JP2000293052A - Image forming device - Google Patents

Abstract

(57) [Problem] To nip the photosensitive drum 3 and the transfer roller 7 irrespective of the position of the lower guide 25 as a result of the sheet material being flipped upward when the rear end of the sheet material passes through the front end portion 28 of the upper guide 27. There was a problem that the image on the sheet material S was disturbed during the transfer near the portion. SOLUTION: An upper guide member 44 and a lower guide member 43 for forming a sheet material conveyance path and guiding the sheet material to the pressure contact position are provided, and an end of the lower guide member on the pressure contact position side is provided with the transfer member. The tangent line 40 of the pressure contact portion on the most upstream side of the charging member 7
An upper end of the upper guide member 44 on the pressure contact position side is opposite to an end of the lower guide member across the conveyance path, or is located downstream thereof, and the lower surface of the upper guide member 44 An angle 47 between the tangent line 40 and the tangent line 40 forms an acute angle.

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 printer, a facsimile, and a copying machine for conveying a sheet material to an image forming section.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view for explaining the structure of a laser beam printer as an example of a conventional image forming apparatus.
A video controller board (image signal generating means) 4 generates an image signal based on information transmitted from an external information device (not shown) such as a personal computer or a word processor. Here, the video controller board 4
Various electronic components installed above are not shown.

The video controller board 4
The laser light L corresponding to the image signal generated by the photosensitive drum 3 is passed through the laser scanner 5 rotating clockwise.
Irradiation is performed on the photosensitive drum to form an electrostatic latent image on the photosensitive drum. The electrostatic latent image formed on the photosensitive drum 3 is sequentially visualized by toner supplied from a developing unit (not shown) in the process unit 6 and is conveyed to a transfer portion between the transfer roller 7 and the transfer unit. You.

On the other hand, the sheet material S stacked and stored in the sheet feeding cassette 8 is sequentially fed one by one from the uppermost sheet material by a half-moon-shaped sheet feeding roller 9 which rotates once in a counterclockwise direction. Is transported to the registration roller pair 12 whose rotation is stopped by the transport roller pair 11. After the sheet material S reaches the registration roller pair 12, the sheet material S is continuously conveyed until a predetermined loop is formed after the leading edge of the sheet material strikes the nip of the registration roller pair 12, and the skew state is corrected.

[0005] The sheet material S, which has been corrected for the skew state, is conveyed to a transfer section by a registration roller pair 12 which starts rotating at the timing of aligning the position with the toner image on the photosensitive drum 3, where the transfer is performed. The toner image on the photosensitive drum 3 is transferred onto the sheet surface by the roller 7. The sheet material S on which the transfer of the toner image has been completed is conveyed to the fixing roller 14 through the conveyance guide 13, where the toner image is fixed on the sheet surface.

[0006] Sheet material S after fixing process of toner image
Is discharged onto a discharge tray 17 above the laser beam printer 1 through a discharge path 16. At this time, the sheet material S is transported by the transport roller pair 18 and
9 is discharged.

FIG. 7 is a view showing the details of the vicinity of the transfer roller 7 and the photosensitive drum 3. The transfer roller 7 receives a spring force of a spring 24 via bearings 21 and bearing holding arms 22, 23.
As a result, the photosensitive drum 3 is pressed against the photosensitive drum 3 with a predetermined inclination. The photosensitive drum 3 and the transfer roller 7 are indicated by arrows A and B
The toner on the photosensitive drum 3 is transferred while the sheet material S is conveyed in the direction of arrow C by rotating in the respective directions. The upper guide member 27 before the transfer and the lower guide member 25 before the transfer are located on the upstream side of the photosensitive drum 3 and the transfer roller 7, and guide the sheet material to the pressure contact portion between the photosensitive drum and the transfer roller. The distal end portion 26 of the lower guide member 25 is located on or above the tangent line 20 extending from the most upstream side of the nip portion between the photosensitive drum 3 and the transfer roller 7. Further, the process unit 6 including the photosensitive drum 3 has an arrow M
In order to avoid damage to the surface of the photosensitive drum during the removal.
Is a position that has escaped to the upstream side.

[0008]

However, in the above-mentioned conventional apparatus, when the end of the lower guide member 25 on the pressure contact position where the sheet material and the image carrier are pressed against each other is located on or above the pressure contact portion tangent line. When the rear end of the sheet material passes through the lower end portion 28 of the upper guide member 27 during the conveyance of the sheet material, the reaction force held down by the lower surface disappears,
With the upper end portion 26 of the lower guide member 25 serving as a fulcrum, the sheet material S jumps upward as shown by the solid line S 'due to the deflection of the sheet material S.
When the top end 26 of the lower guide member 25 is below the tangent line 20 of the press contact portion, the sheet material rear end is directed toward the photosensitive drum 3 due to the deflection of the transfer roller 7. When the rear end of the sheet material passes through the lower end portion 28 of the guide member 27, it is flipped upward. As a result, the transfer image formed on the sheet material during transfer is disturbed near the nip between the photosensitive drum 3 and the transfer roller 7 regardless of the position of the lower guide member 25.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to suppress image sheet jumping upstream of a transfer section and prevent the transfer image from being disturbed. The aim is to obtain a device.

[0010]

According to the present invention, there is provided an image forming apparatus having the following configuration.

(1) In an image forming apparatus according to the present invention, an image carrier holding a charged toner image is pressed against the image carrier and a sheet material, and the toner image on the surface of the image carrier is applied to the sheet material. A transfer charging member for electrostatically adsorbing, an upper guide member and a lower guide member that form a conveyance path for the sheet material and guide the sheet material to the pressure contact position; The end is on the tangent line of the press contact portion on the most upstream side of the transfer charging member, and the end of the upper guide member on the press contact position side is an opposing portion of the end of the lower guide member across the conveyance path. An image forming apparatus, wherein the angle formed between the lower surface of the upper guide member and the tangent to the pressing portion forms an acute angle.

(2) The image forming apparatus according to (1), wherein a part of the upper guide member on the pressing position side is formed of an elastic body.

(3) The image forming apparatus according to the present invention is characterized in that the image carrier is detachable together with a part of the upper guide member on the side of the pressure contact position. Image forming apparatus.

(4) In the image forming apparatus according to the present invention, the first rotating member, which is pivoted about the rotation center of the image bearing member toward the upstream side of the conveying path of the sheet material, is provided with: The rotation center of the member is a rotation fulcrum, the second rotation member flexibly connected to the first rotation member, and the lower guide member is supported movably in parallel with the conveyance path. The image forming apparatus according to any one of (1) to (3), wherein the downstream protruding portion includes the first rotating member and a lower guide supporting member that is bendable and inexpensive. .

[0015]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a diagram showing details of the vicinity of a transfer roller 7 and a photosensitive drum 3 according to a first embodiment of the present invention. The same parts as those of the conventional apparatus shown in FIG. Is omitted. In the figure, a contact 41 on the most upstream side of a nip portion formed by pressure contact of the photosensitive drum 3 with the transfer roller 7 and a pressure contact portion tangent line 40 passing through the contact 41 are placed on the top end 42 of the lower guide member 43.
The lower end portion 45 of the upper guide member 44 is located on the downstream side of the vertical upper side. The angle 47 formed by the intersection 46 of the lower surface of the upper guide member 44 and the tangent line 40 of the press contact portion to the lower surface is an acute angle.

As described above, the upper and lower guide members 44 and 43 are arranged at the upstream portion by the nip portion of the transfer portion, and the end of the lower guide member on the pressure contact position side is the most upstream pressure contact portion of the transfer charging member. The end of the upper guide member on the tangent line on the pressure contact position side is opposite to the end of the lower guide member separated from the conveyance path, or is located downstream thereof, and the upper guide member temporary surface When the rear end of the sheet material S reaches the point S ′ on the tangent line 40, the upper end portion 42 of the lower guide member 43 is used as a fulcrum, The lifting power works. When this is pressed by the upper guide member, it does not jump up. Thereafter, the rear end portion of the sheet material is drawn into the nip portion along the tangent line 40 of the pressure contact portion of the photosensitive drum, so that it is possible to prevent a movement that disturbs the image being transferred.

Embodiment 2 FIG. FIG. 2 is a diagram showing details of the vicinity of a transfer roller 7 and a photosensitive drum 3 according to a second embodiment of the present invention. The same parts as those in the first embodiment shown in FIG. Description is omitted. This is a modification of the first embodiment in which an elastic guide member 48 as an elastic body is used on the conveyance surface at the end of the upper guide member 44 on the photosensitive drum side. According to the second embodiment, the flip-up force of the rear end portion of the sheet material is weakened by the elastic force of the elastic body guide member 48, so that image disturbance can be prevented.

Embodiment 3 FIG. 3 is a diagram showing the details of the vicinity of the transfer roller 7 and the photosensitive drum 3 according to the third embodiment of the present invention. The same parts as those in the first embodiment shown in FIG. Description is omitted.

In the third embodiment, the process unit 6 shown in FIG. 6 including the photosensitive drum 3 in the first embodiment is detachable, and a part of the upper guide member, that is, the upper guide member 50 immediately before the photosensitive drum side is removed. This is a modified example in the case where it is provided on the process unit side.

The rotation center 56 of the photosensitive drum 3 is used as a rotation fulcrum, and the photosensitive drum-side support member 51 is urged to rotate in the direction of arrow E (upstream of the conveyance path) by a spring 60 upstream of the conveyance path of the sheet material S. (First rotating member) and the rotation center 5 of the transfer roller 7.
A transfer supporting member 52 (second rotating member), which is connected to the drum-side supporting member 51 by a contact 54 so as to be able to freely bend, and a supporting point 58 is provided on the upstream side of the lower guide member 59 on the conveying path. And a lower guide-side support member 53 flexibly connected to the photosensitive drum-side support member 51 and a contact point 55. The three support members allow the photosensitive drum 3 and the transfer roller 7 to be connected.
And the position of the top end of the lower guide member 59 is kept constant.

FIG. 4 is a cross-sectional view showing a state in which the sheet material is conveyed in the third embodiment.
0, which prevents image disturbance due to jumping up of the rear end of the sheet material.

FIG. 5 is an explanatory view showing the state of the transfer roller and the transport path upstream thereof when the process unit including the photosensitive drum 3 is removed. At this time, the transfer roller 7
Does not receive the repulsive force from the photosensitive drum 3,
4 moves toward the photosensitive drum 3 by the resilience of the photosensitive drum 3, and with this movement, the three support arms, that is, the photosensitive drum-side support member 51, the transfer-side support member 52, and the lower guide-side support member 53 are moved by arrows F , G, and H directions, but the original sheet material is conveyed by installing the process unit.
This is effective for preventing the photosensitive drum from being damaged during mounting.

[0024]

As described above, according to the present invention, the lower guide is provided with an upper guide member and a lower guide member for forming a sheet material conveyance path and guiding the sheet material to the pressing position. The end of the member on the press contact position side is on the tangent line of the press contact portion on the most upstream side of the transfer charging member, and the end of the upper guide member on the press contact position side is the lower guide member separated from the conveyance path. The upper end of the upper guide member and the tangent line of the press contact portion are formed at an acute angle, so that the rear end portion of the sheet material occurs at the time of transfer. This is effective for avoiding the problem of image distortion due to blur.

Further, in an image forming apparatus provided with a process unit including a detachable photosensitive drum, by applying the above configuration, there is an effect of preventing damage to the photosensitive drum at the time of attachment and detachment.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a photosensitive drum, a transfer roller, and a transport path on an upstream side thereof according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a photosensitive drum, a transfer roller, and a transport path on an upstream side thereof according to a second embodiment.

FIG. 3 is a diagram illustrating a configuration of a photosensitive drum, a transfer roller, and a transport path on an upstream side thereof according to a third embodiment.

FIG. 4 is a cross-sectional view illustrating a state in which a sheet material is conveyed in a photosensitive drum, a transfer roller, and a conveyance path on an upstream side thereof according to a third embodiment.

FIG. 5 is a diagram illustrating a state of a transfer roller and a transport path upstream thereof when a process unit including a photosensitive drum according to a third embodiment is removed.

FIG. 6 is a cross-sectional view illustrating an overall configuration of a laser beam printer.

FIG. 7 is a diagram illustrating a configuration of a photosensitive drum, a transfer roller, and a transport path on the upstream side of a conventional device.

[Explanation of symbols]

3 photosensitive drum (image carrier), S sheet material, 7 transfer roller (transfer charging member), 44, 49 upper guide member,
43 lower guide member, 47 square, 48 elastic body guide (elastic body), 51 photosensitive drum side support member (first rotating member), 52 transfer side supporting member (second rotating member), 53
Lower guide side support member.

Claims (4)

[Claims] An image carrier that holds a charged toner image; a transfer charging member that presses the image carrier and a sheet material to electrostatically attract the toner image on the image carrier surface to the sheet material; An upper guide member and a lower guide member that form a conveyance path for the sheet material and guide the sheet material to the pressure contact position, and the end of the lower guide member on the pressure contact position side is the uppermost end of the transfer charging member. The pressure contact portion tangent line on the upstream side, the end of the upper guide member on the press contact position side is opposite to the end of the lower guide member across the conveyance path, or located downstream therefrom, An image forming apparatus, wherein an angle formed between a lower surface of the upper guide member and a tangent to the pressing portion forms an acute angle. 2. The image forming apparatus according to claim 1, wherein a part of the upper guide member on the pressing position side is formed of an elastic body. 3. The image forming apparatus according to claim 1, wherein the image carrier is detachable together with a part of the upper guide member on the pressing position side. 4. A rotation fulcrum, wherein the rotation center of the image carrier is a rotation fulcrum, a first rotation member urged to rotate on the upstream side of the sheet material conveyance path, and a rotation center of the transfer charging member are a rotation fulcrum, The first
A second rotating member flexibly connected to the rotating member; and a lower guide member movably supported in parallel with the conveyance path and bending a downstream protruding portion of the lower guide member with the first rotating member. The image forming apparatus according to any one of claims 1 to 3, further comprising a lower guide supporting member that is freely inexpensive.