JP2008281930A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which does not cause color shift even when using cardboard by regulating space between an intermediate transfer belt and a secondary transfer roller in accordance with the thickness of a recording medium. <P>SOLUTION: The rotation in a direction shown by an arrow (a) of a drive shaft 60 by a motor 58 makes a shaft 18a rotate in a direction shown by an arrow (b) through gears 57 and 56. The recording medium P held in a transfer nip part N between the intermediate transfer belt 17 and the secondary transfer roller 18 regulated by pitch rings 51a and 51b is conveyed in an upward direction from the downside of a paper surface by rotation in the direction shown by the arrow (b) of the secondary transfer roller 18. When preventing the color shift caused when using the cardboard, the interval of the transfer nip part N is changed. By rotating the pitch rings 51a and 51b whose outer shape is elliptical through the drive shaft 60 and gears 55 and 54, and setting the rotational angle positions of the pitch rings 51a and 51b detected by a photosensor 61 to the rotational angle positions fit for the thickness of the recording medium, the transfer nip part N fit for the thickness of the recording medium is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electronic copying machine, a printer, or a complex machine thereof, and more particularly to an image forming apparatus provided with a color misregistration preventing unit of a color image forming apparatus.

  In a color image forming apparatus, for example, a tandem color image forming apparatus, four image forming units each including a photoconductor and a developing device corresponding to yellow, cyan, magenta, and black toners, and four image forming units And an endless intermediate transfer belt, a primary transfer device, and a secondary transfer roller for transferring a toner image formed on the intermediate transfer belt to a recording medium.

  The production process of the above-described tandem full-color image print is as follows. First, four image forming units are activated by image signals output from a scanner that scans a document image or a personal computer, and each color of yellow, cyan, magenta, and black is formed on the photosensitive member of the image forming unit corresponding to each color. The toner image is formed. The toner images of the respective colors formed on the photoconductor are sequentially superimposed and transferred onto an intermediate transfer belt that moves in a predetermined direction by the action of the primary transfer device, thereby forming a full-color toner image.

  The recording medium is conveyed toward the secondary transfer roller at the timing when the full color toner image on the intermediate transfer belt moving in a predetermined direction moves to the position of the secondary transfer roller, and the full color toner image on the intermediate transfer belt is The image is transferred onto the recording medium by the action of the secondary transfer roller. Thereafter, the full color toner image transferred onto the recording medium is subjected to a fixing process by a fixing device to form a full color image print.

  In the image forming apparatus having such a configuration, when the recording medium is thick (hereinafter, “thick paper”), the thick paper enters the transfer portion (secondary transfer portion) of the secondary transfer roller and moves at a constant speed. It has been found that the speed of the intermediate transfer belt decreases for a short time and color misregistration occurs due to impact.

  As a countermeasure against this inconvenience, the speed control amount of the intermediate transfer belt is changed by a predetermined timing, a predetermined amount, and a predetermined duration, that is, the speed is increased to correct the speed reduction of the intermediate transfer belt, A configuration for maintaining the speed of the intermediate transfer belt constant has been proposed (see Patent Document 1).

  Further, in the image forming apparatus having such a configuration, when the recording medium is thick paper, it is separated from the intermediate transfer belt due to the strength of the thick paper, and the width of the nip portion of the secondary transfer portion is reduced, so that proper transfer can be performed. It turns out that there is an inconvenience that is not done.

As a countermeasure against this inconvenience, it has been proposed to switch the contact pressure between the cardboard and the intermediate transfer belt in a plurality of stages (see Patent Document 2).
JP-A-2005-107118 JP 2002-214943 A

  However, as a countermeasure against the inconvenience that the speed of the intermediate transfer belt that has moved at a constant speed decreases for a short time, the speed of the intermediate transfer belt is set at a predetermined timing, a predetermined amount, and a predetermined duration. If the recording medium deviates from a predetermined arrival time when the recording medium arrives at the nip portion of the secondary transfer portion due to timing of clutch operation of the recording medium conveyance mechanism or component tolerance, the intermediate transfer belt is controlled. Speed control does not work properly.

  In addition, when the recording medium is thick paper, as a countermeasure to the inconvenience that it is separated from the intermediate transfer belt due to the stiffness of the thick paper and the width of the nip portion of the transfer portion is reduced and proper transfer is not performed. When the contact pressure between the intermediate transfer belt and the intermediate transfer belt is switched in a plurality of stages, the amount of biting into the thick paper by the secondary transfer roller that applies the pressure contact force depends on the hardness of the thick paper and is not stable. In addition, it is difficult to manage the left and right balance of the pressing force in the longitudinal direction of the secondary transfer roller only by the pressing force, which causes a skew feeding of the recording medium (thick paper).

  The present invention provides an image forming apparatus that eliminates the above-described disadvantages, prevents color shift due to impact on the nip portion of the secondary transfer portion when passing thick paper, and can form a high-quality full-color image. It is intended to do.

  SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the invention according to claim 1 provides a secondary transfer of a toner image formed on the intermediate transfer member by an image forming device disposed along the endless belt-like intermediate transfer member. In the image forming apparatus for transferring onto a recording medium by a roller, the image forming apparatus includes a regulating member that regulates a distance between transfer nip portions formed between the intermediate transfer member and the secondary transfer roller, and the regulating member includes the transfer nip. The image forming apparatus is characterized in that the interval between the portions is regulated to a predetermined interval corresponding to the thickness of the recording medium passing therethrough.

  The restricting member is an elliptical member arranged coaxially with the secondary transfer roller that can be set at an angular position corresponding to the thickness of the recording medium, and the elliptical member is an angle corresponding to the thickness of the recording medium. The distance between the transfer nips is set to a predetermined distance corresponding to the thickness of the recording medium passing therethrough.

  The regulating member is a plurality of elliptical members arranged coaxially with the secondary transfer roller that can be set at an angular position corresponding to the thickness of the recording medium, and each of the plurality of elliptical members is recorded independently. By setting the angular position corresponding to the thickness of the medium, the interval between the transfer nip portions in the axial direction of the secondary transfer roller can be regulated to a predetermined interval corresponding to the thickness of the recording medium that passes.

  Further, the outer edge of the elliptical member abuts on the abutting portion on the frame of the image forming apparatus, the regulating member is set at an angular position corresponding to the thickness of the recording medium, and the secondary transfer roller The distance between the shaft and the contact portion can be restricted to a predetermined distance corresponding to the thickness of the recording medium.

  The contact portion on the frame with which the restriction member contacts is one or a plurality of step portions corresponding to the thickness of the recording medium.

  In addition, the image forming apparatus may include an operation panel and an operation member that sets the interval of the transfer nip portion to a predetermined interval based on the recording medium thickness information input from the operation panel.

  The image forming apparatus includes a detection device that detects the thickness of the recording medium upstream of the transfer nip portion formed between the intermediate transfer member and the secondary transfer roller in the recording medium conveyance direction, and the detected recording An operation member that operates the restriction member based on medium thickness information to set the interval between the transfer nip portions to a predetermined interval may be provided.

  In this case, the operation member sets the elliptical member of the restricting member at an angular position corresponding to the thickness of the recording medium.

  And the said operation member shall contact | abut the elliptical member of the said limitation member to the step part of the contact part on the flame | frame corresponding to the thickness of a recording medium.

  The present invention relates to an image forming apparatus in which a toner image formed on an intermediate transfer body is transferred onto a recording medium by a secondary transfer roller by an image forming apparatus disposed along the endless belt-shaped intermediate transfer body. Since the interval between the transfer nip portions formed between the transfer body and the secondary transfer roller is regulated to a predetermined interval corresponding to the thickness of the recording medium passing through the nip portion by the regulating member, the sheet is passed. Regardless of the type of recording medium with different thicknesses, the contact pressure between the recording medium and the intermediate transfer belt can always be kept appropriate by regulating the distance between the transfer nip portions according to the thickness of the recording medium. it can. Even when the recording medium is thick paper, color misregistration due to collision with the nip portion of the secondary transfer portion can be prevented during paper feeding, and a high-quality full-color image can be formed.

  Hereinafter, an embodiment in which the present invention is applied to a tandem full-color image forming apparatus will be described.

  FIG. 1 is a diagram for explaining the configuration of a tandem full-color image forming apparatus 10 to which the present invention is applied. The tandem full-color image forming apparatus itself is a known configuration as described in the background art. Only the outline is explained briefly.

  In FIG. 1, image forming units 11, 12, 13, and 14 that form images of yellow (Y), magenta (M), cyan (C), and black (K) colors are a driving roller 15 and a driven roller 16. The intermediate transfer belt 17 is arranged in series under an intermediate transfer belt 17 that is an intermediate transfer member laid between the two, and the intermediate transfer belt 17 is fixed in the direction of arrow a by a driving roller 15 driven through a motor and a driving device (not shown). It is configured to move at speed.

  Each of the image forming units 11 to 14 is provided with a photoreceptor, which is an image carrier, a charging device, an exposure device, a developing device, and a cleaning device. Since the configuration is not the subject of the present invention, the description is omitted here. The image signal processing device 20 receives an image signal output from a scanner (not shown) or an image signal output from a personal computer or the like, and corresponds to the color of the image to be formed in the exposure device of each image forming unit 11-14. The output image signal is output. A paper feeding device 21 is disposed below the image signal processing device 20.

  The image forming units 11 to 14 are not provided with a transfer device. Instead, the primary transfer rollers 11T, 12T, 13T, and 14T are disposed on the opposite side of the image forming units 11 to 14 with the intermediate transfer belt 17 interposed therebetween. Is arranged.

  A secondary transfer roller 18 is disposed in pressure contact with the drive roller 15 across the intermediate transfer belt 17, and a transfer nip N is formed at a contact portion between the intermediate transfer belt 17 and the secondary transfer roller 18. . A cleaning device 19 is disposed on the intermediate transfer belt 17 at a position facing the driven roller 16 with the intermediate transfer belt 17 interposed therebetween.

  On the upstream side of the secondary transfer roller 18 in the recording medium conveyance direction, registration rollers 71 a and 71 b are arranged to form a registration roller pair 71. The leading edge of the recording medium P conveyed from the paper feeding device 21 temporarily stops at the nip portion of the registration rollers 71a and 71b, and the registration rollers 71a and 71b start to rotate based on a paper feeding command from a control device (not shown). The recording medium P is conveyed toward the transfer nip portion N.

  A thickness sensor 70 that detects the thickness of the recording medium P is disposed in the vicinity of the registration rollers 71 a and 71 b, and the thickness sensor 70 includes a light source 73 and a light receiving element 74. The detection of the thickness of the recording medium P by the registration rollers 71a and 71b and the thickness sensor 70 will be described in detail later.

  The operation of the image forming apparatus 10 will be briefly described. When the power is turned on, the intermediate transfer belt 17 starts moving at a constant speed in the direction of arrow a. An image forming operation is started, and yellow (Y), magenta (M), cyan (C), and black (K) toner images are formed on the photoreceptors of the image forming units 11 to 14, respectively. . First, a yellow (Y) toner image is transferred onto the intermediate transfer belt 17 by the operation of the primary transfer roller 11T, and a magenta (M) toner image is superimposed and transferred thereon by the operation of the primary transfer roller 12T. Thereafter, in the same manner, cyan (C) and black (K) toner images are sequentially superimposed and transferred to form a full-color toner image.

  The registration rollers 71a and 71b start rotating in accordance with the timing when the full-color toner image formed on the intermediate transfer belt 17 reaches the position of the secondary transfer roller 18, and the registration rollers 71a and 71b start to rotate and are fed from the sheet feeding device 21. The recording medium P stopped at 71a and 71b is conveyed toward the transfer nip portion N, and a full-color toner image on the intermediate transfer belt 17 is formed by the operation of the secondary transfer roller 18 as a secondary transfer device. Is transcribed.

  Thereafter, the recording medium P is conveyed to the fixing device 22, and the toner image on the recording medium P is fixed and discharged.

  Although transfer residual toner remains on the intermediate transfer belt 17, it interferes with the next image formation. Therefore, the surface of the intermediate transfer belt 17 is cleaned by the cleaning device 19 and the transfer residual toner is removed.

  Further, as a result of the image forming operation, the surface of the secondary transfer roller 18 is formed with a certain amount of fog toner between the images and outside the recording medium, as well as dirt toner such as an external additive or paper dust. Since the image quality is adversely affected, the surface of the secondary transfer roller 18 is cleaned by the secondary transfer device cleaning device 30.

  Next, color misregistration that occurs when a recording medium enters the transfer nip N formed at the contact portion between the intermediate transfer belt 17 and the secondary transfer roller 18 wound on the driving roller 15 will be described. .

  FIG. 2 is an enlarged view near the transfer nip portion N formed at the contact portion between the intermediate transfer belt 17 wound on the drive roller 15 and the secondary transfer roller 18, and FIG. 2A shows a recording medium. FIG. 2B shows the case where the plain paper P1 enters, and FIG. 2B shows the case where the thick paper P2 enters the recording medium.

  FIG. 3 is a diagram for explaining a configuration in which the distance D between the center of the drive roller 15 and the center of the secondary transfer roller 18 is changed. Here, first, the bearing of the secondary transfer roller 18 and the transfer nip are illustrated. A configuration in which the portion N is formed will be described, and a configuration in which the distance D between the center of the driving roller 15 and the center of the secondary transfer roller 18 is changed will be described in detail later.

  The shaft 18a of the secondary transfer roller 18 is rotatably held by a bearing 53. The bearing 53 is wound around the drive roller 15 by the pressing springs 52a and 52b, and the secondary transfer roller 18 and the intermediate transfer belt 17. The intermediate transfer belt 17 and the secondary transfer roller 18 are placed in pressure contact with each other, so that the intermediate transfer belt 17 and the secondary transfer roller 18 are in contact with each other. A transfer nip N is formed at the contact portion.

  Pitch rings 51 a and 51 b that are regulating members that regulate the distance between the intermediate transfer belt 17 wound on the driving roller 15 and the secondary transfer roller 18 are mounted on the shaft 18 a of the secondary transfer roller 18. .

  It is assumed that the distance between the center of the drive roller 15 and the center of the secondary transfer roller 18 is maintained at a predetermined constant distance D. Here, the reason why the predetermined constant distance D is maintained is to explain the occurrence of color misregistration. As described later, the predetermined constant distance D is changed to prevent color misregistration. Configured to do.

  The occurrence of color misregistration will be described with reference to FIG. The conveyance speed S (surface linear velocity of the recording medium P) of the recording medium P is determined by the distance (including the thickness of the intermediate transfer belt 17) from the center of the driving roller 15 to the center of the thickness of the recording medium P. The conveyance speed S of the recording medium P is expressed by the following formula (1).

S = v1 × 2π {r1 + (t / 2)} (1)
S: transport speed of the recording medium P
t: thickness of the recording medium
r1: radius of the driving roller 15 (including the thickness of the intermediate transfer belt)
v1: Rotational speed of the driving roller 15 Further, the linear speed M (surface linear speed of the secondary transfer roller) in the transfer nip portion N of the secondary transfer roller 18 is expressed by the following equation (2).

M = v2 (2π · r2) (2)
M: linear velocity at the transfer nip N of the secondary transfer roller 18
v2: rotational speed of the secondary transfer roller 18
r2: Radius of the secondary transfer roller 18 The conveyance speed S of the recording medium P and the linear speed M of the transfer nip N are equal, that is, the linear speed of the drive roller 15 and the secondary transfer roller 18 so that S = M. Is set, the secondary transfer roller 18 does not become a load on the recording medium P, the recording medium P passes through the transfer nip portion N, and no color misregistration occurs.

  If the recording medium P is plain paper P1 and the thickness thereof is t1 = 0.1 mm, the conveyance speed S1 of the recording medium P1 is S1 = v1 × 2π {r1 + (0.05)} from the equation (1). The linear velocity M1 of the transfer nip portion N is expressed by M1 = v2 (2π · r2) from the above equation (2).

  If the recording medium P is thick paper P2 and its thickness is t2 = 0.3 mm, the conveyance speed S2 of the recording medium P2 is S2 = v1 × 2π {r1 + (0.15)} from the above equation (1). The linear velocity M2 of the transfer nip N is expressed by M2 = v2 (2π × r4) from the above equation (2).

Here, the radius r4 of the secondary transfer roller 18 will be described. Assuming that the distance between the center of the drive roller 15 and the center of the secondary transfer roller 18 is maintained at a constant distance D as in the case of the plain paper P1, the radius of the secondary transfer roller 18 is The thickness difference between the thick paper P2 and the plain paper P1 is reduced by 0.2 (= 0.3-0.1), r4 = (r2-0.2), and the linear velocity M of the transfer nip N is
M2 = v2 (2π × r4) = v2 × 2π (r2-0.2)
It becomes.

For this reason, the relationship between the recording medium conveyance speed S2 and the linear speed M2 of the transfer nip portion N when passing thick paper is S2 = v1 × 2π {r1 + (0.15)}> M2 = v2 × 2π (r2-0) .2)
When the thick paper is passed, the linear velocity M2 of the transfer nip N is slower than the recording medium conveyance speed S2, acting as a resistance to the conveyance of the recording medium, disturbing the movement performance of the intermediate transfer belt, and the color This will cause a shift.

  Therefore, in the present invention, in order to prevent the occurrence of color misregistration, the distance D between the center of the drive roller 15 and the center of the secondary transfer roller 18 defined by the pitch rings 51a and 51b is changed, and the recording medium conveyance speed is changed. Assume that the distance D between the center of the driving roller 15 and the center of the secondary transfer roller 18 is changed so that S2 is equal to the linear velocity M2 of the transfer nip N, that is, S2 = M2.

  For example, in the case of r1 = 15 mm and r2 = 13 mm, the difference in radius of the pitch rings 51a and 51b between the plain paper P1 (thickness 0.1 mm) and the thick paper P2 (thickness 0.3 mm) is expressed by the equations (1) and (1). From (2), it becomes as follows.

First, if the recording medium P is plain paper P1 and its thickness is t1 = 0.1 mm,
S1 = v1 × 2π {15 + 0.05} = v1 × 2π × 15.05
M1 = v2 × 2π × 13
If S1 = M1, that is, v1 × 2π × 15.05 = v2 × 2π × 13, then v1 / v2 = 13 / 15.05 = 0.864.

Next, if the recording medium P is a thick paper P2 and its thickness is t2 = 0.3 mm,
S2 = v1 × 2π {15 + 0.15} = v1 × 2π × 15.15
M2 = v2 × 2π × r4
S2 = M2, that is, v1 × 15.15 = v2 × r4
Therefore, r4 = 15.15 × v1 / v2
= 15.15 x 0.864
= 13.0896
That is, the distance D between the center of the driving roller 15 and the center of the secondary transfer roller 18 is
The distance D1 for plain paper P1 is
D1 = r1 + t1 + r2 = 15 + 0.1 + 13 = 28.1
The distance D2 for cardboard P2 is
D2 = r1 + t2 + r4 = 15 + 0.3 + 13.0896 = 28.386
It becomes.

  That is, when the recording medium P is changed from the plain paper P1 to the thick paper P2, the distance D between the center of the driving roller 15 and the center of the secondary transfer roller 18 is changed from D1 = 28.1 mm to D2 = 28.386. In this case, the secondary transfer roller 18 does not become a load on the recording medium P, and the recording medium P2 smoothly passes through the transfer nip portion N, and color misregistration does not occur.

  Hereinafter, a configuration for changing the distance D between the center of the driving roller 15 and the center of the secondary transfer roller 18 will be described. There are a plurality of examples of the configuration for changing the distance D described above. Hereinafter, description will be made sequentially.

[First embodiment]
FIG. 3 is a diagram for explaining a first embodiment of a configuration for changing the distance D. In FIG. In the first embodiment, the distance D is changed by changing the angular positions of the pitch rings 51a and 51b whose outer shapes which are regulating members are elliptical.

  A gear 57 is attached to a drive shaft 60 extending from a motor 58 that drives the secondary transfer roller 18. The gear 57 meshes with a gear 56 provided on the shaft 18 a of the secondary transfer roller 18, and the rotation of the motor 58 is performed. The secondary transfer roller 18 is rotationally driven through the drive shaft 60, the gear 57, the gear 56, and the shaft 18a.

  On the shaft 18a of the secondary transfer roller, pitch rings 51a and 51b having an elliptical outer shape as a regulating member are mounted, and the elliptical outer edges of the pitch rings 51a and 51b are in contact with the frame 59 of the image forming apparatus. . A gear 54 is fixed to the side surfaces of the pitch rings 51 a and 51 b, and the gear 54 meshes with a gear 55 with a one-way clutch driven by a drive shaft 60. A rotation plate 62 is attached to the drive shaft 60, and the rotation position of the rotation plate 62 is detected by the photosensor 61, and the rotation angle positions of the pitch rings 51a and 51b are detected.

  Next, the operation of this configuration will be described. First, a normal secondary transfer operation will be described. The drive shaft 60 is rotated in the direction of arrow a by the motor 58. The rotation of the drive shaft 60 in the direction of arrow a is transmitted to the shaft 18a via the gear 57 and the gear 56, and rotates the shaft 18a in the direction of arrow b. Due to the rotation of the secondary transfer roller 18 in the direction of arrow b, the recording medium P sandwiched between the transfer nips N is conveyed upward from below in FIG. At this time, the gear 55 with a one-way clutch driven by the drive shaft 60 operates in the direction in which the clutch is disengaged and does not rotate the gear 54 that meshes with the gear 55, so the pitch ring 51 a fixed to the gear 54. , 51b does not rotate.

  Next, the changing operation of the rotation angle positions of the pitch rings 51a and 51b will be described. When this operation is performed, the secondary transfer roller 18 is separated from the intermediate transfer belt 17 wound on the driving roller 15 as a preliminary preparation.

  The motor 58 rotates the drive shaft 60 in the direction opposite to the arrow a direction. The rotation of the drive shaft 60 in the direction opposite to the arrow a is transmitted to the shaft 18a via the gear 57 and the gear 56, and rotates the shaft 18a in the direction opposite to the arrow b, but the secondary transfer roller 18 and the intermediate transfer belt 17 Are separated from each other, and the transfer nip portion N is not formed.

  The rotation of the drive shaft 60 in the direction opposite to the arrow a operates the clutch of the gear 55 with a one-way clutch in the meshing direction and rotates the gear 54 meshed with the gear 55. Since the elliptical pitch rings 51a and 51b fixed to the gear 54 by the rotation of the gear 54 rotate, the rotation angle positions of the pitch rings 51a and 51b are recorded from the rotation position of the rotating plate 62 detected by the photosensor 61. The rotation angle position suitable for the thickness of the medium is set.

  The shaft 18a of the secondary transfer roller into which the pitch rings 51a and 51b are inserted is moved in the direction opposite to the transfer nip portion N by the pitch rings 51a and 51b set at the rotation angle positions suitable for the thickness of the recording medium. As a result, the distance between the secondary transfer roller 18 and the intermediate transfer belt 17 is increased, and a transfer nip portion N suitable for the thickness of the recording medium is formed.

[Second Embodiment]
The second embodiment is basically similar in configuration to the first embodiment described above, but the phase between the two left and right pitch rings 51a and 51b disposed on the shaft 18a of the secondary transfer roller. This is an example in which the unevenness of the depth of the transfer nip N on the left and right in the axial direction of the shaft 18a of the secondary transfer roller is adjusted. The same members as those in the first embodiment are denoted by the same reference numerals.

  FIG. 4 is a diagram illustrating a configuration in the case of changing the phase between the left and right pitch rings 51a and 51b arranged on the shaft 18a of the secondary transfer roller. Although not shown in FIG. 4, a gear 57 is attached to a drive shaft 60 extending from a motor 58 that drives the secondary transfer roller 18 as in the first embodiment shown in FIG. The secondary transfer roller 18 is configured to mesh with a gear 56 provided on the shaft 18a of the secondary transfer roller 18 and rotate the motor 58 via the drive shaft 60, gear 57, gear 56, and shaft 18a. It shall be.

  Originally, it is desirable that the two left and right pitch rings 51a and 51b are moved in synchronism with the same phase, but the outer diameter fluctuation due to the difference in the outer diameter in the longitudinal direction of the secondary transfer roller 18 itself or the change in environment, Due to unevenness in the depth of the transfer nip portion N of the secondary transfer roller 18 due to variations in the pressing force between the press springs 52a and 52b, reaction force generated by driving the secondary transfer roller 18, and the like, the recording medium P In some cases, the amount of biting in is uneven on the left and right in the axial direction.

  As countermeasures, bearings 53a and 53b for independently supporting the shaft 18a of the secondary transfer roller 18 are provided, and motors 58a and 58b for independently driving the two left and right pitch rings 51a and 51b are disposed, and the pitch is set. The rotation angles of the rings 51a and 51b can be set independently. For the motors 58a and 58b, a pulse motor or the like is used so that the rotation angle can be set accurately.

  With this configuration, the phase between the pitch rings 51a and 51b can be changed, and the unevenness of the depth of the transfer nip portion N on the left and right in the axial direction of the shaft 18a of the secondary transfer roller can be adjusted.

  The rotation angles of the left and right pitch rings 51a and 51b are set from an operation panel or the like of an image forming apparatus (not shown) based on the amount of uneven biting of the secondary transfer roller 18 with respect to the recording medium P detected by appropriate means. It shall be set freely by the user.

[Third embodiment]
FIGS. 5A and 5B are diagrams for explaining a third embodiment in which the distance D is changed. FIG. 5A shows a case of plain paper, and FIG. 5B shows a case of thick paper.

  In the third embodiment, the distance D is changed by a plurality of contact portions 65a having different heights (two steps in the configuration of FIG. 5) on the frame 59 of the image forming apparatus with which the elliptical pitch rings 51a and 51b contact. 65b, and the contact portion 65a having the larger distance from the shaft 18a of the secondary transfer roller shown in FIG. 5A is used in the case of plain paper, and is shown in FIG. 5B. The contact portion 65b having the smaller distance from the shaft 18a of the next transfer roller is used for thick paper.

  One shaft end of the shaft 18a of the secondary transfer roller is connected to a solenoid 66 through a flexible joint 67, and can move the shaft 18a in the direction of the arrow c (axial direction) and in the direction opposite to the arrow c (axial direction). It is configured.

  When plain paper is used as the recording medium, the solenoid 66 is operated to move the shaft 18a in the direction opposite to the arrow c, and the pitch rings 51a and 51b are brought into contact with the contact portion 65a. As a result, the secondary transfer roller 18 and the intermediate transfer belt 17 are deeply inserted, and a deep transfer nip portion N suitable for plain paper is formed (see FIG. 5A).

  When thick paper is used as the recording medium, the solenoid 66 is operated to move the shaft 18a in the direction of the arrow c, and the pitch rings 51a and 51b are brought into contact with the contact portion 65b. As a result, the secondary transfer roller 18 and the intermediate transfer belt 17 are shallowly formed, and a shallow transfer nip portion N suitable for thick paper is formed.

  In the first to third embodiments described above, the example in which the pitch ring positioning is set in two stages has been described. However, by setting the pitch ring positioning in two or more stages and a plurality of stages, multiple types of different thicknesses can be obtained. It can correspond to a recording medium.

  FIG. 6 is a diagram illustrating the configuration of the thickness sensor 70 that detects the thickness of the recording medium. The thickness sensor 70 is disposed in the vicinity of the registration rollers 71 a and 71 b on the upstream side of the secondary transfer roller 18 (see FIG. 1), and the recording medium P is formed between the secondary transfer roller 18 and the intermediate transfer belt 17. This sensor detects the thickness of the recording medium P immediately before entering the transfer nip N. FIG. 6A shows the case of plain paper, and FIG. 6B shows the case of thick paper.

  6A and 6B, the registration roller 71a is a metal roller, and the registration roller 71b is a rubber roller. The registration rollers 71a and 71b constitute a registration roller pair 71. The registration roller 71a, which is a metal roller, is always urged toward the registration roller 71b by a spring (not shown), and is configured to be movable in the direction of the reference line L passing through the contact point with which the registration roller pair 71 contacts.

  Outside the registration roller 71a, which is a metal roller, a light source 73 that projects detection light at an incident angle θ with respect to a reference line L that passes through a contact point where the registration roller pair 71 contacts, and reflected light reflected from the registration roller 71a. A light receiving element 74 for receiving light is disposed, and the light receiving element 74 is constituted by a CCD composed of a plurality of elements p1, p2,.

  For example, when the recording medium P is plain paper, the detection light projected from the light source 73 is reflected by the registration roller 71a and detected at p5 of the light receiving element 74 as shown in FIG. When the recording medium P is pressure paper, the registration roller 71a moves to the right as shown by the solid line in FIG. 6B (the dotted line in FIG. 6B indicates the registration when the recording medium P is plain paper). The detection light projected from the light source 73 is reflected by the registration roller 71a and detected by p3 of the light receiving element 74. Thereby, the thickness of the recording medium P can be detected accurately.

  If the incident angle θ is set to be large, the position of the light receiving element 74 to be detected changes greatly with respect to the displacement of the registration roller 71a, and the thickness of the recording medium P can be detected with high accuracy. The incident angle θ may be set to about 40 to 60 °.

  In an electrophotographic image forming apparatus, the distance between the intermediate transfer belt and the secondary transfer roller is adjusted according to the thickness of the recording medium used, and the color of the image formed even when using a thick recording medium The image forming apparatus is free from deviation.

1 is a diagram illustrating a configuration of a tandem full-color image forming apparatus to which the present invention is applied. FIG. FIG. 3 is an enlarged view near a secondary transfer roller of a full-color image forming apparatus. FIG. 6 is a diagram illustrating a configuration for changing a distance D between the center of the driving roller and the center of the secondary transfer roller according to the first embodiment. The figure explaining the structure which changes the phase between two right and left pitch rings arrange | positioned on the axis | shaft of a secondary transfer roller. The figure explaining the structure which changes the distance D of the center of the drive roller of 3rd Example, and the center of a secondary transfer roller. The figure explaining the structure of the thickness sensor which detects the thickness of a recording medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Full color image forming apparatus 11, 12, 13, 14 Image forming unit 11T, 12T, 13T, 14T Primary transfer roller 15 Drive roller 16 Driven roller 17 Intermediate transfer belt 18 Secondary transfer roller 18a Axis (Axis of secondary transfer roller 18 )
DESCRIPTION OF SYMBOLS 19 Cleaning apparatus 20 Image signal processing apparatus 21 Paper feeding apparatus 22 Fixing apparatus 30 Secondary transfer apparatus cleaning apparatus 51a, 51b Pitch ring 52a, 52b Press spring 53, 53a, 53b Bearing 54 Gear 55 Gear with one-way clutch 56 Gear 57 Gear 58, 58a, 58b Motor 59 Frame 60 Drive shaft 61 Photo sensor 62 Rotating plate 65a, 65b Abutting portion 66 Solenoid 67 Flexible joint 70 Thickness sensor 71 Registration roller pair 71a, 71b Registration roller 73 Light source 74 Light receiving element (CCD, P1 , P2,... Pn)

Claims (9)

In an image forming apparatus for transferring a toner image formed on the intermediate transfer member onto a recording medium by a secondary transfer roller by an image forming device arranged along an endless belt-shaped intermediate transfer member,
A regulating member that regulates the interval of the transfer nip formed between the intermediate transfer member and the secondary transfer roller;
The image forming apparatus, wherein the regulating member regulates an interval between the transfer nip portions to a predetermined interval corresponding to a thickness of a recording medium passing therethrough. The restricting member is an elliptical member arranged coaxially with the secondary transfer roller that can be set at an angular position corresponding to the thickness of the recording medium, and the elliptical member is positioned at an angular position corresponding to the thickness of the recording medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is set and the interval between the transfer nip portions is regulated to a predetermined interval corresponding to a thickness of a recording medium that passes therethrough. The restricting members are a plurality of elliptical members disposed coaxially with the secondary transfer roller that can be set at an angular position corresponding to the thickness of the recording medium, and the plurality of elliptical members are independently provided on the recording medium. 2. The angular position corresponding to the thickness is set, and the interval between the transfer nip portions in the axial direction of the secondary transfer roller is regulated to a predetermined interval corresponding to the thickness of the recording medium passing therethrough. The image forming apparatus described. The regulating member is configured such that the outer edge of the elliptical member abuts on a contact portion on the frame of the image forming apparatus, the elliptical member is set at an angular position corresponding to the thickness of the recording medium, and the shaft of the secondary transfer roller The image forming apparatus according to claim 1, wherein an interval between the contact portions is restricted to a predetermined interval corresponding to a thickness of the recording medium. The image forming apparatus according to claim 4, wherein the contact portion on the frame with which the restriction member contacts is one or a plurality of step portions corresponding to the thickness of the recording medium. The image forming apparatus includes: an operation panel; and an operation member that sets a distance between the transfer nip portions to a predetermined distance based on recording medium thickness information input from the operation panel. The image forming apparatus according to claim 5. The image forming apparatus includes a detection device that detects the thickness of the recording medium upstream of the transfer nip portion formed between the intermediate transfer member and the secondary transfer roller in the recording medium conveyance direction, and the detected recording medium thickness. The image forming apparatus according to claim 1, further comprising an operation member that operates the restriction member based on information to set the interval between the transfer nip portions to a predetermined interval. The image forming apparatus according to claim 6, wherein the operation member sets an elliptical member of the restricting member at an angular position corresponding to a thickness of the recording medium. The image forming apparatus according to claim 6, wherein the operation member causes the elliptical member of the restriction member to abut on a step portion of the abutting portion on the frame corresponding to the thickness of the recording medium.

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