JPH0784498A - Image forming device - Google Patents

Abstract

PURPOSE:To realize an electrophotographic printer which has a both-side image- forming function, is miniaturized and enhanses speed and makes print output information coincide on the front and back surfaces in a vertical relation. CONSTITUTION:An image forming device is equipped with: a photosensitive drum 22, with a layer of a photoreceptor 21 on its periphery, which is cylindrical and rotates normally and reversely in its circumferential direction; electrifying means 23A and 23B for uniformly electrifying the surface of the photoreceptor 21; an exposure means 24 for forming arm electrostatic latent image on the surface of the photoreceptor 21; developing means 25A and 25B for attaching developer T to the electrostatic latent image formed on the surface of the photoreceptor 21; a transfer means 26 for transferring the developer T, attached to the surface of the photoreceptor 21, to a recording medium P; and cleaning means 27A and 27B for removing the charges and developer remaining on the surface of the photoreceptor 21.

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,
More specifically, the present invention relates to an image forming apparatus installed in an electrophotographic printer having a double-sided image forming function.

[0002]

2. Description of the Related Art A conventional image forming apparatus of this type performs an image forming process only in one direction of conveyance of a recording medium. Therefore, when double-sided image formation is performed using such an image forming apparatus, the image forming process is performed on one side of the recording medium and then the image forming process is performed on the other side of the recording medium. It is necessary to reverse the front and back sides of the recording medium by some reversing mechanism and convey the recording medium again in the same conveying direction.

A typical example of this reversing mechanism is a switchback reversing mechanism. This can be realized with a relatively simple transport structure. However, with this mechanism,
Since the image forming start positions on the front and back sides of the recording medium are also inverted after reversing, it is inconvenient to create a general left-closed document in which the image forming start positions on the front surface and the back surface are the same.

Further, Japanese Patent Laid-Open No. 63-54060 discloses that the image forming start positions on the front and back sides of a recording medium are made to coincide by using a switchback type reversing mechanism. This is because when the recording medium is subjected to double-sided image forming processing, the photosensitive member is moved in a regular reverse rotation with respect to one of the surfaces, and the image information for latent image processing is sent from the rear end portion of the image information. One page of latent image processing is then performed, and then the photosensitive member is returned to normal rotation to perform transfer processing and fixing processing, so that a good double-sided image forming result in which the top and bottom of the front and back surfaces are the same is obtained. It is the one.

[0005]

However, in the one disclosed in JP-A-63-54060, when the electrostatic latent image is formed, the photoconductor is rotated in the reverse direction to develop the electrostatic latent image. When it is fixed on the paper, it is rotated normally. Therefore, unless the electrostatic latent images for one page are all formed on the photosensitive member at the same time, the next development and fixing steps cannot be started, so that the continuous operation is interrupted between the electrostatic latent image step and the developing and fixing steps. . Therefore, there is an inconvenience that speeding up of print output is significantly impaired. At the same time, the photosensitive member cannot move to the next developing and fixing steps unless the electrostatic latent image for one page is completely formed. However, there is a drawback in that it is impossible to reduce the size of the photoconductor.

Further, the space required for switching back the recording medium must be increased in proportion to the size of the recording medium on which the image forming process is performed. Therefore,
In the above-mentioned conventional example, there has been a problem that the size of the printer apparatus itself is hindered.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the inconvenience of the conventional example, to have a double-sided image forming function, to enable downsizing and speeding up, and to make the top-bottom relation of the print output information coincide with each other. An object of the present invention is to provide an image forming apparatus equipped in an enabled electrophotographic printer.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and is an improvement of an image forming apparatus equipped in an electrophotographic printer having a double-sided image forming function.

That is, a photosensitive drum which has a cylindrical shape having a photosensitive layer on the outer peripheral surface thereof, and which rotates forward and backward in the circumferential direction thereof, and first and second charging means for uniformly charging the surface of the photosensitive body. Exposing means for forming an electrostatic latent image on the surface of the photoconductor, first and second developing means for attaching a developer to the electrostatic latent image formed on the surface of the photoconductor, and Transfer means for transferring the adhered developer to a storage medium,
First and second cleaning means for removing charges and developer remaining on the surface of the photoconductor are provided.

The first charging unit, the exposing unit, the first developing unit, the transferring unit and the first cleaning unit are arranged in this order along the direction of normal rotation of the photosensitive drum. The second charging means, the exposing means, the second developing means, the transfer means and the second cleaning means are arranged on the outer periphery of the photosensitive drum along the reverse rotation direction of the photosensitive drum. The photosensitive drum is sequentially arranged on the outer periphery of the photosensitive drum.

[0011]

When the image is formed on one surface of the recording medium, the photosensitive drum rotates in the forward direction. Then, the following processing is sequentially performed on the rotating photosensitive drum. First, the first charging means uniformly charges the surface of the photoconductor. The exposure means forms an electrostatic latent image on the surface of the photoconductor. The first developing means attaches a developer to the electrostatic latent image. Then, the transfer means transfers the developer attached to the surface of the photoconductor to the storage medium. Finally, the first cleaning means removes the charges and the developer remaining on the surface of the photoconductor. In this case, the second charging means, the second developing means, and the second cleaning means do not operate.

When an image is formed on the other surface of the recording medium, the photosensitive drum rotates in the opposite direction. Then, the following processing is sequentially performed on the rotating photosensitive drum. First, the second charging means uniformly charges the surface of the photoconductor.
The exposure means forms an electrostatic latent image on the surface of the photoconductor. The second developing means attaches a developer to the electrostatic latent image. Then, the transfer means transfers the developer attached to the surface of the photoconductor to the storage medium. Finally, the second cleaning means removes the charges and the developer remaining on the surface of the photoconductor. in this case,
The first charging means, the first developing means, and the first cleaning means do not operate.

[0013]

1 and 2 show an embodiment of an image forming apparatus according to the present invention. 1 is a vertical cross-sectional view taken along the line I-I in FIG. 2, and FIG. 2 is a perspective view of the appearance.

The image forming apparatus according to the present invention uniformly charges the surface of the photosensitive drum 22 and the photosensitive drum 22 which has a cylindrical shape having a layer of the photosensitive body 21 on the outer peripheral surface thereof and rotates in the forward and reverse directions in the circumferential direction. Charging means 23A, 23B, exposure means 24 for forming an electrostatic latent image on the surface of the photosensitive body 21, developing means 25A, 25B for attaching the developer T to the electrostatic latent image formed on the surface of the photosensitive body 21, A transfer unit 26 for transferring the developer T attached to the surface of the photoconductor 21 to the storage medium P;
Cleaning means 27A and 27B for removing charges and developer remaining on the surface are provided.

The forward rotation direction 22 of the photosensitive drum 22
Along the line A, a charging unit 23A, an exposure unit 24, a developing unit 25A, a transfer unit 26, and a cleaning unit 27A are arranged in this order on the outer periphery of the photosensitive drum 22, and along the reverse rotation direction 22B of the photosensitive drum 22. , Charging means 23
B, exposure means 24, developing means 25B, transfer means 26, and cleaning means 27B are arranged in this order on the outer periphery of the photosensitive drum 22.

The photosensitive drum 22 is in the normal direction (forward direction).
It has a mechanism capable of rotating in 22A and the opposite direction 22B. The charging means 23A and 23B are for charging the surface of the photoconductor 21 with negative charges by corona discharge.

The exposing means 24 is the charged photoreceptor 2.
One surface is selectively irradiated with laser light. On the surface of the photoconductor 21, the negative charges in the portion irradiated with the laser light disappear due to the photoconductivity of the photoconductor 21. As a result, an electrostatic latent image is formed.

The developing means 25A, 25B are composed of developing sleeves 30A, 30B, developer containers 31A, 31B, and stirring paddles 32A, 32B, respectively.
The developer T adheres from the developing sleeves 30A and 30B to the surface of the photoconductor 21 on which the electrostatic latent image is formed. Developer T
Is the stirring paddle 3 in the developer containers 31A and 31B.
Since the negative charges are borne by the friction and the like caused by the rotation of 2A and 32B, they adhere to the surface of the surface of the photoconductor 21 where there is no negative charge.

The transfer means 26 applies an electric field from the back side of the storage medium P to the surface of the photoconductor 21 to eliminate the negative charge of the developer T adhering to the surface of the photoconductor 21, thereby developing the developer T.
Is transferred to the surface of the storage medium P.

The cleaning means 27A, 27B is a developer removing brush 33 for removing the remaining developer T.
A and 33B, and charge removal lamps 34A and 34B for removing the residual charge, respectively.
The developer removing brushes 33 </ b> A and 33 </ b> B are rotatably supported by a part of the housing 35 so as to come into contact with and separate from the surface of the photoconductor 21.

Further, the photosensitive drum 22, the charging means 23A,
23B, developing means 25A, 25B, developer removing brush 3
3A, 33B and the like are housed in the housing 35. In the housing 35, a long hole 36 for transmitting the laser light from the exposure unit 24, long holes 37A, 37B for transmitting the light from the charge removing lamps 34A, 34B, and the photoconductor 21.
An elongated hole 38 for transferring the developer T attached to the surface to the storage medium P is provided. The image forming apparatus according to the present invention has a bilaterally symmetrical structure with respect to the central axis 39.

FIG. 3 is a block diagram of an electrophotographic printer equipped with the image forming apparatus of the above embodiment. FIG. 4 shows FIG.
It is an enlarged view of the inside conveyance path selection guide 11. Below, Figure 1
The operation of the image forming apparatus according to the present invention will be described with reference to FIG.

The electrophotographic printer stores the photosensitive drum 22, the exposure unit 24, the transfer unit 26, the casing 35, and the like, which constitute the image forming apparatus according to the present invention, a large number of recording media P, and records at the time of image formation. Recording medium storing means 1 for conveying the medium P one by one to the transfer means 26, and fixing means 5, 12 for fixing the transferred developer T on the recording medium P.
And a sheet conveying means 6 for conveying the recording medium P to the intermediate sheet discharge roller 7, and when the image is formed on only one side, the recording medium P is discharged to the discharge tray 14 and when the image is formed on both sides. By combining with the switching guide 8, the sheet intermediate discharge roller 7 that conveys the recording medium P to the sheet conveying means 6 and the opening / closing movement at the discharge port as shown in the figure are opened upward when the single-sided image is formed. A switching guide 8 that prompts the ejection and closes the recording medium P downward to guide the recording medium P to the reversal sheet conveying means 9 during double-sided image formation.
A reversing sheet conveying means 9 for conveying the recording medium P to the transfer means 26, a sheet detecting means 10 for detecting whether or not the recording medium P has passed through that point, and a conveying path for changing the conveying path of the recording medium P. It is composed of a selection guide 11 and a final ejection roller 13 for ejecting the recording medium P, which has been subjected to the double-sided image forming process, to the ejection tray 15.

The transfer means 26, the fixing means 5, 12 and the like are arranged along the paper running path 20. further,
The transfer means 26 is operated in response to the reversing operation by the photosensitive drum 22 and guides the recording medium P that has passed through the transfer means 26, and again with the same leading end portion of the same recording medium P being turned upside down. An inversion conveyance path 20A for feeding the sheet to the sheet feeding side is provided. The above-mentioned fixing means 5, sheet conveying means 6, reverse sheet conveying means 9 and the like are sequentially installed along the reverse conveying path 20A.

A final discharge path 20C for discharging the recording medium P after completion of transfer on the back side is provided on the first loading side of the recording medium P with respect to the transfer means 26, and this final discharge path 20C is also provided.
Further, a fixing means 12 for fixing the transferred image on the back side is provided.

Between the sheet conveying means 6 and the reversing sheet conveying means 9 provided along the reversing conveying path 20A, a sheet intermediate discharge roller 7 for a sheet for which printing on one side is completed is provided. Further, the paper P fed into the transfer means 26 is guided between the final discharge path 20C and the transfer means 26, and the paper P sent out from the transfer means 26 toward the final discharge path 20C is guided. A transport path selection guide 11 is provided.

As shown in FIG. 4, the transport path selection guide 11 rotates so as to select either (a) or (b). That is, when the recording medium P is conveyed from the recording medium storing means 1 to the transfer means 26, it takes a form as shown in (a), and when the recording medium P is conveyed from the transfer means 26 to the fixing means 12 (b). Takes the form of
The conveyance path of the recording medium P is changed.

Next, the operation of the electrophotographic printer and the image forming apparatus will be described.

A case where the recording medium P is subjected to an image forming process on only one side or a double sided image forming process will be described. First, when image information is sent to the electrophotographic printer by a host computer or the like,
The recording medium P is conveyed to the transfer unit 26 by the recording medium storage unit 1. At this time, the conveyance path selection guide 11 is shown in FIG.
(A) state. Then, the recording medium P is
It is conveyed from left to right with respect to the image forming apparatus of FIG. 1, and at that time, the transfer means 26 forms an image with a developer on one surface.

The image forming process of the image forming apparatus according to the present invention in this case will be described in detail. First, the photosensitive drum 22 rotates in the forward direction 22A. The following processing is sequentially performed on the rotating photosensitive drum 22. First, the charge removing lamp 34A operates the photoconductor 2
1 The electric charge on the surface is removed. Subsequently, the surface of the photoconductor 21 is negatively charged by the charging unit 23A, and then an electrostatic latent image is formed by the exposing unit 24. The surface of the photoreceptor 21 that has been subjected to the latent image processing is subjected to development processing by the developer T by the developing sleeve 30A, and the developer T is transferred to the surface of the recording medium P by the transfer means 26. The developer T remaining on the surface of the photoconductor 21 without being completely transferred is removed by the developer removing brush 33A.

In the image forming process in this case, the charge removing lamp 34B, the charging means 23B, and the stirring paddle 32B do not function, and the developing sleeve 30B is sufficiently separated from the surface of the photoconductor 21. The tip of the developer removing brush 33B is not in contact with the surface of the photoconductor 21.

The recording medium P which has undergone the above-mentioned image forming processing is conveyed to the fixing means 5, and after being subjected to the fixing processing, is conveyed to the sheet intermediate discharge roller 7 via the sheet conveying means 6. Here, the switching 8 is in an open state, and the recording medium P is ejected to the paper ejection tray 14 by the paper intermediate ejection roller 7.
The above is the case of the image forming processing on only one side.

On the other hand, when the image information is for both sides, the switching guide 8 is in a closed state, and the sheet intermediate discharge roller 7 becomes a conveying means in combination with the switching guide 8 so that the recording medium P is reversed. It is conveyed to the conveying means 9. Next, the sheet detecting means 10 existing in the reversing sheet conveying means 9 detects whether or not the recording medium P has passed at that point. When the passage of the recording medium P is detected, the control unit (not shown) of the printer commands the photosensitive drum 22 to rotate in the reverse direction 22B. Accompanying this, the various mechanisms inside and outside the housing 35 also perform the image forming movement when the recording medium P is conveyed in the reverse direction. Thereby,
This time, the image forming process is performed on the back surface of the recording medium P, and the leading end in the transport direction is the same as the image forming process on the front surface of the recording medium P.

The image forming process in that case will be described. First, the photoconductor 2 is driven by the charge removing lamp 34B.
The charges on the first surface are removed, and the charging means 23B performs negative charge processing. Next, after the latent image processing is performed by the exposing means 24, the developing sleeve 30B receives the developing processing, and the transferring means 26 transfers the developer T onto the back surface of the recording medium P. The developer T remaining on the surface of the photoconductor 21 without being completely transferred is removed by the developer removing brush 33B. In these processes, the electric charge removing lamp 34A, the charging means 23A, and the stirring paddle 32A do not function, and the developing sleeve 30A is not used.
Is in a state of being sufficiently separated from the surface of the photoconductor 21,
The tip of the developer removing brush 33A has the photoconductor 2
1 The surface is not in contact with it.

Recording medium P on which the above-mentioned image forming processing has been completed
Can change the conveyance path by the conveyance path selection guide 11,
It is carried to the fixing means 12. At this time, the transport path selection guide 11 is in the state of FIG. After that, the recording medium P is subjected to a fixing process by the fixing means 12 and then ejected to the paper ejection tray 15 by the final ejection roller 13. The above is the image forming process for both sides.

[0036]

As described above, according to the image forming apparatus of the present invention, the photosensitive drum can be rotated in the forward and reverse directions, and the charging means and the like necessary for the image forming process can be rotated in the forward and reverse directions of the photosensitive drum. Since they are separately arranged in correspondence with the rotation direction, an image can be formed on the recording medium in correspondence with both the normal direction and the reverse direction of conveyance of the recording medium. Therefore, by mounting this image forming apparatus on an electrophotographic printer capable of double-sided image forming processing, it becomes possible to reverse the front and back sides of the recording medium and to convey the recording medium to the image forming means without inverting the conveying front end. It is possible to obtain a good double-sided image forming result in which the top and bottom relations of the front surface and the back surface are matched. In addition, since the conveyance distance required for reversing the front and back of the recording medium can be smaller than that of the conventional one, it is possible to achieve downsizing and continuous operation,
It is possible to reduce the time required for each recording medium during the double-sided image forming process.

[Brief description of drawings]

FIG. 1 is a vertical sectional view taken along the line I-I in FIG. 2 showing an embodiment of the present invention.

FIG. 2 is a perspective view showing the appearance of an embodiment of the present invention.

3 is a configuration diagram of an electrophotographic printer equipped with the image forming apparatus of FIG.

FIG. 4 is a partially enlarged view of FIG.

[Explanation of symbols]

 21 Photoreceptor 22 Photosensitive Drum 22A Positive Rotational Direction of Photosensitive Drum 22B Reversed Rotational Direction of Photosensitive Drum 23A, 23B First and Second Charging Means 24 Exposure Means 25A, 25B First and Second Developing Means 26 Transferring Means 27A, 27B 1st and 2nd cleaning means T developer P storage medium

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 6605-2H G03G 21/00 310

Claims (2)

[Claims] 1. A photosensitive drum, which has a cylindrical shape having a photoconductor layer on the outer peripheral surface thereof, and which rotates forward and backward in the circumferential direction, and first and second charging means for uniformly charging the surface of the photoconductor. An exposing means for forming an electrostatic latent image on the surface of the photoreceptor,
First and second developing means for attaching a developer to the electrostatic latent image formed on the surface of the photoconductor, a transfer means for transferring the developer attached to the surface of the photoconductor to a storage medium, and the photoconductor A first and second cleaning means for removing charges and developer remaining on the surface, and the first charging means, the exposing means, and the first developing means along the positive rotation direction of the photosensitive drum. Means, the transfer means, and the first cleaning means are arranged in this order on the outer periphery of the photosensitive drum, and the second charging means, the exposing means, the An image forming apparatus in which a second developing unit, the transfer unit, and the second cleaning unit are arranged in this order on the outer circumference of the photosensitive drum. 2. The first charging means, the first developing means, and the first developing means on the outer periphery of the photosensitive drum, with a line connecting the position of the exposing means and the position of the transferring means being a symmetry axis. The image forming apparatus according to claim 1, wherein the cleaning unit, the second charging unit, the second developing unit, and the second cleaning unit are arranged in line symmetry.