JPH07219289A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image without unevenness by adjusting voltage for electrostatic charging and developing bias voltage and forming a halftone image or a solid image. CONSTITUTION:When a 1st mode is selected, ordinary image forming operation is executed and an electrostatic latent image formed on the surface of a photoreceptor drum 28 is developed with toner. Meanwhile, when a 2nd mode is selected, halftone image forming operation is executed. Namely, the surface of the drum 28 is uniformly electrostatically charged by an electrostatic charger 32, and a toner image is formed by a potential difference between the surface of the drum 28 and a developing device 36. At such a time, by adjusting the voltage for electrostatic charging and the developing bias voltage, the potential difference between the surface of the drum 28 and the developing device 36 is adjusted and image density is adjusted. When the image density is made thick, the solid image is formed.

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,
In particular, the present invention relates to an image forming apparatus which is applied to, for example, an electrostatic copying machine, a facsimile, a printer or the like and can form a halftone image or a solid image.

[0002]

2. Description of the Related Art Conventional electrostatic copying machines are generally provided with an automatic exposure adjustment function. This function is to read the document density, adjust the voltage of the exposure lamp according to the document density, and set the image density to an appropriate value. It is possible to use this function to form a halftone image or a solid image on a specific portion of the paper, but in this case, image unevenness may occur.

[0003]

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an image forming apparatus capable of forming a uniform halftone image or a solid image.

[0004]

SUMMARY OF THE INVENTION According to the present invention, charging means for applying a charging voltage to uniformly charge the surface of a photoconductor,
A light image irradiating means for irradiating a light image on the surface of the photoreceptor to form an electrostatic latent image; a developing means for applying a developing bias voltage to form a toner image on the surface of the photoreceptor; a surface of the photoreceptor and a developing means; A potential difference adjusting means for adjusting the potential difference between the first and second modes by a charging voltage and a bias voltage, and a mode selecting means for selecting either the first mode or the second mode.
When the mode is selected, the electrostatic latent image is developed with toner, when the second mode is selected, the light image irradiating means is stopped, and the potential difference is adjusted by the potential difference adjusting means so that the surface of the photoconductor has a predetermined density. Image forming apparatus for forming the toner image of.

[0005]

When the first mode is selected, a normal image forming operation is executed and the electrostatic latent image formed on the surface of the photoconductor is developed with toner. On the other hand, when the second mode is selected, the halftone image forming operation is executed. That is, the surface of the photoconductor is uniformly charged by the charging means, and a toner image is formed on the surface of the photoconductor by the potential difference between the surface of the photoconductor and the developing means. At this time, the potential difference between the photoconductor surface and the developing means is adjusted by adjusting the charging voltage and the developing bias voltage by the potential difference adjusting means, and the image density is adjusted. When the image density is high, a solid image can be formed.

[0006]

According to the present invention, since a halftone image or a solid image is formed by adjusting the charging voltage and the developing bias voltage, a uniform image can be obtained. The above-mentioned object of the present invention,
Other objects, features and advantages will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrostatic copying apparatus 10 of this embodiment shown in FIG. 1 includes a housing 12, and an optical scanning unit 14, an image forming unit 16 and a paper feeding unit 18 are vertically arranged inside the housing 12. Will be placed. The optical scanning unit 14 includes a document table 20 made of glass formed on the upper surface of the housing 12, and below the document table 20, an exposure lamp 22 for exposing a document (not shown) mounted on the document table 20. , Reflecting mirrors 24a to 24a for guiding the reflected light from the document exposed by the exposure lamp 22 to a photosensitive drum 28 described later.
f and the variable power lens 26 are arranged at predetermined positions.

The image forming section 16 includes a photosensitive drum 28 having a photoconductive layer (not shown) formed on its outer peripheral surface, and a main motor 30 for rotating the photosensitive drum 28 in the arrow direction is provided in the vicinity of the photosensitive drum 28. Will be placed. In addition, the photosensitive drum 2
8 around the photosensitive drum 2 in the direction of rotation.
Charger 32 for uniformly charging 8; erase lamp 34 for removing unnecessary charges; photosensitive drum 2
Developing device 36 for developing the electrostatic latent image formed on the toner with toner, and a transfer charger 3 for transferring the image (toner image) onto a sheet (not shown) supplied to the photosensitive drum 28.
8, a blade type cleaning device 42 for removing the toner remaining on the photosensitive drum 28, and a residual charge eraser 44 for removing the residual charge are sequentially arranged.

When a light image is emitted from the reflection mirror 24f onto the photosensitive drum 28 which is uniformly charged by the charging charger 32, an electrostatic latent image is formed on the photosensitive drum 28 according to its photoconductive property. It is formed. Then, the erase lamp 34 removes unnecessary charges, and the developing device 36 develops the electrostatic latent image with toner. The image (toner image) developed in this manner is transferred by the transfer charger 38 to the sheet supplied from the registration roller 58 described later.

The paper feed section 18 includes a transport path 46 and a paper feed path 4
8 to 52, a transfer path 54 and an inversion path 56. That is, the transport path 46 is formed by the photosensitive drum 28.
A registration roller 58 for supplying a sheet in synchronism with the rotation of the sheet, a conveyance unit 60 driven by the main motor 30 and for conveying the sheet separated from the photosensitive drum 28, and an image (toner image) transferred to the sheet. ) Is fused and fixed, and the sheet that has passed through the fixing unit 62 is picked up by the roller 64 and sent onto a receiving table 66 provided outside the housing 12. A paper sensor 67 is provided at the entrance of the registration roller 58.

The paper feed paths 48 to 52 are for supplying new paper to the registration rollers 58, respectively.
The paper feed path 48 includes a manual paper feed tray 68 provided outside the housing 12. The manually fed sheet is provided to the registration roller 58 by the roller 70. The paper feed paths 50 and 52 include trays 72 and 74 for accommodating sheets of different sizes, respectively.
The papers stored in and 74 are drawn out by rollers 76 and 78, respectively, and given to registration rollers 58 by rollers 80. The transfer path 54 connects the exit of the fixing unit 62 and the registration roller 58, and includes a plurality of guide rollers 82. The reversing path 56 is for reversing the sheet exiting the fixing unit 62, and includes a storage section 84 for temporarily storing the sheet and a roller 86 for storing and pulling the sheet out of the storage section 84.

Flappers 88 to 92 are arranged at the branching portion between the transport path 46 and the transfer path 54 and at the branching portion between the transfer path 54 and the reversing path 56, and these flappers 88 to 92 are controlled. Depending on the route, any one of the normal copy, multiplex copy and double-sided copy is selected. That is, the transfer path 5 is set by the flapper 88.
When 4 is closed, a normal copy path is established, and the paper on which the image has been transferred from the registration roller 58 to the photosensitive drum 28 is sent out onto the pedestal 66 through the transport path 46. When the transfer path 54 is opened and the reversal path 56 is closed, a multi-copy path is formed, and the sheet, which is supplied from the registration roller 58 to the photosensitive drum 28 and on which the first image is transferred, is registered again through the conveyance path 46 and the transfer path 54. It is supplied from the roller 58 to the photosensitive drum 28. Then, after the second image is transferred onto the first image in an overlapping manner, the second image is sent out onto the pedestal 66 through the transport path 46. When the transfer path 54 and the reverse path 56 are opened, a double-sided copy path is formed, and the sheet on which the first image is transferred is reversed by the reverse path 56 and then supplied again from the registration roller 58 to the photosensitive drum 28 through the transfer path 54. . Then, after the second image is transferred to the back surface of the first image, the second image is sent out onto the pedestal 66 through the transport path 46.

The control unit 10 of such an electrostatic copying apparatus 10
As shown in FIG. 2, 0 includes a microcomputer 102 that performs various controls. Microcomputer 102
Includes a scanning panel 104, a paper sensor 67 (FIG. 1), a developing bias circuit 106, a D / A converter 108 for controlling the output of the developing bias circuit 106, a charging voltage circuit 110, and a D for controlling the output of the charging voltage circuit. A / A converter 112, transfer voltage circuit 114, clutch 116 for controlling registration roller 58 (FIG. 1), motor drive circuit 118 for controlling main motor 30, and AVR for controlling exposure lamp 22.
120 etc. are connected.

FIG. 3 is a flow chart showing the image forming operation in this embodiment. When the main routine in the control unit 100 (FIG. 2) is started by pressing the start switch or the like, first, in step S1, the main motor 30 and the photosensitive drum 28 are driven, and then in step S1.
In 3, whether or not the halftone mode is selected,
That is, the halftone density key 12 of the scanning panel 104
It is determined whether 2 (FIG. 2) is turned on. If "YES" is determined in step S3, the process proceeds to any of steps S5a to S5c according to the density selected by the halftone density key 122. In this example,
The halftone density key 122 is configured so that any one of three densities can be selected. When the first density is selected, the developing bias voltage is set to -300V in step S5a, and When 2 densities are selected, the developing bias voltage is − in step S5b.
When the voltage is set to 400V and the third density is selected, the developing bias voltage is set to -500V in step S5c. The charging voltage in this example is -6.
It is fixed at 00V. Therefore, when the first density having the largest difference between the charging voltage and the developing bias voltage is selected, the darkest image can be obtained, and the third density having the smallest difference between the charging voltage and the developing bias voltage is selected. When you can get the thinnest image.

When the developing bias voltage is set, it is determined in step S7 whether or not the paper sensor 67 (FIG. 1) is turned on. If "YES" is determined, the paper reaches the registration roller 58. Therefore, in steps S9 to S15, the registration roller 58, the charging charger 32, the erase lamp 34, and the transfer charger 3 are performed.
8 is turned on, and a series of image forming operations is executed. That is, the surface of the photosensitive drum 28 is uniformly charged by the charging charger 32 (charging voltage: -600 V), and the erase lamp 34 removes the electric charge in the non-image portion. A toner image is formed on the surface of the photosensitive drum 28 due to the potential difference. Then, the toner image is transferred by the transfer charger 38 onto the sheet given from the registration roller 58, and a halftone image (or a solid image) is formed on the sheet.

In step S17, it is determined whether or not the paper sensor 67 is turned off, and if "YES" is determined,
Since the paper feeding operation is completed, step S19
At S29, the registration roller clutch 116, the charging charger 32, the erase lamp 34, the transfer charger 38, the main motor 30, and the developing bias are turned off, and the image forming operation is ended.

On the other hand, if "NO" is determined in step S3, the developing bias voltage is set to a predetermined value in step S31, and the exposure lamp 22 is turned on in step S33. Then, in step S35, it is determined whether or not the paper sensor 67 is turned on. "Y
If it is determined to be "ES", in steps S37 to S43, the registration roller 58, the charging charger 32, the erase lamp 34, and the transfer charger 38 are turned on to execute a normal image forming operation. The surface of the drum 28 is uniformly charged, and an electrostatic latent image is formed on the surface of the photosensitive drum 28 by irradiating a light image from the reflection mirror 24f, and the erase lamp 34 charges the non-image portion. After the removal, the electrostatic latent image is toner-developed by the developing device 36. The toner image is transferred by the transfer charger 38 onto the sheet provided by the registration roller 58.

In step S45, it is determined whether or not the paper sensor 67 is turned off, and if "YES" is determined,
Since the paper feeding operation is completed, step S4
7, the image forming operation is completed through S49 and S21 to S29. According to this embodiment, when the halftone mode is selected, the toner image is formed on the surface of the photosensitive drum 28 by the potential difference between the surface potential of the photosensitive drum 28 and the developing bias voltage, so that there is no unevenness. A halftone image or a solid image can be formed.

By controlling the erase lamp 34 and the charger 32, halftone images of various shapes can be formed. 5 and 6, the charging charger 32 is turned on / off during halftone image formation.
Example of erased stripes and erase lamp 3
An example is shown in which the right half of No. 4 is turned on and a halftone image (hatched portion) is formed in the left half.

When a plurality of normal copies are continuously performed, a halftone image (hatched portion) is formed every predetermined number of sheets (for example, every ten sheets) as shown in FIG. 7, for example. By sandwiching the sheets, it is possible to easily sort the sheets into a predetermined number. Further, when a cover sheet is attached to a plurality of normal copies, the sheet on which the halftone image is formed is discharged at the end so that this sheet can be used as the cover sheet.

By selecting the multiple copy mode, the halftone image can be superimposed on a predetermined portion of the sheet on which the image is formed. In the above-described embodiment, the density of the halftone image is adjusted by fixing the charging voltage (-600V) and changing the developing bias voltage. However, conversely, the developing bias voltage is changed. May be fixed and the charging voltage may be changed to adjust the density of the halftone image. Further, the density of the halftone image may be adjusted by changing both the charging voltage and the developing bias voltage.

In the above embodiment, only one developing device 36 is provided, but two or more developing devices 36 are provided,
The developing devices 36 may form toner images of different colors. If a plurality of developing devices 36 are provided, by selecting the multiple copy mode, it is possible to easily color the paper on which the original is copied. The present invention can be applied to other image forming apparatuses such as a facsimile and a printer, in addition to the electrostatic copying apparatus as in the above-described embodiment.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a control unit in the embodiment of FIG.

FIG. 3 is a flowchart showing the operation of the embodiment in FIG.

FIG. 4 is a flowchart showing the operation of the embodiment in FIG.

FIG. 5 is an illustrative view showing an example of forming a striped pattern with a halftone image.

FIG. 6 is an illustrative view showing an example in which the left half is colored with a halftone image.

FIG. 7 is an illustrative view showing an example in which colored paper is discharged every predetermined number of sheets.

[Explanation of symbols]

 10 ... Electrostatic copying device 14 ... Optical scanning part 16 ... Image forming part 18 ... Paper feeding part 28 ... Photosensitive drum 32 ... Charging charger 34 ... Erase lamp 36 ... Developing device 38 ... Transfer charger 58 ... Registration roller 67 ... Paper sensor

Claims (1)

[Claims] 1. A charging means for applying a charging voltage to uniformly charge the surface of a photoconductor, a light image irradiation means for irradiating a light image on the surface of the photoconductor to form an electrostatic latent image, and a developing device. Developing means for applying a bias voltage to form a toner image on the surface of the photoreceptor, potential difference adjusting means for adjusting the potential difference between the surface of the photoreceptor and the developing means by the charging voltage and the bias voltage, and Mode selection means for selecting either the first mode or the second mode is provided, wherein the electrostatic latent image is toner-developed when the first mode is selected, and the light image irradiation is performed when the second mode is selected. An image forming apparatus in which a toner image having a predetermined density is formed on the surface of the photoconductor by stopping the means and adjusting the potential difference by the potential difference adjusting means.