JP2000010422A - Transfer device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a failure such as an offset by preventing excess toner on the periphery of a photoreceptor drum from being transferred to a transfer roller. SOLUTION: This transfer device of an image forming device is provided with a transfer roller 33 arranged oppositely to a photoreceptor drum 30 and whose the periphery can be electrified to a polarity opposite to that of toner, electrifying blades 73A-73E which are arranged in parallel to the direction of the length of the transfer roller 33 and whose the top ends abut on the periphery of the transfer roller 33 to form electrifying areas 75A-75E onto the periphery of the transfer roller 33 and DC voltage sources 74A-74E which apply voltage to the electrifying blades 74A-74E.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a transfer device for an image forming apparatus, and more particularly to a transfer device for an image forming device for transferring a toner image formed on the peripheral surface of a photoreceptor drum onto a conveyed sheet.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus, a document is placed on a document table provided on an upper surface of the apparatus, and the document image is irradiated with light and reflected from the document. The document image is read based on the. Based on the read document image, an electrostatic latent image is formed on the surface of the photosensitive drum. The photoreceptor drum is charged to a predetermined polarity by the main charging device, and when light is irradiated based on a document image, the charge at that portion is removed to form an electrostatic latent image.

[0003] A developing device for storing toner therein is provided adjacent to the photosensitive drum. The toner contained in the developing device is charged to the same polarity as that of the photoconductor drum, and is attracted to a portion of the photoconductor drum where there is no charge at a position close to the photoconductor drum. Therefore, the electrostatic latent image formed on the peripheral surface of the photosensitive drum is visualized as a toner image.

A transfer device is provided adjacent to the photosensitive drum. This transfer device applies a voltage of the opposite polarity to the toner from the back of the paper to the paper conveyed between the photoconductor drum and attracts the toner on the peripheral surface of the photoconductor drum onto the paper. Transfer the image. A separation device is disposed downstream of the transfer device in the sheet conveyance direction. This separating device sucks the sheet from the back side so that the sheet does not wind around the photosensitive drum. For example, a separating needle to which a predetermined voltage is applied is employed.

Thereafter, the sheet having the toner image formed on the surface thereof is conveyed to a fixing device, and the toner image is heated and fused. The fixing device is provided with a heating roller having a built-in heater therein, and a pressure roller pressed against the heating roller. The fixing roller conveys the paper while nipping the paper between the heating roller and the pressure roller. The heat of the heater is transmitted by the heating roller to fuse and fix the toner image on the paper surface.

A discharge port for discharging paper is provided on the downstream side of the fixing device in the paper transport direction, and a discharge tray for receiving the discharged paper is provided outside the discharge port. The discharge port is provided with a pair of discharge rollers that convey the sheet to the discharge tray side while holding the sheet by pressing the peripheral surfaces thereof to each other. The discharge tray has a certain depth for storing a large number of discharged sheets, and is set such that the end of the bottom surface on the upstream side in the sheet discharge direction is located below the discharge port. .

[0007]

In the above-described apparatus, the transfer device employs a transfer roller which is pressed against the peripheral surface of the photosensitive drum or disposed at a predetermined gap. This transfer roller is configured by attaching a foamed synthetic resin or solid rubber around a rotating shaft made of a conductive metal. When a predetermined high voltage is applied to the rotating shaft, the peripheral surface is on the photosensitive drum peripheral surface. Charged to the opposite polarity to the toner,
The toner image can be transferred onto the sheet by attracting the toner from the back side of the sheet that is being conveyed.

In this case, the peripheral surface of the transfer roller is charged to the opposite polarity to the toner in the entire area in the length direction. Therefore, when the conveyed sheet is smaller in size than the toner image formed on the peripheral surface of the photosensitive drum, the toner in the area without the sheet is directly transferred to the transfer roller. The toner transferred to the transfer roller is transferred to the back surface of the sheet in the next image forming operation, which causes so-called show-through.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent excess toner on the peripheral surface of a photoreceptor drum from being transferred to a transfer roller and to eliminate problems such as show-through.

[0010]

A transfer device of an image forming apparatus according to the present invention is a transfer device of an image forming apparatus for transferring a toner image formed on a peripheral surface of a photosensitive drum onto a sheet to be conveyed. And a transfer roller and a charging unit. The transfer roller is arranged to face the photosensitive drum,
The peripheral surface can be charged to a polarity opposite to that of the toner on the peripheral surface of the photosensitive drum. The charging means forms a charged area and a non-charged area arranged in the length direction on the peripheral surface of the transfer roller.

Thus, if the charged area is formed on the peripheral surface of the transfer roller according to the size of the conveyed paper, the toner image formed on the peripheral surface of the photosensitive drum is larger than the conveyed paper. However, the transfer roller can be prevented from being stained without transferring the toner to the peripheral surface of the transfer roller. Here, the charging means are arranged in parallel in the length direction of the transfer roller, each of which independently contacts the peripheral surface of the transfer roller to form a charged area on the peripheral surface of the transfer roller by applying a predetermined voltage. A plurality of charging members, and an applied voltage control means for selectively applying a voltage to each charging member.

The charging member may be constituted by a plurality of charging blades which are in contact with the peripheral surface of the transfer roller, may be constituted by a plurality of charging rollers, and may be constituted by a plurality of charging blocks. Further, the applied voltage control means selects a charging member according to the size of the sheet conveyed between the photosensitive drum and the transfer roller and forms a charged area on the peripheral surface of the transfer roller, and controls the voltage by selecting the charging member. It can be configured to apply.

[0013]

FIG. 1 is a longitudinal sectional view of a copying machine to which an embodiment of the present invention is applied. The copying machine 1 has a main body 10 and a document holder 11 mounted on the upper part of the main body 10 so as to be openable and closable. An original platen 15 on which an original is placed is disposed on the main body 10 at an upper portion thereof. Inside the main body 10, an image forming unit 16 is provided at the left end as viewed from the front and substantially at the center in the vertical direction.
Further, a paper supply unit 17 for supplying paper to the image forming unit 16 is provided at a lower portion.

The paper supply unit 17 is detachably attached to the main body 10 and stores paper supply cassettes 18 and 19 for storing paper.
And a stack bypass 20 provided thereabove. An optical system 21 for reading image information of a document placed on the document table 15 is provided below the document table 15. The optical system 21 includes a light source 22 for irradiating light to the surface of the document placed on the document table 15 and mirrors 23, 24, and 2 for deflecting light reflected from the surface of the document.
5 and a lens 2 for converging the light from the mirror 25
6 and an image sensor 27 such as a CCD sensor that receives light converged by the lens 26 and generates an image data signal corresponding to an original image.

The image forming section 16 has a photosensitive drum 30 on the surface of which an electrostatic latent image is formed.
0, a main charging device 31, a developing device 32,
It has a transfer roller 33 and a cleaning device 34. The main charging device 31 is a device for charging the surface of the photoconductor drum 30, and is disposed diagonally above and to the right of the photoconductor drum 30. The photosensitive drum 3 is disposed diagonally below and to the right of the photosensitive drum 30 with a predetermined gap from the main charging device 31.
A developing device 32 for forming a toner image on the image sensor 0 is disposed. The developing device 32 stores toner inside, and visualizes the electrostatic latent image formed on the photosensitive drum 30 by the toner. The transfer roller 33 is a device for transferring the toner image on the photosensitive drum 30 to a sheet, and is disposed on the left side of the photosensitive drum 30. The cleaning device 34 is a device for removing residual toner and the like on the surface of the photoconductor drum 30.
0.

On the right side of the photosensitive drum 30, a laser unit 35 for forming an electrostatic latent image on the peripheral surface of the photosensitive drum 30 is provided. The laser unit 35 forms an electrostatic latent image on the peripheral surface of the photosensitive drum 30 based on an image data signal obtained from the image sensor 27. The paper feed unit 17 includes a vertical transport path 41 for transporting paper from each of the paper cassettes 18 and 19 toward the image forming unit 16 and a bypass transport path for transporting paper from the stack bypass 20 to the image forming unit 16. 42 are provided. Each paper cassette 1
Pickup rollers 43, 4 for taking out the stored paper are provided in the stack bypasses 8, 19 and the stack bypass 20.
4, 45 and a pair of paper feed rollers 46, 47, 48 for feeding the paper one by one to the transport path. The vertical transport path 41 is provided with pairs of transport rollers 49 and 50, and the bypass transport path 42 is provided with a pair of transport rollers 51. The vertical transport path 41 and the bypass transport path 42 join below the transfer position where the photosensitive drum 30 and the transfer roller 33 face each other. At the confluence, a registration roller 52 for stopping the conveyed sheet at a predetermined position is provided.

Above the photosensitive drum 30 and the transfer roller 33, a fixing device 53 for fusing and fixing the toner transferred onto the paper is provided. The fixing device 53
A heating roller 54 having a built-in heater and a pressure roller 55 pressing the heating roller 54 are provided. The sheet is nipped between the rollers and transported, and the toner image formed on the surface of the sheet is heated and fixed. Things.

Further above the fixing device 53, a branch 5
6 are provided. On the right side of the branch portion 56, a discharge tray 57 for discharging sheets via a discharge roller pair 60 is provided.
And a discharge roller pair 6 disposed above the discharge tray 57.
1 and a sub-eject tray 58 from which sheets are ejected. A switchback unit 59 for reversing the sheet at the time of double-sided copying is provided at the lower left of the branch unit 56.
Is arranged. The branching portion 56 is provided with a branching claw 62 for switching the sheet conveying direction between the direction of the discharge tray 57 and the direction of the switchback portion 59. Branch claw 62
Two branch claws 63 and 64 are provided on the left side of. Below the two branch claws 63 and 64, a switchback transport path 65 for guiding a sheet to a switchback section 59 is provided.
A sub-tray conveyance path 66 for guiding the sheet to the sub-discharge tray 58 is provided above, and a sheet is conveyed to a finisher (not shown) such as a sorter or a staple sorter between the two branch claws 63 and 64. A finisher transport path 67 is provided. Branch claws 63, 64
Switches the transported paper to the switchback transport path 65,
It is possible to switch so as to guide to either the sub-tray conveyance path 66 or the finisher conveyance path 67. [Transfer Roller] One embodiment of the transfer roller 33 is shown in FIGS.

As shown in FIG. 3, the transfer roller 33 is provided with a roller portion 72 made of an elastic material around a rotation shaft 71. The rotating shaft 71 is made of a material having rigidity, and is made of stainless steel, aluminum, other metal, or a hard synthetic resin material. In particular, since the rotating shaft 71 does not need to be made of a conductive material, the weight is reduced. It is preferable to use a synthetic resin material in order to achieve this. The roller portion 72 is made of an elastic synthetic resin having elasticity such as foam synthetic resin or solid rubber. For example, polyurethane can be used.

In the vicinity of the transfer roller 33, a plurality of charging blades 73A to 73E arranged in parallel in the length direction are provided.
Is attached. Each charging blade 73A to 73E
Has its tip in contact with the peripheral surface of the transfer roller 33,
Areas 75A to 75A where the transfer roller 33 is in contact
5E can be charged. Each charging blade 73A-73E has a DC voltage source 74A-
74E is connected. The DC voltage sources 74A to 74
E, by applying a predetermined high-voltage DC voltage to each of the charging blades 73A to 73E,
A corresponding area of the transfer roller 33 can be charged from A to 73E.

Assuming a case where the center is set with the center position in the width direction of the conveyed sheet as a reference position, the maximum sheet size on which an image can be formed is A3 size. At this time, the areas 75A to 75E of the transfer roller 33 charged by the charging blades 73A to 73E correspond to the A3 size paper width, and the areas 75B, 75C, and 75B of the transfer roller 33 charged by the charging blades 73B, 73C, and 73D. 75D is set to correspond to the A4R size paper width.

Therefore, when an image is formed on A3 size paper, a voltage is applied to all the charging blades 73A to 73E by the DC voltage sources 74A to 74E. As a result, the transfer roller 33
In the areas 75A to 75E where the contacts A to 73E are in contact, the opposite sides of the contact points of the charging blades 73A to 73E (the positions close to the photosensitive drum 30) are charged to the opposite polarity to the toner. This makes it possible to transfer the toner image on the photosensitive drum 30 to the conveyed A3 size paper.

When an image is formed on A4R size paper, a voltage is applied to the charging blades 73B, 73C, 73D by DC voltage sources 74B, 74C, 74D. As a result, the transfer roller 33 is moved to the area 75B where the charging blades 73B, 73C and 73D are in contact.
In 75C and 75D, each charging blade 73B, 73
The opposite side (the position close to the photosensitive drum 30) of the contact point between C and 73D is charged to the opposite polarity to the toner. This makes it possible to transfer the toner image on the photosensitive drum 30 to the transported A4R size paper. At this time, the area 75A of the transfer roller 33,
Even if a toner image is formed in the area of the peripheral surface of the photosensitive drum 30 corresponding to 75E, the transfer roller 3
No toner is transferred to the third regions 75A and 75E. Therefore, even if you select the wrong paper,
Since the toner is not directly transferred from the photosensitive drum 30 to the transfer roller 33, the peripheral surface of the transfer roller 33 can be prevented from being stained.

The size of the sheet conveyed between the photosensitive drum 30 and the transfer roller 33 can be determined based on the size of the sheet stored in the sheet cassette specified by the operator from the operation panel or the like. It is also possible to provide a sensor for detecting the sheet size in the sheet feeding path from the sheet feeding section 17 to the image forming section 16 so as to detect the size of the sheet actually conveyed. is there.

The charging blades 73A to 73E are not limited to those shown in the drawings, and the number and dimensions of the charging blades 73A to 73E can be appropriately set in accordance with the size of a sheet on which an image is to be formed. [Other Embodiments] (A) As shown in FIG. 4, a charging roller 76 can be used instead of the charging blade. Charging roller 76
Is composed of a plurality of rollers each supported by a rotating shaft 77 made of a conductive metal, and can be individually charged by applying a high-voltage DC voltage to each rotating shaft. Each of the charging rollers 76 is arranged similarly to the above-described charging blades 73A to 73E, and is configured such that a predetermined DC voltage is applied by a DC voltage source (not shown). According to the paper size, each of the charging rollers 76 is selected, a voltage is applied, and a predetermined area of the transfer roller 33 is charged.
Transfer toner 3 is transferred to the transfer roller 3
3 can be prevented. (B) As shown in FIG. 5, a charging block 78 can be used instead of the charging blade. Charging block 7
Numeral 8 includes a contact surface that comes into contact with the peripheral surface of the transfer roller 33, and is configured to charge a predetermined area of the transfer roller 33 from the contact surface. Each charging block 78
Are arranged in the length direction of the transfer roller 33 in the same manner as the charging blades 73A to 73E described above, and are configured so that a predetermined DC voltage is applied by a DC voltage source (not shown). By selecting each charging block 78 according to the paper size and applying a voltage to charge a predetermined area of the transfer roller 33, no extra toner is transferred from the photosensitive drum 30 to the transfer roller 33. Thus, the transfer roller 33 can be prevented from being stained.

[0026]

According to the present invention, it is possible to prevent the toner from being directly transferred from the photosensitive drum to the transfer roller, thereby preventing the transfer roller from being stained. Therefore, problems such as show-through can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a copying machine employing an embodiment of the present invention.

FIG. 2 is an explanatory view of a main part.

FIG. 3 is a longitudinal sectional view thereof.

FIG. 4 is a longitudinal sectional view of another embodiment.

FIG. 5 is a longitudinal sectional view of still another embodiment.

DESCRIPTION OF SYMBOLS 1 Copier 10 Main body 15 Document table 16 Image forming unit 17 Feeding unit 20 Stack bypass 21 Optical system 30 Photoconductor drum 32 Developing device 33 Transfer roller 42 Bypass transport path 53 Fixing device 54 Heating roller 55 Pressing Roller 56 Branch portion 57 Discharge tray 58 Sub-discharge tray 60 Discharge roller pair 61 Discharge roller pair 71 Rotary shaft 72 Roller unit 73A to 73E Charging blade 74A to 74E DC voltage source 75A to 75E Area 76 Charging roller 77 Rotating shaft 78 Charging block

Claims (6)

[Claims] 1. A transfer device of an image forming apparatus for transferring a toner image formed on a peripheral surface of a photosensitive drum onto a sheet to be conveyed, wherein the transfer device is disposed to face the photosensitive drum, and the peripheral surface is arranged. An image forming apparatus comprising: a transfer roller capable of being charged with a polarity opposite to that of the toner on the peripheral surface of the photosensitive drum; Equipment transfer device. 2. The transfer device according to claim 1, wherein the charging means is arranged in parallel in a length direction of the transfer roller, and each of the charging means independently contacts the peripheral surface of the transfer roller to apply a predetermined voltage. The transfer device of an image forming apparatus according to claim 1, further comprising: a plurality of charging members that form a charging area on a surface; and an applied voltage control unit that selectively applies a voltage to each of the charging members. 3. The transfer device of an image forming apparatus according to claim 2, wherein said charging member is a plurality of charging blades abutting on a peripheral surface of said transfer roller. 4. The transfer device of an image forming apparatus according to claim 2, wherein said charging member is a plurality of charging rollers abutting on a peripheral surface of said transfer roller. 5. The transfer device according to claim 2, wherein the charging member is a plurality of charging blocks that contact the peripheral surface of the transfer roller. 6. An apparatus according to claim 6, wherein said applied voltage control means controls said charging so as to form a charged area on a peripheral surface of said transfer roller in accordance with a size of a sheet conveyed between said photosensitive drum and said transfer roller. 3. A voltage is applied by selecting a member.
6. The transfer device for an image forming apparatus according to any one of claims 1 to 5, wherein