JPH05158367A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] When a sheet after image recording is conveyed to a fixing device, the sheet is smoothly guided to a fixing nip portion to prevent deterioration of image quality due to occurrence of jitter or the like. A fixing upper guide plate 40 is provided at the lower end of the upper case 31 of the fixing device 21 on the sheet entrance side. Fixing upper guide plate 4
0 is bent so that both sides 40b in the sheet conveying direction face upward. A lower fixing guide plate 41 is provided on the upper end of the lower case 30 on the sheet entrance side, and the lower fixing guide plate 41 rotatably supports the spurs 43 and 44. When the sheet is conveyed after the image transfer, both lower surfaces of the sheet S are supported by the spurs 43 and 44, and the upper surfaces of the leading ends are brought into contact with the upper fixing guide plate 40, and the upper sheet S is moved along the upper fixing guide plate 40 as much as possible. And guides to the fixing nip portion N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system (a system for transferring an image formed on a photoconductor to a sheet such as a sheet or envelope for recording by using a laser, such as a printer, a copying machine, and a facsimile). ) Relates to an image forming apparatus for recording on a sheet.

[0002]

2. Description of the Related Art Conventionally, in a laser printer, for example, as shown in FIG. 5, for example, a toner image is formed on the surface of a belt-shaped photosensitive member 1, and a sheet S is conveyed above the photosensitive member 1. On the lower surface a of the sheet S.
There is a so-called upper conveyance lower writing type in which the upper toner image is transferred by the transfer device 2 and the sheet S after the image transfer is conveyed to the fixing device 3. In the upper conveyance lower writing type, when the sheet S after the image transfer is conveyed to the fixing device 3,
The leading end side of the sheet S is brought into contact with the upper fixing guide plate 4 of the fixing device 3 and guided by the upper fixing guide plate 4 to the fixing nip portion N between the fixing roller 5 and the pressure roller 6 in the fixing device 3. Then, heat and pressure were applied by both rollers 5 and 6 to fix the transferred image on the sheet S.

[0003]

By the way, in this upper conveyance and lower writing laser printer, the toner image is transferred to the lower surface a of the sheet S by the transfer device 2 as described above. Therefore, conventionally, no guide member for receiving the unfixed image on the lower surface a of the sheet S conveyed after the image transfer is provided below the sheet S so as not to rub the unfixed image. However, if the seat S has a weak waist, as shown by the dotted line in FIG.
The leading end thereof hangs down in front of the fixing device 3 and collides with the fixing roller 5 and the like, and the impact causes the sheet S to sway, causing jitters and the like, which deteriorates the image quality.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to smoothly guide a sheet after image recording to a fixing unit to a fixing nip portion to prevent deterioration of image quality due to occurrence of jitter or the like. It is in.

[0005]

Therefore, in the invention described in claim 1, for example, as shown in the following illustrated embodiments, the sheet S after image recording on the lower surface is conveyed to the fixing device 21 and the fixing device 21 is carried out. In an image forming apparatus for fixing a recorded image with the sheet S and recording it on the sheet S, a guide plate such as a fixing upper guide plate 40 with which the upper surface of the sheet S after the image contact comes into contact with the sheet before the fixing device 21. The spurs 43 and 44 are provided so as to be bent so that both sides in the conveying direction are directed upward, and the lower surface of the sheet S after the image recording contacts.
Are rotatably arranged on both sides in the sheet conveying direction.

According to a second aspect of the invention, for example, as shown in the following illustrated embodiment, in the image forming apparatus of the _{first aspect} , the sheet contact positions P ₁ and P ₂ of the spurs 43 and 44 on both sides are set. On the connecting line L, the peak 40 of the guide plate
c is positioned, and the fixing nip portion N of the fixing device 21 is provided almost on the extension of the crest 40c.

According to a third aspect of the present invention, for example, as shown in the following illustrated embodiment, in the image forming apparatus according to the first aspect, the guide plate is provided in a case such as the upper case 31 of the fixing device 21. It is characterized by being formed.

According to a fourth aspect of the present invention, for example, as shown in the following illustrated embodiments, in the image forming apparatus according to the first aspect, the spur 43. 44 is rotatably supported.

[0009]

In the present invention, the sheet S after image recording is performed.
When the sheet S is conveyed to the fixing device 21, the lower surfaces on both sides of the sheet S are supported by spurs 43 and 44, the upper surface of the sheet S is brought into contact with the guide plate, and guided to the fixing device 21 along the guide plate as much as possible.

According to the second aspect of the present invention, at this time, the sheet S is smoothly guided toward the fixing nip portion N by the guide plate and the spurs 43 and 44.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows an overall schematic configuration of an internal mechanism of an upper conveyance lower writing laser printer which is an embodiment of the present invention. Reference numeral 10 in the figure denotes the apparatus main body. The apparatus main body 10 is composed of an upper structure 10a and a lower structure 10b, and the upper structure 10a is connected to the lower structure 10b.
It is attached to b by a shaft 11 so as to be openable and closable. A belt-shaped photoconductor 12 is provided in the main body 10 of the apparatus at substantially the center thereof.

Around the photosensitive member 12, a charging device 13, a developing device 14, and a transfer device 1 are arranged in this order in the driving direction indicated by the arrow.
5. A cleaning device 16 is arranged. And the charger 1
3 and the cleaning device 16 below the optical writing device 17
And a paper feed cassette 18 on the diagonally upper side of the developing device 14.
Is detachably attached.

The sheet S fed from the paper feed cassette 18 by the paper feed roller 19 is further timed by the registration roller 20 and the photosensitive member 12 is moved.
To the upper side of. The photoconductor 12 is driven in the counterclockwise direction indicated by the arrow, and at that time, the surface of the photoconductor 12 is uniformly charged by the charger 13, and the laser beam L from the optical writer 17 is irradiated to electrostatically charge the photoconductor 12. Form a latent image. This latent image is developed by the developing device 1.
When passing through the 4th position, a visible image is formed by the toner. Then, this visible image is transferred by the transfer device 15 to the lower surface of the sheet S conveyed to the upper side of the photoconductor 12. The sheet S after the image transfer is conveyed to the fixing device 21, and the fixing device 21
To fix the transferred image. Then, the sheet S that has exited the fixing device 21 is further conveyed to the paper ejection unit 23 by the paper ejection roller 22, guided by the paper ejection guide 24, and stacked on the paper ejection tray 25.

By the way, in the illustrated laser printer,
As shown in FIG. 3, the fixing device 21 accommodates a fixing roller 32 and a pressure roller 33 in a lower case 30 and an upper case 31, respectively. A heat source 34 such as a heater is built in the fixing roller 32, and the pressure roller 33 is pressed by being biased by a biasing member (not shown).

Further, in the fixing device 21, a fixing upper guide plate 40 is provided substantially horizontally at the lower end of the upper case 31 on the sheet entrance side (right side in the drawing). The upper fixing guide plate 40 includes both rollers 32.
.A plate member that is long along the length direction of 33, and has one end 40
The a side is extended toward the photoconductor 12. Moreover, as shown in FIG. 2 and FIG. 1, both sides 40b in the sheet conveying direction are bent so as to face upward. Further, a ridge 40c protruding downward is formed at the center of the sheet conveying direction.

Further, as shown in FIG. 3, the fixing device 21 is provided with a fixing lower guide plate 41 at the upper end of the lower case 30 on the sheet entrance side. The lower fixing guide plate 41 is provided on the photoreceptor 12.
Bend one end 41a of the side downward and incline. Then, as shown in FIG. 1, the other ends 41 of the both sides 41b in the sheet conveying direction.
The c-side has a downward bent plate portion 41d, and the support shaft 42 is bridged between the bent plate portions 41d on both sides. Then,
Spurs 43 and 44 are integrally and rotatably attached to the utilization ends of the support shaft 42, respectively.

In the above-mentioned embodiment, as shown in FIG. 2, the upper fixing guide plate 40 is located on the uppermost position of the spurs 43 and 44 on both sides, that is, on the line L connecting the sheet contact positions P ₁ and P _2. The peak 40c is located. Then, as shown in FIG. 3, a fixing nip portion N between the fixing roller 32 and the pressure roller 33 is provided almost on the extension of the ridge 40c toward the fixing device 21 side.

In the illustrated laser printer, as shown in FIG. 3, the sheet S after the image transfer is conveyed diagonally upward by the photoconductor 12. At this time, the lower surfaces of both sides of the sheet S are supported by spurs 43 and 44, the upper surfaces thereof come into contact with the upper fixing guide plate 40, and are guided to the fixing nip portion N in the fixing device 21 along the upper fixing guide plate 40 as much as possible. To go.

In the illustrated embodiment described above, the spur 43 is used.
The spurs 43 and 44 are arranged on both sides in the sheet conveying direction so that the 44 does not contact the recording area of the sheet S. But,
Since the spur contact mark is not noticeable even when it is attached to the sheet, the spur may be arranged at a position in contact with the sheet recording area. Further, the lower fixing guide plate 41 and the upper fixing guide plate 40 are respectively attached to the case 30.3 of the fixing device 21.
However, such a guide plate may be provided separately from the case of the fixing device.

[0020]

According to the present invention, therefore, at the time of sheet conveyance after image transfer, the sheet is brought into contact with the guide plates curved upward on both sides to strengthen the waist and the lower surface thereof is supported by spurs. Since it guides the sheet to the fixing device, it prevents the leading edge side of the weak sheet from hanging down and colliding with the fixing roller, etc., and smoothly guides the sheet to the fixing nip portion, which causes an image It is possible to prevent the quality from deteriorating.

According to the second aspect of the present invention, the crest of the guide plate is positioned on the line connecting the sheet contact positions of the spurs on both sides, and the fixing nip portion of the fixing device is provided almost on the extension of the crest. Thus, the sheet can be conveyed to the fixing nip portion more smoothly.

[Brief description of drawings]

FIG. 1 is a perspective view showing a sheet conveying structure after image transfer in a laser printer which is an embodiment of the present invention.

FIG. 2 is a configuration explanatory view illustrating an arrangement positional relationship between a fixing upper guide plate and a spur in the sheet conveying structure.

FIG. 3 is a configuration diagram schematically showing the configuration of the sheet conveying structure and its periphery.

4 is an overall schematic configuration diagram showing an internal mechanism of a laser printer including the sheet conveying structure in FIG.

FIG. 5 is an explanatory diagram of a conveyance state of a sheet after image transfer to a fixing device in a conventional laser printer.

[Explanation of symbols]

21 fuser 30 lower case (case) 31 upper case (case) 40 fixed on the guide plate (guide plate) 40c peak 43, 44 spur L seat contact position line N fixing connecting the nip portion P _1, P ₂ spurs sheet contact Position S seat

Claims (4)

[Claims] 1. An image forming apparatus for conveying a sheet after image recording on a lower surface to a fixing device, fixing the recorded image by the fixing device, and recording on the sheet, in front of the fixing device and after the image recording. The guide plate with which the upper surface of the sheet contacts is curved so that both sides in the sheet transport direction are upward, and the spur with which the lower surface of the sheet after image recording contacts is freely rotatable on both sides in the sheet transport direction. Placed in the
Image forming apparatus. 2. The ridge of the guide plate is located on a line connecting the sheet contact positions of the spurs on both sides, and the fixing nip portion of the fixing device is provided almost on the extension of the ridge. The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the guide plate is formed by a case of the fixing device. 4. The image forming apparatus according to claim 1, wherein the spur is rotatably supported by a case of the fixing device.