JP5029141B2 - Image forming apparatus - Google Patents

Description

  The present invention provides an image forming apparatus that forms a toner image by selectively attaching toner to a latent image due to a difference in electrostatic potential, transfers the toner image to a recording medium, and then heats and pressurizes to form a fixed image. About.

In an image forming apparatus using powdered toner, an image is formed by the process described below.
After the photoreceptor layer formed on the endless peripheral surface of the image carrier is charged almost uniformly, image light is irradiated to form an electrostatic latent image due to a difference in charging potential. The endless peripheral surface of the image carrier moves in a direction along the peripheral surface, and toner is selectively transferred from the developing device to the latent image at a position facing the developing device to form a toner image. . On the other hand, the recording medium conveyed separately from the paper feed tray is conveyed at the timing when the toner image conveyed on the image carrier or the toner image transferred from the image carrier to the intermediate transfer member is conveyed. At the same time, it is sent to a position facing the image carrier or intermediate transfer member. Then, the toner image is transferred onto the recording medium in contact with the image holding member or intermediate transfer member to which the toner image is attached. The recording medium to which the toner image has been transferred is sent to the fixing device and heated, so that the toner image becomes a fixed image on the recording medium, and the image forming operation ends.

  The fixing device used in the image forming apparatus as described above has a fixing rotator having an endless peripheral surface and a pressure member provided so as to face the fixing rotator, and these are pressed against each other. Is generally used. In this fixing device, a recording medium holding an unfixed toner image is sandwiched in a nip portion where the fixing rotator and the pressure member are pressed, and the toner image is heated and pressurized to be pressed onto the recording medium. .

  As a fixing rotator used in such a fixing device, for example, a fixing roller having a built-in heat source as described in Patent Document 1 is used. In this fixing roller, an elastic body layer made of silicone rubber or the like is formed on the surface of a metal cylindrical metal core, and a release layer made of a fluororesin is coated on the surface of the elastic body layer as the outermost layer. Yes. In the fixing roller having the elastic layer, when the pressure member is pressed against the outer peripheral surface, the elastic layer is deformed and a nip having a sufficient length is obtained. Accordingly, when the recording medium holding the toner is sandwiched in the nip while the fixing roller is heated to a high temperature, it is possible to secure time for sufficiently heating the toner on the recording medium. Further, even a color image in which a plurality of color toner images are superposed, the surface is in close contact with the toner image and can be efficiently heated for good fixing.

Further, when the pressure member includes a pressure applying portion that causes a large elastic deformation of the elastic layer of the fixing roller at a downstream portion of the region in pressure contact with the fixing roller, the recording medium passes through this portion. Sometimes, a slight shift occurs between the surface of the fixing roller that is in close contact, and the recording medium is easily peeled off from the fixing roller.
JP 2002-132080 A

In the fixing device as described above, when the recording medium sent between the fixing rotator and the pressure member is repeatedly strongly pressed against the fixing rotator, the leading edge or the side edge of the recording medium is pressed. As a result, the surface of the fixing rotator may be damaged. This damage is likely to occur when a recording medium having a large thickness is used. Further, when the leading edge or the side edge of the recording medium is cut, a sharp portion is generated between the cut surface and the surface, so that damage is more likely to occur.
For example, as shown in FIG. 13, when the fixing rotator 101 has the elastic layer 101b near the surface, a large stress is generated near the surface of the elastic layer as described below.
When the recording medium P is sandwiched between the fixing rotator 101 and the pressing member 102 and pressed strongly, the leading edge or side edge of the recording medium P, that is, the edge Pe is pressed at the position where the fixing rotator 101 is pressed. The amount of deformation of the elastic layer 101b changes suddenly and stress is concentrated. As the thickness of the recording medium P increases, the stress generated by the sudden change in the deformation amount of the elastic layer also increases. Such deformation repeatedly causes damage to the surface, and when the fixing rotator 101 has a release layer 101c made of a fluororesin or the like, the release layer is damaged or peeled off. Cause image defects.

  In general recording media such as PPC paper, the above-mentioned image defects do not occur until about 200000 sheets are passed. However, when a recording medium having a large thickness is used repeatedly, The load acting on the elastic layer and the release layer is increased. Further, as described in Patent Document 1, when the pressure applying portion is provided on the pressure member so that the recording medium is easily peeled off from the surface of the fixing roller, the pressure contact force of the recording medium is increased. Such damage is more likely to occur, and fixing failure due to damage to the release layer or the like may occur earlier than the number of sheets.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to fix a rotating fixing member by a leading edge or a side edge of a recording medium that sequentially passes through a pressure contact portion between the fixing rotating member and a pressure member. It is to prevent surface damage and to enable good image fixing over a long period of time.

In order to solve the above problems, an invention according to claim 1 is directed to an image forming unit that forms a toner image by attaching toner to a latent image due to a difference in electrostatic potential, and a recording medium on which the toner image is conveyed. A transfer device that directly transfers the toner image to a recording medium that is transferred directly to the intermediate transfer body and then transferred to the intermediate transfer body, and a fixing rotator and a pressure member that are pressed against the recording medium on which the toner image has been transferred. And a fixing device for fixing the toner image on the recording medium by heating and pressurizing between them, and a leading edge of the recording medium provided upstream of the fixing device in the conveyance direction of the recording medium A tip compression device that reduces the thickness of the recording medium, and the tip compression device is provided so as to be rotatable around a support shaft parallel to the tip edge of the recording medium to be conveyed. In a certain range of the support shaft A rotary compression member having a protrusion whose distance from the center of rotation is greater than the full width of the recording medium in the axial direction of the support shaft; and a counter member arranged to face the rotary compression member; The rotary compression member provides an image forming apparatus in which the leading edge of the recording medium is sandwiched between the projecting portion and the opposing member, and is rotated to compress the leading edge.

The invention according to claim 2 is the invention according to claim 1 , wherein the rotary compression member has a non-projecting portion that is the opposing member after a tip edge sandwiched between the projecting portion and the opposing member passes. It is controlled to stop at a position opposite to.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the side edge of the recording medium that is provided upstream of the fixing device in the conveyance direction of the recording medium and is conveyed And a side edge compression device for reducing the thickness.

The invention according to claim 4 is the invention according to claim 3 , wherein the side edge compression device is
A side edge compression roller that rotates in contact with a side edge of the recording medium that is conveyed, and a side edge compression roller that faces the side edge compression roller and sandwiches the side edge of the recording medium between the side edge compression rollers to compress the recording medium. It shall have an opposing member.

The invention according to claim 5 is the invention according to claim 4 , wherein the side edge compression roller is set so that a larger compressive force acts on the recording medium on the side edge side of the recording medium than on the center side in the width direction. It is assumed that

As described above, according to the configuration of the image forming apparatus according to the first aspect, since the thickness of the leading edge of the recording medium is reduced by the leading edge compression device, the leading edge of the recording medium is pressed against the fixing rotator. The rapid deformation that occurs on the outer peripheral surface of the fixing rotator when entering the pressure contact portion with the member is alleviated. Thereby, damage to the surface of the fixing rotator can be suppressed, and good fixing can be realized over a long period of time.
The rotary compression member can be pressed by sandwiching the leading edge of the recording medium between the protruding member and the opposing member, and the thickness near the leading edge of the recording medium is reduced.

According to the configuration of the second aspect of the invention, the rotation is stopped at a position where the protruding portion of the rotary compression member does not face the opposing member, so that the interval between the rotary compression member and the opposing member is increased, and the recording medium is It is possible to pass through without compression. Accordingly, the recording medium can be smoothly conveyed after the leading edge of the recording medium is compressed between the protruding portion and the opposing member and passes between the rotary compression member and the opposing member.

According to the configuration of the third aspect of the invention, since the thickness near the side edge of the recording medium is reduced by the side edge compression device, the recording medium is pressed when the recording medium is pressed against the outer peripheral surface of the fixing rotating body. It is alleviated that the pressing force changes suddenly at the portion where the side edge of the medium is pressed. Thereby, damage to the surface of the fixing rotator can be suppressed.

According to the configuration of the invention of claim 4 , since the side edge of the recording medium is sandwiched between the rotating side edge compression roller and the opposing member to compress the side edge, the thickness near the side edge is reduced by a simple device. Can be efficiently reduced.

According to the configuration of the fifth aspect of the invention, compression can be performed in the vicinity of the side edge of the recording medium so that the thickness gradually decreases from the center in the width direction toward the side edge. Accordingly, the side edge can be reliably compressed and the thickness can be reduced, and the concentration of stress acting on the fixing rotating body can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 includes an image forming unit 2 that forms an image based on a digital image signal, an intermediate transfer body 3 to which a plurality of color toner images formed by the image forming apparatus are sequentially transferred, and an intermediate A sheet supply unit 4 for supplying recording sheets one by one to a position facing the transfer body, a secondary transfer device 5 for collectively transferring the toner images superimposed on the intermediate transfer body onto the recording sheet, and a recording sheet A fixing device 6 that heats and presses the unfixed toner image transferred thereon is provided. A paper discharge tray 7 is provided on the downstream side of the fixing device 6 to store the recording sheet fed from the inside of the device.

  The image forming unit 2 includes a cylindrical photosensitive drum 11 on which a latent image is formed on the surface by irradiation with image light after uniform charging, and around the photosensitive drum 11. In addition, the charging device 12 for uniformly charging the surface of the photosensitive drum 11 and the exposure device 13 for irradiating the photosensitive drum 11 with image light to form a latent image due to a difference in electrostatic potential on the surface are different colors. And a developing device 14 of a rotary type for visualizing an electrostatic latent image on the photoconductive drum 11 by selective adhesion of toner, and a photoconductive drum 11. A primary transfer roller 15 for transferring the toner image to the intermediate transfer member 3, a cleaning device 16 for the photosensitive drum for removing toner remaining on the photosensitive drum 11 after the toner image is transferred, and a surface of the photosensitive drum. Remove the charge once And a device 17.

  The photosensitive drum 11 has a metal drum surface with various inorganic photosensitive materials such as Se, a-Si, a-SiC, and Cds, organic photosensitive materials, amorphous selenium photosensitive materials, amorphous silicon photosensitive materials, and the like. What formed the layer can be used.

  The charging device 12 is formed by coating a metal roller having conductivity such as stainless steel, aluminum or the like with a coating of a high resistance material. The charging device 12 is in contact with the photosensitive drum 11 and is driven to rotate. When a predetermined voltage is applied, a continuous discharge is generated in a minute gap in the vicinity of the contact portion between the roller and the photosensitive drum 11, and the surface of the photosensitive drum 11 is charged almost uniformly. It is.

  The exposure device 13 outputs a laser that blinks for each pixel based on an image signal, and exposes and scans the peripheral surface of the photosensitive drum 11 with a polygon mirror. As a result, the potential of the exposed portion is attenuated on the peripheral surface of the photosensitive drum 11, and a latent image is formed due to the difference in electrostatic potential.

  In the rotary developing device 14, four developing devices containing yellow, magenta, cyan, and black toners are rotatably supported, and each developing device is sequentially positioned close to and opposed to the photosensitive drum 11. Move to. The toner is transferred to the latent image corresponding to each color in the electric field generated between the photosensitive drum 11 and a visible image is formed.

  A voltage is applied between the primary transfer roller 15 and the photosensitive drum 11, and the toner on the photosensitive drum having a charge is transferred onto the intermediate transfer body 11 by the generated electric field.

The intermediate transfer member 3 is an endless belt that is stretched around a plurality of rollers 21, 22, and 23, and is disposed so as to come into contact with the photosensitive drum 11. A primary transfer roller 15 is disposed on the back side of the contact portion, and a toner image on the photosensitive drum 11 is transferred thereto. The intermediate transfer body 3 moves in a circular motion, and a toner image of a different color is transferred from the photosensitive drum every rotation, and the toner images of the respective colors are superimposed on the intermediate transfer body 3.
For this intermediate transfer member, a heat-resistant polyimide film whose electric resistance value is adjusted by adding carbon black is used.

The secondary transfer device 5 includes a secondary transfer roller 24 disposed so as to face one of the rollers 23 that stretches the intermediate transfer body 3. The roller 23 that faces the secondary transfer roller 24. A transfer bias voltage is applied between the two.
The secondary transfer roller 24 is a conductive or semiconductive roller, and transfers a toner image on the intermediate transfer member 15d to a recording sheet by applying a voltage between the roller 23 and the opposite roller 23. It is something that can be done.

  As shown in FIG. 2, the fixing device 6 includes a fixing roller 31, an endless belt 32 pressed against the fixing roller 31, and a pressure pad (pressed against the fixing roller 31 via the endless belt 32 ( The pressurizing member) 33 constitutes a main part.

The fixing roller 31 is formed by forming an elastic body layer 31b and a release layer 31c around a cylindrical cored bar (metal core) 31a, and the cylindrical cored bar 31a includes a heating source. Halogen lamp 31d is arranged. The elastic body layer 31b is made of silicone rubber and has a thickness of 0.6 mm. The release layer is formed by covering the elastic layer 31b with a tube made of fluororesin or the like, and has a thickness of about 30 μm.
The temperature of the surface of the fixing roller 31 is measured by a temperature sensor 31e, and the halogen lamp 31d is feedback controlled by a temperature controller (not shown) based on the measurement signal so that the surface of the fixing roller 31 is adjusted to a substantially constant temperature. The

  The endless belt 32 is in contact with the fixing roller 31 so as to be wound around a range of a predetermined central angle, thereby forming a nip portion. The endless belt 32 is made of a heat-resistant resin film such as polyimide, polyamide, or polyimideamide, or a thin member made of metal such as aluminum or stainless steel.

  A pressure pad 33 is supported inside the endless belt 32 while being pressed against the fixing roller 31 via the endless belt 32. The pressure pad 33 is formed of an elastic member 33a for securing a wide nip portion, and a material having rigidity higher than that of the elastic member 33a, and an elastic body layer 31b of the fixing roller 31 on the downstream side of the elastic member 33a. And a pressure applying member 33b that causes large elastic deformation, and these are held by a support member 33c. Further, a belt traveling guide 34 is attached to the support member 33c so that the endless belt 32 can smoothly slide and rotate.

  The fixing roller 31 is rotationally driven in the direction of the arrow shown in the figure by a motor (not shown), and the endless belt 32 is also driven to rotate by this rotation.

  In such a fixing device 6, the recording sheet P onto which the toner image is transferred from the intermediate transfer body 3 is fed between the fixing roller 31 and the endless belt 32, and is conveyed so as to pass through a nip portion where these are pressed against each other. To do. The toner image T on the recording sheet P inserted into the nip portion is heated and pressed by the pressure acting on the nip portion and the heat applied from the fixing roller 31, and is pressed onto the recording sheet P. At this time, since the nip portion is widely set by the pressure pad 33, stable fixing performance is ensured. Since the pressure applying member 33b is made of a material having high rigidity, the elastic layer 31b of the fixing roller 31 is locally deformed greatly, and when the recording sheet P passes through this portion, the fixing roller 31 A minute slip is generated between the surface and the surface of the recording sheet. As a result, the recording sheet P and the fixing roller 31 are easily separated.

  In the present embodiment, the fixing device 6 in which the pressure member 33 is pressed against the fixing roller 31 via the endless belt 32 is employed. However, a pressure roller may be used as a member that is pressed against the fixing roller 31. When a pressure roller is used, an endless belt can also be used as a fixing rotator that is pressed against a recording sheet in a heated state. In a fixing device using an endless belt as a fixing rotator, a pressure pad that can be elastically deformed is disposed inside the endless belt, and the outer peripheral surface of the endless belt is located on the peripheral surface of the pressure roller. Pressed.

  The sheet supply unit 4 includes a plurality of paper feed cassettes 25, 26, 27, and 28 that store recording sheets of different sizes and types, and a manual feed that can be directly supplied from the outside of the image forming apparatus 1. A supply unit 29 is provided. A cassette transport path 25a, 26a, 27a, 28a for transporting the recording sheet pulled out from each paper feed cassette 25, 26, 27, 28 is provided for each paper feed cassette, and this cassette transport path 25a, 26 a, 27 a, and 28 a join the main conveyance path 8. On the other hand, the recording sheet drawn from the manual feed unit 29 is conveyed via a manual conveyance path 29a, and the toner image is transferred from the intermediate transfer body 3 to the manual conveyance path 29a. It joins the main transport path 8 upstream of the position. The main transport path 8 feeds the recording sheet supplied from each paper feed cassette or the manual feed unit to between the secondary transfer roller 24 and the intermediate transfer body 3, that is, to the secondary transfer unit.

The cassette conveying paths 25a, 26a, 27a, 28a are respectively provided with side edge compression devices 60. These side edge compression devices 60 are connected to the pickup cassettes 25, 26, 27, 28 from the pickup rollers. The thickness is reduced by pressing the vicinity of both side edges of the recording sheet pulled out one by one by 25b, 26b, 27b, and 28b.
Further, in the main transport path 8, the position downstream of the position where the cassette transport paths 25 a, 26 a, 27 a, 28 a and the manual feed transport path 29 a merge and upstream of the fixing device 6 is located. The leading end compression device 40 is arranged to compress the vicinity of the leading end edge of the recording sheet to reduce the thickness.

As shown in FIG. 3, the tip compression device 40 includes a compression roller 41 that is a rotary compression member and a counter roller 42 that is disposed to face the compression roller 41.
As shown in FIG. 3, the compression roller 41 is a roller having an elliptical cross section, and is driven to rotate about the intersection of the major axis and the minor axis of the ellipse. Therefore, the direction of the long axis is the protrusion 41a in which the distance from the rotation center to the peripheral surface is increased. Further, the compression roller 41 has a length in the axial direction equal to or larger than the width of the maximum size recording sheet P to be used, and the rotation center axis, that is, the support shaft 41b is perpendicular to the conveyance direction of the recording sheet P. It is supported by.
On the other hand, the opposing roller 42 is a member having a circular cross section, and is supported so as to be rotatable around a support shaft 42a. The supporting position of the facing roller is set so that the gap between both surfaces is about 80 μm when the protruding portion 41a of the compression roller 41 faces.

A recording sheet leading edge detection means (not shown) is provided upstream of the position where the compression roller 41 and the opposing roller 42 are provided. The leading edge of the recording sheet P conveyed by the leading edge detection means is provided. When detected, the rotational drive of the compression roller 41 of the leading end compression device 40 is controlled based on this information, and when the recording sheet P is sent to the opposed portion of the compression roller 41 and the opposed roller 42, FIG. As shown in FIG. 4, the adjustment is made so that the protruding portion of the compression roller 41 contacts the leading edge of the recording sheet P being conveyed. Then, the recording sheet P is sandwiched and rotated, and the vicinity of the leading edge of the recording sheet P thicker than about 80 μm is compressed between the protruding portion 41 a and the opposing roller 42. When the leading edge of the recording sheet P passes through the facing portion between the compression roller 41 and the facing roller 42, the compression roller 41 is positioned at a position where the protruding portion 41a does not face the facing roller 42 as shown in FIG. It is set to stop rotation. As a result, the gap between the opposing regions of the compression roller 41 and the opposing roller 42 is increased, and the rear portion of the recording sheet P that is subsequently conveyed passes through the opposing region smoothly without contacting the compression roller 41.
Further, since a gap of about 80 μm is set between the protrusion 41a and the opposing roller 42, the leading edge of a thick recording sheet having a thickness of 80 μm or more is compressed, but the thickness is 80 μm or less. The recording sheet passes through not only the rear portion but also the leading edge without being compressed by the compression roller 41.

Note that the rotary compression member and the opposing member may have any shape that can be compressed with the leading edge of the recording sheet interposed therebetween, and other forms of members can be used. For example, as shown in FIG. 4, the compression roller may be a partial roller 43 having a curved surface only in a range of a predetermined center angle. Similar to the compression roller 41 shown in FIG. 3, the partial roller 43 has a length in the axial direction that is equal to or larger than the width of the maximum size recording sheet to be used, and is driven to rotate around the support shaft 43b. Is.
On the other hand, as the opposing member, as shown in FIG. 4, a plate-like opposing plate 44 arranged in parallel with the axis of the compression roller 41 or the partial roller 43 can be used. The counter plate 44 is supported in a state where the position is fixed with respect to the support frame of the image forming apparatus main body, and the recording sheet P slides on the surface of the counter plate 44. Then, the vicinity of the leading edge of the recording sheet P is sandwiched between the compression roller 41 or the protruding portions 41a and 43a of the partial roller 43 and compressed.

  The compression roller 41 and the partial roller 43 used as the rotary compression member, and the counter roller 42 and the counter plate 44 used as the counter member can be used in any combination, for example, the compression roller 41 and the counter plate 44 The partial roller 43 and the counter roller 42 may be used in combination.

  On the other hand, in the present embodiment, the position where the tip compression device is provided is downstream from the position where all of the cassette transport paths 25a, 26a, 27a, 28a and the manual feed path 29a merge as shown in FIG. The secondary transfer roller 24 is upstream of the position where the secondary transfer roller 24 faces the intermediate transfer body 3, but is disposed upstream of the fixing device 6 in the recording sheet conveyance path. That's fine. That is, if the thickness of the leading edge of the recording sheet is reduced to such an extent that the elastic layer 31b of the fixing roller 31 is not suddenly deformed when the recording sheet P enters the fixing device 6, the elastic layer 31b and the release layer. The damage of 31c can be suppressed.

Next, another example of the tip compression apparatus will be described with reference to FIGS . 5 and 6 .
As shown in FIG. 5, the tip compression device 50 includes a compression roller 51 and an opposing plate 52 (opposing member) arranged to face the compression roller 51.
The small compression roller 51 is a roller having a circular section capable of compressing the vicinity of the leading edge of the recording sheet with a predetermined width, and is supported so as to be rotatable around an axis perpendicular to the leading edge of the recording sheet. The support shaft 51 a is supported by a holder 51 b that can move along the leading edge of the recording sheet, and the holder 51 b is pressed toward the counter plate 52 via an elastic member 53. The support shaft 51a of the small compression roller 51 is supported with an axis inclined so that a larger compressive force acts on the front side of the recording sheet on the front side in the conveyance direction than on the rear side.
On the other hand, the counter plate 52 disposed to face the compression small roller 51 is a plate-like member that is longer than the width of the maximum size recording sheet to be used, and is against a support frame (not shown) of the image forming apparatus main body. Are supported in a fixed position. The upper surface is parallel to the conveyance direction of the recording sheet P, and the recording sheet P slides on the surface of the counter plate. The small compression roller 51 sandwiches the vicinity of the leading edge of the recording sheet P between the opposing plate 52 and rolls in the width direction of the recording sheet while compressing.

  In such a leading end compression device 50, the recording sheet P being transported is stopped at a position where the leading end edge is on the counter plate 52. Then, the small compression roller 51 sandwiches the leading edge of the recording sheet P and the vicinity thereof with the opposing plate 52, and moves in the width direction of the recording sheet P along the leading edge as shown in FIG. As a result, the vicinity of the leading edge of the recording sheet is compressed between the rolling compact roller 51 and the counter plate 52, and the thickness is reduced. Further, the leading edge of the recording sheet P is crushed by the compression small roller 51 even when the recording sheet is cut into a predetermined size and the cut surface and the surface are sharply sharpened.

  As shown in FIG. 7, the compression roller may have a shape in which the radius of the peripheral surface is enlarged on the downstream side from the upstream side in the recording sheet conveyance direction. Thereby, even when the central axis of the compression roller 54, that is, the support shaft 54a is arranged in parallel with the surface of the recording sheet P being conveyed and the surface of the counter plate 55, the leading edge is strongly compressed from the rear side of the recording sheet, It is possible to reduce the thickness of the leading edge of the recording sheet by efficiently crushing the vicinity of the leading edge. Further, it is desirable to provide a cylindrical curved surface parallel to the rotation support shaft 54 a on the most downstream peripheral surface of the small compression roller 54. As a result, the leading edge of the recording sheet P can be reliably compressed.

  In the above embodiment, plate-like counter plates 52 and 55 having a length equal to or larger than the width of the recording sheet are used as the counter members arranged to oppose the compression small rollers 51 and 54. Alternatively, a roller or a sliding member that faces the compression small rollers 51 and 54 and moves together with the compression small rollers 51 and 54 may be used.

  On the other hand, an elastic layer having a hardness capable of compressing the recording sheet is provided on the surfaces of the compression small rollers 51 and 54 and the opposing member, and pressed between the compression small rollers 51 and 54 and the opposing members 52 and 55. You may comprise so that the area | region made may become large.

Next, the side edge compression device 60 will be described.
As shown in FIG. 1, the side edge compression device 60 includes cassette conveyance paths 25 a, 26 a, 27 a, which guide the recording sheets P supplied from the respective sheet feeding cassettes 25, 26, 27, 28 to the main conveyance path 8. 28a are arranged in accordance with the size of the recording sheet accommodated in the paper feed cassettes 25a, 26a, 27a, 28a. That is, it corresponds to the position of the side edge of the recording sheet accommodated in each paper feed cassette.
In the present embodiment, all the cassette transport paths 25a, 26a, 27a, and 28a corresponding to the paper feed cassettes 25, 26, 27, and 28 are arranged, but some of the paper feed cassettes are also supported. It may be arranged limited to a cassette conveyance path, that is, a cassette conveyance path corresponding to a sheet feeding cassette in which a recording sheet having a large thickness is accommodated.

FIG. 8 is a schematic side view of the side edge compression device 60, and FIG. 9 is a schematic front view of the same side edge compression device. FIG. 10 is a schematic plan view.
As shown in these drawings, the side edge compression device 60 includes a side edge compression roller 61 that is a roller-like member, and a counter roller 62 that is arranged to face the side edge compression roller 61. . Then, as shown in FIG. 10, these rollers are arranged at positions corresponding to both side edges of the recording sheet P conveyed in the cassette conveying paths 25a, 26a, 27a, 28a. These rollers are supported with their positions fixed by holders 63 and 64, respectively, and the side edge compression roller 61 is rotationally driven so that its peripheral surface moves in the same direction as the moving direction of the recording sheet conveyed. The counter roller 62 is driven by the rotation of the side edge compression roller. Therefore, both side edges of the conveyed recording sheet P are sandwiched between the side edge compression roller 61 and the opposing roller 62, and are compressed to reduce the thickness near the side edge of the recording sheet.

  As shown in FIG. 9, the side edge compression roller 61 is supported so that the rotation center axis, that is, the support shaft 61a is inclined so that a larger compression force acts on the side edge side than the center side in the width direction of the recording sheet P. ing.

  In such a side edge compression device, the recording sheet P taken out one by one from one of the paper feed cassettes 25, 26, 27, 28 is side edge compression rollers 61 at both side edges before being fed into the main conveyance path 8. And the opposed roller 62, and is conveyed and compressed. For example, a recording sheet having a thickness of about 150 μm to 250 μm is compressed so that a side edge has a thickness of about 80 μm.

The side edge compression roller can be supported without tilting the support shaft 65a by making the diameter on the center side smaller than the diameter on the side edge side in the width direction of the recording sheet P as shown in FIG. .
Further, the opposing member may be a plate-like member or the like on which the recording sheet can slide, in addition to the opposing roller 62 employed in the present embodiment.

  On the other hand, in the present embodiment, the side edge compression device 60 is provided in each cassette transport path 25a, 26a, 27a, 28a, but can also be provided in the manual transport path 29a. At this time, if the size of the recording sheet stored in the manual feed unit 29 is changed, the positions of the side edge compression roller and the opposing roller of the side edge compression device can be changed in the width direction of the recording sheet. It is desirable to make it possible.

Next, the operation of the image forming apparatus will be described.
When a signal for forming an image is input, the image forming unit 2 causes the photosensitive drum 11 from the exposure device 13 based on an image signal read by a scanner or the like or an image signal input from another device such as a personal computer. Image light is irradiated on the surface, and a latent image is formed due to a difference in electrostatic potential. At a position facing the developing device 14, toner is transferred to the electrostatic latent image to form a toner image, and the toner image is transferred to the intermediate transfer body 3 at a position facing the primary transfer roller 15. Such toner image formation and transfer are performed for each of the colors yellow, magenta, cyan, and black, and the toner images of the respective colors are superimposed on the intermediate transfer member 3.

  On the other hand, the sheet supply unit 4 selects a recording sheet as an image medium based on a signal input by an operator or image information input in accordance with an image signal. When a recording sheet stored in one of the paper feeding cassettes 25, 26, 27, and 28, for example, the uppermost paper feeding cassette 25 is selected as a recording medium, the recording sheets are one by one from the corresponding paper feeding cassette 25. It is pulled out by the pickup roller 25b and sent to the cassette transport path 25a by the transport roller 25c.

  Side edge compression devices 60a, 60b, 60c, and 60d are arranged in the cassette conveyance paths 25a, 26a, 27a, and 28a. When the conveyance of the recording sheet is detected, the side edge compression roller 61 is driven to rotate. Both side edges of the recording sheet are sandwiched between the edge compression roller 61 and the opposing roller 62. As a result, the vicinity of both side edges of the recording sheet is compressed, and if the thickness of the recording sheet is greater than 80 μm, the thickness of both side edges is reduced to about 80 μm. In the case of a recording sheet having a thickness of 80 μm or less, the recording sheet is not pressed in the facing region between the side edge compression roller 61 and the facing roller 62, and passes through without changing the thickness. Thereafter, the recording sheet is conveyed toward the image forming unit 2 through the main conveyance path 8.

  On the other hand, when the sheet feeding from the manual feeding unit 29 is selected, the recording sheets placed on the manual feeding tray are sequentially drawn one by one and sent to the main transport path 8 through the manual transport path 29a. Then, it is conveyed to the image forming unit 2.

  The recording sheet sent to the main conveyance path 8 is detected by a leading edge detection device (not shown), and the conveyance is stopped when the leading edge of the recording sheet reaches the arrangement position of the leading edge compression device 40. Then, the vicinity of the tip edge is compressed by the tip compression device 40, and the thickness of the tip edge is reduced to about 80 μm. The recording sheet that has passed the position where the leading end compression device 40 is provided is sent to a position where the intermediate transfer body 3 and the secondary transfer roller 24 face each other.

The full-color toner image formed on the intermediate transfer body 3 is transferred onto the recording sheet fed at a predetermined timing after passing through the leading end compression device 40 at a portion facing the secondary transfer roller 24. Then, the image is conveyed to the fixing device 6 and is heated and pressurized by passing through the pressure contact portion between the fixing roller 31 and the endless belt 32 to form a fixed image. At this time, since the leading edge of the recording sheet P having a large thickness is compressed and the thickness is reduced, when the leading edge is sandwiched between the fixing roller 31 and the endless belt 32, as shown in FIG. In addition, the elastic layer 31b of the fixing roller 31 is not suddenly deformed. Further, the pressure applying member 33b disposed on the outlet side of the press contact portion is pressed against the fixing roller 31 with a press contact force larger than that of the elastic member 33a, but even if the leading edge of the recording sheet P is sandwiched between these portions, Since a sudden change portion of deformation is not formed in the elastic layer 31b, the load applied to the elastic layer 31b and the release layer 31c covering the outermost surface is small, and damage can be suppressed.
Further, since both side edges of the recording sheet are similarly compressed by the side edge compression device 60 so as to have a thickness of about 80 μm, even when the side edges are repeatedly pressed against the same position of the fixing roller 31, the elastic layer 31b. In addition, damage to the release layer 31c is suppressed.

  Thereafter, the recording sheet on which the toner image is fixed by passing through the pressure contact portion of the fixing device 6 is conveyed by the paper discharge roller 9 and discharged to the paper discharge tray.

In the above-described embodiment, a fixing device that uses the recording sheet P between the fixing roller 31 having the elastic layer 31b and the endless belt 32 pressed against the fixing roller 31 and performs heating and pressurization is used. However, the invention according to the present application can also be applied when a fixing device of another form is used. For example, the present invention can be applied to a case where an endless belt is used as a fixing member, and a fixing device in which the endless belt is pressed against a pressure roller by a pad made of an elastic body. In such an image forming apparatus, the leading edge and side edge of the recording sheet are compressed and the thickness is reduced, so that the endless belt is deformed with a large curvature at a position where the leading edge or side edge is pressed. Is alleviated and damage to the endless belt can be suppressed.
Further, in the above embodiment, the leading edge or side edge of the recording sheet is compressed to a thickness of about 80 μm by the leading edge compression device 40 and the side edge compression device 60, but this thickness is used. It can be changed as appropriate according to the type of recording sheet, the configuration of the fixing roller, and the like. And the invention which concerns on this application is not limited to embodiment described above, It can implement by changing suitably within the range as described in a claim.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a fixing device that can be used in the image forming apparatus shown in FIG. 1. It is a schematic side view of the front-end | tip compression apparatus which can be used with the image forming apparatus shown in FIG. It is a schematic side view which shows the other example of the front-end | tip compression apparatus which can be used with the image forming apparatus shown in FIG. FIG. 5 is a schematic side view showing another example of a tip compression apparatus that can be used in the image forming apparatus shown in FIG. 1 as a reference . It is a schematic plan view of the tip compression apparatus shown in FIG. It is a schematic block diagram which shows the other example of the compression small roller which can be replaced with and used instead of the compression small roller used with the front-end | tip compression apparatus shown in FIG. FIG. 2 is a schematic side view of a side edge compression device that can be used in the image forming apparatus shown in FIG. 1. It is a schematic front view of the side edge compression apparatus shown in FIG. It is a schematic plan view of the side edge compression apparatus shown in FIG. It is a schematic plan view of the side edge compression apparatus which can be used instead of the side edge compression apparatus shown in FIG. FIG. 2 is an enlarged cross-sectional view illustrating a state when a recording sheet is fed into a fixing device in the image forming apparatus illustrated in FIG. 1. It is a figure explaining the subject which this invention tends to solve, Comprising: It is an expanded sectional view which shows a state when a recording sheet is pinched | interposed into the fixing device.

1: image forming device, 2: image forming unit, 3: intermediate transfer member, 4: sheet feeding unit, 5: secondary transfer device, 6: fixing device,
7: paper discharge tray, 8: main transport path, 9: paper discharge roller,
11: Photosensitive drum, 12: Charging device, 13: Exposure device, 14: Development device, 15: Primary transfer roller, 16: Cleaning device, 17: Static elimination device,
21, 22, 23: rollers for stretching the intermediate transfer member, 24: secondary transfer rollers, 25, 26, 27, 28: paper feed cassettes, 25 a, 26 a, 27 a, 28 a: transport paths for cassettes, 25 b, 26 b 27b, 28b: Pickup roller, 25c, 25c, 25c, 25c: Conveying roller, 29: Manual feeding unit, 29a: Conveying path for manual feeding,
31: Fixing roller, 31a: Cylindrical core, 31b: Elastic layer, 31c: Release layer, 32: Endless belt, 33: Pressure pad, 33a: Elastic member, 33b: Pressure applying member, 34: Belt running guide,
40, 50: tip compression device, 41, 43: compression roller, 41a, 43a: protrusion, 41b: support shaft, 42: counter roller, 42a: support shaft, 44: counter plate, 51, 54: compression small roller, 51a, 54a: support shaft, 51b: holder, 52, 55: counter plate, 53: elastic member,
60: Side edge compression device 61, 65: Side edge compression roller 61a, 62a: Support shaft 62: Opposing roller 63, 64: Holder

Claims (5)

An image forming unit that forms a toner image by attaching toner to a latent image due to a difference in electrostatic potential;
A transfer device that directly transfers the toner image to a transported recording medium or transfers the toner image to an intermediate transfer member, and then transfers the toner image to a transported recording medium;
A fixing device that feeds the recording medium onto which the toner image has been transferred between a fixing rotator and a pressure member that are pressed against each other, and heats and pressurizes the recording medium to fix the toner image on the recording medium;
A tip compression device that is provided upstream of the fixing device in the conveyance direction of the recording medium, presses the leading edge of the recording medium, and reduces the thickness;
The tip compression device includes:
A protrusion that is provided so as to be able to rotate around a support shaft parallel to the leading edge of the recording medium to be conveyed and has a greater distance from the rotation center of the support shaft in a partial range in the circumferential direction. A rotary compression member having a range equal to or greater than the full width of the recording medium in the axial direction of the shaft;
An opposing member arranged to face the rotary compression member;
The image forming apparatus according to claim 1, wherein the rotary compression member sandwiches the leading edge of the recording medium between the projecting portion and the opposing member, and rotates to compress the leading edge. The rotary compression member is controlled so that the non-projection portion stops at a position facing the opposing member after the leading edge sandwiched between the projecting portion and the opposing member passes. The image forming apparatus according to claim 1, wherein: 2. The apparatus according to claim 1, further comprising a side edge compression device that is provided upstream of the fixing device in the conveyance direction of the recording medium and presses a side edge of the conveyed recording medium to reduce a thickness. Alternatively, the image forming apparatus according to claim 2 . The side edge compression device comprises:
A side edge compression roller that rotates in contact with the side edge of the recording medium being conveyed;
The image forming apparatus according to claim 3, further comprising an opposing member that opposes the side edge compression roller and compresses the side edge of the recording medium sandwiched between the side edge compression roller. 5. The image forming apparatus according to claim 4, wherein the side edge compression roller is set such that a larger compression force acts on the recording medium on a side edge side of the recording medium than on a center side in a width direction. .

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