JPH07239617A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of preventing the developer on the tip part of a form paper from infiltrating to the rear side of the form paper especially at the time of the full surface image forming and preventing the form paper from the rear side soiling. CONSTITUTION:When the tip part of a toner image formed on a photoreceptor drum 12 reaches a prescribed position, a resist roller pair 34 are turned on in exact timing with this and a form paper fed from a paper feeding cassette 4 is sent toward the photoreceptor drum 12. At this time, the form paper is guided and sent by a pre-transfer guide plate 42. When the resist roller pair 34 are turned on, the timer part is started for the time count, and on counting a prescribed time corresponding to the time for a prescribed length of the tip part of the form paper transported by the resist roller pair 34 to be brought into contact with the surface of the photoreceptor drum 12, a high voltage generation part is turned on by a CPU on detecting that, consequently a prescribed bias voltage is applied to the pre-transfer guide plate 42. When the tailing end of the form paper is completed to pass through the pre-transfer guide plate 42, the application of the bias voltage is cut off.

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 suitable for application to, for example, an analog type or digital type electronic copying machine.

[0002]

2. Description of the Related Art Generally, for example, in an analog type electronic copying machine, an electrostatic latent image corresponding to an image of a document is formed on a rotating photosensitive drum (image carrier) by exposing and scanning a document on a document table. An image is formed, the electrostatic latent image on the photosensitive drum is developed by attaching toner (developer) by a developing device, and the toner image formed by this development is
The transfer charging device transfers the toner image onto a sheet supplied from the sheet feeding means at a predetermined timing, and the toner image transferred onto the sheet is fixed by passing through the fixing device.

In such an electronic copying machine, particularly in full-scale copying, in order to improve the transfer performance when the humidity is high, before the transfer charger, the sheet supplied from the paper feeding means is guided before the transfer. A guide plate (guide member) is provided, and a predetermined bias voltage is applied to the pre-transfer guide plate.

This will be described in detail. For example, as shown in FIG. 5, a transfer charger 112 is provided for a sheet P supplied from a sheet feeding cassette (not shown), which is arranged to face the photosensitive drum 111. A conductive pre-transfer guide plate 114 that guides the paper P while making contact with it is provided between the pair of registration rollers 113 that are supplied to the portion of FIG. Is applied with a predetermined bias voltage (for example, 1 KV).

The application timing of the bias voltage to the pre-transfer guide plate 114 is such that the bias voltage is applied when the copy key is turned on, and the application of the bias voltage is stopped when the corresponding copy operation is completed. .

[0006]

As described above, in the conventional full-face copying, the voltage applied to the pre-transfer guide plate 114 is changed from when the copy key is turned on to improve the transfer performance especially when the humidity is high. Is on until the end.

Therefore, as shown in FIGS. 6A to 6C, the leading edge of the paper P supplied by the registration roller pair 113 is the photosensitive drum 111, as shown in the mechanism of occurrence of the problem.
When the sheet P rushes into the surface of the sheet P, electrostatically adhering the sheet P to the pre-transfer guide plate 114 makes the sheet P rush more strongly, and the toner T at the leading end of the sheet P is scraped. The toner T wraps around to the back side of P.

Therefore, a white spot is generated at the leading edge of the image, and the toner T sneaking into the back side of the paper P stains the surface of the lower roller in the fixing device, and the back side of the paper P is soiled at the roller pitch. There was a problem that it would occur.

Therefore, the present invention provides an image forming apparatus capable of preventing the developer at the leading end of the sheet from wrapping around around the back side of the sheet, especially when forming an image on the entire surface, thus preventing the back side of the sheet from being soiled. To aim.

[0010]

An image forming apparatus of the present invention comprises an image forming means for forming a latent image on a moving image carrier, and a latent image on the image carrier formed by the image forming means. Developing means for developing by attaching a developer, a transfer means for transferring the developer image formed by the developing by the developing means onto a sheet supplied at a predetermined timing, and a transferring means A conductive guide member that guides the paper, a detection unit that detects that the leading end of the paper that is guided by the guide member comes into contact with the image carrier, and a detection result of the detection unit And bias voltage applying means for applying a predetermined bias voltage to the guide member.

Further, the image forming apparatus of the present invention uses an image forming means for forming a latent image on a moving image carrier and a latent image formed on the image carrier by the developer. A developing unit that develops by adhering, a transfer unit that transfers the developer image formed by the development of the developing unit onto a sheet that is supplied at a predetermined timing, and a sheet that supplies the sheet to the transfer unit. Of the conductive guide member, first detecting means for detecting that the leading end of the sheet guided and fed by the guide member contacts the image carrier, and the first detecting means of the first detecting means. Bias voltage applying means that operates based on the detection result and applies a predetermined bias voltage to the guide member, and that the trailing edge of the sheet guided and supplied by the guide member is separated from the guide member. To detect The detection means operates on the basis of the detection result of the second detecting means, and a control means allowed to stop the bias voltage application operation of the bias voltage applying means.

Further, the image forming apparatus of the present invention uses an image forming means for forming a latent image on a moving image carrier and a latent image formed on the image carrier by the developer. A developing unit that develops by adhering, a transfer unit that transfers the developer image formed by the development of the developing unit onto a sheet that is supplied at a predetermined timing, and a sheet that supplies the sheet to the transfer unit. A conductive guide member, a time measuring means for measuring the time after the paper guided by the guide member contacts the image carrier, and the paper contacting the image carrier by the time measuring means. And a bias voltage applying means for applying a predetermined bias voltage to the guide member when a predetermined time has elapsed.

[0013]

By applying a bias voltage to the guide member after the leading edge of the sheet to be fed comes into contact with the image carrier, when the leading edge of the sheet rushes into the image carrier, the sheet and the guide member are moved. Since it is not electrostatically attached to the image carrier, the contact of the paper at the time of contact with the image carrier is reduced, and the leading end of the paper can be smoothly pushed into the image carrier. Therefore, it is possible to prevent the developer at the leading end of the sheet from wrapping around around the back side of the sheet, especially when forming an image on the entire surface, and prevent the back side of the sheet from being soiled.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the configuration of an analog electronic copying machine as an example of the image forming apparatus according to the present invention. In the figure, reference numeral 1 is a main body of a copying machine, and an original table 2 made of transparent glass is provided on the upper surface thereof, and an original cover 3 is provided on the original table 2 so as to be openable and closable.

A small-capacity paper feed cassette 4 and a large-capacity paper feed cassette 5 are detachably mounted on the right side of the body 1 of the drawing. On the left side of the drawing of the main body 1, a paper discharge tray 6 for discharging the copied paper is provided.

In the main body 1, charging, exposure, development, transfer,
An image forming unit 11 that forms an image by an image forming process such as fixing and cleaning is provided. The image forming means 11 has a photosensitive drum 12 as an image bearing member which is rotatably supported in a substantially central portion of the main body 1. Around the photosensitive drum 12, a charging charger 13 is provided. Magnetic brush type developing device 14 using a two-component developer consisting of toner and carrier, transfer charger 15, peeling charger 1
6, the cleaning device 17, and the static eliminator 18 are arranged in order. The photoconductor drum 12 rotates in a clockwise direction, and the surface thereof is uniformly charged by the charging charger 13.

An exposing device 20 as an exposing means is arranged below the document table 2. The exposure device 20 includes an exposure lamp 2 whose back is surrounded by a reflector 21.
2, first, second and third reflection mirrors 23, 24, 25,
The lens 26 and the fourth, fifth and sixth reflection mirrors 2
It is composed of optical systems such as 7, 28 and 29.

That is, an image of a document (not shown) placed on the document table 2 is optically scanned by the exposure device 20 and is exposed on the photosensitive drum 12 of the image forming means 11, An electrostatic latent image is formed on the photosensitive drum 12. The photosensitive drum 1
The electrostatic latent image formed on the second toner is a toner as a developer in the magnetic brush of the developer supplied by the developing device 14.
Is developed into a toner image.

A pickup roller 3 is selectively selected from paper feed cassettes 4 and 5 detachably provided on the right side of the main body 1.
0,31 and paper feed rollers 32,33
It is designed to be taken out one by one.

The sheet taken out from the sheet feeding cassette 4 or 5 is guided to a pair of registration rollers 34, and is guided by the pair of registration rollers 34 to a transfer charger 15 arranged to face the photosensitive drum 12. While being conveyed, the toner image on the photoconductor drum 12 is transferred onto the sheet by the transfer charger 15.

In this case, a pre-transfer guide plate 42 is provided between the registration roller pair 34 and the photosensitive drum 12 as a conductive guide member for guiding the paper fed by the registration roller pair 34 while contacting the paper. Is
A predetermined bias voltage (for example, 1 KV) is applied to the pre-transfer guide plate 42 as described later.

The sheet after transfer is peeled from the photosensitive drum 12 by the peeling charger 16 by AC corona discharge, and is conveyed to the fixing device 36 via the conveying belt 35, and the toner image is formed by the fixing device 36. It is fused and fixed on the paper.

The sheet after fixing is taken out by a take-out roller pair 37 provided on the downstream side of the fixing device 36, and is ejected by switching a gate 38 provided on the downstream side of the take-out roller pair 37. It is configured to be discharged onto a discharge tray 6 provided outside the main body 1 via a pair of paper rollers 39, or to be conveyed again to a reversing means 40 formed on the bottom of the main body 1. .

The sheet conveyed to the reversing means 40 is switched back and guided again between the photosensitive drum 12 and the transfer charger 15 via the pair of registration rollers 41 and 34 and the pre-transfer guide plate 42. This enables double-sided copying.

The residual toner remaining on the photosensitive drum 12 after the transfer of the toner image to the paper and the peeling of the paper is scraped off by the cleaning device 17, and the scraped used toner and waste toner containing foreign matters are scraped off. Are discharged to the outside of the cleaning device 17 by a conveyance roller (not shown). The surface of the photoconductor drum 12 that has been cleaned by the cleaning device 17 has its electric potential removed by a neutralization device 18 to a level below a certain level to enable the next copying operation.

FIG. 2 schematically shows a main part of a control system of the electronic copying machine configured as described above. In the figure, a CPU as a control means for controlling the entire apparatus
(Central Processing Unit) 51,
ROM storing a control program for the CPU 51
(Read-only memory) 52, RAM (random access memory) 53 as a working memory, a timekeeping section 54 for performing a timekeeping operation as necessary, an operation panel 55 provided with various operation keys and a display device, etc. A motor driving circuit 57 for driving and controlling a paper feeding roller motor 56 for driving the paper feeding rollers 32 and 33, and a motor driving circuit for driving and controlling a registration roller motor 58 for driving the registration roller pair 34. 59, a high voltage generator 60 for applying a predetermined high voltage to the transfer charger 15,
Further, a high voltage generator 61 for applying a predetermined bias voltage (for example, about 1 KV) having the same polarity as the high voltage applied to the transfer charger 15 is connected to the pre-transfer guide plate 42, respectively.

Here, the timing section 54 is the pre-transfer guide plate 4
It is for controlling the application timing of the bias voltage to 2 and is mainly composed of, for example, a counter circuit.

Next, the operation of the above arrangement will be described with reference to the flow chart shown in FIG. First, when the copy key is turned on in the operation panel 55, the exposure lamp 22 is turned on, and the original document on the original table 2 is scanned and exposed, so that the image of the original document is displayed on the rotating photosensitive drum 12. An electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 12 is developed into a toner image by being developed by the developing device 14.

On the other hand, after the copy key is turned on, the paper feed roller motor 56 is turned on at a predetermined timing to turn on the paper feed roller 32.
(Or 33) is driven, and the paper in the paper feed cassette 4 (or 5) is taken out and sent to the registration roller pair 34.

When the front end of the toner image formed on the photosensitive drum 12 reaches a predetermined position, the registration roller motor 58 is turned on at the same timing and the registration roller pair 34 is driven to feed the paper. The sheet supplied from the cassette is sent toward the photosensitive drum 12.

At this time, the paper is guided and fed by the pre-transfer guide plate 42, but the leading end of the paper is at the photosensitive drum 12.
When a predetermined length (for example, about 10 mm) is in contact with the surface of the sheet, the high voltage generator 61 is turned on by a command from the CPU 51, and a bias voltage is applied to the pre-transfer guide plate 42.

That is, when the registration roller pair 34 is driven (turned on), the timing section 54 starts the timing operation, and the leading edge of the sheet conveyed by the registration roller pair 34 is transferred onto the surface of the photosensitive drum 12 for a predetermined length. When a predetermined time t1 corresponding to the time until contact (for example, about 10 mm) is timed, the CPU 51 detects it and turns on the high-voltage generator 61, and applies a bias voltage to the pre-transfer guide plate 42. .

By performing such bias voltage application control, as shown in FIGS. 4 (a) to 4 (c), the leading edge of the paper P sent by the registration roller pair 34 is exposed to light. At the time of plunging into the surface of the body drum 12, the bias voltage is not yet applied to the pre-transfer guide plate 42 at this time, so that there is no electrostatic adhesion between the paper P and the pre-transfer guide plate 42, and therefore the photoconductor The contact of the paper P when contacting the drum 12 becomes very small, and the leading end of the paper P can smoothly enter the surface of the photosensitive drum 12.

Therefore, unlike the conventional case, the toner T on the front end of the paper P is not rubbed in, and the toner T does not wrap around to the back side of the paper P. This allows
White spots may occur at the leading edge of the image, or the toner T that has flowed to the back side of the paper P may stain the surface of the lower roller in the fixing device 36, and the back side of the paper P may be soiled at the roller pitch. This problem can be eliminated.

When the leading end of the paper P sent by the registration roller pair 34 reaches the transfer charger 15, the high voltage generator 60 is turned on by the command from the CPU 51 and the transfer charger 15 operates. And the photoconductor drum 12
The upper toner image is transferred onto the sheet and sent to the fixing device 36.

On the other hand, when the trailing edge of the sheet P sent by the registration roller pair 34 has finished passing through the pre-transfer guide plate 42, the high-voltage generating section 61 is turned off by the command from the CPU 51, and the pre-transfer guide plate 42 is turned off. The application of the bias voltage is cut off (turned off).

That is, a predetermined time t2 corresponding to the time until the trailing edge of the sheet conveyed by the registration roller pair 34 finishes passing through the pre-transfer guide plate 42 after the registration roller pair 34 is turned on. CPU51
Detects that and turns off the high-voltage generator 61 to shut off the bias voltage to the pre-transfer guide plate 42.

After the bias voltage to the pre-transfer guide plate 42 is turned off, the CPU 51 controls the registration roller motor 58.
Is turned off to stop (turn off) the rotation of the registration roller pair 34.

The toner image transferred onto the paper sent to the fixing device 36 is fixed by passing therethrough, and then the paper is discharged to the paper discharge tray 6. As explained above,
According to the above-described embodiment, after the front end of the sheet fed by the registration roller pair comes into contact with the surface of the photosensitive drum,
By applying a bias voltage to the pre-transfer guide plate, there is no electrostatic attachment between the paper and the pre-transfer guide plate when the leading edge of the paper rushes into the surface of the photosensitive drum.
The contact of the paper when contacting the photosensitive drum is reduced,
The leading end of the paper can be smoothly projected into the surface of the photosensitive drum. Therefore, it is possible to prevent the toner at the front end of the sheet from wrapping around around the back side of the sheet, especially when copying the entire surface, and prevent the back side of the sheet from being soiled.

Further, since the bias voltage is applied to the pre-transfer guide plate before the leading edge of the sheet receives the transfer current from the transfer charger, the transferability of the toner image by the transfer charger may be deteriorated. Absent.

In the above embodiment, the case where the timing of applying the bias voltage to the pre-transfer guide plate is controlled by the time control using the timing section has been described.
Not limited to this, for example, a detector is provided at a predetermined position,
You may make it based on the output of this detector.
That is, a detector that detects that the leading edge of the paper has contacted the surface of the photosensitive drum for a predetermined length and a detector that detects that the trailing edge of the paper has finished passing through the pre-transfer guide plate are installed. However, the application timing of the bias voltage to the pre-transfer guide plate may be controlled on the basis of the outputs of these detectors. Even in this case, the same effect as that of the above embodiment can be expected.

In the above embodiment, the case where the invention is applied to the analog type electronic copying machine has been described, but the present invention is not limited to this, and for example, a digital type electronic copying machine or an electrophotographic method is used. The same can be applied to the laser printer used.

[0043]

As described in detail above, according to the present invention, it is possible to prevent the developer at the leading end of the paper from wrapping around around the back side of the paper, especially when forming an image on the entire surface, thus preventing the back stain of the paper. An image forming apparatus can be provided.

[Brief description of drawings]

FIG. 1 is a side view schematically showing the configuration of an analog type electronic copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a main part of a control system.

FIG. 3 is a flowchart for explaining the operation.

FIG. 4 is a diagram illustrating a state in which a sheet of paper enters a photosensitive drum.

FIG. 5 is a schematic diagram illustrating a part of a conventional pre-transfer guide plate.

FIG. 6 is a diagram illustrating a state where a sheet of paper rushes into a conventional photosensitive drum.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Copier main body, 2 ... Original document table, 4, 5 ... Paper feed cassette, 11 ... Image forming means, 12 ... Photosensitive drum (image carrier), 13 ... Charging charger, 14 ...... Developing device, 15 …… Transfer charger, 20 …… Exposure device, 22 ・ ・ ・
... exposure lamp, 32, 33 ... paper feed roller, 34 ... registration roller pair, 42 ... pre-transfer guide plate (guide member), 51 ... CPU (control means), 54 ... clock section,
60, 61 ... High-voltage generator, P ... Paper.

Claims (3)

[Claims] 1. An image forming unit for forming a latent image on a moving image carrier, and a developing unit for developing the latent image on the image carrier formed by the image forming unit by attaching a developer. A transfer means for transferring the developer image formed by the development of the developing means onto a sheet supplied at a predetermined timing, and a conductive guide member for guiding the sheet supplied to the transfer means, Detecting means for detecting that the leading end of the sheet guided and fed by the guide member comes into contact with the image carrier, and operating on the basis of the detection result of the detecting means, a predetermined amount is given to the guide member. An image forming apparatus, comprising: a bias voltage applying unit that applies the bias voltage of 1. 2. An image forming means for forming a latent image on a moving image carrier, and a developing means for developing the latent image on the image carrier formed by the image forming means by adhering a developer. A transfer means for transferring the developer image formed by the development of the developing means onto a sheet supplied at a predetermined timing, and a conductive guide member for guiding the sheet supplied to the transfer means, A first detection unit that detects that the leading end of the sheet guided and fed by the guide member comes into contact with the image carrier, and operates based on the detection result of the first detection unit. Bias voltage applying means for applying a predetermined bias voltage to the guide member, and second detecting means for detecting that the trailing edge of the sheet guided and fed by the guide member is separated from the guide member. And this second Detected based on the result the operation of the detecting means, the image forming apparatus characterized by comprising a control means allowed to stop the bias voltage application operation of the bias voltage applying means. 3. An image forming unit for forming a latent image on a moving image carrier, and a developing unit for developing the latent image on the image carrier formed by the image forming unit by applying a developer. A transfer means for transferring the developer image formed by the development of the developing means onto a sheet supplied at a predetermined timing, and a conductive guide member for guiding the sheet supplied to the transfer means, A time measuring means for measuring the time after the paper guided by the guide member comes into contact with the image carrier, and a predetermined time has elapsed since the paper came in contact with the image carrier by the time measuring means. An image forming apparatus comprising: a bias voltage applying unit that applies a predetermined bias voltage to the guide member when measured.