JP4966103B2 - Image forming apparatus - Google Patents

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. 16 to 19, 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). 16 and 17 show the state when the leading edge of the paper 58 enters the pressure contact portion of the transfer portion, and FIGS. 18 and 19 show the state when the trailing edge of the paper 58 comes out from the pressure contact portion of the transfer portion. It is shown. 16A, FIG. 17A, FIG. 18A, and FIG. 19A are cross-sectional views of the transfer portion in the width direction of the paper 58, and FIG. 16B and FIG. b), FIG. 18B, and FIG. 19B are cross-sectional views of the transfer portion 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 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. 18, the transfer roller 57 is pushed down by an amount corresponding to the thickness of the paper 58, 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. 13, 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. 14, 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. 15, 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. 16 to 19, 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 unit that conveys the recording medium to a position where the image carrier and the transfer member abut, and a driving force of the recording medium conveyed by the recording medium conveying unit. A gap forming means for forming a gap at a position where the transfer member abuts is provided.

  With this configuration, a gap is formed at a position where the image carrier and the transfer member abut by the driving force of the recording medium, so that the image carrier and the transfer member are abutted without detecting the leading edge of the recording medium by a sensor or the like. Since the gap can be surely formed immediately before the recording medium enters the contact position, it is possible to reduce the rotational load generated on the image carrier and to perform good image formation.

  In addition, the image forming apparatus according to the present invention includes a determination unit that determines whether or not the gap forming unit forms a gap at a position where the image carrier and the transfer member are in contact with each other. .

  With this configuration, it is determined in advance whether or not to form a gap according to the thickness of the recording medium, so that it is determined whether or not to form a gap based on the set state. When plain paper is used in which the speed fluctuation of the image carrier at the time of entry is small and the influence on the image can be ignored, gap formation can be avoided.

  Further, in the image forming apparatus according to the present invention, the gap forming unit rotates in the same direction as the rotation direction of the transfer member, and the transfer member is positioned at both ends of the position where the image carrier and the transfer member abut. It has a sheet-like gap forming member inserted from the same direction as the rotation direction, and driving means for driving the gap forming member.

  With this configuration, the gaps can be formed uniformly at both ends of the position where the image carrier and the transfer member abut, so that the distribution of the transfer pressure to the recording medium can be made uniform. Further, since a sheet-like gap forming member is used, a desired gap can be formed by changing the thickness of the gap forming member.

  Further, in the image forming apparatus according to the present invention, the gap forming member sandwiches both sides of the recording medium immediately before the image carrier and the transfer member abut at the end of the recording medium in the sub-scanning direction. It is characterized by doing.

  With this configuration, by sandwiching both sides of the recording medium with the gap forming member, the leading edge of the recording medium is not detached from the gap forming member, and the driving force of the recording medium can be stably received. It can be inserted at a position where the image carrier and the transfer member come into contact with the leading edge of the recording medium.

  In the image forming apparatus according to the present invention, the driving unit 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 the gap forming member. It has the supporting member to support, and the control means which suppresses the motion of the said supporting member, It is characterized by the above-mentioned.

  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 member and the control means for transmitting the driving force.

  The image forming apparatus according to the present invention is characterized in that the transmission unit includes a driving force limiting unit that limits and transmits a driving force from the driving source.

  With this configuration, since the driving force from the driving source is limited and transmitted to the gap forming member via the driving force limiting means, the transfer member or the image bearing member is supported when the movement of the support member is suppressed by the control means. No influence on the body drive source. 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 control unit includes a suppression unit that suppresses the rotational movement of the support member in a state where the gap forming member is on a conveyance path of the recording medium. Is set to be larger than the limit torque of the driving force limiting means, and is less than the sum of the limiting torque of the driving force limiting means and the rotational torque that rotates the support member by the driving force of the recording medium. It is characterized by being set small.

  With this configuration, when the recording medium does not enter the gap forming member, rotation of the support member is suppressed by the suppressing unit, and when the recording medium enters the gap forming member, rotation of the support member is allowed by the suppressing unit. Thus, the gap forming member can be inserted into the position where the image carrier and the transfer member come into contact with the leading end of the recording medium.

  Further, the image forming apparatus according to the present invention is characterized in that the control means has a restricting means for restricting the rotational movement of the support member in a state where the gap forming member is not on the transport path of the recording medium. .

  With this configuration, when the determination unit determines not to form a gap, the gap forming member is placed on the conveyance path of the recording medium so that the gap forming member is not inserted at a position where the image carrier and the transfer member are in contact with each other. The rotation of the support member can be restricted in the absence of this.

  In the image forming apparatus according to the present invention, the gap forming member includes a sheet-shaped first member that contacts one surface of the recording medium and a sheet-shaped second member that contacts the other surface of the recording medium. It has a member and the elastic member arrange | positioned between the said 1st member and the said 2nd member, It is characterized by the above-mentioned.

  With this configuration, the recording medium is again put in the standby state after the first member and the second member of the gap forming member are inserted at a position where the image carrier and the transfer member are in contact with each other by the restoring force of the elastic member. It can be opened for easy clamping.

  The image forming apparatus according to the present invention is characterized in that the first member and the second member have flexibility.

  With this configuration, after the leading end of the recording medium is removed from the position where the image carrier and the transfer member abut, the first member and the second member of the flexible gap forming member are bent to facilitate the recording medium. You can leave.

  The image forming apparatus according to the present invention is characterized in that the shapes of the first member and the second member have a distribution with respect to the sub-scanning direction of the recording medium.

  With this configuration, when the shapes of the end portions of the first member and the second member of the gap forming member are cut obliquely in the sub-scanning direction of the recording medium, the image carrier and the transfer member are in contact with each other. It is possible to prevent the speed of the image carrier from fluctuating when the gap forming member enters the contact position.

  In the image forming apparatus according to the present invention, the thicknesses of the first member and the second member have a distribution with respect to the sub-scanning direction of the recording medium.

  With this configuration, when the thicknesses of the end portions of the first member and the second member of the gap forming member are reduced toward the front end in the traveling direction, the image carrier and the transfer member come into contact with each other. It is possible to prevent the speed of the image carrier from fluctuating when the gap forming member enters the position.

  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 23 and a registration pressure roller 24 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 23 is driven by a motor (not shown), and the registration pressure roller 24 is driven in contact with the registration roller 23.

  At the time of the transfer operation, the paper 8 supplied from the paper supply unit 200 stands by at a place where the registration roller 23 and the registration pressure roller 24 are installed, and when the toner image is transferred to the intermediate transfer belt 2, By the registration pressure roller 24, 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 end 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 is transferred by the primary transfer while being sandwiched by the registration roller 23, and the toner image is secondarily transferred onto the paper 8 by the transfer roller 7. A transfer method is adopted. The opposing roller 6 and the transfer roller 7 constitute a transfer unit 102, and the registration roller 23 and the registration pressure roller 24 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. 3 is a perspective view of the transfer unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view of the transfer portion of the image forming apparatus according to the first embodiment of the present invention. FIGS. 5A to 5C are side views of the transfer portion of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIGS. 3 and 4, the transfer unit 102 has a predetermined timing 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 part gap forming member 12 that forms a gap and a transfer part gap forming member support member 11 that supports the transfer part gap forming member 12 are provided. The thickness of the transfer portion gap forming member 12 is set to be thinner than the thickness of the paper 8.

  The transfer part gap forming member 12 is composed of two sheet members 12a and 12b joined in a substantially V shape. As shown in FIG. 5A, the sheet member 12a and the sheet member 12b 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 12 is inserted into the press contact portion when the leading end of the paper 8 is sandwiched between the sheet members 12 a and 12 b and is pushed by the propulsive force of the paper 8. The sheet member 12b in contact with the transfer roller 7 is formed to be longer in the sub-scanning direction, that is, the conveyance direction of the paper 8, than the sheet member 12a in contact with the opposing roller 6, and the leading edge of the paper 8 is shown in FIG. As shown in FIG. 5, the sheet member 12b is first brought into contact with the sheet member 12b, and is then sandwiched between the sheet member 12a and the sheet member 12b as shown in FIG. Further, since the sheet members 12a and 12b have flexibility, as shown in FIG. 5C, the leading edge of the paper 8 is easily separated from the sheet members 12a and 12b.

  The sheet members 12a and 12b constituting the transfer portion gap forming member 12 are required to have sufficient flexibility to be in close contact with both rollers when sandwiched between the counter roller 6 and the transfer roller 7, and the counter roller 6 In a standby state in which the transfer roller 7 is not sandwiched, a certain degree of flatness must be maintained by the restoring force. Therefore, a flexible sheet material is used as the sheet members 12a and 12b. 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. The sheet members 12a and 12b are desirably as thin as possible in order to reduce the running load of the intermediate transfer belt 2 when the leading end of the paper 8 is inserted into the sheet members 12a and 12b.

  Further, a rubber piece 48 as an elastic body is provided between the sheet member 12a and the sheet member 12b, and the interval between the sheet member 12a and the sheet member 12b is transferred as shown in FIG. After receiving the pressure contact at the part 102, the original interval is restored. The thickness when the rubber piece 48 is compressed is preferably set according to the thickness of the paper 8.

As shown in FIG. 5A, the transfer portion gap forming member 12 waits immediately before the pressure contact portion of the transfer portion 102 in the conveyance path of the paper 8 so as to enter the pressure contact portion by the driving force of the paper 8. Further, the transfer unit 102 includes a transfer unit torque limiter 13 which is a transmission member that transmits the rotational driving force of the transfer roller shaft 10 to the transfer unit gap forming member support member 11, and the transfer roller shaft 10 is formed with the transfer unit gap forming. The drive source of the member 12 is used. A transfer portion torque limiter 13 is press-fitted into the transfer portion gap forming member support member 11, and a transfer roller shaft 10 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.

  The transfer unit 102 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 lower part of the transfer roller shaft 10. 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 12 stands by immediately before the pressure contact portion of the transfer portion 102 in the conveyance path of the paper 8. .

  When the restraining member 28 and the fixing member 29 are within a predetermined angle range, the torsion coil 44 is transferred by bringing the restraining member 28 into contact with the transfer portion gap forming member support member 11 by a restoring force as a torsion spring. In addition to suppressing the rotation of the gap forming member 12, and when the suppressing member 28 and the fixing member 29 are opened at a predetermined angle or more, the trajectory of the transfer gap forming member support member 11 is out of the movable range of the suppressing member 28. Thus, the transfer part gap forming member support member 11 is allowed to rotate.

  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 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 end of the paper 8 enters between the transfer portion gap forming members 12. Torque is rF. For this reason, when the leading edge of the paper 8 enters between the transfer portion gap forming members 12, the torsion coil 44 opens by a 2 [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. 6, the boundary conditions of horizontal, vertical fixation, and free rotation are set at the front end 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 102 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.

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

  FIG. 7A to FIG. 7E are side views showing the state of rotational movement of the transfer unit gap forming member support member of the image forming apparatus according to the first embodiment of the present invention in time series.

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

  When the driving of the intermediate transfer belt 2 is started, as shown in FIG. 7B, the transfer roller 7 is rotated, so that the transfer part gap forming member support member 11 is rotated via the transfer part 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 paper 8 enters the transfer portion gap forming member 12, as shown in FIG. 7C, the driving force F of the paper 8 rotates the transfer portion gap forming member support member 11 through the transfer portion gap forming member 12. The transfer portion gap forming member support member 11 rotates to further spread the suppressing member 28 as torque.

  When the paper 8 enters the pressure contact portion of the transfer portion 102, the transfer roller 7 is pushed down with the transfer portion gap forming member 12 sandwiching the leading end of the paper 8 as shown in FIG. 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 102, as shown in FIG. 7E, the transfer portion gap forming member 12 is separated from the front end of the paper 8, and the transfer portion gap forming member support member 11 is Subsequently, it is rotated by drive transmission from the transfer portion torque limiter 13. Thereafter, the transfer portion 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 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 exemplary embodiment causes the transfer unit gap forming member 12 to stand by on the conveyance path of the sheet 8 in the pressure contact portion of the transfer unit 102 and the sheet 8 conveyed by the resist unit 103. Since the transfer portion gap forming member 12 supported by the transfer portion gap forming member support member 11 is caused to enter the pressure contact portion by the propulsive force to form a gap, the pressure contact portion is detected without detecting the front end of the paper 8 by a sensor or the like. Since the gap can be surely formed immediately before the sheet 8 enters, the rotational load generated on the intermediate transfer belt 2 can be reduced and good image formation can be performed.

  Further, in the image forming apparatus according to the present embodiment, the transfer section gap forming member 12 is formed in a sheet shape and rotates in the same direction as the rotation direction of the transfer roller 7, so that both ends of the pressure contact section of the transfer section 102 are Since the transfer section gap forming member 12 is driven while being supported by the transfer section gap forming member support member 11 by the driving force transmitted from the transfer roller shaft 10, the transfer section gap forming member 12 is driven by the driving force transmitted from the transfer roller shaft 10. A gap can be formed evenly at both ends of the pressure contact portion of the transfer portion 102, the distribution of the transfer pressure to the paper 8 can be made uniform, and the thickness of the sheet-like transfer portion gap forming member 12 can be changed. A desired gap can be formed.

  Further, the image forming apparatus according to the present embodiment forms a gap at the pressure contact portion of the transfer portion 102 in a state where the transfer portion gap forming member 12 including the sheet members 12 a and 12 b sandwiches both surfaces of the leading end portion of the paper 8. Therefore, the leading end of the sheet 8 does not come off from the transfer part gap forming member 12, and the driving force of the sheet 8 can be stably received. Accordingly, it can be inserted into the pressure contact portion of the transfer portion 102.

  Further, in the image forming apparatus according to the present embodiment, the transfer portion gap forming member 12 is rotated by the same drive source as the transfer roller 7 or the intermediate transfer belt 2, thereby avoiding a complicated structure. Thus, cost reduction and space saving can be achieved.

  In addition, the image forming apparatus according to the present embodiment includes the suppressing member 28 and the torsion coil 44 that suppress the movement of the transfer portion gap forming member support member 11 that supports the transfer portion gap forming member 12. The gap forming member 12 can be inserted into the pressure contact portion of the transfer portion 102 at an arbitrary timing.

  In the image forming apparatus according to the present embodiment, the driving force is transmitted from the transfer roller shaft 10 to the transfer portion gap forming member support member 11 via the transfer portion torque limiter 13. When the movement of the forming member support member 11 is suppressed, the transfer roller shaft 10 can rotate stably without being affected, and when the movement of the transfer portion gap forming member support member 11 is suppressed. The transfer part gap forming member support member 11 can reliably rotate.

  Further, in the image forming apparatus according to the present embodiment, the suppression torque by the suppression member 28 and the torsion coil 44 is set to be larger than the limit torque of the transfer portion torque limiter 13, and the limit torque of the transfer portion torque limiter 13 is The transfer portion gap forming member support member 11 is set to be smaller than the sum of the rotational torques of the transfer portion gap forming member support member 11. When the paper 8 does not enter the transfer portion gap forming member 12, the transfer portion gap forming member support is supported. When the rotation of the member 11 is suppressed and the paper 8 enters the transfer portion gap forming member 12, the transfer portion gap forming member support member 11 is allowed to rotate, and the transfer portion gap forming member 12 is moved over the paper 8. The tip can be inserted into the pressure contact portion of the transfer portion 102.

  In the image forming apparatus according to the present embodiment, since the rubber piece 48 as the elastic member is provided between the sheet member 12a in contact with the upper surface of the paper 8 and the sheet member 12b in contact with the lower surface of the paper 8, the sheet member 12a and 12b can be opened in a state in which the sheet 8 is easily held again by the restoring force of the rubber piece 48 in a standby state after being inserted into the pressure contact portion of the transfer portion 102.

  Further, in the image forming apparatus according to the present embodiment, since the sheet members 12a and 12b are flexible, the sheet members 12a and 12b are bent after the leading end of the paper 8 is removed from the press contact portion of the transfer unit 102. The paper 8 can be easily detached.

(Second Embodiment)
FIG. 8 is a side view of the transfer unit 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 FIG. 8, the transfer unit 112 includes a mechanism that controls the rotation of the transfer unit gap forming member support member 11 when the transfer unit gap forming member 12 is not on the conveyance path of the paper 8. When it is thin, the transfer portion gap forming member 12 is configured not to be inserted into the pressure contact portion of the transfer portion 112. The transfer unit 112 includes a transfer unit solenoid 15, a transfer unit ratchet 14, and a tension spring 16. That is, the image forming apparatus 50 according to the second embodiment is configured to suppress and allow the rotation of the transfer portion gap forming member support member 11 by electrical control.

  When the transfer portion solenoid 15 is not energized, the transfer portion ratchet 14 moves to the right side of FIG. Thus, the rotation of the transfer portion gap forming member support member 11 is suppressed.

  Further, when the transfer portion solenoid 15 is energized, the transfer portion ratchet 14 moves to the left side of FIG. 8 around the rotation fulcrum 14a. Pulled outwardly, the transfer part gap forming member support member 11 is allowed to rotate.

  FIG. 9 is a block diagram showing a control unit of the transfer unit of the image forming apparatus according to the second embodiment of the present invention.

  As shown in FIG. 9, the control unit 104 includes a microprocessor 21 and a transfer unit solenoid drive circuit 22, and controls the drive of the transfer unit solenoid 15. When the microprocessor 21 detects that a start signal for driving the registration roller 23 is transmitted from a control unit (not shown) of the image forming apparatus 50, the transfer unit solenoid drive circuit 22 causes the transfer unit solenoid 15 to move for a short time (for example, 0.3 seconds).

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

  FIG. 10 is a flowchart for explaining the operation of the control unit of the image forming apparatus according to the second embodiment of the present invention. FIGS. 11A to 11F are side views showing the state of the rotational movement of the transfer portion gap forming member support member of the image forming apparatus according to the second embodiment of the present invention in time series. is there.

  As shown in FIG. 10, the control unit 104 determines whether or not the setting mode is set to the thick paper mode by the user (step S1). If the setting mode is the thick paper mode, the control unit 104 determines whether or not there is a print request. (Step S2). That is, in step S <b> 1, it is determined whether or not a gap is formed in the pressure contact portion of the transfer portion 112 by the gap forming member 12 based on whether or not the setting mode is set to the thick paper mode by the user.

  If it is determined in step S2 that there is a print request, the control unit 104 determines whether or not the registration roller 23 has started to be driven by a control unit (not shown) of the image forming apparatus 50 (step S3).

  As described above, in steps S1 to S3, as shown in FIG. 11A, the transfer part gap forming member support member 11 is in a state in which the rotation is suppressed by the transfer part ratchet 14.

  If it is determined in step S3 that the registration roller 23 has started driving, the control unit 104 turns on the transfer unit solenoid 15 (step S4), and then turns off the transfer unit solenoid 15 (step S5). . The time from when the transfer unit solenoid 15 is turned on at step S4 to when it is turned off at step S5 is as short as 0.3 seconds as described above.

  As described above, in step S4, the print job is started with the thick paper mode selected by the user setting, and the control unit 104 energizes the transfer unit solenoid 15 for a short time in synchronization with the start of driving of the registration roller 23. To do. Accordingly, as shown in FIG. 11B, when the transfer portion ratchet 14 is pulled out of the rotation path of the transfer portion gap forming member support member 11, the transfer portion gap forming member support member 11 is moved to the transfer portion torque limiter. In response to the drive transmission from 13, the rotation starts. Thereafter, as shown in FIG. 11C, when the transfer portion gap forming member support member 11 reaches the installation position of the suppressing member 28, rotation of the transfer portion gap forming member support member 11 is suppressed by the restoring force of the torsion coil 44. Then, the transfer part gap forming member 12 stands by on the conveyance path of the paper 8. Then, as shown in FIG. 11 (d), when the leading edge of the paper 8 collides with the transfer part gap forming member 12, the paper 8 driving force F is converted into the rotational torque of the transfer part gap forming member support member 11. The torsion coil 44 is expanded to an angle outside the rotation orbit of the transfer part gap forming member support member 11 and the transfer part gap forming member support member 11 is rotated, and as shown in FIG. It is inserted into the pressure contact portion of the transfer portion 112 together with the gap forming member 12. After the paper 8 enters the pressure contact portion of the transfer portion 112, the transfer portion gap forming member 12 is separated from the leading end of the paper 8 as shown in FIG. Continues to rotate by drive transmission from the transfer portion torque limiter 13. Thereafter, the transfer part gap forming member support member 11 reaches the installation position of the transfer part ratchet 14 and returns to the standby state shown in FIG.

  On the other hand, if the determination in step S1 is “NO”, that is, the thick paper mode is not set, the control unit 104 assumes that the plain paper mode is set, and does not perform the operations of steps S2 to S5, but the transfer unit solenoid 15. Is kept off, and the transfer part ratchet 14 always suppresses the rotation of the transfer part gap forming member support member 11 and makes the transfer part gap forming member 12 stand by on the conveyance path of the paper 8. For this reason, in the plain paper mode, when the paper 8 has a low Young's modulus and the paper 8 is thin and easily buckled, the paper 8 collides with the transfer portion gap forming member 12 to cause a paper jam or the like. Is prevented. The other end side of the transfer unit 112 is configured in the same manner.

  Note that a detection unit that detects the thickness of the paper 8 is provided, and the control unit 104 determines whether or not to execute the thick paper mode in step S1 according to the thickness of the paper 8 detected by the detection unit. May be. In this case, when the paper 8 is thick, a gap can be automatically formed in the pressure contact portion of the transfer portion 112.

  As described above, the image forming apparatus according to the present embodiment includes the control unit 104 that determines whether or not the transfer unit gap forming member 12 forms a gap in the pressure contact portion of the transfer unit 112. When a sheet 8 having a normal thickness is used in which the speed fluctuation of the intermediate transfer belt 2 is small when the leading end of the sheet 8 enters the pressure contact portion of the transfer unit 112 and the influence on the image can be ignored. It is possible to prevent gap formation without setting the thick paper mode.

  In addition, the image forming apparatus according to the present embodiment always suppresses the rotation of the transfer unit gap forming member support member 11 and causes the transfer unit gap forming member 12 to stand by on the conveyance path of the paper 8. And the transfer portion ratchet 14 driven by the transfer portion solenoid 15, the transfer portion gap forming member 12 is not set in the thick paper mode and the control portion 104 determines that no gap is formed. The rotation of the transfer portion gap forming member support member 11 can be restricted in a state where the transfer portion gap forming member 12 is not on the conveyance path of the paper 8 so that it is not inserted into the press contact portion of the transfer portion 112.

(Third embodiment)
FIG. 12A 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. 12B is a side view of the transfer unit of the image forming apparatus according to the third embodiment of the present invention.

  As shown in FIG. 12A, in the transfer unit 122, the leading end side of the transfer unit gap forming member 12 is cut obliquely in the width direction toward the conveyance direction of the paper 8. Further, as shown in FIG. 12B, the tip of the transfer portion gap forming member 12 has a wedge shape with an inclination in the thickness direction. In other words, in the present embodiment, the shape and thickness of the transfer portion gap forming member 12 are different from those in the above-described embodiments, and have a distribution in the image sub-scanning direction (the conveyance direction of the paper 8). In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. Therefore, the speed fluctuation of the intermediate transfer belt 2 that occurs when the leading end of the transfer portion gap forming member 12 enters the pressure contact portion of the transfer portion 122 is reduced. It should be noted that the transfer portion gap forming member 12 can obtain the same effect even when only one of the width direction and the thickness direction is inclined. The other end side of the transfer unit 122 is configured in the same manner.

  12A and 12B, the leading end side of the transfer portion gap forming member 12, that is, the end portion in the moving direction of the transfer portion gap forming member 12 is moved in the width direction toward the conveyance direction of the paper 8. In contrast to this, it is wedge-shaped with an inclination in the thickness direction. On the contrary, the rear end side of the transfer portion gap forming member 12, that is, the transfer portion gap forming member 12 The end opposite to the traveling direction may be cut obliquely in the width direction toward the conveyance direction of the paper 8 and may be wedge-shaped with an inclination in the thickness direction.

  As described above, in the image forming apparatus according to the present embodiment, the shape of the transfer portion gap forming member 12 in the conveyance direction of the paper 8 has a distribution in the image sub-scanning direction. That is, the leading end side of the transfer portion gap forming member 12 is cut obliquely in the width direction toward the conveyance direction of the paper 8. For this reason, it is possible to suppress the speed fluctuation of the intermediate transfer belt 2 that occurs when the transfer portion gap forming member 12 itself enters the pressure contact portion of the transfer portion 122.

  Further, in the image forming apparatus according to the present embodiment, the thickness of the transfer portion gap forming member 12 in the conveyance direction of the paper 8 has a distribution in the image sub-scanning direction. That is, the thickness of the transfer part gap forming member 12 is reduced toward the tip. Therefore, it is possible to suppress the speed fluctuation of the intermediate transfer belt 2 that occurs when the transfer portion gap forming member 12 enters the pressure contact portion of the transfer portion 122.

  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. 2 is a cross-sectional view of an intermediate transfer unit of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 1 is a perspective view of a transfer unit of an image forming apparatus according to a first embodiment of the present invention. 2 is a cross-sectional view of a transfer unit of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. (A)-(c) is a side view of the transfer part of the image forming apparatus which concerns on the 1st Embodiment of this invention. 2 is a side view of a transfer portion and a resist portion of the image forming apparatus according to the first embodiment of the present invention. FIG. (A)-(e) is a side view which shows the state of the rotational motion of the transfer part gap | interval formation member support member of the image forming apparatus which concerns on the 1st Embodiment of this invention in time series. FIG. 6 is a side view of a transfer unit of an image forming apparatus according to a second embodiment of the present invention. 7 is a block diagram illustrating a control unit of a transfer unit of an image forming apparatus according to a second embodiment of the present invention. FIG. FIG. 10 is a flowchart illustrating an operation of a control unit of an image forming apparatus according to a second embodiment of the present invention. (A)-(f) is a side view which shows the state of the rotational motion of the transfer part gap | interval formation member support 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. (B) is a side 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 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, driving means, transmission means)
12 Transfer part gap forming member (gap forming means, gap forming member)
12a Sheet member (first member)
12b Sheet member (second member)
13 Transfer part torque limiter (driving means, transmitting means, driving force limiting means)
14 Transfer part ratchet (control means, regulation means)
14a Rotating fulcrum 15 Transfer part solenoid (regulating means)
16 Tension Spring 21 Microprocessor 22 Transfer Unit Solenoid Drive Circuit 23 Registration Roller 24 Registration Pressure Roller 28 Suppression Member (Control Unit, Suppression Unit)
29 Fixing member 44 Torsion coil (control means, suppression means)
48 Rubber piece (elastic member)
DESCRIPTION OF SYMBOLS 50 Image forming apparatus 100 Printer part 101 Intermediate transfer part 102,112,122 Transfer part 103 Registration part (Recording medium conveyance means)
104 Control unit (determination 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 means for forming a gap at a position where the image carrier and the transfer member are in contact by a propulsive force of the recording medium conveyed by the recording medium conveying means ;
The gap forming means is provided so as to be rotatable in the same direction as the rotation direction of the transfer member, and at a standby position upstream of the recording medium conveyance direction from the position where the image carrier and the transfer member abut. After waiting, the sheet-shaped gap forming member inserted from both ends of the position where the image carrier and the transfer member are in contact with each other by the driving force of the recording medium from the same direction as the rotation direction of the transfer member; Drive means for rotating the gap forming member in the same direction as the rotation direction of the transfer member and waiting at the standby position;
The gap forming member sandwiches both sides of the recording medium immediately before the image carrier and the transfer member abut at the end of the recording medium in the sub-scanning direction,
The drive means transmits a drive force from the same drive source as the transfer member or the image carrier to the gap forming member, a support member that supports the gap forming member, and movement of the support member Control means for suppressing
The transmission means includes a driving force limiting means for limiting and transmitting a driving force from the driving source;
The control means includes suppression means for suppressing the rotational movement of the support member in a state where the gap forming member is on a conveyance path of the recording medium;
The suppression torque of the suppression means is set to be larger than the limit torque of the driving force limiting means, and the torque limit of the driving force limiting means and the rotational torque that rotates the support member by the driving force of the recording medium. An image forming apparatus, wherein the image forming apparatus is set smaller than the sum . The image forming apparatus according to claim 1, wherein the control unit includes a regulating unit that regulates the rotational movement of the support member in a state where the gap forming member is not on a conveyance path of the recording medium . The gap forming member includes a sheet-like first member in contact with one surface of the recording medium, a sheet-like second member in contact with the other surface of the recording medium, the first member, and the first member. The image forming apparatus according to claim 1, further comprising an elastic member disposed between the two members . The image forming apparatus according to claim 3 , wherein the first member and the second member have flexibility . The image forming apparatus according to claim 3, wherein the shapes of the first member and the second member have a distribution with respect to a sub-scanning direction of the recording medium . 6. The image according to claim 3, wherein thicknesses of the first member and the second member have a distribution in a sub-scanning direction of the recording medium. Forming equipment.

Images