JPH07287458A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus capable of preventing the deterioration of the transfer efficiency, the backside of paper, and the destruction of the photosensitive layer of the toner image carrier due to the leakage of the transfer current. In an image forming apparatus having a paper feed cassette 100 that is detachable from the apparatus main body 10 and having a transfer roller 6 as a transfer unit, the transfer roller 6 is disposed integrally with the paper feed cassette 100, The length of the transfer roller 6 is set according to the length of the paper stored in the paper feed cassette 100 in the width direction.

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 having a paper feed cassette which is attachable to and detachable from a main body of the apparatus and having a transfer roller as a transfer means.

[0002]

2. Description of the Related Art In an image forming apparatus based on the electrophotographic principle,
A record carrier having various lengths, that is, widths in the direction perpendicular to the moving direction is used.

However, in the contact transfer method, since the transfer member and the image carrier are in contact with each other in a portion where the record carrier is not present, a recording carrier having a width smaller than the width of the transfer member is used and the residual developer is left on the image carrier. In this case, the developer adheres to the surface of the transfer member, and eventually transfers to the back surface of the recording carrier as dirt at the next transfer. Alternatively, if foreign matter such as dust or a hard substance in paper powder adheres to the surface of the transfer member, it may damage the surface of the image carrier. In particular, since the transfer bias is applied with a polarity for attracting the developer, if the bias is applied to the transfer member where there is no record carrier, the stain becomes remarkable.

Further, in a portion where there is no record carrier, the electric resistance between the transfer member and the image carrier is reduced by the amount of the record carrier, so that the transfer current is concentrated in the low resistance portion and the effective transfer bias is generated. If it is lowered, or in an extreme case, current leakage or discharge may cause damage to the photosensitive layer of the image bearing member.

In order to solve this problem, Japanese Patent Laid-Open No. 48-4
As disclosed in Japanese Patent No. 0442 (first conventional example), several kinds of transfer rollers are prepared according to the width of the transfer paper, and one of the transfer rollers is properly used according to the size of the transfer paper. Can be considered.

Further, as disclosed in Japanese Utility Model Laid-Open No. 55-19946 (second conventional example), one transfer roller is allowed to move laterally in the axial direction, and the length of the photosensitive drum in the axial direction is increased. When using a transfer paper having a width smaller than that, one side edge of the transfer paper is aligned with one end of the photoconductor drum, and the transfer roller is moved to set the transfer roller to the photoconductor drum only in the range where the transfer paper exists. Opposition is also proposed.

Further, as disclosed in Japanese Patent Application Laid-Open No. 5-027613 (third prior art example), a transfer roller having a length corresponding to the minimum width of the transfer paper to be used and a length less than that are used. A plurality of transfer rollers including a transfer roller having the transfer roller are provided, and at least one of the transfer rollers is laterally moved according to the width of the transfer paper to be used to obtain a transfer roller width corresponding to the width of the transfer paper as a whole. It is also proposed.

Further, as disclosed in Japanese Patent Application Laid-Open No. 4-336576 (fourth prior art), the transfer roller is divided into a plurality of regions in the direction perpendicular to the moving direction of the transfer paper to obtain the width of the transfer paper. Accordingly, it has been proposed to apply the transfer bias only to the substantially same width of the transfer roller.

On the other hand, the image forming apparatus can use sheets having various thicknesses, as well as sheets having various widths. When the thickness of the paper changes, the traveling direction of the front end of the paper after passing through the nip portion between the photosensitive drum and the transfer roller changes due to the difference in the stiffness (rigidity) of the paper. That is, since the thick paper has high rigidity, the separability from the photoconductor drum is good, and the progress is almost in the nip direction (tangential direction at the nip), and the thin paper has low rigidity, so the separability from the photoconductor drum is poor. , The toner is biased toward the photosensitive drum side rather than the nip direction.

When the traveling direction of the leading edge of the sheet changes depending on the thickness of the sheet as described above, the sheet cannot normally enter the fixing roller pair depending on the type of the sheet, and image rubbing, wrinkling of the sheet, bending of the leading edge of the sheet, and sheet There is a problem that jams (jams) may occur.

To solve this, Japanese Patent Laid-Open No. 4-335
As disclosed in Japanese Patent No. 5486 (fifth conventional example), it has been proposed to provide a paper pressure sensor and a mechanism for changing the nip width between the photosensitive drum and the transfer roller in the apparatus body.

[0012]

In the first conventional example, there is a problem that the transfer device becomes large and complicated, and the cost becomes high.

Further, the second conventional example has a problem that a large space is required for lateral movement of the transfer roller.

Also, in the third conventional example, similarly to the above, there are problems that the device is large, complicated, and high in cost.

Although the fourth conventional example does not lead to an increase in size of the apparatus, it is difficult to form a transfer roller that is electrically non-conductive and divided into a plurality of regions, and it is difficult to process a gap at the boundary. There was a problem.

Further, in the fifth conventional example, the size of the device is increased,
There were problems of complexity and high cost.

A first object of the present invention is not to increase the size and complexity of the apparatus with a simple structure, but to reduce transfer efficiency, stain the back of the paper, and damage the photosensitive layer of the toner image carrier due to leakage of transfer current. An object of the present invention is to provide an image forming apparatus that can prevent the jammed paper and can easily remove the jammed paper by removing the paper feed cassette from the apparatus main body when the paper is jammed.

A second object of the present invention is to provide a paper pressure sensor and a mechanism for changing the nip width between the photosensitive drum and the transfer roller in the main body of the apparatus without complicating the apparatus.
An object of the present invention is to provide an image forming apparatus that can easily obtain good transfer efficiency and paper conveyance performance.

[0019]

A first object of the present invention is to provide an image forming apparatus having a paper feed cassette detachable from the apparatus main body and having a transfer roller as a transfer means, wherein the transfer roller is The transfer roller is disposed integrally with the paper feed cassette, and the length of the transfer roller is achieved by the first means having a length corresponding to the length of the paper stored in the paper feed cassette in the width direction.

The above-mentioned second object is, in the first means,
This is achieved by the second means provided in the paper feeding cassette with an adjusting mechanism for adjusting the contact pressure of the transfer roller with respect to the toner image carrier or the amount of bite.

[0021]

In the first means, the transfer roller corresponding to the width of the sheet is prepared in the sheet feeding cassette, so that the apparatus is simple and does not become large in size and complicated, and the transfer efficiency is reduced and the backside of the sheet is prevented from becoming dirty. It is possible to prevent the photosensitive layer of the toner image bearing member from being broken due to the leakage of the transfer current.

In the second means, the transfer roller is brought into contact with the toner image carrier, that is, the paper feed cassette is provided with an adjusting mechanism for adjusting the contact pressure or the amount of bite. The contact pressure suitable for the thickness of the paper stored in it can be set in advance.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing the overall structure of an image forming apparatus to which the present invention is applied, FIG. 2 is an explanatory view showing the structure of a paper feed cassette according to the first embodiment, and FIG. FIG. 6 is an explanatory diagram showing a relationship between lengths of transfer rollers.

As shown in FIG. 1, the apparatus main body 10 has a sheet feeding cassette 100 at the bottom thereof, and above the sheet feeding roller 1, registration rollers 2a and 2b, a photosensitive drum (toner image carrier). ) 3, a charger 4 such as a corona charger or a charging roller, a developing device 5 having a developing roller 5a, a transfer roller 6, fixing rollers 7a and 7b, and discharge rollers 8a and 8
b, a cleaner 9 and the like.

Paper P stored in the paper feed cassette 100
Is fed from the paper feed roller 1 in the direction of the registration rollers 2a and 2b, and is conveyed to the photosensitive drum 3 at a timed timing by the registration rollers 2a and 2b. The photosensitive drum 3 has a photosensitive layer formed on a conductive supporting portion with a photosensitive material having organic or inorganic photoconductivity.
The photosensitive drum 3 is driven to rotate clockwise, and at that time,
The surface is charged by the charger 4 and irradiated with light L emitted from an exposure device (not shown) such as a laser or an LED to obtain a potential contrast and an electrostatic latent image is formed.

On the other hand, the developing device 5 conveys the toner by the developing roller 5a and develops the toner. The developing roller 5a is pressed against the photosensitive drum 3 with a predetermined pressure, and the toner is transferred to the pressing portion. Then, a developing electric field is formed by the potential contrast of the photoconductor drum 3 and the developing bias applying means (not shown), the toner charged according to the developing electric field adheres to the photoconductor drum 3, and the electrostatic latent image becomes visible. To be imaged.

Further, the visible image is a nip between the transfer roller 6 and the photosensitive drum 3 to which a transfer bias is applied at a potential such that the charged toner is electrostatically attracted from a transfer power supply device (not shown). In the set, it is transferred to the conveyed paper P.

The transferred visible image on the paper P is fixed by heat and pressure by the fixing rollers 7a and 7b, and discharged to the outside of the machine by the discharge rollers 8a and 8b to obtain a desired image.

On the other hand, the photosensitive drum 3 after the transfer of the visible image is
The cleaner 9 removes the residual toner, and returns to the initial state.

Next, the paper feed cassette according to the first embodiment will be described with reference to FIGS. As shown in these drawings, a transfer roller 6 is attached to the paper feed cassette 100, and the transfer roller 6 is detachable from the apparatus body 10 together with the paper feed cassette 100. In addition, the paper feed cassette 100 includes a registration roller 2
a is attached.

The transfer roller 6 comprises a shaft 6b made of a conductive material such as a metal material, and a roller layer 6a formed on the shaft 6b.
a is a suitable elastic resin foam material to which a conductivity-imparting agent such as carbon, zinc oxide or tin oxide is added, for example, polyurethane foam, silicone foam, EPR foam, EPD
It is composed of M foam, IR foam and the like.

In this embodiment, the roller layer 6a is made of foam, but solid rubber may be used as long as it has appropriate elasticity, and the present invention is not limited to foam.

The transfer roller 6 is provided with the shaft 6 when the paper feed cassette 100 is mounted on the apparatus main body 10 (FIG. 1).
The transfer roller 6 is movably supported in the direction of the photoconductor drum 3 via bearings (not shown) at both ends of b.
As shown in FIG. 2, the pressurizing device 11 presses the photosensitive drum 3 with a predetermined pressure. A spring is suitable for the pressurizer 11. One end of the pressurizer 11 is locked to the shaft 6b and the other end of the pressurizer 11 is locked to the frame of the sheet feeding cassette 100. Further, the transfer roller 6 rotates counterclockwise due to the rotation accompanying the pressure contact with the photosensitive drum 3. The transfer roller 6 may be rotationally driven by a drive device (not shown), for example, gear coupling from the photoconductor drum 3, and the present invention is not limited to the accompanying rotation drive.

Here, the length in the longitudinal direction of the transfer roller 6 is substantially the same as the width of the paper P to be stored in the paper feed cassette 100 (the length in the direction perpendicular to the moving direction of the paper P). . That is, as shown in FIG. 3, in the paper feed cassette 100 in which the size of the paper P1 is to be stored, the length of the roller layer 6a of the transfer roller 6 is W1 and the paper feed cassette 100 in which the size of the paper P2 is to be stored. In the above, the length of the roller layer 6a of the transfer roller 6 is W2.

However, in the case where the driving method of the transfer roller 6 is the rotation accompanied by the pressure contact with the photosensitive drum 3, the roller layer 6a of the transfer roller 6 is formed to prevent slippage.
It is desirable to make the length of the sheet P longer than the width of the sheet P in the range of 1 to 20 mm at both ends, and to provide a region where the transfer roller 6 directly contacts the photosensitive drum 3.

As described above, in the first embodiment, the transfer roller 6 corresponding to the width of the paper P is attached to the paper feed cassette 100.
It is possible to prevent damage to the photosensitive layer of the toner image carrier due to a decrease in transfer efficiency, dirt on the back side of the paper, and leakage of transfer current without making the device large and complicated with a simple configuration. become.

Further, as shown in FIG. 2, if one of the registration rollers 2a is arranged on the side of the paper feed cassette 100, the paper P
By removing the paper feed cassette 100 from the apparatus main body 10 at the time of jam (paper jam) or the like, the jammed paper can be easily removed.

In this embodiment, the pressure developing method is used as the developing method, but the present invention is not limited to the developing method.

Next, the paper feed cassette according to the second embodiment will be described. FIG. 4 is an explanatory diagram showing the configuration of the paper feed cassette according to the second embodiment.

In the second embodiment, one end of the pressurizer 11 is locked to the shaft 6b, and the flat plate 12 is locked to the other end of the pressurizer 11. The flat plate 12 is centered on the shaft 13a. Is in contact with the rotating cam 13. Since the outer peripheral surface of the cam 13, that is, the sliding surface of the flat plate 12 is not equal in distance from the shaft 13a, the pressing roller 11 is expanded and contracted by rotating the cam 13 so that the transfer roller 6 contacts the photosensitive drum 3. That is, the contact pressure can be adjusted.

In the second embodiment, the sheet feeding cassette 100 is provided with the contact pressure adjusting mechanism so that the sheet feeding cassette 100 is suitable for the thickness of the sheet P previously stored in each sheet feeding cassette 100. The contact pressure can be set.

Therefore, good transfer efficiency and conveyance performance can be easily achieved without complicating the apparatus by providing a paper pressure sensor and a mechanism for changing the nip width between the photosensitive drum 3 and the transfer roller 6 in the apparatus main body 10. Obtainable.

Although the contact pressure adjusting mechanism adjusts the end of the pressurizer 11 by the cam 13 in the second embodiment, the present invention is not limited to this. For example, instead of adjusting the pressing force, a regulation member (not shown) that regulates the amount of the transfer roller 6 biting into the photosensitive drum 3 may be adjusted.

As the paper feeding cassette 100, a plurality of dedicated paper feeding cassettes for each paper size are prepared, and a single common paper P for storing multi-size paper P while moving the side fence and the back fence. A paper feed cassette (so-called universal cassette) may be used.

[0046]

According to the first aspect of the present invention, the transfer roller corresponding to the width of the sheet is prepared in the sheet feeding cassette, so that the apparatus has a simple structure without making the apparatus large and complicated, and the transfer efficiency is lowered. It is possible to prevent damage to the photosensitive layer of the toner image carrier due to dirt on the back of the paper, leakage of transfer current, etc., and also to remove the jammed paper by removing the paper feed cassette from the main body when the paper is jammed. Can be done easily.

According to the second aspect of the invention, in addition to the action and effect produced by the first aspect of the invention, the state in which the transfer roller is in contact with the toner image carrier, that is, the adjustment for adjusting the contact pressure or the bite amount is adjusted. By providing the paper feed cassette with the mechanism, the contact pressure suitable for the thickness of the paper stored in each paper feed cassette can be set in advance. Therefore, it is possible to easily obtain good transfer efficiency and paper conveyance performance without complicating the device such as providing a paper pressure sensor and a mechanism for changing the nip width between the photosensitive drum and the transfer roller in the main body of the device. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory diagram showing a configuration of a sheet feeding cassette according to the first exemplary embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a relationship between a width of a sheet and a length of a transfer roller.

FIG. 4 is an explanatory diagram showing a configuration of a paper feed cassette according to a second embodiment of the present invention.

[Explanation of reference numerals] 1 paper feed rollers 2a, 2b registration roller 3 photosensitive drum (toner image bearing member) 4 charger 5 developing device 5a developing roller 6 transfer rollers 7a, 7b fixing roller 8a, 8b paper discharging roller 9 cleaner 10 Device main body 11 Pressurizer 12 Flat plate 13 Cam 100 Paper feed cassette

Claims (2)

[Claims] 1. An image forming apparatus having a paper feed cassette detachable from the main body of the apparatus and having a transfer roller as a transfer means, wherein the transfer roller is provided integrally with the paper feed cassette,
The image forming apparatus is characterized in that the length of the transfer roller is set according to the length of the paper stored in the paper feed cassette in the width direction. 2. The image forming apparatus according to claim 1, wherein the sheet feeding cassette is provided with an adjusting mechanism for adjusting a contact pressure or a biting amount of the transfer roller with respect to the toner image carrier.