JPH03144670A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent picture quality deterioration by setting the gap between the image carrier and the electrifying means to a prescribed width at the time of electrification, controlling an amount of current supplied to the electrifying means, electrifying an image carrier surface to a prescribed potential, exposing the image carrier, forming an electrostatic latent image, developing this, and transferring it onto an image formation medium. CONSTITUTION:When a photosensitive drum is electrified in terms of surface potential, the gap between the electrifying wire 11a for a photosensitive drum and an electrifier 11 and the grid 11b is set to a prescribed width. Additionally, the photosensitive drum is electrified to a prescribed potential by controlling an amount of current supplied to the electrifier 11. Then, the photosensitive drum is exposed by an exposing/scanning device 40 to form an electrostatic latent image, and this image is developed and transferred. For example, when current which is supplied to the electrifier is weakened, it can be maintained at the range within which electrification can be controlled by a grid voltage, by reducing the gap. Thus, a half-tone picture free of irregularity can be obtained, the range of the control of an amount of electrification can be widened, and picture quality deterioration can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic method.

(Prior Art) Conventionally, in image forming apparatuses such as copying machines and printers that employ an electrophotographic method, the surface of a photoreceptor is uniformly charged to a predetermined potential by a charging device, and the charged photoreceptor is An electrostatic latent image is formed by exposure according to the image, and this electrostatic latent image is developed with a developer and transferred to paper to form an image.

Charging the photoreceptor in such an image forming apparatus
:; As spot angle chargers, there are Flotron chargers that perform positive discharge, lj; electric devices, and Scorotron chargers that perform negative discharge.

On the other hand, in the image forming apparatus described above, it is necessary to change the gradation depending on the type of image to be formed, for example, a photographic image or a character image, and perform image formation suitable for each image. In order to control such gradation, a method of changing the surface potential of the photoreceptor is used.

In order to change the surface potential of the photoreceptor, the method of charging the photoreceptor with a corotron charger that performs positive discharge is to control the amount of charge on the photoreceptor by changing the amount of current to the charging wire. is used. Also,
A scorotron charger that charges a photoreceptor with negative discharge changes the amount of current in the charging wire, and also
By changing the grid voltage, the amount of charge on the photoreceptor can be changed.
In other words, it is widely used to control the gradation of an image by changing the surface potential. To change the grid voltage mentioned above, 1. lj) This is to control the uneven discharge of the electric wire using the grid and realize uniform sliding electricity to the photoreceptor.

However, when the amount of current to the charging wire is reduced in order to control the surface potential of the photoreceptor, the balance between the amount of current in the charging wire and the grid voltage is disrupted, causing uneven discharge characteristic of negative corona discharge, resulting in photosensitive There was a drawback that the body surface became non-uniformly charged and the unevenness of the halftone image became noticeable. In addition, simply controlling the current amount of the charging wire and ear and the grid voltage limits the control range of the surface potential of the photoreceptor, resulting in a disadvantage that the necessary surface potential cannot be obtained and the image quality deteriorates.

(Problem 8 to be Solved by the Invention) As described above, the present invention uses a negative discharge scorotron charger that charges a photoreceptor as an image bearing member to use a battery that changes the amount of current of the charging wire, and a grid voltage. A method is used to control the gradation of an image by changing the surface potential of the photoreceptor by changing the surface potential of the photoreceptor, but reducing the amount of current to the charging wire to control the surface potential of the photoreceptor The balance between the amount of current in the wire and the grid voltage is disrupted, causing uneven discharge characteristic of negative corona discharge, resulting in uneven charging on the surface of the photoreceptor, and unevenness in halftone images. This was done to eliminate the drawback that simply controlling the amount and grid voltage limits the control range of the surface potential of the photoreceptor, making it impossible to obtain the necessary surface potential of the photoreceptor, resulting in deterioration of image quality. It is an object of the present invention to provide an image forming device that can charge the body surface uniformly to obtain a uniform halftone image, and that can also obtain the necessary surface potential of a photoreceptor and thus prevent deterioration of image quality. shall be.

[Structure of the Invention] (Means for Solving the Problems) The image forming apparatus of the present invention charges an image carrier 4;)
a setting means for setting a gap between the current saving means and the image carrier; and a control means for controlling the amount of current supplied to the charging means when the setting means sets a predetermined gap. , the image is charged to a predetermined potential by supplying a current amount controlled by the control means to the charging means. an exposure means for exposing the 1J carrier, a developing means for developing the electrostatic latent image formed on the image carrier by the exposure of the exposure means, and a developer image developed by the developing means for forming a portrait image. It is characterized by comprising both image forming means for forming an image by transferring it to a medium.

(Function) When the image bearing member is charged, the present invention sets the gap between the image bearing member and the charging means to a predetermined width using a setting means, and controls the amount of current supplied to the charging means. Image formation is performed by charging the surface to a predetermined potential, exposing the image bearing member charged to the predetermined potential to form an electrostatic latent image, and developing this D electrostatic latent image and transferring it to a portrait-forming medium. It was designed to do so. As a result, even if, for example, the current supplied to the charging wire of the charging means is reduced, the balance with the grid voltage can be maintained by reducing the gap between the image carrier and the charging means, resulting in uniform halftones. You can also get the image
Since the amount of charge and the surface potential of the image carrier can be controlled over a wide range, the necessary surface potential of the image carrier can be obtained, and deterioration of image quality can be prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 2 shows the external appearance of a copying machine employing an electrophotographic method as an example of an image forming apparatus according to the present invention, and FIG. 3 shows its internal configuration. In other words, 1 is a copying machine main body, and the top surface of this copying machine main body 1 is provided with a document table 2 on which a document is placed.
is provided so that it can be opened and closed freely. In addition, the copying machine main body l
An operation panel 21 is provided at the end of the upper surface.

The operation panel 21 includes a display device 31 that displays various statuses of the copying machine, and a copy start key 32 that instructs to start copying.
In addition, various operation keys (not shown) such as a document size designation key, a paper size designation key, a magnification designation key, and a dual image selection key for selecting whether the images to be copied are photographs or letters are provided. The display device 31 is configured by arranging, for example, light emitting diodes in a row, and its lighting and lighting are controlled by a control signal from a control circuit 50, which will be described later.

The document placed on the document table 2 is scanned by an exposure scanning device 40 consisting of an exposure lamp 4 and mirrors 5, 6.7, which reciprocates along the lower surface of the document table 2 in the direction indicated by the arrow cd. Exposure scanning is performed during the reciprocating movement.

Furthermore, when the exposure scanning device 4o exposes and scans the document,
The mirror 6.7 follows the exposure lamp 4 and the mirror 5 in the same direction at 1/2 the speed in order to keep the optical path length of the reflected light from the document constant until it reaches the photosensitive drum 1o. It has become. The light reflected from the original by the illumination of the exposure lamp 4 is reflected by the mirrors 5, 6.7, passes through the lens 8, is further reflected by the mirror 9, and is guided to the photoreceptor drum 10, where it forms an image of the original. is formed into an image on the surface of the photoreceptor drum 10.

The photosensitive drum 1o rotates in the direction of the arrow e in the figure, and its surface is first charged by the stern charger 11. The details of this charging S11 will be described later. Thereafter, the image of the document is exposed to slit light to form an electrostatic latent image, and this electrostatic latent image is made visible by applying toner by the developing device 12.

Further, below the developing device 12, a paper feeding device 13 is provided that supplies paper P to an image transfer section 22 formed below the photosensitive drum 10. This paper feeding device 13 has upper and lower parts 2 that store a plurality of sheets of paper P that can be attached and detached to the side of the main body 1.
paper feed cassettes 14.15 of the stages, and a paper feed roller 1 that feeds paper P one sheet at a time from these paper feed cassettes 14.15.
6.degree. 17, and guide paths 18 and 19 for respectively guiding the paper P sent out by these paper feed rollers 16 and 17. The sheet P sent through the guide paths 18 and 19 is positioned by a pair of aligning rollers 20 that position and convey the leading edge of the sheet P, and is supplied to the image transfer section 22. Further, one of the paper feed cassettes 14 and 15 can be selected by a selection switch (not shown) on the operation panel 21.

The paper P sent to the image transfer section 22 comes into close contact with the surface of the photoreceptor drum 10 on which the toner image has been formed at the transfer charger 23, and the sheet P is transferred to the photoreceptor drum 10 by the action of the transfer charger 23. The toner image on lo is transferred. After the residual toner is removed from the surface of the photosensitive drum 10 after the transfer, the residual toner is removed by the cleaner 24, and then the charge is removed by the charge removal lamp 25, so that the surface returns to the initial state.

On the other hand, the paper P after the transfer is electrostatically peeled off from the photosensitive drum 1o by the action of the peeling device 26, and then transferred to the heat rollers 28a and 28b provided in the fixing device 28 by the paper conveyance path 27. The transferred image on the paper P is heated and fixed by passing there. Then, the paper P after fixing is transferred to the tray 3 of the main body 1 by a paper ejection roller 29.
It is designed to be discharged to o.

Note that 33 is a cooling device, which causes air to flow by rotating a fan (not shown) at the same time to prevent the temperature inside the main body 1 from rising.

Next, the main parts of the control system of the vehicle forming apparatus will be explained with reference to the block diagram shown in FIG. In the figure, a control circuit 50 controls the entire device, and is, for example, a microcomputer.

It is composed of peripheral circuits, memory, etc.

This control circuit 50 performs various controls as described below. First, a control signal is sent to the high voltage power source 51 to control the charging of the charging charger 11, the transfer charger 23, and the peeling charger 26 connected to the high voltage power source 51. The charging device 11 includes a charging wire 11a and a grid Il.
b, each of which is supplied with wire current and grid voltage. Further, the charging wire 11a and the grid llb constituting the charging device 11 are each independently perpendicular to the surface of the photoreceptor drum 10 by a drive device 56 driven by a control signal from the control circuit 50. It is movable in the direction (arrow ab direction shown in FIG. 3).

As described above, the display device 31 is provided on the operation panel 21 to display various states of the copying machine, and its lighting and extinguishing are controlled by control signals from the control circuit 50.

The various solenoids 52 are controlled on/off by control signals from the control circuit 50, and thereby control, for example, the contact and separation of a cleaning blade (not shown) with respect to the photoreceptor drum 10. ing. The various switches 53 include the copy start key 32 provided on the operation panel 21, various other operation keys (not shown) such as an original size specification key, a paper size specification key, a magnification specification key, an image selection key, or a set of keys. It includes microswitches (not shown) for detecting the size of paper stored in the paper feed cassettes 14 and 15, and information from these is supplied to the control circuit 50. The control circuit 50 controls the entire copying machine in accordance with signals manually inputted from the various switches 53 mentioned above. Further, the control circuit 50
The exposure scanning operation by the exposure scanning device 40 mentioned above and the paper feeding operation by the paper feeding bag @13 are controlled.

Further, the main motor 54 rotates the photosensitive drum 10, and the fan motor 55 rotates the fan of the cooling device 33. Furthermore, the fixing device 1t28
As described above, the toner image transferred to the paper P is melted and fixed, and the temperature of the heat rollers 28a and 28b detected by a temperature sensor such as a thermistor (not shown) is sent to the control circuit 50. In addition to being used for temperature control, the heating or stopping of heating of the heat rollers 28a and 28b is controlled by a control signal from the control circuit 50 to maintain the fixing temperature at a predetermined value. Furthermore, as described above, the charge eliminating lamp 25 is used to remove the charged state of the photoreceptor drum 10 and return the photoreceptor drum 10 to its initial state.

In the above configuration, the charging operation of the photoreceptor drum 10 will be mainly described in detail.

After the operator operates the operation panel 21 to make desired settings, the copying operation is started when the operator presses the copy start key 32. First, the control circuit 50 controls the drive device 56
is driven to determine the positions of the charging wire 11a of the charging device 11 and the grid Ilb from the surface of the photoreceptor drum 10.

This position, that is, charging wire 11a and grid ll
The gap between b and the surface of the photosensitive drum 10 is determined by the operator operating an image selection key (not shown) to specify whether the image to be copied is, for example, a photographic image or a character image. Information regarding the width of this gap is provided by the control circuit 5.
0 is stored in advance in a memory (not shown). Then,
A predetermined control signal is sent from the control circuit 50 to the high voltage power supply 51, and the high voltage power supply 51 supplies a predetermined amount of current to the charging wire IIa of the charging charger 11, and also supplies a predetermined grid voltage to the grid Ilb. supply As a result, corona discharge is started from the charging device 11, and the surface of the photoreceptor drum 10 is uniformly charged to a predetermined potential.

FIG. 4 shows the relationship between the wire current flowing through the charging wire 118 and the surface potential of the photoreceptor drum 10 during the charging operation as described above, and the gap between the grid and the photoreceptor when the surface potential is 700V and 600V, and the charging wire. Shows the gap between photoreceptors. As shown, charging wire 11
It can be seen that if the distance between a and grid llb and the surface of the photoreceptor drum 10 is small, a high photoreceptor surface potential can be obtained with a small wire current.

As a result of image formation under the above conditions, 700V and 600V
At v, the gradation properties of both images were the same, and the image quality, such as halftones, was also good.

Further, when the above charging operation is completed, an image forming operation similar to that described above is performed. That is, the image of the document is slit-exposed onto the surface of the photoreceptor drum 10 by the exposure scanning device 40 to form an electrostatic latent image. This electrostatic latent image is converted into a dJ N image by applying toner to the developing device 12 . The image is then transferred to the paper P supplied from the paper feeder 13 by the image transfer 22, further fixed by the fixing device 28, and then discharged to the paper discharge tray 30.

As described above, when charging the surface potential of the photoreceptor drum 10 to a predetermined potential, the driving device 26 is driven to increase the gap between the photoreceptor drum 1o and the charging wire 11a of the charging device 11 and the grid 11b to a predetermined width. At the same time, the amount of current supplied to the charging wire 11a of the charging charger 11 is controlled to charge the photoreceptor drum 10 to a predetermined potential. Since an electrostatic latent image is formed by exposure to light, this electrostatic latent image is developed by the developing device 12, and is transferred to the paper P to make a copy, for example, the charging wire 11a of the charging device 11 When the supplied current is reduced, by reducing the above-mentioned gap, the charging by the grid voltage can be maintained within a controllable range, making it possible to obtain an even halftone image. The surface potential can be controlled over a wide range, and image quality deterioration can be prevented.

Although the above embodiment describes the case where the present invention is applied to an electronic copying machine, the present invention is not limited thereto, and can be widely applied to image forming apparatuses that employ an electrophotographic method. also has the same effect as above.

[Advantageous Effects of the Invention 1] As detailed above, according to the present invention, it is possible to uniformly charge the surface of the photoreceptor to obtain an even halftone image, and also to obtain the necessary surface potential of the photoreceptor. Therefore, it is possible to provide an image forming apparatus that can prevent deterioration of image quality.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention. Fig. 1 is a block diagram showing the main parts of the control system of an electronic copying machine, Fig. 2 is a perspective view showing the external appearance, and Fig. 3 is a schematic diagram of the internal configuration. FIG. 4 is a diagram showing the relationship between the wire current and the surface potential of the photosensitive drum. 10... Photosensitive drum (image carrier) 11..., H
t Charger for charging (6 stages of charger), 11a...Charging wire 11b...Grid, 12...Developer (developing means), 23...Charger for transfer (image forming means), 4
0... Exposure scanning S2 position (D destination means), 5o... Control circuit (control means) 56... Drive device (setting means) P... Paper (image forming medium)

Claims (1)

[Scope of Claims] Charging means for charging an image bearing member; Setting means for setting a gap between the charging means and the image bearing member; and Setting means for setting a gap between the charging means and the image bearing member; a control means for controlling the amount of current supplied to the charging means; an exposure means for exposing the image carrier charged to a predetermined potential by supplying the amount of current controlled by the control means to the charging means; a developing means for developing an electrostatic latent image formed on the image carrier by exposure to light; and an image forming means for forming an image by transferring the developer image developed by the developing means to an image forming medium. An image forming apparatus comprising: