JP2000003087A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a transfer roller from being soiled because toner is transferred from a photoreceptor drum to a resist roller accompanying the generation of a paper jamming. SOLUTION: This image forming device is provided with the resist roller 52 making paper stand by at a specified position, a pretransfer sensor 232 arranged on the downstream side from the roller 52 in a paper carrying direction and detecting paper carried between the photoreceptor drum 30 and the transfer roller 33. Thus, voltage impressed on the roller 33 is controlled based on the detected result by the sensor 232.

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, and more particularly to an image forming apparatus for transferring a toner image formed on a peripheral surface of a photoreceptor drum to a conveyed sheet by applying a predetermined voltage to a transfer roller. Related to the device.

[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, a registration roller for temporarily holding a sheet at a predetermined position upstream of the photosensitive drum and the transfer roller in the sheet conveying direction is provided. If there is an instruction to perform image formation, the designated sheet is conveyed from a paper feed cassette, a bypass tray, or the like, and is made to stand by at a registration roller. At the same time, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum, and the developing device starts to visualize the latent image into a toner image. When the leading end position of the toner image developed on the peripheral surface of the photoconductor drum reaches the transfer roller, the paper is moved from the registration roller 2 at a time so that the paper reaches between the photoconductor drum and the transfer roller. Feed next. Thereafter, at a timing when the sheet reaches between the photosensitive drum and the transfer roller, a predetermined voltage is applied to the transfer roller to transfer the toner image. Thus, the position of the toner image transferred onto the sheet can be made appropriate.

However, the sensor for detecting a sheet conveyed downstream of the registration roller in the sheet conveyance direction is usually a discharge detection switch provided downstream of the photosensitive drum and the transfer roller in the sheet conveyance direction. In the meantime, no sensor for detecting the paper is provided. Therefore, if a paper jam occurs between the registration roller and the photosensitive drum and the paper does not reach between the photosensitive drum and the transfer roller, this cannot be detected.

In this case, although paper is not conveyed between the photosensitive drum and the transfer roller, voltage application to the transfer roller is started, and toner on the peripheral surface of the photosensitive drum adheres to the transfer roller. Become. Although it is conceivable to provide a cleaning blade that presses against the surface of the transfer roller and provide a cleaning device that removes toner attached to the surface, it is difficult to collect the toner that has once left the photoconductor drum. Includes the problem of increased consumption.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus for preventing toner from being transferred from a photosensitive drum to a registration roller when a paper jam occurs, thereby preventing the transfer roller from being soiled.

[0011]

An image forming apparatus according to the present invention comprises a photosensitive drum, a developing device, a transfer roller, a paper feeding means, a registration roller, a pre-transfer paper detecting means,
Transfer voltage control means. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum. The developing device visualizes the electrostatic latent image formed on the peripheral surface of the photosensitive drum into a toner image. The transfer roller transfers a toner image on the peripheral surface of the photosensitive drum to a sheet to which a predetermined voltage is applied and conveyed to the peripheral surface of the photosensitive drum. The paper supply unit supplies paper between the photosensitive drum and the transfer roller. The registration roller makes the paper supplied from the paper feeding means stand by at a predetermined position on the upstream side of the photosensitive drum and the transfer roller in the paper transport direction. The pre-transfer paper detecting means is disposed downstream of the registration roller in the paper transport direction and detects the paper transported between the photosensitive drum and the transfer roller. The transfer voltage control means controls voltage application to the registration roller based on the detection result of the pre-transfer paper detection means.

Here, the transfer voltage control means, when the pre-transfer paper detection means does not detect the paper within a predetermined period,
It can be configured that the application of voltage to the transfer roller is stopped when it is determined that a paper jam has occurred downstream of the registration roller in the paper transport direction. Further, it is possible to further provide a development control unit for stopping the operation of the developing device when the pre-transfer paper detection unit does not detect the paper within a predetermined period.

Further, the transfer voltage control means may be configured to start applying a voltage to the transfer roller based on a detection result of the pre-transfer paper detection means. Thus, even if a paper jam occurs on the downstream side of the registration roller in the paper conveyance direction, if this is detected and the voltage application to the transfer roller is stopped, the toner is not transferred from the photosensitive drum to the transfer roller. In addition, the transfer roller can be prevented from being stained. In addition, if the application of the voltage to the transfer roller is started based on the detection result of the pre-transfer paper detection means, the transfer timing can be accurately synchronized.

[0014]

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 feed unit 17 for supplying a document to the image forming unit 16 is provided below.

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
Are provided with two branch claws 63 and 64 on the left side. 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 Device] As shown in FIG. 2, a registration switch 23 for detecting whether or not there is a sheet waiting by the registration roller 52 near the registration roller 52.
1 is provided. If the paper is started from the paper feed cassettes 18 and 19 or the stack bypass 20 and the paper is not detected by the registration switch 231 within a predetermined time, it is considered that a paper jam has occurred in the paper feed path. When the toner image is transferred to the sheet, the registration switch 231 determines whether the registration roller 52 actually holds the sheet.

A pre-transfer sensor 23 for detecting passage of a sheet is provided between the registration roller 52 and the transfer roller 33.
2 are provided. As the pre-transfer sensor 232, a reflection-type photoelectric sensor, a transmission-type photoelectric sensor, a microswitch, or the like is employed. The sheet waiting on the registration roller 52 is conveyed to the photosensitive drum 30 in synchronization with the photosensitive drum 30 so that the toner image on the photosensitive drum 30 is transferred to a predetermined position. Registration roller 5
If the pre-transfer sensor 232 detects the paper within a predetermined time after the secondary paper feed from
A predetermined voltage is applied to 3 to start the transfer of the toner image formed on the peripheral surface of the photosensitive drum 30 onto the paper. Also,
If the sheet is not detected by the pre-transfer sensor 232 within a predetermined time after the secondary sheet feeding from the registration roller 52 is started, it is determined that a paper jam has occurred between the registration roller 52 and the transfer roller 33. Then, the application of the voltage to the transfer roller 33 is stopped.

Thus, when the paper is not actually conveyed between the photosensitive drum 30 and the transfer roller 33, the toner image formed on the peripheral surface of the photosensitive drum 30 is transferred to the transfer roller 33. The transfer roller 33 is not stained without being transferred to the transfer roller 33. In addition, a control signal for starting voltage application to the transfer roller 33 can be generated based on a detection signal when the leading edge of the conveyed sheet is detected by the pre-transfer sensor 232. In this case, as compared with the case where a control signal for starting voltage application to the transfer roller 33 from the timing of starting the secondary sheet feeding from the registration roller 52 is generated, the photosensitive drum 3
The toner image on the zero circumference and the sheet to be conveyed can be more accurately synchronized, and the displacement of the toner image formed on the sheet can be minimized.

Further, if the secondary paper feeding from the registration roller 52 is started and the paper is not detected by the pre-transfer sensor 232 within a predetermined time, the voltage application to the transfer roller 33 is stopped and the photosensitive member is stopped. It can be configured that the visualization of the electrostatic latent image formed on the peripheral surface of the drum 30 is stopped. For example, by lowering the developing bias of the developing device 32, it is possible to prevent the toner from being attracted to the peripheral surface of the photosensitive drum 30 from the developing device 32. As a result, the cleaning device 34 or the developing device 32 can be used without attaching extra toner to the peripheral surface of the photosensitive drum 30.
Thus, the amount of toner collected on the peripheral surface of the photosensitive drum 30 can be reduced as much as possible.

[0023]

According to the present invention, there is provided a pre-transfer paper detecting means which is disposed downstream of the registration roller in the paper transport direction and detects paper transported between the photosensitive drum and the transfer roller. Since voltage application to the registration roller is controlled based on the detection result of the pre-transfer paper detection unit, even if a paper jam occurs downstream of the registration roller, it is possible to prevent toner from being transferred from the photosensitive drum to the transfer roller. The transfer roller can be prevented from being stained.

[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 a schematic diagram illustrating a transport path from a registration roller to a fixing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 copier 10 main body 15 document table 16 image forming unit 17 paper feeding unit 20 stack bypass 21 optical system 30 photoconductor drum 32 developing device 33 transfer roller 42 bypass conveyance path 53 fixing device 54 heating roller 55 pressure roller 56 branching unit 57 Discharge tray 58 Sub discharge tray 60 Discharge roller pair 61 Discharge roller pair 231 Registration switch 232 Pre-transfer sensor 241 Main heater 242 Sub heater

Claims (4)

[Claims] A photosensitive drum on which an electrostatic latent image is formed on a peripheral surface; a developing device for visualizing the electrostatic latent image formed on the peripheral surface of the photosensitive drum into a toner image; Is applied, and a transfer roller that transfers the toner image on the photosensitive drum peripheral surface to a sheet conveyed between the photosensitive drum peripheral surface, and a sheet between the photosensitive drum and the transfer roller. A sheet feeding unit for supplying, a registration roller for holding a sheet supplied from the sheet feeding unit at a predetermined position on the upstream side of the photoconductor drum and the transfer roller in the sheet conveyance direction, and a downstream side of the registration roller in the sheet conveyance direction. A pre-transfer paper detection unit that detects a paper conveyed between the photoconductor drum and the transfer roller, and detects the paper conveyed between the photoconductor drum and the transfer roller; An image forming apparatus including a transfer voltage control means for controlling the voltage application, the. 2. The transfer voltage control means according to claim 1, wherein said pre-transfer paper detection means detects no paper within a predetermined period.
2. The image forming apparatus according to claim 1, wherein it is determined that a paper jam has occurred on the downstream side of the registration roller in the paper conveyance direction, and the voltage application to the transfer roller is stopped. 3. The image forming apparatus according to claim 1, further comprising a developing control means for stopping the operation of the developing device when the pre-transfer paper detecting means does not detect the paper within a predetermined period.
An image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein said transfer voltage control means starts applying a voltage to said transfer roller based on a detection result of said pre-transfer paper detection means. .