JP2001226017A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the grade of an image without causing the disorder of a toner image in feeding a medium. SOLUTION: An image forming device comprises an image forming unit provided with an image carrier for forming a toner image on the surface of the image carrier, transfer means opposed to the image carrier for transferring the toner image to the medium, fixing means for fixing the transferred toner image to the medium, a medium feed passage for feeding the medium, and a medium deforming means formed in the upstream of the fixing means in the medium feed passage for curving the medium into a protruded shape. The medium deforming means for curving the medium into the protruded shape in the upstream of the fixing means prevents the rubbing of the medium at its upper face in feeding and the disorder of the toner image transferred to the medium. The grade of the image is thus improved.

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.

[0002]

2. Description of the Related Art Conventionally, electrophotographic printers, copiers,
In an image forming apparatus such as a facsimile apparatus, an electrostatic latent image formed on a photosensitive drum is developed to form a toner image, and the toner image is transferred to a sheet as a medium.
The image is fixed and an image is formed.

FIG. 2 is a schematic view of a conventional printer, and FIG. 3 is a view showing a state of a rear end of a sheet in the conventional printer.

In the drawing, reference numeral 11 denotes a developing unit,
The developing unit 11 is rotatably disposed in the case 12, a photosensitive drum 13 which is rotatably disposed in the case 12, and is rotated by driving a driving source (not shown), and is rotatably disposed in the case 12. A charging roller 14 for uniformly and uniformly charging the surface of the photosensitive drum 13, and a photosensitive drum 1 outside the case 12.
3, an LED head 15 that exposes the charged surface of the photoconductor drum 13 to form an electrostatic latent image, and that is rotatably disposed in the case 12; A developing roller 16 that develops a latent image to form a toner image, a cleaning roller 17 that is rotatably disposed in the case 12 and that removes toner remaining on the photosensitive drum 13, are provided.

A transfer roller 21 is provided outside the case 12 so as to face the photosensitive drum 13 and to be rotatable with respect to a paper guide 22.
1 is rotated in synchronization with the photosensitive drum 13 by a gear (not shown). And the photosensitive drum 1
A transfer portion is formed between the transfer roller 3 and the transfer roller 21.

In the developing unit 11 configured as described above, the surface of the photosensitive drum 13 is uniformly and uniformly charged by the charging roller 14 and is exposed by the LED head 15 to form an electrostatic latent image. Then, the electrostatic latent image is developed by the developing roller 16 to form a toner image. Subsequently, the toner image is transferred to a sheet P as a medium supplied from a sheet cassette (not shown) in a transfer unit.
Is transferred by the transfer roller 21. Then, the sheet P is sent to the fixing device 23, where the toner image is fixed on the sheet P, and an image is formed.

The fixing device 23 includes an upper frame 24 disposed facing the paper guide 22 and adjacent to the developing unit 11, and a heat roller rotatably disposed relative to the upper frame 24. 25, a pressure roller 26 opposed to the heat roller 25 and rotatably disposed with respect to the paper guide 22, a heating source disposed in the heat roller 25 for heating the heat roller 25 Lamp 27 as the heat roller 2
5, a heat roller 25 for rotatably supporting the bearing 5
The separation claw 32 that peels off the paper P adhered to the heat roller 25 from the heat roller 25, a bearing 33 that rotatably supports the pressure roller 26, and the pressure roller 26 via the bearing 33.
The spring 34 is provided as urging means for pressing the heat roller 25 against the heat roller 25. A hole (not shown) is formed on the upper surface of the upper frame 24, and the upper frame 24 can be fixed to a mechanical frame (not shown) by screws passing through the hole.

The paper guide 22 is provided in the case 12
Is formed between the developing unit 11 and the upper frame 24, and forms a paper transport path R for transporting the paper P between the developing unit 11 and the upper frame 24.

A fixing section is formed between the heat roller 25 and the pressure roller 26, and the toner image on the sheet P conveyed through the sheet conveying path R is transferred to the heat roller 25 while passing through the fixing section. And is pressed by the pressure roller 26 to be fixed on the sheet P. When an image is formed in this manner, the sheet P is further conveyed through the sheet conveying path R and discharged to a stacker (not shown) by a discharge roller (not shown).

While the paper P passes through the fixing section, a nip n is formed by the contact pressure between the heat roller 25 and the pressure roller 26.

[0011]

However, in the above-mentioned conventional printer, the front end (right end in the figure) of the paper P reaches the fixing unit and is caught by the heat roller 25 and the pressure roller 26. Thereafter, when the rear end (left end in the figure) of the sheet P falls out of the transfer portion, as shown in FIG. 3, the rear end of the sheet P rises upward as the nip n is formed, and the case 12 Will contact the lower cover 12a on the lower surface of the.

In this case, the paper P
Is rubbed (rubbed) by the lower cover 12a, and the toner image transferred to the paper P is disturbed. as a result,
Image quality is degraded.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of solving the problems of the conventional printer and improving the image quality without disturbing the toner image due to the conveyance of the medium. And

[0014]

For this purpose, an image forming apparatus according to the present invention comprises an image carrier and an image forming unit for forming a toner image on the surface of the image carrier.
A transfer unit disposed to face the image carrier, for transferring a toner image to a medium, a fixing unit for fixing the transferred toner image to the medium, a medium conveyance path for conveying the medium, A medium deforming unit formed upstream of the fixing unit in the medium transport path and configured to curve the medium in a convex shape.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. In this case, an electrophotographic printer as an image forming apparatus will be described.

FIG. 1 is a schematic view of a printer according to the first embodiment of the present invention, and FIG. 4 is a view showing a state of sheet transport in the first embodiment of the present invention.

In FIG. 1, reference numeral 11 denotes a developing unit as an image forming unit. The developing unit 11 is rotatably disposed in the case 12 and the case 12.
A photosensitive drum 13 as an image carrier rotated by driving a drive source (not shown);
2, the photosensitive drum 1
A charging roller 14 serving as a charging unit for uniformly and uniformly charging the surface of the photosensitive drum 3 outside the case 12 so as to face the photosensitive drum 13;
An LED head 15 as an exposing means for exposing the charged surface of the device to form an electrostatic latent image, rotatably disposed in the case 12, and developing the electrostatic latent image to form a toner image And a cleaning roller 17 rotatably disposed in the case 12 to remove toner remaining on the photosensitive drum 13.

A transfer roller 21 as transfer means is disposed outside the case 12 so as to face the photosensitive drum 13 and rotatably with respect to a paper guide 22 as a medium guide. Is rotated in synchronization with the photosensitive drum 13 by a gear (not shown). Then, the photosensitive drum 13 and the transfer roller 2
1, a transfer portion is formed.

In the developing unit 11 configured as described above, the surface of the photosensitive drum 13 is uniformly and uniformly charged by the charging roller 14 and is exposed by the LED head 15 to form an electrostatic latent image. Then, the electrostatic latent image is developed by the developing roller 16 to form a toner image. Subsequently, the transfer roller 21 transfers the toner image onto a sheet P as a medium supplied from a sheet cassette (not shown) as a medium cassette in a transfer section. Then, the sheet P is sent to a fixing unit 23 as a fixing unit, and the toner image is fixed on the sheet P in the fixing unit 23 to form an image.

The fixing device 23 includes an upper frame 24 disposed opposite the paper guide 22 and adjacent to the developing unit 11, and a heat roller rotatably disposed relative to the upper frame 24. 25, a pressure roller 26 opposed to the heat roller 25 and rotatably disposed with respect to the paper guide 22, a heating source disposed in the heat roller 25 and heating the heat roller 25 Lamp 27, bearing 31 for rotatably supporting heat roller 25, heat roller 2
A separating claw 32 for peeling the paper P adhered to the heat roller 25 from the heat roller 25, a bearing 33 for rotatably supporting the pressure roller 26, and an urging means for pressing the pressure roller 26 against the heat roller 25 via the bearing 33. Spring 34 as
Is provided. A hole (not shown) is formed on the upper surface of the upper frame 24, and the upper frame 24 can be fixed to a mechanical frame (not shown) by screws passing through the hole.

The paper guide 22 is provided in the case 12.
Is formed between the developing unit 11 and the upper frame 24 to form a paper transport path R as a medium transport path for transporting the paper P between the developing unit 11 and the upper frame 24. I do.

A fixing section is formed between the heat roller 25 and the pressure roller 26. The toner image on the sheet P conveyed through the sheet conveyance path R is transferred to the heat roller 25 while passing through the fixing section. And is pressed by the pressure roller 26 to be fixed on the sheet P. When an image is formed in this manner, the sheet P is further conveyed through the sheet conveying path R and discharged to a stacker (not shown) by a discharge roller (not shown).

While the paper P passes through the fixing section, a nip n (see FIG. 3) is formed by the contact pressure between the heat roller 25 and the pressure roller 26. Then, when the front end (right end in the figure) of the sheet P reaches the fixing unit and is engaged by the heat roller 25 and the pressure roller 26, the rear end (left end in the figure) of the sheet P comes out of the transfer unit. In order to prevent the rear end of the sheet P from rising upward, the sheet P is located downstream of the transfer unit in the sheet conveyance direction and upstream of the fixing unit 23 (fixing unit) in the sheet conveyance path R. A projection 51 as a medium deformation means is formed so as to protrude upward.

The projection 51 extends in a trapezoidal shape from the approximate center point a1 between the transfer section and the fixing section on the sheet transport path R at the center in the width direction of the sheet P toward the fixing section. And an inclined surface S1 extending obliquely in the height direction, and a top surface S2 extending substantially horizontally from the upper end of the inclined surface S1 toward the fixing portion, and the highest portion of the top surface S2, The vertex a2 is located on a line connecting the transfer section and the fixing section.

By the way, in order to prevent the paper P from wrinkling when the paper P passes through the fixing section, the outer diameter of both ends of the heat roller 25 is made slightly larger than the outer diameter of the central part. Both ends Pb of the paper P are in the center Pa
It is designed to be transported slightly faster. In this case, after the rear end of the sheet P passes through the transfer section, when the sheet P passes over the protrusion 51, the central portion Pa comes into contact with the vertex a2 and is moved while being maintained at the height of the vertex a2. On the other hand, both ends Pb are moved at a position lower than the vertex a2 (this was also confirmed by experiments). That is, the sheet P is curved in a convex shape from the portion of the protrusion 51 to the rear end so that the central portion Pa projects upward.

Accordingly, as the nip n is formed, the rear end of the paper P does not rise upward, and a member disposed along the paper transport path R, for example, the lower surface of the case 12 Can be prevented from contacting the lower cover 12a.

Since the upper surface of the paper P is not rubbed by the lower cover 12a when the paper P is transported, the toner image transferred to the paper P is not disturbed. As a result, image quality can be improved.

Next, a second embodiment of the present invention will be described. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.

FIG. 5 is a schematic view of a printer according to the second embodiment of the present invention.

In this case, the projection 61 as a medium deforming means
Are pivotally disposed in the direction of the arrow around a shaft 62 disposed at the end on the transfer section side, and are urged upward by a spring 63 as urging means. Then, the vertex a2 of the projection 61 when the paper P as a medium does not pass over the projection 61 is positioned on a line connecting the transfer section and the fixing section.

Therefore, when the front end (right end in the figure) of the sheet P reaches the protrusion 61, the protrusion 61 is pushed down by the stiffness of the sheet P, so that the resistance to the conveyance of the sheet P can be reduced. As a result, the paper P is smoothly bitten by the fixing unit.

Then, the rear end of the sheet P (left end in the figure)
Is passed through the transfer section, the projection 61 is pushed upward by the urging force of the spring 63. Accordingly, when the paper P passes over the protrusion 61, the central portion Pa (FIG. 4)
Is in contact with the vertex a2 and is moved while being maintained at the height of the vertex a2, whereas both ends Pb are moved at positions lower than the vertex a2. That is, the paper P is
From the part 1 to the rear end, the central part Pa is curved so as to protrude upward.

Next, a third embodiment of the present invention will be described. In addition, about what has the same structure as 2nd Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.

FIG. 6 is a schematic view of a printer according to the third embodiment of the present invention.

In this case, the projection 61 as a medium deforming means
Are pivotally disposed in the direction of the arrow around a shaft 62 disposed at the end on the transfer section side, and are urged upward by a spring 63 as urging means. A reciprocating motion generating means 71 is provided between the shaft 62 and the spring 63.
Is arranged. The reciprocating motion generating means 71 includes a solenoid 72 as an actuator, and a lever 73 swingably connected to the protrusion 61 and the solenoid 72.
Consists of Then, the vertex a2 of the projection 61 when the paper P as a medium does not pass over the projection 61 is positioned on a line connecting the transfer section and the fixing section.

A sensor lever 74 is disposed on the paper transport path R as a medium transport path on the upstream side of the transfer section so as to be swingable about a shaft 75. A transmission type photosensor 76 as a detection unit is provided, and the photosensor 76 is fixed to a substrate 77. When the sheet P does not pass over the sensor lever 74, the sensor signal is turned off because the sensor lever 74 blocks the photosensor 76, and while the sheet P passes over the sensor lever 74, the sensor signal is turned off. Since the sensor lever 74 is rotated so as not to block the photo sensor 76, the sensor signal is turned on.

The solenoid 72 swings the projection 61 in accordance with the state of conveyance of the sheet P. For this purpose, the solenoid 72 is turned on / off in synchronization with the on / off of the sensor signal.
1 is rotated clockwise to retreat from the paper transport path R,
When it is off, the projection 61 is rotated counterclockwise to project into the paper transport path R.

Therefore, after the front end (right end in the figure) of the sheet P passes through the sensor lever 74, the solenoid 72 is turned on until the rear end (left end in the figure) passes through the sensor lever 74 and is separated by a distance A. And protrusion 6
1 is retracted from the paper transport path R. As a result, the resistance to the conveyance of the paper P can be reduced,
The paper P is smoothly bitten by the fixing unit. The protrusion 61
Is positioned below the paper guide 22 as a medium guide as it is withdrawn from the paper transport path R, so that even when the paper P is weak, the paper P is smoothly bitten by the fixing unit. .

After the trailing edge of the sheet P is separated by the distance A, the solenoid 72 is turned off, and the projection 61 is made to protrude into the sheet transport path R by the urging force of the spring 63. Accordingly, when the sheet P passes over the protrusion 61, the central portion Pa (FIG. 4) comes into contact with the vertex a2 and is moved while being maintained at the height of the vertex a2.
Both end portions Pb are moved at positions lower than the vertex a2 (this was also confirmed by experiments). That is,
The paper P is curved in a convex shape from the portion of the protrusion 61 to the rear end so that the central portion Pa projects upward.

The present invention is not limited to the above embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0041]

As described above in detail, according to the present invention, an image forming apparatus includes an image carrier, and an image forming unit for forming a toner image on the surface of the image carrier. A transfer unit disposed to face the image carrier, for transferring a toner image to a medium, a fixing unit for fixing the transferred toner image to the medium, a medium conveyance path for conveying the medium, A medium deforming unit formed upstream of the fixing unit in the medium transport path and configured to curve the medium in a convex shape.

In this case, the toner image formed on the surface of the image carrier by the image forming unit is transferred to the medium by the transfer means, and then fixed to the medium by the fixing means. At this time, since the medium deformation unit curves the medium in a convex shape on the upstream side of the fixing unit, the upper surface of the medium is not rubbed with the conveyance, and the toner image transferred to the medium is not disturbed. .

Therefore, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a printer according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a conventional printer.

FIG. 3 is a diagram illustrating a state of a rear end portion of a sheet in a conventional printer.

FIG. 4 is a diagram illustrating a sheet conveyance state according to the first embodiment of the present invention.

FIG. 5 is a schematic view of a printer according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram of a printer according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Developing unit 13 Photoreceptor drum 21 Transfer roller 23 Fixing device 51, 61 Projection 34, 63 Spring 72 Solenoid a2 Vertex P Paper R Paper conveyance path

Claims (5)

[Claims] 1. An image forming unit comprising: (a) an image carrier, for forming a toner image on a surface of the image carrier; and (b) a toner image disposed to face the image carrier. (C) fixing means for fixing the transferred toner image to the medium, (d) a medium conveying path for conveying the medium, and (e) a medium conveying path for conveying the medium. An image forming apparatus, comprising: a medium deforming unit formed upstream of the fixing unit to curve the medium in a convex shape. 2. The image forming apparatus according to claim 1, wherein the medium deforming unit is a projection that protrudes into a medium conveyance path. 3. The image forming apparatus according to claim 2, wherein the apex of the protrusion is located on a line connecting a transfer portion between the image carrier and the transfer device and a fixing portion of the fixing device. 4. The image forming apparatus according to claim 2, wherein (a) the projection is swingably disposed, and (b) biasing means for biasing the projection upward is disposed. 5. The image forming apparatus according to claim 4, further comprising an actuator that swings the protrusion in accordance with a state of transporting the medium.