JP2003345141A - Pre-transfer guide device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pre-transfer guide member 60 that guides transfer paper to a transfer section composed of a photoreceptor drum 12 and a transfer roller 62, so that transfer is carried out satisfactorily even on a thick paper or thin paper. <P>SOLUTION: The pair of pre-transfer guide members 60, upper and lower, guide sheet transported by a pair of resist rollers 5, or a pair or transport rollers, to the transfer section where a toner image formed on the photosensitive body drum 12, or an image carrier, is transferred to a sheet. The upper one (toner face guide) 72 of the pre-transfer guide members is provided with an elastic member 80 which has a free end 84 on the upstream side in the direction in which the sheet is transported. Thus, the transport guide that satisfactorily handles paper, from thick paper to thin paper, is realized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-transfer guide device used in an image forming apparatus such as a copying machine, a printer or a facsimile, which uses an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art A conventional copying machine utilizing an electrophotographic system,
In an image forming apparatus such as a printer or a facsimile, a charging step of uniformly charging a rotating drum type electrophotographic photosensitive member as an image carrier, an exposing step of exposing the surface of the photosensitive drum to form an electrostatic latent image, and a toner. By a developing step of developing the electrostatic latent image with a (developer) to form a toner image, a transfer step of transferring the toner image on the photosensitive drum onto a sheet, and a fixing step of fixing the toner image transferred onto the transfer material. Image formation is performed.

The transfer process for forming a toner image on a sheet in each of the above-mentioned electrophotographic processes is an important process for determining the quality of the image formed on the sheet. for that reason,
In an image forming apparatus that employs an electrophotographic method, normally, it is attempted to ensure good transfer performance by performing transfer in a state where a sheet is electrostatically adhered to a photoconductor. Recently, in this transfer process, a transfer roller is used as a transfer member, the transfer roller is brought into contact with the photosensitive member, the transfer material is conveyed to the transfer nip portion therebetween, and a transfer bias voltage is applied to the transfer roller to transfer the transfer material onto the photosensitive drum. It is also widely used to transfer the toner image of No. 1 to a transfer material. In this case as well, the transfer is performed by bringing the sheet into close contact with the photoconductor from the upstream side of the nip position between the photoconductor and the transfer roller.

Therefore, a pair of pre-transfer guides for guiding both sides of the sheet are provided so that the sheet conveyed by the pair of conveying rollers can be closely attached to the photosensitive member from the upstream side of the transfer position and delivered to the transfer position. Efforts are being made to arrange the sheet between the transfer area and the registration roller pair, guide the sheet sent out from the registration roller pair to a good position by this guide, and secure conveyance for obtaining high transfer performance.

By the way, in the conventional image forming apparatus having the above-mentioned pre-transfer guide, the guide design is mainly made of the high-quality paper which is the most frequently used sheet, and the thicker paper has a larger basis weight than the high-quality paper. In many cases, good guidance was not always made for sheets and, conversely, for thin sheets with a small basis weight.

Specifically, in the case of a thick sheet having a large basis weight, the rear end portion of the sheet that has passed through the pair of registration rollers may jump up greatly due to the rigidity of the sheet itself.
This jumping operation disturbs the transfer, and as a result, the toner transfer image formed on the sheet is disturbed.
In order to prevent this, it has been proposed that an elastic guide member is attached to the conveyance guide to prevent the jumping phenomenon (see Japanese Patent Laid-Open No. 8-76607).

[0007]

However, even if the elastic body absorbs the jumping up of the rear end of the thick sheet by simply attaching the guide means of the elastic body, even if it is possible to prevent the jumping up, it is possible to use a thin sheet. The guide means of the elastic body does not elastically deform with respect to the sheet, and as a result, the original conveying direction of the conveying guide is deflected.
Without the additional use of such elastic guide means,
As a method for preventing the jumping-up phenomenon caused by the transport guide means itself, it is conceivable to set the space between the pair of pre-transfer guides narrow. In this case, the thick sheet can be prevented from jumping up, but a large load is applied to the conveyed sheet, which causes sheet conveyance resistance. Since this conveyance resistance acts, as it were, on the conveyed sheet so as to apply a brake, image misalignment may occur depending on the type of sheet. In particular, when there is no conveyance force in the transfer area as in the transfer charger, it will occur remarkably.

On the contrary, when the pre-transfer guide space is designed to be a little wider in order to prevent the phenomenon of jumping up and to suppress the rubbing force when the thick sheet is conveyed, when the thin sheet is conveyed this time. Has a large transport guide space,
The thin sheet may pick up the vibration of the machine body and flap, resulting in unstable conveyance and image blurring.

Therefore, the present invention provides a conveyance guide that prevents the thick sheet from bouncing up and does not serve as a brake during conveyance, so that a good image can be obtained for a wide range of sheets from thin sheets to thick sheets. An object of the present invention is to provide an image forming apparatus capable of obtaining the above.

[0010]

To achieve the above object, the present invention guides a sheet conveyed by a pair of conveying rollers to a transfer position where a toner image formed on an image carrier is transferred onto the sheet. A pair of pre-transfer guide members for transferring the toner image at the transfer position of the pre-transfer guide member, and an elastic body having a free end on the upstream side in the sheet conveying direction. It is characterized in that a member is provided.

Further, in the invention of claim 2, the elastic other member is attached to the downstream side of the toner image side guide member in the sheet conveying direction, and a curved portion is provided between the free end portion and the attaching portion. It is characterized by having. Due to the action of the curved portion, the conveyed sheet can be supported without generating a large rubbing force, and stable conveyance can be ensured.

According to the invention of claim 4, the toner image formed on the image carrier is transferred to the sheet conveyed by the pair of conveying rollers, so that the sheet is guided to the transfer position formed by the image carrier and the transfer means. An image forming apparatus having a sheet guide mechanism that is configured to include a pair of guide members, and a guide member on the side on which a toner image is transferred at a transfer position is downstream in a sheet conveying direction. It is characterized in that an elastic member having a sticking portion on the side and a free end portion on the upstream side is provided.

Further, in the invention of claim 3 or 5, the curved portion formed on the elastic member is positioned substantially in contact with a line orthogonal to the normal line of the nip portion of the conveying roller pair. It is characterized by being. By locating the curved portion in this way, it becomes possible to reliably receive and support the sheet sent from the pair of registration rollers in the conveyance guide.

Further, the invention of claim 6 is characterized in that the transfer means is a roller type transfer means. When the transfer unit is a transfer roller, a nip is formed between the photosensitive member and the transfer roller, and as a result of applying a conveying force to the sheet, it is easy to give various kinds of vibration to the conveyed sheet. By using the guide, stable transfer can be performed.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of a copying machine according to an embodiment of the image forming apparatus of the present invention.

As shown in this drawing, in the copying machine indicated by 1 as a whole, a photosensitive drum (image carrier) 10 rotating in the direction of the arrow in the drawing is uniformly charged by a charging device 11 to read an original. Based on the original image data read by the unit 20, a laser scanning unit (exposure unit;
Called "LSU". ) 30 irradiates a scanning beam to form an electrostatic latent image on the photoconductor drum 10, and the electrostatic latent image is developed by the developing device 40 to form a toner image.

On the other hand, the transfer paper (sheet) is supplied from the paper feed cassettes 21 and 22 at the bottom of the apparatus or the exposure unit 30.
After being fed by the paper feed roller 2 from the bypass tray 23 disposed below the sheet, the conveyance roller 4 conveys it to the registration roller pair 5 via each conveyance path, and the registration roller pair 5 adjusts the timing. By the re-feeding drive, the sheet is conveyed toward the transfer position on the side of the photoconductor drum 10, and the transfer device 12 transfers the toner image on the surface of the photoconductor drum 10 to the transfer sheet. The residual toner on the photosensitive drum 10 is removed by the cleaner 13.

In the case of general one-sided copying, the transfer paper on which the toner image is transferred is transferred from the transfer position to the photosensitive drum 10.
The toner image is fixed by the upper fixing device 14, and the branch claw 16
A pair of discharge rollers 50, 51, each of which is configured by a pair of upper and lower rollers in FIG.
Is discharged to the discharge tray 24. In this discharge roller pair, for example, the upper roller 50 is the driving side roller, and the lower roller 51 is the driven side roller.
When the rotation is transmitted to the roller pair 50, 51, the roller pair rotates, and the transfer sheet can be discharged to the discharge tray 24.

On the other hand, reference numeral 25 is a double-sided conveyance path used when images are formed on both sides of the transfer paper. In the case of forming images on both sides, first, as described above, the transfer sheet having the image formed on one side is fixed by the fixing device, and then the pair of discharging rollers 241 is rotated by way of the branch claw 16 to rotate the discharging tray 241. It is conveyed toward 24. At this time, the transfer sheet on which the toner image is formed on one side is temporarily stopped with the downstream end side in the discharge direction being sandwiched by the discharge roller pair 241, and after this stop, the discharge roller pair 241 is reversed to switch. It is moved back and carried into the double-sided transport path 25 via the second transport path. By this switchback operation, the surface of the paper on which the toner is transferred is reversed, and the paper is conveyed to the upstream side (lower side) of the transfer position in order to form an image on the remaining surface different from the surface on which the toner image was previously formed. It is like this.

A predetermined space 42 is provided above the developing device 40.
A toner container (toner accommodating device) 41 is disposed via the. Further, the LSU 30 is disposed on the side of the developing device 40 and irradiates the photosensitive drum 10 with a scanning beam through the gap 42. This LSU30
Is disposed on one side of the image forming apparatus (on the right side in FIG. 1).
The exterior plate 39 is detachably attached to the outside (right side) of the LSU 30 by a screw 391. By removing the exterior plate 39, one side surface (right side in FIG. 1) of the LSU 30 is exposed to the outside. It is like this. Further, the LSU 30 is obliquely attached so as to have a climbing inclination toward one side outside the device. As a result, a large space is secured above the bypass tray 23, and excellent operability can be obtained in setting transfer paper on the bypass tray 23, jam processing, and the like.

As can be understood from FIG. 1, the copying machine 1 is of a vertical conveyance type, and the entire main body is compact. As the developing unit 34, the developing roller 45 is located at the upper side, and the toner storing portion 41 is at this position. The shape is located below the developing roller 45.

In this copying machine, after the document information read by the image reading section 20 is image-processed as an ordinary copying machine, laser emission control is performed by the LSU 30 to form an electrostatic latent image on the photosensitive drum. When it is formed, it becomes a toner image by the action of the developing unit, or it is connected to the network and print information accompanied by a print command is sent from a PC also connected to the network,
It can also be used as a printer for performing image processing according to a command from a control device (not shown) of the main body and forming a toner image by a similar method.

In either case, a paper feed command is issued from the control device to the paper feed cassette 21 or 22, and the paper feed roller 2
The paper housed in the cassette is fed by the rotation of, and is temporarily stopped by the action of the registration roller pair 5.
In synchronism with the toner image, it is transferred onto a sheet by a transfer device 12, conveyed to a fixing device 14 and thermally fixed there, and then formed between the image reading section 20 and the main body of the copying machine 1. The sheet is discharged to the sheet discharge tray 24.

Next, the pre-transfer guide device, which is a feature of the present invention, will be described with reference to FIG. In order to make the description easy to understand, the sheet surface that carries the toner in the transfer area will be referred to as the toner surface, and the sheet surface that is in contact with the transfer roller will be referred to as the back surface. The pre-transfer guide indicated by 60 as a whole is located between the transfer area formed at the nip position 64 between the photosensitive drum 10 and the transfer roller 62 as the transfer device 12 and the registration roller pair 5 (the transfer area upstream side in the transport direction). ) Is a conveyance guide for guiding the toner image formed on the photoconductor drum 12 to the transfer area so that the toner image formed on the sheet re-fed by the registration roller pair 5 can be satisfactorily transferred.

The pre-transfer guide 60 is located on the transfer roller 62 side of the sheet conveying path, and is located in the transfer area.
It is composed of a back surface guide 70 for guiding the sheet surface in contact with and a toner surface guide 72 which is located on the side of the photoconductor drum 10 and carries the toner image transferred in the transfer area. Space 7 formed by both guides 70, 72
4 (sheet conveying surface) has a large opening on the registration roller pair 5 side and a narrower side on the photoconductor drum 10 and directs the sheet to a predetermined position on the upstream side of the transfer area as viewed in the rotation direction of the photoconductor drum 10. It is formed to let. This is to secure good transfer by temporarily electrostatically adhering the sheet to the upstream side of the transfer area of the photosensitive drum 10 and performing transfer in the contact area. Therefore, specifically, the back surface guide 70 is largely curved in an arc shape from one roller of the registration roller pair 5 toward the predetermined position of the photoconductor, and the toner surface guide 72 is exposed from the other roller of the registration roller pair 5. It is formed by bending the body drum 10 toward the predetermined position. The sheet re-fed by the registration roller pair 5 enters the pre-transfer guide 60 from the wide space 74, is guided by the pre-transfer guide 60, and is guided to the predetermined position of the photoconductor drum 10. Becomes

A feature of the present invention is that a member 80 formed of an elastic body is provided on the toner surface side guide 72 of the pre-transfer guide 60 formed in this way. The elastic member 80 is, for example, PET (polyethylene terephthalate).
It is a plate-like member formed of a metal material typified by stainless steel such as a film or SUS304CSP-1 / 2H, and has a sticking portion 82 on the side of the photoconductor drum 10 (downstream side when viewed in the transport direction). The toner surface side guide 72 is adhered over the entire sheet conveyance width by any adhesive means such as a double-sided tape, an adhesive, or spot welding. Further, a curved portion 86 bent in an arc shape is provided on the registration roller pair 5 side (upstream side in the transport direction) which is the free end 84 side of the elastic member 80. And this music part 86
Of the nip portion 90 formed by the registration roller pair is perpendicular to a line 91 (a line connecting the rotation centers of the registration roller pair and shown by a dashed line in the figure) (the sheet is a registration roller pair). It is positioned on the side substantially indicated by the dashed line in the drawing on the surface substantially conveyed from No. 5. By arranging the elastic body 80 in this way, the sheet can perform good transfer in the transfer area.

That is, the sheet delivered by the pair of registration rollers 5 reaches the back side guide 70 in a state where the surface on which the toner image is transferred is rubbed by the elastic body. The sheet is guided to a predetermined position on the photoconductor drum 10 by the action of the back side guide 70. When the leading edge of the sheet reaches the photoconductor drum 10 and is subsequently sent to the transfer area, the sheet is conveyed with the toner surface side being stably supported by the action of the elastic body 80. At this time, the sheet having a large basis weight (thick paper) works to lift the elastic body 80 by the action of the waist of the sheet itself, and as a result, the elastic body 80 is subjected to the reaction by the waist of the sheet (elastic force of the elastic body). Can reliably support the seat.

The trailing edge of the sheet has a pair of registration rollers 5.
When the sheet is separated from the sheet, it is possible to reliably prevent the sheet from jumping up toward the toner surface side guide 72 due to the action of the waist of the sheet itself. Moreover, the elastic body 80 supports the seat.
Therefore, a large resistance at the time of conveyance unlike the case of being supported by the guide surface itself which is a rigid body does not occur, so that the vibration due to the friction between the toner surface side guide 72 and the sheet during conveyance is also suppressed. Further, a sheet having a small basis weight (thin paper) does not have a repulsive force unlike a thick sheet because the sheet itself has a weak rigidity, but the sheet itself tends to shake due to a slight vibration generated during conveyance. However, also in this case, since it is supported by the curved portion of the elastic member 80 from the time when it is conveyed from the registration roller pair 5 to the pre-transfer guide 60, the pre-transfer guide side of the registration roller pair 5 as shown in the figure. Even if a large space 74 is formed, stable transportation can be ensured. In this way, the sheet for which stable conveyance is ensured by the action of the elastic member 80 from thin to thick is satisfactorily transferred in the transfer area, and the toner image can be secured on the sheet. Then, the sheet on which good transfer has been completed is conveyed to the fixing device 14 along the conveyance guide 100.

The elastic body 80 used for the pre-transfer guide 60 described above has a thickness of 0.15 to 0.25 mm when a PET film is used, and SUS as a metal plate. 0.1 if used
Those having a thickness of about 0 to 0.20 mm are desirable from the viewpoint of elasticity. Further, when a PET film is used among these elastic bodies 80, the surface thereof is treated with a conductive material such as a conductive resin and grounded to the main body of the apparatus through the pre-transfer guide 60, so that frictional charges generated at the time of conveyance are generated. Can be effectively prevented.

[0030]

As described above, according to the present invention,
By providing an elastic member on the toner side of the transport guide,
Stable conveyance can be realized for a wide range of papers from thick sheets to thin sheets, and the disorder of the transfer image in the transfer area does not occur.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an outline of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating the configuration of a pre-transfer guide used in the image forming apparatus of the present invention.

[Explanation of symbols]

10 ... Photosensitive drum 12: Transfer device 14: Fixing device 25: Double-sided transport path 60 ... Pre-transfer guide 62 ... Transfer roller 70 ... Back guide 72 ... Toner surface guide 80: Elastic member 84: Free end 86: Music section 92 ... Line orthogonal to normal

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H072 AA03 AB06 CA01 CB07                 2H200 FA04 FA17 GA23 GA34 GA44                       HA03 HB12 HB22 JA02 JB12                       JB16 JB17 JB20 JB45 JB47                       MA01 MA04 MA20 MC01 MC20                 3F101 FA01 FB04 FC12 FD04 FE01                       LA02 LB03

Claims (6)

[Claims] 1. A transfer unit for transferring a toner image formed on an image carrier to a sheet and a pair for guiding the sheet conveyed by a pair of conveying rollers to a transfer position formed by the image carrier. In the pre-transfer guide member, the guide member on the side to which the toner image is transferred at the transfer position is provided with an elastic member having a free end on the upstream side in the sheet conveying direction. A pre-transfer guide device characterized by being provided. 2. The elastic member is attached to the downstream side of the toner image side guide member in the sheet conveying direction and has a curved portion between the free end portion and the attaching portion. Item 1
The pre-transfer guide device described. 3. The curved portion formed on the elastic member is positioned substantially in contact with a line orthogonal to the normal line of the nip portion of the pair of conveying rollers.
The pre-transfer guide device described in 1. 4. A toner image formed on an image carrier is transferred to a sheet conveyed by a pair of conveying rollers,
An image forming apparatus having a sheet guide mechanism for guiding to a transfer position formed by an image carrier and a transfer unit, wherein the sheet guide mechanism comprises a pair of guide members and a toner image at the transfer position. The image forming apparatus is characterized in that the guide member on the side to which is transferred is provided with an elastic member having a pasting portion on the downstream side in the sheet conveying direction and a free end portion on the upstream side. 5. A curved portion is formed between the sticking portion and the free end portion of the elastic member, and the curved portion is substantially in contact with a line orthogonal to the normal line of the nip portion of the conveying roller pair. The image forming apparatus according to claim 4, wherein the image forming apparatus is positioned at a position. 6. The image forming apparatus according to claim 1, wherein the transfer unit is a roller type transfer unit.