to the transfer part gap forming member 12 so that the transfer part gap forming member 12 rotates on the same surface as the contact surface on which the intermediate transfer belt 2 and the transfer roller 7 contact. The driving force from the roller 7 can be transmitted to the transfer part gap forming member 12. Further, since the transfer portion torque limiter 13 restricts the driving force from the transfer roller 7 and transmits it to the transfer portion gap forming member 12, the movement of the transfer portion gap forming member support member 11 is suppressed. When the transfer roller 7 is not affected by the rotation of the transfer roller 7 and the movement of the transfer part gap forming member support member 11 is not suppressed, the transfer part gap forming member support member 11 can reliably rotate. .

  In addition, the image forming apparatus according to the present embodiment uses the bevel gears 23 and 24 so that the axial direction of the rotation shaft of the transfer roller 7 and the axial direction of the rotation shaft of the transfer portion gap forming member 12 are orthogonal to each other. 7 is transmitted to the transfer part gap forming member 12, the driving force from the transfer roller 7 can be transmitted to the transfer part gap forming member 12 easily and inexpensively.

(Second Embodiment)
FIG. 9A is a plan view of the pressure contact portion of the transfer portion of the image forming apparatus according to the second embodiment of the present invention. FIG. 9B is a cross-sectional view of the transfer portion of the image forming apparatus according to the second embodiment of the present invention. FIG. 9C is a perspective view of the transfer portion gap forming member of the image forming apparatus according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted.

  As shown in FIGS. 9A and 9B, the transfer unit 112 includes a suppressing member 28 that suppresses rotation of the transfer unit gap forming member support member 11, a torsion coil 44, and a fixing member 29. The fixing member 29 is fixed to the side surface of the side plate 25. The restraining member 28 can be rotated within a predetermined angle range with respect to the fixing member 29 via a torsion coil 44 which is a torsion spring. The suppressing member 28 suppresses the rotation of the transfer portion gap forming member support member 11 so that the transfer portion gap forming member 120 stands by immediately before the pressure contact portion of the transfer portion 112 in the conveyance path of the paper 8. .

  The torsion coil 44 causes the restraining member 28 to abut on the protrusion 11a of the transfer part gap forming member support member 11 by a restoring force as a torsion spring when the restraining member 28 and the fixing member 29 are within a predetermined angle range. As a result, the rotation of the transfer portion gap forming member 120 is suppressed, and the orbit of the transfer portion gap forming member supporting member 11 is movable when the suppressing member 28 and the fixing member 29 are opened at a predetermined angle or more. The transfer part gap forming member support member 11 is allowed to rotate out of the range.

  Here, an initial angle formed by the suppressing member 28 and the fixing member 29 is a1 [rad], and a predetermined angle, that is, a limit angle at which the suppressing member 28 suppresses the rotation of the transfer portion gap forming member support member 11 is a2 [ rad] and the torsion spring constant of the torsion coil 44 is K [N · m / rad], the maximum torque that suppresses the rotation of the transfer portion gap forming member support member 11 is k (a2-a1) [N · m]. It becomes. Further, if the limit torque TL [N · m] of the transfer portion torque limiter 13 is set to be equal to or less than k (a2-a1) [N · m], the angle formed between the suppressing member 28 and the fixing member 29 is a predetermined angle a2. Until [rad], the drive transmission by the transfer portion torque limiter 13 is cut off, and the rotation of the transfer portion gap forming member support member 11 is suppressed. For this reason, the following relational expression is established with respect to the conditions for establishing the limit torque TL of the transfer portion torque limiter 13.

  Further, when the driving force of the paper 8 is F and the radius of the transfer roller 7 is r, the rotation that acts on the transfer portion gap forming member support member 11 when the leading edge of the paper 8 enters between the transfer portion gap forming members 120. Torque is rF. Therefore, when the leading edge of the paper 8 enters between the transfer portion gap forming members 120, the torsion coil 44 opens by a2 [rad] or more, and the trajectory of the transfer portion gap forming member support member 11 moves within the movable range of the suppressing member 28. In order for the transfer portion gap forming member support member 11 to rotate out of rotation, the following relational expression must be satisfied.

  Therefore, the limit torque TL of the transfer portion torque limiter 13, the torsion spring constant k of the torsion coil 44, the initial angle a1, and the predetermined angle a2 may be set so as to satisfy the relational expressions of Expressions 1 and 2.

  Further, since the propulsive force F of the paper 8 is equal to the buckling load P, it can be obtained by calculating the buckling load of the paper 8 from Euler's equation. Here, as shown in FIG. 11, boundary conditions of horizontal, vertical fixed, and free rotation are set at the leading edge of the paper 8, the Young's modulus of the paper 8 is E, the cross-sectional secondary moment of the paper 8 is I, and the resist portion When the distance from 103 to the transfer portion 112 is 1, the following relational expression is established with respect to the buckling load P of the paper 8.

  Since the paper driving force F is equal to the buckling load P, the buckling load P of the paper 8 is calculated by using Equation 3 and set using Equations 1 and 2.

  Further, as shown in FIG. 9C, the transfer portion gap forming member 120 is configured by joining two sheet members 120a and 120b in a substantially V shape. The sheet member 120a and the sheet member 120b are configured such that the downstream side in the transport direction of the paper 8 is connected and the upstream side in the transport direction of the paper 8 is opened. Further, the transfer portion gap forming member 120 is inserted into the pressure contact portion of the transfer portion 112 when the leading edge of the paper 8 is sandwiched between the sheet members 120 a and 120 b and is pushed by the propulsive force of the paper 8. . The sheet member 120b in contact with the transfer roller 7 is formed to be longer in the sub-scanning direction than the sheet member 120a in contact with the opposing roller 6, and the leading end of the paper 8 is first a sheet as shown in FIG. After contact with either or both of the member 120a and the sheet member 120b, as shown in FIG. 10 (b), the sheet is held between the sheet member 120a and the sheet member 120b by the opposing roller 6 and the transfer roller 7. It has become. Further, since the sheet members 120a and 120b rotate together with the transfer part gap forming member support member 11, the sheet 8 gradually becomes a sheet after the leading end of the paper 8 is sandwiched between the press contact parts of the transfer part 112 shown in FIG. It is separated from the members 120a and 120b.

  At the pressure contact portion of the transfer portion 112, the linear velocity at the tip portion of the transfer portion gap forming member 120 is higher than the linear velocity on the surface of the transfer roller 7. Therefore, the transfer portion torque limiter 13 limits the driving force in both the forward and reverse rotation directions so that the transfer portion gap forming member 120 does not receive excessive shearing force at the press contact portion of the transfer portion 112. It has become. Further, a Teflon (registered trademark) tape or the like having a low friction coefficient is attached to the transfer portion gap forming member 120 so that the transfer portion gap forming member 120 does not receive excessive shearing force at the press contact portion of the transfer portion 112. Also good. In addition, the larger the contact portion between the transfer portion gap forming member 120 and the paper 8, the more stably the transfer portion gap forming member 120 is rotated by the paper 8, so the transfer portion gap forming member 120 in the axial direction of the transfer roller 7. It is preferable to increase the length.

  Next, the operation of the image forming apparatus 50 configured as described above will be described.

  12 (a) to 12 (c), 13 (a), and 13 (b) show the rotational movement of the transfer portion gap forming member of the image forming apparatus according to the second embodiment of the present invention. It is a side view shown by a series.

  In the print standby state, as shown in FIG. 12A, since the transfer roller 7 does not rotate, the transfer portion gap forming member support member 11 is stationary, and the suppressing member 28 maintains the initial angle a1.

  When the driving of the intermediate transfer belt 2 is started, as shown in FIG. 12B, the transfer roller 7 is rotated, so that the transfer portion gap forming member support member 11 is rotated via the transfer portion torque limiter 13 and the suppressing member. 28 is spread. The suppressing member 28 suppresses the rotation of the transfer portion gap forming member support member 11 until the angle of the suppressing member 28 becomes a2 and the restoring force of the torsion coil 44 reaches the limit torque TL of the transfer portion torque limiter 13.

  When the sheet 8 enters the transfer portion gap forming member 120, as shown in FIG. 12C, the driving force F of the sheet 8 rotates the transfer portion gap forming member support member 11 through the transfer portion gap forming member 120. The transfer portion gap forming member support member 11 rotates to further spread the suppressing member 28 as torque.

  When the sheet 8 enters the pressure contact portion of the transfer unit 112, the transfer roller 7 is pushed down with the transfer unit gap forming member 120 sandwiching the leading end of the sheet 8 as shown in FIG. When the restraining member 28 is further expanded by the rotation of the transfer part gap forming member support member 11, the trajectory of the transfer part gap forming member support member 11 deviates from the movable range of the restraining member 28. At this time, the suppression member 28 becomes the initial angle a <b> 1 by the restoring force of the torsion coil 44.

  After the paper 8 enters the pressure contact portion of the transfer portion 112, the transfer portion gap forming member 120 is separated from the leading end of the paper 8 as shown in FIG. Subsequently, it is rotated by drive transmission from the transfer portion torque limiter 13. Thereafter, the transfer section gap forming member support member 11 reaches the installation position of the suppressing member 28 and the above-described operation is repeated every time the paper 8 is conveyed to the transfer section 112. The other end side of the transfer unit 112 is configured in the same manner.

  As described above, in the image forming apparatus according to the present embodiment, the transfer portion gap forming member 120 is pushed by the driving force of the paper 8 conveyed by the resist portion 103 and inserted into the pressure contact portion of the transfer portion 112. As a result, a gap is formed in the transfer section 112 immediately before the sheet 8 enters the transfer section 112. Therefore, the gap is formed in a timely manner immediately before the sheet 8 enters the pressure contact section of the transfer section 112. be able to.

  Further, in the image forming apparatus according to the present embodiment, the transfer portion gap forming member 120 receives driving force from the transfer roller 7 via the bevel gears 23 and 24 and the transfer portion torque limiter 13, and the torsion coil 44. Since the control member 28 is controlled so as to wait on the conveyance path of the paper 8, there is no need to provide a separate drive source for driving the transfer portion gap forming member 120, thereby avoiding the complicated structure. Therefore, the cost can be reduced and the space can be saved, and the transfer part gap forming member 120 can be inserted into the pressure contact part of the transfer part 112 in a timely manner.

(Third embodiment)
FIG. 14A is a plan view of the pressure contact portion of the transfer portion of the image forming apparatus according to the third embodiment of the present invention. FIG. 14B is a cross-sectional view of the transfer portion of the image forming apparatus according to the third embodiment of the present invention. FIG. 15 is a side view of the transfer unit of the image forming apparatus according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted.

  As shown in FIGS. 14A, 14B, and 15, the transfer unit 122 includes a hypoid gear 123 that is press-fitted into the transfer roller shaft 10 and a hypoid gear 124 that meshes with the hypoid gear 123. , 124 transmits the driving force of the transfer roller shaft 10 to the transfer portion gap forming member support member 11. The hypoid gear 124 meshes with the hypoid gear 123 on the upstream side in the transport direction of the paper 8 with respect to the press contact portion of the transfer unit 122. That is, the hypoid gear 124 is offset from the pressure contact portion of the transfer portion 122 on the upstream side in the conveyance direction of the paper 8, and the axial direction of the transfer roller shaft 10 and the rotation shaft of the transfer portion gap forming member 120 are provided. Axis is related to the position of twist.

  A rotary shaft 124a is press-fitted into the hypoid gear 124, and a transfer portion torque limiter 13 is provided on the outer peripheral portion of the rotary shaft 124a. The rotation of the rotation shaft 124 a is transmitted to the transfer part gap forming member support member 11 via the transfer part torque limiter 13.

  The transfer part gap forming member 120 supported by the transfer part gap forming member support member 11 stands by in a state parallel to the width direction of the paper 8 on the upstream side in the conveyance direction of the paper 8 with respect to the press contact part of the transfer part 122. It is like that. The other end side of the transfer unit 122 is configured in the same manner.

  The reduction ratio of the hypoid gears 123 and 124 is a value of 1 or less, and the rotation of the transfer portion gap forming member support member 11 is slower than the rotation of the transfer roller shaft 10. Therefore, the transfer portion torque limiter 13 limits the driving force in both the forward and reverse rotation directions so that the transfer portion gap forming member 120 does not receive excessive shearing force at the press contact portion of the transfer portion 122. It has become. Further, a Teflon (registered trademark) tape or the like having a low friction coefficient is attached to the transfer portion gap forming member 120 so that the transfer portion gap forming member 120 does not receive excessive shearing force at the pressure contact portion of the transfer portion 122. Also good.

  As described above, in the image forming apparatus according to the present embodiment, the driving force is transmitted and received through the hypoid gears 123 and 124, and the axial directions of the rotation shafts of both the transfer roller 7 and the transfer portion gap forming member 120 are twisted. In addition, the transfer portion gap forming member 120 waits in a state parallel to the width direction of the paper 8 on the upstream side in the conveyance direction of the paper 8 with respect to the press contact portion of the transfer portion 122. Therefore, the degree of freedom regarding the installation position of the rotation axis of the transfer unit gap forming member 120 can be improved, and the rotation axis of the transfer unit gap forming member 120 is upstream of the rotation axis of the transfer roller 7 in the conveyance direction of the paper 8. By disposing the transfer portion gap forming member 120 on the side, the transfer portion gap forming member 120 can stand by in parallel with the width direction of the paper 8, and when the transfer portion gap forming member 120 is pushed by the paper 8, It is possible to receive.

  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. FIG. 3 is a cross-sectional view of an intermediate transfer unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 2A is a plan view of a pressure contact portion of a transfer portion of the image forming apparatus according to the first embodiment of the present invention. FIG. 2B is a side view of the transfer unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 2A is a plan view of a pressure contact portion of a transfer portion of the image forming apparatus according to the first embodiment of the present invention. FIG. 2B is a cross-sectional view of the transfer unit of the image forming apparatus according to the first embodiment of the present invention. 3 is a block diagram illustrating a control unit of a transfer unit of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. FIG. 5 is a flowchart illustrating an operation of a control unit of the image forming apparatus according to the first embodiment of the present invention. (A)-(c) is a top view which shows the rotational motion of the transfer part gap | interval formation member of the image forming apparatus which concerns on the 1st Embodiment of this invention in time series. (A)-(c) is a top view which shows the rotational motion of the transfer part gap | interval formation member of the image forming apparatus which concerns on the 1st Embodiment of this invention in time series. (A) is a top view of the press-contact part of the transfer part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. FIG. 6B is a cross-sectional view of a transfer portion of the image forming apparatus according to the second embodiment of the present invention. (C) is a perspective view of a transfer part gap forming member of an image forming apparatus according to a second embodiment of the present invention. (A)-(c) is a side view of the transfer part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. FIG. 6 is a side view of a transfer unit and a resist unit of an image forming apparatus according to a second embodiment of the present invention. (A)-(c) is a top view which shows the rotational motion of the transfer part gap | interval formation member of the image forming apparatus which concerns on the 2nd Embodiment of this invention in time series. (A), (b) is a top view which shows the rotational motion of the transfer part gap | interval formation member of the image forming apparatus which concerns on the 2nd Embodiment of this invention in time series. (A) is a top view of the press-contact part of the transfer part of the image forming apparatus which concerns on the 3rd Embodiment of this invention. FIG. 6B is a cross-sectional view of a transfer portion of an image forming apparatus according to a third embodiment of the present invention. FIG. 10 is a side view of a pressure contact portion of a transfer portion of an image forming apparatus according to a third embodiment of the present invention. FIG. 10 is a side view illustrating a configuration of a transfer roller of a conventional image forming apparatus. It is a side view which shows the structure of the transfer member of the conventional image forming apparatus. (A), (b) is a side view which shows the structure of the transfer member of the conventional image forming apparatus. (A), (b) is sectional drawing of the transfer part of the conventional image forming apparatus. (A), (b) is sectional drawing of the transfer part of the conventional image forming apparatus. (A), (b) is sectional drawing of the transfer part of the conventional image forming apparatus. (A), (b) is sectional drawing of the transfer part of the conventional image forming apparatus.

Explanation of symbols

1 Photosensitive drum 2 Intermediate transfer belt (image carrier)
3 Drive roller 4 Driven roller 5 Tension roller 6 Opposing roller 7 Transfer roller (transfer member)
8 paper (recording medium)
9 Compression spring 10 Transfer roller shaft (drive source)
11 Transfer part gap forming member support member (gap forming means)
11a Protrusion 12 Transfer part gap forming member (gap forming means, gap forming member)
13 Transfer part torque limiter (driving force limiting means)
15 Transfer part solenoid (control means)
15a Plunger 16 Tension spring 19 Transfer section paper passage detection sensor 21 Microprocessor 22 Transfer section solenoid drive circuit 23, 24 Bevel gear (axial direction changing means)
24a Rotating shaft 25 Side plate 25a Bracket 26 Registration roller 27 Registration pressure roller 28 Suppression member (control means)
29 Fixing member 44 Torsion coil (control means)
48 Rubber piece 50 Image forming apparatus 100 Printer unit 101 Intermediate transfer unit 102, 112, 122 Transfer unit 103 Resist unit (recording medium conveying means)
104 Control unit (control means)
120 Transfer part gap forming member (gap forming means, gap forming member)
120a, 120b Sheet member (gap forming member)
123, 124 Hypoid gear (Axial direction changing means)
200 Paper Feeding Unit 300 Scanner Unit 301 Contact Glass 400 Automatic Document Conveying Unit 401 Document Tray

Claims (6)

An image carrier that carries an image and rotates;
A transfer member that rotates in contact with the image carrier and transfers an image formed on the surface of the image carrier to a recording medium;
A recording medium conveying means for conveying a recording medium to a position where the image carrier and the transfer member are in contact with each other;
A gap forming member that rotates on a contact surface where the image carrier and the transfer member abut, and immediately before the recording medium enters the position where the image carrier and the transfer member abut, An image forming apparatus comprising: a gap forming unit that inserts the gap forming member to form a gap.   The gap forming means forms the gap immediately before the recording medium enters the position where the image carrier and the transfer member come into contact with each other by the driving force of the recording medium conveyed by the recording medium conveying means. The image forming apparatus according to claim 1, wherein a gap is formed by inserting a member. Drive means having transmission means for transmitting a driving force from the same drive source as the transfer member or the image carrier to the gap forming member; and a support member for supporting the gap forming member;
The image forming apparatus according to claim 1, further comprising a control unit that suppresses the movement of the support member.   Axial direction changing means for transmitting the driving force from the driving source to the gap forming member so that the transmitting means has a different axial direction of the rotating shaft of the driving source and the rotating shaft of the gap forming member. The image forming apparatus according to claim 3, further comprising a driving force limiting unit that limits and transmits the driving force from the driving source.   The axial direction changing means transmits the driving force from the driving source to the gap forming member so that the axial direction of the rotating shaft of the driving source and the axial direction of the rotating shaft of the gap forming member are orthogonal to each other. The image forming apparatus according to claim 4.   The axial direction changing means applies a driving force from the driving source to the gap forming member so that the axial direction of the rotating shaft of the driving source and the axial direction of the rotating shaft of the gap forming member are in a torsional position relationship. The image forming apparatus according to claim 4, wherein the image forming apparatus transmits the image.

Images