JPH1048982A - Sheet conveying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the shock absorbing space of the loop of a sheet material resulting from the conveying condition, as well as to prevent a shock when the sheet material rushes in to a nip part, in a sheet conveying device in which the sheet material conveyed by a conveying means is to be led in to the nip part of a fixing device having a fixing roller and a pressurizing roller. SOLUTION: In this device, a sheet material P is conveyed by a conveying means 105, and the sheet material P conveyed by the conveying means 105 is to be led in to the nip part 4 of fixing devices 1 and 2 by a conveying guide 3. In this case, the operating position of the conveying guide 3 is made variable, and it is composed to take a specific operating position before the sheet member reaches to the nip part 4, 4 an operating position turning a little, just before the sheet material advances to the nip part 4, and an operating position turning larger, after the tip of the sheet material has passed the nip part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a laser printer, and the like, and more particularly to a sheet conveying device disposed between a transfer device and a fixing device.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
A recording material conveyance guide fixed to the fixing device is provided between the transfer device and the fixing device, or a method of conveying the recording material on a rubber belt over a relatively long distance is adopted. Was.

[0003] In addition, there have been devised ones in which the position of the transport guide is variably configured, but these change the position in two stages.

[0004]

However, the prior art described above has the following drawbacks caused by the difference in the speed of the recording material described later.

That is, at the moment when the leading end of the recording material that has passed through the transfer portion enters the fixing nip portion, this rush shock propagates through the recording material and propagates to the transfer portion, causing image disturbance. In general, the conveyance speed in the fixing device is set slightly lower than the conveyance speed in the transfer device so that an image defect does not occur by pulling the recording material in the transfer portion. Accordingly, the recording material forms a loop between the transfer unit and the fixing unit, and conversely, when the recording material is pushed backward, that is, upstream in the transport direction in the transfer unit, an image defect may occur, or recording may occur. The image surface of the material may come into contact with an upper structure to cause image rubbing.

In order to solve such a problem, the distance between the transfer unit and the fixing unit is increased, and further, a transfer device using a rubber belt is provided between the transfer unit and the fixing unit. There is a drawback that the entire device becomes large.

[0007] Even when the conveyance guide is swung and the guide surface is made variable, only an effect of slightly increasing the loop space can be obtained, which eliminates the rush shock to the fixing nip and achieves compatibility with the recording material conveyance. Did not provide a sufficient effect.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to achieve both the ability to convey a recording material, the elimination of a rush shock, and the elimination of an image defect due to the formation of a loop, and to cope with a reduction in the size of the apparatus.

[0009]

In order to achieve the above object, according to a first aspect of the present invention, there is provided a sheet conveying apparatus which conveys a sheet material and a sheet material conveyed by the conveying means. In a sheet conveyance device having a conveyance guide for guiding a nip portion of a fixing device, the operation position of the conveyance guide is variably configured, and the operation position has at least three operation positions.

According to a second aspect of the present invention, there is provided a detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveying guide, and the driving means based on a detection signal from the detecting means. And control means for driving the.

According to a third aspect of the present invention, there is provided a sheet conveying apparatus having conveying means for conveying a sheet material, and a conveying guide for guiding the sheet material conveyed by the conveying means to a nip portion of a fixing device. It has a first rotation center near the fixing nip portion between the fixing roller and the pressure roller, and a second rotation center near the rotation center of the pressure roller. A first operation position for introducing the sheet material and a second operation position slightly rotated downward from the first operation position are taken, and the second operation center is further moved from the second operation position by the second rotation center. The third that turned down greatly
Characterized in that it is configured to take the operation position of

According to a fourth aspect of the present invention, the conveyance guide is pivotally supported at a front portion in the sheet conveyance direction by a rotating member substantially coaxial with a pressure roller of the fixing device, and is biased at a rear portion in the conveyance direction by an urging means. It is characterized in that it is brought into contact with the moving member and the rotation is controlled by a cam that opposes the urging means.

According to a fifth aspect of the present invention, the transport guide rotates instantaneously from the first operating position to the second operating position and gradually rotates from the second operating position to the third operating position. It is characterized by.

According to a sixth aspect of the present invention, there is provided a detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveying guide, and the driving means based on a detection signal from the detecting means. And control means for driving the.

According to a seventh aspect, in the image forming apparatus, the transferable image formed and carried on the image carrier is transferred to a recording material by a transfer device, and the recording material is introduced into a fixing device to fix the image. A recording material transport guide is provided between the apparatus and the fixing device, and the operation position of the recording material transport guide is variably configured, and at least two or more moving directions are used in changing the operation position. Features.

According to an eighth aspect of the present invention, the recording material transport guide comprises:
The fixing device has a first rotation center near the fixing nip portion, and a second rotation center near or near the rotation center of the pressure roller of the fixing device.

According to a ninth aspect, the recording material transport guide comprises:
A first operating position for introducing the recording material from the transfer device to the fixing nip, a second operating position slightly rotated about the first center of rotation, and a second operating position. And a third operating position which is largely turned down about the center of rotation.

In a tenth aspect of the present invention, the transport guide is configured to rotate a first operating position for introducing a sheet material from a transfer device to a fixing nip, and to rotate slightly downward about the first rotation center. A second operating position, and a third operating position further pivoted largely downward about the second pivot center.

According to an eleventh aspect of the present invention, there is provided a detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveying guide, and a control for driving the driving means based on the detection signal. Means.

According to a twelfth aspect, before the leading end position of the conveyed sheet material reaches the nip portion of the fixing device, the conveying guide is in the first operating position, and the leading end position of the sheet material is in the first operating position. At the moment of reaching the nip, the transport guide is in the second position.
The conveyance guide moves to the third operation position after the leading end position of the sheet material has passed through the nip portion at the operation position.

According to a thirteenth aspect of the present invention, there is provided an image forming apparatus, comprising: an image carrier on which a transferable image is formed; transfer means for transferring the transferable image on the image carrier to a sheet material; A fixing device for fixing the transferred image to the sheet material, and a sheet conveying device according to any one of the first to twelfth inventions provided between the transfer means and the fixing device.

The operation of the above solution is performed as follows.
A sheet material conveyance guide provided between the transfer device and the fixing device has the following three operation positions.

1st Normal position, where the leading edge of the sheet material is introduced into the fixing nip.

Second, a position slightly rotated downward, and a fixing rush shock is eliminated.

Third, a position further pivoted downward,
A sufficient loop space is ensured to prevent image defects.

The operating position of the conveyance guide is changed by detecting the leading end of the conveyed sheet material and measuring the timing based on the detection signal.

The center of rotation of the guide from the first operating position to the second operating position is located in the vicinity of the fixing nip, so that the leading end of the guide always faces the fixing nip, so that the sheet material transportability is stable. I do.

The center of rotation from the second operating position to the third operating position is further downward, for example, at or near the center of the pressure roller, so that the center of rotation can be further increased while avoiding interference with the roller. And a sufficient loop space formed by the speed difference between the fixing device and the conveying device can be secured.

The movement from the first operating position to the second operating position is instantaneous, whereby the operation of introducing the leading end of the sheet material into the fixing nip can be continued until immediately before, and at the moment when a rush shock occurs, the operation is started. Release the shock downward.

The movement from the second operating position to the third operating position is gradually performed, and the space is expanded in accordance with the growth of the loop, so that the load applied to the sheet material can be kept constant, and the image forming operation can be performed. The effect can be minimized, and the occurrence of image defects can be prevented by securing a sufficient loop space.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

 <First Embodiment> This will be described with reference to FIGS.

FIG. 2 is a schematic structural view of an image forming apparatus main body having a sheet conveying device according to the present invention. Copy sheets P, which are sheet materials stacked in the sheet cassette 101, are fed out one by one by a sheet feeding device 102 and are conveyed to registration rollers 103. The registration roller 103 sends out the copy sheet P to the transfer section in synchronization with the timing of image formation.

A copy sheet P as a recording material is attracted onto the transfer belt 104 and moves in the direction of arrow A. During this time, for example, a latent image is formed on the electrophotographic drum 110 as an image carrier by a laser beam, images of the respective colors of YMCK developed by the developing unit 111 are sequentially transferred, and a full-color image is formed on the copy paper P. You.

The copy paper P, which has reached the left end of the transfer belt 104, moves on the transport guide 3 while being separated from the transfer belt 104 by a curvature, and forms a fixing nip formed between the fixing roller 1 and the pressure roller 2. 4 and the image is fixed on the copy paper.

FIG. 1 is a detailed view for explaining the operation state of the sheet conveying apparatus according to the present invention. The copy sheet P separated from the transfer belt 104 is guided by the transport guide 3 and heads toward the fixing nip 4. Fixing roller 1 and pressure roller 2
Are arranged such that the fixing nip 4 formed between these rollers is slightly above the separation point 106 from the transfer belt, and a straight line connecting the centers of the fixing roller 1 and the pressure roller 2 is fixed to the fixing nip 4. Straight line 19 orthogonal to nip 4
(FIG. 3) passes slightly below the separation point 106. Transport guide 3 at first position
The guide surface is substantially coincident with the straight line 19, the leading end of the guide surface extends to the vicinity of the fixing nip 4, and the copy paper P
It is reliably guided to the nip 4 from a position lower than the nip 4 (FIG. 1- (a)). Next, as shown in FIG.
At the moment when the leading edge of the copy sheet P enters the fixing nip 4 or a predetermined time before, the transport guide 3 slightly rotates downward from the position shown by the dotted line and moves to the position shown by the solid line (second position). . Therefore, the vibration due to the shock generated at the moment when the sheet enters the fixing nip 4 is absorbed by the copy sheet P flexing downward, and the vibration is transmitted to the copy sheet P to reach the image forming unit, thereby causing image defects such as blurring. It does not occur.

At the moment when the copy sheet P enters the fixing nip 4, the behavior of the copy sheet P is unstable, and the copy sheet P tends to cause slow motion or JAM. In the second position, the leading end of the guide faces the fixing nip 4 even in the second position.

Next, when the copy paper P is further transported by the fixing roller pair, the transport speed by the fixing roller pair is set slightly lower than the transport speed by the transfer belt. Deflection occurs in P and the loop amount increases. Therefore, as shown in FIG. 1C, the transport guide 3 is further pivoted downward to take the third position and the loop space is increased, so that the copy sheet P is sufficiently flexed downward. Thus, it is possible to prevent the reaction force due to the stiffness, that is, the rigidity of the paper, from being transmitted to the image forming unit and causing image defects. In addition, since a loop is generated downward, even if a large loop occurs, the image surface (upper surface)
Does not rub against the upper guide or the like to cause an image defect.

Next, a specific configuration will be described with reference to FIGS.

In FIG. 3, when the leading edge of the copy paper P reaches the sensor lever 6, the lever 6 is turned counterclockwise to avoid the flag of the photo-interrupter 7 that has blocked the infrared light, A tip detection signal is output and transmitted to a control device 31 (not shown) (FIG. 4). The control device calculates the time when the leading edge of the copy sheet P further advances and reaches the fixing nip 4, and sends it to the driving device 32 for operating the transport guide 3 at the moment when the leading edge of the sheet enters the nip 4 or before a predetermined time. Is given. The driving device is a half-turn clutch, a stepping motor, or the like, and rotates the cam 8 clockwise at a predetermined timing (FIG. 5). The transport guide 3 is urged downward by a spring 9, and a part thereof contacts the cam surface of the cam 8. (A) to (c) in FIG. 5 correspond to (a) to (c) in FIG.
The cam position in the same state as that shown in FIG.

When the cam 8 is rotated to the position shown in FIG. 5B, the transport guide 3 is instantaneously slightly rotated by a small step provided on the cam surface. This operation is called copy paper P
The vibration of the paper can be effectively released by synchronizing the movement of the paper into the fixing nip 4. The movement to the state of FIG. 5C is performed in accordance with the loop growth of the copy paper P.
The transport guide 3 is gradually rotated along the cam surface. As a result, it is possible to widen a sufficient loop space while keeping the load applied to the copy sheet P to a minimum and constant.

When the copy sheet P passes through the transport guide 3 and the cam 8 further rotates, the transport guide 3 is pushed up against the spring force by the cam surface and returned to the first operating position.

<Other Embodiments> In addition to the first embodiment,
An embodiment in which the transport guide 3 has two rotation centers will be described.

That is, as shown in FIG. 6, FIG.
(B) is the initial rotation (the leading edge of the copy paper P is the fixing nip 4).
6A or for a while thereafter), the conveyance guide has a center of rotation at or near the fixing nip portion, and in the rotation shown in FIGS. It has a center of rotation at or near the center. Therefore, until the copy paper P enters the fixing nip 4 and the transportability thereof is sufficiently stabilized, the leading end of the transport guide 3 is always directed toward the fixing nip 4, and thereafter, rotates along the outer periphery of the surface of the pressure roller 2. Because of the movement, a wider rotation angle can be obtained.

FIG. 7 is a perspective view showing the schematic configuration.

The guide table 25 is rotatable with respect to the axis 22 and is urged in the direction of arrow A by a spring (not shown).
It is in contact with the stopper 26 at a portion 25b. The transport guide 3 is rotatably supported on the axis 21 with respect to the guide table 25, and is urged in the direction of arrow B by a spring (not shown), so that the projecting portion 3 a of the transport guide 3 contacts the cam surface of the cam 8. Touched. Here, the axis 22 is set at or near the rotation center of the pressure roller 2, and the axis 21 is set at or near the fixing nip 4.

As in the first embodiment, in the first operating position shown in FIG. 6 (a), the transport guide 3 is restricted to a position in contact with the cam surface of the cam 8, and The guide table 25 is restricted to a position where it is in contact with the stopper 26.

Similarly to the above-described embodiment, when the driving device is driven by the ON signal given from the control device, the cam 8 rotates clockwise, and the conveyance guide 3 is instantaneously moved by a minute step provided on the cam surface. 6B, and takes the second position (the state shown in FIG. 6B). In this case, the transport guide 3 rotates about the axis 21 on the guide table 25. When the cam 8 further rotates, the transport guide 3 gradually rotates along the cam surface, and the contact portion 3a of the transport guide comes into contact with the contact portion 25a of the guide table. After that, the spring force FB
Overcomes the spring force FA, and the contact portion 25b
6, the swing guide 3 is moved along with the guide base 25 along the axis 2.
6 and further takes a third position (FIG. 6).
(State of (c)). Then, the copy paper P is transferred to the conveyance guide 3.
When the cam 8 further rotates, the conveyance guide 3 is pushed up against the spring force FB by the cam surface, and the guide table 25 is also lifted up by the spring force FA to come into contact with the stopper 26. 1 is returned to the operating position.

[0048]

As described above, the sheet conveying apparatus according to the present invention is configured such that the sheet conveying guide for guiding the sheet conveyed to the fixing device can take at least three operating positions. Therefore, the leading end of the sheet material is reliably introduced into the fixing nip at the first operating position of the sheet conveying guide, the rush shock to the fixing nip is eliminated at the second operating position, and the sheet material is transported at the third operating position. Thus, the loop space described above can be sufficiently secured, and thus the occurrence of an image defect formed on the sheet material can be prevented.

Further, the sheet conveying guide has two rotation centers for taking the three operating positions.
The above effects are more effectively exhibited. By controlling the rotation timing, the above-described effect is more effectively exhibited.

The above-mentioned image defect can be prevented without increasing the size of the apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an operation state of a sheet conveying apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention.

FIG. 3 is a diagram illustrating a specific configuration of an embodiment of a sheet material conveying device according to the present invention.

FIG. 4 is a view for explaining a drive system in the embodiment of the sheet conveying apparatus according to the present invention.

FIG. 5 is a diagram illustrating a specific configuration of an embodiment of a sheet material conveying device according to the present invention.

FIG. 6 is a diagram illustrating an operation state of a second embodiment according to the present invention.

FIG. 7 is a diagram illustrating a specific configuration of a second embodiment according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Pressure roller 3 ... Conveyance guide 4 ... Fixing nip 7 ... Photo interrupter 8 ... Cam 31 ... Control device 32 ... Drive device 110 ... Photosensitive drum 111 ... Developing means P ... Copy paper

Claims (13)

[Claims] In a sheet conveying apparatus having a conveying means for conveying a sheet material and a conveying guide for guiding the sheet material conveyed by the conveying means to a nip portion of a fixing device, the operation position of the conveying guide is variable. The sheet conveying device is configured and has at least three operation positions. 2. A detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveyance guide, and a control for driving the driving means based on a detection signal from the detecting means. 2. The sheet conveying apparatus according to claim 1, further comprising means. 3. A sheet conveying apparatus having a conveying means for conveying a sheet material, and a conveying guide for guiding the sheet material conveyed by the conveying means to a nip portion of a fixing device, wherein the conveying guide is fixed to a fixing roller. It has a first rotation center near the fixing nip portion between the pressure rollers and a second rotation center near the rotation center of the pressure roller, and the sheet material of the fixing nip is introduced by the first rotation center. And a second operating position that is slightly rotated downward from the first operating position, and is further rotated downward from the second operating position by the second rotation center. A sheet conveyance device, wherein the sheet conveyance device is configured to take a third operation position that has been moved. 4. The conveyance guide is rotatably supported at a front portion in a sheet material conveyance direction by a rotation member substantially coaxial with a pressure roller of a fixing device, and is abutted against the rotation member at a rear portion in the conveyance direction by an urging means. 4. The transfer device according to claim 3, wherein the transfer device is contacted and rotation-controlled by a cam opposing the urging means. 5. The transport guide according to claim 1, wherein the transport guide rotates instantaneously from the first operating position to the second operating position and gradually rotates from the second operating position to the third operating position. The sheet conveying device according to claim 3. 6. A detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveying guide, and a control for driving the driving means based on a detection signal from the detecting means. The sheet conveying apparatus according to claim 3, further comprising: 7. An image forming apparatus in which a transferable image formed and carried on an image carrier is transferred to a recording material by a transfer device, and the recording material is introduced into a fixing device to fix the image. A sheet having a recording material conveyance guide between the recording medium and the recording material conveyance guide, the operation position of the recording material conveyance guide being variably configured, and having at least two or more moving directions for changing the operation position. Transport device. 8. The recording material conveyance guide has a first rotation center near the fixing nip portion of the fixing device and a second rotation center near or near the rotation center of the pressure roller of the fixing device. The sheet conveying device according to claim 7, wherein the sheet conveying device includes the sheet conveying device. 9. The recording material transport guide pivots slightly downward about a first operating position for introducing a recording material from the transfer device to a fixing nip, and about the first rotational center. 9. The sheet conveying device according to claim 7, further comprising a second operating position, and a third operating position that is further turned downward largely around the second turning center. 10. . 10. The transfer guide includes a first operating position for introducing a sheet material from a transfer device to a fixing nip;
A second operating position that is slightly downwardly rotated about the first rotation center, and a third operating position that is further largely downwardly rotated about the second rotation center. The sheet conveying device according to claim 7, wherein: 11. A detecting means for detecting a leading end position of a conveyed sheet material, a driving means for changing an operation position of the conveyance guide, and a control means for driving the driving means based on the detection signal. 8. The method according to claim 7, wherein
11. The sheet conveying device according to any one of claims 10 to 10. 12. The conveying guide reaches the first operating position and the leading end position of the sheet material reaches the nip portion before the leading end position of the conveyed sheet material reaches the nip portion of the fixing device. 2. The transport guide moves to a second operating position at the moment of the movement, and further moves to a third operating position after the leading end position of the sheet material passes through the nip portion. 12. The sheet conveying apparatus according to any one of claims 1 to 11. 13. An image carrier on which a transferable image is formed,
Transfer means for transferring the transferable image on the image carrier to a sheet material, a fixing device for fixing the image transferred by the transfer means to the sheet material, and a fixing device provided between the transfer means and the fixing device. Item 13. An image forming apparatus comprising the sheet conveying device according to any one of Items 1 to 12.