JP2001051526A - Electrophotographic transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a transfer device preventing the deformation of a pretransfer guide, securing a fixed transfer point and having a stable transfer performance, which transfer device adopts a non-contact type transfer roller and is used for transferring a toner image to a transfer paper in an electrophotographic image forming system. SOLUTION: The device is provided with a transfer roller 14 for transferring the toner image on a photoreceptor drum 10 onto a transfer sheet, a pair of distance control rolls 40 arranged coaxially with the transfer roller 14 so as to maintain a prescribed distance between the transfer roller 14 and the photoreceptor drum 10, a roll energizing means for pressing the distance control rolls 40 against the photoreceptor drum surface, the pre-transfer guide 42 for supplying the transfer sheet in between the photoreceptor drum 10 and the transfer roller 14, positioning means which are arranged at both end parts of the pre-transfer guide 42 so as to position the guide 42 with reference to the photoreceptor drum 11, and a pressing/energizing means for energizing the positioning means toward the photoreceptor drum. And, the positioning means arranged on at least one side of the guide 42 is constituted of a spiral element whose projection from the guide 42 is adjustable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to a transfer device including a transfer roller used for an electrophotographic device such as a facsimile.

[0002]

2. Description of the Related Art In an electrophotographic apparatus represented by a copying machine, the surface of a photosensitive drum is uniformly charged, and an electrostatic latent image corresponding to a document image is formed on the surface of the photosensitive drum by image exposure. The electrostatic latent image is developed to form a toner image on the surface of the photoconductor drum, and the toner image is transferred from the surface of the photoconductor drum onto a transfer sheet such as paper, and the transferred toner image is subjected to heat, pressure, or the like. By fixing, an image is formed.

In such an electrophotographic apparatus, the transfer of the toner image formed on the surface of the photosensitive drum onto the transfer sheet is performed by using a corona charger (transfer charger) so that the back surface of the transfer sheet is reversed from the toner image. This has been done by charging to a polarity. However, when a transfer is performed using a corona charger, the transfer sheet is electrostatically attracted to the surface of the photoconductor drum. Therefore, in order to separate the transfer sheet on which the toner image has been transferred from the surface of the photoconductor drum, an AC charger is used. Must be used together, and there is a problem that the transfer mechanism becomes complicated. Another problem is that ozone is generated by corona charging.

Accordingly, at present, a transfer roller has attracted attention as a transfer device that replaces the corona charger, and has been put to practical use. The transfer of the toner image using the transfer roller is performed by arranging the transfer roller facing the surface of the photoconductor drum, and applying a voltage to the transfer roller so as to have a polarity opposite to that of the toner image on the surface of the photoconductor drum, This is performed by passing a transfer sheet between the two. When a toner image is transferred using such a transfer roller, the transfer sheet on which the toner image has been transferred can be easily separated from the surface of the photosensitive drum, and there is no need to use a separation unit such as a transfer charger. There is an advantage that ozone is not generated by corona charging.

When a toner image is transferred using a transfer roller, if the toner image on the surface of the photosensitive drum is pressed against the surface of the transfer material, an image defect such as a dropout in the transferred toner image is likely to occur. That is, the toner image on the surface of the photosensitive drum is expanded by pressing against the surface of the transfer material. As a result, the density of the transferred toner image obtained on the transfer sheet is high at the peripheral portion of the image, but at the central portion of the image. Is more likely to occur. In order to prevent such a dropout, the transfer roller is arranged so that a fixed minute gap is formed between the transfer roller and the photosensitive drum without contacting the transfer roller.

However, the distance between the transfer roller and the photosensitive drum must be set strictly. If the interval is too small, when the transfer is performed by passing through the transfer sheet, the toner image on the surface of the photoconductor is pressed against the transfer sheet surface, and the above-described problem of the void in the transfer toner image is likely to occur. If the interval is too large, the transfer efficiency is reduced.

Accordingly, in a transfer device using a transfer roller which is conventionally known, in a transfer roller non-contact type in which the transfer roller is provided in non-contact with the surface of the photoreceptor drum, the rotation shafts at both ends of the transfer roller are provided with the transfer roller. Also, a large-diameter gap regulating roller is provided, and the gap regulating roller is pressed against the surface of the photosensitive drum to urge the photosensitive drum to a predetermined distance (usually 0.1 to 0.1 mm) between the transfer roller and the photosensitive drum surface. 5 mm).

In the case where the transfer roller is provided in non-contact with the photosensitive drum, it is necessary to provide a pre-transfer guide in order to bring the transfer sheet passing between them into good contact with the surface of the photosensitive drum. The pre-transfer guide is provided close to the surface of the photoconductor drum. At least both ends of the pre-transfer guide are provided so that the entire transfer sheet is in close contact with the surface of the photoconductor drum at a fixed position (transfer point). It is urged toward the photosensitive drum.

[0009]

However, in the transfer roller non-contact type transfer device of the related art, the pre-transfer guide is twisted, the transfer point is partially shifted, and the transfer performance becomes unstable. There is a problem. That is, in the transfer roller non-contact transfer device described above, a pre-transfer guide is attached to a frame that rotatably holds the rotation shaft of the transfer roller, and both ends of the pre-transfer guide are provided on the photosensitive drum side. Is pressed so as to come into contact with the stopper. At the same time, a pair of interval regulating rollers provided on the rotating shafts at both ends of the transfer roller are urged to contact the surface of the photosensitive drum. As described above, the positions of the pair of gap regulating rollers and the pre-transfer guide are all related to the position of the frame that rotatably holds the rotation shaft of the transfer roller, and the pair of gap regulating rollers and both ends of the pre-transfer guide are It is practically impossible to set a total of four contact points on the same plane. Even if any three contact points are set on the same plane, the remaining one point is
It is in a state of floating from a predetermined surface. In this case, since the pair of gap regulating rollers and the surface of the photosensitive drum are pressed firmly, the one end of the pre-transfer guide is strongly pressed against the stopper on the surface of the photosensitive drum. As a result, the pre-transfer guide is deformed (twisted).

Accordingly, an object of the present invention is to prevent deformation of a pre-transfer guide in a transfer roller non-contact transfer device,
An object of the present invention is to provide a transfer device in which a fixed transfer point is secured and which has stable transfer performance.

[0011]

According to the present invention, there is provided a transfer roller for transferring a toner image onto a transfer sheet on a photosensitive drum, and a transfer roller and a photosensitive drum provided coaxially with the transfer roller. , A pair of interval regulating rollers for maintaining a predetermined interval, roller biasing means for pressing the interval regulating rollers against the surface of the photosensitive drum, and a pre-transfer for supplying the transfer sheet between the photosensitive drum and the transfer roller. A guide, positioning means provided at both ends of the pre-transfer guide for positioning the pre-transfer guide with respect to the photosensitive drum, and pressing urging means for urging the positioning means toward the photosensitive drum. Wherein the positioning means provided on at least one side of the pre-transfer guide is a member whose protrusion amount from the pre-transfer guide is adjustable. It is subjected.

In the transfer apparatus according to the present invention, a member that can adjust the amount of protrusion from the pre-transfer guide, for example, a screw, is used as a means for positioning the pre-transfer guide provided on at least one side of the pre-transfer guide. Is a remarkable feature. That is, by using such a positioning means capable of adjusting the amount of protrusion, a pair of interval regulating rollers for maintaining the transfer roller and the photosensitive drum at a predetermined interval are urged so as to come into contact with the surface of the photosensitive drum. Even if the pre-transfer guide is adjusted, the position of the pre-transfer guide can be adjusted by the positioning means, and the torsion of the pre-transfer guide can be effectively prevented.

The positioning means capable of adjusting the protrusion amount is provided at one end of the pre-transfer guide, and a positioning protrusion having a constant protrusion amount is provided at the other end of the pre-transfer guide. These positioning means can be pressed and urged toward the photoreceptor drum. However, any of the positioning means at both ends of the pre-transfer guide may be positioning means capable of adjusting the amount of protrusion. As described above, when the positioning means capable of adjusting the amount of protrusion is provided at both ends of the pre-transfer guide, an advantage that the distance between the pre-transfer guide and the photosensitive drum can be appropriately adjusted according to the thickness of the transfer sheet. There is.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific examples shown in the accompanying drawings. First, prior to the description of the structure of the transfer device of the present invention, an outline of the overall arrangement of an electrophotographic apparatus that transfers a toner image using a transfer roller will be described. In FIG. 1 showing the overall arrangement of such an electrophotographic apparatus, in this electrophotographic apparatus, a main charging device 11 and an exposure mechanism are provided around a photosensitive drum 10 rotatably provided in the direction of the arrow in FIG. 12, a transfer device including a developing device 13, a transfer roller 14, a charge removing device 15, and a cleaning device 16 are arranged in this order along the rotation direction of the photoconductor drum.
A transfer sheet, for example, a transfer paper 20 is passed between the transfer paper 20 and a fixing device 21 on a discharge path of the transfer paper 20.

The photosensitive drum 10 includes an inorganic photosensitive drum in which a photosensitive layer such as selenium or amorphous silicon is provided on a conductive base roller such as aluminum, or a charge generating agent or a charge transporting agent in a binder resin. An organic photosensitive drum provided with an organic photosensitive layer in which is dispersed is used.

As the main charging device 11, there is a roller-type contact charging device, but a corona charger is generally used, and the surface (photosensitive layer) of the photosensitive drum 10 is It is uniformly charged to a predetermined polarity according to the type of the layer. The main charging potential at this time is usually 200 to
It is about 1000 V (absolute value).

Next, the image exposure mechanism 12 irradiates the surface of the photosensitive drum with dot light such as a laser beam corresponding to the original by reflected light of the original or an electric signal from a computer or the like, and the potential of the irradiated portion is attenuated. , An electrostatic latent image is formed.

In the developing device 13, the photosensitive drum 1
0, and a developer transport sleeve is disposed so as to face the photosensitive drum 1 by the developing sleeve.
The electrostatic latent image is supplied to a developing area between the sleeve 0 and the sleeve to develop the electrostatic latent image. As the developer, a two-component developer composed of a magnetic carrier and an insulating toner and a one-component developer composed of a magnetic toner are generally used. The development of the electrostatic latent image is performed. The charge polarity of the toner is opposite to the charge polarity of the surface of the photoconductor drum 10 when the image is formed by so-called regular development, and is opposite to the surface of the photoconductor drum 10 when the image is formed by the reverse development. Has the same polarity as the charging polarity of

The toner image 25 formed on the surface of the photosensitive drum 10 by the development by the developing device 13 is transferred to the transfer paper 20 passing between the photosensitive drum 10 and the transfer roller 14.
Transfer paper 2 having a transfer toner image 26 transferred to the surface thereof
0 is conveyed to the fixing device 21 and the transfer toner image 26 is fixed on the surface of the transfer paper 20 by heat, pressure or the like. On the other hand, after the toner image 25 is transferred onto the transfer paper 20, the surface charge of the photosensitive drum 10 is removed by light irradiation by the charge removing device 15. Further, the toner remaining on the surface of the photosensitive drum 10 is scraped and collected by the cleaning device 16 including a cleaning blade and the like, and the next image forming process is performed. The cleaning device 16
The toner collected in step (1) is recycled to the developing device 13 as needed, and is reused.

The transfer roller 14 is made of a metal roller, a conductive powder such as a metal powder or a carbon powder, or a rubber, a resin, or a foam thereof made conductive by the addition of ions. The transfer roller 14 has a power source 2
8 is connected, and a transfer voltage that gives a potential having a polarity opposite to the charge polarity of the toner image 25 is applied, so that the transfer of the toner image 25 onto the transfer paper 20 is performed efficiently. This transfer voltage is such that the current flowing into the roller 14 during the transfer is 2 to 40 μA,
Usually, it is about 100 to 4000 V (absolute value). It is preferable that the transfer roller 14 is set so that the distance between the surface of the transfer roller 14 and the surface of the photosensitive drum 10 is 0.1 to 0.5 mm. If the distance is smaller than 0.1 mm, the toner image 25 is pressed against the surface of the transfer paper 20 passing between the two, and the transfer toner image 26 is liable to cause an image defect such as a hollow image. The transfer roller 14 is liable to shake or the like due to an impact when the transfer roller 14 is passed, and transfer unevenness is likely to occur. If this interval is larger than 0.5 mm, the transfer voltage applied to the transfer roller 14 becomes insufficient, and poor transfer and uneven transfer are likely to occur.

Although not shown in FIG. 1, a drive transmission gear is provided on the rotation shaft of the transfer roller 14, and the drive transmission gear is meshed with the drive gear of the photosensitive drum 10. As a result, the transfer roller 14
Is driven to rotate with respect to the photosensitive drum 10 so as to send the transfer paper 20 toward the fixing device 21.

Referring to the sectional side view of FIG. 2 showing the transfer device of the present invention having the above-described transfer roller 14 together with the photosensitive drum 10, and the front view of FIG. A) is disposed to face the photoconductor unit B provided with the photoconductor drum 10, and the photoconductor unit B is provided with a stopper 30 so as to face the transfer device A. Although not shown in FIG. 2, the main charging device 11, the exposure mechanism 12, the developing device 13, the neutralizing device 15, and the cleaning device 16 shown in FIG. It is arranged other than A.

The transfer device A generally includes a transfer roller 14, a pair of interval regulating rollers 40 provided on both sides of a rotation shaft 14 a of the transfer roller 14, and a housing for accommodating the transfer roller 14. 41, and a pre-transfer guide 42 attached to the housing 41.

As is apparent from FIG. 3, the rotary shaft 14a of the transfer roller 14 is provided with bearings 45 at both ends thereof, and the bearing 45 is attached to the photosensitive drum by a pressing spring 46 (see FIG. 2). It is urged toward the side 10. That is, one end of the push spring 46 is connected to the bearing 4.
5 and the other end is supported by a support plate (not shown) fixed to the apparatus frame. On the other hand, the spacing regulating rollers 40
Is formed slightly larger in diameter than the transfer roller 14.
Therefore, the rotating shaft 14a is
Is pressed and urged toward the photoreceptor drum 10, so that the interval regulating rollers 40 come into close contact with the surface of the photoreceptor drum 10,
As a result, a certain gap is secured between the transfer roller 14 and the photosensitive drum 10. That is, the transfer roller 1
The difference in diameter between the transfer roller 14 and the photosensitive drum 10 corresponds to the diameter difference between the transfer roller 14 and the photosensitive drum 10.

Referring to FIG. 4 which is a left side view of the housing 41 (AA side view in FIG. 3) together with FIG. 3, the housing 41 includes a rear frame 41a and a bottom frame 41b.
And a side frame 41c (in FIG. 4, a part of the side frame 41c is omitted).
A pre-transfer guide 42 is attached to the side of the side frame 41c opposite to the rear frame 41a (toward the photosensitive drum 10). The pre-transfer guide 42 may be formed integrally with the side frame 41c, or may be attached to the side frame 41c with screws or the like. Further, the rotation shaft 14a of the transfer roller 14 is provided on the side frame 41c.
And a bearing 48 having a concave portion that fits with
The housing 41 provided with the pre-transfer guide 42 is rotatably held around the rotation shaft 14a. Further, the rear frame 41a is provided with a push spring 50 for urging the casing 41 to rotate counterclockwise in FIG. 2 or FIG. That is, this push spring 5
One end of O is supported by a back frame 41a (a central portion in FIG. 3), and the other end is supported by a support plate (not shown) fixed to the apparatus frame, similarly to the push spring 46. That is, the pre-transfer guide 42 is urged to rotate counterclockwise in FIG. 2 with the housing 41 by using the rotation shaft of the transfer roller 14 as a fulcrum by the urging force of the pressing spring 50. .

As is clear from FIGS. 3 and 4, a position adjusting screw 55 is provided at one end of the pre-transfer guide 42, and this screw 55 is provided from the rear frame 41a side. 42 extend through the end of the ridge. A positioning protrusion 5 is provided on the other end of the pre-transfer guide 42.
6 are provided. That is, referring also to FIG. 2, since the pre-transfer guide 42 is urged to rotate counterclockwise by the above-described pressing spring 50, the position adjusting screws at both ends of the pre-transfer guide 42 are provided. The tip of the projection 55 and the tip of the positioning projection 56 abut against the stopper 30 provided on the photoconductor unit B, whereby the pre-transfer guide 42 is arranged at a fixed position with respect to the photoconductor drum 10. That is. In the above-described example, the position adjusting screw 55 is connected to the pre-transfer guide 42 from the rear frame 41a.
However, it may be provided so as to penetrate only the pre-transfer guide 42. In addition, in order to easily adjust the amount of protrusion by rotating the screw 55, the screw 55 may be positioned outside the side frame 41c.

The rotating shaft 14a of the transfer roller 14
Is biased by a pressing spring 46, and is positioned in a state where a pair of interval regulating rollers 40, 40 are in contact with the surface of the photosensitive drum 10. That is, when the leading ends of the positioning members provided at both ends of the pre-transfer guide 42 are in contact with the stopper 30, the contact between the positioning member at one end of the transfer guide 42 and the stopper 30 is performed by the gap regulating roller 40. Are located on the same plane as the two contact points between the transfer guide 42 and the surface of the photosensitive drum 10, but the contact point between the positioning member at the other end of the transfer guide 42 and the stopper is different from the other three contact points. It is located above (it is practically impossible to locate the four contact points on the same plane in terms of design accuracy and the like). Therefore, when the leading ends of the positioning members provided at both ends of the pre-transfer guide 42 are brought into contact with the stoppers 30 by the urging force of the press springs, the pre-transfer guide 42 always undergoes deformation such as twisting. When the pre-transfer guide 42 is deformed, the transfer paper 10 guided between the transfer roller 14 and the photoconductor drum 10 by the guide 42 varies in the contact point (transfer point) with the surface of the photoconductor drum 10. As a result, the transfer characteristics become unstable, and the transfer image formed on the transfer paper 10 tends to cause image defects such as distortion.

However, according to the transfer device of the present invention described above, one of the positioning members provided at both ends of the pre-transfer guide 42 can be adjusted in position (the amount of protrusion from the pre-transfer guide 42 can be adjusted). Since the pre-transfer guide 42 is formed by the screw 55, it is possible to effectively prevent deformation such as twisting of the pre-transfer guide 42. That is, the positioning spring 56 at one end of the pre-transfer guide 42 is pressed by the pressing spring 55.
And the stopper 30 are in contact with each other, and the other end of the screw 5
When the screw 5 is urged so as to be in contact with the stopper 30, the amount of protrusion of the screw 55 from the pre-transfer guide 42 can be adjusted by rotating the screw 55. Therefore, by adjusting the amount of protrusion of the screw 55 while keeping the tip of the screw 55 in contact with the stopper 30,
The deformation of the pre-transfer guide 42 can be eliminated.

In the present invention described above, the screw 55 is
Although the screw 55 is provided only at one end of the pre-transfer guide 42, the screw 55 may be provided at both ends of the pre-transfer guide 42. When the screws 55 are provided at both ends of the pre-transfer guide 42, the pre-transfer guide 42 and the photosensitive drum 10
Can be freely changed. Therefore, by changing the distance between the pre-transfer guide 42 and the photosensitive drum 10 according to the thickness of the transfer paper 20, the advantage that constant transfer characteristics can always be ensured is achieved.

[0030]

According to the present invention, in a transfer apparatus in which transfer is performed by facing a photosensitive drum at a predetermined interval with a transfer roller, at least one end of a guide before transfer is adjusted with a screw or the like. By providing a possible positioning member, the deformation of the pre-transfer guide can be effectively prevented, and the contact point (transfer point) between the transfer sheet such as paper and the photosensitive drum can always be kept at a fixed position. As a result, stable transfer characteristics can be secured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of an overall arrangement of an electrophotographic apparatus employing a transfer method using a transfer roller.

FIG. 2 is a side sectional view showing the transfer device of the present invention together with a photosensitive drum.

FIG. 3 is a front view of the transfer device of FIG. 1;

FIG. 4 is a sectional view on the AA side of a housing in the transfer device of FIG. 3;

[Explanation of symbols]

 10: Photoreceptor drum 14: Transfer roller 30: Stopper 40: Distance regulating roller 41: Housing 42: Guide before transfer 46, 50: Push spring 55: Screw 56: Positioning protrusion

Claims (5)

[Claims] 1. A transfer roller for transferring a toner image onto a transfer sheet on a photosensitive drum, and a pair of intervals provided coaxially with the transfer roller and maintaining a predetermined interval between the transfer roller and the photosensitive drum. Regulating rollers, roller biasing means for pressing the spacing regulating rollers against the surface of the photoconductor drum, a pre-transfer guide for supplying the transfer sheet between the photoconductor drum and the transfer roller, and both ends of the pre-transfer guide. And positioning means for positioning the pre-transfer guide with respect to the photoconductor drum, and pressing urging means for urging the positioning means toward the photoconductor drum, wherein at least one side of the pre-transfer guide is provided. Wherein said positioning means is a member whose amount of protrusion from said pre-transfer guide is adjustable. 2. A positioning means provided on one end of the pre-transfer guide is a member capable of adjusting the amount of protrusion, and a positioning means provided on the other end of the pre-transfer guide is a positioning projection. The transfer device according to claim 1. 3. The transfer device according to claim 1, wherein the members whose protrusion amount can be adjusted are provided at both ends of a pre-transfer guide. 4. The transfer pre-transfer guide is attached to a housing that rotatably holds a shaft of a transfer roller, and presses against the housing by pressing the positioning unit toward the photosensitive drum. 4. The transfer device according to claim 1, further comprising means. 5. The transfer device according to claim 1, wherein the member whose protrusion amount is adjustable is a screw extending through an end of the pre-transfer guide.