JP2004075305A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate inconvenience due to adhesion and deposit of toner in a paper sheet inversion conveyance mechanism having such a configuration that a branch member is lifted by a paper sheet and is moved in the vicinity of a paper sheet conveyance passage in a fixation part for fixing toner image by heating and pressurizing it. <P>SOLUTION: A rotary member 40 is rotatably provided in substantially central part of the branch member 35, outer surface of the rotary member 40 protrudes more than conveyance faces 35a, 35b on both upper and lower sides in the branch member 35, and the paper sheet P fed from a fixing device 26 side comes into contact with the rotary member 40 in the branch member 35. Since the rotary member 40 comes into contact with toner image on the paper sheet P and rotates together with the paper sheet P, it does not rub the toner image and toner adheres to the conveyance face 35a on the lower side of the branch member 35 to suppress deposit of the toner there. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is applied to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and particularly relates to an image forming apparatus including an electrostatic electrophotographic process and a fixing unit and an image forming apparatus having an automatic double-sided printing function. .
[0002]
[Prior art]
Some image forming apparatuses have an automatic double-sided printing function to enable image formation on both sides of a sheet. In general, the paper transport configuration in the automatic duplex printing function includes a feed member for transporting the paper in a part of the paper transport path in a paper discharge direction and a direction opposite to the paper discharge direction, and a paper guide. The paper transport branch path is provided with a rotatable branch member for switching the paper transport path.
[0003]
As the drive configuration of the branch member, a configuration in which the timing of paper transport is adjusted by a sensor or the like, the drive force of a solenoid or a stepping motor or the like is transmitted, and the branch member is rotated to switch the transport direction of the paper is often seen. Can be
[0004]
[Problems to be solved by the invention]
On the other hand, the basic configuration of the branching member, which is a problem to be solved by the present invention, is different from the conventional configuration in that the leading end of the paper presses the branching member to rotate the branching member and switch the paper transport path. Things. A specific description will be given based on FIGS. 9 to 13.
[0005]
FIG. 9 is a configuration diagram illustrating an example of the image forming apparatus. In the image forming apparatus main body 1 illustrated in FIG. 9, a manual sheet feeding table 2 for performing manual sheet feeding is openable and rotatable on a right side surface thereof. The manual paper feed table 2 is usually housed in the image forming apparatus main body 1, and is used by turning it outward around the fulcrum 3 as needed and tilting it. It has become. An auxiliary table 4 slidably housed in the manual sheet feeding table 2 can be pulled out from the tip side of the manual sheet feeding table 2.
[0006]
The image forming section 5 includes a charging device 7 that performs a charging process on the surface of the photoconductor 6 around the drum-shaped photoconductor 6 as an image carrier, and irradiates the surface of the photoconductor 6 with laser light based on image information. An exposure device 8 for forming an electrostatic latent image on the surface of the photoconductor 6, a developing device 9 for visualizing the electrostatic latent image formed on the surface of the photoconductor 6 with toner, and a toner developed on the photoconductor 6 A transfer device 10 for transferring an image onto a sheet P, a cleaning device 11 for removing and collecting toner remaining on the surface of the photoconductor 6 after transfer, and the like are arranged.
[0007]
The paper supply unit 12 includes a paper supply cassette 13 for mainly storing and storing unused paper P. The paper feed cassette 13 is detachable from the front of the apparatus main body 1 to improve operability and workability at the time of paper supply. The paper P is stacked on the bottom plate 15 rotatably supported in the paper cassette 13, and is pressed by a spring 17 so as to press the uppermost paper P against the paper feed roller 16.
[0008]
In the paper supply unit 12, when an image forming command is issued, the topmost paper P is sent out of the paper supply cassette 13 by the rotation of the paper supply roller 16, and is transferred by a registration roller 18 provided on the upstream side in the transport direction of the transfer device 10. Transportation is temporarily stopped. Then, the sheet P is fed at a set timing so that the positional relationship between the toner image on the photoreceptor 6 and the leading end of the sheet P becomes a predetermined position, and the toner image is copied when passing through the transfer device 10. You.
[0009]
In the image reading section 19, in order to scan an image of a document (not shown) placed on the contact glass 20, a reading traveling body 23 including a document illumination light source 21 and a plurality of mirrors 22 is reciprocated. Has become. Image information scanned by the reading traveling body 23 is read as an image signal by a photoelectric conversion element 25 such as a CCD installed behind the lens 24. The read image signal is digitized and processed. An electrostatic latent image is formed on the surface of the photoconductor 6 by light emission of a laser diode (not shown) in the exposure device 8 based on a signal processed by the image reading unit 19.
[0010]
That is, the laser light from the laser diode reaches the photoconductor 6 via a known polygon mirror or lens, and forms an electrostatic latent image on the surface of the photoconductor 6. The electrostatic latent image moves with the rotation of the photoconductor 6, is visualized by the toner supplied from the developing device 9, and further moves toward the transfer device 10. The transfer device 10 transfers the toner image to the paper P fed in a timely manner. The transferred paper P is sent to a fixing device 26 where the image is fixed.
[0011]
In the fixing device 26, a heating roller 27 and a pressure roller 28 are disposed in an apparatus housing. The heating roller 27 is made of a material made of a heat conductive material disposed on the side that comes into contact with the toner image transferred to the paper P. It comprises a hollow cylinder and a roller member having a release layer on the surface of the hollow cylinder, and a heat source (not shown) is disposed inside. The pressure roller 28 is composed of a roller member having an elastic layer on the surface of a cored bar. The pressure roller 28 rotates together with the heating roller 27 while being in pressure contact with the heating roller 27, thereby forming a fixing nip portion when nipping and conveying the sheet P. It has become. When the toner image carried on the sheet P is nipped and conveyed by the heating roller 27 and the pressure roller 28, the image is fixed by receiving a heating / pressing action.
[0012]
In a space S between the image forming section 5 and the image reading section 19, a paper discharge tray 29 for storing the paper P discharged from the fixing device 26 after the fixing is arranged. The paper P is discharged and stacked on the discharge tray 29.
[0013]
Next, the flow of paper during duplex printing will be described with reference to FIGS. 10 to 12 are enlarged views of the vicinity of the sheet conveyance branch 31 in FIG. 9, and the conveyance path branches right and left on the downstream side (upper side in the drawing) of the fixing device 26 in the sheet conveyance direction. The left transport path 32 is a paper discharge path communicating with the paper discharge tray 29 shown in FIG. 9 through the portion where the paper discharge roller pair 30 is disposed, and the right transport path 34 is viewed from the side of the fixing device 26. 9 is a reversing passage reaching the registration roller 18. Further, a branch member 35 is provided in the transport branch path 31, and the branch member 35 has a shape whose tip is narrowed toward the right transport path 34, and one end is rotatable at a fulcrum 36 on the right transport path 34 side. Have been.
[0014]
As shown in FIG. 10, during the fixing process, the branch member 35 is waiting at a position to close the transport branch path 31, and when the leading end of the paper P contacts the branch member 35, the paper P is stiffened (elasticity and stickiness). The branching member 35 guides the paper P toward the discharge roller pair 30 in the left transport path 32 while being rotated and pushed up about the fulcrum 36 as shown in FIG.
[0015]
Further, as shown in FIG. 13, the branching member 35 includes a sensor 37 for detecting the presence / absence of paper passage at the end outside the paper passage range in the paper conveyance path. That is, while the sheet P is passing, the branch member 35 is lifted up, and the presence of the sheet is detected by the sensor 37. However, the rear end of the sheet P passes through the branch member 35 and the branch member 35 is moved to a predetermined standby position. At the same time when the sensor 37 detects the return, the discharge roller pair 30 is rotated in the reverse direction. At this time, since the branch member 35 has returned to the predetermined standby position shown in FIG. 12, the leading end of the sheet P is guided along the upper transport surface of the branch member 35 to the reversing path of the right transport path 34.
[0016]
Then, as shown in FIG. 9, the sheet P is sent to the registration roller 18 by the intermediate conveyance roller 38 in the reversing path, and the image forming unit 5 forms an image on the surface opposite to the surface on which the image is already formed. Will be done.
[0017]
Although the paper reversing and conveying mechanism as described above is provided with an automatic double-sided printing function, as shown in FIG. 11, the branch member 35 is lifted by a strainer of the paper P, and furthermore, while the paper P is passing therethrough. As a result, the force due to its own weight to return to the predetermined standby position continues to act, and as a result, the branching member 35 keeps in contact with the sheet P while constantly applying pressure to the sheet P.
[0018]
In normal single-sided printing, a toner image is not formed on the surface of the sheet P in contact with the branch member 35, and there is no problem. However, in duplex printing, toner adheres to the side of the sheet P in contact with the branch member 35. are doing. The surface in contact with the branch member 35 is on the side of the pressure roller 28, and the toner is not completely in a molten state. However, since the warmed toner image contacts in a semi-molten state, image disorder is likely to occur. This is a state in which it easily adheres to the member 35. Therefore, the toner is deposited on the branch member 35.
[0019]
Initially, the level is not noticed by the user, but as the amount of accumulated toner increases over time, the amount of toner scraped off the paper P also increases, eventually causing an image to be lost, and eventually the transport surface of the branch member 35 The paper P is caught by the toner that has adhered and accumulated, causing a paper jam.
[0020]
A similar problem also occurs in the transport guide portion of the branch member 35 immediately after the downstream side in the transport direction. That is, the transport guide (for example, portion A in FIG. 11) on the side where the sheet P is pressed by the branch member 35 may be in a state where the sheet P is pressed by the own weight of the branch member 35 in some cases. , A problem of accumulation occurs, which causes a phenomenon that the toner image on the paper P is scraped off.
[0021]
Regarding such a problem, Japanese Patent Application Laid-Open No. H11-327231 discloses an invention in which toner from a sheet after the fixing device is prevented from adhering to a sheet passing rib. It does not consider the problem of toner adhesion and accumulation.
[0022]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and to provide a sheet reversing transport mechanism having a structure in which a branch member is moved by lifting a sheet in the vicinity of a sheet transport path of a fixing unit for fixing a toner image by heating and pressing. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which eliminates a problem caused by toner adhesion and accumulation.
[0023]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a fixing unit for fixing a toner image transferred to a sheet by heating and pressing, and a sheet discharged from the fixing unit in a sheet discharging direction or the discharging direction. An image forming apparatus comprising: a sheet conveying unit that conveys a sheet in a direction opposite to a sheet direction; and a branch member provided in a sheet conveying path and that switches a sheet conveying direction to a sheet discharging direction or a direction opposite to the sheet discharging direction. The branch member is slidably in contact with the sheet, pivotally supported so as to receive the sheet conveying force, and further provided with a conveyance assisting member for smoothing the sheet conveyance in a sheet sliding contact portion of the branch member. According to this configuration, the sliding contact of the paper at the branch member is smooth, and the resistance of the paper sliding contact portion of the branch member is reduced, so that toner adhesion and accumulation at the branch member are suppressed. What Disturbance of paper formed image, the jamming of the sheet can be prevented.
[0024]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transport assisting member slides on a sheet transported in the sheet discharging direction and a sheet transported in a direction opposite to the sheet discharging direction. As described above, the toner is disposed on the branching member, and with this configuration, toner adhesion and accumulation are suppressed as described above at the paper sliding contact portions of the branching member in both transport directions.
[0025]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the transport assisting member is constituted by a rotating member that rotates by slidingly contacting the sheet. Thus, the sheet is smoothly slid and conveyed at the branch member.
[0026]
According to a fourth aspect of the present invention, in the image forming apparatus of the first, second, or third aspect, the conveyance auxiliary member is formed from a material having excellent toner separability. The toner is less likely to adhere to the portion of the sheet that is in sliding contact with the sheet, and toner adhesion and accumulation are further suppressed.
[0027]
According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, a conveyance assisting member that rotates in sliding contact with a sheet on a sheet guide member downstream of the branch member in the sheet conveyance direction and near the branch member. With this configuration, a rotating member is provided. With this configuration, not only the sheet sliding contact portion of the separating member but also the sheet guide member near the branch member is provided with a transport assisting rotating member that rotates while sliding on the sheet. Accordingly, the resistance is reduced at each portion where the sheet comes into sliding contact, so that toner adhesion and accumulation at the branch member are suppressed, and it is possible to prevent disturbance of a formed image on both sides of the sheet and jamming of the sheet.
[0028]
According to a sixth aspect of the present invention, in the image forming apparatus of the first aspect, the sheet guide member on the downstream side of the branch member in the sheet conveying direction and near the branch member is made of a material having excellent toner separation properties. It is characterized in that a conveyance assisting member is provided, and with this configuration, toner hardly adheres to each part where the paper slides, and toner adhesion and accumulation are suppressed.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0030]
Note that this embodiment is basically described as applied to the image forming apparatus shown in FIG. In the following description, members corresponding to the members described in FIGS. 9 to 13 are denoted by the same reference numerals, and detailed description is omitted.
[0031]
FIG. 1 and FIG. 2 are configuration diagrams illustrating a sheet conveying branching path for explaining the first embodiment of the present invention. A rotating member 40 composed of a roller as a conveying auxiliary member rotates at a substantially central portion of a branching member 35. It is provided so that the outer surface of the rotating member 40 protrudes from the upper and lower conveying surfaces 35 a and 35 b of the branching member 35. As a result, the sheet P sent from the fixing device 26 comes into contact with the rotating member 40 at the branch member 35.
[0032]
Since the rotating member 40 is rotatably held, even if the rotating member 40 comes into contact with the toner image on the sheet P, the rotating member 40 rotates together with the sheet P, so that the rotating member 40 does not rub against the toner image. It can be prevented from adhering and depositing on the surface 35a. Moreover, the branch member 35 comes into contact with the paper P or the toner image only when a part of the front and rear ends of the paper P where the rotating member 40 is hardly in contact with the paper P, and also comes into contact with the paper end surface on which the toner image is not normally formed. Therefore, toner adhesion and accumulation on the branch member 35 can be prevented twice.
[0033]
A roller, a spur, or the like can be used as the rotating member 40 that is the transport assisting member.
[0034]
Also, as shown in FIG. 2, the turning member 40 is provided so as to protrude from the upper conveying surface 35 b of the branch member 35 on the inverted sheet P, thereby preventing the contact between the branch member 35 and the sheet P. As described above, the effect of preventing the toner from adhering and accumulating on the branch member 35 can be obtained. However, in this case, since the paper P passes through the branching member 35 after being inverted after heating, the toner image is also cooled from the molten state to the solidified state, and it can be said that the risk of toner adhesion and deposition is originally small.
[0035]
FIGS. 3 to 5 are configuration diagrams showing a sheet conveying branching path for explaining the second embodiment of the present invention. In the second embodiment, a plurality of sheets exist in a direction orthogonal to the sheet conveying direction as shown in FIG. Some of the branching members 35 are formed to have a shape with the transport assisting portion 41 protruding from the other branching members as shown by oblique lines, so that the same effect as the rotating member 40 as the transport assisting member is obtained. It is possible.
[0036]
In general, the material of the branching member 35 disposed on the paper conveyance path immediately after fixing is made of a heat-resistant resin and further contains glass reinforced fiber, and the separation property (release property) from the toner is not so good. Absent. Therefore, the material for forming the transport assisting portion 41, which is a portion in sliding contact with the paper, is made of a fluorine-based resin or a material coated with a fluorine-based coating and having excellent releasability from the toner. Adhesion and deposition can be suppressed.
[0037]
It is also possible to mold the branch member 35 itself with a fluorine-based resin, or to coat the entire branch member 35 with a fluorine-based resin. However, since the fluorine-based resin is often expensive, it is preferable to partially use the fluorine-based resin. Is advantageous in terms of cost.
[0038]
As shown in FIG. 4, in the second embodiment, the upper conveying surface 35 b of the branch member 35 is made to project the fluorine-based resin similarly to the lower conveying surface 35 a, so that the branch member 35 and the inverted member are inverted. The sliding contact resistance of the sheet P can be reduced, and an effect of suppressing toner adhesion and accumulation on the branch member 35 of the sheet P after reversal can be obtained.
[0039]
As shown in FIG. 6, the paper P is pressed against the conveyance guide plate 42 on the downstream side in the conveyance direction of the branch member 35 and near the branch member 35 by the weight of the branch member 35 (A portion indicated by an arrow). Similarly, the toner image may be rubbed. In this case, the contact is on the first surface side of the printing, and the above-described problem occurs even in the case of single-sided printing. In particular, it is expected to occur on recording paper with weak stiffness.
[0040]
Therefore, in the third embodiment of the present invention, as shown in FIGS. 7 and 8, the rotating member 43 composed of a roller serving as a transport assisting rotating member is provided on the downstream side in the transport direction of the branch member 35 and near the branch member 35. The sheet P is rotatably held on the conveyance guide plate 42 and is protruded from the conveyance guide plate 42 so as to be rotatably held. As a result, the sheet P preferentially comes into contact with and slidably contacts the rotating member 43. As described above, the adhesion and accumulation of the toner on the transport guide plate 42 are prevented.
[0041]
As shown in FIG. 8, a suitable number of rotating members 43 according to the third embodiment are installed between a plurality of transport guide plates 42 that are spaced apart in a direction perpendicular to the paper transport direction, for example.
[0042]
Further, a fluororesin is provided on the sliding contact portion A with the paper P on the transport guide plate 42 of the third embodiment, or a fluorine coating is applied to improve the releasability of the sliding contact portion A from the toner. Thereby, toner adhesion and deposition can be suppressed.
[0043]
Further, the present invention is not limited to a composite type image forming apparatus having both functions of a copying machine and a printer as shown in FIG. 9, but is also applicable to a single function image forming apparatus such as a copying machine, a printer, a facsimile machine, and the like. You can do it.
[0044]
【The invention's effect】
As described above, according to the present invention, there is provided a sheet reversing and conveying mechanism configured to move a branch member by lifting a sheet in the vicinity of a sheet conveying path of a fixing unit for fixing a toner image by heating and pressing. However, since the sliding contact of the paper at the branch member or the paper guide member becomes smooth, and the resistance of the paper sliding contact portion at the branch member or the paper guide member can be reduced, the toner adhesion at the branch member or the paper guide member can be reduced. The accumulation is suppressed, and it is possible to prevent the disturbance of the formed image on the sheet and the jam of the sheet which are caused by the accumulation.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a sheet conveyance branch portion for explaining a first embodiment of the present invention (at the time of conveyance in a sheet discharge direction).
FIG. 2 is a configuration diagram illustrating a sheet conveying branch path portion according to the first embodiment of the present invention (when the sheet is conveyed in the sheet reversing direction).
FIG. 3 is a configuration diagram illustrating a sheet transport branching path for explaining a second embodiment of the present invention (at the time of transport in the sheet discharge direction).
FIG. 4 is a configuration diagram showing a sheet conveyance branch path in Embodiment 2 of the present invention (at the time of conveyance in the sheet reversing direction).
FIG. 5 is a perspective view showing a branch member portion in Embodiment 2 of the present invention. FIG. 6 is a configuration diagram showing a sheet conveying branch path portion for explaining Embodiment 3 of the present invention (conveyance in the sheet discharging direction). Time)
FIG. 7 is a configuration diagram showing a sheet conveyance branch path portion in Embodiment 3 of the present invention (at the time of conveyance in the sheet discharge direction).
FIG. 8 is a perspective view showing an installation portion of a discharge roller and a branch member according to a third embodiment of the present invention. FIG. 9 is a configuration diagram showing an example of an image forming apparatus to which the present invention is applied. Configuration diagram showing the paper transport branch path for explaining the problem (when discharging from the paper fixing device)
FIG. 11 is a configuration diagram illustrating a sheet conveying branch path for explaining the problem of the present invention (at the time of conveying in the sheet discharging direction).
FIG. 12 is a configuration diagram illustrating a sheet conveyance branching path for explaining the problem of the present invention (at the time of conveyance in the sheet reversing direction).
FIG. 13 is a perspective view showing a configuration of a sensor for detecting the presence or absence of paper passage in the branch member.
26 Fixing Device 27 Heating Roller 28 Pressurizing Roller 30 Discharge Roller Pair 31 Conveying Branch 32 Left Conveying Path (Discharge Path)
34 Right transport path (reversing path)
35 branch member 40, 43 rotating member 41 transport assist section 42 transport guide plate P paper

Claims (6)

A fixing unit for fixing the toner image transferred to the sheet by heating and pressing, a sheet conveying unit for conveying the sheet discharged from the fixing unit in a sheet discharging direction or a direction opposite to the sheet discharging direction, and a sheet conveying unit An image forming apparatus comprising: a branch member provided on a path for switching a sheet conveying direction to a sheet discharging direction or a direction opposite to the sheet discharging direction.
The branch member is slidably in contact with the sheet, pivotally supported so as to receive the sheet conveying force, and further provided with a conveyance assisting member for smoothing the sheet conveyance in a sheet sliding contact portion of the branch member. Image forming apparatus. 2. The branching member according to claim 1, wherein the transport assisting member is disposed on the branch member so as to slidably contact a sheet transported in a sheet discharging direction and a sheet transported in a direction opposite to the sheet discharging direction. Image forming apparatus. The image forming apparatus according to claim 1, wherein the transport assisting member includes a rotating member that rotates while sliding on a sheet. 4. The image forming apparatus according to claim 1, wherein the transport assisting member is formed of a material having excellent toner separability. 2. The image forming apparatus according to claim 1, wherein a transport assisting rotation member that rotates in sliding contact with a sheet is provided on a sheet guide member downstream of the branch member in the sheet transport direction and near the branch member. 3. apparatus. 2. A transport assisting member made of a material having excellent toner separability is provided on a paper guide member on the downstream side of the branch member in the paper transport direction and near the branch member. Image forming device.

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